Water-Cooled Chiller
Understand how the water-cooled chiller works. Explore component overviews, measurements, and additional resources.
Overview
The water-cooled chiller system produces chilled water through the basic refrigeration cycle and consists of an evaporator, a compressor, a condenser, and an expansion valve. The system can be constant-speed or variable-speed.
A constant-speed water-cooled chiller has a compressor motor that runs at a constant speed based on the total capacity of the chiller and adjusts the refrigerant flow with modulating vanes in the compressor when partial capacity of the chiller is needed.
A variable-speed water-cooled chiller has a variable frequency drive on the compressor motor and can reduce the speed of the compressor during partial load conditions.
Components
Compressor
The compressor increases the temperature and pressure of the refrigerant between the evaporator and condenser sections of a chiller. Water-cooled chillers typically have centrifugal compressors which can be driven with a constant-speed or variable speed motor.
Evaporator
The expansion valve depressurizes the warm refrigerant between the condenser and evaporator to reduce the temperature of the refrigerant. Then, the cold refrigerant is delivered to the evaporator to pick up more heat from the chilled water loop.
Condenser
The condenser rejects heat from the refrigerant to the condenser water loop through a heat exchanger.
Expansion Valve
The expansion valve reduces the pressure in the refrigerant, allowing it to collect heat in the evaporator.
How do I…
Assess System Energy Usage
The chiller is one of the largest energy-consuming systems in a cooling plant The primary energy consumption in a water-cooled chiller is the electricity used by the compressor motor.
Quantify Electricity Usage (kWh)
Measure the hourly average true RMS power draw of the chiller package, evaporator chilled water entering and leaving temperatures (chilled water supply and return), chilled water flow rate, outdoor air temperature and relative humidity.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure the chiller package hourly true RMS power draw in kW.
Use this technique to measure hourly outdoor air temperature.
Use this technique to measure hourly outdoor air relative humidity.
Use this technique to measure hourly temperature of chilled water entering and leaving the evaporator or chilled water supply and return temperatures.
Use this technique to measure hourly flow of chilled water in the loop (gpm)
Borrow Equipment and Download Calculator
Reserve loggers, download the calculator, and enter your measured data.
Water-Cooled Chiller Energy Calculator
Provides the coefficient of performance (COP) of a water-cooled chiller.
Measurement Locations
Assess System Performance
The thermal energy rejected by the chiller to the outdoors can also be measured to evaluate the overall performance of the chiller, which can be expressed as kilowatts of power consumption per ton of cooling provided (kW/ton).
Quantify the cooling load delivered and heat rejected to the outdoors (Btu)
Measure the supply and return water temperatures of the chilled and condenser water loops. Additional measurements of water flow rate should be taken of both water loops.
How to Measure
Click any measurement below for detailed setup, data collection, and troubleshooting instructions.
Use this technique to measure hourly temperature of chilled water entering and leaving the evaporator and condenser.
Use this technique to measure hourly flow of chilled and condenser water in the loop (gpm).
Measurement Locations
Further Reading
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 38. COMPRESSORS. I-P Edition.
Consulting Specifying Engineer (2021). “Understanding chilled water plant performance”. Consulting - Specifying Engineer | Understanding chilled water plant performance (csemag.com).