April 10, 2013
Air source heat pumps mainly use the heat-absorbing medium in the air source heat pump device, namely the refrigerant, to directly collect heat energy from the natural environment or the air, and then use the compressor to compress it to increase the temperature of the refrigerant. At the same time, the refrigerant releases heat through the heat exchanger to increase the temperature of the cold water, and releases cold air after heating. The hot water produced by this technology can directly serve people through the water circulation system, can be directly used as hot water supply, and can also be delivered to users for heating.
Ultra-low temperature air source heat pumps are mainly due to their lower operating environment temperature, but their working efficiency and reliability are higher, which is very different from the common air source heat pump type. Since the temperature in northern my country is lower in winter, the market for ultra-low temperature air source heat pumps in the north is very broad, and now it has developed into a designated product for coal-to-electricity conversion in most areas, and has been widely used in actual use. In recent years, many experts and scholars in the world have done a lot of research and investigation to improve the applicability of air source heat pumps in low temperature environments. The key research is to work normally and achieve heating when the ambient temperature is as low as -20℃ or even as low as -25℃.
The operation of air source heat pumps is still based on the reverse Carnot cycle principle: the liquid working medium first absorbs the heat in the air in the evaporator and then vaporizes. The latent heat of vaporization is the heat we want to recover. After being compressed by the compressor, it forms a high-temperature and high-pressure gas, which then enters the condenser for liquefaction. The liquid transfers the absorbed heat to the cold water that needs to be heated. The liquid working medium is reduced in pressure by the expansion valve and then returns to the expansion valve. It absorbs heat and evaporates, thus realizing a complete cycle process. This cycle repeats, and the heat of low-temperature energy is continuously absorbed and transferred to the cold water that needs to be heated, and the heated cold water reaches the ideal temperature.
Compared with common air source heat pumps, ultra-low temperature air source heat pumps have an additional injection enthalpy increase branch connected to the compressor. In general, air source heat pumps will reduce evaporation due to low evaporation temperature in -10℃ and lower environments, so the compressor return air volume is relatively small, and the condensation heat release effect will be greatly reduced. However, after using ultra-low temperature air source heat pumps, due to the addition of injection enthalpy increase branch connected to the compressor, it can directly replenish air to the compressor when the compressor return air is insufficient, so that the heat release of the condenser is increased, so the ultra-low temperature air source heat pump can also work normally to achieve heating in an environment of -25℃. It can also be seen in the wide application of ultra-low temperature air source heat pumps that when the ambient temperature is as low as -20℃, its comprehensive COP is still as high as about 2.0, and it can also operate normally when the temperature is as low as -25℃. From this point of view, the air source heat pump can operate normally for heating when the lowest operating ambient temperature is -25℃.
In general, air source heat pumps are increasingly recognized by the government and industry as a clean and environmentally friendly energy source, and are being vigorously developed as an energy source. Air source heat pumps are particularly suitable for hot summer and warm winter areas as energy stations to produce domestic hot water. Although there are still problems with equipment selection and equipment performance, their unique advantages are irreplaceable. As an environmentally friendly energy source, air source heat pumps have a wider range of applications.
