frosting has always been a major issue restricting the development of air energy heat pump . In this issue, we will learn about the reasons, frosting patterns and solutions for heat pump frosting.
frosting affects
2. Increase heat exchanger thermal resistance, heat exchange capacity decreases;
3. Frequent defrost, endless defrost, defrost process is an air conditioner operation process. It not only cannot heat water, but also needs to consume the original energy consumption of hot water. The discharged frozen water is back into the insulation water frost, causing the water temperature to drop further;
4. The evaporation temperature decreases, energy efficiency is lower than , and the heat pump operation performance deteriorates until it cannot work normally.
5. Because the unit cannot work normally, it directly causes economic losses to customers, and even fear of heat pump products has aroused, causing the entire industry to enter a more difficult situation.
Several forms of heat pump frosting
Reason: When the temperature of the heat exchanger is lower than the dew point temperature of the ambient air, condensation water will be generated on the surface of the heat sink on the entire heat exchanger. When the temperature of the ambient air is lower than 0℃, the condensation water will condense into thin frost. When frost is severe, it will affect the heating effect. Generally, heat pump products have an automated frost function to ensure the normal operation of air conditioner .
2. Abnormal frost:
2. The outdoor ambient temperature is greater than 0℃ and the machine will be turned on soon. The frost on the bottom of the outdoor heat exchanger (begins at the outlet of the capillary ) is very thick, and most of the heat exchanger has no condensation. As time delays, frost will extend from bottom to top; the indoor fan is always running at low speed against cold air; the air conditioner is ordinary defrost. This fault is generally due to the lack of refrigerant in the system. Solution: First check the system leakage point repair and add refrigerant.
3. The outdoor ambient temperature is greater than 0℃ and the machine will be turned on soon. The frost is very thick in the upper half of the outdoor heat exchanger (at the outlet of the heat exchanger and the return air pipe), and the frost extends over time on the heat exchanger (with the outlet of the heat exchanger towards the inlet of the heat exchanger) and the heating effect is poor; the air conditioner is ordinary defrost. This fault is generally due to excessive refrigerant in the system. Faults often occur after repair and refrigerant. Solution: Put refrigerant until normal operation.
frosting cause analysis
1. The problems that air energy heat pump water heater in winter are mostly caused by unreasonable system matching. For example:
2. The system installation match is unreasonable: Many heat pump projects adopt large-circulation installation method, using hot water while replenishing cold water. The unit operates at low temperature for a long time, resulting in frost.
3. Insufficient air exhaust volume: The air energy heat pump water heater unit should be used normally in cold areas in winter. If the temperature is too low and the humidity is high, it is necessary to strengthen the unit ventilation or use auxiliary electricity to prevent icing, etc., and optimize the defrost procedures according to the characteristics of the region, and carry out scientific and reasonable careful design and installation. In this way, the air-energy heat pump water heater unit can be used by users even in cold winters.
4. Lack of necessary environmental simulation experiments: The engineering design of air energy heat pump water heater unit must take into account the use level of different environments and different regions, and different defrost parameters must be formulated. For example, defrost time, defrost start temperature, and defrost end temperature all need to set different parameters according to the minimum temperature and humidity in different regions. It is difficult to achieve the ideal effect without environmental simulation experimental equipment.
defrost method analysis
Blue flame high-tech air The gas engine heat pump adopts waste heat recovery technology. Using the waste heat of the gas engine, the intelligent defrost can be achieved, achieving the defrost effect of with multiple frost removal and frost-free removal without . The waste heat recovery can not only defrost, but also heat water, providing free domestic hot water.
2. Thermal defrosting
By installing the resistor of appropriate power on the heat exchanger, when the frost layer on the evaporator accumulates to a certain level, the switch is turned on, and the resistor wire is powered on to generate heat and melt frost. This method is simple and easy to use, but it is not advisable from an energy-saving perspective.
3. Reverse cycle defrosting
One is to install a temperature sensor on the evaporator coil to determine whether frosting is performed by detecting the outdoor coil temperature. Another way is to determine whether the outdoor evaporator is frosted by detecting the difference between the condenser coil temperature and room temperature (or water temperature). That is, when the evaporator is frosted, its thermal efficiency of is reduced, resulting in a decrease in the heat exchange of condenser and the temperature of coil . When it is detected that the difference between the condenser coil temperature and room temperature (or water temperature) is lower than a certain value, it can be judged that the outdoor heat exchanger has serious frosting. When defrosting, start the reversing defrosting program. The four-way reversing valve acts to change the flow direction of the refrigerant, and let the unit change from the heating operation state to the refrigeration operation state. The high-temperature gas discharged from the compressor is switched to the outdoor heat exchanger through the four-way valve to the outdoor heat exchanger for melting. When the outdoor coil temperature rises to a certain temperature value, the defrosting ends.
4. Refrigerant supercooling, exothermic defrosting,
This method is to supercool the refrigerant from the condenser and throttle it, and then enter the evaporator to melt the frost layer on the evaporator.
In the defrosting state of heating conditions, only one of the 4 solenoid valves is opened. The liquid refrigerant from the condenser enters the fin heat exchanger from the opened solenoid valve for supercooling and exothermic defrosting, and then enters the gas-liquid separator corresponding to the opened solenoid valve. The refrigerant coming out of the outlet of the gas-liquid separator enters the liquid collector, then enters the distributor through the throttle valve , enters the remaining 3 pipelines through the check valve , and enters the evaporator to evaporate. The gaseous refrigerant enters the corresponding gas-liquid separator, and then collects from the outlet to the gas collector and then enters the compressor through the Stone reversing valve to complete the circulation. The frost is removed when the frost is set, so that the unit is operated in a frost-free state.
5. Fan reversal method defrost
This method is improved on the basis of commutation defrost, that is, during the defrost process, fan reversal is enabled to send air in the opposite direction, forcing the air to enter the air-side heat exchanger from the non-frosted side and flow to the frosted side, blowing the heated air to the frosted layer and defrosted. This defrost method fully utilizes the heat of the wind-side heat exchanger, and relies on three heat transfer methods: convection, heat conduction and radiation to melt the frost at the same time, which is significantly better than the traditional defrost method.At the same time, a certain wind pressure can also cause the frost shell to collapse and escape from the surface of the heat exchanger, and the addition of convective heat exchange makes the defrost process proceed quickly and thoroughly. However, due to the addition of devices such as intermediate relay and pressure switch , production costs have been increased.
6. Hydraulic defrost
For large heat pump systems, hydraulic defrost measures are often used. The purpose of defrosting is achieved by rinsing the outdoor evaporator with hot water. This defrosting method is simple, but it causes the humidity content of the air around the evaporator to be too high after defrosting, which makes it easy to frost again, making it not suitable for use in areas with lower temperatures such as the north. Moreover, there is a large waste of water resources and an independent water system is needed.
7. Pneumatic defrost
This method uses compressed air to generate a high-speed jet to directly blow the defrost layer, and remove tiny frost on the surface of the evaporator at any time, so that the surface of the evaporator always remains frost-free. Its biggest advantage lies in the continuous heating of the indoor heat environment, which fluctuates slightly, ensuring comfort. However, compressed air requires additional power consumption, and the construction cost of the whole machine is also relatively high.
defrost cause and solution
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