Water Chiller System

What is the difference between a water chiller system and a window air conditioner?

In a window air conditioner, refrigerant is flowing through the coil that cools the room's air.

In a chilled water air conditioning system, cold water is flowing through the coil that cools the room's air.

The air conditioning machine that cools the water is called a chiller, and it will be located in a dedicated machinery area somewhere in the building, on the roof, or outside.

In the chiller, refrigerant flows through the coil that cools the chilled water.

The chilled water is pumped through a piping loop to air handlers in the spaces to be cooled, where it absorbs heat from the air that flows over the air handling coil.

The warmed up water then returns through the piping loop back to the chiller, where the heat it absorbed is released to the refrigerant flowing through the chiller's evaporator coil.

The chilled water circuit of a typical water chiller system will consist of a pump, cooling coils, expansion tank, and piping valves and controls, in a closed loop.

The temperature of the chilled water supplied to the loop will depend on the set point of the chiller.

The temperature in the spaces being cooled will be controlled by thermostats.

They will sense room temperature, and keep the room at the set temperature by controlling water flow and/or air flow through the air handler.

The compressor in the chiller unit might be a reciprocating type, a screw type, a scroll type, or it might be a centrifugal compressor.

On a water cooled chiller, water flows through the condenser to cool the hot discharge gas to condensing temperature.

On an air cooled chiller, air flows through the condenser coils to cool the hot discharge gas to condensing temperature.

An air cooled water chiller system with a reciprocating compressor will operate at pressures and temperatures very similar to those of a window air conditioner that's running in the same outdoor climate, with the same indoor room temperature.

The normal temperature for the chilled water leaving the chiller is about 44°or 45°, so the low side pressure should be equivalent to about 35° to 38° when the water is near 44° to 45°, which is only a few degrees below the design evaporating temperature for a window air conditioner.

Superheat will depend on the manufacturer's specifications, but I would expect a water chiller system with a reciprocating compressor to have 20° to 30° of superheat at the compressor inlet.

You'd look for much the same conditions in a window air conditioner.

The design chilled water temperature drop through the chiller is normally 10°, so when the supply chilled water temperature is at or near 44° to 45°, look for the chilled water to be returning to the chiller at about 54° to 55°.

Condensing pressure should be equivalent to 20° to 35° above ambient temperature.

Look for the air temperature to rise 20° to 30° through the condenser coil.

A rise of over 30° is too high.

Similar to what you'd look for in a window air conditioner.

Look for 10° to 15° of subcooling, unless the manufacturer specifies otherwise.

Once again, similar to what you'd find in a window air conditioner.

Are you troubleshooting the solid state controls on a large water chiller system?

If so, you're going to have to get a copy of the manufacturers troubleshooting guide for the controls, or else bring in a professional technician who has the manuals and knows how to use them.

With regard to water chiller system operating pressures and temperatures, you might find our Air Conditioning and Refrigeration System Evaluation Manual helpful.

It has cycle diagrams for air cooled and water cooled chillers, and guidance about evaluating a chiller's pressure and temperature readings, and operating characteristics.

With regards to maintenance, a water chiller system requires more maintenance than a standard air conditioning system, and our Chiller Maintenance page will introduce you to some important maintenance procedures.

If you're an equipment owner considering cutting maintenance costs, you might be interested in the comments on our Reduce Chiller Maintenance page, and there's a brief discussion of several proven ways to help your chiller run more efficiently on our Improve Chiller Efficiency page.

I hope this page has helped, and please feel free to contact us with any specific HVAC questions you might have, including questions about air conditioning on Guam, or refrigeration on Guam.