Calculating Cooling Loads
Calculating chiller and cooling tower refrigeration loads - 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. For commercial and industrial refrigeration systems most of the world uses the kilowatt (kW) as the basic unit of refrigeration. Some commercial and industrial refrigeration systems are rated in Tons of Refrigeration (TR, tons).
A water-chiller refrigeration ton is defined as:
1 Refrigeration Ton (RT) = 1 TONS cond = 12000 Btu /h = 200 Btu /min = 3025.9 k Calories /h = 12661 kJ/h = 3.517 kW
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
| Btu/h | Refrigeration Ton | kW |
|---|---|---|
| 6000 | 1/2 | 1.76 |
| 12000 | 1 | 3.52 |
| 18000 | 1 1/2 | 5.28 |
| 24000 | 2 | 7.03 |
| 30000 | 2 1/2 | 8.79 |
| 36000 | 3 | 10.6 |
| 42000 | 3 1/2 | 12.3 |
| 48000 | 4 | 14.1 |
| 54000 | 4 1/2 | 15.8 |
| 60000 | 5 | 17.6 |
Cooling Tower Tons
A cooling tower ton is defined as:
1 cooling tower ton = 1 TONS evap = 1 TONS cond x 1.25 = 15000 Btu /h = 3782 k Calories /h = 15826 kJ/h = 4.396 kW
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)
where
h = heat load (Btu/h)
cp = specific heat, 1 (Btu/lbm oF) for water
ρ = 8.33 (lbm /US gal) 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 10 oF 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
Typical Cooling Loads
| Type of Room | Cooling Load (ft2/ton) |
|---|---|
| Arenas | 150 - 200 |
| Classroom | 200 - 250 |
| Clean room | 100 - 300 |
| Conference room | 100 - 200 |
| Data room | 80 - 100 |
| Meeting room | 200 - 250 |
| Office | 300 - 350 |
| Residence | 600 - 700 |
Related Topics
-
Air Conditioning Systems
Design of Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.
Related Documents
-
Air Conditioner Efficiency
The ratio between heat removed and power (watt) used - EER and SEER. -
Chilled Water Systems
Chilled water system equations - evaporator and condenser flow rates. -
Cooling Load - Convert between kW/ton to COP or EER
Convert between cooling load units like kW/ton, COP and EER. -
Cooling Power vs. Airflow and Duct Sizes
Typical relations between cooling power (tons cooling), air flow and duct size -
Cooling Tower Efficiency
Maximum cooling tower efficiency is limited by the cooling air wet-bulb temperature. -
Cooling Water - Pipe Lines
Sizing cooling water pipe lines - maximum allowable flow, velocity and pressure drops. -
Heat Losses from Electrical Equipment
Heat loss from electrical equipment like switch-gear, transformers and variable frequency drives. -
Heat Pumps - Performance and Efficiency Ratings
Performance and efficiency rating of heat pumps. -
Refrigeration Formulas
Calculate compression work, coefficients of performance and more. -
Refrigeration Machinery - Required Ventilation
Ventilation required for refrigeration machinery and compressors in hot areas. -
Water Evaporator and Condenser Equations
Air conditioner heat loads and evaporator and condenser water flow rates.
