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Air Conditioning and Ventilation
Published in John Knight, Peter Jones, Newnes Building Services Pocket Book, 2012
To work as a heat pump (Figure 3.24(b)), a reversing valve in the unit casing is operated to alter the direction of flow of the refrigerant gas. Hot gas flows from the compressor to the coil in the unit, which now acts as an air-cooled condenser, rejecting heat into the room in order to offset heat losses.
Performance evaluation of proton exchange membrane fuel cell and air source heat pump system with energy storage for residential application
Published in International Journal of Green Energy, 2023
Houchang Gao, Liang Cai, Ying Fang, Zhenxi Ma, Huimin Wang
As shown in Figure 1, the PEMFC-CCHP system includes a proton membrane fuel cell, a gas supply subsystem, a thermal management subsystem, and a heat pump system. Among them, the gas supply system includes a hydrogen supply system and an oxygen supply system. The thermal management system includes a circulating water pump, radiator, and hot water storage tank. The heat pump subsystem includes a compressor, outdoor heat exchanger, indoor heat exchanger, throttle valve, and reversing valve. The waste heat generated by the fuel cell is stored in the storage hot water tank while the excess heat is dissipated by the radiator, and the electricity from the fuel cell is supplied to the user and the compressor. In winter, when the waste heat is not enough to meet the demand of the user, the ASHP is turned on for heating. In summer, the ASHP is turned on for cooling to realize the CCHP supply for the user. The parameters of the PEMFC in the system are shown in Table 1.
Evaluating Recharge Options for Phase-Change Material Storage of a Personal Conditioning System
Published in Science and Technology for the Built Environment, 2019
Rohit Dhumane, Yiyuan Qiao, Jan Muehlbauer, Jiazhen Ling, Vikrant Aute, Yunho Hwang
Experiments were conducted in an environmental chamber. The ambient temperature was set to 26 °C. Before and during the test, the fluctuation of ambient temperature was less than 0.5 °C. A cooling cycle was performed before the PCM recharge cycle. Three ball valves should be closed before the cooling cycle. Then, by starting the compressor and fan, the cooling cycle could be operated. After 4.5 h of cooling, the PCM regeneration cycle could be started to solidify the PCM. In the thermosyphon system, the compressor should be stopped first, and after 30 s, three ball valves can be opened to begin the recharge mode. In the heat-pump system, the reversing valve could achieve the mode transfer. The uncertainty in temperature measurement is 0.5 °C, and that of the system pressure is 1.7 kPa.
The numerical study of the thermal performance of a condensing gas-water heater
Published in Numerical Heat Transfer, Part A: Applications, 2018
Weixue Cao, Fengguo Liu, Xue-Yi You
Figure 9 shows the flow trajectory and pressure distribution of water in the heat exchanger. Cold water enters the water channel from the inlet and passes through the flow channel and reversing valves before it is discharged from the outlet. The cross section of the water channel is rectangular, and there are eight reversing valves in the water channel. The shape of the reversing valve is cylindrical, and the base of the reversing valve is divided into two parts by the baffle. One forms the inlet and the other forms the outlet. The water changes its flow direction in these reversing valves. Specifications of the water flow are shown in Figure 9. To measure the drop in pressure in the water flow in more detail, the drop in pressure was divided into the drop in pressure observed in the reversing valve (local pressure drop) and the frictional resistance of fluid flowing through the water channel (frictional resistance). The drop in pressure shown in the white area represents the drop in frictional resistance pressure, and the drop in pressure shown in the red column represents the local drop in pressure. It is evident that the drop in frictional resistance pressure is minor but that the local drop in pressure is large because the water flow changes direction in the reversing value. This means that the local drop in pressure is the main component of water flow pressure decline, which accounts for 89.7% of the total drop in pressure. Therefore, reducing the local drop in pressure in the reversing valve is essential for the reduction of heat exchanger energy consumption.