Condenser Water Loop
Understand how the condenser water loop works. Explore component overviews, measurements, and additional resources.
Overview
A condenser water (CW) loop consists of a CW pump and motor, an evaporative cooling tower with a fan and motor, and a CW piping network. The CW loop system is designed to reject the heat given off by the condenser side of the chiller.
Components
Condenser Water Pump and Motor
A condenser water pump and motor circulates condenser water from the condenser section of the chiller to the cooling tower. A condenser loop pump and motor can be constant speed or equipped with variable frequency drives (VFDs).
Condenser water pumps can operate at:
Evaporative Cooling Tower
An evaporative cooling tower rejects heat from the condenser section of the chiller, using forced airflow and the latent heat of evaporation to provide the cooling effect on the condenser water. A cooling tower may have one or more sections (called cells). Each cell typically has one fan and motor.
The cooling tower fan can operate at:
Condenser Water Piping Network
The condenser water piping network carries the condenser water from the chiller condenser to the cooling tower to the reject heat to the outdoors.
Typical CW Loop Configurations
A CW loop can have different configurations. Below are the common configurations, how they work, and how to quantify the entire system.
Variable-Speed Fans and Constant-Flow CW Loop
A variable-speed constant-flow CW loop consists of variable-speed cooling tower fans and constant-speed CW pumps.
Cooling towers with variable speed fans and motors generally operate the fans at the lowest speed possible and stage fans based on the overall CW heat rejection needed to satisfy the specific sequence of operation of the chilled water plant.
A constant-speed condenser pump provides a fixed flow to the cooling tower and chiller, independent of cooling tower heat rejection capacity or building cooling load.
How Do I...
Assess System Energy Usage
The primary energy consumption of a condenser water loop is the electricity used for the pump motors and the cooling tower fans.
Quantify Electricity Usage (kWh)
Determine power draw of pump motor and total operating runtime.
Equipment to Measure
Constant flow system.
What to Measure:
- Hourly motor runtime (minutes) of the pump motor.
- Average of spot measurements of true RMS power (kW) of the pump motor.
Variable speed.
What to Measure:
- Average hourly true RMS power (kW) draw of the fan motor.
- Total operating time (hours) of the fan.
- Average hourly outdoor air temperature (°F).
Measurement Locations
Assess System Performance
The performance of the condenser water loop system is dependent on the amount of heat rejected to the outdoors by the cooling towers.
Quantify Heat Rejected to the Outdoors (Btu)
Determine condenser water flow rate and the cooling tower entering and leaving temperatures.
Equipment to Measure
Condenser Water Loop
What to Measure:
- Average hourly flow rate (gpm) of condenser water in the loop.
Cooling Tower Cell
What to Measure:
- Average hourly condenser water temperature (°F) entering the cooling tower.
- Average hourly condenser water temperature (°F) leaving the cooling tower.
Measurement Locations
Variable-Speed Fans and Variable-Flow CW Loop
A variable-speed variable-flow CW loop consists of variable-speed CW pumps and a cooling tower with variable-speed fans.
Cooling towers with variable speed fans and motors generally operate the fans at the lowest speed possible and stage fans based on the overall CW heat rejection needed to satisfy the specific sequence of operation of the chilled water plant.
A variable-speed CW pump and motor modulates the flow to the cooling tower and chiller based on the heat rejection capacity of the cooling tower and the minimum flow rate required through the condenser section of the chiller.
How Do I...
Assess System Energy Usage
The primary energy consumption of a condenser water loop is the electricity used for the pump motors and the cooling tower fans.
Quantify Electricity Usage (kWh)
Determine power draw of pump motor, outdoor air temperature and total operating runtime.
Equipment to Measure
Variable flow system.
What to Measure:
- Average hourly true RMS power (kW) draw of the pump motor.
- Total operating time (hours) of the pump.
- Average hourly outdoor air temperature (°F).
Variable speed.
What to Measure:
- Average hourly true RMS power (kW) draw of the fan motor.
- Total operating time (hours) of the fan.
- Average hourly outdoor air temperature (°F).
Measurement Locations
Assess System Performance
The performance of the condenser water loop system is dependent on the amount of heat rejected to the outdoors by the cooling towers.
Quantify Heat Rejected to the Outdoors (Btu)
Determine condenser water flow rate and the cooling tower entering and leaving temperatures.
Equipment to Measure
Condenser Water Loop
What to Measure:
- Average hourly flow rate (gpm) of condenser water in the loop.
Cooling Tower Cell
What to Measure:
- Average hourly condenser water temperature (°F) entering the cooling tower.
- Average hourly condenser water temperature (°F) leaving the cooling tower.
Measurement Locations
Constant-Speed Fans and Constant-Flow CW Loop
A constant-speed constant-flow CW loop consists of constant-speed cooling tower fans and constant-speed CW pumps.
The overall cooling capacity of the condenser water loop in a cooling tower with multiple cells and constant speed fans and motors is controlled by staging (turning on) the cells.
A constant-speed condenser pump provides a fixed flow to the cooling tower and chiller, independent of cooling tower heat rejection capacity or building cooling load.
How Do I...
Assess System Energy Usage
The primary energy consumption of a condenser water loop is the electricity used for the pump motors and the cooling tower fans.
Quantify Electricity Usage (kWh)
Determine power draw of pump motor and total operating runtime.
Equipment to Measure
Constant flow system.
What to Measure:
- Hourly motor runtime (minutes) of the pump motor.
- Average of spot measurements of true RMS power (kW) of the pump motor.
Constant speed.
What to Measure:
- Average hourly true RMS power (kW) draw of the fan motor.
- Total operating time (hours) of the fan.
Assess System Performance
The performance of the condenser water loop system is dependent on the amount of heat rejected to the outdoors by the cooling towers.
Quantify Heat Rejected to the Outdoors (Btu)
Determine condenser water flow rate and the cooling tower entering and leaving temperatures.
Equipment to Measure
Condenser Water Loop
What to Measure:
- Average hourly flow rate (gpm) of condenser water in the loop.
Cooling Tower Cell
What to Measure:
- Average hourly condenser water temperature (°F) entering the cooling tower.
- Average hourly condenser water temperature (°F) leaving the cooling tower.
Measurement Locations
Further Reading
ASHRAE (2020). “ASHRAE Handbook: HVAC Systems and Equipment,” Chapter 40. COOLING TOWERS. I-P Edition.
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.