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Experimental investigation of yearly energy loss through a heat
recovery ventilator unit in Newfoundland
Rabbani Rasha
Mechanical Engineering
Faculty of Engineering and Applied
Science, Memorial University
St. John’s, Canada
rrasha@mun.ca
M. Tariq Iqbal
Electrical Engineering
Faculty of Engineering and Applied
Science, Memorial University
St. John’s, Canada
tariq@mun.ca
Abstract— Nowadays the demand for energy-efficient houses
is increasing in order to reduce heating and cooling demand, to save
energy used in houses. A mechanical induced ventilation system,
also known as heat recovery ventilator (HRV) is required in all
houses constructed after the year 2000. An HRV unit can contribute
to increase energy efficiency and to reduce greenhouse gases
emission by recovering heat from the inside of the house and
delivering preheated fresh air to the house. Such a mechanical
ventilator also leads to losses. This paper presents an energy
consumption and logged heat loss data of a heat recovery ventilator
unit in Newfoundland. MATLAB and Microsoft Excel are used to
do all calculations and detailed analysis. The logged data shows that
the cost of running an HRV in Newfoundland for a year in a house
could be as high as $484 per year with an unknown air quality
improvement.
Keywords— heat recovery ventilator, thermal comfort, energy
consumption, and loss analysis with simulation.
I. INTRODUCTION
Energy requirements for space heating have increased and
most of the space heating source is fossil fuel based. So, the
researchers have focused on finding alternative energy source
as well as the best practice of using energy efficiently. One of
the possible and successful options is to improve the existing
energy systems integrated with heat recovery ventilation
(HRV), also recognized as mechanical ventilation heat
recovery (MVHR). A typical heat recovery unit can extract
about (60 -95) % of residual heat and contribute to increasing
the energy efficiency of the buildings [1]. This unit has been
used not only in the residential sector but also in the industry
since last two decades, as the total 26 % of industrial energy
is still wasted as hot gas or fluid in many countries of the
world [2]. In terms of industrial use, this system is normally
called waste heat recovery unit due to the huge amount of air
exchange between two sources at various temperatures. The
earliest study of mechanical ventilation system with heat
recovery unit of building has been done in Denmark and the
result showed that mechanical ventilation with heat pump
recovery is useful in terms of reduction in mite populations
in mattresses and carpets [1].
Nazoroff et al. [3] studied the mechanical ventilation
system with a counter-flow heat recovery unit to find out the
effectiveness of this type of system, using energy-efficient
control technique. They demonstrated that this kind of system
might satisfy the energy conservation goal and able to meet
the indoor air quality of the house by following the strategy
of building tight houses at an affordable cost. Apart from the
advantages, this system has a major disadvantage because it
consumes a large amount of electrical power as an input that’s
why in some cases, it mentioned that household’s electricity
consumption is increased. To resolve and recover the energy
loss, researchers have emphasized to build a system that can
integrate with heat recovery unit [4]. Nguyen et al. [5] have
studied the overall performance of mechanical ventilation
heat pump system with heat recovery by using forced
ventilation. They used four types of different system to
recover the sensible heat during ventilation process and the
systems are no heat recovery, separate sensible heat recovery,
single heat recovery as integration of heating ventilation, and
double heat recovery with heat pump. Their result concluded
that the most efficient and energy-saving system was
integrated mechanical double heat recovery system for
maintaining the air quality of indoor space. An advanced
mechanical ventilation heat recovery (MVHR) unit with the
help of heat pump was developed by Riffat and Gillott [6].
Their findings showed that this type of system is less
expensive with less maintenance and air change per hour
(ACH) compiled with the ASHRAE standards to provide
fresh and quality indoor air. Manz et al. [7] did both the
experiment and numerical simulations in order to evaluate the
performance for single-room ventilation unit with
regenerative mechanical ventilation heat recovery. The result
reported that it is possible to obtain the temperature
efficiencies up to 78% at lower electrical energy input. Also,
this unit can exchange the inside and outside air efficiently at
the highest comfort level. In cold climate country or artic
region where the seasonal difference is more, it is not easy to
maintain and balance of indoor air quality by using traditional
heat recovery unit because of the continuous moisture
problems and the tendency of outside air drops below the
freezing point.
To mitigating this issue, extensive research has been going
on worldwide. Kragh et al. [8] have made an innovative
mechanical ventilation heat recovery system. It is determined
that this type of system can defrost itself without taking
additional input energy in cold or arctic climates with high
heat recovery efficiency and accomplished to defrost below
the freezing point. The temperature efficiency at freezing
condition and the overall system efficiency was about 88%
and 85% respectively. Cuce and Riffat [9] did experimental,
theoretical, simulation analysis with thermodynamic
performance assessment of heat recovery systems. They also
discussed the way of integrating this unit with mechanical
ventilation system and the running cost of the fans of this unit
to overcome the pressure loss of it. It indicated that this unit
can diminish the energy consumption for heating, cooling,
and ventilation in order to make the energy-efficient house.
Lu et al. [10] demonstrated a crossflow, plastic film type heat
recovery unit to attain the optimal performance of it. The
research ended with few conclusions like pressure drop
increases with air flow rate and decreases with film thickness,
film vibration enhances the heat transfer rate of this system,
and the effectiveness of this type of heat exchanger varies
from 0.65 to 0.85 with increasing the airflow rate. However,
maintaining higher air quality in the house causes increasing
ventilation loss. That is why researchers have been trying to
develop new design of heat recovery ventilation system.
Hviid and Svendsen [11] have constructed a state-of-the-art
passive ventilation system with heat recovery unit and
cooling for temperature changes. The result showed that the
pressure drops, and heat transfer efficiency was about 0.37 Pa
and 75.6% respectively for the respective air flow rate 560
. Persily et al. [12] discussed an air to air heat exchanger
in order to acquire the recovery efficiency of a typical house,
equipped with heat recovery ventilator unit. The recovery
efficiency relied on the fan speed of an HRV and it mentioned
around (50-60) % of heat recovery efficiency without taking
the losses in fan power as well as the heat conduction through
the metal case of the heat exchanger.
It is likely to save the energy to reduce the mismatch
between energy and demand as well as to put less pressure on
using conventional energy. Research showed that it is
possible to save energy from HVAC system, using the heat
recovery unit. Ke and Yanming [13] focused a study on
estimating the applicability of heat recovery ventilator
employing various sites in China. This study revealed that
double heat exchanger instead of single heat exchanger
ventilation system should be able to adapt the requirement of
energy recovering through ventilation system in the climate
as mentioned above zones. Cost and payback analysis of this
type of system are important in order to make this system
more affordable and familiar to people. The overall cost of
this heat recovery system completely relies on the technology
that they have. The payback period normally varies from a
couple of years to 15 years, and their lifespan is mostly
greater than 30 years [1]. Among the various heat recovery
technologies, mechanical ventilation with heat recovery is
more efficient in terms of cost and the amount of recovered
energy. Tommerup and Svendsen [14] mentioned that
mechanical ventilation with heat recovery can be installed for
approximately 30
however, from the literature
search it was found that the operational cost of air to air heat
recovery system is quite high due to the running electrical
cost of fans of this system.
From the literature search, it is found that heat recovery
unit with mechanical ventilation plays an essential role in
order to make energy efficient with low energy consumed.
This system can contribute significantly to reduce the heating
demand of the house, as the waste heat or exhaust heat of
occupied space is used to preheat the incoming air for
enhancing thermal comfort. Most of the researchers have
performed and did a cost analysis of different types of
mechanical ventilation heat recovery system. In our research,
we discussed the energy consumption and heat loss scheme
of a heat recovery unit in a house for 12 months period. No
such study has been done for Newfoundland, Canada.
In this research, section 2 will present the HRV
components and operation, section 3 will describe the
methodology and experimental setup. Calculation method,
simulation results with discussion will be discussed
respectively, and the paper will end with a conclusion.
II. HRV COMPONENTS AND OPERATION
Heat recovery ventilation (HRV) is an energy-efficient
appliance and plays a significant role to maintain the indoor
air quality of the house. It also contributes to making an
energy-efficient house by incorporating the HVAC system.
This system provides cost-effective and environmentally
friendly energy to mitigate energy consumption and the
operating cost of the building [15]. This type of system
consists of fans, filters, airtight insulated casing, heat
exchanger or core, drain, sensors with controllers, and inlets
and exhaust passage. The air streams can flow in cross flow or
counter flow directions. In our research, a crossflow type HRV
was used that is showed by figure 1. The working principle of
this system is simple as stale air from indoor passes through
the core and exchange the heat with fresh air that comes from
outside. After taking the heat, the incoming air gets heated and
then this preheated fresh air directly goes to the indoor space
to provide the excellent quality air in order to continue the
highest level of thermal comfort for the occupants. Finally, the
exhaust air goes outside by releasing its heat. Thus, a heat
recovery unit works efficiently to exchange the indoor and
outdoor air. When heat is transferred from the exhaust to the
outdoor air stream during the heating season, condensation
can form inside the heat exchange core. For this reason, drain
pans are located inside the HRV to collect any water buildup,
and the HRV is connected to a sanitary drain [16].
Fig. 1. A typical heat recovery unit [17]
III. EXPERIMENTAL SET UP WITH METHODOLOGY
Our selected house was in St. John’s, NL, Canada with latitude
(47.56 °N) and longitude (52.71 °W). A heat recovery
ventilator (HRV) was installed there. The model of the HRV
was VENMAR AVS CONSTRUCTO 1.5 with dimensions
(height: 419 mm, width: 768 mm, depth: 438mm). The main
objective of it is to provide comfortable, healthy fresh air for
the building’s occupants. However, the problem is the heat
loss of it. So, we built an experimental set up that is showed
by the figure (2), with the help of HRV, data logger, computer
and so on to find out the amount of yearly heat loss through
HRV. The working principle of this set up is modest like
during the winter the inlet air fan takes the outside air and in
the same time the exhaust air from room exchange heat with
this incoming air to make preheated and fresh air for the room.
After that, this incoming air goes directly to room and the
exhaust air directly goes into environment by releasing the
heat. The temperature sensor LM 35 sense both the
temperature of incoming air and exhaust air. The temperature
data are amplified with the amplifier that has gain 13.42. Then
the amplified data are logged by the national instrument data
logger (Model: USB 1208LS). Finally, these logged data were
displayed in the Laptop, running with MATLAB code. The
block diagram of this operation procedure is shown in figure
(3).
IV. CALCULATION METHOD
To calculate the heat loss through heat recovery ventilator,
we logged the monthly inlet and outlet temperature difference
data by using MATLAB. We set up the data logger like a way
that can log data per minute. So, it can log about 525600 data
in one year. The diameter of inlet and outlet air duct
connected to HRV is 0.1524 meter. We also measured the air
velocity through the duct using anemometer and got around
2.75
.These parameters were used to calculate the flow
rate through the duct. We used several equations to get heat
loss as well as the flow rate. These equations are as follows,
Heat loss through, (1)
Where, flow rate, = =
=
Density of air, =
Specific heat of air,
Temperature difference of inlet and exhaust air of HRV
After putting all values in equation (1), we calculated the heat
loss of the heat recovery ventilator per minutes. We took
44640 data for January, March, May, October, and
December. Also, we took 43200 data for April, September,
November and 40320 for February. It is evident that we
turned off the HRV for June, July, and August so for these
three months the heat loss through HRV is equivalent to zero.
All the necessary graphs are shown in the result and
discussion section. Here, the heat recovery ventilator also
consumes electricity over the year to run its motor.
The electricity consumption of the HRV is calculated using
equation (2),
Electrical energy consumption=Power*24*273 (2)
Here, power of the HRV is measured using the Kill a Watt
device. Kill a Watt is an electrical device that can be used to
measure volt, current, power, and frequency of any electrical
equipment’s. Our measured power of the HRV is 110 Watt.
After putting this value in equation (2), the total electricity
consumption of the HRV is 720 kWh excluding the summer
months June, July and August as in these months the
windows of the house were open for natural air circulation to
maintain the air quality of the house. That is why the HRV
was turned off for these months. So, the total HRV losses are
found by the equation (3),
Total HRV losses= HRV losses + electrical energy
consumption (3)
Here, we got the HRV losses 2508 kWh from equation (1) for
the whole year and electrical energy consumption of HRV
720 kWh from equation (2) excluding the summer months.
So, the total HRV loss (2508+720) =3228 kWh per year. That
Fig. 2. Experiment set up of HRV
Fig. 3. Block diagram of the experiment procedure
is a very significant heat loss. Cost of that will be about
(3228*0.15) = $484 per year.
V. EXPERIMENTAL RESULTS AND DISCUSSION
After logging the temperature difference data for one year,
we calculated the energy loss as well as the power
consumption of the HRV. After that, we analyzed these data
through proper way and plotted using Microsoft Excel. Fig.
4. shows the monthly heat loss of the heat recovery unit. From
the result, it can be said that the heat loss was high in winter
because the need of heating load is comparatively higher in
winter months than the summer months. The total yearly heat
loss was found 2508 kWh with highest value 402 kWh in
December.
Fig. 4. Monthly HRV energy loss
Fig. 5. demonstrates the heat loss of the HRV throughout the
whole year. The heat recovery unit was turned off in summer
months. That is why the accumulated loss in summer is zero.
As the temperature difference of incoming and exhaust air is
high in extreme cold months, so the heat loss from HRV was
high in those months. From the analysis, it is noticeable that
the maximum value of heat loss was 1134 W in December,
when it was very cold outside.
Fig. 5. HRV heat loss of per minute
Fig. 6. offers the BE opt software analysis with heat recovery
losses annually. Building Engineering Optimization (BE opt)
is thermal modeling software that can be used to find out the
different thermal loads of the selected house. For this software
requirement, various house parameters with physical
properties of the appliances are given as an input in this
software. Among these loads, Mechanical ventilation unit
(2010, HRV, 70%), specified as a fraction of ASHRAE
standard 62.2 is mentioned in this software. The result showed
that the total amount of energy loss from this software is 700
kWh, but from the experimental result, the value was obtained
2508 kWh. Simulation error and the wrong selection of HRV
properties are responsible for these discrepancies.
Relative humidity of the house from BE opt is shown by the
fig. 7. As the thermal comfort and indoor air quality are the
matter, we kept the controller knob in the comfort zone in
winter and in the summer the knob was placed in summer
mode. The relative humidity comfort zone range was (30-60)
%. In the user guide, it is mentioned that humidity level should
not be selected below 30 % to avoid the excessive dryness in
the air. This dryness makes the discomfort for the occupants.
From the fig. 7, it is concluded that the relative humidity is
reached at the highest level at 70 % in summer and maintained
within the comfort zone during the winter. The result showed
a good agreement with the literature.
Fig. 6. HRV loss from BE opt software
Fig. 7. Relative humidity of the house from BE opt software
V. CONCLUSION
In this research, yearly power consumption and heat loss
analysis of a heat recovery ventilator were done
experimentally in a cold climate area’s house. Electrical
energy consumption of the HRV was calculated 720 kWh per
year with constant running fan. A simple calculation approach
is used to find out the heat loss of the HRV annually. The total
amount of heat loss is obtained around 2508 kWh. As the
heating energy demand is high in winter months, so the HRV
loss followed the same trend with the highest heat loss amount
402 kWh in December. Heat recovery ventilator is a useful
part in order to make the house more energy-efficient, energy
savings and proper utilization of energy. Though the system
has enormous advantages in various sectors in especially in
domestic buildings for their potential of saving energy and
mitigating greenhouse gas emissions in the environment, it
has certain amount of cost including power consumption as an
input, maintenance and operation cost and the labor cost for
making the condensation water vapor pan empty. In a nutshell,
it can be said that a house with heat recovery ventilator
enhanced indoor air quality but there is an associated cost that
could be as high as $484 per year.
ACKNOWLEDGMENT
The authors would like to thank Memorial university for
supporting this research. In addition, The authors would like
to thank NSERC for supporting the research as well.
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