表冷器-热泵联合集热系统的优化及可用能分析

为进一步提升表冷器-热泵联合集热系统的放热性能，并为系统进行节能优化提出方向和途径建议，首先计算了储热池优化水温42℃目标下的实际蓄水量，试验并分析了蓄水量的减少对系统集放热性能的影响；在此基础上，进行了两种集热方式、一种放热方式的可用能分析，进一步明确了系统在3种运行方式时可用能损失的主要位置和原因；最后，提出了表冷器-热泵联合集热系统主要工作部件节能优化的建议。试验结果表明：优化蓄水量为8.4 m3的条件下，系统的放热功率和放热性能系数分别为27.1 kW和6.2，提升了33.5%和37.8%，放热性能提升显著。可用能分析表明，水泵的可用能效率最高，最高可达98.8%；表冷器-风机的可用能效率在表冷器-风机集热方式、热泵与表冷器-风机联合集热方式、放热模式下分别为89.3%、87.8%、60.1%，传热温差造成的不可逆损失是放热模式下效率较低的原因；热泵机组可用能效率最低，仅为46.4%，是后续系统节能优化的重点。该研究为优化提升主动集放热系统的节能性，提供了方向指导和解决新思路。

Optimization and exergy analysis of fan-coil units-heat pump combined heat collection system

Many environmental factors have posed an important impact on crop growth in a greenhouse. Among them, the temperature is often the dominated factor in the greenhouse production. Water is also suitable for the medium of heat transfer or storage. Most research has been focused on the active heat collection and release system using water circulation and heat storage for nighttime warming in the greenhouse. A fan-coil units-heat pump combined heat collection system (FUHPS) has been developed, where a heat pump has been added to the fan-coil units and heat storage pool for the heat collection (TSFU). A systematic investigation has been made to explore the performance under three modes of heat collection in different sizes of horticultural facilities. However, the water temperature of the storage tank cannot be raised by more than 12°C from the beginning to the end of the heat collection process in the field test. The reason was that the water temperature of the storage tank was not high enough to cause a small temperature difference between the water and gas during the heat release. As such, there was a relatively small Coefficient of Performance (COP) of heat release. Therefore, it is necessary to improve the heat release COP of the system. The initial water temperature of heat release can be expected to effectively improve the heat release performance of the TSFU. Furthermore, the heat release performance of the FUHPS with the same heat release mode can also be used to increase the initial water temperature of heat release. It is probable to reduce the actual water storage capacity of the heat storage pool. This study aims to improve the heat release performance of the FUHPS, and then further optimize the heat collection system. The actual water storage capacity was firstly calculated at the target water temperature. Secondly, an analysis was made to clarify the impact of water storage capacity on the heat release performance of the system. Thirdly, the exergy analysis was carried out under two kinds of heat collection modes and one kind of heat release mode, in order to determine the specific location and main reasons for the loss of exergy. Finally, optimization was proposed for each component of the FUHPS. The results show that the heat release power and COP of the optimized system were 27.1 kW and 6.2, respectively, which increased by 33.5% and 37.8% than before. The overall performance coefficient was also improved after optimization. The exergy analysis demonstrated that an excellent energy utilization quality was achieved in this case, indicating the highest exergy efficiency of the water pump. Specifically, the exergy efficiencies of the heat-collecting device and fan-coil units were 89.3%, 87.8%, and 60.1% under the fan-coil units'' heat collection mode, combined heat collection mode of fan-coil units+heat pump, and heat-releasing mode, respectively. In addition, some consideration was made for the irreversible loss caused by heat transfer temperature difference. Nevertheless, the lowest exergy efficiency was obtained in the heat pump unit, which was the key point of the energy-saving transformation of the system. This finding can provide a new idea to optimize and improve the performance of the active heat collection and release technology.