# 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

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 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 ^{o}F 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 = c_{p}ρ q dt

=(1 Btu/lb_{m}^{o}F) (8.33 lb_{m}/US gal) q(60 min/h) dt

= 500 q dt(1)

where

h= heat load (Btu/h)

c_{p}= specific heat, 1 (Btu/lb_{m}^{o}F) for water

ρ = 8.33 (lb_{m}/US gal) for water

q= water volume flow rate (US gal/min)

dt= temperature difference (^{o}F)

### Example - Water Chiller Cooling

Water flows with *1 gal/min* and *10 ^{o}F* temperature difference. The ton of cooling load can be calculated as:

h = 500 (1 US gal/min) (10^{ o}F)

= 5000 Btu/h

= (5000 Btu/h) / (12000 Btu/ton)

= 0.42 ton

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