General Overview
An air-cooled chilled water plant consists of an air-cooled chiller system and a chilled water loop system operating to meet the cooling demand in a facility. The air-cooled chiller produces chilled water through the basic refrigeration cycle. The primary chilled water pump circulates the chilled water between the chiller and the chilled water loop. In some cases, a secondary chilled water pump distributes the chilled water produced by the chiller to air handling units (AHUs) in the building.
Air-cooled Chilled Water Plant Systems and Components
Air-cooled Chiller System
Figure 2 shows an air-cooled chiller providing chilled water to the chilled water loop system and components.
Chilled Water Loop System
A chilled water loop system consists of a closed loop distribution system that supplies chilled water to the building and includes components (see Figure 3).
Evaluation of Energy Consumption
The primary energy consumption of an air-cooled chilled water plant is the sum of the energy consumption of the components of each system. The thermal energy rejected from the building to the outdoors can also be measured to evaluate the overall performance of the plant, usually in kilowatts of power consumer per ton of cooling provided (kW/ton). Table 1 provides a summary of system component measurements and values needed to quantify the annual energy consumption and operating characteristics of an air-cooled chilled water plant.
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Plant Quantification |
Values to be Quantified |
Energy Consuming Component |
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Air-cooled chilled water plant electricity usage (kWh) |
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Cooling load on building/Heat rejected to the outdoors |
Average hourly thermal load of chiller evaporator (Btu/h) |
Further Reading
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ASHRAE (2020). 2020 ASHRAE Handbook: HVAC Systems and Equipment. Atlanta, GA: ASHRAE.
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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.
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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.