| Heat pump is one of the effective energy-saving technologies, and has been widely used in the heating supply and domestic hot water production. It can save a considerable amount of high quality energy, such as electricity, natural gas, oil and etc., which can reduce the carbon emissions. Therefore, heat pump technology not only has economic benefits, but also has society benefits. It matches the policies of the environmental protection and energy-saving. The cycle of heat pump water heater (HPWH) is the same as the cycle of refrigeration, except HPWH using the heat released from the condenser for water heating, while the latter using the cold energy of the evaporator for space cooling. Nowadays, air-source HPWH and air conditioner are separate systems, and are often in vacant condition.Thus, studying and developing the multi-functional HPWH, which can produce hot water with functions of air-conditioner, can improve the utilization ratio and increase the system performance, and have extensive prospect. Since the flow organization and the performance of the equipment and key components in multi-functional HPWH are different from that in air-conditioner, the thesis is focus on the related experimental and theoretical research on the multi-functional HPWH system.The outlet water temperature of HPWH is often fixed at about 55℃,but the environment temperature fluctuates widely from summer to winter. Therefore, the thermodynamic analysis of HPWH under modes of producing hot water and space cooling coupled with producing hot water were firstly carried out. The relations of the system performance varying with the environment temperature, condensing temperature and evaporating temperature were revealed and discussed. The comparison of multi-functional HPWH with the other water heaters was made and the energy-saving and the social benefits of multi-functional HPWH were analyzed.Secondly, a multi-functional HPWH with multi-loop was developed. This system has four independent cycles by adding few parts to the ordinary air-conditioner and using the least of valves to control the cycle-switch. It achieved the integration of air-conditioner and water heater. In summer, it can be operated at three modes, namely single hot water production, single cooling, cooling and hot water production. In spring and autumn, it can be operated at single hot water production mode. In winter, it can provide heating and hot water simultaneous. The utilization ratio of such production can be improved and the energy-saving effect of heat pump can be fully fulfilled.The hot water-condenser is a key heat exchanger component of HPWH, but the traditional immersion coil heat exchanger can't satisfy the requirements of HPWH. In this thesis, the heat exchanger with draft tube and the compact coil finned tube heat exchanger were proposed. The model of the heat exchanger with draft tube was developed. The temperature and velocity distributions under the conditions of heating without water supply and with the water supply of 240L/h were calculated by using Fluent. Compared with the ordinary immersion coil heat exchanger, the new heat exchanger has higher heat transfer performance. The related results and the analysis method can be considered as the basis for the modification and optimization of such heat exchanger. The heat transfer performance and flow resistance of the compact coil finned tube heat exchanger were investigated by means of experiments, and the related experimental correlations were obtained by using the regression method. The results can practically be used for calculation and designing this type heat exchanger.Finally, a multi-functional HPWH system was established by using an air conditioner. The heat exchanger with draft tube was employed as the hot water-condenser in the system. The pressure distributions and variations under several running modes were investigated. The results show that the coefficient of heat transfer varied from 430 W/m~2×Kto 625 W/m~2×Kwith the water flow rate from 120L/h to 240L/h. Since the velocity of water in the heat exchanger was very low, such high coefficient of heat transfer can prove that the heat exchanger with draft tube is suitable for the HPWH. The experiment results in winter condition show that the multi-functional HPWH still has high coefficient of performance, and it can play a important role in energy-saving. The experimental system runs steady and the functions can be switched smoothly.At the end of the thesis, some advices are put forward for further research on the HPWH on the basis of theory and experiment results. |
PDF Full Text Request