The heating mode of air conditioner is not electronic expansion valve, but four-way reversing valve. Generally, only inverter has electronic expansion valve. The constant frequency machine is usually capillary tube whether it has heat pump function or not. As for the difference between single chiller and heat pump, it is whether there is a four-way reversing valve!
The capillary tube of electronic expansion valve is used to change the circulating working medium in the compressor. The cooling and heating circulating working medium needs to change the heat in the phase-change suction chamber and the heat in the outdoor, and the heat in the outdoor is released and heated in the indoor! Therefore, in order to increase the heating function of the air conditioner, it is not the electronic expansion valve but the four-way reversing valve.
That is to say: the electronic expansion valve is used with the frequency conversion compressor to control the refrigerant flow and evaporation process more accurately. If only need to make hot occasion, such as air source heat pump water heater, then can use capillary tube as throttling equipment with constant frequency compressor, there is no problem.
The electronic expansion valve is necessary for the current dual-purpose air conditioner, whether refrigeration or heating. In the compression refrigeration cycle, evaporator, condenser, throttling device and compressor are the basic four kinds of accessories, which are necessary. But now the general air conditioning throttling devices are mostly capillary throttles. The high-end ones use electronic expansion valve. The electronic expansion valve is more precise in control, better in comfort and more energy-saving in theory.