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How to Select a Chiller Based on Inlet Water Temperature
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Inlet water temperature is a critical parameter that affects a chiller’s Kühlleistung and operational stability. Ignoring inlet water temperature when purchasing a chiller can result in a mismatch between cooling capacity and operating conditions or compressor damage. What is inlet water temperature? How can we choose the right chiller based on the inlet water temperature? Keep reading!
What is inlet water temperature?
Inlet water temperature refers to the temperature of the chilled water upon entering the evaporator inlet after removing heat from the equipment or process. This temperature is related to the outlet water temperature, the setpoint temperature, and the amount of heat generated by the process. Therefore, the inlet water temperature of chillers varies for different processes.
How does inlet water temperature affect chiller performance? Why should inlet water temperature be considered when purchasing a chiller?
Inlet water temperature and cooling capacity
Cooling capacity represents a chiller’s ability to remove heat from the coolant. It is directly proportional to the coolant’s flow rate, specific heat capacity, and the temperature difference between the evaporator inlet and outlet. For a constant outlet water temperature, the higher the inlet water temperature, the greater the temperature difference, and the more heat the chiller removes per unit time, meaning the greater the cooling capacity.
Inlet Water Temperature and Evaporator Load
As coolant flows through the evaporator, it exchanges heat with the low-temperature refrigerant inside. The refrigerant absorbs heat and vaporizes, lowering the coolant’s temperature. A higher inlet water temperature indicates that the coolant carries more heat energy, requiring the evaporator to absorb more heat to reach the set temperature. However, the evaporator’s heat exchange area is fixed. If the heat load exceeds its maximum heat transfer capacity, the evaporation temperature will rise, reducing heat exchange efficiency.
Inlet Water Temperature and Compressor
The compressor compresses the high-temperature refrigerant gas that has absorbed a large amount of heat and evaporated in the evaporator. Its load is related to the temperature and volume of the gas transported by the evaporator. As the inlet water temperature rises, the heat in the coolant increases. Given limited evaporator heat exchange area and a limited refrigerant residence time in the evaporator, the cooling system adjusts the expansion valve opening to increase the refrigerant flow rate to achieve the set temperature.
This increases the refrigerant’s flow rate, potentially preventing the refrigerant from fully evaporating in the evaporator before being transported to the compressor. Unevaporated refrigerant is a mixture of gas and liquid. However, compressors are designed to compress gas, not liquid. Forced compression can cause liquid hammer and damage the compressor.
Furthermore, as refrigerant flow increases, the compressor needs to compress more gas. This not only consumes more power but also increases the discharge temperature and pressure.
Inlet Water Temperature and Condensing Pressure
Condensing pressure is the pressure generated when the refrigerant releases heat in the condenser and transforms into a liquid state. It is affected by the inlet water temperature through the system load. As the inlet water temperature rises, the compressor has to compress a larger volume of refrigerant gas, which is hotter and has a higher heat content.
This increases the discharge pressure and temperature, and the temperature of the gas that the condenser has to cool also increases. While cooling conditions remain unchanged, the increased load on the condenser may not be able to remove heat quickly enough, resulting in incomplete condensation and an increase in the condensing temperature and pressure.
Because the refrigeration cycle is a continuous, closed process, this also affects the throttling of the expansion valve and the heat exchange efficiency of the evaporator, creating a vicious cycle. As a result, the chiller may consume more electricity, while cooling capacity actually decreases, lowering the COP of the equipment.
Selecting a Chiller Based on Inlet Water Temperature
We’ve found that many users, when inquiring about Industriekälteanlagen, only focus on the device’s outlet water temperature. In reality, for more stable operation, the maximum inlet water temperature under maximum heat load should be of greater concern. We typically recommend that customers allow for approximately 5°C of margin to accommodate high loads or abnormal operating conditions. If your operating inlet water temperature is 30°C and you require an outlet water temperature of 20°C, we recommend choosing a device that can maintain this outlet water temperature at 35°C.
Some users also select a chiller based on its standard cooling capacity. However, we must remind you that some chiller manufacturers claim cooling capacity based on test conditions. If the manufacturer tests at a 25°C inlet water temperature, and your actual operating inlet water temperature is 35°C, the actual cooling performance will differ significantly. Therefore, when purchasing equipment, it’s important to consider the inlet water temperature conditions under which the cooling capacity was tested.
Schlussfolgerung
Before purchasing an industrial chiller system, it’s important to consider both your actual operating conditions and the equipment’s test conditions to avoid a situation where the model doesn’t match your operating conditions upon receipt. LNEYA provides detailed selection guidance to help you understand the various factors to consider and design the optimal cooling system within your budget based on your actual operating conditions.
Contact us for chiller selection guidance.
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