While a geothermal heat pump extracts energy from soil on 7-10 Celsius temperature all year round, the air-to-air equipment use the outside air on various temperature for the same purpose. As the outside temperature is decreasing, higher performance of the compressor is needed to achieve the same flow temperature. The standard technology has placed a heat cartridge at the suction side of the heat pump to avoid overburden the compressor and to preheat the incoming air. With this solution there was a guarantee for the stable operation of the equipment in case of lower performance of the compressor even in cold weather. At the same time the energy efficiency of the machinery was deteriorating in the heating season.
The solution is, in the past few years spreading EVI technology (EVI stands for Enhanced Vapor Injection). The development makes possible the creation of the increased performance of the compressor. Hereby the operation in cold weather can be ensured without the preheating cartridge as well.
The essence of EVI is that after the condenser, a separate circuit is built in the heat pump. This circuit is automatically activating in case of low temperature and the liquid working medium leaving the condenser drains 10-25 % to a separate so-called aftercooler humidifier. Hereby the pressure is decreasing on the main humidifier. During the post-cooling, the separated working medium passes through a heat exchanger where it cools further and converted back to gas. The cooled, gaseous working medium is cooled by injecting it into the compressor head between two compressor strokes. The compressor head can be actively cooled by the working medium which was injected, namely the limit of the compressor performance can be pushed out and high heating performance can be achieved at low temperature as well.
The use of the technology is a major advance primarly in the heat pumps sourced by the air, as it pushed the limits of the economical adaptability of the heat pump. If you are thinking to buy a heat pump, it is worthy to include the existence of the modern EVI technology in your choice.
