Who can tell me how to calculate the approach temperature in the picture below?

If the refrigerant high and low pressures are normal and the two approaching temperatures of the condenser and evaporator are calculated, it can be seen whether scaling is serious. But after asking a few friends about this, they all forgot how to calculate it in detail.

This is also the first time I have heard of this concept... waiting for expert analysis!

This post was finally edited by mechanical nutritionist Hu Shaoshao on 2020-7-27 08:05. After asking several experts, I finally figured it out. The approach temperature is a parameter indicating the heat transfer capacity of the heat exchanger. It is a quantity related only to the heat transfer coefficient. The smaller the value, the better the heat transfer effect. When the heat exchange area approaches infinity, the approach temperature should be close to 0. In the cold machine, the approach temperature of the evaporator is called the evaporation approach temperature, which is the difference between the outlet temperature of the chilled water and the evaporation temperature of the refrigerant. ； The approach temperature of the condenser is called the condensation approach temperature, which is the difference between the refrigerant condensation temperature and the cooling water outlet temperature. Calculation formula: Evaporation approach temperature = Chilled water outlet temperature - Refrigerant evaporation temperature Condensation approach temperature = Refrigerant condensation temperature - Cooling water outlet temperature Taking commonly used R22 Freon as an example, the evaporation temperature and condensation temperature can be found on Baidu.

That is to say, when the high and low pressures are normal, if a high pressure alarm occurs, you can first check the cooling water inlet temperature. If the water temperature is high, it may be caused by environmental effects or scaling of the filling of the water tower and uneven water distribution, resulting in poor cooling and heat dissipation. If the inlet water temperature is normal and the outlet water temperature difference is small, you can measure the condenser approach temperature to know whether scaling causes low flow and poor heat dissipation.

Taking the above data and table as an example, the exhaust pressure is 1.45, which means the exhaust temperature is about 40 degrees, and the cooling water outlet temperature is 35, which means the condenser approach temperature difference is 5 degrees. The old master told me that 5-8 degrees is normal, but if it is higher than 10 degrees, be aware that a high-pressure alarm may occur at any time.