Generally, when the outdoor temperature is about 10℃ and the indoor temperature is about 20℃, the air conditioner can still perform refrigeration operation.

In some special places, such as computer exchange centers, libraries, etc. Refrigeration is also needed in the extremely low temperature environment in winter, so it is necessary to develop refrigeration and air conditioning with sub-zero temperature.

Extended data

Principle of air conditioning refrigeration

Liquid vaporization refrigeration uses the heat absorption of liquid vaporization and the heat release of condensation to realize refrigeration. Liquid evaporates to form steam. When the liquid (refrigerant) is in a closed container, there is no other gas except the vapor generated by the liquid and the liquid itself, and the liquid and the vapor will reach equilibrium under a certain pressure. At this time, the gas is called saturated steam, the pressure is called saturated pressure, and the temperature is called saturated temperature.

When the liquid is in equilibrium, it will no longer evaporate. At this time, if a part of steam is pumped out of the container, the liquid will inevitably continue to vaporize to generate a part of steam to maintain this balance. When a liquid vaporizes, it absorbs heat, which is called latent heat of vaporization.

The latent heat of vaporization comes from the cooled object, which makes the cooled object cool. In order to make this process continue, it is necessary to continuously extract steam from the container and condense it into liquid before returning to the container.

If the vapor extracted from the container is directly condensed into liquid, the temperature of the required cooling medium is lower than the evaporation temperature of the liquid. We hope that the condensation of steam is carried out at room temperature, so it is necessary to increase the pressure of steam to the saturation pressure at room temperature.

Refrigerant will evaporate at low temperature and low pressure, resulting in cold effect; And condense at normal temperature and high pressure to release heat to surrounding environment or cooling medium. Steam condenses into high-pressure liquid at normal temperature and high pressure, and its pressure needs to be reduced to evaporation pressure before it can enter the container.

The liquid vaporization refrigeration cycle consists of four processes: working medium vaporization, steam pressurization, high-pressure steam condensation and high-pressure liquid decompression.

References:

Baidu Encyclopedia: Air Conditioning