Waterside Economizer

Understand how the waterside economizer works. Explore component overviews, measurements, and additional resources.

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Overview

A waterside economizer is used to fully or partially cool the chilled water without mechanical heat transfer when outdoor air temperatures are cold enough to meet the building’s cooling demand. Typical waterside economizer systems have an external heat exchanger; however, the chiller itself may occasionally be set up to perform the function of a waterside heat exchanger.

Components

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External Heat Exchanger

Heat exchangers transfer heat between two fluids using a temperature difference without direct contact between them. Typical heat exchangers installed in waterside economizers are plate-and-frame heat exchangers (PFHX).

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Piping, Fittings, and Valves

Piping can have different arrangements to allow the desirable operation of the waterside economizer.

info Plate-and-frame Heat Exchanger Configurations

Plate-and-frame heat exchangers can be configured as integrated and non-integrated economizers. Non-integrated configuration consists of a PFHX in parallel with chillers and requires the heat exchanger to supply the entire cooling load. In an integrated configuration, the PFHX are arranged in series allowing the chiller to utilize pre-cooled chilled water and minimizing the energy required by chillers.

How do I…

Assess System Energy Usage

Waterside economizers alter the electrical energy consumption of all the motorized components in a central cooling plant. Due to the highly interactive effects between the indoor loads, the chilled water loop, condenser water loop, chiller, and outdoor conditions, the energy calculations for a waterside economizer must be done on an hourly basis.

Assess System Performance

The performance of a waterside economizer can be determined by quantifying the amount of heat removed from the chilled water loop.

Quantify Amount of Heat/Cooling Provided to the Space (Btu)

Determine the total amount of heat removed from the chilled water loop with the heat exchanger.

Equipment to Measure

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Heat Exchanger

What to Measure

Average hourly water flow rate (gpm) of fluid 1.
Average hourly water flow rate (gpm) of fluid 2.
Average hourly temperature (°F) of fluid 1 entering the heat exchanger.
Average hourly temperature (°F) of fluid 1 leaving the heat exchanger.
Average hourly temperature (°F) of fluid 2 entering the heat exchanger.
Average hourly temperature (°F) of fluid 2 leaving the heat exchanger.

Measurement Locations

Diagram of a waterside economizer indicating measurement points. — Measurements needed to quantify the performance of a water-cooled chilled water system with waterside economizing.