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
The process of cooling is called refrigeration. Refrigeration or cooling capacity can be measured in tons.
A water-chiller refrigeration ton is defined as:
1 kW = 0.2843 Refrigeration Ton (RT)
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. The heat required to melt 1 lb of ice at 32 oF to water is 144 Btu.
1 Ton Refrigeration = (2000 lb) (144 Btu/lb) / (24 hr)
= 12000 Btu/hr
Converting between Btu/h and Tons of Refrigeration
Cooling Tower Tons
A cooling tower ton is defined as:
The equivalent ton on the cooling tower side actually rejects about 15000 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 (1500 pound/hour) of water 10°F, which amounts to 15000 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 = cp ρ q dt
= (1 Btu/lbm oF) (8.33 lbm/US gal) q (60 min/h) dt
= 500 q dt (1)
h = heat load (Btu/h)
cp = specific heat, 1 (Btu/lbm oF) for water
q = water volume flow rate (US gal/min)
dt = temperature difference (oF)
Example - Water Chiller Cooling
Water flows with 1 gal/min and 10oF temperature difference. The ton of cooling load can be calculated as:
h = 500 (1 US gal/min) (10 oF)
= 5000 Btu/h
= (5000 Btu/h) / (12000 Btu/ton)
= 0.42 ton