There are two cases of heating air in the process of air conditioning: the first is heating before air being treated by water, usually under the condition of low temperature in winter, usually known as the first heating or preheating. The purpose is to increase the enthalpy and reduce the humidity of fresh air, and increase the humidifying capacity of outdoor air in the waste water chamber, so as to increase the percentage of fresh air and meet the hygienic requirements. The heater used is called the preheater, and its position is set at the outlet of the new wind chamber.

第二种是在空气被水处理后进行加热，通常称为第二次加热或再热。其目的主要是补偿车间热量的不足。所使用的加热器即称为再热器，一般设置在喷水室挡水板之后。预热器与再热器虽然都是用来加热空气用的，但它们的作用是不完全相同的，二者不可混淆和替代，否则车间空气状态就会发生改变。

The second is to heat the air after it is treated by water, usually called second heating or reheating. The main purpose is to compensate for the shortage of heat in the workshop. The heater used is called reheater, which is usually set after the water spray chamber. Preheater and reheater are all used for heating air, but their functions are not the same. The two must not be confused or replaced, otherwise the air state of the workshop will be changed.