Air-Cooled Chiller
Understand how the air-cooled chiller works. Explore component overviews, measurements, and additional resources.
Overview
An air-cooled chiller consists of an evaporator, a compressor, condenser fans, and an expansion valve. The system produces chilled water through the basic refrigeration cycle. Air-cooled chillers may be customized with a variety of high-performance components, such as variable frequency drives (VFD) on condenser fans and compressors, high efficiency compressor designs, thermostatic or electronic expansion valves, condenser coils with enhanced heat transfer characteristics, optimized condenser fan design and system airflow characteristics, and digital direct control systems that optimize the energy efficiency of the chiller.
Components
Condenser fans cool down the refrigerant by forcing airflow over the condenser coils using outdoor air. A constant-speed, constant-volume (CSCV) fan uses a power-driven rotating impeller to circulate air at a single speed.
Condenser fans cool down the refrigerant by forcing airflow over the condenser coils using outdoor air. A variable-speed, variable-volume (VSVV) fan uses a power-driven rotating impeller to circulate air. Air flow rates fluctuate as required by the plant and system it serves.
Compressor
The compressor increases the temperature and pressure of the refrigerant; a chiller may have one or more compressors. Air-cooled chillers typically have screw, scroll and reciprocating compressors.
Expansion Valve
The expansion valve reduces the pressure in the refrigerant, allowing it to collect heat in the evaporator.
Evaporator
The evaporator transfers heat from the chilled water to the refrigerant.
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 of an air-cooled chiller is the electricity used for the compressor motor and condenser fan motors.
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 a kit, download the calculator, and enter your measured data.
Air-Cooled Chiller Energy Calculator
Provides an estimate of a single chiller’s annual energy usage using the coefficient of performance (COP), evaporator load and typical meteorological year (TMY3) data.
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 Cooling Load Delivered and Heat Rejected (Btu)
Measure the supply and return water temperatures of the chilled water loop, and the water flow rate.
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 or chilled water supply and return temperatures.
Use this technique to measure hourly flow of chilled water in the loop (gpm)
Measurement Locations
Further Reading
ASHRAE (2020). 2020 ASHRAE Handbook: HVAC Systems and Equipment. Atlanta, GA: ASHRAE.
Gordon, J.M.; Ng, K.C. (2000). Cool thermodynamics: The engineering and physics of predictive, diagnostic and optimization methods for cooling systems. Cambridge International Science Publishing; pp. 159-177.
Wei, J.; Reddy, T.A. (2003). “Reevaluation of the Gordon-Ng Performance Models for Water-Cooled Chillers.” ASHRAE Transactions, Vol. 109, Part 2. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers.