Sizing

Sizing by Nominal Tons

There are three basic selection methods you can use to size a chiller. The first and the easiest is to size by nominal systems tons. The second method is to use compressor capacity. The third and recommended method is sizing by range, low and approach.

Sizing by nominal tons is done according to ARI standards. Chillers can be selected on a nominal system tons basis, as shown in the catalog, or reflected in the model name. For example, an TXB–50–2 is a nominal 50 ton dual–circuit barrel.

Nominal ton ratings are based on the conditions of ARI Standard 480 utilizing R–22, which are:
54° F water in
44° F water out
35° F refrigerant temperature
7° superheat
0.00025 additive fouling factor (0.0005 total)
100° F liquid refrigerant entering the low control

This method is reasonably accurate for sizing air–conditioning systems. However, it is not recommended for evaporating temperature below 34° F, or when the fluids used are other than water and R–22.

Sizing by Compressor Capacity

You may also size by compressor capacity. Compressor manufacturer performance curves of compressor Btu per hour data can be used to select chiller barrels for a given system. By reading the performance curve for the compressor at the conditions that you require, you can determine the maximum capacity of the chiller barrel you will need.

Sizing by Range and Flow

The most precise way to size a chiller barrel when water is used is by range and low, as seen in this formula.
Btu/hr capacity = Range x gpm x 500
To obtain the Btu per hour capacity, just multiply the