| The multi-functional heat pump system (MHPS) which combines the air conditioner with water heater are developed in this study. The system not only improves the comprehensive energy efficiency and equipment utilization, but also reduces the heat release to the environment in the summer therefore further achieves the purpose of energy saving. However, the application of such technology is greatly limited by the safety and stability of MHPS due to its plenty of work modes, unstable operating conditions and complexity of controlling. In addition, the usage condition of MHPS is actually very complicated. The efficiency of system is also tightly related with location, habit and water demands from users. Therefore, it is very significant to develop an efficient method and standard to evaluate the actual energy-saving effect of the system. Based on the factors above, corresponding research work was done as follows:The principles of building MHPS system and designing of components and control system are: First, the system is simple, reliable, few moving parts; Second, stable controlling, especially the strong ability to adapt to variable conditions. The thermodynamic analysis was compared between MHPS and conventional air conditioner. It reveals the relationship among the thermal performance of system, structural parameters of components, operating conditions, work modes and refrigerant. Also, it provides strong basis for the optimization and control of such a system.Sanitary water heating only is one of the main work modes of MHPS. Before the experiments of MHPS, we first studied the controlling laws of the electronic expansion valve (EEV) in the heat pump water heater (HPWH). According to the property of HPWH, we proposed an adaptive dual fuzzy control method specialized for HPWH to set the EEV initial opening during the start-up and adjust the EEV during heating process. The experimental results show that wet compression and huning problems could be avoided using above method for controlling EEV, thereby improved the efficiency of the system. Compared with the system with thermalstactic expansion valve (TEV), the heating coeficiency of performance (COP) of EEV-controlled HPWH can be improved 8.2%, 5.5% and 6.1% at the ambient temperature 5 oC, 20 oC and 35 oC, respectively. Moreover, the stability of system was obviously enhanced.In the space cooling combined with condensing heat recovery mode, we compared the condensation temperature, evaporation temperature, superheat, subcooling, compressor discharge temperature, compressor power, cooling capacity and cooling COP before and after the start of heat recovery. Moreover, we analyzed the relevant mechanism in-depth, revealed the essence for the variations of the system performance and parameters before and after the heat recovery, and proposed the pre-judging control strategy for EEV. The experimental results show that when the water temperature in the tank is low, the heat recovery will lead to a sudden drop in the cooling capacity. Then, the cooling capacity will quickly recover and maintain at the same value before the heat recovery in about 10 min. The compressor power, meanwhile, decreased greatly during the heat recovery, which increases the average cooling COP in the process of heat recovery and makes the overall system operation more economical.We analyzed the impact of location, water demands and habits of users on the energy efficiency of operation under HPWH mode, and proposed the method which employed annual comprehensive working conditions for evaluating the energy efficiency of HPWH. We investigated some key issues during testing process of MHPS, such as test method for cooling capacity and heating capacity under different work modes, equivalent volume of water tank, evaluation of thermal insulation property of water tank, water heating proportion contributed by heat exchanger for hot water versus auxiliary resistive elements, and so on. Besides, according to the characteristics of five difference climatic regions, we also did cumulative time distribution study under various work modes and ambient temperature zones, and provided the basis of calculating APF of MHPS.Our study and results is of great significance to the development of practical and commercial multi-function heat pump and its related criterion. |
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