Air Source Heat Pump Defrosting Control Method

Air source heat pump defrosting control method

The purpose of defrosting is to improve the performance of the unit and ensure the normal operation of the unit. At present, the research on air source heat pump defrosting technology mainly focuses on two aspects: accelerating the defrosting process and inhibiting the frosting technology. During the defrosting process, the operating state of the unit has not yet reached the defrosting requirement. At this time, the unit has entered the defrosting mode due to the automatic setting, or the thickness of the frost layer on the surface of the unit heat exchanger has reached the defrosting requirement. Without defrosting, this unbalanced supply and demand condition resulted in false defrosting of the unit, increased the burden on the unit, and greatly increased the power consumption of the system. Scholars have proposed various defrosting control methods for inverter air source heat pumps. Direct measurement is a relatively accurate control method, but it is restricted by the actual operating environment and engineering cost. Rarely used, indirect measurement is the most commonly used defrost control method at present, and there are the following three types:

 

(1) Time-temperature method

• The most commonly used control method at present, the time-temperature defrosting control method is to set a temperature sensor on the surface of the heat exchanger. When the temperature of the surface of the outdoor evaporator heat exchange coil or fin surface is lower than a certain set value, the Record the running time of the compressor. When the time reaches the set value (usually 45min), the air source heat pump system enters the defrosting mode. The defrost mode program design logic is simple, it is a relatively simple, economical, and widely used defrost control method. However, in the time-temperature method, since the time setting must be a fixed value, in the actual operation process, this method cannot accurately grasp when the unit will defrost, and the phenomenon of “misdefrosting” of the unit occurs frequently, which seriously affects the unit’s performance. performance and efficiency.

(2) Fuzzy intelligent defrosting

• Fuzzy intelligent defrosting is a modular intelligent defrosting control method, which includes data acquisition and A/D conversion module, input quantity fuzzification module, fuzzy reasoning module, defrosting control module, and monitoring and adjustment module. Logic operations are performed sequentially, and the specific operation process is shown in the figure. Although the automation module greatly improves the effectiveness of the defrosting process, it still cannot completely solve the problem of "false defrosting".

(3) Frost thickness method

• The principle of the method is simple. The frost layer thickness sensor is used to detect the frost layer thickness on the surface of the evaporator coil. When the thickness reaches a predetermined defrosting thickness, the frost starts to be defrosted. This method needs to set the defrost thickness reasonably according to the actual pipe diameter and coil position. However, how to properly set the defrosting thickness is one of the key factors for the application of this method; meanwhile, high-gain signal amplifiers and sensors are required in terms of hardware, and the price is relatively expensive.

 

Winter antifreeze tips for air source heat pump units:

1. Preventing power off of air source heat pump units

• The ambient temperature in autumn and winter in the north is relatively low. If the air source heat pump heating equipment is powered off, it will inevitably freeze after the temperature drops, and the casing heat exchanger of the air source heat pump may freeze and crack. Especially when the fluorine pipe and the copper pipe of the water are all frozen and cracked, and the heat pump compressor is running after the power is turned on, the compressor will pump the water in the water system into the fluorine pipe, which will cause damage to the air source heat pump equipment. Therefore, when starting the air source heat pump heating unit in a sub-zero environment, the power must not be cut off. If you must cut off the power, the water in the air source heat pump unit, water system and circulating pump must be drained.

2. Keep the circulation pipeline well insulated

• The heat preservation of the air source heat pump circulation pipeline is extremely critical in autumn and winter, because the ambient temperature is too low. If there is no pipeline insulation, the heating and hot water will drop a lot after passing through the pipeline. Therefore, in the autumn and winter seasons, it is of great significance to wear a "coat" for the air source heat pump heating pipeline, because this will better prevent the water temperature from dropping. Facts have proved that when the insulation layer of the buffer tank is 50mm, the hot water in the water tank drops by about 10 degrees Celsius for half a day (12 hours) under the working condition of 0-5 degrees Celsius. When the insulation layer is 100mm, the temperature of the same working environment drops for half a day. not exceed 3°C. A 0.3 mm thick aluminum skin is used on the surface and fixed with rivets. Further strengthening the thermal insulation layer, the reduction of the hot water temperature is reduced, which is equivalent to improving the working thermal efficiency of the air source heat pump and reducing the working time. As a result, the set temperature will certainly not be reached.

3. Ensure that defrost water flows out in time

• When the air source heat pump heating unit is started, the cold evaporator encounters air that is slightly higher than its temperature, which will produce condensed water or frost. If the sink is blocked by debris, it will freeze, so check the drain before entering the winter. At the same time, it is also necessary to frequently observe whether the defrosting of the main engine is normal. If the defrosting time is long or the defrosting is incomplete, the parameters of the unit must be adjusted in time.

4. When it snows in winter, clear the surrounding snow in time

• The working principle of the air source heat pump unit is to absorb the heat of the surrounding environment and transfer it to the water, and the water is circulated to the room for heating. Therefore, the air source heat pump must ensure the surrounding air circulation. If the air source heat pump unit is covered with snow, it should be cleaned up in time to ensure that it can absorb the surrounding air smoothly.

5. Add antifreeze as much as possible to air source heat pump system

• In order to ensure that the air source heat pump unit is not damaged by freezing, try to add antifreeze to the heating pipeline of the air source heat pump to prevent the circulating water in the pipeline from freezing at low temperature. In the selection of antifreeze, an antifreeze that is suitable for the local climate temperature should be selected.