Effect of load pattern on solar-boosted heat pump water heater performance

The performance of a solar-boosted heat pump water heater (HPWH) operating under full load and part load conditions was determined in an outdoor experimental study. The system utilised flat unglazed aluminium solar evaporator panels to absorb solar and ambient energy. Absorbed energy was transferred to the water tank by means of the heat pump and a wrap around condenser coil on the outside of the tank. The system COP was found to be in the range of 5–7 under clear daytime conditions and 3–5 under clear night-time conditions. Using part load testing of the HPWH system it was found that concentrating the coils in the lower portion of the tank could increase the efficiency of the condenser coil. It was also shown that there exists a generalised linear relationship that can be used to describe the system COP in terms of the temperature difference between the water in the storage tank and the ambient air.     

Numerical simulation and performance assessment of a low capacity solar assisted absorption heat pump coupled with a sub-floor system

A prototype low capacity (10 kW) single stage Li–Br absorption heat pump (AHP), suitable for residential and small building applications has been developed as a collaborative result between various European research institutes and industries. The primary heat source for the AHP is supplied from flat plate solar collectors and the hot/chilled water from the unit is delivered to a floor heating/cooling system. In this paper we present the simulation results and an overview of the performance assessment of the complete system. The calculations were performed for two building types (high and low thermal mass), three climatic conditions, with different types of solar collectors and hot water storage tank sizes and different control systems for the operation of the installation. The simulations were performed using the thermal simulation code TRNSYS. The estimated energy savings against a conventional cooling system using a compression type heat pump was found to be in the range of 20–27%.     

System optimization and experimental research on air source heat pump water heater

This paper deals with the system optimization of air source heat pump water heater (ASHPWH), including calculating and testing. The ASHPWH system consists of a heat pump, a water tank and connecting pipes. Air energy is absorbed at the evaporator and pumped to storage tank via a Rankine cycle. The coil pipe/condenser releases condensing heat of the refrigerant to the water side. An ASHPWH using a rotary compressor heated the water from initial temperature to the set temperature (55 °C). The capillary tube length, the filling quantity of refrigerant, the condenser coil tube length and system matching are discussed accordingly. From the testing results, it could be seen that the system performance COP could be improved obviously.     

Analysis and simulation of a solar water pump for lift irrigation

A solar water pump for lift irrigation, which was shown to be economically viable, was proposed by Rao and Rao [5]. A “modified pump” is suggested, which is suitable for village water supply. The thermodynamic analysis of the pumps is presented. Though the solar water pump is intended to be operated with flat-plate collectors, it is analysed whether the pump could be run more efficiently when coupled with concentrating collectors. The analysis is also applicable for bellow actuated solar water pumps.Preliminary experimental studies showed that the heat losses are 2–3 times the theoretical energy requirement and the losses to the water tank shell accounted for a major part of the total heat losses. To reduce these losses, it is proposed that the inner surface of the water tank shell be lined with a resin bonded cork insulation. A method to evaluate the heat losses to the shell with insulation by solving the unsteady state heat conduction equation for a composite cylindrical body with time varying convective boundary conditions is presented. The heat losses are reduced to 5–15 per cent of the theoretical energy requirement with the use of the internal insulation. The major problem encountered in operating the pump was the inadequate condensation of the working fluid, which resulted in failure of the suction of water into the water tank. To ensure proper suction of water, the conditions to be maintained are analysed. The presence of water vapor and air in the spent vapor has to be taken into consideration while designing the condenser.An algorithm to evaluate the year round performance of the water-cooled pump for any location, given the lift and collector area, is presented. The cost of the water-cooled pump is compared with the costs of other types of solar water pumps and it is shown that the pump under consideration costs several times less than the other ones. The conditions at which the pump will be economical vis-a-vis diesel and electrical pumps are presented.     

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...     

Performance of solar assisted heatpump systems in residential applications

In this experimental study, several solar-assisted heating and cooling configurations have beenconsidered for a basic system comprised of a two-speed heat pump, photovoltaic (PV) arrays, solar thermal collectors, and thermal storage. The objective of the study was to determine the performance of the PV arrays at decreased insolation, the effects of air preheat by solar thermal energy on heat pump operation, and cooling system performance under two different configurations. During the entire operation, the PV arrays converted 4.7 per cent (9.5 MWh) of the incident solar insolation to d.c. power, of which 54.6 per cent was used by the residence. This contributed 23.4 per cent of the total house electrical demand. The remaining 45.4 per cent of the output was fed to the utility, indicating the arrays and the heat pump were not properly sized with each other. Based on results from the winter heating operation, it is shown that for the particular heating system consdered, the best performance is attained when the solar heating is used alone. By using the heat pump as a booster, the remaining available solar energy left in the storage tank can be used with good seasonal performance factor. Summer cooling operation consisted of two sequential cooling configurations. In the first cooling test, the heat pump was operated to either the house or storage when the PV array generation level was greater than the energy demand of the heat pump and associated equipment. When the array output level was less than the cooling system demand, the operating strategy was that of an off-peak cooling operation to chill the water storage. Utilization of chilled water storage was not realized in the first cooling test because of the inherent inefficient design of the Tri-X coil. The capacity at low-speed heat pump operation was too small to effect significant cooling of the water loop; whereas high-speed heat pump operation in attempting to chill water (fan operation absent) caused frosting of the coil. The heat pump was utilized only to maintain chilled water storage in the second cooling test, without heat transfer through the Tri-X coil. Cooling system performance obtained in cooling test 2 using the Ametex exchanger was considerably improved over the test 2 performance with the Tri-X coil.     

Solar-assisted absorption heat pumps feasibility

An absorption system can be used for space cooling as well as for space heating. This dual purpose may be achieved by using the system as heat pump in wintertime. Absorption heat pump heating may be an interesting alternative, particularly for countries where there is a shortage of electric power.When an absorption unit is used as heat pump, its mode of operation is not modified: the internal temperatures of the cycle are only raised. Commercially available LiBr units were tested as heat pumps. COP and heating capacity were considered as a function of cold source temperature for different temperatures of the useful heat. The COP arrived at 1.7, which must be considered a high value for a thermally driven heat pump.Simulations were carried out in order to compare the performance of “conventional” solar, solar assisted heat pump and the combined series system under two different climate conditions. The series system showed performance 25–75 per cent better than “conventional” solar alone.     

Solar assisted heat pump

The paper describes a series solar heat pump, using Freon 11 as the working fluid. The heat pump is specifically designed for use in a tropical climate where the normal daytime ambient of above 25°C permits the evaporator to be operated at a high temperature (15–50°C depending on solar input). The use of Freon 11 permits conventional reciprocating refrigeration compressors to be used at elevated temperatures without exceeding design pressure limits. A single unit acts as the evaporator and solar collector. When solar insolation is low the evaporator pressure automatically drops so that energy is received from the atomsphere. However the C.O.P. and output are so low in this mode that the system cannot correctly be termed dual source. The water cooled condenser operates in the temperature range of 35–90°C, the heated water representing the useful output of the system. Operation in the air conditioning mode is not possible due to the large specific volume of Freon 11 at low temperatures. A theoretical analysis is presented to describe the system operation, and the experimental results are shown to agree well with the computer simulation. Average values of C.O.P. of between 2.5 and 3.5 were obtained for the small prototype developed with high side storage temperatures of up to 80°C.     

A study on the design and analysis of a heat pump heating system using wastewater as a heat source

In this study, the compression heat pump system using wastewater, as a heat source, from hotel with sauna was designed and analyzed. This study was performed to investigate the feasibility of the wastewater use for heat pump as a heat source and to obtain engineering data for system design. This heat pump system uses off-peak electricity that is a cheap energy compared to fossil fuel in Korea. For this, the charging process of heat into the hot water storage tank is achieved only at night time (22:00–08:00). TRNSYS was used for the system simulation with some new components like the heat pump, which we create ourselves.As a result, it was forecasted that the yearly mean COP of heat pump is about 4.8 and heat pump can supply 100% of hot water load except weekend of winter season. The important thing that should be considered for the system design is to decrease the temperature difference between condenser and evaporator working fluids during the heat charging process by the heat pump. This heat pump system using wastewater from sauna, public bath, building, etc. can therefore be effectively applied not only for water heating but also space heating and cooling in regions like as Korea.     

Performance of a multi-functional direct-expansion solar assisted heat pump system

This paper reports on the long-term performance of a direct-expansion solar assisted heat pump (DX-SAHP) system for domestic use, which can offer space heating in winter, air conditioning in summer and hot water during the whole year. The system employs a bare flat-plate collector array with a surface area of 10.5 m², a variable speed compressor, a storage tank with a total volume of 1 m³ and radiant floor heating unit. The performance under different operation modes is presented and analyzed in detail. For space-heating-only mode, the daily-averaged heat pump COP varied from 2.6 to 3.3, while the system COP ranged from 2.1 to 2.7. For water-heating-only mode, the DX-SAHP system could supply 200 l or 1000 l hot water daily, with the final temperature of about 50 °C, under various weather conditions in Shanghai, China. For space-cooling-only mode, the compressor operates only at night to take advantage of a utility’s off-peak electrical rates by chilling water in the thermal storage tank for the daytime air-conditioning. It shows that, the multi-functional DX-SAHP system could guarantee a long-term operation under very different weather conditions and relatively low running cost for a whole year.     

基于线热源理论的垂直U型埋管换热器传热模型的研究

基于经典常热流线热源理论,通过引入叠加原理、阶跃负荷及孔洞热阻思想将其发展为能够适用于变热流埋管换热与地源热泵系统模拟的变热流线热源模型,并与改进的经实验与理论验证的圆柱源理论模型进行了比较与分析。结果表明:所发展的变热流线热源模型能够有效地模拟地下埋管的换热过程,可作为地下垂直U埋管换热过程的计算模型,为地源热泵地下埋管换热器的设计计算及地源热泵系统的模拟提供了一种新的简单而又实用的计算方法。     

Thermal performance of a solar-aided latent heat store used for space heating by heat pump

In this study, the cylindrical phase change storage tank linked to a solar powered heat pump system is investigated experimentally and theoretically. A simulation model defining the transient behaviour of the phase change unit was used. In the tank, the phase change material (PCM) is inside cylindrical tubes and the heat transfer fluid (HTF) flows parallel to it. The heat transfer problem of the model (treated as two-dimensional) was solved numerically by an enthalpy-based finite differences method and validated against experimental data. The experiments were performed from November to May in the heating seasons of 1992–1993 and 1993–1994 to measure both the mean temperature of water within the tank and the inlet and outlet water temperature of the tank. The experimentally obtained inlet water temperatures are also taken as inlet water temperature of the simulated model. Thus, theoretical temperature and stored heat energy distribution within the tank have been determined. Solar radiation and space heating loads for the heating seasons mentioned above are also presented.     

Feasibility study of hybrid fuel cell and geothermal heat pump used for air conditioning in Algeria

Hybrid Energy System (HES) is mainly based on proton exchange membrane fuel cell (PEMFC) technology, which is supplied by a fuel reforming process for hydrogen production, starting from natural gas. The exhaust heat from the PEMFC is evacuated to a thermal storage tank (TST) mixed with water provided by geothermal source, The bath (Hammam) Sidi Aïssa 47 °C, TST hot water maintained to 47 °C is used in a fan coil for canteen heating in Si Ben Salah School located in Saïda (NW of Algeria). Cooling is assured by the air conditioning sub-system made of a fan coil and heat pump using cool water tank. The experimental analysis of the air conditioning device is done for canteen application for cooling and heating modes. The feasibility study shows that using the geothermal sources located in Northern Algeria and low temperature PEMFC for air conditioning is a promising solution.     

Numerical simulation of solar assisted ground-source heat pump heating system with latent heat energy storage in severely cold area

Solar assisted ground-source heat pump (SAGSHP) heating system with latent heat energy storage tank (LHEST) is investigated. The mathematical model of the system is developed, and the transient numerical simulation is carried out in terms of this model. The operation characteristic of the heating system is analyzed during the heating period in Harbin (N45.75°, E126.77°). From the results of the simulation, the average coefficient of performance (COP) of the heating system is 3.28 in heating period. In the initial and latter heating period, the COP of the heating system is higher, and the highest value is 5.95, because the system can be operated without heat pump. During the middle heating period the COP of the heating system and the operation stability of the system are improved due to solar energy and soil alternately or together as the heat source of heat pump. LHEST is a very important role in operation of the system. The system can be operated more flexibly, effectively, and stably by the charge and discharge heat of LHEST, and the effect becomes especially obvious in the initial and latter heating period.     

太阳能-土壤源热泵耦合系统及其地埋管系统

建立了太阳能-土壤源热泵耦合型热水系统实验平台,研究了在秋冬季不同运行条件下该系统的运行特性,分析了地下埋管系统中钻孔回填材料、U型管工作模式、套管内循环液流动模式、套管外管与内管的导热系数比等对系统制热效果的影响。研究表明,太阳能土壤源热泵系统在国内亚热带地区可以获得良好的应用,并给出了埋地换热器的合理形式。     

圆柱源理论用于地下U型盘管换热器的模拟研究

分析介绍了引入“负荷聚合”方法的改进型圆柱热源(热汇)理论模型，并运用圆柱源理论对太阳能一土壤源联合运行热泵系统全天运行模拟，指出联合运行模式较单独土壤源运行模式节能10％～12％，为圆柱源理论模型应用和太阳能-土壤源热泵运行模式的选择提供参考。     

复合热源太阳能热泵供热系统及其性能模拟

提出了一种复合热源太阳能热泵供热系统,通过阀门切换,可根据不同的天气状况改变运行模式,以空气和太阳辐射作为热源制取供暖用水。针对所设计的10kW供热系统,建立了系统的数学模型,对热泵串联集热器(SC+HP)及集热器串联热泵(H+SC)两种运行模式下的循环性能进行了计算机模拟分析,并计算了系统的全年运行状况。从模拟结果可以看出,在模拟进水温度区间内,HP+SC模式下热泵COP较高,最高比SC+HP模式高2.58%;而SC+HP模式集热器热性能较好,总热效率更高,最高比HP+SC模式高2.62%。     

A study on the optimized control strategies of geothermal heat pump system and absorption chiller‐heater

The world is becoming increasingly interested in renewable energy including geothermal energy. The utilization of geothermal systems is currently low because geothermal systems and existing source systems are used independently, but the supply rate of a geothermal system is increasing. Therefore, suggesting efficient operation plans and evaluations of the energy consumption and efficiency of a geothermal system is needed. This paper reports the results of a field study and survey of the present applications and operation conditions of a geothermal system. In addition, this paper proposes an efficient operation strategy for a geothermal system and compares this operation strategy with an existing operation strategy through simulation. The problems of existing operation condition were found out through a field study, and alternatives were proposed. The improvements were evaluated using the transient systems simulation program. And it would be possible for the reduction of the energy consumption through the comparative analysis of equipment efficiency and energy consumption. The result of analyzing the proposed combination header method through simulations compared with existing operation conditions can increase the use of geothermal systems, but the combined cooling and hot water of a geothermal heat pump and existing thermal source system reduced the efficiency of the heat pump. As a result of simulation on individual load‐sharing method, efficiency of geothermal system is increasing compared with the combination header method. This method was especially made to separate geothermal system's water loop and existing thermal source system's water loop. Copyright © 2013 John Wiley & Sons, Ltd.     

太阳能-空气源热泵联合干燥系统设计及干燥枸杞的实验研究

为缩短枸杞干燥时间,提高干制枸杞的质量,减少能源消耗,本文提出了一种新型太阳能–空气源热泵联合干燥系统。该系统主要由太阳能集热器和空气源热泵机组等设备组成,可以实现太阳能单独干燥、热泵单独干燥和太阳能–空气源热泵联合干燥三种工作模式。本文根据枸杞的干燥特性,分段设定最佳的干燥温度,进行了热泵单独运行和太阳能–热泵联合运行两种工作模式下干燥枸杞的对比实验。结果表明,干燥50 kg枸杞,太阳能–热泵联合运行比热泵单独运行节省了2.9 kW?h电能,若同时除去系统本身的耗能,节省的电能占热泵单独运行耗电量的29.5%。同时,与太阳能单独干燥相比,太阳能–热泵联合干燥具有较高的除湿能耗比,两者最大差值为0.71 kg/(kW?h)。本文提出的太阳能–热泵联合干燥系统具有提高干燥产品的品质、缩短干燥时间和节约干燥成本等优点,适宜推广。     

Experimental Analysis of the Effects of Particulate Fouling on Heat Exchanger Heat Transfer and Air-Side Pressure Drop for a Hybrid Dry Cooler

It is well known that significant fouling by particulate matter can have a deleterious effect on the performance of enhanced surface heat exchangers, and the same is true for hybrid heat exchangers. Hybrid heat exchangers are heat exchangers that are typically run in dry mode to reject heat. When the ambient conditions require more heat rejection than can be provided by sensible heat transfer, a water pump is turned on and water flows over the fins, and the evaporation of water provides a further cooling effect. Fouling in dry-mode operation is physically similar to that of air-cooled heat exchangers, but in evaporative mode the flow of the water over the coil eliminates the impact of fouling. A hybrid dry cooler heat exchanger of 60 cm × 60 cm frontal area has been installed in a well-instrumented wind tunnel to measure the heat exchanger's performance. Hot water flows through the coil to provide the load, and air flows over the coil to provide cooling. During evaporative mode operation another stream of water flows over the outside face of the coil, adhering mainly to the louvered fins. The louvered fins are specially designed for optimized water flow during wetting mode. The fins are made of aluminum, the tubes are copper, and protection against corrosion is realized by a special E-coating. This coil has been tested clean and fouled with ASHRAE standard dust, for both dry and wet operation. Results are presented for the air-side pressure drop and overall heat transfer conductance of the coil under all conditions for which 50% increases in air-side pressure drop are found under heavy fouling. The influence of fouling on heat transfer is small. Also, using the wetting water to wash the fouling off the coil is investigated and is found to be of some limited utility.