How to select the chiller and what should be paid attention to when using the evaporator
For customers who have used water chillers, the selection of water chillers is already familiar, and they are all aware of the various requirements. For customers who buy a chiller for the first time, they may not know too much about the size of the chiller to choose. So, how do we choose the most suitable chiller for you?
The chiller is a kind of refrigeration equipment that can provide industrial chilled water to various industries to achieve the purpose of cooling. According to different heat dissipation methods, it can be divided into air-cooled chillers and water-cooled chillers. It can control the temperature at 5-35 degrees. The low-temperature chiller can even control the temperature between 0 and -40 degrees. When selecting the chiller, we must accurately understand the chiller's inlet temperature, outlet temperature, flow rate, and water tank size, etc., and know the working environment of the chiller, such as the ambient temperature and seasonal changes in ambient temperature. , Environmental space, etc.
A high-quality and low-cost chiller is a guarantee for the success of the engineering design, and it also has a long-term impact on the operation of the system:
1. Cooling water flow: refers to the cooling circulating water flow of the chiller that needs to be supplied when the refrigeration equipment is in use.
2. Cooling capacity: how much cooling capacity is needed. Commonly used cooling capacity units are Kcal/h, kw, etc.
3. Outlet water temperature: return water temperature or outlet and return water temperature difference requirements: outlet water temperature refers to the required chilled water temperature, and return water temperature refers to the cooling water temperature. Some equipment with stricter heat dissipation requirements will have cooling water supply temperature requirements.
4. Water outlet pressure: Some devices that require heat dissipation have a certain pressure requirement on the cooling water supply due to their complicated internal heat dissipation structure. At this time, it is necessary to consider whether the rated water outlet pressure of the chiller can meet this requirement.
5. The head of the pump: If it is a one-to-one use of a single machine, the head of the pump should not be a problem. If multiple water-cooled chillers are connected in parallel to form a system for multiple cooling equipment applications, the resistance of the piping system needs to be taken into consideration to calculate how much pump head needs to be configured.
6. Requirements for control and regulation: generally refers to pressure control and temperature control.
7. The safety protection function requirements of the chiller: A. Compressor delay start protector B. High and low pressure protection function C. Reverse (missing) phase protection D. Compressor overload protection E. Anti-freezing protection F. Compressor overheating protection G The compressor frequently starts the protector and abnormal indicator light and various protection switches.
The evaporator is one of the four major components of the refrigeration system, and it is the ultimate embodiment of the refrigeration effect and efficiency. The evaporator is generally designed by the chiller manufacturer, and the user need not worry about it. But in order to better maintain the refrigeration system and ensure its efficient operation, the following points should be paid attention to in the use of the chiller evaporator:
1. The effect of liquid level on evaporation temperature. Due to the height of the refrigerant liquid column, the evaporation temperature at the bottom of the flooded evaporator is higher than the evaporation temperature of the liquid surface. The evaporation temperature of different refrigerants at different liquid levels is affected differently by the height of the static liquid. Regardless of the refrigerant, the lower the evaporation temperature of the liquid surface, the greater the influence of the hydrostatic height on the evaporation temperature. Therefore, only when the evaporation pressure is high, the influence of the hydrostatic height on the evaporation temperature can be ignored. When the evaporation temperature is low, it cannot be ignored. In other words, it becomes uneconomical to use a flooded evaporator at this time.
2. The possibility of freezing of the refrigerant. If the evaporating temperature is lower than the freezing temperature of the refrigerant, the refrigerant may freeze. In the last process of the refrigerant, the temperature of the refrigerant is the lowest and the possibility of freezing is the greatest. When water is used as the refrigerant, theoretically, the temperature of the inner wall of the tube can be as low as 0°C. However, for safety reasons, the temperature of the inner wall of the pipe at the outlet end of the last process is usually kept above 0.5°C. In the case of brine as the refrigerant, according to the same principle, the temperature of the inner wall of the tube should be higher than the freezing temperature of the refrigerant by more than 1°C.
3. The pressure loss of the refrigerant in the evaporator. When the refrigerant flows through the evaporator, pressure loss is caused, which will inevitably make the pressure p2 of the refrigerant at the outlet of the evaporator be lower than the pressure p1 at the inlet, thereby reducing the suction pressure of the compressor, resulting in a decline in the refrigeration capacity.