Experimental study on the performance of air source heat pump system with multiple parallel outdoor units

This paper presents a novel air source heat pump for heating of buildings named air source heat pump with multiple parallel outdoor units (ASHPMO). Multiple outdoor units were connected in parallel with the aim of realising alternate defrosting and uninterrupted heating simultaneously. An experimental apparatus of the ASHPMO system was developed. The defrosting performance was experimentally investigated under different outdoor air temperatures, outdoor air relative humidity, and condensation temperatures, among other factors. The test results showed that the novel ASHPMO system could provide continuous heating when defrosting even under an outdoor air temperature of −10°C. Variations in compressor vapour suction and discharge pressure and temperature were observed. The minimum heating capacity could still reach 60% of that without defrosting. Under the defrosting condition with outdoor air temperature −10°C, both the heating coefficient of performance (heating COP) and total energy efficiency ratio (EER) of the system can reach to 2.0 and 2.32, respectively.     

复合地源热泵系统冬季供暖运行实验研究

介绍了地源热泵在冬季运行供暖的实验研究,具体分析了长期连续运行时土壤温度的变化规律,热泵机组系统的COP变化情况,以及太阳能辅助系统与地源热泵系统联合运行时土壤温度的变化规律,热泵机组系统的COP变化情况.试验数据表明了增加太阳能辅助地源热泵系统后,显著地提高了冷凝器出口温度和室内温度,有效地提高了热负荷,增加了供热面积.总结出了本地区地源热泵系统的一般运行规律.     

Exergy analysis of latent heat storage systems with sensible heating and subcooling of PCM

The effect of sensible heating of the phase-change material (PCM) before melting and subcooling after solidification, on the performance of the latent heat storage system (LHSS), is studied in terms of first- and second-law efficiencies for the overall charge–discharge cycle. The external heat transfer irreversibilities on account of the interaction between the heat transfer fluid and the storage element are characterized and the optimum phase-change temperature for maximum second-law efficiency is studied. The performance of the LHSS operation is assessed with and without sensible heating before melting and subcooling after solidification. It is observed that the optimum phase-change temperature is higher, and, the overall second-law efficiency is greater for LHSS with sensible heating and subcooling beyond a certain phase-change temperature compared to latent heat storage alone. In addition, the first-law overall efficiency is found to exhibit a minimum and a pre-heated discharge stream is shown to result in a substantial improvement of the second-law efficiency. © 1998 John Wiley & Sons, Ltd.     

Exergetic performance assessment of a ground‐source heat pump drying system

In evaluating the efficiency of heat pump (HP) systems, the most commonly used measure is the energy (or first law) efficiency, which is modified to a coefficient of performance (COP) for HP systems. However, for indicating the possibilities for thermodynamic improvement, energy analysis is inadequate and exergy analysis is needed. This study presents an exergetic assessment of a ground‐source (or geothermal) HP (GSHP) drying system. This system was designed, constructed and tested in the Solar Energy Institute of Ege University, Izmir, Turkey. The exergy destructions in each of the components of the overall system are determined for average values of experimentally measured parameters. Exergy efficiencies of the system components are determined to assess their performances and to elucidate potentials for improvement. COP values for the GSHP unit and overall GSHP drying system are found to range between 1.63–2.88 and 1.45–2.65, respectively, while corresponding exergy efficiency values on a product/fuel basis are found to be 21.1 and 15.5% at a dead state temperature of 27°C, respectively. Specific moisture extraction rate (SMER) on the system basis is obtained to be 0.122 kg kW^?1 h^?1. For drying systems, the so‐called specific moisture exergetic rate (SMExR), which is defined as the ratio of the moisture removed in kg to the exergy input in kW h, is also proposed by the authors. The SMExR of the whole GSHP drying system is found to be 5.11 kg kW^?1 h^?1. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental performance evaluation of a closed‐loop vertical ground source heat pump in the heating mode using energy analysis method

An experimental study is performed to determine the performance of a ground source heat pump (GSHP) system in the heating mode in the city of Erzurum, Turkey. The GSHP system using R‐134a as refrigerant has a single U‐tube ground heat exchanger (GHE) made of polyethylene pipe with a 16 mm inside diameter. The GHE was placed in a vertical borehole with 55 m depth and 203.2 mm diameter. The average coefficients of performance (COP) of the GSHP system and heat pump in heating mode are calculated as 2.09 and 2.57, respectively. The heat extraction rate per meter of the borehole is determined as 33.60 W m^?1. Considering the current gas and electric prices in Erzurum city, the equivalent COP of the GSHP system should be 2.92 for the same energy cost comparing with natural gas. The virgin ground in Erzurum basin has high permeability and low thermal conductivity. In order to improve the thermal efficiency of GHE and thus improve COP of a GSHP in the basin, the borehole should be backfilled with sand as low‐cost backfill material and a 1 to 2 m thick surface plug of clay should be inserted. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental investigation of the performance of a solar‐assisted ground‐source heat pump system for greenhouse heating

The main objective of the present study is to investigate the performance characteristics of a solar‐assisted ground‐source heat pump system (SAGSHPS) for greenhouse heating with a 50 m vertical 1¼ in nominal diameter U‐bend ground heat exchanger. This system was designed and installed in the Solar Energy Institute, Ege University, Izmir (568 degree days cooling, base: 22°C, 1226 degree days heating, base: 18°C), Turkey. Based upon the measurements made in the heating mode, the heat extraction rate from the soil is found to be, on average, 54.08 Wm^?1 of bore depth, while the required borehole length in meter per kW of heating capacity is obtained as 12.57. The entering water temperature to the unit ranges from 8.2 to 16.2°C, with an average value of 9.1°C. The greenhouse air is at a maximum day temperature of 25°C and night temperature of 14°C with a relative humidity of 40%. The heating coefficient of performance of the heat pump (COP_HP) is about 2.13 at the end of a cloudy day, while it is about 2.84 at the end of sunny day and fluctuates between these values in other times. The COP values for the whole system are also obtained to be 5–15% lower than COP_HP. Copyright © 2004 John Wiley & Sons, Ltd.     

A performance comparison between an air‐source and a ground‐source reversible heat pump

In this study, the performance of a reversible ground‐source heat pump coupled to a municipality water reticulation system, is compared experimentally and with simulations to a conventional air‐source heat pump for space cooling and heating. A typical municipality water reticulation system comprises hundreds of kilometres of pipes designed in loops that will ensure adequate circulation of water. This results in a substantial heat exchanger with great potential. Indirect heat transfer occurs between the refrigerant and ground via the municipality water reticulation system that acts as the water‐to‐ground heat exchanger. The experimental and simulated comparisons of the ground‐source system to the air‐source system are conducted in both the cooling and the heating cycles. Climatalogical statistics are used to calculate the capacities and coefficients of performance of the ground‐source and air‐source heat pumps. Results obtained from measurements and simulations indicate that the utilization of municipality water reticulation systems as a heat source/sink is a viable method of optimizing energy usage in the air conditioning industry, especially when used in the heating mode. Copyright © 2001 John Wiley & Sons, Ltd.     

基于动态热负荷的太阳能——地源热泵运行模式研究

建立了太阳能-地源热泵系统一体化模型,以大连地区气候条件为基础,计算了供暖季某天内房间热负荷的逐时值.在动态热负荷基础上,对联合供暖系统在不同串联运行模式和并联运行模式不同分流比的运行工况进行了模拟计算,将模拟结果与实脸数据对比,两者吻合较好.结果表明:房间热负荷的变化可影响热泵机组COP.联合运行模式在地温的恢复和系...     

分液热泵空调系统的制热性能研究

随着热泵空调的普及,热泵空调的能耗占比不断增大,其节能问题成为了关注焦点。换热器对系统性能有着重要的影响,如何通过改进换热器来提升系统性能则成为了研究的热点。其中分液冷凝器作为一种新型的换热设备,能对系统制冷性能产生积极影响。但热泵空调系统在制热工况下,分液冷凝器变成气液分离式蒸发器,其系统制热性能尚未可知。通过实验研究,调整毛细管长度和制冷剂充注量,发现在国家标准工况下分液热泵空调系统的最大制热量比原系统高4.50%,C OP比原系统高7.93%,所对应的毛细管长度为700 mm,制冷剂充注量为700 g。且制冷剂过充注的情况下,分液热泵空调系统的制热性能比较稳定。     

Correlations for cost of ground‐source heat pumps and for the effect of temperature on their performance

Ground source heat pump systems are becoming more and more popular, even though their high initial cost is an obstacle to their wider penetration of the heating and cooling market. The purchase of the heat pump itself is one of the dominant costs, and the heat pump selection also influences the operation costs through its coefficient of performance (COP) value. However, few studies are available on this topic. Based on 23 water–water heat pump models available on the market, a correlation was developed to estimate their purchase cost as a function of the nominal cooling load of the heat pump. These heat pumps can be used in geothermal applications as well as in other heating, ventilating, air conditioning and refrigeration (HVAC&R) systems. The correlation is valid for a nominal cooling load between 20 and 841 kW. The nominal COP of the heat pumps was found to have virtually no effect on their purchase costs. Also, two correlations were developed to relate variations of cooling power and COP to the temperature levels on both sides of the heat pump. The heating mode is also considered. The correlations are useful to estimate the required nominal size of a heat pump given design operating conditions and to optimize ground source heat pump systems from a techno‐economical standpoint. Copyright © 2014 John Wiley & Sons, Ltd.     

别墅型建筑地源热泵空调系统设计

地源热泵是一种利用土壤所储藏的太阳能资源作为冷热源进行能量转换的供暖制冷空调系统,通过输入少量的高品位能源(如电力、机械功、燃气和液体燃料),实现热量从低温热源向高温热源的转移.以上海某小型别墅为对象,设计了一套家用地源热泵空调系统.首先计算了夏季冷负荷和冬季热负荷,然后根据冷、热负荷选择一套水源热泵机组(MWH080CR型机组)和相应的风机盘管,进行了室内水管环路系统、土壤热交换器和地板采暖的设计选型,最后对系统的能效比进行了计算.结果表明,该空调系统具有节能环保、稳定可靠、舒适耐用等优点.     

Heat storage-type floor heating system with heat pump driven by nighttime electric power

We performed tests for heat storage-type floor heating that employs a heat pump driven with nighttime electric power for 8 h (11 PM to 7 AM) as the heat source. The phase change material (PCM) applied was a package of mirabilite (Na₂SO₄ · 10H₂O). The melting point is 32 °C, the freezing point 30 °C, and the stored heat amount 43 W · h/kg (ΔT = 10 °C). The test room for floor heating was a wooden structure without windows, and the floor area was 40 m². The hot water panel (5 mm in thickness, made of plastic, 26 m²) was laid on the stage (1.2 m in height) inside the room and the PCM was superimposed on the upper surface of the stage (the total stored heat amount was 28.5 kW). Since the heat pump runs in cycles of 8-h operation and 16-h nonoperation, it needs an extracted heat amount of three times compared with the case of round-the-clock operation. For this reason, we have developed a wet film-type vertical heat extracting tube with a built-in Freon flashing pump to obtain extracted heat about three times greater than was previously possible. We have calculated the heat balance from the results of the tests for floor heating and have studied the practicability of this system. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 122–130, 1997     

超临界补气增焓高温CO2热泵热风机实验研究

针对工业上循环加热工况下,CO₂热泵气体冷却器出口温度过高、能效显著降低的问题,文章提出了带有超临界补气的高温CO₂热泵循环,并对系统进行了实验研究。主要分析了主路膨胀阀开度、压缩机频率、气体冷却器的风机频率对出风温度、性能系数COP等参数的影响。实验结果表明:出风温度随着主路膨胀阀开度的增大呈现降低趋势而COP呈升高趋势;降低气体冷却器的风机频率对出风温度的提升效果最为明显,风机频率每调低1%,出风温度最大提升5.07%。以得到最高出风温度为目标的实验数据表明,该系统在气体冷却器出口温度为75℃以上时,出风温度可达130℃以上,对应COP为1.40~1.50。     

Cooling characteristics of ground source heat pump with heat exchange methods

The objective of this study is to investigate the influence of the cooling performance for a water-to-water ground source heat pump (GSHP) by using the counter flow and parallel flow methods. The GSHP uses R-410A as a refrigerant, and its main components are a scroll compressor, plate heat exchangers as a condenser, an evaporator, a thermostatic expansion valve, a receiver, and an inverter. Based on our modeling results, the heat transfer rate of the counter flow evaporator is higher than that of the parallel flow evaporator for a heat exchanger length greater than 0.42 m. The evaporator length of the GSHP used in this study was set to over 0.5 m. The performance of the water-to-water GSHP was measured by varying the compressor speed and source-side entering water temperature (EWT). The cooling capacity of the GSHP increased with increased compressor RPMs and source side EWT. Also, using the counter flow method, compared to the parallel flow method, improves the COP by approximately 5.9% for an ISO 13256-2 rated condition.     

Studies on a compression‐absorption heat pump for simultaneous cooling and heating

A thermodynamic analysis has been carried out on a compression‐absorption system that can be used for simultaneous heating and cooling applications. Refrigerant and absorbent pair of R‐22 and DMETEG has been considered. The results are obtained for a system that can be used in dairy plants for pasteurization and chilling of milk for subsequent storage. Results show that by operating the system at marginally higher discharge pressures (about 30 bar) than normal (about 25 bar) one can achieve excellent performance despite the required large temperature lift. A comparison with a single stage vapour compression system shows that, the compression‐absorption system yields much better overall performance especially when the temperature lifts are high. Copyright © 2004 John Wiley & Sons, Ltd.     

回热器对跨临界CO_2水源热泵的影响判别式及实验研究

分析了回热器对跨临界CO2压缩循环效率等的影响,推导出回热器对系统的制热效率影响的判别式。在带回热器和不带回热器两种情况下完成了跨临界CO2水源热泵系统的实验。实验结果表明：带回热器的跨临界CO2水源热泵系统的制热效率和制冷效率略高于不带回热器时系统的效率;带回热器时热泵系统的制热效率比不带回热器系统的制热效率高约4%-8%。     

污水源热泵供热的工程应用及分析

齐鲁石化水厂原来利用热电厂蒸汽换热后制备低温热水对车间和办公楼进行供热,运行费用高.根据该厂有丰富的工业污水的特点,现设计采用污水源热泵机组为车间及办公楼提供热.分析表明,一个采暖季即可节省运行费用约68万元,而且使用效果良好.     

Energy analysis of a low‐temperature heat pump heating system in a single‐family house

Energy costs and environmental concerns have made energy optimisation a viable option for buildings. Energy‐efficient heating systems together with an effective use of buildings thermal mass and tightness have a significant impact on the energy requirement and on the possibility for sizeable running cost savings. In this study we use the simulation tool TRNSYS‐EES to model and analyse the performance of a residential house and the low‐temperature heating system that serves its thermal needs. The building is a single‐family house with controlled ventilation and the chosen heating system is a hydronic floor heating system connected to an exhaust air heat pump. The aim of the simulation is to study the performance of the building, the heating system and the controls in an integrated manner. Overall, the results indicate that the energy efficiency issue implicates system design and system thinking concerns as well as techno‐economic difficulties. The controls and the choice of the operation mode are of a great importance. Copyright © 2004 John Wiley & Sons, Ltd.     

Thermoeconomic analysis of ground‐source heat pump systems

A thermoeconomic analysis of a ground‐source heat pump (GSHP) system with a vertical or horizontal ground heat exchanger, a type of heat delivery system, was performed using the modified productive structure analysis method. In this analysis, the unit cost of geothermal heat delivered to a room using GSHP system was estimated. The unit cost of heat delivered was calculated to be $0.063/kWh for input of electricity with a unit cost of $0.140/kWh for a GSHP with a coefficient of performance (COP) of 3.27. Exergy destruction and monetary losses due to the irreversibility that occurs at each component of the system were also estimated. The unit cost of heat was found to be inversely proportional to the COP of the heat pump and proportional to the electricity input. The greatest monetary loss occurs in the geothermal heat exchanger in which considerable mass of brine flows in long pipes and in the fan‐coil unit which features a complex configuration of pipes in the air passages, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on a direct‐expansion solar‐assisted heat pump water heating system

Analytical and experimental studies were performed on a direct‐expansion solar‐assisted heat pump (DX‐SAHP) water heating system, in which a 2 m² bare flat collector acts as a source as well as an evaporator for the refrigerant. A simulation model was developed to predict the long‐term thermal performance of the system approximately. The monthly averaged COP was found to vary between 4 and 6, while the collector efficiency ranged from 40 to 60%. The simulated results were used to obtain an optimum design of the system and to determinate a proper strategy for system operating control. The effect of various parameters, including solar insolation, ambient temperature, collector area, storage volume and speed of compressor, had been investigated on the thermal performance of the DX‐SAHP system, and the results had indicated that the system performance is governed strongly by the change of solar insolation, collector area and speed of compressor. The experimental results obtained under winter climate conditions were shown to agree reasonably with the computer simulation. Copyright © 2003 John Wiley & Sons, Ltd.