Discussion on the discussion of hot water heating in winter

2 system and experimental device introduction

The system consists of a solar system and a heat pump system. The solar energy system includes a heat collecting plate, a heat insulating water tank with a coil heat exchanger, a water pump, and the like; the heat pump system includes a casing heat exchanger in addition to the four components of a compressor, an evaporator, a condenser, and a throttling device. Combine the solar system with the heat pump system.

This system combines solar water heaters and heat pump air conditioners. The following five modes can be realized by controlling the valve opening and closing: (1) cooling the room separately; (2) cooling the room and heating the living room; (3) making the room separately (4) Room heating and domestic hot water; (5) Separate hot water.

In winter, solar energy is used as a low-temperature heat source, and its operating conditions can be divided into dynamic and static operating conditions. The dynamic operating condition refers to the heat collector of the solar collector while the heat pump unit is also operating. Dynamic operation can effectively reduce the surface temperature of the collector, improve the efficiency of the collector, and at the same time obtain a higher evaporation temperature than the air source heat pump, thereby improving the performance of the heat pump system.

Static operating conditions refer to the collector's disposable heat collection, and the heat is stored in the water tank as a low-temperature heat source for the heat pump unit. Static operation increases the system's evaporation temperature and prevents frost on the evaporator surface, improving the performance of the heat pump system. This paper mainly studies two modes of heating alone in winter: 1) Air source heat pump operation mode: the refrigerant absorbs heat in the atmosphere in the evaporator, and then supplies heat to the room after compression by the compressor; 2) Operation mode of the water source heat pump The water heated by the solar energy circulates between the water tank and the casing heat exchanger through the water pump, and the heat absorbed by the refrigerant absorbs water, and is heated by the compressor to supply heat to the room, that is, the above static operation condition.

3 experimental principles and methods

In this experiment, the 1.5p compressor unit was placed in a temperature-controlled climate chamber to simulate outdoor and indoor environments in winter. Control the outdoor temperature to -3, the indoor to 10, and then experiment.

3. 1 air source heat pump heating principle and experimental method

When heating, the four-way valve in the integrated machine is switched to the heating mode, the valves 3, 16, 17, 11, 12 in the system diagram are closed, the valve 15 is opened, the one-way valves 18, 19 are opened, and the three-way valve is opened. The valve connected to the casing heat exchanger 10 is closed. This is a simple heat pump air conditioner. When the system is running, the low-pressure working fluid vapor is compressed by the compressor, and becomes a high-pressure high-temperature gas. The condenser enters the indoor unit 7 and condenses and releases heat. The condensed liquid working fluid is throttled by the throttle valve to reduce the temperature and reduce the pressure, and absorb the ambient atmosphere. The heat in the vapor is evaporated into a low pressure gas into the compressor to complete a cycle.

Experimental method: record outdoor ambient temperature, indoor temperature, system operation start time, end time, ammeter reading, etc. From compressor start-up to stable operation, data is recorded every two minutes; from steady operation to the end, data is recorded every 5 minutes. In this experiment, the wind speed and the inlet temperature are measured by the average method. That is, the windward surface of the rectangular heat exchanger is divided into nine parts according to the well word, and the speed and temperature of each part are measured separately, and the average value is taken as the wind speed and the inlet temperature on the whole surface; The exit is an eight-part round face, similar to the exit temperature.

Data collection includes evaporation pressure, condensing pressure, exhaust gas temperature, suction temperature, wind speed and inlet and outlet temperature when the air flows through the condenser, and operating current of the compressor. The condensation temperature and the evaporation temperature correspond to the condensation pressure and the evaporation pressure, and are obtained by checking the thermal property table of R22, and the system COP is calculated.

3. 2 water source heat pump heating principle and experimental method

The heat absorbed by the refrigerant absorbs hot water into low-pressure steam, which is compressed by the compressor, heated and pressurized, and then cooled and phase-changed in the condenser to provide heat to the room; the condensed high-pressure liquid refrigerant is cooled and throttled by the throttle valve. After that, it becomes a low-temperature and low-pressure liquid, and the heat flowing through the casing heat exchanger to absorb the high-temperature water evaporates into a gas, and finally returns to the compressor to complete a cycle.

Experimental method: The hourly solar radiation of the representative day of January in Beijing can be found. The average collector efficiency of the collector is generally 45%. The relevant formula can be used to obtain the effective energy on the collector plate, and then the water in the tank is obtained. The heat gained. According to the load calculation, the area of ​​the heat collecting plate is 3m 2 and the effective volume of the water tank is 130L. The time for obtaining the solar radiant energy of the heat collecting plate is from 8:00 am to 5:00 pm. Assuming that there is no hot water during the day, programming in C can be used to find the final water temperature of the day. The calculated water temperature is 45. The solar energy saved by the experiment is used as a low-temperature heat source of the heat pump to achieve the purpose of supplying heat to the room. The initial water temperature of the experiment was 45, and the corresponding time was recorded for each degree of decline. The indoor and outdoor temperature and other data collection were compared with the air source heat pump operation experiment.

4 experimental results and analysis

When the compressor is started, the pressure is low. As the refrigerant is sucked in and compressed, the pressure gradually rises. After ten minutes, the operation is stable, the pressure remains constant, and it does not change.

When the compressor is started, the torque is large and the power consumption is high. Therefore, the average COP of the system in the first 10 minutes is very low, only about 1.2. With the operation of the compressor, the high and low pressures are increased, and the exhaust gas temperature is gradually increased. Because the ambient temperature is stable, the heat exchange between the refrigerant and the outside is gradually balanced, and the high and low pressure of the press gradually stabilizes, so the middle system COP has a tendency to grow first and then stabilize. The system is operated for 1 hour, and the average COP is 2. 51.

When the system is started, the original balance is broken, the high pressure is gradually increased, and the low pressure is gradually reduced. Therefore, the compressor discharge pressure is relatively low at the beginning, and the suction pressure is relatively high. As the working fluid is continuously compressed, the exhaust pressure gradually rises and tends to stabilize after 18 minutes. At about 15 bar, the inspiratory pressure changes after the adjustment, and the water temperature decreases.

In the first 18 minutes of smooth operation, the press consumes a lot of power, the refrigerant flow rate is small, and the water temperature drops at a slower rate, and drops once in 9 minutes. After the system runs smoothly, the water temperature drops at a steady rate, dropping by an average of 4 minutes. The system is running for three hours and the water temperature drops by 40. Before the system runs smoothly, the compressor discharge pressure is very low, the refrigerant flow rate is small, the heat released in the condenser is small, and the COP value is very low, only 1. 75; With the continuous operation of the compressor, the suction pressure gradually increases, the evaporation temperature increases, and the COP gradually increases. Changes in water temperature cause fluctuations in operating pressure and volatility in COP. It can be seen that when the water temperature is 45 13 , the COP fluctuates greatly; at 15:00, the COP fluctuates relatively little and begins to gradually decrease, and the minimum value is above 3.0. The decrease of the water temperature causes the evaporation temperature and the evaporation pressure to decrease, the heat absorbed by the refrigerant in the evaporator decreases, the corresponding exhaust pressure increases, and the compressor consumes more power, resulting in a decrease in the coefficient of performance.

The system COP is relatively stable when the air source heat pump system is working. When the water source heat pump system is working, the water temperature drop causes the system COP to change drastically, but the coefficient of performance is better than the air source heat pump.

The experiment found that after 40 minutes of operation of the air source heat pump system, the evaporator showed frost formation, which not only increased the flow resistance of the air, but also affected the heat exchange efficiency of the refrigerant and the air, so the system must be defrosted. The four-way valve reverses the defrosting, the compressor consumes power, and the room does not get heat, which is also the reason for the low COP. The water heated by the solar energy is used as a low-temperature heat source, and there is no frosting of the evaporator. Although the pressure fluctuates, the average COP of the system reaches 3.56, which is significantly higher than that of the air source heat pump.

5 Conclusion

Through the experimental research on the heating of the dual heat source integrated machine in winter, the following conclusions are obtained:

1) When the outdoor temperature is low in winter, the air source heat pump air conditioner is difficult to work normally. When the outdoor temperature is -3, the evaporator has frosting, and the system COP changes smoothly. The average value is 2. 51.

2) Under the same conditions, the water source heat pump is operated for 1 hour, the system COP changes drastically, and the average value is 3.41. Compared with the air source heat pump, the energy saving effect is obvious. In order to solve the drastic changes caused by the water temperature, the thermal expansion valve can be used to replace the capillary tube, and the flow rate of the refrigerant is adjusted according to the change of the water temperature to make the system run stably.

3) The water source heat pump system is operated for 3 hours, the system COP averages 3.56; the water temperature drops to 5, and the COP is still above 3.0. If the stored water temperature is slightly lower, more hot water can be produced and the room can be heated for a long time. In order to prevent the water from freezing at low temperatures and affect the operation of the system, antifreeze should be added to the water.

When the outdoor temperature is low in winter, the system switches to the water source heat pump operation, which not only makes full use of solar energy, but also improves the system operation efficiency. This paper analyzes the static utilization of solar energy and small heat pump devices, and lays a foundation for the study of the combination of solar energy and large central air conditioning.

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