Air Source Heat Pump Technology

The efficiency and performance of today's air source heat pumps are the result of technological advances, as follows:
1. Thermostatic expansion valve for more precise control of refrigerant flow to indoor coils
2 . Inveter speed compressor & motor for greater efficiency and can compensate for some of the adverse effects of restricted ducts, dirty filters and dirty coils
3. Improved coil design greatly
4. Improved brushless DC motor and inveter peed compressor design
5. All heat pump inside Copper tube, internally grooved to increase surface area.

The air source heat pump unit is selected : under the rated working condition, theambien is 35 °C standard, outlet water temperature is 7 °C, the air heat pump summer cooling performance coefficient COP value is about 3.0, and the winter (climate 7 °C, outlet water is45 °C)  we do not calculate The frost loss and the heating coefficient COP value are also about 3.0. The cooling and heating performance of the air source heat pump has a direct relationship with the outdoor climate.

The heating characteristics of the air source heat pump hot and cold water unit are more complicated. When the surface temperature of the coil is lower than the air dew point temperature, the air will condense. At this time, the phase change heat exchange is generated on the surface of the coil, which is beneficial to improve the heat pump Heating capacity, but when the coil surface temperature is lower than the air freezing point temperature (below 0 °C), if the relative humidity in the air reaches a certain level , the surface of the coil will be frosted. If it is not defrosted in time, the frost layer will be thicker and thicker, then the actual air flow will be affected, and the heat exchange on the coil will be hindered. and freeze will come out --the compressor will have a low pressure protection and stop work. 

Under different headwind speed conditions, there are three states of humid air on the outdoor air coil of the heat pump unit. ABC is the frosting area, ABD is the condensation area, and the CBD is the dry and cold area-that is no frost and no condensation. The AB line is the frost transition curve--which is close to the isotherm temperature line on the wetting diagram. When the oncoming wind speed is 2.5M/S, the ambient temperature is 0°C, and the relative humidity is 73%, the coil begins to frost, if the oncoming wind speed is increased to 4M / S, the ambient temperature is 0 ° C, the relative humidity reaches 82%, the coil begins to frost, the condensation dew frost transition line shifts to the left, increasing the wind speed can slow down the frost. It is the frosting rate line when the oncoming wind speed is 2M/S. 

So It can be seen that the outdoor air dry bulb temperature is 0-5 ° C, and the relative humidity is >85%, the frosting is the most serious. When tw<-5 °C, the frosting rate is slowed down, which is due to the moisture content in the air has been significantly reduced.