Water-Cooled Chilled Water Plant
Understand how the water-cooled chilled water plant works. Explore system overviews, measurements, and additional resources.
Overview
A water-cooled chilled water plant consists of a water-cooled chiller system, a condenser water loop system and a chilled water loop system operating to meet cooling demand in a facility. If a waterside economizer is implemented in the facility, the chilled water plant includes a waterside economizer system as well.
Systems
Water-Cooled Chiller
A water-cooled chiller produces chilled water using the basic refrigeration cycle, which is then distributed through the chilled water loop to the facility.
Chilled Water Loop
A chilled water loop system consists of a closed loop distribution system that supplies chilled water to the building and includes components.
Condenser Water Loop
A condenser water loop consists of an open loop distribution system that circulates condenser water from a chiller condenser to a cooling tower where the condenser water is cooled and returned to the chiller condenser.
Waterside Economizer
Waterside economizers may use an external plate-and-frame heat exchanger between the condenser and chilled water loop, or the chiller itself may be set up to perform the function of a waterside heat exchanger.
How do I…
Assess Plant Energy Usage
The primary source of energy consumption of a water-cooled chilled water plant are the chillers. Chilled water pumps are also substantial and consistent users of energy within the plant. The condenser water pumps and cooling tower fan energy should be quantified as well to provide a complete assessment.
Quantify Electricity Usage (kWh)
Determine the total amount of electricity used to operate all the chillers, pumps and fans in the plant.
Equipment to Measure
What to Measure:
- Average hourly true RMS power draw (kW) of the chiller package.
What to Measure:
- Average hourly true RMS power draw (kW) of the chilled water pumps.
What to Measure:
- Average hourly true RMS power draw (kW) of the condenser water pumps.
- Average hourly true RMS power draw (kW) of the cooling tower cells.
What to Measure:
- Average hourly true RMS power draw (kW) of the waterside economizer heat exchanger water pumps.
Measurement Locations
Assess Plant Performance
The thermal energy rejected from the building to the outdoors can also be measured to assess the plant’s overall performance, typically expressed in kilowatts of power consumed per ton of cooling provided (kW/ton).
Quantify Evaporator Thermal Load (Btu)
Determine the cooling load on building / heat rejected to the outdoors.
Equipment to Measure
What to Measure:
- Average hourly flow rate (gpm) of chilled water in the loop
- Average hourly temperature (°F) of chilled water supply
- Average hourly temperature (°F) of chilled water return
Measurement Locations
Quantify Cooling Plant Coefficient of Performance (COP)
Determine the cooling load on building / heat rejected to the outdoors
Equipment to Measure
Chiller Evaporator
What to Measure:
- Average hourly true RMS power draw (kW) of the chiller package.
- Average hourly temperature (°F) of chilled water supply.
- Average hourly temperature (°F) of chilled water return.
- Average hourly flow rate (gpm) of chilled water in the loop.
Further Reading
ASHRAE (2019). “ASHRAE Handbook: HVAC Applications,” Chapter 43. SUPERVISORY CONTROL STRATEGIES AND OPTIMIZATION. I-P Edition.
ASHRAE (2019). “ASHRAE Handbook: HVAC Applications,” Chapter 48. DESIGN AND APPLICATION OF CONTROLS. I-P Edition.
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 38. COMPRESSORS. I-P Edition.
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 40. COOLING TOWERS. I-P Edition.
Consulting Specifying Engineer (2021). “Understanding chilled water plant performance”. Consulting - Specifying Engineer | Understanding chilled water plant performance (csemag.com).
Taylor, S (2012). “Optimizing Design & Control of Chilled Water Plants Part 5: Optimized Control Sequences”. ASHRAE Journal, Vol. 54, No 6. American Society of Heating, Refrigerating and Air Conditioning Engineers; pp: 56-74.
Taylor, S (2014). “How to Design & Control Waterside Economizers.” ASHRAE Journal, Vol. 56, No 6. American Society of Heating, Refrigerating and Air Conditioning Engineers; pp: 30-36.