Review of Heat Recovery Technologies for Building Applications

Abstract

In recent years, interest in heat recovery systems for building applications has resurged due to concerns about the energy crisis and global climate changes. This review presents current developments in four kinds of heat recovery systems for residential building applications. A extensive investigation into the heat recovery integrated in energy-saving systems of residential buildings is also covered, including passive systems for building components, mechanical/natural ventilation systems, dehumidification systems, and the thermoelectric module (TE) system. Based on this review, key issues have been identified as follows: (1) The combination of heat recovery and energy-efficient systems could be considered as a promising approach to reduce greenhouse gas emissions and make residential buildings meet high performance and comfort requirements. However, real-life evaluation of these systems with economic analysis is insufficient; (2) When heat recovery is applied to mechanical ventilation systems, issues such as pressure leakages and air shortcuts should be addressed; (3) The heat pipe heat recovery system enjoys more potential in being combined with other sustainable technologies such as thermoelectric modules and solar energy systems due to its advantages, which include handy manufacturing and convenient maintenance, a lack of cross contamination, and greater thermal conductance.

Full text

energies
Review
Review of Heat Recovery Technologies for
Building Applications
Qi Xu *, Saffa Riffat and Shihao Zhang
Department of Architecture and Built Environment, Faculty of Engineering, the University of Nottingham,
University Park, Nottingham NG7 2RD, UK; saffa.riffat@nottingham.ac.uk (S.R.);
shihao.zhang@nottingham.ac.uk (S.Z.)
*Correspondence: qi.xu1@nottingham.ac.uk
Received: 27 January 2019; Accepted: 23 March 2019; Published: 3 April 2019


Abstract:
In recent years, interest in heat recovery systems for building applications has resurged
due to concerns about the energy crisis and global climate changes. This review presents current
developments in four kinds of heat recovery systems for residential building applications. A extensive
investigation into the heat recovery integrated in energy-saving systems of residential buildings is
also covered, including passive systems for building components, mechanical/natural ventilation
systems, dehumidification systems, and the thermoelectric module (TE) system. Based on this review,
key issues have been identified as follows: (1) The combination of heat recovery and energy-efficient
systems could be considered as a promising approach to reduce greenhouse gas emissions and
make residential buildings meet high performance and comfort requirements. However, real-life
evaluation of these systems with economic analysis is insufficient; (2) When heat recovery is applied
to mechanical ventilation systems, issues such as pressure leakages and air shortcuts should be
addressed; (3) The heat pipe heat recovery system enjoys more potential in being combined with
other sustainable technologies such as thermoelectric modules and solar energy systems due to
its advantages, which include handy manufacturing and convenient maintenance, a lack of cross
contamination, and greater thermal conductance.
Keywords: heat recovery; energy-efficient systems; residential building applications
1. Introduction
Rapid growth in world energy use has caused concerns about supply difficulties, energy depletion,
and serious environmental impacts. For instance, climate change and ozone layer depletion have been
key issues with which people have had to deal [
1
]. According to the reviewed literature, building
energy consumption, including its operation and maintenance, currently accounts for 40% of the total
global energy demand [
2
,
3
]. Moreover, heating, ventilation, and air conditioning systems (HVACs)
consume 40–60% of a building’s energy consumption, with the precise value varying by climate [
1
].
Meanwhile, this energy consumption causes a large amount of greenhouse gas emissions, such as
the emission of carbon dioxide (CO
2
). It is predicted that continued increases in carbon dioxide
emissions will lead to major climate change [
4
]. Therefore, governments are making efforts to develop
energy-saving and eco-friendly building technologies [5].
A great many energy-saving processes and techniques have been proposed for residential building
applications, including recovering the waste energy of buildings, which is also referred to as a heat
recovery system. In the context of the global energy crisis, on the one hand, the improvement of
indoor air quality is required. On the other hand, there is an urgent need to promote energy-saving
emission reductions in the field of HVAC. The application of air-to-air heat recovery would solve the
contradiction between abundant fresh air supply and the reduction of energy consumption. According
Energies 2019,12, 1285; doi:10.3390/en12071285 www.mdpi.com/journal/energies

Energies 2019,12, 1285 2 of 22
to Cuce et al., heat recovery systems are regarded as a greatly promising technology because of their
ability to provide significant energy savings for residential buildings [6].
The purpose of this review is partly to summarize the current development of heat
recovery systems for residential building applications, including their normal types, characteristics,
and technical energy-saving possibilities, and partly to discuss the application of heat recovery
in energy-efficient systems of buildings, including heat recovery combined with passive systems,
mechanical ventilation systems, dehumidification systems, and thermoelectric module (TE) systems of
buildings. Finally, a summary and outlook of these systems will be presented.
2. The Definition of Heat Recovery Systems
Heat recovery is often referred to as a device operating between two air sources at different
temperatures which transfers energy from one side to the other. In other words, it is based on
preheating the incoming air to the interior through recycled waste heat. In general, heat recovery
systems could be classified into sensible heat recovery and enthalpy heat recovery. Because of its
ability to recover both the sensible heat and the latent heat, enthalpy heat exchangers have a better
sustainability effect because of the large proportion of the wet load in the ventilation system and the
requirements of the indoor air humidity for modern buildings.
A representative heat exchanger system in residential buildings is usually composed of a heat
exchanger core, a fresh air inlet and separate contaminated air exhaust outlet, and a fan, as shown in
Figure 1[
7
]. At present, heat recovery systems can recover about 60–95% of waste energy, which is
very promising [
6
]. This review focuses on four categories of heat recovery for sustainable residential
building systems, including rotary wheel, fixed-plate, heat pipe, and run-around systems, which will
be discussed in later sections.
Energies 2019, 12, x FOR PEER REVIEW 2 of 23
According to Cuce et al., heat recovery systems are regarded as a greatly promising technology
because of their ability to provide significant energy savings for residential buildings [6].
The purpose of this review is partly to summarize the current development of heat recovery
systems for residential building applications, including their normal types, characteristics, and
technical energy-saving possibilities, and partly to discuss the application of heat recovery in energy-
efficient systems of buildings, including heat recovery combined with passive systems, mechanical
ventilation systems, dehumidification systems, and thermoelectric module (TE) systems of buildings.
Finally, a summary and outlook of these systems will be presented.
2. The Definition of Heat Recovery Systems
Heat recovery is often referred to as a device operating between two air sources at different
temperatures which transfers energy from one side to the other. In other words, it is based on
preheating the incoming air to the interior through recycled waste heat. In general, heat recovery
systems could be classified into sensible heat recovery and enthalpy heat recovery. Because of its
ability to recover both the sensible heat and the latent heat, enthalpy heat exchangers have a better
sustainability effect because of the large proportion of the wet load in the ventilation system and the
requirements of the indoor air humidity for modern buildings.
A representative heat exchanger system in residential buildings is usually composed of a heat
exchanger core, a fresh air inlet and separate contaminated air exhaust outlet, and a fan, as shown in
Figure 1 [7]. At present, heat recovery systems can recover about 60–95% of waste energy, which is
very promising [6]. This review focuses on four categories of heat recovery for sustainable residential
building systems, including rotary wheel, fixed-plate, heat pipe, and run-around systems, which will
be discussed in later sections.
Figure 1. Typical heat recovery system for a residential building application [7].
3. Types of Heat Recovery Systems for Residential Building Applications
According to the classification of different constructions, heat recovery systems can be divided
into four types: rotary wheel, fixed-plate, heat pipe, and run-around.
3.1. Rotary Wheel
The rotary wheel heat recovery system is a motor-driven rotating porous wheel. When heat and
moisture exchange happen, the two streams alternately pass through the wheel, as shown in Figure
2. The speed of rotors is usually low, ranging from 3 rpm to 15 rpm [7].
Figure 1. Typical heat recovery system for a residential building application [7].
3. Types of Heat Recovery Systems for Residential Building Applications
According to the classification of different constructions, heat recovery systems can be divided
into four types: rotary wheel, fixed-plate, heat pipe, and run-around.
3.1. Rotary Wheel
The rotary wheel heat recovery system is a motor-driven rotating porous wheel. When heat and
moisture exchange happen, the two streams alternately pass through the wheel, as shown in Figure 2.
The speed of rotors is usually low, ranging from 3 rpm to 15 rpm [7].

Energies 2019,12, 1285 3 of 22
Energies 2019, 12, x FOR PEER REVIEW 3 of 23
Figure 2. Diagram of rotary wheel heat exchanger working mode [7].
The overall efficiency of rotary wheel heat recovery is generally much higher than that of any
other air-side heat recovery system due to the nature of the heat wheels, which allow heat to transfer
from the exhaust stream to the supply stream without having to pass directly through the exchange
medium. Normally, rotary wheel heat recovery is able to obtain a heat exchange efficiency of above
80% [7]. It is stated in [8] that the rotary wheel system has been proven to be one of the most efficient
solutions for handling the moisture carried by the ventilation air. However, the rotary wheel heat
recovery barely recovers 40% of the available enthalpy. Atmospheric conditions [9], the air mixing
rate [10], rotation speed [11], and wheel materials [12] could be the major contributing factors in terms
of the performance of rotary wheel heat recovery have a significant influence.
Many researchers have been working on achieving high performance of rotary wheel heat
recovery. The optimal values of length and porosity can be obtained through the numerical model
from Dallaire et al. [13]. The schematic representation of the optimal rotary wheel is shown in Figure
3 [13].
Figure 3. A schematic representation of the optimal rotary wheel [13] (redrawn by the authors).
Besides their high heat transfer efficiency, rotary wheels can also recover both sensible and latent
heat, which makes them able to be desiccant wheels for dehumidification and enthalpy recovery
[14,15].
With regard to economic factors, a recent study in Chicago showed that the application of a
rotary wheel heat exchanger enjoys a much shorter payback period in new buildings (less than one
year) than in retrofitted existing building (two to four years) [16]. Another work from Chicago found
that normally, total life cycle costs are 25–50% lower with the application of a rotary wheel than
without it [17].
All the aforementioned studies show the advantages of the rotary wheel heat exchanger, these
advantages being its rather high heat exchanger effectiveness and relatively short payback period
[16]. However, the development of rotary wheel heat recovery is limited by the problems of air short
circuiting and cross contamination [18]. Air short circuits can circulate air in unintended directions,
greatly reducing the efficiency of the system.
Figure 2. Diagram of rotary wheel heat exchanger working mode [7].
The overall efficiency of rotary wheel heat recovery is generally much higher than that of any
other air-side heat recovery system due to the nature of the heat wheels, which allow heat to transfer
from the exhaust stream to the supply stream without having to pass directly through the exchange
medium. Normally, rotary wheel heat recovery is able to obtain a heat exchange efficiency of above
80% [
7
]. It is stated in [
8
] that the rotary wheel system has been proven to be one of the most efficient
solutions for handling the moisture carried by the ventilation air. However, the rotary wheel heat
recovery barely recovers 40% of the available enthalpy. Atmospheric conditions [
9
], the air mixing
rate [
10
], rotation speed [
11
], and wheel materials [
12
] could be the major contributing factors in terms
of the performance of rotary wheel heat recovery have a significant influence.
Many researchers have been working on achieving high performance of rotary wheel heat recovery.
The optimal values of length and porosity can be obtained through the numerical model from Dallaire
et al. [13]. The schematic representation of the optimal rotary wheel is shown in Figure 3[13].
Energies 2019, 12, x FOR PEER REVIEW 3 of 23
Figure 2. Diagram of rotary wheel heat exchanger working mode [7].
The overall efficiency of rotary wheel heat recovery is generally much higher than that of any
other air-side heat recovery system due to the nature of the heat wheels, which allow heat to transfer
from the exhaust stream to the supply stream without having to pass directly through the exchange
medium. Normally, rotary wheel heat recovery is able to obtain a heat exchange efficiency of above
80% [7]. It is stated in [8] that the rotary wheel system has been proven to be one of the most efficient
solutions for handling the moisture carried by the ventilation air. However, the rotary wheel heat
recovery barely recovers 40% of the available enthalpy. Atmospheric conditions [9], the air mixing
rate [10], rotation speed [11], and wheel materials [12] could be the major contributing factors in terms
of the performance of rotary wheel heat recovery have a significant influence.
Many researchers have been working on achieving high performance of rotary wheel heat
recovery. The optimal values of length and porosity can be obtained through the numerical model
from Dallaire et al. [13]. The schematic representation of the optimal rotary wheel is shown in Figure
3 [13].
Figure 3. A schematic representation of the optimal rotary wheel [13] (redrawn by the authors).
Besides their high heat transfer efficiency, rotary wheels can also recover both sensible and latent
heat, which makes them able to be desiccant wheels for dehumidification and enthalpy recovery
[14,15].
With regard to economic factors, a recent study in Chicago showed that the application of a
rotary wheel heat exchanger enjoys a much shorter payback period in new buildings (less than one
year) than in retrofitted existing building (two to four years) [16]. Another work from Chicago found
that normally, total life cycle costs are 25–50% lower with the application of a rotary wheel than
without it [17].
All the aforementioned studies show the advantages of the rotary wheel heat exchanger, these
advantages being its rather high heat exchanger effectiveness and relatively short payback period
[16]. However, the development of rotary wheel heat recovery is limited by the problems of air short
circuiting and cross contamination [18]. Air short circuits can circulate air in unintended directions,
greatly reducing the efficiency of the system.
Figure 3. A schematic representation of the optimal rotary wheel [13] (redrawn by the authors).
Besides their high heat transfer efficiency, rotary wheels can also recover both sensible and latent
heat, which makes them able to be desiccant wheels for dehumidification and enthalpy recovery [
14
,
15
].
With regard to economic factors, a recent study in Chicago showed that the application of a
rotary wheel heat exchanger enjoys a much shorter payback period in new buildings (less than one
year) than in retrofitted existing building (two to four years) [
16
]. Another work from Chicago found
that normally, total life cycle costs are 25–50% lower with the application of a rotary wheel than
without it [17].
All the aforementioned studies show the advantages of the rotary wheel heat exchanger, these
advantages being its rather high heat exchanger effectiveness and relatively short payback period [
16
].
However, the development of rotary wheel heat recovery is limited by the problems of air short
circuiting and cross contamination [
18
]. Air short circuits can circulate air in unintended directions,
greatly reducing the efficiency of the system.

Energies 2019,12, 1285 4 of 22
3.2. Fixed-Plate
Fixed-plate heat exchangers use thin plates stacked together to create flow channels, which are
illustrated below in Figure 4[
7
]. The first plate type heat exchanger was invented by Dr Richard
Seligman in 1923 and was used for indirect heating/cooling fluid [
19
]. There are three types of airflow
arrangement, including counter flow, cross flow, and parallel flow. When the plates are made of
a material with thermal conductivity and moisture permeability, they constitute an enthalpy heat
exchanger. Mardiana-Idayu et al. introduced an experiment to investigate a novel enthalpy recovery
system with a micro heat and mass cell cycle core, as shown as Figure 5. The results showed that
the sensible energy efficiency was close to 66%, whereas for latent energy it was 59% [
20
]. Similarly,
Nasif et al. conducted a fixed-plate heat recovery system by using a porous membrane material, shown
as Figure 6. The thermal effectiveness of the new system was found to be about 75% of the sensible
energy efficiency and 65% for the latent equivalent [21].
Energies 2019, 12, x FOR PEER REVIEW 4 of 23
3.2. Fixed-Plate
Fixed-plate heat exchangers use thin plates stacked together to create flow channels, which are
illustrated below in Figure 4 [7]. The first plate type heat exchanger was invented by Dr Richard
Seligman in 1923 and was used for indirect heating/cooling fluid [19]. There are three types of airflow
arrangement, including counter flow, cross flow, and parallel flow. When the plates are made of a
material with thermal conductivity and moisture permeability, they constitute an enthalpy heat
exchanger. Mardiana-Idayu et al. introduced an experiment to investigate a novel enthalpy recovery
system with a micro heat and mass cell cycle core, as shown as Figure 5. The results showed that the
sensible energy efficiency was close to 66%, whereas for latent energy it was 59% [20]. Similarly, Nasif
et al. conducted a fixed-plate heat recovery system by using a porous membrane material, shown as
Figure 6. The thermal effectiveness of the new system was found to be about 75% of the sensible
energy efficiency and 65% for the latent equivalent [21].
Figure 4. A fixed-plate heat exchanger [7].
Figure 5. Graph results for an air-to-air enthalpy heat exchanger [20].
Figure 4. A fixed-plate heat exchanger [7].
Energies 2019, 12, x FOR PEER REVIEW 4 of 23
3.2. Fixed-Plate
Fixed-plate heat exchangers use thin plates stacked together to create flow channels, which are
illustrated below in Figure 4 [7]. The first plate type heat exchanger was invented by Dr Richard
Seligman in 1923 and was used for indirect heating/cooling fluid [19]. There are three types of airflow
arrangement, including counter flow, cross flow, and parallel flow. When the plates are made of a
material with thermal conductivity and moisture permeability, they constitute an enthalpy heat
exchanger. Mardiana-Idayu et al. introduced an experiment to investigate a novel enthalpy recovery
system with a micro heat and mass cell cycle core, as shown as Figure 5. The results showed that the
sensible energy efficiency was close to 66%, whereas for latent energy it was 59% [20]. Similarly, Nasif
et al. conducted a fixed-plate heat recovery system by using a porous membrane material, shown as
Figure 6. The thermal effectiveness of the new system was found to be about 75% of the sensible
energy efficiency and 65% for the latent equivalent [21].
Figure 4. A fixed-plate heat exchanger [7].
Figure 5. Graph results for an air-to-air enthalpy heat exchanger [20].
Figure 5. Graph results for an air-to-air enthalpy heat exchanger [20].

Energies 2019,12, 1285 5 of 22
Energies 2019, 12, x FOR PEER REVIEW 5 of 23
Figure 6. Z-flow fixed-plate heat exchanger (HE) built using porous membrane material [21].
When plates (including metal plates and plastic plates, etc.) cannot absorb moisture, the material
thermal conductivity and geometry is paramount for recovery of sensible heat. Normally, sensible
heat recovery can achieve a heat exchange rate between 50% and 80% [22]. The factors that could
affect the heat transfer efficiency of fixed-plate type heat recovery include:
1. Plate types and constructions (such as different arrangement and orientation) [23,24];
2. Heat exchanger materials [21,25];
3. Flow pattern [26].
Recently, some commercial products have achieved a better heat exchanger rate. One improved
fixed-plate heat recovery system produced by a Danish company can achieve a heat recovery rate of
93%, as certificated by Passive House Institute, Darmstadt [27,28]. Therefore, fixed-plate type heat
exchangers enjoy a promising future in higher thermal performance in residential building
applications.
3.3. Heat Pipe
Heat recovery systems using heat pipes to transfer heat combine the principles of heat
conduction and phase change to effectively transfer heat between two solid interfaces. The typical
heat pipe consist of two closed tubes filled with working fluid [29]. The heat pipe transfers thermal
energy from one side to the other side with a small temperature difference [30]. During operation,
the condensed liquid travels to the evaporation section due to the wick structure exerting capillary
action or the gravitational force [29].
Typical heat pipe exchangers can achieve thermal efficiency of around 50% [31]. Experiments
from Shao et al. have proven that the efficiency of a heat pipe recovery system in a naturally
ventilated house can achieve 50% with pressure loss less than 1Pa [32]. The effectiveness will decrease
with increasing air flow rate, and substandard thermal contact between plates and heat pipe occurs
[33]. In terms of factors that could affect heat pipe effectiveness, there are some key points [34,35]:
working fluid, the arrangement of the pipes, the air velocity and the inlet temperature of the
evaporator part.
For the last decade, many researchers have focused on the application of heat pipe type recovery.
El-Baky et al. have developed an experiment to test its thermal performance and to collect data for
the effectiveness of heat pipe systems for heat recovery in air conditioning applications, shown as
Figure 7. The results have shown that the heat transfer rate for both the evaporator and condenser
sections has increased to around 48% [36].
Figure 6. Z-flow fixed-plate heat exchanger (HE) built using porous membrane material [21].
When plates (including metal plates and plastic plates, etc.) cannot absorb moisture, the material
thermal conductivity and geometry is paramount for recovery of sensible heat. Normally, sensible
heat recovery can achieve a heat exchange rate between 50% and 80% [
22
]. The factors that could affect
the heat transfer efficiency of fixed-plate type heat recovery include:
1. Plate types and constructions (such as different arrangement and orientation) [23,24];
2. Heat exchanger materials [21,25];
3. Flow pattern [26].
Recently, some commercial products have achieved a better heat exchanger rate. One improved
fixed-plate heat recovery system produced by a Danish company can achieve a heat recovery rate of
93%, as certificated by Passive House Institute, Darmstadt [
27
,
28
]. Therefore, fixed-plate type heat
exchangers enjoy a promising future in higher thermal performance in residential building applications.
3.3. Heat Pipe
Heat recovery systems using heat pipes to transfer heat combine the principles of heat conduction
and phase change to effectively transfer heat between two solid interfaces. The typical heat pipe
consist of two closed tubes filled with working fluid [
29
]. The heat pipe transfers thermal energy from
one side to the other side with a small temperature difference [
30
]. During operation, the condensed
liquid travels to the evaporation section due to the wick structure exerting capillary action or the
gravitational force [29].
Typical heat pipe exchangers can achieve thermal efficiency of around 50% [
31
]. Experiments
from Shao et al. have proven that the efficiency of a heat pipe recovery system in a naturally ventilated
house can achieve 50% with pressure loss less than 1 Pa [
32
]. The effectiveness will decrease with
increasing air flow rate, and substandard thermal contact between plates and heat pipe occurs [
33
].
In terms of factors that could affect heat pipe effectiveness, there are some key points [
34
,
35
]: working
fluid, the arrangement of the pipes, the air velocity and the inlet temperature of the evaporator part.
For the last decade, many researchers have focused on the application of heat pipe type recovery.
El-Baky et al. have developed an experiment to test its thermal performance and to collect data for the
effectiveness of heat pipe systems for heat recovery in air conditioning applications, shown as Figure 7.
The results have shown that the heat transfer rate for both the evaporator and condenser sections has
increased to around 48% [36].

Energies 2019,12, 1285 6 of 22
Energies 2019, 12, x FOR PEER REVIEW 6 of 23
Figure 7. Heat pipe heat exchanger in an air conditioning system and graphs of effects under different
conditions on effectiveness [36].
From Yau et al. it can also be found that using heat pipe recovery systems can lead to significant
energy savings in domestic appliances within tropical climates [37,38]. Recently, Diao et al. provided
a new study involving a small flat heat pipe heat recovery device which applies a flat micro-heat pipe
array with welded, serrated, and staggered fins on its surface, as shown in Figure 8. The results
showed that the maximum heat exchange rate and coefficient of performance (COP) could be 78%
and 91.9, respectively, under experimental conditions [39]. This study of a small flat heat pipe heat
recovery system indicates the potential for improving the thermal performance of heat pipe heat
recovery. However, further real-life evaluation is still needed.
Figure 8. Schematic representation of a micro-heat pipe recovery system [39].
In summary, heat pipe heat recovery enjoys the following advantages: handy manufacturing
and convenient maintenance, a lack of cross contamination, and greater thermal conductance [40].
3.4. Run-Around
Figure 7.
Heat pipe heat exchanger in an air conditioning system and graphs of effects under different
conditions on effectiveness [36].
From Yau et al. It can also be found that using heat pipe recovery systems can lead to significant
energy savings in domestic appliances within tropical climates [
37
,
38
]. Recently, Diao et al. provided
a new study involving a small flat heat pipe heat recovery device which applies a flat micro-heat
pipe array with welded, serrated, and staggered fins on its surface, as shown in Figure 8. The results
showed that the maximum heat exchange rate and coefficient of performance (COP) could be 78%
and 91.9, respectively, under experimental conditions [
39
]. This study of a small flat heat pipe heat
recovery system indicates the potential for improving the thermal performance of heat pipe heat
recovery. However, further real-life evaluation is still needed.
Energies 2019, 12, x FOR PEER REVIEW 6 of 23
Figure 7. Heat pipe heat exchanger in an air conditioning system and graphs of effects under different
conditions on effectiveness [36].
From Yau et al. it can also be found that using heat pipe recovery systems can lead to significant
energy savings in domestic appliances within tropical climates [37,38]. Recently, Diao et al. provided
a new study involving a small flat heat pipe heat recovery device which applies a flat micro-heat pipe
array with welded, serrated, and staggered fins on its surface, as shown in Figure 8. The results
showed that the maximum heat exchange rate and coefficient of performance (COP) could be 78%
and 91.9, respectively, under experimental conditions [39]. This study of a small flat heat pipe heat
recovery system indicates the potential for improving the thermal performance of heat pipe heat
recovery. However, further real-life evaluation is still needed.
Figure 8. Schematic representation of a micro-heat pipe recovery system [39].
In summary, heat pipe heat recovery enjoys the following advantages: handy manufacturing
and convenient maintenance, a lack of cross contamination, and greater thermal conductance [40].
3.4. Run-Around
Figure 8. Schematic representation of a micro-heat pipe recovery system [39].
In summary, heat pipe heat recovery enjoys the following advantages: handy manufacturing and
convenient maintenance, a lack of cross contamination, and greater thermal conductance [40].

Energies 2019,12, 1285 7 of 22
3.4. Run-Around
Run-around heat recovery systems consist of two individual heat exchangers and a coupling
liquid, as shown in Figure 9. With the help of the pump, it allows liquid to transfer absorbed heat from
one stream into the other side [7].
Energies 2019, 12, x FOR PEER REVIEW 7 of 23
Run-around heat recovery systems consist of two individual heat exchangers and a coupling
liquid, as shown in Figure 9. With the help of the pump, it allows liquid to transfer absorbed heat
from one stream into the other side [7].
Figure 9. The working principles of run-around heat recovery [7].
Run-around heat recovery can avoid cross contamination because of the separation of the two
heat exchangers [41]. The heat exchange rate of run-around heat recovery ranges from 45% to 65%
under normal conditions [7]. Using a run-around heat recovery system in a building can increase the
ventilation airflow rate without increasing energy consumption [42]. As to the thermal performance
of run-around heat recovery, Vali et al.’s experimental results showed that for a given total surface
area of exchangers, the highest overall sensible effectiveness was achieved with exchangers which
have a small exchanger aspect ratio [41].
In addition, the effectiveness of run-around heat recovery is significantly dependent on outdoor
conditions. Run-around heat recovery systems are often positioned within the supply and exhaust
air streams of industrial processes.
Table 1 compares the basic performance of different types of heat recovery systems.
Table 1. A comparison of the four types of heat recovery systems based on their thermal performance.
Types of Heat
Recovery Rotary Wheel Fixed-Plate Heat Pipe Run-Around
Main airflow
arrangements
Counter flow,
parallel flow
Cross flow, counter
flow, parallel flow
Counter flow,
parallel flow N/A
Typical efficiency Above 80% 50~80% 45~55% 45~65%
Air speed (m/s) 2.5~5 0.5~5 2~4 1.5~3
Air pressure (Pa) 100~170 25~370 100~500 100~500
Temperature range
(°C) −60~800 −60~800 −40~35 −45~500
Advantages [7]
High efficiency,
compact
equipment,
potential to recover
sensible and latent
heat.
Compact, relatively
high heat transfer
coefficient, no cross
contamination, easy
maintenance, can
be coupled with
counter-current
flow which enables
the production of
closed-temperature
differences, capable
of recovering
sensible and latent
heat.
Fixed components,
no extra power
supply, high
reliability, separate
air duct, compact,
suitable for
naturally ventilated
building, fully
reversible, easy
maintenance but
only capable of
recovering sensible
heat.
Air ducts can be
located side by
side, ducts can be
physically
separated, no cross
contamination,
only capable of
recovering sensible
heat.
Figure 9. The working principles of run-around heat recovery [7].
Run-around heat recovery can avoid cross contamination because of the separation of the two
heat exchangers [
41
]. The heat exchange rate of run-around heat recovery ranges from 45% to 65%
under normal conditions [
7
]. Using a run-around heat recovery system in a building can increase the
ventilation airflow rate without increasing energy consumption [
42
]. As to the thermal performance of
run-around heat recovery, Vali et al.’s experimental results showed that for a given total surface area
of exchangers, the highest overall sensible effectiveness was achieved with exchangers which have a
small exchanger aspect ratio [41].
In addition, the effectiveness of run-around heat recovery is significantly dependent on outdoor
conditions. Run-around heat recovery systems are often positioned within the supply and exhaust air
streams of industrial processes.
Table 1compares the basic performance of different types of heat recovery systems.
Table 1.
A comparison of the four types of heat recovery systems based on their thermal performance.
Types of Heat Recovery Rotary Wheel Fixed-Plate Heat Pipe Run-Around
Main airflow
arrangements Counter flow, parallel flow Cross flow, counter flow,
parallel flow Counter flow, parallel flow N/A
Typical efficiency Above 80% 50~80% 45~55% 45~65%
Air speed (m/s) 2.5~5 0.5~5 2~4 1.5~3
Air pressure (Pa) 100~170 25~370 100~500 100~500
Temperature range (◦C) −60~800 −60~800 −40~35 −45~500
Advantages [7]
High efficiency, compact
equipment, potential to
recover sensible and
latent heat.
Compact, relatively high heat
transfer coefficient, no cross
contamination, easy
maintenance, can be coupled
with counter-current flow which
enables the production of
closed-temperature differences,
capable of recovering sensible
and latent heat.
Fixed components, no extra
power supply, high reliability,
separate air duct, compact,
suitable for naturally ventilated
building, fully reversible, easy
maintenance but only capable of
recovering sensible heat.
Air ducts can be located side by
side, ducts can be physically
separated, no cross
contamination, only capable of
recovering sensible heat.
By sorting through 100 research papers published in the last five years about the study of the
application of heat recovery systems in residential buildings, such a summary could be given as follows.
Figure 10 shows the distribution of the main studies according to the four heat recovery system types.
Nearly one third of researchers were interested in heat pipe heat recovery (HPHR). Around 40%
of these newly published articles were related to fixed-plate heat recovery (FPHR). About 21% of
researchers focused on rotary wheel heat recovery. However, just 3% considered run-around heat
recovery. Normally, run-around heat recovery systems are more popular in the industrial field and are

Energies 2019,12, 1285 8 of 22
not as common in domestic building applications. The following sections discussing fixed-plate, rotary
wheel, and heat pipe heat recovery combined with energy-efficient systems for building applications.
Energies 2019, 12, x FOR PEER REVIEW 8 of 23
By sorting through 100 research papers published in the last five years about the study of the
application of heat recovery systems in residential buildings, such a summary could be given as
follows. Figure 10 shows the distribution of the main studies according to the four heat recovery
system types. Nearly one third of researchers were interested in heat pipe heat recovery (HPHR).
Around 40% of these newly published articles were related to fixed-plate heat recovery (FPHR).
About 21% of researchers focused on rotary wheel heat recovery. However, just 3% considered run-
around heat recovery. Normally, run-around heat recovery systems are more popular in the
industrial field and are not as common in domestic building applications. The following sections
discussing fixed-plate, rotary wheel, and heat pipe heat recovery combined with energy-efficient
systems for building applications.
Figure 10. Heat recovery system research article distribution.
4. Applications of Heat Recovery in Energy-Saving Systems of Residential Buildings
The combination of heat recovery and different energy-efficient systems could contribute to
reducing heat loss, stabilizing heat flux, and improving the thermal performance of residential
buildings. This section reviews the recent development in heat recovery combined with energy-
efficient technologies of buildings over four subsections.
4.1. Heat-Recovery-Assisted Decentralized Ventilation System
Mechanical ventilation systems are applied for achieving the desired airflow and obtaining a
comfortable interior environment. However, mechanical ventilation can consume much electrical
energy, and, can at times increase household power consumption by up to 50% [43]. Tommerup et
al. have reported that with heat recovery technology, up to 90% of ventilation heat loss (about 30–35
kWh/m2 per year) can be recovered depending on airtightness and the insulation of the building [2].
Compared with centralized ventilation, pressure loss can be minimized within decentralized
ventilation, due to the shorter distance of the air routing [44]. Several researchers have tested the
performance of heat recovery units with decentralized ventilation systems based on different
outdoors conditions. Baldini et al. has conducted a decentralized cooling and dehumidification
system, as shown in Figure 11. Multi-stage type heat recovery could help to reduce the temperature
compared to a single heat exchanger. Experimental results showed that under an environment
temperature of around 30 °C and a humidity ratio of 20 g/kg, the application of the multi-stage heat
recovery could reach the preferred target, with the supply air at 14–15 °C and 8–9 g/kg. Additionally,
because of the free reheating, the system is able to save about 4–5% of cooling energy demand [44].
Fixed-Plate
40%
Rotary
Wheel
21%
Heat Pipe
36%
Run-around
3%
Fixed-Plate Rotary Wheel Heat Pipe Run-around
Figure 10. Heat recovery system research article distribution.
4. Applications of Heat Recovery in Energy-Saving Systems of Residential Buildings
The combination of heat recovery and different energy-efficient systems could contribute to
reducing heat loss, stabilizing heat flux, and improving the thermal performance of residential
buildings. This section reviews the recent development in heat recovery combined with energy-efficient
technologies of buildings over four subsections.
4.1. Heat-Recovery-Assisted Decentralized Ventilation System
Mechanical ventilation systems are applied for achieving the desired airflow and obtaining a
comfortable interior environment. However, mechanical ventilation can consume much electrical
energy, and, can at times increase household power consumption by up to 50% [
43
]. Tommerup et al.
have reported that with heat recovery technology, up to 90% of ventilation heat loss (about
30–35 kWh/m
2
per year) can be recovered depending on airtightness and the insulation of the
building [2].
Compared with centralized ventilation, pressure loss can be minimized within decentralized
ventilation, due to the shorter distance of the air routing [
44
]. Several researchers have tested the
performance of heat recovery units with decentralized ventilation systems based on different outdoors
conditions. Baldini et al. has conducted a decentralized cooling and dehumidification system, as
shown in Figure 11. Multi-stage type heat recovery could help to reduce the temperature compared
to a single heat exchanger. Experimental results showed that under an environment temperature of
around 30
◦
C and a humidity ratio of 20 g/kg, the application of the multi-stage heat recovery could
reach the preferred target, with the supply air at 14–15
◦
C and 8–9 g/kg. Additionally, because of the
free reheating, the system is able to save about 4–5% of cooling energy demand [44].
Another novel rotary wheel unit in Europe has been described by Smith et al. (shown in Figure 12),
which uses plastic as the heat transfer material and was installed in the exterior wall of an individual
room vent, requiring minimal space. Testing results indicated that this novel unit could recover
about 84% of sensible heat with a ventilation rate of 7.8 L/s [
45
]. In addition, bypass leakage was
observed during the experiment and the pressure drop reached around 18% [
45
]. High-pressure
leakage could cause discomfort noise due to the higher fan speed required to achieve the desired
vent rate. Therefore, proper sealing and slowing of the rotational speed to prevent frost accumulation
should be ensured [45].

Energies 2019,12, 1285 9 of 22
Energies 2019, 12, x FOR PEER REVIEW 9 of 23
Figure 11. Arrangement of the three heat exchangers [44].
Another novel rotary wheel unit in Europe has been described by Smith et al. (shown in Figure
12), which uses plastic as the heat transfer material and was installed in the exterior wall of an
individual room vent, requiring minimal space. Testing results indicated that this novel unit could
recover about 84% of sensible heat with a ventilation rate of 7.8 L/s [45]. In addition, bypass leakage
was observed during the experiment and the pressure drop reached around 18% [45]. High-pressure
leakage could cause discomfort noise due to the higher fan speed required to achieve the desired vent
rate. Therefore, proper sealing and slowing of the rotational speed to prevent frost accumulation
should be ensured [45].
Figure 12. Schematic representation of the plastic rotary wheel system [45].
Plate type heat exchangers can also be integrated within ventilation systems. Coydon et al. have
evaluated different facades combined with heat recovery ventilation units seasonally, as shown in
Figure 13. The results showed that integration, including counter flow heat recovery, achieved
recovery ranging from 64.6% to 70.0% of heat [46]. Another unit which adopted regenerative heat
recovery could recover between 72.8% and 80.2% of heat [46].
Figure 11. Arrangement of the three heat exchangers [44].
Energies 2019, 12, x FOR PEER REVIEW 9 of 23
Figure 11. Arrangement of the three heat exchangers [44].
Another novel rotary wheel unit in Europe has been described by Smith et al. (shown in Figure
12), which uses plastic as the heat transfer material and was installed in the exterior wall of an
individual room vent, requiring minimal space. Testing results indicated that this novel unit could
recover about 84% of sensible heat with a ventilation rate of 7.8 L/s [45]. In addition, bypass leakage
was observed during the experiment and the pressure drop reached around 18% [45]. High-pressure
leakage could cause discomfort noise due to the higher fan speed required to achieve the desired vent
rate. Therefore, proper sealing and slowing of the rotational speed to prevent frost accumulation
should be ensured [45].
Figure 12. Schematic representation of the plastic rotary wheel system [45].
Plate type heat exchangers can also be integrated within ventilation systems. Coydon et al. have
evaluated different facades combined with heat recovery ventilation units seasonally, as shown in
Figure 13. The results showed that integration, including counter flow heat recovery, achieved
recovery ranging from 64.6% to 70.0% of heat [46]. Another unit which adopted regenerative heat
recovery could recover between 72.8% and 80.2% of heat [46].
Figure 12. Schematic representation of the plastic rotary wheel system [45].
Plate type heat exchangers can also be integrated within ventilation systems. Coydon et al. have
evaluated different facades combined with heat recovery ventilation units seasonally, as shown in
Figure 13. The results showed that integration, including counter flow heat recovery, achieved recovery
ranging from 64.6% to 70.0% of heat [
46
]. Another unit which adopted regenerative heat recovery
could recover between 72.8% and 80.2% of heat [46].
Recently, Cuce et al. proposed a novel polycarbonate heat recovery system. The experiment
carried out measurements of temperature, relative humidity, and CO
2
in a period of one week.
The results indicated that through the application of the novel system within the testing house,
a sensible increment, about 7
◦
C, was observed in the temperature of fresh air and a considerable
decrease, about 4
◦
C, was achieved in the temperature of stale air [
47
]. They also showed that the
average relative humidity in the testing room in the post-retrofit case was around 57%, which was
within the desired range [
47
]. Figure 14 shows a temperature monitoring diagram during the testing
period. The Cuce et al. experiments proved that by utilizing a combination of heat exchanger and

Energies 2019,12, 1285 10 of 22
ventilation, except for the mitigation of the heating or cooling load, the actual comfort conditions for
indoor environments including CO
2
concentrate and relative humidity reaching the desired range can
also be achieved [47].
Energies 2019, 12, x FOR PEER REVIEW 10 of 23
Figure 13. Facade system with (a) counter flow heat recovery and (b) regenerative heat recovery [46].
Recently, Cuce et al. proposed a novel polycarbonate heat recovery system. The experiment
carried out measurements of temperature, relative humidity, and CO2 in a period of one week. The
results indicated that through the application of the novel system within the testing house, a sensible
increment, about 7 °C, was observed in the temperature of fresh air and a considerable decrease,
about 4 °C, was achieved in the temperature of stale air [47]. They also showed that the average
relative humidity in the testing room in the post-retrofit case was around 57%, which was within the
desired range [47]. Figure 14 shows a temperature monitoring diagram during the testing period. The
Cuce et al. experiments proved that by utilizing a combination of heat exchanger and ventilation, except
for the mitigation of the heating or cooling load, the actual comfort conditions for indoor environments
including CO2 concentrate and relative humidity reaching the desired range can also be achieved [47].
Figure 14. Temperature monitoring during testing [47].
The following problems of integrated systems of heat recovery and decentralized ventilation can
be found based on the aforementioned studies:
1. Unexpected air bypass leakage [45];
2. Noise from fans to achieve ventilation requirements [45];
3. Lack of ventilation unit operation and airflow control strategy [44,46].
4.2. Heat Recovery Combined with Passive Systems for Building Components
Recently, heat recovery systems have been considered to be combined with building
components such as building walls [48–51], roofs [52] and wind towers [53–56]. For example, it has
been found that wind towers can provide significantly higher airflow rates than open windows with
the same area [57]. However, application of wind towers is generally limited to tropical climates
because seasonal temperatures in colder climates are too low to circulate directly into interior spaces.
Wind towers are usually closed to avoid loss of heating energy in winter [55]. To address this
limitation, combining heat recovery technology with wind towers could be a sensible solution. This
kind of integration would be helpful for stabilizing the heat flux of buildings to reduce total energy
consumption demands and enhance indoor thermal comfort.
Table 2 summarizes the studies of different building components integrated into heat recovery.
Figure 13.
Facade system with (
a
) counter flow heat recovery and (
b
) regenerative heat recovery [
46
].
Energies 2019, 12, x FOR PEER REVIEW 10 of 23
Figure 13. Facade system with (a) counter flow heat recovery and (b) regenerative heat recovery [46].
Recently, Cuce et al. proposed a novel polycarbonate heat recovery system. The experiment
carried out measurements of temperature, relative humidity, and CO2 in a period of one week. The
results indicated that through the application of the novel system within the testing house, a sensible
increment, about 7 °C, was observed in the temperature of fresh air and a considerable decrease,
about 4 °C, was achieved in the temperature of stale air [47]. They also showed that the average
relative humidity in the testing room in the post-retrofit case was around 57%, which was within the
desired range [47]. Figure 14 shows a temperature monitoring diagram during the testing period. The
Cuce et al. experiments proved that by utilizing a combination of heat exchanger and ventilation, except
for the mitigation of the heating or cooling load, the actual comfort conditions for indoor environments
including CO2 concentrate and relative humidity reaching the desired range can also be achieved [47].
Figure 14. Temperature monitoring during testing [47].
The following problems of integrated systems of heat recovery and decentralized ventilation can
be found based on the aforementioned studies:
1. Unexpected air bypass leakage [45];
2. Noise from fans to achieve ventilation requirements [45];
3. Lack of ventilation unit operation and airflow control strategy [44,46].
4.2. Heat Recovery Combined with Passive Systems for Building Components
Recently, heat recovery systems have been considered to be combined with building
components such as building walls [48–51], roofs [52] and wind towers [53–56]. For example, it has
been found that wind towers can provide significantly higher airflow rates than open windows with
the same area [57]. However, application of wind towers is generally limited to tropical climates
because seasonal temperatures in colder climates are too low to circulate directly into interior spaces.
Wind towers are usually closed to avoid loss of heating energy in winter [55]. To address this
limitation, combining heat recovery technology with wind towers could be a sensible solution. This
kind of integration would be helpful for stabilizing the heat flux of buildings to reduce total energy
consumption demands and enhance indoor thermal comfort.
Table 2 summarizes the studies of different building components integrated into heat recovery.
Figure 14. Temperature monitoring during testing [47].
The following problems of integrated systems of heat recovery and decentralized ventilation can
be found based on the aforementioned studies:
1. Unexpected air bypass leakage [45];
2. Noise from fans to achieve ventilation requirements [45];
3. Lack of ventilation unit operation and airflow control strategy [44,46].
4.2. Heat Recovery Combined with Passive Systems for Building Components
Recently, heat recovery systems have been considered to be combined with building components
such as building walls [
48
–
51
], roofs [
52
] and wind towers [
53
–
56
]. For example, it has been found
that wind towers can provide significantly higher airflow rates than open windows with the same
area [
57
]. However, application of wind towers is generally limited to tropical climates because seasonal
temperatures in colder climates are too low to circulate directly into interior spaces. Wind towers are
usually closed to avoid loss of heating energy in winter [
55
]. To address this limitation, combining heat
recovery technology with wind towers could be a sensible solution. This kind of integration would
be helpful for stabilizing the heat flux of buildings to reduce total energy consumption demands and
enhance indoor thermal comfort.
Table 3summarizes the studies of different building components integrated into heat recovery.

Energies 2019,12, 1285 11 of 22
Table 2. A summary of heat recovery systems integrated into building components.
Building
Component Images Research Methodology Key Features Outcomes Economic Analysis Reference
Building wall
Energies 2019, 12, x FOR PEER REVIEW 11 of 23
Table 2. A summary of heat recovery systems integrated into building components.
Building
Component Images Research
Methodology Key Features Outcomes Economic
Analysis Reference
Building
wall
Experimental
investigation with
1720 mm × 1720 mm
wall implanted with
heat pipes (WIHP)
and theoretical
analysis
A new type of passive solar
utilization technology; WIHP;
different direction facing wall
according to the located regions.
Application of the
integration could
reduce heat loss by
more than 14.47% in
winter.
NA [48,49]
MATLAB based
simulation
Multilayer wall with capillary
pipe network; significantly
reduces building load; three
locations for heat pipes including
external, middle, and internal.
The wall could help
save power energy from
2 W to 39 W with
variation in outdoor air
temperature depending
on the season.
NA [50]
TRNSYS software
simulation
A pipe-embedded wall integrated
with ground source-coupled heat
exchanger; multi-criteria system
design.
Using the same number
of ground source-
coupled heat
exchangers (GDHE) the
system could achieve
over 30% energy
savings in hot summer
and cold winter
climates.
NA [51]
Roof
Experimental
investigation with a
real-scale test house
A plate-type heat exchanger
parallel-flow arrangement under
roof application; recovers waste
heat; preheats fresh air using stale
air.
Heat recovery efficiency
was found to be around
89%. The coefficient of
its thermal performance
is 4.5.
Relatively low
cost of
polycarbonate
sheet-based roof
type heat
recovery panel,
about €14.31/m2.
[52]
Experimental investigation
with 1720 mm ×1720 mm
wall implanted with heat
pipes (WIHP) and
theoretical analysis
A new type of passive solar
utilization technology; WIHP;
different direction facing wall
according to the
located regions.
Application of the integration
could reduce heat loss by
more than 14.47% in winter.
NA [48,49]
Energies 2019, 12, x FOR PEER REVIEW 11 of 23
Table 2. A summary of heat recovery systems integrated into building components.
Building
Component Images Research
Methodology Key Features Outcomes Economic
Analysis Reference
Building
wall
Experimental
investigation with
1720 mm × 1720 mm
wall implanted with
heat pipes (WIHP)
and theoretical
analysis
A new type of passive solar
utilization technology; WIHP;
different direction facing wall
according to the located regions.
Application of the
integration could
reduce heat loss by
more than 14.47% in
winter.
NA [48,49]
MATLAB based
simulation
Multilayer wall with capillary
pipe network; significantly
reduces building load; three
locations for heat pipes including
external, middle, and internal.
The wall could help
save power energy from
2 W to 39 W with
variation in outdoor air
temperature depending
on the season.
NA [50]
TRNSYS software
simulation
A pipe-embedded wall integrated
with ground source-coupled heat
exchanger; multi-criteria system
design.
Using the same number
of ground source-
coupled heat
exchangers (GDHE) the
system could achieve
over 30% energy
savings in hot summer
and cold winter
climates.
NA [51]
Roof
Experimental
investigation with a
real-scale test house
A plate-type heat exchanger
parallel-flow arrangement under
roof application; recovers waste
heat; preheats fresh air using stale
air.
Heat recovery efficiency
was found to be around
89%. The coefficient of
its thermal performance
is 4.5.
Relatively low
cost of
polycarbonate
sheet-based roof
type heat
recovery panel,
about €14.31/m2.
[52]
MATLAB based simulation
Multilayer wall with
capillary pipe network;
significantly reduces building
load; three locations for heat
pipes including external,
middle, and internal.
The wall could help save
power energy from 2 W to 39
W with variation in outdoor
air temperature depending
on the season.
NA [50]
Energies 2019, 12, x FOR PEER REVIEW 11 of 23
Table 2. A summary of heat recovery systems integrated into building components.
Building
Component Images Research
Methodology Key Features Outcomes Economic
Analysis Reference
Building
wall
Experimental
investigation with
1720 mm × 1720 mm
wall implanted with
heat pipes (WIHP)
and theoretical
analysis
A new type of passive solar
utilization technology; WIHP;
different direction facing wall
according to the located regions.
Application of the
integration could
reduce heat loss by
more than 14.47% in
winter.
NA [48,49]
MATLAB based
simulation
Multilayer wall with capillary
pipe network; significantly
reduces building load; three
locations for heat pipes including
external, middle, and internal.
The wall could help
save power energy from
2 W to 39 W with
variation in outdoor air
temperature depending
on the season.
NA [50]
TRNSYS software
simulation
A pipe-embedded wall integrated
with ground source-coupled heat
exchanger; multi-criteria system
design.
Using the same number
of ground source-
coupled heat
exchangers (GDHE) the
system could achieve
over 30% energy
savings in hot summer
and cold winter
climates.
NA [51]
Roof
Experimental
investigation with a
real-scale test house
A plate-type heat exchanger
parallel-flow arrangement under
roof application; recovers waste
heat; preheats fresh air using stale
air.
Heat recovery efficiency
was found to be around
89%. The coefficient of
its thermal performance
is 4.5.
Relatively low
cost of
polycarbonate
sheet-based roof
type heat
recovery panel,
about €14.31/m2.
[52]
TRNSYS software
simulation
A pipe-embedded wall
integrated with ground
source-coupled heat
exchanger; multi-criteria
system design.
Using the same number of
ground source-coupled heat
exchangers (GDHE) the
system could achieve over
30% energy savings in hot
summer and cold winter
climates.
NA [51]
Roof
Energies 2019, 12, x FOR PEER REVIEW 11 of 23
Table 2. A summary of heat recovery systems integrated into building components.
Building
Component Images Research
Methodology Key Features Outcomes Economic
Analysis Reference
Building
wall
Experimental
investigation with
1720 mm × 1720 mm
wall implanted with
heat pipes (WIHP)
and theoretical
analysis
A new type of passive solar
utilization technology; WIHP;
different direction facing wall
according to the located regions.
Application of the
integration could
reduce heat loss by
more than 14.47% in
winter.
NA [48,49]
MATLAB based
simulation
Multilayer wall with capillary
pipe network; significantly
reduces building load; three
locations for heat pipes including
external, middle, and internal.
The wall could help
save power energy from
2 W to 39 W with
variation in outdoor air
temperature depending
on the season.
NA [50]
TRNSYS software
simulation
A pipe-embedded wall integrated
with ground source-coupled heat
exchanger; multi-criteria system
design.
Using the same number
of ground source-
coupled heat
exchangers (GDHE) the
system could achieve
over 30% energy
savings in hot summer
and cold winter
climates.
NA [51]
Roof
Experimental
investigation with a
real-scale test house
A plate-type heat exchanger
parallel-flow arrangement under
roof application; recovers waste
heat; preheats fresh air using stale
air.
Heat recovery efficiency
was found to be around
89%. The coefficient of
its thermal performance
is 4.5.
Relatively low
cost of
polycarbonate
sheet-based roof
type heat
recovery panel,
about €14.31/m2.
[52]
Experimental investigation
with a real-scale test house
A plate-type heat exchanger
parallel-flow arrangement
under roof application;
recovers waste heat; preheats
fresh air using stale air.
Heat recovery efficiency was
found to be around 89%.
The coefficient of its thermal
performance is 4.5.
Relatively low cost of
polycarbonate
sheet-based roof type
heat recovery panel,
about €14.31/m2.
[52]

Energies 2019,12, 1285 12 of 22
Table 3. A summary of heat recovery systems integrated into building components.
Building
Component Images Research Methodology Key Features Outcomes Economic Analysis Reference
Wind tower
Energies 2019, 12, x FOR PEER REVIEW 12 of 23
Wind tower
CFD software
simulation
A cooling wind tower
incorporating heat pipe
technology and cool sink; passive
cooling system.
System can cool down
air flow up to 12 °C, and
at lower weed speeds
(1–2 m/s), it can reduce
the temperature
significantly.
NA [53,54]
CFD software
simulation and
experimental
investigation (1:10
scale experimental
platform)
Heat pipes integrated into a
multi-directional wind tower;
recovers exhaust heat.
The application of the
system can heat the
supply air by up to 4.5
°C. In addition, the heat
pipes can slow down
the air supply rates by
up to 8–17%.
NA [55]
(Redrawn by authors)
Experimental
investigation using a
large-scale chamber (3
m × 3 m × 5.6 m) with
a wind catcher unit
(0.7 m× 3.2 m × 0.45 m)
Integrated system with heat
recovery and wind catcher; helps
to assist air flow.
The combination system
can cool down the inlet
air temperature up to
0.9–1.8 °C. The heat
exchange rate of the
unit varies from 50% to
70% with different air
flow velocities, which
range from 1.2 to 3.1
m/s.
NA [56]
NA: Not available
CFD software simulation
A cooling wind tower
incorporating heat pipe
technology and cool sink;
passive cooling system.
System can cool down air
flow up to 12 ◦C, and at
lower weed speeds (1–2
m/s), it can reduce the
temperature significantly.
NA [53,54]
Energies 2019, 12, x FOR PEER REVIEW 12 of 23
Wind tower
CFD software
simulation
A cooling wind tower
incorporating heat pipe
technology and cool sink; passive
cooling system.
System can cool down
air flow up to 12 °C, and
at lower weed speeds
(1–2 m/s), it can reduce
the temperature
significantly.
NA [53,54]
CFD software
simulation and
experimental
investigation (1:10
scale experimental
platform)
Heat pipes integrated into a
multi-directional wind tower;
recovers exhaust heat.
The application of the
system can heat the
supply air by up to 4.5
°C. In addition, the heat
pipes can slow down
the air supply rates by
up to 8–17%.
NA [55]
(Redrawn by authors)
Experimental
investigation using a
large-scale chamber (3
m × 3 m × 5.6 m) with
a wind catcher unit
(0.7 m× 3.2 m × 0.45 m)
Integrated system with heat
recovery and wind catcher; helps
to assist air flow.
The combination system
can cool down the inlet
air temperature up to
0.9–1.8 °C. The heat
exchange rate of the
unit varies from 50% to
70% with different air
flow velocities, which
range from 1.2 to 3.1
m/s.
NA [56]
NA: Not available
CFD software simulation
and experimental
investigation (1:10 scale
experimental platform)
Heat pipes integrated into a
multi-directional wind tower;
recovers exhaust heat.
The application of the system
can heat the supply air by up
to 4.5 ◦C. In addition,
the heat pipes can slow down
the air supply rates by
up to 8–17%.
NA [55]
Energies 2019, 12, x FOR PEER REVIEW 12 of 23
Wind tower
CFD software
simulation
A cooling wind tower
incorporating heat pipe
technology and cool sink; passive
cooling system.
System can cool down
air flow up to 12 °C, and
at lower weed speeds
(1–2 m/s), it can reduce
the temperature
significantly.
NA [53,54]
CFD software
simulation and
experimental
investigation (1:10
scale experimental
platform)
Heat pipes integrated into a
multi-directional wind tower;
recovers exhaust heat.
The application of the
system can heat the
supply air by up to 4.5
°C. In addition, the heat
pipes can slow down
the air supply rates by
up to 8–17%.
NA [55]
(Redrawn by authors)
Experimental
investigation using a
large-scale chamber (3
m × 3 m × 5.6 m) with
a wind catcher unit
(0.7 m× 3.2 m × 0.45 m)
Integrated system with heat
recovery and wind catcher; helps
to assist air flow.
The combination system
can cool down the inlet
air temperature up to
0.9–1.8 °C. The heat
exchange rate of the
unit varies from 50% to
70% with different air
flow velocities, which
range from 1.2 to 3.1
m/s.
NA [56]
NA: Not available
(Redrawn by authors)
Experimental investigation
using a large-scale chamber
(3 m ×3 m ×5.6 m) with a
wind catcher unit (0.7 m×
3.2 m ×0.45 m)
Integrated system with heat
recovery and wind catcher;
helps to assist air flow.
The combination system can
cool down the inlet air
temperature up to 0.9–1.8 ◦C.
The heat exchange rate of the
unit varies from 50% to 70%
with different air flow
velocities, which range from
1.2 to 3.1 m/s.
NA [56]
NA: Not available.

Energies 2019,12, 1285 13 of 22
According to aforementioned studies, the superiority of the combination system can be described
as follows:
1.
Can reach the desired airflow rate (8 L/s to 10 L/s per person) for wind tower combination
system applications [54];
2.
Can help to stabilize the heat flux of buildings to reduce the total energy consumption demands
and enhance indoor thermal comfort [48–51];
3.
Can heat the indoor air (which varies from 0.9 to 4.5
◦
C) through heat recovery, reducing
energy loss [53–56].
However, except for the potential of energy savings, the limitations of the systems may also be
summarized:
1. Insufficient data of real-scale investigations for heat pipes combined with walls. Latest research
focuses on computational simulations or testing of single wall prototypes [48,49,51];
2.
Lack of real-life testing. There is insufficient data to evaluate performance of durability, cost,
and easy-operation. Further modelling using different climate zones needs to be investigated as
well [53];
3. The side effects of air pollution on heat recovery systems and inlet air are ignored [55];
4.
For heat pipe heat recovery, the optimization of heat pipe space and plans are also
disregarded [53–55].
4.3. Heat Recovery in Dehumidification Systems
Heat recovery is an important component of a dehumidification system [
12
]. Kabeel has stated
that higher pressure drops and uneven humidity distribution are caused by using densely packed
beds [
58
]. Many studies have been carried out to investigate the performance of dehumidification with
heat recovery systems. Table 4lists the development on common types of heat recovery, including
rotary wheel exchangers, fixed-plate exchangers, and desiccant-coated heat exchangers, combined
with dehumidification systems.
According to the aforementioned studies, the following summary could be given:
1.
Rotary desiccant wheels are always the better choice for adjusting the relative humidity of
airflows [
59
]. These systems can achieve moisture removal rates of 1.7 g/kg~7 g/kg [
60
,
61
].
Rotary desiccant wheels find wide use in various climate conditions, mostly in humid and hot
climates. However, more optimal models and verification are needed, including extensive
cross-sectional area [
62
], airflow and rotation speed control [
63
], and lower pressure drop
strategies [59];
2.
For fixed-plate heat exchangers, enthalpy heat recovery can improve frost resistance compared to
fixed-plate sensible heat recovery, as well as better sensible and latent effectiveness and smaller
space due to its more compact design compared to common cross-flow heat recovery system [
64
].
Fixed-plate enthalpy heat recovery enjoys a bright future in residential building applications as it
helps to avoid cross contamination and to improve air quality with the dehumidification system.
To achieve better thermal performance of enthalpy heat exchangers and more wide-ranging
applications for different climate conditions, increasing transfer units or changing the properties
of membrane materials chemically might be considered;
3.
Solid desiccant cooling technology is energy-saving and eco-friendly. Desiccant-coated heat
recovery can transfer sensible and latent heat at the same time. It has been found that
silica gel-coated heat recovery has better performance than polymer-coated heat recovery [
65
].
As the dehumidification and regeneration cycles greatly affect the dehumidification process,
the best adjustable mode should be identified. However, it would be hard to repair or replace
desiccant-coated heat recovery system, as this would bring about high costs to the system, making
it unsuitable for small-scale residential building applications.

Energies 2019,12, 1285 14 of 22
Table 4. A summary of different types of heat exchangers with dehumidification systems.
Type Images Key Features Research Methodology Results Climate Conditions Reference
Rotary desiccant
wheel
Energies 2019, 12, x FOR PEER REVIEW 14 of 23
Table 3. A summary of different types of heat exchangers with dehumidification systems.
Type Images Key Features
Research
Methodology Results Climate
Conditions Reference
Rotary
desiccant
wheel
Rotary wheel with polymer
composite desiccant,
sandwiched between the
condenser and evaporator
section of a heat pump with air
channels
Laboratory
experiment
Moisture removal capacity can
achieve 7 g/kg. The desiccant
wheel-heat pump system can
decrease relative humidity
from 59% to 45% and cool
down the air from 32 °C to 29
°C during testing.
Humid
subtropical
climate
[60]
Rotary desiccant wheel with
passive ventilation, coated in
silica gel particles
Laboratory
experiment
and CFD
simulation
The model can achieve 55% of
airflow dehumidification with
lower regeneration air
temperature and a lower
pressure drop.
Temperate
marine
climate
[59]
(Redrawn by authors)
Periodic total rotary heat
recovery with
polymer/alumina composite
desiccant
Laboratory
experiment
Silica gel and active alumina
desiccant material can achieve
high moisture removal, 2.1
g/kg and 1.7 g/kg, at
regenerating temperatures of
40 °C and 25 °C, respectively.
Humid
subtropical
climate
[66]
Heat pump-driven two-stage
desiccant wheel system
Mathematical
model and
laboratory
experiment
The COP was calculated as 5.5
under summer conditions with
a supply air humidity ratio of
10 g/kg.
Humid
continental
climate
[63]
Rotary wheel with polymer
composite desiccant, sandwiched
between the condenser and
evaporator section of a heat pump
with air channels
Laboratory experiment
Moisture removal capacity can
achieve 7 g/kg. The desiccant
wheel-heat pump system can
decrease relative humidity from
59% to 45% and cool down the
air from 32 ◦C to 29 ◦C
during testing.
Humid subtropical
climate [60]
Energies 2019, 12, x FOR PEER REVIEW 14 of 23
Table 3. A summary of different types of heat exchangers with dehumidification systems.
Type Images Key Features
Research
Methodology Results Climate
Conditions Reference
Rotary
desiccant
wheel
Rotary wheel with polymer
composite desiccant,
sandwiched between the
condenser and evaporator
section of a heat pump with air
channels
Laboratory
experiment
Moisture removal capacity can
achieve 7 g/kg. The desiccant
wheel-heat pump system can
decrease relative humidity
from 59% to 45% and cool
down the air from 32 °C to 29
°C during testing.
Humid
subtropical
climate
[60]
Rotary desiccant wheel with
passive ventilation, coated in
silica gel particles
Laboratory
experiment
and CFD
simulation
The model can achieve 55% of
airflow dehumidification with
lower regeneration air
temperature and a lower
pressure drop.
Temperate
marine
climate
[59]
(Redrawn by authors)
Periodic total rotary heat
recovery with
polymer/alumina composite
desiccant
Laboratory
experiment
Silica gel and active alumina
desiccant material can achieve
high moisture removal, 2.1
g/kg and 1.7 g/kg, at
regenerating temperatures of
40 °C and 25 °C, respectively.
Humid
subtropical
climate
[66]
Heat pump-driven two-stage
desiccant wheel system
Mathematical
model and
laboratory
experiment
The COP was calculated as 5.5
under summer conditions with
a supply air humidity ratio of
10 g/kg.
Humid
continental
climate
[63]
Rotary desiccant wheel with
passive ventilation, coated in silica
gel particles
Laboratory experiment
and CFD simulation
The model can achieve 55% of
airflow dehumidification with
lower regeneration air
temperature and a lower
pressure drop.
Temperate marine
climate [59]
Energies 2019, 12, x FOR PEER REVIEW 14 of 23
Table 3. A summary of different types of heat exchangers with dehumidification systems.
Type Images Key Features
Research
Methodology Results Climate
Conditions Reference
Rotary
desiccant
wheel
Rotary wheel with polymer
composite desiccant,
sandwiched between the
condenser and evaporator
section of a heat pump with air
channels
Laboratory
experiment
Moisture removal capacity can
achieve 7 g/kg. The desiccant
wheel-heat pump system can
decrease relative humidity
from 59% to 45% and cool
down the air from 32 °C to 29
°C during testing.
Humid
subtropical
climate
[60]
Rotary desiccant wheel with
passive ventilation, coated in
silica gel particles
Laboratory
experiment
and CFD
simulation
The model can achieve 55% of
airflow dehumidification with
lower regeneration air
temperature and a lower
pressure drop.
Temperate
marine
climate
[59]
(Redrawn by authors)
Periodic total rotary heat
recovery with
polymer/alumina composite
desiccant
Laboratory
experiment
Silica gel and active alumina
desiccant material can achieve
high moisture removal, 2.1
g/kg and 1.7 g/kg, at
regenerating temperatures of
40 °C and 25 °C, respectively.
Humid
subtropical
climate
[66]
Heat pump-driven two-stage
desiccant wheel system
Mathematical
model and
laboratory
experiment
The COP was calculated as 5.5
under summer conditions with
a supply air humidity ratio of
10 g/kg.
Humid
continental
climate
[63]
(Redrawn by authors)
Periodic total rotary heat recovery
with polymer/alumina composite
desiccant
Laboratory experiment
Silica gel and active alumina
desiccant material can achieve
high moisture removal, 2.1 g/kg
and 1.7 g/kg, at regenerating
temperatures of 40 ◦C and 25 ◦C,
respectively.
Humid subtropical
climate [66]
Energies 2019, 12, x FOR PEER REVIEW 14 of 23
Table 3. A summary of different types of heat exchangers with dehumidification systems.
Type Images Key Features
Research
Methodology Results Climate
Conditions Reference
Rotary
desiccant
wheel
Rotary wheel with polymer
composite desiccant,
sandwiched between the
condenser and evaporator
section of a heat pump with air
channels
Laboratory
experiment
Moisture removal capacity can
achieve 7 g/kg. The desiccant
wheel-heat pump system can
decrease relative humidity
from 59% to 45% and cool
down the air from 32 °C to 29
°C during testing.
Humid
subtropical
climate
[60]
Rotary desiccant wheel with
passive ventilation, coated in
silica gel particles
Laboratory
experiment
and CFD
simulation
The model can achieve 55% of
airflow dehumidification with
lower regeneration air
temperature and a lower
pressure drop.
Temperate
marine
climate
[59]
(Redrawn by authors)
Periodic total rotary heat
recovery with
polymer/alumina composite
desiccant
Laboratory
experiment
Silica gel and active alumina
desiccant material can achieve
high moisture removal, 2.1
g/kg and 1.7 g/kg, at
regenerating temperatures of
40 °C and 25 °C, respectively.
Humid
subtropical
climate
[66]
Heat pump-driven two-stage
desiccant wheel system
Mathematical
model and
laboratory
experiment
The COP was calculated as 5.5
under summer conditions with
a supply air humidity ratio of
10 g/kg.
Humid
continental
climate
[63]
Heat pump-driven two-stage
desiccant wheel system
Mathematical model and
laboratory experiment
The COP was calculated as 5.5
under summer conditions with a
supply air humidity ratio of
10 g/kg.
Humid continental
climate [63]
Energies 2019, 12, x FOR PEER REVIEW 15 of 23
Internally cooled 64%
desiccant-coated wheel with
heat exchanger
Laboratory
experiment
The overall cooling capacity
can increase by 64% and the
EER by 21% with this model
compared to those using an
adiabatic desiccant wheel.
Humid
subtropical
climate
[62]
Desiccant wheel using
humidity swing adsorption
(HSA)
Theoretical
study and
laboratory
experiment
The unit can achieve a
temperature rise of up to 9.4 °C
with an adsorption-to-
regeneration air ratio of 1:2
and 8 rph rotary speed.
Humid
continental
climate
[61]
Fixed-plate
Membrane heat exchanger
using Kraft paper to transfer
heat and moisture, assisting
heating, ventilation, and air
conditioning (HVAC) system.
Laboratory
experiment
and HPRate
software
analysis
The unit can help save up to
8% of annual energy
consumption in hot and humid
climates.
Humid
subtropical
climate
[21]
Novel quasi-counter-flow
membrane energy exchanger
Theoretical
calculation
and
laboratory
experiment
Under cold conditions, the unit
can obtain 88.5–94.5% sensible
effectiveness and 73.7–83.5%
latent effectiveness with
supply air temperature
ranging from −4 to 10 °C.
Cold climate [64]
Heat exchanger with
asymmetric composite
membranes
Mathematical
model
(outdoor
relative
humidity
range
45%−90%)
For cooling, increasing outdoor
relative humidity will cause
decreased sensible heat
transfer efficiency and
increased latent heat transfer
efficiency. For heating with
outdoor relative humidity
below 60%, a higher relative
humidity (RH) rate will cause
a slightly increased latent
NA [67]
Internally cooled 64%
desiccant-coated wheel with heat
exchanger
Laboratory experiment
The overall cooling capacity can
increase by 64% and the EER by
21% with this model compared
to those using an adiabatic
desiccant wheel.
Humid subtropical
climate [62]

Energies 2019,12, 1285 15 of 22
Table 4. Cont.
Type Images Key Features Research Methodology Results Climate Conditions Reference
Energies 2019, 12, x FOR PEER REVIEW 15 of 23
Internally cooled 64%
desiccant-coated wheel with
heat exchanger
Laboratory
experiment
The overall cooling capacity
can increase by 64% and the
EER by 21% with this model
compared to those using an
adiabatic desiccant wheel.
Humid
subtropical
climate
[62]
Desiccant wheel using
humidity swing adsorption
(HSA)
Theoretical
study and
laboratory
experiment
The unit can achieve a
temperature rise of up to 9.4 °C
with an adsorption-to-
regeneration air ratio of 1:2
and 8 rph rotary speed.
Humid
continental
climate
[61]
Fixed-plate
Membrane heat exchanger
using Kraft paper to transfer
heat and moisture, assisting
heating, ventilation, and air
conditioning (HVAC) system.
Laboratory
experiment
and HPRate
software
analysis
The unit can help save up to
8% of annual energy
consumption in hot and humid
climates.
Humid
subtropical
climate
[21]
Novel quasi-counter-flow
membrane energy exchanger
Theoretical
calculation
and
laboratory
experiment
Under cold conditions, the unit
can obtain 88.5–94.5% sensible
effectiveness and 73.7–83.5%
latent effectiveness with
supply air temperature
ranging from −4 to 10 °C.
Cold climate [64]
Heat exchanger with
asymmetric composite
membranes
Mathematical
model
(outdoor
relative
humidity
range
45%−90%)
For cooling, increasing outdoor
relative humidity will cause
decreased sensible heat
transfer efficiency and
increased latent heat transfer
efficiency. For heating with
outdoor relative humidity
below 60%, a higher relative
humidity (RH) rate will cause
a slightly increased latent
NA [67]
Desiccant wheel using humidity
swing adsorption (HSA)
Theoretical study and
laboratory experiment
The unit can achieve a
temperature rise of up to 9.4 ◦C
with an
adsorption-to-regeneration air
ratio of 1:2 and 8 rph
rotary speed.
Humid continental
climate [61]
Fixed-plate
Energies 2019, 12, x FOR PEER REVIEW 15 of 23
Internally cooled 64%
desiccant-coated wheel with
heat exchanger
Laboratory
experiment
The overall cooling capacity
can increase by 64% and the
EER by 21% with this model
compared to those using an
adiabatic desiccant wheel.
Humid
subtropical
climate
[62]
Desiccant wheel using
humidity swing adsorption
(HSA)
Theoretical
study and
laboratory
experiment
The unit can achieve a
temperature rise of up to 9.4 °C
with an adsorption-to-
regeneration air ratio of 1:2
and 8 rph rotary speed.
Humid
continental
climate
[61]
Fixed-plate
Membrane heat exchanger
using Kraft paper to transfer
heat and moisture, assisting
heating, ventilation, and air
conditioning (HVAC) system.
Laboratory
experiment
and HPRate
software
analysis
The unit can help save up to
8% of annual energy
consumption in hot and humid
climates.
Humid
subtropical
climate
[21]
Novel quasi-counter-flow
membrane energy exchanger
Theoretical
calculation
and
laboratory
experiment
Under cold conditions, the unit
can obtain 88.5–94.5% sensible
effectiveness and 73.7–83.5%
latent effectiveness with
supply air temperature
ranging from −4 to 10 °C.
Cold climate [64]
Heat exchanger with
asymmetric composite
membranes
Mathematical
model
(outdoor
relative
humidity
range
45%−90%)
For cooling, increasing outdoor
relative humidity will cause
decreased sensible heat
transfer efficiency and
increased latent heat transfer
efficiency. For heating with
outdoor relative humidity
below 60%, a higher relative
humidity (RH) rate will cause
a slightly increased latent
NA [67]
Membrane heat exchanger using
Kraft paper to transfer heat and
moisture, assisting heating,
ventilation, and air conditioning
(HVAC) system.
Laboratory experiment
and HPRate software
analysis
The unit can help save up to 8%
of annual energy consumption in
hot and humid climates.
Humid subtropical
climate [21]
Energies 2019, 12, x FOR PEER REVIEW 15 of 23
Internally cooled 64%
desiccant-coated wheel with
heat exchanger
Laboratory
experiment
The overall cooling capacity
can increase by 64% and the
EER by 21% with this model
compared to those using an
adiabatic desiccant wheel.
Humid
subtropical
climate
[62]
Desiccant wheel using
humidity swing adsorption
(HSA)
Theoretical
study and
laboratory
experiment
The unit can achieve a
temperature rise of up to 9.4 °C
with an adsorption-to-
regeneration air ratio of 1:2
and 8 rph rotary speed.
Humid
continental
climate
[61]
Fixed-plate
Membrane heat exchanger
using Kraft paper to transfer
heat and moisture, assisting
heating, ventilation, and air
conditioning (HVAC) system.
Laboratory
experiment
and HPRate
software
analysis
The unit can help save up to
8% of annual energy
consumption in hot and humid
climates.
Humid
subtropical
climate
[21]
Novel quasi-counter-flow
membrane energy exchanger
Theoretical
calculation
and
laboratory
experiment
Under cold conditions, the unit
can obtain 88.5–94.5% sensible
effectiveness and 73.7–83.5%
latent effectiveness with
supply air temperature
ranging from −4 to 10 °C.
Cold climate [64]
Heat exchanger with
asymmetric composite
membranes
Mathematical
model
(outdoor
relative
humidity
range
45%−90%)
For cooling, increasing outdoor
relative humidity will cause
decreased sensible heat
transfer efficiency and
increased latent heat transfer
efficiency. For heating with
outdoor relative humidity
below 60%, a higher relative
humidity (RH) rate will cause
a slightly increased latent
NA [67]
Novel quasi-counter-flow
membrane energy exchanger
Theoretical calculation
and laboratory
experiment
Under cold conditions, the unit
can obtain 88.5–94.5% sensible
effectiveness and 73.7–83.5%
latent effectiveness with supply
air temperature ranging from
−
4
to 10 ◦C.
Cold climate [64]
Energies 2019, 12, x FOR PEER REVIEW 15 of 23
Internally cooled 64%
desiccant-coated wheel with
heat exchanger
Laboratory
experiment
The overall cooling capacity
can increase by 64% and the
EER by 21% with this model
compared to those using an
adiabatic desiccant wheel.
Humid
subtropical
climate
[62]
Desiccant wheel using
humidity swing adsorption
(HSA)
Theoretical
study and
laboratory
experiment
The unit can achieve a
temperature rise of up to 9.4 °C
with an adsorption-to-
regeneration air ratio of 1:2
and 8 rph rotary speed.
Humid
continental
climate
[61]
Fixed-plate
Membrane heat exchanger
using Kraft paper to transfer
heat and moisture, assisting
heating, ventilation, and air
conditioning (HVAC) system.
Laboratory
experiment
and HPRate
software
analysis
The unit can help save up to
8% of annual energy
consumption in hot and humid
climates.
Humid
subtropical
climate
[21]
Novel quasi-counter-flow
membrane energy exchanger
Theoretical
calculation
and
laboratory
experiment
Under cold conditions, the unit
can obtain 88.5–94.5% sensible
effectiveness and 73.7–83.5%
latent effectiveness with
supply air temperature
ranging from −4 to 10 °C.
Cold climate [64]
Heat exchanger with
asymmetric composite
membranes
Mathematical
model
(outdoor
relative
humidity
range
45%−90%)
For cooling, increasing outdoor
relative humidity will cause
decreased sensible heat
transfer efficiency and
increased latent heat transfer
efficiency. For heating with
outdoor relative humidity
below 60%, a higher relative
humidity (RH) rate will cause
a slightly increased latent
NA [67]
Heat exchanger with asymmetric
composite membranes
Mathematical model
(outdoor relative
humidity range
45%−90%)
For cooling, increasing outdoor
relative humidity will cause
decreased sensible heat transfer
efficiency and increased latent
heat transfer efficiency. For
heating with outdoor relative
humidity below 60%, a higher
relative humidity (RH) rate will
cause a slightly increased latent
effectiveness while also
producing a rather stable and
sensible effectiveness.
NA [67]
Desiccant-coated heat
exchanger
Energies 2019, 12, x FOR PEER REVIEW 16 of 23
effectiveness while also
producing a rather stable and
sensible effectiveness.
Desiccant-
coated heat
exchanger
Desiccant-coated heat
exchanger, desiccant cooling
system
Mathematical
model
Under simulated conditions,
the lowest humidity ratio of
supply air decreases from
about 9.5 g/kg to 8 g/kg. The
cooling capacity of the model
increased by 30% compared
with other desiccant-coated
heat recovery systems without
self-cooled recovery.
Humid
subtropical
climate
[68]
Fin-tube heat exchanger with
silica gel coating
Outdoor
experiment
investigation
The average moisture removal
rate is 5.3 g/kg and the average
thermal COP was calculated as
being 0.34.
Humid
subtropical
climate
[69]
Solid desiccant-coated heat
exchanger
Outdoor
experiment
investigation
The average moisture removal
rate was 8 g/kg and the
thermal COP was calculated as
being 1.2.
Humid
subtropical
climate
[70]
NA: Not available
Desiccant-coated heat exchanger,
desiccant cooling system Mathematical model
Under simulated conditions,
the lowest humidity ratio of
supply air decreases from about
9.5 g/kg to 8 g/kg. The cooling
capacity of the model increased
by 30% compared with other
desiccant-coated heat recovery
systems without
self-cooled recovery.
Humid subtropical
climate [68]

Energies 2019,12, 1285 16 of 22
Table 4. Cont.
Type Images Key Features Research Methodology Results Climate Conditions Reference
Energies 2019, 12, x FOR PEER REVIEW 16 of 23
effectiveness while also
producing a rather stable and
sensible effectiveness.
Desiccant-
coated heat
exchanger
Desiccant-coated heat
exchanger, desiccant cooling
system
Mathematical
model
Under simulated conditions,
the lowest humidity ratio of
supply air decreases from
about 9.5 g/kg to 8 g/kg. The
cooling capacity of the model
increased by 30% compared
with other desiccant-coated
heat recovery systems without
self-cooled recovery.
Humid
subtropical
climate
[68]
Fin-tube heat exchanger with
silica gel coating
Outdoor
experiment
investigation
The average moisture removal
rate is 5.3 g/kg and the average
thermal COP was calculated as
being 0.34.
Humid
subtropical
climate
[69]
Solid desiccant-coated heat
exchanger
Outdoor
experiment
investigation
The average moisture removal
rate was 8 g/kg and the
thermal COP was calculated as
being 1.2.
Humid
subtropical
climate
[70]
NA: Not available
Fin-tube heat exchanger with silica
gel coating
Outdoor experiment
investigation
The average moisture removal
rate is 5.3 g/kg and the average
thermal COP was calculated as
being 0.34.
Humid subtropical
climate [69]
Energies 2019, 12, x FOR PEER REVIEW 16 of 23
effectiveness while also
producing a rather stable and
sensible effectiveness.
Desiccant-
coated heat
exchanger
Desiccant-coated heat
exchanger, desiccant cooling
system
Mathematical
model
Under simulated conditions,
the lowest humidity ratio of
supply air decreases from
about 9.5 g/kg to 8 g/kg. The
cooling capacity of the model
increased by 30% compared
with other desiccant-coated
heat recovery systems without
self-cooled recovery.
Humid
subtropical
climate
[68]
Fin-tube heat exchanger with
silica gel coating
Outdoor
experiment
investigation
The average moisture removal
rate is 5.3 g/kg and the average
thermal COP was calculated as
being 0.34.
Humid
subtropical
climate
[69]
Solid desiccant-coated heat
exchanger
Outdoor
experiment
investigation
The average moisture removal
rate was 8 g/kg and the
thermal COP was calculated as
being 1.2.
Humid
subtropical
climate
[70]
NA: Not available
Solid desiccant-coated
heat exchanger
Outdoor experiment
investigation
The average moisture removal
rate was 8 g/kg and the thermal
COP was calculated as being 1.2.
Humid subtropical
climate [70]
NA: Not available.

Energies 2019,12, 1285 17 of 22
For all combination systems, strategies for controlling airflow and real-life investigation under
different climate conditions are needed.
4.4. Heat Recovery with Thermoelectric Units
Since passive heat recovery systems take advantage of temperature differences between indoor
and outdoor air streams, exhaust heat cannot be fully recovered. To tackle this disadvantage
of conventional heat recovery, some researchers have proposed novel thermoelectric heat pump
recovery systems [
71
–
74
]. Thermoelectric modules are solid state heat pumps that utilize the Peltier
effect. During operation, DC current flows through the thermoelectric module, causing heat to be
transferred from one side of the thermoelectric device to the other and creating a cold and hot side [
75
].
Temperature difference could be an approach to achieve heat recovery. Thermoelectric modules
can also create electric energy when there is heat flux, which is called the thermoelectric generator
(TEG) and works via the Seebeck effect [
75
]. Much focus has been placed on heat exchangers with
thermoelectric generators for industrial and car waste heat recovery over decades, especially with
the heat pipe type [
76
–
79
]. Currently, several studies about fixed-plate and heat pipe heat exchangers
combined with thermoelectric modules for building ventilation application have appeared.
Table 5lists current studies of heat recovery combined with thermoelectric units, including key
features and economic evaluation.
From the current literature, some prospects and outlooks may be described:
1.
Heat exchangers combined with TE modules have more potential to achieve better thermal
performance under optimal condition simulations [
71
]. However, further study is needed to
investigate their long-term operation in domestic building applications;
2.
These novel systems benefit from their compact size, low electric energy consumption,
environmental-friendly device structure, and rather low cost [
71
], which makes them a sensible
choice with which to deal with heat loss during building ventilation;
3.
Since TE modules create redundant heat during their operation, the application of energy storage
materials might be considered to balance out cooling and heating needs [72].

Energies 2019,12, 1285 18 of 22
Table 5. Heat recovery systems integrated with thermoelectric (TE) modules.
Type Images Extent of Study Research Methodology/Software Outcomes Economic Analysis Suggestions Reference
Fixed-plate
Energies 2019, 12, x FOR PEER REVIEW 18 of 23
Table 4. Heat recovery systems integrated with thermoelectric (TE) modules.
Type Images Extent of
Study
Research
Methodology/Software Outcomes Economic Analysis Suggestions Reference
Fixed-
plate
Theoretical
analysis
Mathematical model
including cost-
performance model
By controlling
operating variables,
including
thermoelectric
numbers, filling
factors, length of P-
N legs, couple
numbers of
thermoelectric
cooler (TEC), and
overall thermal
conductance,
separately, the COP
of the system varies
from 2.18 to 4.37.
Under the optimal
parametric conditions,
the operating cost of
the heat exchanger with
thermoelectric module
(HE-TE) system is
lower than 0.02 $/kWh.
Further study is
needed to test the
feasibility of cost-
performance
conditions when
multiple TECs
are applied.
[71]
Experimental
investigation
Establish an
experimental platform
This novel system
can achieve overall
coefficients of
cooling and heating
of about 50.6% and
57.9%, respectively,
under optimal
operating current
and voltage.
NA
Phase change
material (PCM)
could be
considered as the
thermal energy
storage of the
solar-driven
exhaust air
thermoelectric
heat pump
recovery
(SDEATHP)
system to balance
the cooling or
heating needs of
fresh air
handling.
[72]
Theoretical analysis Mathematical model including
cost-performance model
By controlling operating variables,
including thermoelectric numbers,
filling factors, length of P-N legs,
couple numbers of thermoelectric
cooler (TEC), and overall thermal
conductance, separately, theCOP of
the system varies from 2.18 to 4.37.
Under the optimal parametric
conditions, the operating cost of
the heat exchanger with
thermoelectric module (HE-TE)
system is lower than 0.02 $/kWh.
Further study is needed to test
the feasibility of
cost-performance conditions
when multiple TECs are applied.
[71]
Energies 2019, 12, x FOR PEER REVIEW 18 of 23
Table 4. Heat recovery systems integrated with thermoelectric (TE) modules.
Type Images Extent of
Study
Research
Methodology/Software Outcomes Economic Analysis Suggestions Reference
Fixed-
plate
Theoretical
analysis
Mathematical model
including cost-
performance model
By controlling
operating variables,
including
thermoelectric
numbers, filling
factors, length of P-
N legs, couple
numbers of
thermoelectric
cooler (TEC), and
overall thermal
conductance,
separately, the COP
of the system varies
from 2.18 to 4.37.
Under the optimal
parametric conditions,
the operating cost of
the heat exchanger with
thermoelectric module
(HE-TE) system is
lower than 0.02 $/kWh.
Further study is
needed to test the
feasibility of cost-
performance
conditions when
multiple TECs
are applied.
[71]
Experimental
investigation
Establish an
experimental platform
This novel system
can achieve overall
coefficients of
cooling and heating
of about 50.6% and
57.9%, respectively,
under optimal
operating current
and voltage.
NA
Phase change
material (PCM)
could be
considered as the
thermal energy
storage of the
solar-driven
exhaust air
thermoelectric
heat pump
recovery
(SDEATHP)
system to balance
the cooling or
heating needs of
fresh air
handling.
[72]
Experimental
investigation
Establish an experimental platform
This novel system can achieve
overall coefficients of cooling and
heating of about 50.6% and 57.9%,
respectively, under optimal
operating current and voltage.
NA
Phase change material (PCM)
could be considered as the
thermal energy storage of the
solar-driven exhaust air
thermoelectric heat pump
recovery (SDEATHP) system to
balance the cooling or heating
needs of fresh air handling.
[72]
Energies 2019, 12, x FOR PEER REVIEW 19 of 23
Experimental
investigation
Laboratory conditions
and MATLAB
mathematic model
The finned heat sink
with thermoelectric
units has relatively
poor output
performance
compared to the
heat pipe with TE
units.
Heat exchanger cost is
$15.12/(W/K). [73]
Heat
pipe
Theoretical
analysis and
experimental
investigation
Theoretical model
using effectiveness-
NTU (number of
transfer unit) method
and laboratory scale
with two separate air
ducts (170 mm × 160
mm)
With increasing air
flow velocity, the
heat recovery
efficiency increased
from 67.9% to
72.4%.
N/A [74]
Experimental
investigation
Laboratory condition
and mathematic model
The heat pipe
combined with the
thermoelectric unit
cooling method
shows better output
performance
compared to that of
the heat sink.
Heat exchanger cost is
$10.67/(W/K). [73]
NA: Not available. P: p-type semiconductor; N: n-type semiconductor.
Experimental
investigation
Laboratory conditions and
MATLAB mathematic model
The finned heat sink with
thermoelectric units has relatively
poor output performance
compared to the heat pipe with
TE units.
Heat exchanger cost is
$15.12/(W/K). [73]
Heat pipe
Energies 2019, 12, x FOR PEER REVIEW 19 of 23
Experimental
investigation
Laboratory conditions
and MATLAB
mathematic model
The finned heat sink
with thermoelectric
units has relatively
poor output
performance
compared to the
heat pipe with TE
units.
Heat exchanger cost is
$15.12/(W/K). [73]
Heat
pipe
Theoretical
analysis and
experimental
investigation
Theoretical model
using effectiveness-
NTU (number of
transfer unit) method
and laboratory scale
with two separate air
ducts (170 mm × 160
mm)
With increasing air
flow velocity, the
heat recovery
efficiency increased
from 67.9% to
72.4%.
N/A [74]
Experimental
investigation
Laboratory condition
and mathematic model
The heat pipe
combined with the
thermoelectric unit
cooling method
shows better output
performance
compared to that of
the heat sink.
Heat exchanger cost is
$10.67/(W/K). [73]
NA: Not available. P: p-type semiconductor; N: n-type semiconductor.
Theoretical analysis and
experimental
investigation
Theoretical model using
effectiveness-NTU (number of
transfer unit) method and
laboratory scale with two separate
airducts (170 mm ×160 mm)
With increasing air flow velocity,
the heat recovery efficiency
increased from 67.9% to 72.4%.
N/A [74]
Energies 2019, 12, x FOR PEER REVIEW 19 of 23
Experimental
investigation
Laboratory conditions
and MATLAB
mathematic model
The finned heat sink
with thermoelectric
units has relatively
poor output
performance
compared to the
heat pipe with TE
units.
Heat exchanger cost is
$15.12/(W/K). [73]
Heat
pipe
Theoretical
analysis and
experimental
investigation
Theoretical model
using effectiveness-
NTU (number of
transfer unit) method
and laboratory scale
with two separate air
ducts (170 mm × 160
mm)
With increasing air
flow velocity, the
heat recovery
efficiency increased
from 67.9% to
72.4%.
N/A [74]
Experimental
investigation
Laboratory condition
and mathematic model
The heat pipe
combined with the
thermoelectric unit
cooling method
shows better output
performance
compared to that of
the heat sink.
Heat exchanger cost is
$10.67/(W/K). [73]
NA: Not available. P: p-type semiconductor; N: n-type semiconductor.
Experimental
investigation
Laboratory condition and
mathematic model
The heat pipe combined with the
thermoelectric unit cooling method
shows better output performance
compared to that of the heat sink.
Heat exchanger cost is
$10.67/(W/K). [73]
NA: Not available. P: p-type semiconductor; N: n-type semiconductor.

Energies 2019,12, 1285 19 of 22
5. Summary
This review has presented a summary of heat recovery technologies for residential building
applications, including the integration of heat recovery with some energy-saving systems. Some
conclusions about and limitations of these current studies are the following:
1.
The combination of heat recovery with passive systems of building components can obviously
reduce heat losses and inlet air flow rate. The combination of heat pipe and rotary wheel heat
recovery with wind towers would be more compact than normal fixed-plate heat recovery [
40
].
However, unexpected noise from the DC motor for rotary wheel heat recovery could be an issue.
Further real-scale testing is needed for complex building wall systems to improve their heat flux
stability. In addition to wind towers and roofs, chimneys and transom could also be chosen to be
combined with heat recovery technology.
2.
The effects of air pollution on decentralized ventilation with heat recovery systems lack further
investigation. Future study is also needed to deal with bypass leakages during operation [44].
3.
Regarding heat recovery-assisted dehumidification systems, desiccant material should have low
sensible heat effectiveness [
63
]. Meanwhile, for membrane heat recovery, increasing transfer units
could be considered as a means to process better heat transfer.
4.
Heat recovery combined with TE modules should be developed due to its compact size, low
electric energy consumption, environmental-friendly devices, and rather low cost. Further study
is needed to investigate its long-term operation in domestic building applications.
5.
Heat pipe heat recovery systems enjoy more potential to be combined with other sustainable
technologies such as thermoelectric modules and solar energy systems due to its advantages,
including handy manufacturing and convenient maintenance, a lack of cross contamination,
and greater thermal conductance [39,73].
6.
As seen in the current literature, many studies focus on mathematical model-based economic
analysis for heat recovery systems [
71
]. Further investigations into real-life evaluations with
economic analysis should be developed [56].
Funding:
This research was funded by Innovate UK (project code: 104019). And the APC was funded by WSSET
(world society of sustainable energy technologies).
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Pérez-Lombard, L.; Ortiz, J.; Pout, C. A review on buildings energy consumption information. Energy Build.
2008,40, 394–398. [CrossRef]
2.
Tommerup, H.; Svendsen, S. Energy savings in Danish residential building stock. Energy Build.
2006
,38, 618–626.
[CrossRef]
3.
Omer, A.M. Energy, environment and sustainable development. Renew. Sustain. Energy Rev.
2008
,12, 2265–2300.
[CrossRef]
4.
Cox, P.M.; Betts, R.a.; Jones, C.D.; Spall, S.A.; Totterdell, I.J. Acceleration of global warming due to
carbon-cycle feedbacks in a coupled climate model. Nature 2000,408, 184–187. [CrossRef]
5.
Zhao, D.X.; He, B.J.; Johnson, C.; Mou, B. Social problems of green buildings: From the humanistic needs to
social acceptance. Renew. Sustain. Energy Rev. 2015,51, 1594–1609. [CrossRef]
6.
Cuce, P.M.; Riffat, S. A comprehensive review of heat recovery systems for building applications. Renew. Sustain.
Energy Rev. 2015,47, 665–682. [CrossRef]
7. Mardiana-Idayu, A.; Riffat, S.B. Review on heat recovery technologies for building applications. Renew. Sustain.
Energy Rev. 2012,16, 1241–1255. [CrossRef]
8.
Waugaman, D.G.; Kini, A.; Kettleborough, C.F. A review of desiccant cooling systems. J. Energy Resour. Technol.
1993,115, 1–8. [CrossRef]
9.
Nóbrega, C.E.L.; Brum, N.C.L. Modeling and simulation of heat and enthalpy recovery wheels. Energy
2009
,
34, 2063–2068. [CrossRef]

Energies 2019,12, 1285 20 of 22
10.
Tu, R.; Liu, X.H.; Jiang, Y. Performance comparison between enthalpy recovery wheels and dehumidification
wheels. Int. J. Refrig. 2013,36, 2308–2322. [CrossRef]
11.
Ruivo, C.R.; Angrisani, G.; Minichiello, F. Influence of the rotation speed on the effectiveness parameters of a
desiccant wheel: An assessment using experimental data and manufacturer software. Renew. Energy
2015
,
76, 484–493. [CrossRef]
12.
Jani, D.B.; Mishra, M.; Sahoo, P.K. Solid desiccant air conditioning - A state of the art review. Renew. Sustain.
Energy Rev. 2016,60, 1451–1469. [CrossRef]
13.
Dallaire, J.; Gosselin, L.; da Silva, A.K. Conceptual optimization of a rotary heat exchanger with a porous
core. Int. J. Therm. Sci. 2010,49, 454–462. [CrossRef]
14.
Golubovic, M.N.; Hettiarachchi, H.D.M.; Worek, W.M. Evaluation of rotary dehumidifier performance with
and without heated purge. Int. Commun. Heat Mass Transf. 2007,34, 785–795. [CrossRef]
15.
Sauer, H.J.; Howell, R.H. Promise and potential of air-to-air energy recovery systems. Int. J. Refrig.
1981
,4, 182–194.
[CrossRef]
16.
Simonson, C. Heat and Energy Wheels. In Encyclopedia of Energy Engineering and Technology; CRC Press: Boca
Raton, FL, USA, 2007; Volume 2, pp. 794–800.
17. Besant, R.W.; Simonson, C.J. Air-To-Air Energy Recovery. ASHRAE J. 2000,42, 31–42.
18.
Roulet, C.A.; Heidt, F.D.; Foradini, F.; Pibiri, M.C. Real heat recovery with air handling units. Energy Build.
2001,33, 495–502. [CrossRef]
19. Richard, S.; Frederick, G.H. Plate-Type Heat Exchanger. U.S. Patent US2,193,405A, 12 March 1940.
20.
Mardiana-Idayu, A.; Riffat, S.B. An experimental study on the performance of enthalpy recovery system for
building applications. Energy Build. 2011,43, 2533–2538. [CrossRef]
21.
Nasif, M.; Al-Waked, R.; Morrison, G.; Behnia, M. Membrane heat exchanger in HVAC energy recovery
systems, systems energy analysis. Energy Build. 2010,42, 1833–1840. [CrossRef]
22.
Sammeta, H.; Ponnusamy, K.; Majid, M.A.; Dheenathayalan, K. Effectiveness charts for counter flow
corrugated plate heat exchanger. Simul. Model. Pract. Theory 2011,19, 777–784. [CrossRef]
23.
Abu-Khader, M.M. Plate heat exchangers: Recent advances. Renew. Sustain. Energy Rev.
2012
,16, 1883–1891.
[CrossRef]
24.
Khan, T.S.; Khan, M.S.; Chyu, M.C.; Ayub, Z.H. Experimental investigation of single phase convective heat
transfer coefficient in a corrugated plate heat exchanger for multiple plate configurations. Appl. Therm. Eng.
2010,30, 1058–1065. [CrossRef]
25.
Lu, Y.; Wang, Y.; Zhu, L.; Wang, Q. Enhanced performance of heat recovery ventilator by airflow-induced
film vibration (HRV performance enhanced by FIV). Int. J. Therm. Sci. 2010,49, 2037–2041. [CrossRef]
26.
Gherasim, I.; Taws, M.; Galanis, N.; Nguyen, C.T. Heat transfer and fluid flow in a plate heat exchanger part
I. Experimental investigation. Int. J. Therm. Sci. 2011,50, 1492–1498. [CrossRef]
27. Feist, W. Cool, Temperate Climate; Passive House Institute: Skive, Denmark, 2019.
28.
TECHNICAL INFORMATION HCC 2 Home Ventilation Unit for Suspended Ceiling. Available online: https:
//www.dantherm.com/media/2351812/home-ventilation-hcc2-datasheet.pdf (accessed on 6 March 2019).
29.
Yau, Y.H.; Ahmadzadehtalatapeh, M. A review on the application of horizontal heat pipe heat exchangers in
air conditioning systems in the tropics. Appl. Therm. Eng. 2010,30, 77–84. [CrossRef]
30.
Kreith, F.; Manglik, R.M.; Bohn, M.S. Principles of Heat Transfer; Cengage learning: Boston, MA, USA, 2012;
ISBN 1133714854.
31.
Chaudhry, H.N.; Hughes, B.R.; Ghani, S.A. A review of heat pipe systems for heat recovery and renewable
energy applications. Renew. Sustain. Energy Rev. 2012,16, 2249–2259. [CrossRef]
32.
Shao, L.; Riffat, S. Flow loss caused by heat pipes in natural ventilation stacks. Appl. Therm. Eng.
1997
,17, 393–399.
[CrossRef]
33.
Gan, G.; Riffat, S.B. Naturally ventilated buildings with heat recovery: CFD simulation of thermal
environment. Build. Serv. Eng. Res. Technol. 1997,18, 67–75. [CrossRef]
34.
Srimuang, W.; Amatachaya, P. A review of the applications of heat pipe heat exchangers for heat recovery.
Renew. Sustain. Energy Rev. 2012,16, 4303–4315. [CrossRef]
35.
Ersöz, M.A.; Yildiz, A. Thermoeconomic analysis of thermosyphon heat pipes. Renew. Sustain. Energy Rev.
2016,58, 666–673. [CrossRef]
36.
Abd El-Baky, M.A.; Mohamed, M.M. Heat pipe heat exchanger for heat recovery in air conditioning. Appl. Therm. Eng.
2007,27, 795–801. [CrossRef]

Energies 2019,12, 1285 21 of 22
37.
Yau, Y.H. Application of a heat pipe heat exchanger to dehumidification enhancement in a HVAC system
for tropical climates-A baseline performance characteristics study. Int. J. Therm. Sci.
2007
,46, 164–171.
[CrossRef]
38.
Lin, S.; Broadbent, J.; McGlen, R. Numerical study of heat pipe application in heat recovery systems. Appl. Therm.
Eng. 2005,25, 127–133. [CrossRef]
39.
Diao, Y.H.; Liang, L.; Kang, Y.M.; Zhao, Y.H.; Wang, Z.Y.; Zhu, T.T. Experimental study on the heat recovery
characteristic of a heat exchanger based on a flat micro-heat pipe array for the ventilation of residential
buildings. Energy Build. 2017,152, 448–457. [CrossRef]
40.
Zeng, C.; Liu, S.; Shukla, A. A review on the air-to-air heat and mass exchanger technologies for building
applications. Renew. Sustain. Energy Rev. 2017,75, 753–774. [CrossRef]
41.
Vali, A.; Simonson, C.J.; Besant, R.W.; Mahmood, G. Numerical model and effectiveness correlations for a
run-around heat recovery system with combined counter and cross flow exchangers. Int. J. Heat Mass Transf.
2009,52, 5827–5840. [CrossRef]
42.
Dhital, P.; Besant, R.W.; Schoenau, G.J. Integrating Run-Around Heat Exchanger Systems into the Design of Large
Office Buildings; American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.: Atlanta,
GA, USA, 1995.
43.
Manz, H.; Huber, H. Experimental and numerical study of a duct/heat exchanger unit for building
ventilation. Energy Build. 2000,32, 189–196. [CrossRef]
44.
Baldini, L.; Kim, M.K.; Leibundgut, H. Decentralized cooling and dehumidification with a 3 stage LowEx
heat exchanger for free reheating. Energy Build. 2014,76, 270–277. [CrossRef]
45.
Smith, K.M.; Svendsen, S. Development of a plastic rotary heat exchanger for room-based ventilation in
existing apartments. Energy Build. 2015,107, 1–10. [CrossRef]
46.
Coydon, F.; Herkel, S.; Kuber, T.; Pfafferott, J.; Himmelsbach, S. Energy performance of façade integrated
decentralised ventilation systems. Energy Build. 2015,107, 172–180. [CrossRef]
47.
Cuce, P.M.; Cuce, E. Toward cost-effective and energy-efficient heat recovery systems in buildings: Thermal
performance monitoring. Energy 2017,137, 1–8. [CrossRef]
48.
Sun, Z.; Zhang, Z.; Duan, C. The applicability of the wall implanted with heat pipes in winter of China.
Energy Build. 2015,104, 36–46. [CrossRef]
49.
Zhang, Z.; Sun, Z.; Duan, C. A new type of passive solar energy utilization technology - The wall implanted
with heat pipes. Energy Build. 2014,84, 111–116. [CrossRef]
50.
Niu, F.; Yu, Y. Location and optimization analysis of capillary tube network embedded in active tuning
building wall. Energy 2016,97, 36–45. [CrossRef]
51.
Li, A.; Xu, X.; Sun, Y. A study on pipe-embedded wall integrated with ground source-coupled heat exchanger
for enhanced building energy efficiency in diverse climate regions. Energy Build.
2016
,121, 139–151.
[CrossRef]
52.
Cuce, P.M.; Cuce, E.; Riffat, S. A novel roof type heat recovery panel for low-carbon buildings: An experimental
investigation. Energy Build. 2016,113, 133–138. [CrossRef]
53.
Calautit, J.K.; Hughes, B.R. A passive cooling wind catcher with heat pipe technology: CFD, wind tunnel
and field-test analysis. Appl. Energy 2016,162, 460–471. [CrossRef]
54.
Calautit, J.K.; Hughes, B.R.; O’Connor, D.; Shahzad, S.S. CFD and Wind Tunnel Study of the Performance of
a Multi-Directional Wind Tower with Heat Transfer Devices. Energy Procedia
2015
,75, 1692–1697. [CrossRef]
55.
Calautit, J.K.; O’Connor, D.; Hughes, B.R. A natural ventilation wind tower with heat pipe heat recovery for
cold climates. Renew. Energy 2016,87, 1088–1104. [CrossRef]
56.
Mardiana, A.; Riffat, S.B.; Worall, M. Integrated heat recovery system with wind-catcher for building
applications: Towards energy-efficient technologies. Mater. Process. Energy Commun. Curr. Res. Technol. Dev.
2013
, 720–727. Available online: http://www.formatex.info/energymaterialsbook/book/720-727.pdf
(accessed on 6 March 2019).
57.
Aflaki, A.; Mahyuddin, N.; Al-Cheikh Mahmoud, Z.; Baharum, M.R. A review on natural ventilation
applications through building façade components and ventilation openings in tropical climates. Energy Build.
2015,101, 153–162. [CrossRef]
58.
Kabeel, A.E. Adsorption-desorption operations of multilayer desiccant packed bed for dehumidification
applications. Renew. Energy 2009,34, 255–265. [CrossRef]

Energies 2019,12, 1285 22 of 22
59.
O’Connor, D.; Calautit, J.K.; Hughes, B.R. A novel design of a desiccant rotary wheel for passive ventilation
applications. Appl. Energy 2016,179, 99–109. [CrossRef]
60.
Chen, C.H.; Hsu, C.Y.; Chen, C.C.; Chiang, Y.C.; Chen, S.L. Silica gel/polymer composite desiccant wheel
combined with heat pump for air-conditioning systems. Energy 2016,94, 87–99. [CrossRef]
61.
Tsujiguchi, T.; Osaka, Y.; Kodama, A. Feasibility study of simultaneous heating and dehumidification using
an adsorbent desiccant wheel with humidity swing. Appl. Therm. Eng. 2017,117, 437–442. [CrossRef]
62.
Zhou, X.; Goldsworthy, M.; Sproul, A. Performance investigation of an internally cooled desiccant wheel.
Appl. Energy 2018,224, 382–397. [CrossRef]
63.
Tu, R.; Liu, X.H.; Jiang, Y. Performance analysis of a two-stage desiccant cooling system. Appl. Energy
2014
,
113, 1562–1574. [CrossRef]
64.
Liu, P.; Justo Alonso, M.; Mathisen, H.M.; Simonson, C. Performance of a quasi-counter-flow air-to-air
membrane energy exchanger in cold climates. Energy Build. 2016,119, 129–142. [CrossRef]
65.
Ge, T.S.; Dai, Y.J.; Wang, R.Z.; Peng, Z.Z. Experimental comparison and analysis on silica gel and polymer
coated fin-tube heat exchangers. Energy 2010,35, 2893–2900. [CrossRef]
66.
Chen, C.H.; Huang, P.C.; Yang, T.H.; Chiang, Y.C.; Chen, S.L. Polymer/alumina composite desiccant
combined with periodic total heat exchangers for air-conditioning systems. Int. J. Refrig.
2016
,67, 10–21.
[CrossRef]
67.
Engarnevis, A.; Huizing, R.; Green, S.; Rogak, S. Heat and mass transfer modeling in enthalpy exchangers
using asymmetric composite membranes. J. Memb. Sci. 2018,556, 248–262. [CrossRef]
68.
Ge, T.S.; Dai, Y.J.; Wang, R.Z.; Li, Y. Feasible study of a self-cooled solid desiccant cooling system based on
desiccant coated heat exchanger. Appl. Therm. Eng. 2013,58, 281–290. [CrossRef]
69.
Zhao, Y.; Ge, T.S.; Dai, Y.J.; Wang, R.Z. Experimental investigation on a desiccant dehumidification unit
using fin-tube heat exchanger with silica gel coating. Appl. Therm. Eng. 2014,63, 52–58. [CrossRef]
70.
Zhao, Y.; Dai, Y.J.; Ge, T.S.; Wang, H.H.; Wang, R.Z. A high performance desiccant dehumidification unit
using solid desiccant coated heat exchanger with heat recovery. Energy Build.
2016
,116, 583–592. [CrossRef]
71.
Cai, Y.; Mei, S.-J.; Liu, D.; Zhao, F.-Y.; Wang, H.-Q. Thermoelectric heat recovery units applied in the energy
harvest built ventilation: Parametric investigation and performance optimization. Energy Convers. Manag.
2018,171, 1163–1176. [CrossRef]
72.
Liu, Z.; Li, W.; Zhang, L.; Wu, Z.; Luo, Y. Experimental study and performance analysis of solar-driven
exhaust air thermoelectric heat pump recovery system. Energy Build. 2019,186, 46–55. [CrossRef]
73.
Lv, S.; He, W.; Jiang, Q.; Hu, Z.; Liu, X.; Chen, H. Study of different heat exchange technologies in fl uence on
the performance of thermoelectric generators. Energy Convers. Manag. 2018,156, 167–177.
74.
Remeli, M.F.; Verojporn, K.; Singh, B.; Kiatbodin, L.; Date, A. Passive Heat Recovery System using
Combination of Heat Pipe and Thermoelectric Generator. Energy Procedia 2015,75, 608–614. [CrossRef]
75.
Ioffe, A.F.; Stil’Bans, L.S.; Iordanishvili, E.K.; Stavitskaya, T.S.; Gelbtuch, A.; Vineyard, G. Semiconductor
thermoelements and thermoelectric cooling. Phys. Today 1959,12, 42. [CrossRef]
76.
Fairuz, M.; Date, A.; Orr, B.; Chet, L.; Singh, B.; Dalila, N.; Affandi, N.; Akbarzadeh, A. Experimental
investigation of combined heat recovery and power generation using a heat pipe assisted thermoelectric
generator system. Energy Convers. Manag. 2016,111, 147–157.
77.
Emre, M.; Dincer, I. Performance assessment of a thermoelectric generator applied to exhaust waste heat
recovery. Appl. Therm. Eng. 2017,120, 694–707.
78.
Orr, B.; Akbarzadeh, A.; Lappas, P. An exhaust heat recovery system utilising thermoelectric generators and
heat pipes. Appl. Therm. Eng. 2017,126, 1185–1190. [CrossRef]
79.
Cao, Q.; Luan, W.; Wang, T. Performance enhancement of heat pipes assisted thermoelectric generator for
automobile exhaust heat recovery. Appl. Therm. Eng. 2018,130, 1472–1479. [CrossRef]
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