"Cooling, heating, sanitary hot water" type air source heat pump system and analysis

Preface In the face of the increasing global warming energy crisis, China, as a big energy consuming country, is still not high in energy utilization rate. However, with the encouragement of various national policies, the restriction of laws and regulations and the promotion of incentive mechanisms, The more attention. In the balance of energy budget, heat loss accounts for a large part of the air conditioning system condensing heat belongs to the low temperature waste heat, easy to use and from the perspective of enthalpy, heat loss is not large. In our country, the central air conditioner generates a large amount of condensation heat during operation, which is discharged into the atmosphere in vain, resulting in the loss of available energy. At the same time the central air conditioning with the hotel, the hotel need to provide hot water throughout the year, the general use of steam water, due to the winter high summer low demand, designed according to the needs of winter hot water boilers in the summer are often at low load operation. If you can recover the heat of condensation to generate hot water to meet the hot water demand in summer, to share the boiler heat supply and reduce energy consumption in winter will be an energy-saving way to turn waste into treasure. 1 system 1.1 without cooling heat recovery air-cooled chiller cycle Figure 1 with fully enclosed reciprocating compressor air-cooled heat pump unit lg ph Figure 1, 2 to 5 points for the entire process of condensation, of which 2 ~ 3 o'clock is the refrigerant overheated section to show sensible heat, 3 ~ 4 points refrigerant latent heat, 4 to 5 points is the sub-cooling section of the sensible heat process. Operating in cooling conditions, 4 ℃ evaporation, 49 ℃ condensation, 5 ℃ inspiratory overheating, 5 ℃ throttling cold, condensation heat up to 1.15 to 1.3 times the refrigeration capacity. Isentropic, the compressor discharge port t2s is about 70 ℃, in fact, the compressor exhaust overheating, t2 can reach about 83 ℃, it is possible to provide 55 ~ 65 ℃ domestic hot water. Taking R22 as an example, the low-temperature waste heat that can be recovered per unit of refrigerant is 2-3 stages of heat, accounting for about 17% of the condensation heat. The remaining condensable liquid of the liquid phase is still larger than the 6-1 evaporable heat, Part of the heat is recovered, the winter can still meet the thermal load design. 1.2 with heat recovery of air-cooled chiller 1.2.1 The heat recovery unit schematic diagram: 1. Compressor 9. Thermal expansion valve 17. Descaling device 2. Electromagnetic three-way valve Check valve 18. Water pressure sensor 3. Heat recovery heat exchanger 11. Check valve 19. Air conditioning water temperature sensor 4. Electromagnetic four-way valve 12. Check valve 20. Outlet 5. Air side heat exchanger 13. Thermal expansion valve temperature package 21. Intake pipe 6. Fan 14. Gas-liquid separator 22. Domestic hot water outlet pipe 7. Check valve 15. Air conditioning pumps 23. Tap water inlet pipe 8. High pressure receiver. Water side heat exchanger Figure 2 Schematic diagram of heat recovery unit Refrigerant circuit: the exhaust port of the compressor 1 in turn connected to the four-way valve 4, air-side heat exchanger 5, check valve 7, high pressure receiver 8, heat The expansion valve 9, the check valve 11, the water-side heat exchanger 16, the four-way valve 4, the gas-liquid separator 14, and then back to the suction port of the compressor 1 are connected to the outlet of the check valve 11 and the outlet of the check valve 7 A check valve 12 is arranged between the four-way valve 4 and the gas-liquid separator 14 in the connecting line between the four-way valve 4 and the gas-liquid separator 14; 1.2.2 Characteristics of the heat recovery unit (1) A heat recovery heat exchanger is arranged between the exhaust port of the compressor of the device and the inlet of the four-way valve, the exhaust pipe of the compressor is connected with the inlet of the refrigerant passage inside the heat recovery heat exchanger, the heat recovery heat exchange The outlet of the device is connected with the inlet of the four-way valve, and the entrances and exits of the domestic hot water passage are respectively connected with the inlet of the domestic hot water inlet pipe and the heat recovery heat exchanger water passage. (2) an electromagnetic three-way valve is arranged between the exhaust port of the compressor of the air conditioner and the heat recovery heat exchanger, the inlet of the electromagnetic three-way valve is connected with the exhaust port of the compressor, and the other two outlets are respectively connected with the four The inlet of the through valve is connected to the inlet of the heat recovery heat exchanger refrigerant passage, and the outlet of the heat recovery heat exchanger refrigerant passage is connected to the inlet of the four-way valve. (3) In order to solve the problem of easy fouling of the domestic hot water pipeline in the traditional scheme, in addition to adding a descaling device in the hot water pipeline, an electromagnetic tee is provided between the exhaust pipe of the compressor and the heat recovery heat exchanger Valve, the use of electromagnetic three-way valve to convert the flow of high temperature refrigerant in the hot water unit is not running hot water, high temperature gas refrigerant without heat recovery refrigerant directly bypass into the electromagnetic four-way valve to avoid high temperature Gaseous refrigerant will continue to heat the water in the heat recovery heat exchanger to cause hot water pipeline fouling. 2 Components 2.1 Compressor The heat recovery unit compressor selection and ordinary air-cooled hot and cold water units, that is, according to various types of compressor cooling capacity and evaporation temperature, condensation temperature curve (performance curve) generally Provided by the manufacturer. If there is no performance curve as a reference, according to compressor product samples provided by the gas selection. As mentioned earlier in this paper, the amount of heat that can be recovered theoretically can reach 17%, but in actual operation, because the heat exchange side is the gas phase and the thermal resistance is large, plate heat exchangers with high heat exchange efficiency may reach Not so much. To design a 20kW heat recovery unit, for example, according to the general engineering example, the hot water supply required by the hotel is about 20-30% of its cooling capacity [5], a slightly larger capacity compressor may be properly selected, That is, the evaporation temperature and the condensing temperature are unchanged, the cooling capacity is increased to 1.2-1.3 times of the designed load, which meets the heat supply of the hot water. In this article, the design itself is to ensure that the cooling effect as a precondition, as far as possible recovery of waste heat. In the case of large demand for hot water in winter, also need to use auxiliary heat source. 2.2 air-side heat exchanger design air-cooled condenser, the heat load of Figure 1 (lg ph) on the refrigerant 5 points and 3 point enthalpy difference, less than the heat recovery unit without the design heat load, because part of the heat of condensation For heat recovery, heat recovery heat exchanger, so the unit of the air-cooled condenser heat transfer area must be no heat recovery unit air-cooled condenser heat transfer area is small. Calculated in winter, calculated from Figure 1 (lg ph chart) available in the winter 3-5 condensation heat release is still slightly larger than the design load, and the selection of the appropriate enlargement of the compressor capacity to meet the winter Heat supply. 2.3 heat recovery heat exchanger heat recovery unit of the unit, the heat recovery process shown in Figure 1 (lg ph chart) from 2:00 to 3:00 process, high temperature and pressure refrigerant gas is discharged from the compressor, the gas Sensible heat and tap water are exchanged in the heat recovery heat exchanger to heat the tap water to obtain 55 to 65 ° C domestic hot water. The heat transfer is the difference between the enthalpy of refrigerant at 3 o'clock and 2 o'clock on Figure 1 (lg ph). Summer tap water inlet temperature 28 ~ 30 ℃, domestic hot water outlet temperature 65 ℃, combined with the refrigerant inlet and outlet temperature to calculate the average temperature difference Δtm, only 5-40 ℃, so only a small flow of continuous preparation of hot water by the formula A = Q / (KΔtm), the heat transfer coefficient of the heat recovery heat exchanger needs to be estimated. For small central air conditioning, heat recovery load is small, the gas side of the thermal resistance, the general use of plate heat exchanger or plate-fin heat exchanger. Tap water circulation: get the heat transfer coefficient, tap water circulation can be calculated according to W = Q / (cpΔt). 2.4 water side heat exchanger Water side heat exchanger in the summer is the evaporator. The selection or design method is the same with the ordinary air-cooled chiller, when the compressor chooses slightly larger capacity, according to the new load to determine the evaporator heat transfer area, select the appropriate evaporator and calculate the refrigerant (water) flow . 3 System Analysis 3.1 Summer alone cooling: air-conditioning cooling operation, but the user does not use hot water, the compressor 1 is running, four-way valve 4 is closed cooling conditions, air-conditioning pump 15 operation, this time, the electromagnetic three-way valve 2 is closed , To cut off the flow of high temperature refrigerant to the reheater 3 and bypasses the four-way valve 4. The refrigerant is condensed into high-pressure liquid refrigerant in the air-side heat exchanger 5 through the four-way valve 4 and flows along the check valve 7 flows into the high-pressure receiver 8, after throttling and decompression by the thermal expansion valve 9, it enters the water-side heat exchanger 16 along the check valve 11 to absorb the heat of the air conditioning water returned by the air conditioning water pump 15 and evaporate, Pass valve 4, gas-liquid separator 14 back to the compressor 1, to achieve air-conditioning system cooling operation. 3.2 Summer Cooling and Heating Water Combined Operation: When the air conditioner is in cooling operation and the user uses hot water, the compressor 1 runs, the four-way valve 4 is closed, and the air conditioning water pump 15 is operated. At this time, the water pressure sensor 18 instructs the electromagnetic three- The valve 2 is opened to cut off the high-temperature refrigerant flow path directly into the four-way valve 4 to bypass the high-temperature refrigerant to the heat recovery heat exchanger 3; after the high-temperature gaseous refrigerant releases a part of the heat in the heat recovery heat exchanger 3, Way valve 4, after which the refrigerant flows in the same direction as in the case of cooling alone. In the hot water plant, the tap water enters the heat recovery heat exchanger 3 after entering the descaling device 17 through the hot water inlet pipe of the living and is heated by a part of the heat of the compressor exhaust gas, then the water pressure sensor 18, the domestic hot water outlet pipe 22 to the user. 3.3 Winter heating alone: ​​air-conditioning heating operation, but the user does not use hot water, the compressor 1 is running, four-way valve 4 is open, air-conditioning pump 15 is running, this time, the solenoid valve 2 closed, cut off the high temperature refrigerant Flows to the flow path of the heat recovery heat exchanger 3, and bypasses the four-way valve 4 which is taken in, and the refrigerant passes through the four-way valve 4 and flows into the water-side heat exchanger 1

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