R290直膨式太阳能热泵供暖系统实验研究

为分析直膨式太阳能热泵耦合地板辐射供暖系统在北方寒冷地区的实际运行特性,设计并搭建以丙烷(R290)为工质的直膨式太阳能热泵供暖实验平台,分析冬季不同运行工况下环境参数对系统热力性能的影响。实验结果表明：系统可实现室内供暖的稳定性,实验测试期间平均室温保持在16.1～20.8℃之间,热泵系统性能系数(COP)保持在2.57～4.30之间,供暖系统COP保持在2.24～3.98之间。太阳辐照度每增加50 W/m²,热泵系统COP提升4.9%;环境温度每升高1℃,热泵系统COP提升2.4%。太阳辐照度对热泵系统的电子膨胀阀开度和工质质量流量影响较为显著。当终止水温从45℃提升至55℃时,热泵系统COP降低12.2%;而在终止水温为50℃时,供暖系统COP达到最大值3.37。     

太阳能对热泵循环性能的影响

利用太阳能-土壤源复合热泵实验平台进行太阳能热泵运行实验,分析提高蒸发器进口水温对热泵性能的影响。实验结果表明:随着蒸发器进口水温的升高,热泵吸热量和制热量增速较大,输入功率增速较小,因而机组COP和系统COP也随之升高。压缩机排气压力和吸气压力也随之升高,但排气压力的增速小于吸气压力的增速,压缩比逐渐减低。提高蒸发器进口水温可以提高蒸发温度,进而明显改善热泵的性能状态。     

间接膨胀式太阳能高温热泵系统运行性能实验研究

为研究间接膨胀式太阳能高温热泵系统实际应用的可行性和有效性,搭建实验平台,在天津地区气象条件下对高温热泵全天动态运行特性开展实验研究,分析太阳辐射强度、水箱储热性能、冷凝温度及膨胀阀开度对系统运行性能影响。结果表明:平均太阳辐射强度由396 W/m2增加到563 W/m2,高温热泵性能系数COP由3.62增至3.93;因水箱储热功能,间接膨胀式系统在太阳辐射强度剧烈波动时能够保持高温热泵相对稳定的蒸发温度;当蒸发温度固定时高温热泵COP随冷凝温度升高而降低,冷凝温度由70 ℃增至80 ℃,COP由4.32降至2.76;膨胀阀开度由150步增至250步,高温热泵全天平均COP由3.14升至5.12,排气压力降低46%。     

真空管直膨式太阳能热泵系统性能分析

该文将真空管集热器与直膨式太阳能热泵结合,提出一种真空管直膨式太阳能热泵系统。实验研究典型工况下太阳辐照度、循环水温度对系统性能的影响,并探讨压缩机变频条件下系统的动态性能。结果表明,提高太阳辐照度、降低循环水温度有利于提高系统性能,在太阳辐照度为850 W/m2,循环水温度为55℃时系统取得最大COP,为5.36。压缩机频率为42 Hz的系统COP为4.08,较45、47、50 Hz分别提高1.23%、8.5%、13.6%。     

直膨式太阳能热泵制热性能的对比研究

直膨式太阳能热泵(direct expansion solar assisted heat pump,DX-SAHP)可直接吸收利用太阳能,进而提高热泵的蒸发温度和性能系数(COP),有利于改善热泵的热性能和结霜。本文在带有太阳模拟发射器的焓差实验室中建立直膨式太阳能热泵和常规直彭热泵的对比实验,对不同条件下的热泵系统参数进行测量并进行性能对比和分析。实验结果显示,直膨式太阳能热泵能够吸收太阳能,在辐照度分别为100和200 W/m~2的工况下,系统制热功率比无辐照时的制热功率分别提高9.8%和21.8%,COP分别提高11.7%和23.7%,且除霜启动延迟23 min;辐照度为200 W/m~2时,直膨式太阳能热泵在环境温度5℃下的制热功率比1℃下的制热功率提高16.92%;在室外温度为1℃,相对湿度为95%的工况下,提高太阳辐照度,可有效减小涂层蒸发器进出口温度的波动,提高蒸发器运行的稳定性。此外,直膨式太阳能热泵在运行过程中吸收的太阳辐射被用来蒸发液态制冷剂工质,导致压缩机进气量增加,系统的制热功率和COP提高。     

工质为R415b的空气源热泵热水器性能实验研究

通过对工质为R415b的空气源热泵热水器的性能实验,给出了环境温度和相对湿度不同时,随着水箱内水温的升高,热泵系统内蒸发压力、冷凝压力、压比、吸气温度、液管温度、冷凝侧过热度和过冷度、蒸发侧过热度以及COP的变化规律,指出了空气源热泵热水器的COP不仅随水温动态变化,而且与气温及湿度有关。同时,还对水箱内水的升温规律以及与热泵循环参数的关联进行了研究。     

热回收式CO2制冷系统性能研究

对热回收式CO2制冷系统性能COP进行了计算和分析,结果表明:蒸发温度、气体冷却器出口CO2温度、热水加热器入口水温是影响其COP的主要因素;回热器出口过热度对COP的影响较小,对压缩机的排气温度影响较大;随着排气压力的升高,COP是否出现峰值,取决于气体冷却器入口制冷剂的特征温度;在相同工况下,蒸发温度、气体冷却器出口CO2温度、回热器出口过热度对最佳排气压力的影响较小,热水加热器入口水温是影响最佳排气压力的主要因素。     

PV/T-SAHP系统实验研究

通过系统在不同运行模式下的实验研究,分析太阳辐照度、温度等参数对系统光伏光热性能的影响,结果表明光伏热泵组件发电效率比传统光伏组件提高16.4%;在获得同样热水情况下,混联运行比串联运行每天多输出1.7 k Wh的净发电量,热泵平均COP从1.9升高到3.4。间接式光伏热泵系统将集热器的热量在蒸发器与冷凝器间进行合理分配后,比直膨式光伏热泵系统具有更好的综合性能。     

直膨式太阳能热泵运行特性的实验研究

对直接膨胀式太阳能热泵热水系统进行了实验研究,实验期间,太阳能辐照度变化范围为143.12~664.6 W/m2,分别采用三种不同结构的集热器和蒸发器,得出系统COP为2.49~3.47,表明该系统在各种天气情况下均能够可靠地生产45℃的生活热水,热性能稳定,可以全天候地提供生活热水且具有节能效果;同时选取双集热器的两组数据,分析了太阳辐照度对热泵系统运行的影响。     

电子膨胀阀开度对PV/T-SAHP系统性能的影响

压缩机频率固定,不同的电子膨胀阀开度下,对PV/T-sAHP系统的动态性能进行了实验和分析,根据实验结果发现,系统的COP值随冷凝水温的升高而降低,光电效率的峰值发生在工质蒸发对光伏模块的冷却作用与太阳辐照度和空气对集热,蒸发器表面的加热作用的平衡点,而并非太阳辐照度最高点.在电子膨胀阀开度一定时,随着太阳辐照度的升高,压缩机功率出现振动,当电子膨胀阀开度最大时,系统振动更加明显.由此提出了光伏.太阳能热泵(PV/T-SAHP)的系统稳定性原理.同时指出优化PV/T-SAHP系统的关键问题是找到系统集热,蒸发器的MSS线(Q-Tsh关系曲线).     

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.     

风力机直驱蒸汽压缩式热泵系统实验研究

从现有风能直驱式热泵系统存在的突出问题入手,利用软连接管路突破了风能直驱热泵系统硬连接的瓶颈问题,提出新型风力机直驱蒸汽压缩式热泵系统,并对该系统进行了实验研究。实验结果表明,热泵机组制热量随压缩机转速呈近似线性规律,热泵机组COP随转速呈近似指数变化规律,机组存在最佳转速;金属软管阻力损失对制冷剂焓值影响可以忽略,但是对冷凝温度有较显著影响,如需要保证热水温度,则需要提高冷凝压力,相应COP会降低,机组运行稳定,初步证明系统可行。     

The performance of a solar assisted heat pump water heating system

Analytical and experimental studies were performed on a solar assisted heat pump water heating system, where unglazed, flat plate solar collectors acted as an evaporator for the refrigerant R-134a. The system was designed and fabricated locally, and operated under meteorological conditions of Singapore. The results obtained from simulation are used for the optimum design of the system and enable determination of compressor work, solar fraction and auxiliary energy required for a particular application. To ensure proper matching between the collector/evaporator load and compressor capacity, a variable speed compressor was used. Due to high ambient temperature in Singapore, evaporator can be operated at a higher temperature, without exceeding the desired design pressure limit of the compressor, resulting in an improved thermal performance of the system. Results show that, when water temperature in the condenser tank increases with time, the condensing temperature, also, increases, and the corresponding COP and collector efficiency values decline. Average values of COP ranged from about 4 to 9 and solar collector efficiency was found to vary between 40% and 75% for water temperatures in the condenser tank varying between 30°C and 50°C. A simulation model has been developed to analyse the thermal performance of the system. A series of numerical experiments have been performed to identify important variables. These results are compared with experimental values and a good agreement between predicted and experimental results has been found. Results indicate that the performance of the system is influenced significantly by collector area, speed of the compressor, and solar irradiation. An economic analysis indicates a minimum payback period of about two years for the system.     

基于动态分布参数模型的光伏太阳能热泵系统的数值模拟

采用分布参数法,根据平衡均相流理论,建立了光伏太阳能热泵(PV-SAHP)系统的动态分布参数模型.通过数值模拟对系统在动态工况下的光电光热性能进行研究.研究结果显示PV-SAHP系统具备优越的光电光热性能,系统的COP为3.1-5.8,全天的平均值为4.8,明显高于普通的风冷热泵;系统光电转换效率为12.38%-13.31%;系统全天的平均光电功率为375W,相当于系统平均功耗(474.8W)的79%.对模拟结果进行对比分析后发现系统光电光热性能主要由太阳辐照强度所决定,并受环境温度的影响.     

Performance modeling of air cycle heat pump water heater in cold climate

Air (reverse Brayton) cycle has promising features in cold climate heat pump applications. In this study, an air cycle heat pump water heater (ACHPWH) simulation model considering the off-design performance of components was developed and validated with experimental data from literature. With this model, the performance of ACHPWH was numerically compared with two typical vapor compression heat pump water heaters (VCHPWH) under two different heating schemes, namely instantaneous heating and recirculation heating. For instantaneous heating, the COP of ACHPWH is comparable to that of VCHPWH when supplying high temperature water or operating at low ambient temperature. A significant improvement on annual performance would be achieved as well if higher efficient compressor and expander were applied in ACHPWH system. For recirculation heating, although the COP gap got larger, ACHPWH would save plenty of heating time when operating at low ambient temperature.     

Thermal performance analysis of a direct-expansion solar-assisted heat pump water heater

A direct-expansion solar-assisted heat pump water heater (DX-SAHPWH) is described, which can supply hot water for domestic use during the whole year. The system mainly employs a bare flat-plate collector/evaporator with a surface area of 4.2 m², an electrical rotary-type hermetic compressor, a hot water tank with the volume of 150 L and a thermostatic expansion valve. R-22 is used as working fluid in the system. A simulation model based on lumped and distributed parameter approach is developed to predict the thermal performance of the system. Given the structure parameters, meteorological parameters, time step and final water temperature, the numerical model can output operational parameters, such as heat capacity, system COP and collector efficiency. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions. The effect of various parameters, including solar radiation, ambient temperature, wind speed and compressor speed, has been analyzed on the thermal performance of the system.     

Performance analysis of an air-source heat pump using an immersed water condenser

A distributed model of an air-source heat pump (ASHP) system and its experimental setup using an immersed water condenser were presented. Dynamic performance of the ASHP was then evaluated by both simulation and experiment. The results indicated that the system coefficient of performance (COP) decreased as the condenser temperature increased, ranging from 4.41 to 2.32 with the average COP equaling 3.29 during the experiment. Comparisons between simulation results and experimental measurements demonstrated that the model was able to yield satisfactory predictions. Furthermore, temperature profiles of the refrigerant in the evaporator and condenser were also given. This paper provides the theoretical and experimental background for ASHP system optimization and a valuable reference for a solar air-source heat pump water heater when the solar irradiation energy is insufficient on cloudy or rainy days.     

Theoretical thermal performance analysis of two solar‐assisted heat‐pump systems

The thermal performance of two different schemes of solar‐assisted heat‐pump systems has been theoretically studied. In first scheme, the evaporator of the heat pump is taken directly as the solar collecting plate and always maintained at the ambient temperature. As there is no heat loss from the collecting plate, the thermal efficiency of the collector is high and equals the solar absorptivity of the collecting plate. As suggested, the heat‐pump evaporator of the second scheme is placed in a novel fresh water solar pond/tank with high efficiency. Since the evaporator operates at a relatively high temperature, the COP of the heat pump can be increased. The calculated results show that the COP of a solar‐assisted heat pump using the second scheme is considerably higher than that of the first scheme. Copyright © 1999 John Wiley & Sons, Ltd.