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Efficiency of energy recovery ventilator with various weathers and its energy saving performance in a residential apartment
Abstract
The energy recovery ventilator (ERV) is an effective method, which can transfer heat and moisture from the exhaust air into the outdoor fresh air to save energy in buildings. Nowadays, ERV has been widely used in the commercial, industrial and residential buildings in China. Its energy saving performance depends on a lot of factors, such as the outdoor environmental conditions, the enthalpy efficiency of the exchanger, and so on. Based on the relationship among sensible heat, latent heat and enthalpy efficiency, we analyzed the weighted coefficient equations for describing the performance of ERV in different climatic zones in China. According to China weather data, enthalpy efficiency of the exchanger mainly depends on sensible heat efficiency in winter and latent heat efficiency in summer. The energy simulations of a sample apartment in a residential building were made under different operation conditions to study the performance of ERV. The energy saving performances of the ERV were studied with five different outdoor climatic conditions, the enthalpy efficiency, fan power consumption of ERV and fresh air change rate. To improve energy saving performance, better efficient enthalpy exchange material and higher effiencient fans must be explored, while reasonable fresh air change rate as well as proper operation period according to local climate should also be carefully considered.
... Its sensible and latent heat transfer abilities made the ERV system suitable for energy recovery in both heating and cooling processes. Hence the ERV systems have been successfully used in Europe for many years, and become popular in China in recent years [2]. Indirect Evaporative Cooling system (IEC) is an alternative to utilize the energy of the exhaust air, specifically. ...
... The hot air leaves the channel at flow outlet (1) to a specified static pressure. The hot air with temperature 300.15 [K] 60% RH and velocity of 1 [m/s] enters the heat exchanger from flow inlet(2). It passes the heat exchanger channels without mixing with the cold stream and leave the heat exchanger from flow outlet(2). ...
... The hot air with temperature 300.15 [K] 60% RH and velocity of 1 [m/s] enters the heat exchanger from flow inlet(2). It passes the heat exchanger channels without mixing with the cold stream and leave the heat exchanger from flow outlet(2). ...
The indirect evaporative cooling system and heat recovery system utilize the return (secondary) air to condition the fresh (primary) air by means of air-to-air heat exchange between the two streams. The temperature difference between the primary and secondary air streams in indirect evaporative cooling system is relatively small. Therefore, efficient heat exchangers should be used since they play a major role in the overall system performance and economics. The parallel plate type heat exchangers have been widely adopted in Indirect Evaporative Cooling (IEC) systems due to their high efficiency in operating at small temperature difference. In this paper we present a theoretical analysis of different designs of counter flow aluminium plate type heat exchanger and results of CFD analysis of pressure drop, flow velocity and thermal effectiveness. For improving the heat transfer between the plates and minimizing the energy loss, the analysis proves useful in the optimization method for selecting parameters of the plate heat exchangers.
... Typical performance of heat recovery in residential ventilation systems shows temperature efficiencies of approximately 80% and above, which means that there is an extensive benefit from having heat recovery in ventilation systems. Both catalogue data [3][4][5] and scientific literature confirms this [6][7][8]. The efficiency is a matter of an optimization between fan electricity and heat recovery where a larger heat recovery unit gives higher efficiency and higher pressure drop, and apparently in the magnitude of 80% has been found to be a reasonable compromise. ...
... The figures given on efficiencies of heat recovery ventilation may well be valid in non-frosting conditions, but in frosting conditions they will not. Figure 17 indicates a simulated efficiency far lower than the more than 80% given in catalogues etc., which is also expected [3][4][5][6][7][8]. Particularly when the outdoor temperature is low, a high efficiency would be most useful, which means that the maximum power saving with heat recovery ventilation will not be as high as the energy saving. ...
Objectives of this paper are to propose a reasonable simulation model that can handle condensation and frost formation in heat exchangers dependent on moisture concentration and outdoor climate conditions, and to analyze risk of frost formation and discuss different frost protection strategies. Using psychometrics, American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) heat exchanger calculation, condensation and frost calculation methods, simulations models for heat recovery ventilation and energy recovery ventilation are developed. It is concluded that the risk of frost in heat exchangers is higher in northern Sweden than in southern Sweden and Denmark due to low outdoor air temperatures during the winter, however heat recovery systems in Copenhagen and Gothenburg still has a risk of frost formation even though these cities has relatively warm weather conditions. Out of several simulation models that are created during the study, the detailed model that takes condensation effect into consideration, is proven to be worthy to be used in further investigations, due to results that more accurately represent real word conditions. Risk of frost formation becomes significantly lower in every city when heat recovery ventilation is changed into energy recovery ventilation. Even though heat recovery ventilation is simulated only with the simplified model, it is safe to assume that it will still be effective in reality. Although bypass strategies were effective at eliminating the risk of frost in heat recovery units, they are not as efficient from an energy perspective. The more air is by-passed through the cross-flow plate heat exchanger, the fewer opportunities there are to recover energy from exhaust air, which leads to lower supply air temperatures and higher energy need for heating a living space.
... of ventilation systems with respect to heating and cooling energy demand. However, under real conditions in real houses, enthalpy efficiency is not constant because both indoor and outdoor air conditions can influence its efficiency [13][14][15][16] . ...
... Some studies used simulation methods to study the performance of ERVs in different weather conditions. Liu et al. [16] analyzed the weighted coefficient equations for describing the performance of ERVs in different climatic zones in China. They concluded that, in most areas in China, the total heat (enthalpy) efficiency of an enthalpy exchanger is determined, for the most part, by the sensible heat efficiency in winter and the latent heat efficiency in summer. ...
... Many works can be found in the literature that assess the performance of recovery ventilators [18,[21][22][23][24][25][26][27][28][29] . Three performance indicators are traditionally considered. ...
... The denominator in Eq. (25) represents the maximum useful work that can be extracted from the exhausted air stream before it is discharged in the ambient. Thus, η represents the fraction of the exhaust air exergy that is recovered. ...
The increased attention to energy savings has contributed to more widespread use of energy recovery systems for building ventilation. We investigate the efficiency of such systems under different outdoor conditions using exergy analysis and nonequilibrium thermodynamics. This analysis makes it possible to assess performance in terms of loss of work potential, to account for the different quality of energy and to localize and compare the different sources of loss in the system. It also enables the use of exergy efficiency as a single performance parameter, in contrast to the several indicators that are commonly used. These more common indicators are difficult to compare and relate to each other. Further, since there is no obvious optimal trade-off between them, it is challenging to combine them and develop a global performance indicator that allows for a sensible comparison of different technical solutions and different types of recovery devices. We illustrate the concepts by applying the analysis to a heat recovery ventilator (HRV) and to a structurally similar membrane energy recovery ventilator (MERV) that can exchange both heat and moisture. We show how the exergy efficiency can be used to identify the range of operating conditions for which the recovery ventilator is not beneficial as the energy cost is greater than the energy recovery. This is not trivial using traditional performance parameters, yet it is a natural outcome of exergy analysis. In addition, we identify the mechanism by which work potential is lost, which can help the eventual optimization of both the recovery process and the auxiliary systems present in ventilation systems.
... The effectiveness of indoor heating and cooling energy reduction varies according to regional climatic characteristics, such as the number of days for heating and cooling, outdoor temperature, and humidity, which considerably influence the effectiveness of ERV. Liu et al. [13] demonstrated that with an ERV efficiency of 75% during the heating season in five cities in China, heating energy could be reduced by 20%. Rasouli et al. [14] argued that up to 20% of cooling energy can be saved annually if the ERV is operated under the proposed optimal control. ...
To reduce national greenhouse gas emissions, the South Korean government has encouraged new energy businesses and implemented policies to reduce energy consumption in buildings, and aims to construct all new buildings as zero-energy buildings by 2025. According to the promotion of policies on passive houses and zero-energy buildings, the thermal insulation and airtight performance of new buildings have been further enhanced. However, to enhance indoor comfort and air quality in new airtight buildings, it is critical to secure an adequate amount of ventilation. Heat recovery ventilators (HRVs) in South Korea have been used for more than 20 years as high-efficiency energy equipment; however, the high-efficiency standard 20 years ago (cooling efficiency 45%, heating efficiency 70%) is still being employed without any change. Most HRVs in the Korean market either meet or exceed this standard. This study examined HRV performance changes from 2010 to 2020 based on the data of 847 HRV performance certifications given by a certification agency. It also analyzed how institutional strategies and related laws contributed to the enhancement of such performance. As HRVs in South Korea are only required to satisfy the pre-defined efficiency criteria, the development and use of HRVs focus more on cost reduction rather than efficiency enhancement. Under such market conditions, it is challenging to research and design highly efficient HRVs along with customer satisfaction. If better market conditions are offered that would welcome HRVs with higher efficiency, the development of better HRVs, as compared to those analyzed in this research study, would be possible.
... The total heat exchanger (commercial name ''heat recovery ventilator") [9][10][11] is the most popular energy-saving equipment for heat recovery in fresh air exchange which has already been commercialized. The total heat exchanger is used to recover the waste cold/heat of the exhaust room air to reduce power consumption of air conditioning equipment to save energy. ...
Fresh air exchange without using heat recovery ventilator in a closed space causes additional power consumption of the air conditioner. In the present study, we propose a novel design of heat-pump fresh air
exchanger (HPFAE) which utilizes a heat pump to cool the intake outdoor hot fresh air in the evaporator
before entering the room and to cool the condenser using the exhausted cold indoor air to increase COP of
the heat pump. Three prototypes were built from retrofitting a window-type air conditioner and tested.
The HPFAE with an additional boost fan (HPFAE-B) is shown to be able to reduce power consumption. The
net COP (COPFAE) for room cooling reaches 3.76 which is higher than COP of the original air conditioner
(3.42). This shows that HPFAE can provide space cooling with fresh air exchange and reduce power
consumption.
... However, split-type air-conditioner is not able to introduce the fresh air. Due to this reason, application of energy recovery ventilator (ERV) is one of ideal solution to this issue in residential building and ERV comes into widespread in Europe and Asia countries (Fehrm, Reiners, and Ungemach, 2002;Zhou, Wu, and Wang, 2007;Dieckmann, Roth, and Brodrick, 2003;Liu et al., 2010;Han et al., 2013). Heat recovery term is referring to an air-to-air heat or energy recovery system which is defined as the process of recovering energy (heat/mass) from a stream at a high temperature to a low temperature stream that is effective and economical to run (Riffat and Gan, 1998). ...
Recently, Energy Recovery Ventilator (ERV) has been installed to secure energy saving and Indoor Air Quality (IAQ) in multi-residential building. A lot of effort has been devoted to the development of various types of ERV systems for the purpose of improving heat exchange efficiency, preventing condensation problems in the elements, and increasing usability etc. Among various ERV systems, a ventilation system using a new concept called Alternating Ventilation (AC ventilation) such as Bi-directional Heat Recovery Ventilator (BdHRV) has been developed and broadly installed. The performance of a heat (sensitive / latent / enthalpy) recovery ventilators are defined as a fixed value by measurement under specified indoor and outdoor conditions, and this value used as input data for the energy simulation. However, the heat exchange efficiency of Bi-directional Heat Recovery Ventilator (BdHRV) in which air supply and exhaust process are repeated over a period of time and heat is accumulated in the exhaust mode through the heat storage element and heat is released in the supply process is not constant but varies with time. In this study, the transient heat exchange efficiency of BdHRV was measured with test chamber measurement. The simulation method considering the transient heat exchange characteristics of BdHRV has been proposed. The effect of ventilation with BdHRV on heating/cooling energy usage are analyzed.
... The lack of ducts is a clear advantage since the most common problems are caused by the poor installation quality of ducts and inadequate project design [4]. It is also essential for the ventilation unit to have a low electric power consumption, suitable acoustic properties [26] and sufficient energy saving performance, which is strongly related to outdoor climatic conditions, the enthalpy efficiency, fan power consumption and necessary fresh air change rate [27]. ...
Single room ventilation units with heat recovery is one of the ventilation solutions that have been used in renovated residential buildings in Estonia. In multi-story buildings, especially in a cold climate, the performance of units is affected by the stack effect and wind-induced pressure differences between the indoor and the outdoor air. Renovation of the building envelope improves air tightness and the impact of the pressure conditions is amplified. The aim of this study was to predict the air pressure conditions in typical renovated multi-story apartment buildings and to analyze the performance of room-based ventilation units. The field measurements of air pressure differences in a renovated 5-story apartment building during the winter season were conducted and the results were used to simulate whole-year pressure conditions with IDA-ICE software. Performance of two types of single room ventilation units were measured in the laboratory and their suitability as ventilation renovation solutions was assessed with simulations. The results show that one unit stopped its operation as a heat recovery ventilator. In order to ensure satisfactory indoor climate and heat recovery using wall mounted units the pressure difference values were determined and proposed for correct design.
... The moisture resistance of a thin film membrane depends on the inlet air humidity [5][6][7][8][9][10][11][12][13] and it affects the transported amounts of moisture across the membrane. In low humidity climate, inlet conditions might not affect significantly the variation in moisture transportation. ...
Membrane heat exchanger is one of the main components of green HVAC systems. Performance of a thin-membrane heat exchanger has been examined for different membrane materials. A computational fluid dynamics (CFD) approach was utilized to conduct the current study. The CFD model consisted of a single channel for hot stream and another channel for cold stream. Four membranes were investigated: 45 gsm and 60 gsm Kraft paper, modified cellulose acetate membrane and PVA/LiCl blend membrane. Obtained values of thermal effectiveness at typical HVAC system conditions showed that different membrane materials produced different thermal performance values. The amount of energy recovered from the modified cellulose acetate membrane heat exchanger was the highest. Finally, heat exchanger performance is found to be very sensitive to ambient air relative humidity variation.
... Several studies have been conducted to evaluate the energy-saving performance of ERV systems. The main methodology involves chamber tests and simulations [13][14][15]. Chamber tests can provide accurate results but under controlled conditions, particularly steady-state conditions. The purpose of the chamber test is typically to compare the nominal performance among devices. ...
Energy-recovery ventilators (ERVs) are regarded as important energy-saving systems in buildings. It has been reported that they have high energy-saving rates compared with conventional ventilators that operate without energy recovery, but the saving rates have been obtained typically by employing chamber tests and simulations. In this work, a field-test method is proposed that uses a single test room but alternates the tested ventilation modes hourly. This proposed method is useful because an additional comparison room is not always available and can be a source of uncertainty for field tests. The test is performed in a classroom during a heating period, and the results are calibrated to account for different experimental conditions during the test period. The calibrated energy-saving rates indicate the effectiveness of the ERV; however, they are lower in the early hours of the system operation, for two reasons: (1) the maximum power control schemes of the heat pumps are applied for cases where the indoor temperatures are far lower than the set-point temperature; (2) the ventilation load seemingly represents a decreasing proportion of the total heating load in early hours owing to the thermal-capacity effects for the building, which was cooled for many hours. The findings are verified via a chamber test and simulations. As a consequence, it is important to account for actual system characteristics affected by the thermal behaviors of classrooms when the overall performance of a system is evaluated.
... Traditional exhaust heat recovery ventilators are used to reduce the energy consumption of fresh air handling if the exhaust air system is available in buildings [4][5][6][7] . Actually, the energy saving effect of exhaust heat recovery technique is remarkable only in certain situations [8][9][10] . Moreover, if the climate is suitable, e.g. in the dry and hot climate regions, the evaporative cooling technique is always used to produce cooling fresh air for buildings [11][12][13][14][15][16] . ...
... Many works can be found in literature that assess the performance of recovery ventilators [18,[21][22][23][24][25][26][27][28][29]. Three performance indicators are traditionally considered. ...
The increasing attention to energy savings has contributed to the increased use of energy recovery systems for building ventilation. However, the use of such systems might not be always beneficial from an energy point of view. We investigate the efficiency of these systems under different outdoor conditions using second-law analysis. This analysis makes it possible to assess performance in terms of loss of work potential, and to account for the different quality of energy. We use the second-law energy efficiency as single performance parameter, in contrast to the several indicators commonly used to characterize recovery systems. We consider and compare the performance of a heat recovery ventilator (HRV) with that of a structurally similar membrane energy recovery ventilator (MERV) which can exchange both heat and moisture. We show that the second-law efficiency can be used to identify the range of operating conditions for which the recovery ventilator is not beneficial as the energy cost is greater than the energy recovery. This is not trivial using traditional performance parameters, yet it is a natural outcome of the second law analysis. In addition we identify the location and the mechanism by which work potential is lost, which can help the eventual optimization of both the recovery process and the devices used to carry them out.
... Zhong and Kang [8] investigated the applicability of air-to-air heat recovery systems in four different climates in China and showed that the selection of the type of heat recovery system and its efficiency is strongly related to the climate. Other studies [9][10][11] focused on the significant impact of the climate conditions on the energy savings achieved by HR 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.
... The total heat exchanger (commercial name ''heat recovery ventilator") [9][10][11] is the most popular energy-saving equipment for heat recovery in fresh air exchange which has already been commercialized. The total heat exchanger is used to recover the waste cold/heat of the exhaust room air to reduce power consumption of air conditioning equipment to save energy. ...
Fresh air exchange without using heat recovery ventilator in a closed space causes additional power consumption of the air conditioner. In the present study, we propose a novel design of heat-pump fresh air exchanger (HPFAE) which utilizes a heat pump to cool the intake outdoor hot fresh air in the evaporator before entering the room and to cool the condenser using the exhausted cold indoor air to increase COP of the heat pump. Three prototypes were built from retrofitting a window-type air conditioner and tested. The HPFAE with an additional boost fan (HPFAE-B) is shown to be able to reduce power consumption. The net COP (COPFAE) for room cooling reaches 3.76 which is higher than COP of the original air conditioner (3.42). This shows that HPFAE can provide space cooling with fresh air exchange and reduce power consumption.
... Ensuring high regenerative capacity of heat exchangers is an important problem. The effectiveness of recovery heat exchanger depends on many factors, including both thermophysical proper-ties of heat exchanger materials and the ambient temperature and humidity [10][11][12]. The choice of the most suitable material for heat exchangers, even for simple operating conditions, is a complex problem. ...
The physico-mathematical model of the regenerative heat exchanger with periodic changes of air flow direction has been developed. The model takes into account phase transitions both on the surface of air channels of heat exchange matrix and directly in the airflow. In this paper, the results of the influence of parameter groups on the heat exchanger effectiveness are generalized. Such generalization is reached by identifying the governing dimensionless groups in the system of equations. The analysis using the generalized parameters allows considerably simplifying the study of processes with a large number of parameters. In addition, the influence of air humidity and temperature on the sensible and latent effectiveness of the heat exchanger has been analyzed. Computations enable determining the heat exchange matrix material that is the most suitable in terms of its thermophysical properties.
... They find that an ERV not properly controlled may increase the cooling demand, but conclude that an ERV can save energy by up to 10% for an office building in Chicago and 15% in Miami using an optimal control strategy, compared with the use of an HRV only. Liu et al. [10] simulate an apartment in five cities in China demonstrating that the ERV is an effective energy saving method in some of them, but conclude that an ERV is better for non-residential buildings that need more fresh air. ...
Mechanical ventilation systems are essential for ensuring the indoor quality of air in nZEB (nearly Zero Energy Buildings) with a high level of airtightness. In cold countries, it has already been demonstrated that Heat Recovery Ventilators (HRV) recovering the sensible energy from air ventilation are needed to achieve the energy demand goals for nZEB set by Passivhaus. In tropical areas with hot temperatures and high relative humidity in the ambient air, the necessity of recovering latent and sensible energy with Energy Recovery Ventilators (ERV) has also been demonstrated. However, in warm climates with medium relative humidity levels, for example in cities located on the Mediterranean coast, the evaluation of the effectiveness of an EVR for residential buildings has to be analyzed and optimized.
As a representative heat recovery device, the fixed-plate enthalpy exchanger possesses the advantages of high recovery effectiveness, low pressure drop, and small space occupied. Still, indoor contaminants may transfer to fresh air through the enthalpy exchanger simultaneously, causing cross-contamination risk. However, the cross-contamination risk of the fixed-plate enthalpy exchanger has been under-researched in previous studies. As a result, this study experimentally investigates the energy performance, formaldehyde and ammonia transfer rates of paper-based and membrane-based enthalpy exchangers. The results illustrate that the enthalpy recovery effectiveness of the plate exchangers ranges from 60%–85%. The formaldehyde transfer rate through the exchangers varies from 5%–23%, and the ammonia transfer rate is 0–15%. The high effectiveness and low contaminant transfer rates are conducive to the promising application of the fixed-plate enthalpy exchangers. In addition, the energy reclaimed increases with the increase of the absolute indoor-outdoor enthalpy difference. The formaldehyde and ammonia transfer rates and cross-contamination risk slightly decrease with increasing temperature but significantly increase with increasing humidity. Moreover, the experimental results demonstrate that the contaminant transfer rates through the membrane-based exchanger are lower than those of the paper-based exchanger. This study provides a reference for the fixed-plate enthalpy exchanger design in practical applications.
Responding to climate change and adapting to global warming requires creative solutions. In Iraq, the most reliable and popular tool to have buildings cooled is airconditioning units (AC). While an evaporative cooler is not enough to achieve thermal comfort in a very hot climate, AC units consume a lot of energy which causes a significant load on the grid in Iraq resulting in increasing the emissions of CO 2 . This paper investigates the potential energy-saving associated with adopting a new arrangement of heat recovery ventilation (HRV) unit and evaporative cooler to achieve thermal comfort with far less energy. Two sets of efficiencies of both HRV and the evaporative cooler have been considered, and two different envelope performances are also investigated. To properly size the proposed system, an iterative process has been used until the smallest size of the proposed system enough to cool the building is determined. The proposed system has achieved considerable energy savings comprising a reduction of up to 66% in the cooling load energy consumption and a reduction of up to 44% in the overall energy consumption.
Fresh air volume control is of great significance in reducing energy consumption in nearly zero energy buildings. Previous studies have shown that the operating fresh air volume often deviates significantly from the design value, resulting in unnecessary energy consumption. To overcome this problem, this study proposes an energy efficiency fresh air system for NEBs by using pressure-independent dampers to balance system resistance and control the operating fresh air volume accurately. A typical fresh air system used in a typical NZEB was tested both in laboratory and on site for a whole heating season. Based on the test data, the energy consumption model of the proposed fresh air system was established and validated. The energy performance of the proposed system was analyzed comprehensively. Results show that using the pressure-independent damper in the fresh air system to control the fresh air flow rate can significantly reduce the fresh air load by 39.2%, 49.4%, 52.3% and 45.5% in Harbin, Beijing, Shanghai and Guangzhou, respectively; The annual energy saving rates in these cities are approximately 29.3%, 28.7%, 27.0% and 19.1%, respectively. These energy saving rates are smaller than the corresponding fresh air load reductions due to the additional energy consumption caused by the pressure-independent damper; Furthermore, replacing the pressure-independent damper with an ideal variable speed ventilator for fresh air flow rate control can further increase the energy saving rate by 12%∼16%. This study identifies the energy saving potential of fresh air systems and contributes to achieving sustainable development in nearly zero energy buildings.
Green building technologies (GBTs) play an important role in carbon emission reduction in the building sector. China is currently in the booming phase of green buildings construction and numerous studies have been conducted on green building technologies, especially on the potential of reducing buildings' energy consumption and carbon emissions. This paper provides a comprehensive overview of various GBTs, including high performance envelope, lighting and daylighting, natural ventilation, HVAC (heating, ventilation and air conditioning) system and the utilization of renewable energy. After describing the phases of the building life cycle and the calculation method of building carbon emissions, the literature review focuses on the applications of GBTs in different climate areas in China as well as the main findings and innovations on their carbon reduction potentials. Finally, recommendations for GBTs development are proposed based on the existing researches to facilitate carbon neutrality in the building sector.
Due to the complicated nature of desiccant-coated heat exchangers (DC-HXs), solving the highly-coupled transient heat and mass transfer equations using numerical simulations are rather time-consuming and as a result may be impractical for real-time system optimization and seasonal simulations. On the other hand, the approach of majority of studies associated with DC-HXs is numerical and experimental analyses and there is no analytical model that can accurately predict the heat and moisture transfer in a DC-HX in the literature. Thus, in this paper, a new closed-form analytical solution is proposed to accurately predict the heat and moisture transfer in a DC-HX for the first time. The governing equations are simplified to a set of linear ordinary differential equations with initial conditions and then solved analytically. In the present analytical model, both linear and exponential profiles are assumed for the air temperature and humidity ratio along the DC-HX and the results are compared to experimental data collected in our lab. A new DC-HX coated with AQSOA™-FAM-Z02 is also fabricated and tested in our custom-built testbed under a wide range of operating conditions for model validation and performance assessment. Our results indicate that the present analytical solution with exponential profile assumption predicts the experimental data with an average relative difference of less than 10 %, while the linear profile assumption results in a relative difference of ∼ 20 % with the experimental data. The new analytical solution is capable of predicting the performance of DC-HXs, which is crucial for design, optimization and operating dehumidification systems in a variety of applications.
Passive dehumidification and solar collection (PDSC) employs fibrous insulation materials with excellent moisture adsorption and desorption characteristics to conduct dehumidification using renewable energy. This study proposes an improved PDSC-integrated energy recovery ventilation (ERV) system (PSE) to dehumidify indoor environments. Energy recovery ventilation (ERV) promotes the exchange of moisture and heat between returned and supplied air to reduce energy loss caused by ventilation. We explained the fundamental moisture movement principle based on thermodynamic energy and designed the air circulation paths of the proposed system for dehumidification and energy recovery. Five house models were simulated and compared: conventional house with no moisture effect, conventional house, conventional house with integrated ERV, the PDSC model, and the PSE model. Simulation results show that the PSE model has the best dehumidification performance, with an approximately 2.9 times latent heat load reduction effect compared with the PDSC model, in hot and humid summer. This study confirms that the proposed system has significant potential for dehumidifying the indoor environment and provides guidance for the future application of the PSE system to dwellings.
The use of single-core energy recovery ventilator (ERV) reduces the heating energy use in northern houses, but has the disadvantage of reducing the required outdoor air supplied to the house during the defrost operation by air recirculation, which might affect the indoor air quality. A dual-core ERV also reduces the heating energy use, but in addition supplies a continuous outdoor air flow rate in compliance with standards. This paper evaluates the advantage of using the dual-core ERV in northern houses. First, this paper presents new correlation-based models of supply air temperature and humidity after the ERV unit, based on laboratory-controlled experimental data. Second, the energy use for ventilation and heating, and ventilation rates are simulated with TRNSYS program for northern houses at three arctic locations. They are compared with Montreal conditions as reference. The single-core ERV unit significantly reduces heating energy use in arctic locations by about 27%, compared with the case without heat recovery, however the outdoor airflow rate during the defrost is smaller than minimum standard requirements by about 13% in Kuujjuaq (below Arctic Circle) and 24% in Resolute (above Arctic Circle). The dual-core ERV unit removes the frost while continuously supplying the minimum required outdoor air to the indoors, however at the cost of minor increase of the heating and fan energy use compared with the single-core ERV unit.
Membrane-based Energy Recovery Ventilators (ERV) have become an important part of modern ventilation systems for commercial and residential buildings due to their high sensible and latent effectiveness. Using ERVs in winter conditions, however, can result in condensation and frost formation. Whereas frost formation requires extremely low temperatures, condensation can occur even in mild winter weather conditions. In this study, a widely used ERV is experimentally tested under various indoor and outdoor operating conditions. Short time tests are used to determine the onset of condensation while long time tests are used to investigate the effect of channel blockage due to condensation on pressure drop and effectiveness of the ERV. The presence of condensation is inferred from visual observation of water in the exchanger, investigation of the sensible and latent effectiveness, and measurements of pressure drop over the exchanger. It is shown that condensation increases the sensible effectiveness of the supply side and decreases the sensible effectiveness of the exhaust side. Additionally, the latent effectiveness of both air streams increases when condensation occurs, although the increase in exhaust side latent effectiveness is more significant. Increasing the relative humidity and temperature of the indoor air increases the possibility of condensation and its rate, while increasing flowrate only increases the rate of condensation and does not affect its onset. Finally, the accumulation of water in the channels significantly increases the pressure drop in the exhaust side while it does not significantly impact the effectiveness.
To achieve required indoor air quality, fresh air supply in buildings should meet relevant standards and regulations. However, the handling of fresh air introduced a cooling load that takes up a large portion of building energy consumption, especially in tropical and subtropical areas. A proper way should be employed to reduce the cooling load of fresh air. Radiative sky cooling, which is the process that an object cools itself by emitting thermal radiation to outer space without any energy input, is a cost-effective and eco-friendly technology. In this work, a fresh air pre-cooling system using radiative sky cooling is proposed to reduce fresh air cooling load. The system, consisting of filters, a radiative air-cooling system, an air handling unit (AHU), fans, etc., is installed on the rooftop of the modeled building. Six cities in low-latitude areas are selected and investigated. Results show that with the radiative air-cooling system installed, annual cooling energy consumption of the modeled building can be reduced by around 10% in most cities. For arid areas, e.g., Abu Dhabi, the system has even better performance with 19.34% annual cooling energy saving.
Many factors and aspects of the construction and operation of buildings depend on climatic parameters and climatic zones, so these will be fundamental for adapting and mitigating the effects of climate change. For this reason, the number of climate-oriented publications in building is increasing. This research presents an analysis on the most-cited climate-oriented studies in building in the period 1979–2019. The main themes, the typologies of these investigations and the principal types of climatic zoning used in these studies were analysed through bibliographic and manual analysis. A broad spectrum of themes directly and indirectly related to climate and climatic zones and buildings was demonstrated. It was found that 88% of all climate-oriented investigations, to one degree or another, are within the scope of the general topic of energy conservation. A thorough understanding of all climate-dependent aspects will help in designing dwellings appropriately in different climate zones. In addition, a methodology that facilitates the establishment of a typology of climate-oriented research is presented. This typology can be used in future research in different scientific areas. It was also revealed that the climate zones of the National Building Codes of China, the USA and Turkey prevailed in the studies analysed.
Hygrothermal properties have usually the specific features in every building. The temperature and humidity have a direct influence on the building materials as well as the human well-being and comfort feeling. The energy consumption is also predominated with influence of the climate, building materials, and the type of the building envelope. Another factor which can directly influence the conditions in the room is a ventilator. Hygrothermal properties in connection with the air ventilation have also the direct influence on the health of the building residents. In our experimental work, we used the Internet connection for collecting the data to avoid the external influences on experiment running. The resulting data were analyzed using the mathematical modeling as well as the statistical methods. The characteristics of mathematical modeling describe the hygrothermal properties in case if the ventilator is turned off and turned on. The results are compared and evaluated through the curve fitting using the least square methods as well as the numerical differentiation.
The indirect evaporative cooler (IEC), used as a novel energy recovery component for central air-conditioning (AC) systems, can cool and dehumidify the fresh air by capturing the waste thermal energy of exhaust air. To facilitate its implementation in hot and humid areas, the applicability of the hybrid AC system integrated with IEC needs to be addressed. This study quantitatively evaluated the cooling and energy-saving potentials of an IEC for energy recovery and compared it to a traditional hybrid AC system with a heat recovery wheel (HRW). On-site performance measurements were conducted in a wet market located in Hong Kong, where two air-handling units were integrated with a newly-designed IEC prototype and a commercial HRW respectively. Simulation models of the two hybrid AC systems were established based on TRNSYS platform by incorporating the numerical model of IEC and HRW respectively. The field-measurement data was used to validate the component models, and further calibrate the system models. To compare the regional adaptability of the two systems, annual simulations were conducted among 8 selected cities in southern China. Results showed that the total cooling capacities of IEC and HRW are closely related to local ambient relative humidity. Compared with the baseline AC system, the AC + IEC provides an annual energy saving intensity of 64.2–73.4 MJ/m² for cities with hot and moderate humid climates, which is more competitive than the AC + HRW (45.5–51.8 MJ/m²). The annual energy saving ratios of the two types of hybrid systems range from 14.4% to 26.4%.
Energy recovery ventilators (ERVs) are used to recover sensible and latent heat to reduce the heating and cooling load caused by outdoor air intake into indoor environments. The efficiency of the heat exchanger, comprising flow channels and constituent materials, determines the heat exchange performance of the ERV. Understanding the heat and mass transfer mechanisms in the ERV and optimizing the geometry and materials of the flow channel are essential for improving the ERV performance. Herein, numerical methods for predicting and clarifying the hygrothermal transfer mechanism in the heat exchange element of an ERV were developed, and their prediction accuracy was confirmed by analysing the exchange efficiencies in the scaled-down ERV unit model. The verified numerical model was applied to sensitivity analyses to clarify the rate-limiting factors influencing the total heat exchange efficiency of the ERV. Our findings have clarified that under Japan Industrial Standard cooling conditions, a 50-fold increase in the thermal conductivity of the spacer plate, the total heat recovery performance was enhanced by 13%, as for a 2-fold increase in the moisture conductivity, the performance was enhanced by 20%. The findings of this research can be expected to contribute to the energy saving effect in buildings.
Energy recovery ventilators (ERVs) have been utilized within air conditioning systems to enhance energy efficiency and to improve indoor air quality. ERV performance contributes significantly towered lowering electrical consumption and emissions of the installed systems. Annual energy savings resulted from integrating a hybrid flow ERV to a conventional HVAC system is numerically investigated in the current research. Thermal performance of air to air ERV is estimated with the aid of computational fluid dynamics (CFD) approach, and the average annual energy consumption of the simulated building is estimated using hourly analysis program (HAP) software at different locations worldwide. Based on CFD simulations, a correlation for the total effectiveness of the ERV was developed (εt = 4.2ΔTR0.06377Re−0.29458) which is a function of dry and wet bulb temperature at design conditions of a given location (ΔTR) and Reynolds number (Re) of air flowing through the ERV. Furthermore, CFD simulations showed that the amount of latent energy recovered could be as high as 6 times the amount of sensible energy recovered as the ambient conditions approaches the tropical humid conditions or as ΔTR decreases. Building simulations using HAP showed that the ERV has reduced the size of the cooling/heating coils which resulted in lowering the electrical energy needed to run the HVAC equipment. Utilizing the ERV could also contribute to coil downsizing of up to 40.5 kW, a total electrical load recovery of up to 8648 kWh and RER values of up to 662 for tropical cities such as Singapore. Moreover, an up to 16,000 kgCO2e could be reduced with an annual cost saving of up to US$3000 when adopting the ERV unit. Therefore, it is recommended to design the ERV to serve at relatively low Re values which reflects on obtaining higher effectiveness, lower pressure drop and the greatest possibility for energy recovery.
This study evaluates the energy-saving potential of a prediction model-based pre-heat coil operation method for frost prevention in energy recovery ventilators, compared to existing approaches. Energy recovery ventilator (ERV) requires pre-heating of the incoming outdoor air to prevent undesirable condensation and frost formation in the enthalpy exchanger during winter. Conventionally, the introduced outdoor air is pre-heated to a certain constant temperature using a pre-heat coil, resulting in unnecessary energy consumption. Maintaining a constant pre-heat temperature during the operation of the ERV is not ideal as the frost threshold temperature varies with the outdoor air temperature and humidity. Therefore, to reduce pre-heating energy consumption, a prediction model-based pre-heat coil operation method is proposed herein. A numerical model predicting the frost threshold temperature based on the outdoor air and exhaust air conditions was developed, and validated using the optimal Latin hypercube design method. Subsequently, a series of energy simulations was performed considering an identical residential model, located in 8 cities with different climatic conditions, to evaluate the energy-saving potential of the proposed pre-heat coil operation method compared to conventional methods. The proposed method consumed 7%-72% less energy in the ERV operation and required a 1%-21% smaller pre-heat coil capacity than the conventional method. Thus, the proposed operation method is superior to the conventional method as it prevents frost formation and consumes a minimal amount of energy.
With the present leaning towards well-insulated and airtight energy-efficient buildings and houses, air-to-air heat/energy exchangers have become very important for maintaining a good indoor air quality (IAQ) via continuous mechanical ventilation along with decreasing energy needed to condition the inbound fresh air. The present study aims to experimentally evaluate the performances of a dual-core ERV-HRV system in terms of heat and energy recovery in residential environment under Atlantic Canada weather. An IoT platform was designed and integrated to this ventilation system in order to collect and log real-time data. Moreover, this paper presents a detailed mathematical model of the proposed system to predict its energy exchange efficiency, using the effectiveness-NTU (i.e. ε-NTU) approach. The model was subsequently validated against experimental measurements within laboratory environment. As proved by experimental data, the theoretical model can predict, with a relative discrepancy less than 10%, the system energy exchange efficiency. Results from a real house located at Sainte-Anne-de-Kent in New-Brunswick, Canada are presented in this study, and the system efficiency was assessed under hot and cold weather conditions. The research findings show that, in the winter, the measured sensible and latent efficiencies are in ranges of 65.66–85.05% and 38.46–58.96%, respectively. Whereas, for the summer season, the corresponding effectiveness ranged from 31.7% to 85.72%, and from 68.51% to 92.69%, respectively. As consequence, the experimental results analysis revealed that the proposed dual-core exchanger is efficient during both heating and cooling seasons.
The application of energy recovery system has been proven as one of the key solutions to produce energy savings and to provide fresh outdoor air in building ventilation. The performance of the system can be evaluated in terms of efficiency and recovered energy (heat and mass transfer) through its heat exchanger. The efficiency can be determined using ASHRAE standard, effectiveness–NTU method and global efficiency. Meanwhile, recovered energy is calculated based on the heat and mass transfer rates of the system. This chapter provides a background of the performance evaluation of energy recovery system from existing established data and previous works in the literature.
The concept of Smart Buildings was introduced by the Energy Performance Building Directive, with the aim to promote energy flexibility, renewable energy production and user interaction. A wide range of definitions have been introduced in the literature to characterize smart buildings yet, at present, its’ concept and features are not clearly and uniquely defined. Simultaneously, building energy retrofit concept has been introduced to facilitate achieving the nearly Zero-Energy Building target and reduce energy consumption in existing buildings. Up to 90% of the existing European building stock will still be standing and in use in 2050. Thus, there is a need to upgrade the existing retrofitting strategies into Smart Retrofitting, to achieve the nearly Zero Energy Building target and be able to respond to external dynamic conditions such as the weather and the grid. The aim of this research is first to review the concept of smartness in the built environment, highlighting the main features, functions, and technologies of smart buildings, also discussing the possible challenges for smart retrofit applications. The second part of the paper reviews the existing Key Performance Indicators that measure the performance and success in achieving goals in smart buildings. The need to develop a quantified guideline to improve energy and technological innovation is the basis for the increase of the smartness in buildings. Consequently, a set of nine groups of representative performance indicators for smart buildings is developed. This work shows current gaps in the literature and highlights the space for foreseeable future research.
The air-to-air heat exchanger is a fresh air device that can reduce the energy consumption of air conditioners and improve heat exchange efficiency. In this paper, a mathematical model for heat transfer coupling of air film based on user-defined scalar (UDS) is proposed, and the model calculation is realized by Fluent. The comparison with previous experimental results verifies the accuracy of the calculation model. The influence of core channel height on core efficiency and the influence of inflow angle on heat exchanger performance are simulated when the length of counterflow section is changed. Considering the length of the counterflow section and the setting of the fresh air and exhaust air inflow angle, it is recommended that the length of the counterflow section should be set to 400 mm, and the inlet airflow direction of outdoor air and exhaust air is symmetrically set to 135° or 45° with respect to the symmetry axis of the heat exchanger. The channel height should be set above 2.0 mm.
The energy recovery ventilator (ERV) is a type of mechanical equipment that provides ventilation into the building while reducing the energy required to condition the ventilation air. A computer modelling approach was used to assess energy consumption (the energy used to run the air-conditioning and ERV) and indoor PM2.5 exposure concentrations from both indoor and outdoor sources in Hong Kong high-rise residential flats under various ERV control strategies. Three varying inputs, including ventilation mode (energy-exchange, bypass or a hybrid of both), filter efficiency and ventilation rate, were used to develop different ERV control strategies. The estimated energy consumption and indoor PM2.5 exposure concentration were monetised using per-occupant cost functions, in order to allow a direct combination between the two. Results show that the ERV switching between energy-exchange and bypass modes according to outdoor weather conditions saves 43% of the annual energy cost compared with that operating in bypass mode, while the ERV operating in energy-exchange mode saves 28%. Integrating an air filter with a high PM2.5 removal efficiency into the ERV causes a reduction in the annual exposure cost with increased ventilation. By combining energy and exposure costs, this study has been able to determine the most cost-effective ventilation rate of the ERV, which costs an occupant approximately HK$ 2692 over the course of a year. Varying the ventilation rate as a function of outdoor temperatures, outdoor humidity ratios or outdoor enthalpy further reduces the combined cost compared with operating the ERV at the most cost-effective ventilation rate.
The paper presents the mathematical model, based on the narrow-channel approximation, for calculating the processes of heat and moisture transfer in membrane heat exchangers and taking into account possible condensation on heat exchange surfaces. The possibility of humidifying the supply air with moisture from the exhaust air in the cold period is considered. It is shown that the membrane co-current heat exchangers can operate without freezing up to the outdoor temperature equal to -20 °C.
Thermal performance enhancement of membrane based energy recovery ventilators (ERV) under turbulent flow conditions is investigated utilizing the computational fluid dynamics (CFD) approach. The standard k-ε model was adopted with the enhanced wall treatment option to simulate conjugate heat and mass transfer across the membrane. A user defined function was developed and incorporated into FLUENT to simulate the heat and mass transfer processes across a variable resistance 60 gsm membrane. A mesh sensitivity analysis was conducted and the developed CFD model was validated against an in-house experimental data. The performance of the investigated ERV was tested under different number of: flow channels, flow configurations, weather conditions and air flowrates. Results have shown that face velocity is more significant than flow separator in affecting the thermal performance of the investigated ERVs with a ratio of almost 5 to 1. Furthermore, the layout of the quasi-counter flow might present a preferable overall option over the L-Shape hybrid flow option. The final decision would be dependent on the HVAC system in-use and the higher priority between pressure drop, thermal energy recovered, manufacturability and/or installation.
Heat recovery devices can help ventilation systems conserve energy, however, they cause a pressure drop in the system, and hence the system incurs an electricity consumption. In the present paper, the maximum allowable pressure drop of the recovery units is achieved from thermodynamic and economic points of view. The novelty of the research is that, unlike the existing criterion which does not differ for different cities, the introduced criteria can be calculated for each city with individual weather, economic, power plants, and energy conditions. Although the methods presented to calculate the criteria consider a broad range of effective parameters, there is no need to use complex energy simulation methods. Moreover, for each city, four types of criteria are introduced, which allows the city authorities to choose the best ones according to their city conditions, and then calculate the chosen criteria by the data of the city. In order to gain the criteria, modified enthalpy-hours and bin method variables are introduced to calculate sensible and latent energy consumption due to ventilation. The criteria are numerically calculated for Kerman city in Iran, and the results show that the recovery type and the chosen viewpoint has a considerable effect on the allowable pressure drop. The sensitivity of the results to different variables is analyzed in the end.
Our aim was to evaluate the protective and antioxidant effects of ginger extract against cadmium-induced renal toxicity in animal models and to support the use of ginger as anti-renal failure natural remedy. Seventy rats were examined in a 4-week experiment to evaluate the effect of Ginger (Zingiber officinale) at doses of 100 and 200. mg/kg body weight on molecular DNA content, antioxidant status, and renal function in rats intoxicated with cadmium at dose of (5. mg/kg) using biochemical and histological analysis. Renal dysfunction, kidney tissue damage, and oxidative effect were evident in cadmium intoxicated rats as estimated by significant increase in (creatinine, urea), decrease in (creatinine clearance and reabsorption rate of urine albumin), increase in MDA, decrease in total antioxidant status (TAC), reduction in DNA content, and histopathological changes of kidneys' tissues compared to control rats. Treatment with ginger resulted in significant restoring of renal function biomarkers, TAC, molecular DNA, and histological improvements which occurs via free radical scavenging and regenerative mechanisms. The activity of ginger was supported by estimation of bioactive phenolic and falvinods constituents. Twenty-eight polyphenolic compounds were estimated in ginger extract; [6]-gingerol, [6]-shogaol, citral and pyrogallol were the highest amounts in ginger, and supposed to be responsible for its major antioxidant and free radical scavenging activity as shown by In vitro DPPH/β-carotene-linolic acid assay tests. Consequently, ginger extracts could have a potent protective effects against nephrotoxicity induced by various toxicants.
Since the 1990s, the rising problem that gonad reproductive toxicity on adult female after exposing to cadmium (Cd), an environmental endocrine disruptor, has attracted high attention at home and abroad,and was systematically studied. Our research focuses on a further problem is that early cadmium exposure (during birth to before puberty) impact on development and function of ovarian cells and its possible mechanism. Our research focuses on the changes of ovarian cells growth and development after the newborn rat ovaries with cadmium exposure in vitro, and different expression of ovarian cells development-related factors, SCF/c-kit and changes of their DNA methylation status. We obtained ovaries from 4-day-old SD rats and cultured them in DMEM/F12 mixed with α-MEM media in vitro. Different doses of cadmium were designed as control, 0.5, 5, 10 and 50 μM, and then the constituent ratio of ovarian follicle and follicular oocytes diameter were observed with microscope after 4-h exposure. We found that the increased constituent ratio of original follicle and decreased diameter of all levels of follicular oocytes(compared with control, with statistically significant differences, P < 0.01).After the measurement of expression of SCF/c-kit by qRT-PCR and Western Blotting, the mRNA and protein expression of SCF/c-kit in ovarian were both decreased. We further found that the increased constituent ratio of growth follicle and increased diameter of oocytes under the treatment of adding SCF in cell culture media. Finally, MALDI-TOF-MS method showed DNA-low methylation status of SCF/c-kit promoter region after Cd exposure. Overall, we concluded that the exposure of cadimium (5–50 μM) on newborn rats ovaries could inhibit follicle development.SCF/c-kit system might mediate follicle development damage caused by cadmium, which is associated with DNA hypomethylation of SCF/c-kit promoter region may be worthy of further study.
The indoor temperature of a building increases during the day due to solar radiation. This behavior is significant in school buildings that are finished with high thermal capacity materials. Moreover, in school buildings, windows cannot be opened until the class has finished owing to the security policy of schools. Consequently, classrooms maintain a high temperature throughout the morning. It is thus important to remove the indoor heat before the commencement of classes in order to reduce the cooling energy needed. The Energy Recovery Ventilator (ERV) system is currently being installed in school buildings for ventilating the classrooms. Night-purge control using ERV can be a good strategy to cool the classroom in advance of the operation of the cooling system. However, the optimal operation method of the ERV for night-purge control has not yet been reported. In this study, the effect of night-purge control with ERV in school buildings is analyzed by simulation method. The results of this study showed that the energy saving effect of night-purge control with ERV is most effective in the case of 2 hours operation prior to the commencement of the first lass and when enthalpy based outdoor air cooling is used.
Increased awareness of climate change has precipitated more stringent mitigation targets. Public sector institutions in Canada are committed to becoming carbon neutral to attain a leadership position in climate change mitigation-related initiatives. Recent statistics reveal that buildings account for the majority of the corporate carbon footprint of public sector institutions. Hence, there is an increasing interest towards developing net zero energy and net zero emission buildings to comply with climate action targets. With limited financial resources, public sector institutions must optimize investments into building energy retrofits by considering lifecycle cost (LCC), overall energy performance, and related greenhouse gas (GHG) emission. The aim of this paper is to develop an investment planning approach for net zero emission buildings (NZEB). First, an investment planning approach for NZEB is proposed. A typical recreational centre building in British Columbia, Canada, was used as the archetype to demonstrate the concept. Second, innovative and proven building energy retrofits were analysed using energy simulation software to assess the impact on energy consumption reduction, GHG emissions, and LCC. Third, impacts of geographical location, tariff regimes, and grid emission factors on energy retrofits were studied by locating the same building in other provinces of Canada. This study revealed that net zero energy investment has a strong correlation to the grid emission factor. The proposed approach in this paper will assist building managers and owners in retrofitting and budget planning.
The EnergyPlus building energy simulation software has been tested using the IEA HVAC BESTEST E100–E200 series of tests. The volume 1 final report for the International Energy Agency (IEA) solar heating and cooling programme task 22 building energy simulation test and diagnostic method for heating, ventilating, and air conditioning equipment models (HVAC BESTEST) was recently published in January 2002. HVAC BESTEST is a series of steady-state tests for a single-zone DX cooling system. Cases range from dry to wet coil, low to high part load, and low to high temperatures. This published test suite includes three sets of analytical solutions and results from several other simulation programs for comparison.This test suite was initially used to test EnergyPlus beginning with beta versions prior to its official public release, and it is also applied as an ongoing quality assurance test. The application of these tests proved to be very useful in several ways:•revealed input model shortcomings, which resulted in new user inputs being added;•revealed reporting errors which were fixed;•revealed algorithmic errors which were fixed;•revealed algorithmic shortcomings which were improved or eliminated through the use of more rigorous calculations for certain components;•in later versions, caught newly introduced bugs before public release of updates.Overall, the application of this test suite has been extremely useful in debugging and verifying the DX cooling algorithms in EnergyPlus. This paper summarizes the difficulties encountered and the benefits gained in applying the tests.
Many of the popular building energy simulation programs around the world are reaching maturity — some use simulation methods (and even code) that originated in the 1960s. For more than two decades, the US government supported development of two hourly building energy simulation programs, BLAST and DOE-2. Designed in the days of mainframe computers, expanding their capabilities further has become difficult, time-consuming, and expensive. At the same time, the 30 years have seen significant advances in analysis and computational methods and power — providing an opportunity for significant improvement in these tools.In 1996, a US federal agency began developing a new building energy simulation tool, EnergyPlus, building on development experience with two existing programs: DOE-2 and BLAST. EnergyPlus includes a number of innovative simulation features — such as variable time steps, user-configurable modular systems that are integrated with a heat and mass balance-based zone simulation — and input and output data structures tailored to facilitate third party module and interface development. Other planned simulation capabilities include multizone airflow, and electric power and solar thermal and photovoltaic simulation. Beta testing of EnergyPlus began in late 1999 and the first release is scheduled for early 2001.
More and more air handling units are equipped with heat recovery systems, with the aim of decreasing the energy use in buildings for heating and cooling. The efficiency of the heat recovery system is often used to calculate the energy saving. However, air-handling units do not always function as planned. In particular, parasitic shortcuts and leakage may decrease dramatically the efficiency of ventilation and heat recovery. In addition, these units need electrical energy for fans, which may be more precious than saved heat. Measurements, using tracer gas dilution technique have detected various malfunctions in several units.This paper addresses real energy recovery with air handling units from a theoretical point of view and presents results of measurements on 13 units. In the best three cases, the real, global heat recovery efficiency was between 60 and 70% for units having a 80% nominal efficiency. In the three worst cases, the global efficiency was less than 10%. For these cases, the heat recovery system uses more energy than it saves.
Many of the popular building energy simulation programs around the world are reaching maturity--some use simulation methods (and even code) that originated in the 1960s. For more than two decades, the U.S. government supported separate development of two hourly building energy simulation programs, BLAST and DOE--2. Designed in the days of mainframe computers, expanding their capabilities further became difficult, time-consuming, and prohibitively expensive. At the same time, significant advances in analysis and computational methods and power occurred---providing an opportunity for significant improvement in these tools. In 1996, the U.S. Department of Energy (DOE) began developing a new building energy simulation tool called EnergyPlus. This work built on development experience with two existing programs: DOE--2 and BLAST. EnergyPlus includes a number of innovative simulation features---such as variable time steps, user-configurable modular systems that are integrated with a heat and mass balance-based zone simulation---and input and output data structures tailored to facilitate third party module and interface development. Other planned simulation capabilities include multizone airflow, and electric power and solar thermal and photovoltaic simulation. Beginning in late 1999, a series of five beta test versions were released. Version 1.0 of EnergyPlus was released in April 2001.
By analyzing an example of plate total heat exchanger, the relational expressions of total heat efficiency, sensible heat efficiency and latent efficiency for the total heat exchanger were deduced with weight coefficient method. The influences of sensible heat efficiency and latent efficiency on total heat efficiency in different climatic areas of China were determined according to weight coefficients of sensible heat efficiency and latent heat efficiency, showing that the weight coefficient of latent heat efficiency is bigger than that of sensible heat efficiency under the summer air-conditioning condition. The total heat efficiency of the total heat exchanger was mainly influenced by the latent heat efficiency under summer condition in most areas of China, while by sensible heat efficiency in winter. As a result the weight coefficients of the sensible and latent heat efficiency are different in different climatic areas, and the effects of the sensible and latent efficiency on the all-year energy consumption, should be taken in to account in order to save cost and energy.
Heat recovery in ventilation systems can be obtained from both the sensible fraction and the latent fraction. The possible sensible and total heat recovery depends on the climate and on the operating period. Total heat recovery is limited in winter by the humidity of the supply air; this lowers the exchange capacity in the heating period. Three different climates are considered (Milan, Rome, Palermo), evaluating the recovery for unitary air ventilation how rate and the economic savings, also taking into account the reduction in the heating or cooling capacity. Heat recovery in a ventilating system must always be evaluated, since the investment is often profitable. (C) 1997 Elsevier Science Ltd.
Extracted ventilation air rated heat recovery efficiency is defined under standard rating conditions as ‘the efficiency of separate heat recovery equipment’. Real heat recovery efficiency depends not only on single unit efficiency but also on a building's heat gain/loss ratio. Maximum efficiency of heat recovery becomes unnecessary when heat gain compensates heat demand from a heat generator.The demand of recovered heat gradually lessens when the outdoor temperature rises and heat recovery is switched off if the outdoor temperature exceeds the thermal balance temperature of a premise. Thus, the mean annual heat recovery's efficiency is less than a technically possible one. This phenomenon is hardly perceptible in poorly insulated buildings where transmission loss plays the main role. The decrease of heat recovery's efficiency becomes significant in large, well-insulated buildings where ventilation heat loss is many times more than its transmission loss.
A study of the energy requirements for conditioning ventilation air and the yearly performance of a membrane-based energy recovery ventilator (MERV) in Hong Kong is carried out. The weather data are classified into six process regions in the psychrometric chart and the percentage of annual hours in each region is determined to describe different energy requirements. The variations in the amount of required heating and cooling energy are calculated for different indoor temperature and humidity set points. It is found that the required annual energy is primarily used to remove moisture from fresh air, with only a small fraction used for sensible cooling. The energy for heating in cold weather is negligible. Energy recovery ventilators are employed to study the possible annual energy savings. Hour-by-hour calculations disclose that in hot and humid regions like Hong Kong, about 58% of the energy required for conditioning fresh air could be saved annually with an MERV, which recovers both latent and sensible energy, while only about 10% of the energy could be saved with a traditional sensible-only energy recovery ventilator (SERV). The more humid the weather, the more superior is an MERV in comparison with an SERV.
Using water as the working fluid, air-to-air heat exchangers using thermosyphon heat pipes were designed, constructed and tested under medium temperature (below 300°C) operating conditions. A heat exchanger test rig has been constructed and developed wherein the heated air is recycled to the counterflow heat exchanger. The lengths of both the evaporator section and the condenser section of the heat exchangers were 300 mm and the central adiabatic section was 150 mm. The heat exchangers which were tested used (1) continuous plate finned copper tubes, (2) circular, spirally-finned steel tubes and (3) bare copper tubes for their respective heat pipes. The working fluid was water with a fill ratio of 60% of the evaporator section length. The air face velocity range was from 1.5 to 5 m/s and the heat input into the evaporator section inlet was varied between 4 and 20 kW using electric heating elements. The heat exchangers showed high effectiveness compared with similar heat exchangers using other working fluids, such as Freon 22 (R22). The rectangular plate finned copper thermosyphon heat exchanger had the best performance but there was a limitation on testing this configuration that the adiabatic section temperature operating condition did not exceed 200°C, in order not to exceed the safe working pressure. A steel pipe heat exchanger will be used in the industrial application to which the project is directed.This heat exchanger has been designed, manufactured and tested for heat recovery in industry with medium temperatures (lower than 300°C), for example in bakeries to recover flue gas energy from the oven to heat up the proofing oven or other low temperature heating functions.
The performance correlations for the effectiveness of heat and moisture transfer processes in an enthalpy exchanger with membrane cores are presented. The physical phenomena relevant to the heat and moisture transfer in these devices have been used to develop a novel set of correlations based on the relevant dimensionless parameters. The total enthalpy effectiveness can be calculated from sensible effectiveness, latent effectiveness, and the ratio of latent to sensible energy differences across the unit. Studies show that the sensible effectiveness is a function of NTU, the number of transfer units for heat; while the latent effectiveness is a function of NTU L , the number of transfer units for moisture. The relations between NTU L and NTU are derived and studied with the proper sepa-ration of moisture resistance for membranes. This newly developed dimensionless param-eter, NTU L , is to summarize the sorption characteristics of membrane material, the exchanger configurations, as well as the operating conditions. A number of experi-mental results on an enthalpy exchanger with novel hydrophilic membrane cores has been used to valid these correlations.
This paper presents a detailed heat and mass transfer model for an energy recovery ventilator (ERV) with a porous hydrophillic membrane core. Through finite difference simulations, the temperature, and humidity fields in the unit are calculated. The coupled heat and mass transfer mechanism for the system is discussed. It is found that for the present cross-flow arrangement, the membrane area is not effectively used in heat and moisture exchange. The heat and mass transfer rate is larger near the inlets of fluids. There is a ridge on the membrane in the direction of left-lower to upper-right where permeability is relatively higher.
Based on the generic dynamic building energy simulation environment, EnergyPlus, the simulation model of energy recovery ventilator (ERV) is developed in this paper. With different indoor temperature set-points, the energy performance of ERV along with the availability of ERV is investigated both for Beijing and Shanghai weathers in China in terms of the ratio of heat recovery to energy supply by HVAC devices and ERV. Simulation results show that the seasonal average of the ratio is linear with indoor temperature set-points. The availability of ERV in Shanghai is better than that in Beijing during the winter. In summer, the utilization of ERV is uneconomical if the indoor temperature set-point is higher than 24 °C for the Beijing climate. The indoor temperature set-points have the reverse effects to the availability of ERV in the mid-season and to that in the hottest months. Meanwhile, the heating amount recovery in summer and the cooling amount recovery in winter, both of which impair the strong points of the energy recovery, are analyzed quantitatively.
The fundamental dimensionless groups for coupled heat and moisture transfer in a cross flow air-to-air enthalpy exchanger with hydrophilic membrane cores are derived and validated with experimental data. The thermal and moisture transfer mechanisms in membranes are studied. The finite difference numerical solutions of the model are used to study heat and moisture transfer in enthalpy exchangers. The variations of sensible, latent, and enthalpy effectiveness with various operating parameters are calculated for different types of material. Studies show that the sensible effectiveness is mainly determined by number of transfer units (NTU) of the exchanger, while the latent effectiveness is influenced by both the material and the operating conditions. Unlike thermal diffusive resistance, the moisture diffusive resistance in membrane is not a constant. It is co-determined by the slopes of sorption curves and the operating conditions. To account for these influences, a new dimensionless factor named the coefficient of moisture diffusive resistance (CMDR) is defined. With this coefficient, the performance of an enthalpy exchanger can be more easily predicted and clearly understood. By comparing the performances with different membrane materials, it is revealed that the membrane material with a linear sorption curve performs better than other materials under common conditions.
Heat and mass transfer mechanisms in a cross-flow parallel plate membrane-based enthalpy exchanger for heat and moisture recovery from exhaust air streams are investigated. The flow is assumed laminar and hydrodynamically fully developed, but developing in thermal and concentration boundaries. Contrary to the traditional methods to assume a uniform temperature (concentration) or a uniform heat flux (mass flux) boundary condition, in this study, the real boundary conditions on the exchanger surfaces are obtained by the numerical solution of the coupled equations that govern the transfer of momentum, thermal energy, and moisture in the two cross-flow air streams and through the membrane. The naturally formed heat and mass boundary conditions are then used to calculate the local and mean Nusselt and Sherwood numbers along the cross-flow passages, in the developing region and thereafter. A comparison was made with those results under uniform temperature (concentration) and uniform heat flux (mass flux) boundary conditions, for rectangular ducts of various aspect ratios. An experiment is done to verify the prediction of outlet moisture content.
Buildings are slowly replacing long-term investments that consume a lot of energy. Given current economic, as well as environmental constraints on energy resources, the energy issue plays an important role in the design and operation of buildings. Careful long-term decisions in the design and operation of buildings can significantly improve their thermal performance and thus reduce their consumption of energy. Alternative building design strategies, standards compliance and economic optimization can be evaluated using available energy analysis techniques. These range from simplified manual energy analysis methods for approximate energy use estimates to detailed computerized hourly simulation. The availability and ease of use of today’s computers make them effective tools in the decision-making process of building design. This paper reviews the most common building energy analysis techniques and the potential applications of computer technology in the energy simulation and optimization of buildings.
The cross-flow operation of hollow fiber membrane contactors offers many advantages and is preferred over the parallel-flow contactors for gas-liquid mass transfer operations. However, the analysis of such a cross-flow membrane gas-liquid contactor is complicated due to the change in concentrations of both phases in the direction of flow as well as in the direction perpendicular to flow. In addition, changes in the volumetric flow rate of compressible fluid can also occur over the volume of membrane contactor. These hollow fiber membrane contactors resemble to the more conventional shell and tube cross-flow heat exchanges where a similar variation in the local driving force within the module occurs. Hence heat transfer analogy can be applied to predict the performance of these contactors. Analytical expressions are derived in this work to describe the mass transfer in these hollow fiber cross-flow contactors analogously to heat transfer in cross-flow shell and tube heat exchangers. CO2 absorption experiments were carried out in a commercial as well as in the lab-made single-pass cross-flow hollow fiber membrane contactors to check the applicability of this heat transfer analogy under different conditions. Experimental results show that the derived analytical expressions can be applied to the cross-flow membrane gas-liquid contactor under the asymptotic conditions of negligible or small volumetric flow changes. However, in the case of significant changes in the flow rate of compressible fluid, the application of heat transfer analogy results into slight under predictions of the module performance. A more rigorous model is then required for an accurate prediction of the performance.
Practical Design Handbook of Heating and Air Conditioning
- Y Q Lu
Y.Q. Lu, Practical Design Handbook of Heating and Air Conditioning, Building Industry Press of China, Beijing, 1993 (in Chinese).
Total heat exchanger—a new type of energy saving equipment for air condition units
- Yang
S.B. Yang, Total heat exchanger—a new type of energy saving equipment for air condition units, Journal of Shijiazhuang Railway Institute 5 (1) (1992) 64–70 (in Chinese).