Range or Temperature Drop by gpm low, and convert to pounds of water per hour by multiplying by 500. The Btus can then be divided by 12,000 to yield the tons of load.

For example—

With a incoming water temperature of 55° F., outgoing water temperature of 45° F., and a 479 gpm water low. Btu capacity can be calculated like this:

(55° – 45°) x 479 gpm x 500 = 2,395,000 Btu/hr

2,395,000 Btu/hr ÷ 12,000 Btu/ton = 199.5 tons

Standard’s sales catalog is designed to make your selection job easy after you have determined the cooling load. Once fluid range has been determined, locate the table for that range. If no table exists, use the next lowest range.

Next, locate an acceptable approach at the top of the table and read down the tons column to the capacity that is adequate for the job.

The water pressure drop in psi is listed to the right. To determine gpm multiply tons by the gpm factor at the bottom of each range chart.

In this case, an FSX–150 will provide the duty at a 10° range and 11° approach with a 34° suction.

In cases where the fluid being cooled is other than water, capacity can be determined by adding the specific heat and specific gravity into the equation:

Btu/hr = Range x gpm x 500 x Sp Heat x SP Gravity

This equation will give you the capacity required, but chiller selection should be made by your factory representative since the fluid is not water.

All of Standard’s rating data is based on ARI standards, a suction temperature of thirty–five degrees, using water as the fluid Contact your local Standard representative for special fluid conditions.

All heat exchangers have capacity limits. Careless sizing of chiller barrels leads to needless performance problems.

Undersizing can lead to insufficient cooling and inefficient compressor operation.
Oversizing can lead to control valve hunting, poor performance, oil logging, and refrigerant slugging.