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Air-to-air energy recovery
Abstract
Auxiliary energy loads for supply air heating or cooling sometimes can substantially reduce the need for dehumidifying or humidifying by using air-to-air heat or energy exchangers. Applying air-to-air heat/energy exhangers in buildings is a cost-effective and reliable way of conditioning outside ventilation air. This paper shows that air-to-air heat/energy recovery can reduce the capital costs and energy consumption of auxiliary heating and cooling equipment.
... The ratio can be even higher in hot and humid climates or cold climates, due to larger difference between outdoor and indoor air conditions. Air-to-air heat/energy recovery is a well-known and effective method to improve energy efficiency of air-conditioning systems because the heat/energy exchangers can precondition outdoor air through transferring heat (or moisture) between outdoor supply air and indoor exhaust air [2][3][4][5][6]. Besant and Simonson [2] reported that the annual energy consumption can be reduced between 31% and 64% by using an energy wheel and a heat wheel in a Chicago building air-conditioning system. ...
... Air-to-air heat/energy recovery is a well-known and effective method to improve energy efficiency of air-conditioning systems because the heat/energy exchangers can precondition outdoor air through transferring heat (or moisture) between outdoor supply air and indoor exhaust air [2][3][4][5][6]. Besant and Simonson [2] reported that the annual energy consumption can be reduced between 31% and 64% by using an energy wheel and a heat wheel in a Chicago building air-conditioning system. Rasouli et al. [4] found that a run-around membrane energy exchanger (RAMEE) provided up to 40% annual heating energy saving and up to 20% annual cooling energy saving in an office building, depending on the climate and exchanger effectiveness. ...
... Rasouli et al. [4] found that a run-around membrane energy exchanger (RAMEE) provided up to 40% annual heating energy saving and up to 20% annual cooling energy saving in an office building, depending on the climate and exchanger effectiveness. Moreover, the air-to-air heat/energy exchangers can significantly downsize the heating/cooling equipment, such as boilers and chillers, in new buildings [2,3]. ...
... Air-to-air heat exchangers for a new building have payback durations of one to five years in warm humid climates (Besant and Simonson 2000), and for enthalpy wheels, the payback could be even smaller (less than 3 years (Sekhar 2007)). Typical heat and enthalpy exchanger efficiencies range from 55 % to almost 80 % (Dieckmann et al. 2003). ...
... The desiccant material in an OA dehumidification system should be periodically reactivated with dry exhaust or dedicated hot air. Application of an enthalpy wheel is favored generally if the humidity ratio is greater than 0.012 kg/kg (Besant and Simonson 2000). Air dehumidification could also be provided with low-grade solar energy dehumidification systems that separate the control of sensible and latent cooling load. ...
The commercial buildings sector in the United States used 18 percent (17.93 Quads) of the U.S. primary energy in 2006. Office buildings are the largest single energy consumption category in the commercial buildings sector of the United States with annual energy consumption around 1.1 Quads. Traditional approaches used in commercial building designs are not adequate to save energy in both depth and scale. One of the most effective ways to reduce energy consumption is to improve energy performance of HVAC systems. High-performance HVAC systems and components, as well as application of renewable energy sources, were surveyed for buildings in hot and humid climates. An analysis of performance and energy saving potential estimation for selected HVAC systems in hot and humid climates was developed based on energy consumption simulation models in DOE-2.1E. A calibrated energy consumption model of an existing office building located in the hot and humid climate conditions of Texas was developed. Based on this model, the energy saving potential of the building was estimated. In addition, energy consumption simulation models were developed for a new office building, including simulation of energy saving measures that could be achieved with further improvements of HVAC system above the energy conservation codes requirements. The theoretical minimum energy consumption level for the same office building was estimated for the purpose of evaluating the whole building energy efficiency level. The theoretical minimum energy consumption model of the office building was designed to provide the same level of comfort and services to the building occupants as provided in the actual building simulation model. Finally, the energy efficiency of the building that satisfies valid energy conservation codes and the building with an improved HVAC system was estimated based on theoretically minimum energy consumption level. The analysis provided herein can be used for new building practitioners and existing building owners to evaluate energy reduction potential and the performance of innovative technologies such as dedicated outdoor air system, displacement ventilation, improved cooling system efficiency, air source heat pumps and natural gas heat pumps.
... In the past, energy recovery systems in buildings have been designed with the main focus on sensible heat transfer and with little emphasis on latent heat transfer or moisture transfer (Carnes 1984;Sauer and Howell 1981). Typically, fixed plate, sensible heat transfer wheel, heat pipe, and coil run-around loop heat exchangers have been used (Besant and Simonson 2000). These heat exchangers cannot, however, be used to directly control the indoor humidity. ...
... The calculations needed to evaluate the operating energy cost involve functions of these parameters integrated over time and are quite complex (ASHRAE 2000). Besant and Simonson (2000) present a discussion of the various configurations of heat and energy recovery devices and guidelines on how the operating energy cost may be evaluated. It is the purpose of this paper to show how this air-to-air heat and energy system design problem can be formulated for a simple HVAC configuration and solved for the least life-cycle cost system while still retaining a small payback period. ...
This paper shows how air-to-air heat and energy system design problems can be formulated for a simple HVAC configuration and solved for the least life-cycle cost system while still retaining a small payback period. Mathematical expressions and design tables are presented to facilitate the design process. The design process is illustrated for the city of Chicago where both large heating and cooling loads occur in HVAC applications. The example design problem presented shows that payback periods of less than one year are often achieved for energy wheels and sometimes for sensible heat exchangers. The life-cycle cost savings for auxiliary heating and cooling ventilation air far exceeds the capital cost of the energy exchanger (sensible or total), even when only a ten-year life cycle is considered.
... Ventilation systems with heat recovery have been recognized since the 1970s as a means to decrease heating and cooling energy consumption [7]. Mechanical ventilation systems with HR, implemented in modern buildings, can reduce building heating and cooling energy by up to one-third [8]. The Energy Performance of Buildings Directive (EPBD) mandates incorporating heat recovery in mechanical ventilation systems [9]. ...
Buildings have become a key issue in developing of sustainable solutions due to their significant contribution to total CO2 emissions and substantial energy consumption. Special attention is devoted to building ventilation, which has a significant rate of building energy consumption. HVAC systems are essential for maintaining a healthy environment for building occupants. Natural ventilation uses natural forces such as wind and temperature differences to fresh air circulation. Mechanical venti- lation systems are designed to provide continuous circulation of fresh air in buildings, thereby im- proving indoor air quality. Modernly designed mechanical ventilation systems utilize advanced tech- nologies such as heat recovery units, which reduce energy consumption and improve building energy efficiency. This paper presents modeling of different ventilation strategies in a residential building, using EnergyPlus software. Simulations were provided for selected summer and winter days. Ob- tained results for natural ventilation showed zone ventilation heat losses and gains, while mechanical ventilation system with heat recovery is modeled with emphasis on indoor air quality.
... ERVs reduce the peak load, which reduces the size of the heating and cooling equipment and, thereby, the upfront capital costs. In cold climate conditions like those in Chicago, Besant and Simonson (2003) found that the size of the boiler and the size of the chiller required could be reduced by 44% and 52%, respectively. For similar climatic conditions, Rasouli et al. (2013) found savings in the peak heating and cooling load by 30% and 18%, respectively. ...
Ventilation plays a crucial role in preventing indoor airborne disease transmission. Nevertheless, ventilation increases the energy consumption of HVAC systems. Therefore, energy efficiency measures or alternative methods must be adopted to reduce the energy demand of HVAC systems, which is necessary to achieve sustainability in the building sector. This study proposes a method of utilizing an energy recovery ventilator (ERV) to provide supplementary ventilation to reduce airborne disease transmission. The proposed method is tested for an office building with one source room (with an infected occupant) and two connected rooms (no infection source). The contributions of the present study are (i) the development and verification of a new supplement ventilation method using an ERV to reduce the probability of infection from airborne pathogens and (ii) providing the economic and environmental benefits of the proposed method to promote its adaption by the building managers/HVAC engineers. The results of the present study show that the proposed method can reduce the probability of infection by 10 to 40% and demonstrate that utilizing an ERV is a sustainable and economical method to improve ventilation to reduce indoor airborne disease transmission.
... At the building level, to reduce the total energy demand, in general, the recovery of the exhausted heat through ventilation and air conditioning (HVAC) systems is approached. Energy efficiency directives [1], [4], [5] and specialized literature show that the combination of thermal rehabilitation of buildings (sealing of envelope elements) and the use of ventilation with heat recovery leads to considerable reductions in total energy consumption for space heating/cooling, but also greenhouse gas emissions [6], [7], [8], [9]. ...
... Therefore, decentralised devices for alternating air supply and exhaust are becoming more and more popular [11][12][13]. Because these solutions are characterised by lower flow resistance, they consume less energy to drive the fan [15][16][17][18]. Air is transported through the façade of the building, allowing the shortest flow path between the interior of the room and the external environment [19]. ...
... Total energy wheels are passive devices used in buildings to exchange heat and moisture between fresh outdoor air and building exhaust (Simonson & Besant, 2000). Energy wheels consist of a metal substrate coated with a solid desiccant. ...
This paper presents an overview of ASHRAE RP-1780, which developed a test method to evaluate gaseous contaminant transfer in energy wheels. The method was validated with data measured in the project. A new performance parameter called Exhaust Contaminant Transfer Ratio (ECTR) was introduced to quantify the cross contamination. In this paper, the proposed methodology is demonstrated using experimental data of two gaseous contaminants in two desiccant coated rotary wheels. Manufacturers and test laboratories can apply the test method to quantity gaseous contaminant transfer in energy wheels with an uncertainty of less than ±3%. These test data will assist designers select energy wheels to reduce energy consumption while minimizing the cross-contamination of gaseous contaminants to improve indoor air quality and health.
... Recuperators simultaneously exchange heat/energy between the air streams through a dividing plate or a membrane. Plate, tubular, and membrane-type exchangers are examples of recuperators [48], [49]. The operating principle of most common ERVs is explained in the following subsections. ...
Increasing ventilation is an effective method to reduce indoor airborne disease transmission. An Energy recovery ventilator (ERV) is a passive energy recovery device used to reduce the energy consumption of heating, ventilation and air-conditioning (HVAC) systems for conditioning the ventilation air. It preconditions the ventilation air by transferring energy from building exhaust air. Therefore, the ventilation and exhaust air streams interact directly/indirectly in the ERV for energy transfer. It is surmised that the ERV may transfer bioaerosols (with pathogens) from the exhaust air to ventilation air, resulting in the spread of infectious diseases. Consequently, many pandemic HVAC guidelines recommend that the use of ERVs be limited. This is a highly unsustainable direction given the increased energy requirements associated with the high ventilation provision advocated for pandemic operation. It must be noted that no validated experimental evidence exists in literature for bioaerosol transfer in ERVs. Hence, it is necessary to conduct extensive bioaerosol transfer research before adopting the unsustainable practice of limiting the utilization of ERVs. The main objective of this review study is to summarize the experimental methods and instrumentation for bioaerosol transfer research in ERVs. This comprehensive article provides a detailed overview of the generation, sampling, and analysis of bioaerosols for conducting the experiments. Further, it explains the possible mechanisms for bioaerosol transfer in various types of ERVs based on which the ERVs that need immediate attention are identified. The main contribution of this research paper is that it provides a novel experimental method which encompasses the biosafety aspects, instrumentation, performance parameters and uncertainties in conducting virus contained bioaerosol transfer study in ERVs. The findings from this review will be helpful in designing bioaerosol transfer experiments and developing future ERV test standards for such experiments.
... Therefore, decentralised devices for alternating air supply and exhaust are becoming more and more popular [11][12][13]. Because these solutions are characterised by lower flow resistance, they consume less energy to drive the fan [15][16][17][18]. Air is transported through the façade of the building, allowing the shortest flow path between the interior of the room and the external environment [19]. ...
... With increasing awareness of the indoor environment and energy crisis, various energy-saving methods [6] have been used to reduce the building energy consumption of HVAC (heating, ventilating, and air conditioning) systems, including natural ventilation [7,8], ventilative cooling [9], and different sorts of energy recovery devices [10]. Reports present that energy recovery is one of the most cost-effective means to save energy consumption, and the use of heat recovery ventilation in airtight buildings can reduce the annual energy consumption for heating and cooling loads by up to one-third [11][12][13]. ...
To manage energy-efficient indoor air quality, mechanical ventilation with a heat recovery system provides an effective measure to remove extra moisture and air contaminants, especially in bathrooms. Previous studies reveal that heat recovery technology can reduce energy consumption, and its calculation needs detailed information on the thermal performance of exhaust air. However, there are few studies on the thermal performance of bathroom exhaust air during and after showers. This study proposed a detailed thermal performance prediction model for bathroom exhaust air based on the coupled heat and mass transfer theory. The proposed model was implemented into the AccuRate Home engine to estimate the thermal performance of residential buildings with heat recovery systems. The time variation of the water film temperature and thickness on the bathroom floor can be estimated by the proposed model, which is helpful in determining whether the water has completely evaporated. Simulation results show that changing the airflow rate in the bathroom has little effect on drying the wet floor without additional heating. The additional air heater installed in the bathroom can improve floor water evaporation efficiency by 24.7% under an airflow rate of 507.6 m³/h. It also demonstrates that heat recovery can significantly decrease the building energy demand with the fresh air load increasing and contribute about 0.6 stars improvement for the houses in Hobart (heating-dominated region). It may be reduced by around 3.3 MJ/(m²·year) for the houses in other regions. With this study, guidelines for optimizing the control strategy of the dehumidification process are put forward.
... These solutions are associated with lower pressure losses [13] and therefore energy consumption for ventilation [14][15][16]. As pointed out in the paper by E. Zender-Świercz [17] as a literature review, there are still not enough studies relating to heat recovery in decentralised façade ventilation. ...
A study of heat recovery in a façade ventilation unit was carried out under laboratory conditions using a climate chamber that allowed stable outdoor and indoor conditions to be simulated. The unit, equipped with a reversible fan and a chamber for the heat exchanger, controlled by an automation control system, was designed to exchange air in the room by alternating supply and exhaust cycles of specific durations. Three types of heat exchangers were tested, which were filled with different phase change materials, in order to estimate the efficiency of the façade ventilation unit in terms of its heat recovery capability. The efficiency of the unit was determined based on the temperature efficiency of heat recovery for 144 setting combinations. The best efficiency results between 73.56% and 76.29% were obtained with a solution using a heat exchanger consisting of cylinders with an external diameter of 10 mm and a wall thickness of 1 mm filled with jojoba oil in a one minute cycle. The tests confirmed that the heat exchangers, which are part of the façade ventilation unit, fulfil their function and allow heat recovery from the exhaust air to pre-heat the supplied air. The study complements the existing scientific knowledge on the efficiency of heat exchangers filled with phase change material, operating in winter conditions with work cycles up to 5 min.
... The reason for using the recirculated air is to reuse the thermal energy inside the pig house. This technology is widely investigated in industrial environments to save air conditioning costs by recycling the energy inside buildings [8][9][10][11][12][13]. In particular, standards for air recirculation have been developed in general industrial processes, and the allowable concentration standards for hazardous substances in reused air are suggested [14]. ...
As the pig industry develops rapidly, various problems are increasing both inside and outside pig houses. In particular, in the case of pig houses, it is difficult to solve the main problems even if automation and mechanization are applied with Information and Communications Technologies (ICT). The air recirculation technology can be applied as a technology that can solve these typical problems in the pig industry, such as growth environment, livestock disease, odor emission, energy cost, and pig productivity. The air recirculated ventilation system (ARVS) can minimize the inflow of air from the outdoors and recycle the internal thermal energy of the pig house. The ARVS consists of (1) an air scrubber module, (2) an external air mixing module, (3) a UV cleaning module, (4) a solar heat module, and (5) an air distribution module. In this study, the growth environment of piglets was predicted using a numerical model when the ARVS was applied. Since the concept of air recirculation was used, numerous equations for predicting the internal environment should be iteratively calculated. Furthermore, it was necessary to determine the optimum condition of the modules by applying various boundary conditions. Therefore, the model was designed for numerical analysis based on the balance equations of environmental factors inside the piglet room. For each module, the module coefficient and equations were considered based on the previous studies. The analysis was conducted according to the system diagram of each module, and the growth environment inside the piglet room was evaluated according to the various environmental conditions. As a result of calculating the numerical model, the ventilation rate of 40 CMM or more was advantageous to properly maintaining the gas environment. In the summer season, it was necessary to additionally use the cooling device and dehumidifier. In the winter season, when using a heat exchanger and solar module, was more advantageous for maintaining air temperature inside the piglet room.
... Conditioning outdoor air is an energy-intensive process, and it accounts for about 60% of commercial building energy consumption in developed countries (Natural Resources Canada 2020). One way to reduce energy consumption for conditioning the outdoor air is to use air-toair energy exchangers (AAEEs) (Besant and Simonson 2000) that exchange heat and moisture between the building exhaust and supply airstreams. Figure 1 shows a schematic of an HVAC system that provides conditioned air into a building. ...
This article presents a literature review on experimental studies for measuring gaseous contaminant transfer in different energy exchangers. The experimental methods, measured contaminant transfer rates and uncertainties (where available) for different gases are summarized, although most studies do not include any uncertainty analysis. The measured transfer rates vary between 0% and 75%, with uncertainties between 1% and 30%. The literature review shows that mechanisms for gaseous contaminant transfer in energy exchangers are air leakage, carryover, and phase change mechanisms such as: adsorption/desorption, condensation/evaporation, and absorption/evaporation. There is an established test methodology to quantify the gaseous contaminant transfer in energy exchangers due to air leakage and carryover; however, there is no method in the literature to quantify gaseous contaminant transfer due to the phase change mechanisms. Thus, a method to determine the contaminant transfer due to the phase change mechanisms is proposed and applied to the available literature data.
... 2 Fig. 1-1. The impact of humidity on human health (Arundel et al., 1986) Energy consuming mechanical devices, such as air conditioning (AC) systems, are commonly used to cool an environment and maintain optimal RH levels (Di Giuseppe and D'Orazio, 2014;Besant and Simonson, 2000). However, these systems demand regular maintenance, which is not often systematically done, and a good understanding of their functioning and optimal use. ...
High or low indoor relative humidity (RH) levels may have negative effects on people’s
health and well-being. To regulate the humidity, air conditioning systems can be used,
requiring energy and increasing the environmental emissions. However, some materials,
like clay and gypsum, which are described as hygroscopic, can passively regulate the
indoor climate, reducing peaks of internal relative humidity, when applied on exposed
surfaces to the room air. Their capacity to moderate indoor humidity fluctuations is
due to their ability to adsorb and desorb moisture, a process referred to as moisture
buffering. This property is evaluated through the Moisture Buffering Value (MBV),
which allows for a simplistic calculation of the potential of materials by considering the
material properties and humidity regulation. Due to the simplified interpretation of
moisture buffering, the testing methods are not representative of the material behaviour
in a real building. Furthermore, moisture buffering can be measured, following various
standards that are not directly comparable. Alternative experimental studies have
attempted to investigate the actual performance of materials in real buildings, but
there is no standard methodology yet and no established relationship between moisture
buffering and building performances.
This PhD aimed to understand the moisture buffering effects in the indoor
environment, by establishing a method to measure this property in full-scale
experimentation and laboratory testing. The research was initially developed, by
considering three independent approaches: laboratory testing, field work and
simulations. In the laboratory testing, clay, gypsum, lime and plasterboard’s
hygrothermal properties were tested, to observe and compare their moisture buffering
behaviour and investigate the correlation between material properties and moisture
buffering potential. Successively, the testing protocol boundary conditions and test
protocol were investigated. The effect of temperature, RH fluctuation and air velocity
on moisture buffering capacity of plasters was investigated.
Field work aimed to study the response of real size rooms to humidity fluctuations, to
evaluate the impact of moisture buffering, when buildings are exposed to external
climate variations, ventilation and indoor temperature variations. Two hygroscopic
rooms were compared to a reference room (non-hygroscopic). The testing
methodology and equipment were designed to observe the moisture exchange through
ventilation, building infiltration and wall moisture buffering capacity. The
investigation showed the important impact of hygroscopic materials on the regulation
iii
of the indoor moisture content. When the humidity increases, the walls store
moisture from the indoor reducing the amount of moisture removed through
ventilation. When the absolute humidity is low, the cold air that moves into the
building through ventilation constantly replaces the indoor moist air. Therefore, the
outdoor air over-dries the indoor environment. In this case walls release moisture in
the room to counterbalance the moisture removed by ventilation.
Based on the rooms tested in field work, simulations were used to analyse the
contribution of sub-layers and wall design on the moisture buffering performance of
plasters. Materials in direct contact with the environment are responsible for the
regulation of the indoor moisture. Materials exposed to the indoor stored and
released most of the moisture and depending on the humidity level and moisture load,
those materials regulate the amount of moisture that moves into the sub-layers.
The culmination of this investigation converged the three research approaches in
order to compare and investigate the behaviour of indoor materials in laboratory and
in a real building. By merging the three approaches, significant differences between
simulations and experimental in-situ testing were found. In simulations, walls buffer
more moisture than in the experimental cells. On the other hand, simulations showed
a good agreement with the experimental laboratory testing that demonstrates
numerical models are based on laboratory measured properties, which are not always
representative of the real moisture buffering behaviour of a material when applied to
a building.
The ability to test the moisture buffering performance of buildings is the key for
material performance assessment. This thesis provides guidelines that reduce
uncertainty to assess moisture buffering. It investigated and introduced different
approaches to evaluate the materials performances from the material development to
their application on buildings. The impact of this research is to push the development
of new moisture control materials at a laboratory scale, with new confidence in their
larger scale performance. This will result in an indoor environment that is healthier
and more comfortable, by maintaining of the optimal indoor RH level, whilst reducing
the risk of condensation and decay of construction materials.
... The ventilation systems with heat recovery as a way to reduce the consumption of heat and cooling energy have been known since the 1970s [37]. The use of heat recovery in airtight buildings can reduce the annual energy consumption for heating and cooling by up to one-third [38][39][40]. The Energy for Buildings Directive (EPBD) even imposes an obligation to use heat recovery in mechanical ventilation systems [41]. ...
The purpose of the article was to present information on heat recovery in ventilation systems and to highlight what has not been sufficiently researched in this regard. A lot of information can be found on methods and exchangers for heat recovery in centralized systems. Decentralized, façade systems for cyclical supply and exhaust air have not been sufficiently researched. It is known that these devices are sensitive to the influence of wind and temperature, hence heat recovery may be ineffective in their case. The literature describes the aspect of heat recovery depending on the location in climatic zones, depending on the number of degree days (HDD). Attention was also paid to the risk of freezing of heat recovery exchangers. The literature review also showed the lack of a universal method for assessing heat recovery exchangers and the method of their selection depending on the climate.
... In order to combine the appropriate IAQ in the premises and energy savings, various methods are used to control centralized systems, for example, based on the relative humidity level [122] or the concentration of carbon dioxide in the internal air [123]. In many existing buildings, it may not be possible to install centralised ventilation systems [124][125][126][127][128]. For this purpose, hybrid ventilation systems or decentralised façade ventilation can be used [129][130][131][132]. ...
Poor indoor air quality affects the health of the occupants of a given structure or building. It reduces the effectiveness of learning and work efficiency. Among many pollutants, PM 2.5 and 10 dusts are extremely important. They can be eliminated using mechanical ventilation equipped with filters. Façade ventilation devices are used as a way to improve indoor air quality (IAQ) in existing buildings. For their analysis, researchers used carbon dioxide as a tracer gas. They have shown that façade ventilation devices are an effective way to improve IAQ, but require further analysis due to the sensitivity of façade ventilation devices to the effects of wind and outdoor temperature. In addition, legal regulations in some countries require verification in order to enable the use of this type of solution as a way to improve IAQ in an era characterised by the effort to transform buildings into passive houses (standard for energy efficiency in a building).
... 1) Reducing the peak energy rates as well as operation cost 2) Allows for a higher ventilation rates that will help in creating a better indoor air quality rates at a minimum auxiliary energy consumption that will help not in only provide a better environment for the inhabitants but will also reduce the cost of operation [12]. ...
... Regenerative heat and mass exchangers, commonly found in the form of active desiccant wheels, are used in the so-called desiccant cooling cycles [1][2][3][4], which employ water as the effective refrigerant and require low-grade energy sources, or in the form of enthalpy wheels (also called passive desiccant wheels), which are commonly employed for reducing air-conditioning costs in ventilated buildings by recovering energy from the exhaust air to the supply air [5][6][7][8] Additional studies [9,10] have also shown that these devices have potential applications for a combined use with air-refrigeration cycles. These types of exchangers are composed by numerous mini-channels through which airstreams flow, transferring mass and energy to the chanels' hygroscopic walls. ...
A transient two-dimensional model for coupled heat and mass transfer in channels with hygroscopic walls has been developed. The formulation employs a generalized form that is valid for both circular tubes and parallel-plates channels with walls composed of a desiccant material that can physically adsorb humidity from a moist airstream. The model equations are normalized in terms of physically relevant dimensionless groups, and then solved using a computational implementation based on the Numerical Method of Lines (NUMOL) using the Finite Volumes Method (FVM) for the spatial discretization. Validation results are presented by comparing the periodic solutions of the proposed formulation with experimental data for two different cases, showing very good agreement. Finally, illustrative results of the proposed formulation are presented for two typical situations found in desiccant wheel applications: dehumidification and regeneration. An analysis of the simulated data shows that the convective coefficients can strongly depend in both space and time, which suggests that lumped models based on constant convective coefficients for simulating desiccant and enthalpy wheels should be used with care.
... Therefore, HVAC system designers and researchers have a great interest in developing energy-efficient and environmental-friendly technologies without compromising thermal comfort and indoor air quality in buildings. Current HVAC systems often include air-to-air energy exchanger to improve the system efficiency by utilizing the energy of building exhaust to condition the supply air [4][5][6]. Airto-air energy exchangers reduce the load on the HVAC unit thus lowering the size of the unit as well as the energy consumption. The selection of a suitable energy exchanger is based on climate data, application, indoor and outdoor conditions and maintenance cost [7,8]. ...
Fixed-bed regenerators (FBR) transfer heat (and moisture) between supply and exhaust air streams in heating, ventilating and air conditioning (HVAC) systems to reduce building energy consumption. This paper presents a new small-scale testing facility to evaluate the performance (i.e. sensible effectiveness) of FBRs for HVAC applications. The major contributions of this paper are: development of a new small-scale experimental facility and methodology for testing FBRs, quantification of uncertainties, and verification of small-scale test data over a large range of FBR design conditions. A numerical model and two well-known design correlations are used to verify the results and testing methodology. The advantages of small-scale testing are that it requires low volume of conditioned airflow, has low uncertainty, requires less exchanger material and has a low cost per test. Moreover, the small-scale testing methodology of FBR would benefit heat exchanger manufacturers to perform detailed sensitivity studies and optimize the exchanger performance over a wide range of design and operating parameters prior to the fabrication of full-scale exchangers.
... Several mathematical models are developed for the heat and moisture transfer in thermal wheels [9][10][11] and some of them have been partially validated using experimental setups [12][13][14]. Besant and Simonson [15] have performed an economic analysis considering the US winter and summer climatic conditions to calculate the energy saving and cost saving from rotary thermal wheels. ...
Buildings in hot and humid climates spend more than 60% of the total energy cost for Air Conditioning and Mechanical Ventilation Systems (ACMV) to maintain the required thermal comfort for occupants. The required air conditioning load drastically increases with the fresh air demand of the conditioned space which leads to excessive energy bills for central air conditioning systems of buildings, particularly in hot and humid climates. Therefore, this study mainly focuses to investigate and evaluate the applicability of rotary thermal wheel to recover the energy available on the return air of the air handling unit (AHU) of the central air conditioning systems in hot and humid climates. The results reveal that, the percentage energy saving due to the rotary thermal wheel increases when the temperature and the relative humidity of outdoor fresh air increases, and also when Coefficient of Performance (COP) of the central chiller decreases. Moreover, case studies show that the simple payback period of a building which is supplied with 20% fresh air varies from 1.1 years to 4 years depending on the fresh air mass flow rate. Results reveal that the use of rotary thermals in the hot and humid climates is highly recommended.
... 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]. ...
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.
... Heating, ventilation, and air conditioning (HVAC) systems and moisture control devices [3,4] were developed to provide optimal thermal comfort and maintain RH at ideal levels, but they require additional energy [5,6]. Some materials, described as hygroscopic, have the ability to passively control the indoor climate, reducing operational energy. ...
It is important to control indoor humidity level in buildings as it influences occupant's health and comfort. Hygroscopic building materials present great potential to passively regulate air humidity due to their ability to adsorb and desorb moisture. In recent years researchers have focused on this capacity, referred to as Moisture Buffering, as it has the potential to improve indoor thermal comfort and reduce HVAC usage and their consequent energy consumption. However, building designers generally do not consider this property an important factor, due to its unclear influence and difficulty in the quantification of its effects in real buildings. Therefore, it is complicated to develop an appropriate laboratory scale testing. The aim of this paper is to investigate the challenges related to moisture buffering measurement and to examine the approaches adopted by researchers. The significance of this study is to identify discrepancies between existing methods in the evaluation of the dynamic adsorption properties and presents areas for further development in testing.
... The energy and economic performance of a passive energy recovery system depends on its effectiveness, cost, maintenance, climate and indoor design parameters. Besant and Simonson [92] studied the performance of energy wheel and heat wheel in a building HVAC system in Chicago. The results showed that the capacity of the boiler and chiller for associated air-conditioning system can be reduced up to 44% and 52%, respectively. ...
... This temperature, which may be 120Co or more, influences the amount of heat that can be recovered and used for process applications [25]. During operation, heat-recovery mufflers should not create excessive backpressure on the reciprocating engine because high backpressure reduces the engine efficiency and increases the exhaust gas temperature [26]. In selecting the location for a reciprocating engine, it is important to realize that sharp bends in the exhaust system piping can create excessive backpressure and should be avoided. ...
Energy demand is increasing worldwide, Iraqi people
severe of power shortages from long years ago. Refrigeration and
heating of homes consume the bulk of energy. In this study, a
proposed system leads to use small electrical power generators for
generating electricity and use the exhaust gas thermal energy for
heating hot water that can be supplied for Iraqi houses. This system
will satisfy more than 90% of the fuel used for heating water in
winter.
In fact this system is applied in many modern countries from long
time ago, but for huge units not applied for small units. Small
electrical generators have maximum thermodynamic efficiency about
27%, and there is about 73% of the fuel energy go to ambient as
waist energy. The aim of this research is to verify the ability of
thermal energy utilization of 5kw benzene electrical generator for the
purposes of heating and hot water supply in winter to an Iraqi house.
... Fehrm et al [5] showed that HR is a necessity in northern and central European climatic conditions and concluded that primary energy consumption can be reduced by a minimum of 20% in Germany and Sweden. Besant and Simonson [6] calculated the energy recovered and the annual savings, by installing an air-to-air sensible HE in the HVAC system of a building. Lazzarin and Gasparella [7] evaluated heat recovery ventilation (HRV) systems in three cities with different climates in Italy by taking into account the recovered energy, the reduction in heating and cooling capacity, and the operation time of the systems. ...
In many heating, ventilation and air-conditioning (HVAC) applications, heat recovery devices are installed, aiming at reducing energy consumption. Especially in buildings requiring a high percentage of outside air for ventilation, there is a high potential for heat recovery from exhaust air. Climatic conditions are an important parameter which affects the recovered heat and the payback period of the heat recovery device. In this paper, a 250 person auditorium is used as a model to estimate the applicability of an air-to-air fixed-plate heat exchanger installed in the air handling unit of the HVAC system. The application is considered for four cities, representative of climatic zones A, B, C, D of Greece, which also represent typical Mediterranean climate conditions. Zone A, Crete and Southern Greece, is similar to Nicosia (Cyprus) and Palermo (Sicily), Zone B, with Athens, corresponds to Rome (Italy) and coastal Spain, Zone C with Thessaloniki is similar to the Toulon (France) and Split (Croatia) and Zone D, with its continental climate is more like Milan (Italy) and Lyon (France). An energy analysis with the modified bin method energy calculation was performed to calculate (a) the heating and cooling energy that can be recovered, (b) the reduction in HVAC equipment, and (c) the expected payback period. For the specific climatic conditions examined, it was proven that: heating energy consumption decreased by 31 to 40%, depending on occupancy, while electric energy consumption didn't change notably; the payback period does not exceed 24 months, depending on climate zone and occupancy.
... Another monitored parameter, frequently given by constructors too, is the temperature ratio according to EN 308:1997. Almost always this parameter is known in literature as efficiency or as effectiveness, when referring to the ratio of supply air mass flow rate and the minimum mass flow rate (between the supply air and exhaust air) [8]. A set of NTC temperature probes are installed around the heat exchanger (T E , T O , T DIS ST and T S ST in Fig. 2) to evaluate the heat transfer between supply and exhaust airstream. ...
In this study, a mechanical ventilation system with heat recovery integrated by heat pump was analysed. The recovery unit can works according different arrangements: passive plus thermodynamic recovery, only passive or active recovery and freecooling. The study was carried out to evaluate the energy performances of the system during the control of temperature in winter season. Tests were performed at different temperature values of simulated outdoor air To (−5 °C, 0 °C, 5 °C and 10 °C) and a fixed (reference) indoor simulated temperature (20 °C). Each trial was performed with a ventilation flow rate of 535 m3/h. The coefficient of performance of the overall system (COPs) is 9.50 at 0 °C, 8.86 at 5 °C and 6.62 at 10 °C respectively. At −5 °C the compressor behaved as an on-off type. This is due to a safety mechanism for the evaporator defrost. This behavior suggests the existence of a temperature value at which is preferable to switch from the static plus thermodynamic operation mode to another arrangement and vice-versa. Also a comparison with other prototypes found in literature and with a common commercial system was made. It results that SIVeMeC has higher energy performances in a wide range of temperature than other system analysed.
... If cooling was important, the benefits of an air-toair energy exchanger would increase from those documented here, especially since cooling is often accomplished with electrical chillers, which have a greater environmental impact than most heating solutions. The benefits could be further increased in a cooling climate by applying an air-to-air energy exchanger that transfers both sensible heat and water vapor (Besant and Simonson 2000). To perform the analysis properly for a cooling climate, the materials and energy associated with the cooling coil as well as the environmental impact of providing the cooling energy would need to be included. ...
The life-cycle assessment (LCA) methodology is used in this paper to assess the environmental effects of air-handling units (AHU) over a 20-year life cycle. This assessment is based on quantifying the consumption of resources (energy and materials), the harmful emissions into the environment (air, water, and soil), and the potential changes in the environment (climate change, acidification, and ozone production). A normal AHU, with a face velocity of 3 m/s (600 fpm), and a small AHU, with a face velocity of 4 m/s (800 fpm), are investigated with and without two types of air-to-air energy exchangers (plate and rotating wheel). The research demonstrates the following benefits of air-to-air energy exchangers: reduced energy consumption, reduced emissions to the environment, and reduced potential harmful changes in the environment. For both of the AHUs studied, these benefits are several times greater than the burdens arising from the production and operation of the AHU, where the function of the AHU is to provide 2000 L/s (4200 cfm) of outdoor air to the building space for 2500 h/year, but not to condition this air. A larger AHU with an air-to-air energy exchanger of higher efficiency has the smallest harmful effect on the environment.
... Furthermore, energy consumption in buildings due to ventilation and infiltration accounts for approximately 30 to 50% of total energy consumption [25]. In Europe for instance, with the consolidation of the demand for thermal comfort and IAQ, the energy demand for heating from ventilation air tends to reach about 60 to 70% of the total annual energy demand for the building [26]. Since the envelope of building equipped with HVAC systems is becoming tighter, the energy consumption resulted by the ventilation can be much higher than that caused by the heat transfer through the building shell [27,28]. ...
Climate change has become an undoubted environmental challenge in last couple of decades in every continent and all sectors across the world. It occurs due to increase in temperature of atmosphere by burning of fossil fuels and releasing of greenhouse gases. These days, vast quantities of fossil fuels have been used for energy source to power the economy of a country. This scenario significantly contributes to a large percentage of carbon dioxide emissions. By comparing with other economic sectors, it was reported in the literature that the consumption of energy in buildings accounts for about one third of the total consumption and responsible for an equal portion of carbon dioxide emissions in both developed and developing countries. In order to have a deeper understanding into existing knowledge concerning this area, this paper presents a review on building energy consumption and its related carbon dioxide emissions as threat to climate change.
... In air-to-air membrane energy exchangers, heat and moisture transfer between the supply and exhaust airstreams through the membrane. Air-to-air membrane energy exchangers are efficient for energy recovery and significantly reduce HVAC energy consumption [49][50][51][52][53][54][55]. Zhang and Niu [51] reported that in hot and humid climates such as Hong Kong, installing an air-to-air membrane energy recovery ventilator reduced the annual total cooling and ventilation energy consumptions by 12% and 58%, respectively, whereas installing a sensible recovery ventilator saved only 2% and 10%. ...
Buildings are responsible for a significant portion of the global energy consumption. In particular, heating, ventilation, and air-conditioning (HVAC) systems in buildings consume significant amounts of energy. Liquid desiccant dehumidification and energy recovery are effective energy conservation technologies in HVAC systems. Direct-contact liquid desiccant air-conditioning systems have the risk of carry-over of aerosol droplets to the supply airstream, which may cause health problems for occupants and corrosion of the ducting system. Liquid-to-air membrane energy exchanger (LAMEE) is a novel semi-permeable membrane-based liquid desiccant energy exchanger, which transfer heat and moisture simultaneously but can eliminate the desiccant solution aerosol carry-over problem. Two LAMEEs can also be used to constitute a run-around membrane energy exchanger (RAMEE) system to recover heat and moisture from exhaust air in buildings. In the past decade, research and development of LAMEEs has been very active to show that high effectiveness is possible. This paper presents a comprehensive review of the design and performance of LAMEEs.
... Extensive research has been conducted for different types of energy recovery ventilators (ERVs), e.g. energy wheels [5][6][7], permeable membrane plate exchangers [8][9][10], twin-tower enthalpy recovery loops [11]. ERVs can precondition the outdoor ventilation air by transferring both heat and moisture between exhaust air and outdoor ventilation air. ...
... However, Sweeten et al. [35] and other researchers found that when the moisture content of the open lot surface is between 25% and 40%, both dust and odor potential are at manageable levels. Indoor RH can significantly affect the thermal comfort [36][37][38][39][40], the perception of IAQ [41,42], occupant health [43][44][45][46][47], the durability of building materials [48,49], material emissions [50] and energy consumption [51,52]. ...
... Extensive research has been conducted for different types of energy recovery ventilators (ERVs), e.g. energy wheels [5][6][7], permeable membrane plate exchangers [8][9][10], twin-tower enthalpy recovery loops [11]. ERVs can precondition the outdoor ventilation air by transferring both heat and moisture between exhaust air and outdoor ventilation air. ...
... There are three types of energy recovery (ER) devices available to recover both heat and moisture from an exhaust air stream in buildings; these are: air-to-air membrane energy exchangers (AA-MEE), energy wheels and liquid-to-air energy exchangers used in run-around liquid desiccant coupled systems [1,2]. In AAMEEs the heat and moisture transfer between supply and exhaust air streams through a semi-permeable membrane. ...
h i g h l i g h t s Liquid-to-air membrane energy exchangers are called LAMEEs in this paper. For the first time, the solution-side (SS) effectiveness are introduced for LAMEEs. The SS effectiveness is very important when a LAMEE is used as a regenerator. Both the air-side and solution-side effectiveness of the LAMEE increase with Cr ⁄ . The air-side and solution-side effectiveness values are different in most cases. a b s t r a c t A liquid-to-air membrane energy exchanger (LAMEE) is an energy exchange device that transfers heat and moisture between air and salt solution streams through a semi-permeable membrane which is per-meable for water vapor but impermeable for liquid water. LAMEEs have been used as a dehumidifier/ regenerator in air-conditioning systems. In this paper, the solution-side effectiveness are presented for a small-scale single-panel LAMEE when it is used to regenerate the solution flow. The solution-side effec-tiveness are very important in regenerators where the main focus is on the salt solution, and the solution properties (i.e. solution outlet concentration) are important. The small-scale LAMEE is tested under air dehumidification and solution regeneration test conditions using a LiCl solution at one NTU (i.e. NTU = 5) and three different Cr ⁄ values (Cr ⁄ = 2, 4 and 6). The results show that both the air-side and solu-tion-side effectiveness of the LAMEE increase with Cr ⁄ . The solution-side latent effectiveness is lower for the regenerator in comparison to the dehumidifier (e.g. 43% lower at Cr ⁄ = 6). Also, the numerical results for a small-scale LAMEE which were presented in literature are used in this paper to evaluate the solu-tion-side effectiveness of the LAMEE under different test conditions. The numerical results show that the difference between the air-side and solution-side latent effectiveness are negligible. Therefore, the air-side latent effectiveness can be used to evaluate the solution-side latent effectiveness of LAMEEs.
... Moghaddam). weather data, installation and maintenance costs, energy recovery system design and performance [4][5][6][7]. A run-around membrane energy exchanger (RAMEE) is a recent technology, which has been used to transfer both heat and moister between supply and exhaust air streams. ...
Energy and Buildings j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / e n b u i l d Small-scale single-panel liquid-to-air membrane energy exchanger (LAMEE) test facility development, commissioning and evaluating the steady-state performance: Small-scale exchanger Liquid-to-air membrane energy exchanger Steady-state effectiveness NTU Heat capacity ratio a b s t r a c t A new test facility was developed to assess the performance of a small-scale single-panel liquid-to-air membrane energy exchanger (LAMEE). Mass and energy balances of the exchanger were computed for each test. The steady-state performance of the small-scale LAMEE was experimentally investigated under different operating conditions. Water was used as a liquid transfer media for the experiments and the exchanger was tested for air heating and humidifying (H&H), air cooling and humidifying (C&H), and air cooling and dehumidifying (C&D) at three different NTU values (2.5, 3.5 and 4.5) and Cr* = 7. The experimental results were compared to results from a numerical and two analytical models. In most cases, reasonable agreement among the experimental, numerical and analytical results was achieved except for the sensible effectiveness in the H&H and latent and total effectiveness in the C&H test cases. The results showed that the effectiveness of the small-scale LAMEE always increased with NTU for all test conditions. Sensible and latent effectiveness contour maps of the small-scale LAMEE were generated numerically for different inlet air conditions and for NTU = 3.5 and Cr* = 7, while the water inlet temperature was set at 22 • C. Finally, the effectiveness contour maps were compared with three experimental test conditions.
En este trabajo se presenta un prototipo de intercambiador de calor aire-aire de flujo cruzado. El empaquetamiento del intercambiador de calor posee un volumen de 12,96dm3 y un área de transferencia de calor de 3,06m2. Las mediciones fueron realizadas en diferentes condiciones de funcionamiento. Se obtuvieron efectividades de 37%, 50%, 64% y 74% y transferencias de calor de 300 W y 1 kW. Además, se presenta un modelo físico-matemático para predecir el comportamiento termoenergético. El modelo funciona a partir de los datos de temperatura de entrada del flujo caliente, frío, flujos másicos y características constructivas del prototipo. El modelo fue validado con los datos medidos de temperaturas de salidas y comparando las efectividades. Se obtuvieron ajustes satisfactorios en todos los ensayos realizados.
As the pig industry develops rapidly, various problems are appearing both inside and outside the pig houses. In particular, in the case of pig houses, it is difficult to solve the main problems even if automation and mechanization are applied with ICT technology. The main current issues are: (1) preventing infectious diseases amongst livestock, (2) reducing the emission of harmful gas and odors, (3) improving the growth environment inside the pig house, (4) reducing energy costs, (5) improving the farm management and operating system, and 6) improving the livestock product quality. Air recirculation technology can be applied as a technology that can solve these typical problems in the pig industry. An air-recirculated ventilation system can minimize the inflow of air from outdoors and recycle the internal thermal energy of the pig house. The air-recirculated ventilation system consists of (1) an air scrubber module, (2) external air-mixing module, (3) UV cleaning module, (4) solar heat module, and (5) air-distribution module. First, in this study, the field data were collected to analyze the main problems of the target piglet house for the application of the air-recirculated ventilation system. In addition, a computational fluid dynamics (CFD) model was developed and validated for seasonal aerodynamic analysis. The applicability of the air-recirculated ventilation system was evaluated based on the CFD computed results for various environmental conditions. As a result of evaluating the internal environment according to the ventilation rates and external-air-mixing ratio of the air-recirculated ventilation system, the required ventilation rate and external air-mixing ratio to maintain the proper temperature and gas concentration were determined.
Enthalpy wheels are often used for air dehumidification and waste heat recovery. Application scenarios include air conditioning systems and industrial systems.
Frost formation inside the enthalpy wheel is common in cold climates and has serious impacts on operational reliability and heat recovery performance. It is found that frost type, frosting area and frosting limit vary between different scenarios. Experimental and numerical investigations are conducted in the present research. For a certain wheel, inlet parameters of supply air and outlet parameters of exhaust air are the key factors influencing frosting formation. The enthalpy wheel will operate regularly without frost formation if exhaust temperature is higher than the frosting limit. Reducing the enthalpy wheel rotation speed below 6 rpm is an effective method to prevent the enthalpy wheel from frosting, but heat recovery efficiency is correspondingly reduced. Industrial systems are less affected by the cold climate, especially at higher exhaust air temperatures. Even if the climate temperature drops to −30 °C, the heat recovery efficiency can still exceed 85%. The research is anticipated to be useful for the application of enthalpy wheels in cold climates.
The application of exhaust air heat pumps as an energy efficient heating technology to cover the heating and ventilation demand of highly efficient residential buildings is becoming popular. Available studies on exhaust air heat pumps tend mostly to focus only on comparing different technologies in efficient buildings. Most of the existing studies ignore the usual presence of the electrical heaters as backup. Moreover, the impact of varying boundary conditions on the heat pump's performance is often not considered in depth. In this sense, there is still a need for discussion on the influence of different buildings’ standards and control strategies on heating performance. The present paper aims to consider the energy efficiency of exhaust air heat pumps under different operating conditions. In this study, the results of a long-term field monitoring are utilized to model the dynamic behavior of an exhaust air heat pump in MATLAB/Simulink using black box modeling approach. The impact of different boundary conditions such as outdoor and exhaust air conditions on the heat pump’s efficiency is studied and additionally compared to other studies. Moreover, a physical approach to model the defrosting process of the evaporator was developed and integrated into the black-box model; to use annual simulations of ventilation-based heating systems in three different building standards. Finally, the influence of six different control strategies on system performance is investigated. The core findings of this study reveal that: (1) Due to the limited exhaust air volume flow rate the impact of the exhaust air moisture content with its condensation enthalpy on the HP performance is significant. (2) In designing ventilation-based heating systems with exhaust air heat pumps due to their limited power (e.g. 6 Wh/m³ at A-2), the control strategy of backup electrical heaters must be selected carefully. (3) Conventional heating control methods such as Nighttime Temperature Reduction (NTR) following a reference room are hardly suitable in ventilation-based heating systems. (4) However, employing the deployed control strategy, the electrical energy consumption of the system could be reduced up to 40% compared to the conventional heating control methods.
In this study, the exergy analysis of an AHU equipped with a heat and exergy recovery unit was investigated. The equations obtained from energy and exergy balance were solved based on a program developed in engineering equation solver. Through the air-to-air heat exchanger, the energy is transferred from the fresh air to the exhaust one but the exergy is transferred from the exhaust air to the fresh one. Therefore, the cooling coil power consumption and irreversibility were reduced. The efficacy of installing an air-to-air heat exchanger is dependent on the temperature and relative humidity of the ambient. Based on the results, at the lowest ambient temperature and relative humidity, the power consumption is reduced by 10.8%, while in the highest ambient temperature and relative humidity, this figure was 33%. Under ambient conditions with low temperatures and high relative humidity, installation of heat recovery unit reduced the irreversibility by 5.18%, while in the highest temperature and lowest relative humidity this figure was 12.8%.
Oscillating heat pipes (OHP) which are constructed from a serpentine-arranged capillary tube possess a desirable aerodynamic form factor and provide for relatively high heat transfer rates via cyclic evaporation and condensation of an encapsulated working fluid with no internal wicking structure required. In last two decades, OHP has been extensively investigated for its potential application in thermal management of various applications. This study presents an experimental investigation on the heat transfer performance of an atypically long finned OHP. The heat transfer performance of the proposed OHP was analyzed and compared with a bare tube OHP with similar overall dimensions. Results show that a unit row of finned OHP filled with n-pentane with fill ratio of 70% can recover up to (400±40) W of heat from a typical waste exhaust air stream. The additional pressure drop due to fins was estimated to be (6.8±2) Pa resulting in an increase of 1–2 W of fan power consumption. The average heat recovery rate via finned OHP was found to be almost 80% more than bare tube OHP filled with same working fluid with same fill ratio.
Dies ist ein Kapitel der 12. Auflage des VDI-Wärmeatlas.
Heat/energy recovery technologies are exclusively applied in buildings so that more energy can be saved. Based on previous literatures, this chapter presents an analysis over the heat/energy recovery technologies in buildings. Firstly, the significance of heat/energy recovery technologies for building energy consumption was given briefly and some terms were introduced. Secondly, the components of a general heat/energy recovery system including heat exchanger, fan, and duct were explained. Particularly, as the core of heat/energy recovery system, different heat exchangers, such as fixed-plate, heat pipe, thermosyphon, loop and rotary wheel heat/energy exchangers were described in details. Then the performance indexes of heat/energy recovery system will be introduced and some impact factors on the performance will be discussed. Also, this chapter presents an analysis over experimental methods and rigs of these indexes. Together with that, the models in the literature for heat and mass transfer in the heat/energy recovery system to predict the performance were mentioned in details. Lastly, some typical application of heat/energy recovery in integrated energy-efficient system in buildings including heat/energy recovery ventilation, run-around heat/energy recovery system, heat pump with heat/energy recovery, and other potential application with heat/energy recovery in buildings were described to demonstrate the practical application of heat/energy recovery in buildings.
This paper shows how a combined air-to-air heat and energy recovery system design problem can be formulated for HVAC cabinet units and solved for the least life-cycle cost system while still retaining a small time period payback. Mathematical expressions are presented to address the complicating interaction between the components of the unit to facilitate the design process. The design process is illustrated for the city of Chicago where both large heating and cooling loads occur in HVAC applications. The example design problem presented shows that payback periods of a little over a year are often achieved for retrofitted units, and the life-cycle cost savings for auxiliary heating and cooling ventilation air far exceeds the capital cost even when only a 10-year life cycle is considered.
The energy recovery ventilator (ERV) is an important equipment for indoor air conditioning, where outdoor fresh air is pre-cooled when passing through the heat reclamation equipment in summer. The building energy-consuming simulation software eQUEST is used to analyze the load change of a building in Xiamen. For the commercial building of 6,912 m, the air-conditioning system with ERV has an electric power saving of 13,298 kWh in July and 12,927 kWh in August, and then about 8,205 Yuan can be saved in July and 7,976 Yuan can be saved in August. When ERV fan power consumption is considered, the electric power saving is 3,680 kWh in July and 3,312 kWh in August. Comprehensive comparison shows that, installation of ERV for an air-conditioning system is more economical by recovering additional cooling energy.
A run-around membrane energy exchanger (RAMEE) has been introduced in the literature as a novel energy recovery system that transfers heat and moisture between the ventilation and exhaust air. The RAMEE consists of two separate (supply and exhaust) flat-plate exchangers made of water-vapor permeable membranes and coupled with an aqueous salt solution. In this paper, the application of a RAMEE in an HVAC system is investigated. The paper discusses the dependency of RAMEE performance on ventilation air and salt solution flow rates and indoor and outdoor air conditions and describes how to control the RAMEE in different operating conditions (summer, winter, and part load). An artificial neural network (ANN) that is able to predict the optimal system performance was developed in previous research. The ANN results are used for TRNSYS computer simulation of the RAMEE system when operating in an office building in four different climates. The results show up to 43% heating energy saving in cold climates and up to 15% cooling energy saving in hot climates. Cost analysis proves the important role of pressure drop across the exchangers in life cycle cost and predicts a payback period ranging from 2 to 5 years for the RAMEE.
A liquid-to-air membrane energy exchanger (LAMEE) is an energy exchange device that transfers heat and moisture between air and salt solution streams through a semi-permeable membrane which is permeable for water vapor but impermeable for liquid water. LAMEEs have been used as a dehumidifier/regenerator in air-conditioning systems. In this paper, the solution-side effectiveness are presented for a small-scale single-panel LAMEE when it is used to regenerate the solution flow. The solution-side effectiveness are very important in regenerators where the main focus is on the salt solution, and the solution properties (i.e. solution outlet concentration) are important. The small-scale LAMEE is tested under air dehumidification and solution regeneration test conditions using a LiCl solution at one NTU (i.e. NTU = 5) and three different Cr* values (Cr* = 2,4 and 6). The results show that both the air-side and solution-side effectiveness of the LAMEE increase with Cr*. The solution-side latent effectiveness is lower for the regenerator in comparison to the dehumidifier (e.g. 43% lower at Cr* = 6). Also, the numerical results for a small-scale LAMEE which were presented in literature are used in this paper to evaluate the solution-side effectiveness of the LAMEE under different test conditions. The numerical results show that the difference between the air-side and solution-side latent effectiveness are negligible. Therefore, the air-side latent effectiveness can be used to evaluate the solution-side latent effectiveness of LAMEEs.
In comfort applications, air-to-air heat exchangers (HEs) lower the enthalpy of the building supply air during warm weather and raise it during cold, by transferring energy between the outdoor ventilation and exhaust airstreams. In this paper, a 250 person capacity auditorium located in Thessaloniki, Greece, is used as a model to calculate (i) the heating and cooling energy that can be recovered, (ii) the reduction in heating, ventilation, and air conditioning equipment, and (iii) the expected payback period from the installation of a fixed-plate, cross-flow HE in the air-handling unit of the system. An energy analysis with the modified bin method energy calculation was used to compare the energy consumption with and without HE, and with full or half occupancy. It is proved that, at the climatic conditions of Thessaloniki much more heating than cooling energy can be recovered and that the payback period of the HE is between 1 and 2 years.
For installations requiring a high percentage of outside air for ventilation, the energy consumption to cool and to heat outside air, especially in cold winter and hot summer climates, is usually very high. These requirements often foster high humidity problems, especially at part-load conditions in hot and humid areas. To reduce ventilation-based energy consumption, heat recovery systems such as heat wheels, air-to-air heat exchangers, heat pipes, or runaround loop systems can be used to recover heat from exhaust airstreams. To reduce humidity problems, a reheat coil after a cooling coil is normally provided to dehumidify the space by adding sensible heat to the room cooling load. A 1,000 ft2 smoking room located in the interior space of a building can be used as a model to explain the process and to compare the cooling and reheat loads of each system.
Hirschi and Gottfredson have recently argued that proposed sociological explanations of the observed relationship between age and crime are in error. This present article contends that their arguments rest on faulty logic and on misstatements of the empirical evidence currently available.
The effect of using run-around heat exchanger systems on energy use and the energy life-cycle cost of a typical large office building was investigated. By incorporating an existing computer program into DOE-2.1, both the building systems and the run-around systems were simulated. By conducting another investigation, the maximum outdoor air ventilation rate a run-around heat exchanger system allows without any increase in energy use for the building was determined. In general, results were found to be significant.
Eight studies reported in the literature compare absence from work or number and duration of respiratory illnesses of the occupants of two building or two rooms, one of which is maintained at a higher relative humidity than the other. In six of the eight studies, the absence from work or the occurrence of respiratory illnesses is significantly lower in the humidified space. This paper reports the latest study that was conducted in hospitals and discusses the difficulties in assessing the results of the investigations. It concludes there is a high probability that increased indoor relative humidity in winter decreases the number of respiratory illnesses and that further experiments are warranted in view of the cost of absenteeism from work.
The fundamental dimensionless groups for air-to-air energy wheels that transfer both sensible heat and water vapor are derived from the governing non-linear and coupled heat and moisture transfer equations. These dimensionless groups for heat and moisture transfer are found to be functions of the operating temperature and humidity of the energy wheel. Unlike heat exchangers that transfer only sensible heat, the effectiveness of energy wheels is a function of the operating temperature and humidity as has been observed by several energy wheel manufacturers and researchers. The physical meaning of the dimensionless groups and the importance of the operating condition factor (H∗) are explained. The dimensionless groups are used in Part II to develop effectiveness correlations for energy wheels.
Effectiveness correlations are presented which allow the designer to predict the sensible, latent and total effectiveness of energy wheels when the operating conditions are known. The correlations agree with simulation data within ±2.5% for sensible, latent and total effectiveness when the desiccant coating on the energy wheel has a linear sorption curve. The sensitivity of the sorption curve and operating condition factor are studied and the use of the design correlations is shown with an example.