Calculating Cooling Loads

Calculating chiller and cooling tower refrigeration in tons

Cooling towers tons pairs the water-cooled chiller tons and the water-cooled condenser tons. 

Chiller Refrigeration Tons

A water-chiller refrigeration ton is defined as:

1 refrigeration ton = 1 TONS_cond = 12,000 Btu/h = 3,025.9 k Calories/h = 12,661 kJ/h

A ton is the amount of heat removed by an air conditioning system that would melt 1 ton (2000 lbs.) of ice in 24 hours:

288,000 BTU/24 hr = 12,000 BTU/hr

Converting Btu to Tons of Refrigeration

Btu per hour	Tons of Refrigeration
6000	1/2
12000	1
18000	1 1/2
24000	2
30000	2 1/2
36000	3
42000	3 1/2
48000	4
54000	4 1/2
60000	5

Cooling Tower Tons

A cooling tower ton is defined as:

1 cooling tower ton = 1 TONS_evap = 1 TONS_cond x 1.25 = 15,000 Btu/h = 3,782 k Calories/h = 15,826 kJ/h

The equivalent ton on the cooling tower side actually rejects about 15,000 Btu/h due to the heat-equivalent of the energy needed to drive the chiller's compressor. This equivalent ton is defined as the heat rejection in cooling 3 U.S. gallons/minute (1,500 pound/hour) of water 10°F, which amounts to 15,000 Btu/hour, or a chiller coefficient-of-performance (COP) of 4.0 - a COP equivalent to an energy efficiency ratio (EER) of 13.65.

Heat Load and Water Flow

A water systems heat load in Btu/h can be simplified to:

h = c_p ρ q dt

    = (1 Btu/lb_m ^oF) (8.33 lb_m/gal) q (60 min/h) dt

    = 500 q dt         (1)

where

h = heat load (Btu/h)

c_p = 1 (Btu/lb_m ^oF) for water

ρ = 8.33 (lb_m/gal) for water

q = water volume flow rate (gal/min)

dt = temperature difference (^oF)

Example - Water Chiller Cooling

Water flows with 1 gal/min and 10^oF temperature difference. The ton of cooling load can be calculated as:

Cooling load = 500 (1 gal/min) (10 ^oF) / 12,000

    = 0.42 ton