Foreword R410A evi heat pump for stable house heating/cooling, sanitary hot water supply in cold climate area. air source heating system,heat pump water heater,floor heating pump Guangdong New Energy Technology Development Co., Ltd. , https://www.newenergy-e.com
In the face of the rising energy crisis that the world faces together, our country, as a big energy-consuming country, still has a low energy utilization rate. However, with the encouragement of various policies and the restriction of laws and regulations, and the promotion of incentive mechanisms, people are becoming more and more energy-efficient 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 for hot water, due to the winter hot 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 heat recovery of air-cooled chiller refrigeration cycle
Figure 1 fully enclosed reciprocating compressor air-cooled heat pump unit lg ph map
From Figure 1, 2 to 5 points for the entire process of condensation, of which 2 to 3 points is the refrigerant overheated section of the sensible heat, 3-4 points refrigerant latent heat, 4 to 5 points is the sub-cooling 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 design can still meet the thermal load in winter.
1.2 with heat recovery of air-cooled hot and cold water units
1.2.1 Schematic diagram of the heat recovery unit device:
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 into the water pipe
8. High pressure receiver. Water side heat exchanger
Figure 2 Schematic diagram of heat recovery unit
Refrigerant circulation circuit: The exhaust port of the compressor 1 is connected to the four-way valve 4, the air-side heat exchanger 5, the check valve 7, the high-pressure receiver 8, the thermal expansion valve 9, the check valve 11, The heat exchanger 16, the four-way valve 4, the gas-liquid separator 14, and then to the intake port of the compressor 1, a check valve 12 is provided between the outlet of the check valve 11 and the outlet of the check valve 7, The temperature sensing package 13 is installed on the connecting pipe between the four-way valve 4 and the gas-liquid separator 14;
1.2.2 The characteristics of the heat recovery unit
(1) A heat recovery heat exchanger is provided between the exhaust port of the compressor of the air conditioner and the inlet of the four-way valve, and the exhaust pipe of the compressor is connected to the inlet of the refrigerant passage inside the heat recovery heat exchanger , The outlet of the heat recovery heat exchanger is connected with the inlet of the four-way valve, the inlet and the outlet of the domestic hot water channel are respectively connected with the inlet of the domestic hot water inlet pipe and the heat recovery heat exchanger water channel.
(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 parts
2.1 compressor
The heat recovery unit compressor selection and the ordinary air-cooled chiller, that is based on various models 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
When designing an air-cooled condenser, the heat load is the enthalpy difference between 5 and 3 points of the refrigerant in Figure 1 (lg ph), which is smaller than the design heat load of the unit without heat recovery because part of the heat of condensation is used for heat recovery, Heat recovery heat exchanger bear, so the unit of 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
The unit heat recovery heat exchanger, heat recovery process shown in Figure 1 (lg ph chart) from 2 o'clock to 3 o'clock process, high temperature and pressure refrigerant gas is discharged from the compressor, the gas sensible heat and tap water in the heat Recycling exchange heat exchanger to heat the tap water to obtain 55 ~ 65 ℃ 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
The water side heat exchanger is the evaporator in summer. 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 when the summer alone cooling:
When the user does not use hot water, the compressor 1 runs, the four-way valve 4 turns off the cooling condition, and the air conditioner water pump 15 runs. At this time, the electromagnetic three-way valve 2 is closed and the high-temperature refrigerant flows to the reheater 3 bypass, and into the four-way valve 4, the refrigerant through the four-way valve 4 in the air side heat exchanger 5 condenses into high-pressure liquid refrigerant and flows along the one-way valve 7 into the high pressure receiver 8 After throttling and depressurizing, the thermal expansion valve 9 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 to evaporate, and finally evaporates through the four-way valve 4, the gas-liquid separator 14 Return to the compressor 1, to achieve air-conditioning system cooling operation.
3.2 Summer cooling and hot water combined operation:
When the user operates the hot water, the compressor 1 runs, the four-way valve 4 is closed and the air-conditioning water pump 15 is operated. At this moment, the water pressure sensor 18 instructs the electromagnetic three-way valve 2 to open and cut off to directly enter the four-way valve 4 Of high temperature refrigerant flow path, so that the high temperature refrigerant bypass heat recovery heat exchanger 3, the high temperature gaseous refrigerant in the heat recovery heat exchanger 3 to release part of the heat into the four-way valve 4, then the flow of refrigerant The same direction and when 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. After the water pressure sensor 18, the domestic hot water outlet pipe 22 to the user.
3.3 winter alone when heating:
When the air conditioner is in heating operation, when the user does not use the hot water, the compressor 1 runs, the four-way valve 4 is turned on and the air conditioning pump 15 is operated. At this time, the electromagnetic three-way valve 2 is closed and the high temperature refrigerant flows to the heat recovery heat exchanger 3, and bypasses the four-way valve 4, the refrigerant passes through the four-way valve 4, flows into the water-side heat exchanger 16, releases the heat into the air-conditioning hot water in the water-side heat exchanger 16 and condenses into High pressure liquid refrigerant flows into the high pressure accumulator 9 along the check valve 12 and is throttled and decompressed by the thermal expansion valve 9. After the check valve 10 enters the air side heat exchanger 5 to absorb the heat of outdoor air and evaporate, Finally, the four-way valve 4, gas-liquid separator 14 back to the compressor, to achieve air-conditioning system heating operation.
3.4 Winter heating and hot water combined operation:
When the user uses hot water, the compressor 1 runs, the four-way valve 4 is opened and the air-conditioning water pump 15 is operated. At this moment, the water pressure sensor 18 instructs the electromagnetic three-way valve 2 to open and cut off to directly enter the four-way valve 4 Of the high temperature refrigerant flow path, so that the high temperature refrigerant by-pass into the heat recovery heat exchanger 3, the high temperature refrigerant in the heat recovery heat exchanger 3 to release part of the heat into the four-way valve 4, then the refrigerant flow direction Same as when heating alone. In the hot water plant, tap water through the hot water inlet pipe into the descaling device 17 into the heat recovery heat exchanger 3, the use of compressor exhaust heat after some of the heat, the water pressure sensor 18, domestic hot water primary water pipe 22 to the user.
4 Conclusion
General air-cooled chillers emit large amounts of condensing heat during operation, the unit set a heat recovery heat exchanger between the compressor exhaust port and the four-way valve inlet, to ensure that the refrigeration cycle is not affected under the premise of the air-conditioning During operation, part of the condensing heat is recovered, that is, the gas of the refrigerant gas with high temperature and high pressure is sensible to heat to make domestic hot water, which is suitable for hotels and hotels. Due to the smaller amount of hot water in summer than in winter, hot water can be supplied by the heat recovery heat exchanger completely without auxiliary heat source. In winter, due to the large amount of hot water, auxiliary heat source must be used. From the economic analysis we can see that the unit to ensure that the refrigeration cycle at the same time, only added a heat recovery heat exchanger, the system selection, the load can be designed according to the required cooling capacity of 1.2-1.3 times the calculation, with the maximum possible recovery Waste heat, to undertake the demand for hot water supply in summer. In winter, if the hot water demand is large, the auxiliary heat source is used for secondary heating without unlimited capacity of large-capacity components to meet the supply of winter hot water, Waste of heat.
references
1 Guo Qingtang Wu Jinfa, concise air conditioning with refrigeration design manual, Beijing: China Building Industry Press, 1999.4
2 Jiang Nengzhao Zhang Hua, home central air conditioning practical technology, Beijing: Mechanical Industry Press, 2002.3
3 Yang Xuelin, Plate Heat Exchanger Engineering Design Handbook, Beijing: Mechanical Industry Press, 1995
4 ASHRAE Transaction technical and symposium papers presented at the 2001 winter meeting in Atlanta, Georgia of the American Society of Heating, Refrigeration and Air-conditioning Engineers, Inc, 2001, volume 107, part 1
5 Dong Ming. Star-class hotel central air-conditioning condensing heat recovery and utilization [J] China Water Supply and Drainage, 2004,4