表冷器-热泵联合集热系统不同运行模式的集热性能

针对现有的表冷器-风机主动集放热系统集热能力不足的问题,该研究在现有系统的基础上加入热泵,设计了一套表冷器-热泵联合集热系统。该系统共有3种集热运行模式:仅表冷器-风机集热(风机模式);表冷器-风机集热+热泵与表冷器-风机联合集热(混合模式);仅热泵与表冷器-风机联合集热(联合模式)。依据不同天气下的不同需求确定指标赋分方式,并对各指标赋分,最终总分最高模式作为该天气下的最佳集热模式。试验结果表明:晴天时,风机模式的集热性能系数(COP)最高,达到了6.0±0.7,联合模式的集热量最大,为(763.9±17.1) MJ,而混合模式的集热COP及集热量均居中。多云天时,混合模式的集热COP最高,为4.8±0.3,联合模式的集热量最大,为(519.7±30.5) MJ。在两种天气下,平均水-气温差均呈现出风机模式、混合模式、联合模式递增的趋势。通过对各指标赋分后得出,晴天时混合模式为最佳集热模式;多云天时联合模式为最佳集热模式。该研究可为主动集放热技术的性能提升提供新思路。

Heat collection performance of different modes of fan-coil units-heat pump combined heat collection system

Solar greenhouses with various types of walls gradually appear to replace the traditional ones that occupied large areas with high construction costs in various regions of China. In this case, the back wall has no function of heat storage, but only the function of heat preservation. Therefore, this new type of back wall greenhouse needs auxiliary heating measures to increase the night temperature. Among them, the air temperature in the greenhouse is relatively high during the day, while containing abundant heat energy of air for the night warming. A thermal collecting and releasing developed with fan-coil units and heat storage pool for heat collection (TSFU) was employed to avoid high cost and air pollution in conventional heating. However, the efficiency and capacity of heat collection decreased in this system, with the decrease of difference between the heat storage pool and indoor air temperature. It is difficult to ensure an appropriate temperature for a solar greenhouse in a frigid region, or when it encountered weather conditions with weak solar radiation. An energy-saving and high-efficiency energy lifting device, namely a heat pump, was utilized to collect low-level heat energy from water for high-level heat energy. Therefore, the heat pump has widely been applied to improve the potential of heat collection and release devices in a greenhouse. In this study, a combined heat collection system with fan-coil units and a heat pump (FUHPS) was designed to improve the heat collection performance of TSFU. The system included fan-coil units, heat collection pool, heat storage pool, water and heat pump. The heat pump unit was used to transfer the heat from the heat collection pool to the heat storage pool at any time, particularly to reduce the circulating water temperature for high efficiency of heat collection. The FUHPS was divided into three modes of heat collection: fan-coil units heat collection mode (fan mode); fan-coil units + heat pump mixed heat collection mode (mixed mode); combined heat collection mode of fan-coil units + heat pump (combined mode). On sunny days in the test, the coefficient of performance (COP) of heat collection in fan mode was the highest of (6.0±0.7), while the amount of heat collected in the combined mode was the highest of (763.9±17.1) MJ, while the COP and amount of heat collected in the mixed mode were in the middle. On cloudy days, the heat collection COP of the mixed mode was the highest of (4.8±0.3), and the amount of heat collected in the combined mode was the highest of (519.7±30.5)MJ. The best mode of heat collection under different weather conditions was determined, where the assigning indexes to each heat collection mode were adopted: the mixed mode was the best on sunny days; whereas, the combined mode was the best on cloudy days. The system presented significant energy saving and emission reduction benefits. On sunny days, it was assumed that the system needed to collect 400 MJ of heat in three modes, and the amount of CO2 released by coal-fired hot water heating mode was 93.4%, 88.0%, and 84.7% higher than that of the fan, mixed and combined mode, respectively. In addition, the system was also expected to achieve real zero emission of greenhouse gases, particularly with the gradual popularization and application of clean energy power generation, indicating outstanding environmental benefits. Moreover, the system was a mature industrial product to collect the heat energy in indoor air for a broad application prospect in various gardening and breeding facilities.