1、 Design tasks and known conditions

According to the requirements, the fan coil unit is used as the end device, the chilled water temperature is 7 ℃, the air conditioning return water temperature is 11 ℃, the total cooling capacity is 400KW, and the cooling water system uses circulating water from the cooling tower.

2、 Determination of refrigeration compressor model and quantity

1. Determine the total cooling capacity of the refrigeration system

The total cooling capacity of the refrigeration system should include the actual cooling capacity required by the user, as well as the cooling losses of the refrigeration system itself and the cooling supply system. It can be calculated according to the following formula: where - the total cooling capacity of the refrigeration system (KW) - the actual cooling capacity required by the user (KW)

A - Cold loss additional coefficient.

For indirect cooling systems, when the air conditioning cooling capacity is less than 174KW, A=0.15~0.20； When the cooling capacity of the air conditioner is 174-1744 kW, A=0.10~0.15； When the cooling capacity of the air conditioner exceeds 1744KW, A=0.05~0.07； For direct cooling systems, A=0.05~0.07。

2. Determine the type of refrigerant and system form

According to the design requirements, ammonia is selected as the refrigerant and indirect cooling method is adopted.

3. Determine the design operating conditions of the refrigeration system

Determining the design operating conditions of a refrigeration system mainly refers to determining working parameters such as evaporation temperature, condensation temperature, compressor suction temperature, and subcooling temperature. The determination of the main working parameters is calculated based on the "Refrigeration Engineering Design Manual".

When determining the condensation temperature, the inlet and outlet temperatures of the condenser cooling water should be determined based on the usage of the cooling water.

① Determination of Condensation Temperature

According to the "Refrigeration Engineering Design Manual", the average outdoor wet bulb temperature (℃) in summer is not guaranteed for 50 hours per year

℃

For a circulating water system using a cooling tower, the inlet temperature of the cooling water is calculated according to the following formula:

℃

In the formula - temperature of cooling water entering the condenser (℃);

——The average outdoor wet bulb temperature (℃) for 50 hours per year is not guaranteed in the local summer;

——Safety value, for mechanical ventilation cooling towers, is 2~4 ℃.

The temperature of the cooling water exiting the condenser (℃) is related to the temperature of the cooling water entering the condenser and the form of the condenser.

Determine according to the following formula:

Choose a vertical shell and tube condenser=+(2~4)=31.2+3=34.2 ℃

Note: Usually not exceeding 35 ℃.

The system uses water as the cooling medium, with a heat transfer temperature difference of 4-6 ℃. Therefore, the condensation temperature is

℃

In the formula - condensation temperature (℃).