在空调过程中加热空气有两种情况：第一种是在空气被水处理前进行加热，一般在冬季气温偏低的情况下使用，通常称为第一次加热或预热。其目的是提高新风的焓值及降低湿度，增加室外空气在废水室内的加湿能力，以提高新风百分比，满足卫生的要求。所使用的加热器即称为预热器，其位置设置在新风小室出风端。
There are two kinds of heating air in the process of air conditioning: the first is to heat the air before it is treated by water. It is usually used in the case of low temperature in winter. It is usually called the first heating or preheating. Its purpose is to increase the enthalpy of fresh air and reduce humidity, and to increase the humidifying capacity of outdoor air in wastewater and indoor, so as to increase the percentage of fresh air and meet the hygienic requirements. The heater used is called preheater, which is located at the outlet of the fresh air 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 has been treated with water, usually called second heating or reheating. Its main purpose is to compensate for the lack of heat in the workshop. The heater used is called reheater, which is usually set behind the water baffle of the sprinkler chamber. Preheaters and reheaters are used to heat air, but their functions are not identical. They can not be confused and replaced, otherwise the air condition in the workshop will change.