Chiller Cooling Capacity - How to calculate

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How to calculate the cooling capacity of a chiller. Chillers provide chilled water which is then used to provide air conditioning within buildings. The amount of cooling they produce varies and it’s important to know how much cooling a chiller is producing or is able to produce. There is a video tutorial at the bottom of the page also.

Firstly to perform this calculation we need to know a few things.

• The volume flow rate of water into the evaporator
• The inlet and outlet chilled water temperature

We then need to lookup the properties of water for the following

• The density of the water at the average temperature (inlet temp + outlet temp)/2
• The Specific Heat Capacity of the chilled water at the average temperature (inlet temp + outlet temp)/2

A recommended website to look these properties up is: PeaceSoftware.de

Let look at how to calculate the cooling capacity. We’ll first look at how to calculate in metric units and then imperial.

Metric units:
The water flow rate of chilled water into the evaporator is 0.0995m3/s, the inlet temperature is 12*c and the outlet temperature is 6*c. This means the average temperature is 9*c so we lookup the water properties at this temperature to find the density of 999.78kg/m3 and a specific heat capacity of 4.19kJ/kg/K.

Using the energy equation of Q = ṁ x Cp x ΔT we can calculate the cooling capacity.

Q = (999.78kg/m3 x 0.0995m3/s) x 4.19kJ/kg/K x ((12*c+273.15K) – (6*c+273.15K))

We add 273.15K to the celcius to convert it to units of Kelvin. The Specific heat capacity (Cp) is measured in units of kJ per kg per Kelvin.

This gives us a final answer of Q = 2,500kW of cooling. Full calculations are shown below.

Now lets look at how to calculate the cooling capacity of a chiller in imperial units

Imperial units:

The flow rate of chilled water into the evaporator is measured as 12,649ft3/h and the chilled water inlet temperature is 53.6*F the outlet temperature is 42.8*F. The average temperature is 48.2*F so we need to calculate the water properties at this temperature.

A good website for this is peacesoftware.de the although we will need to convert the units to imperial so for that we will use Specific heat capacity and density of water

This will give us a specifi heat capacity of 1.0007643BTU/lb.F and density of 62.414lb/Ft3

Using the energy equation of Q = ṁ x Cp x ΔT we can calculate the cooling capacity.

Q = (16,649FT3/h x 62.414lb/ft3) x 1.0007643BTU/lb.F x (53.6F – 42.8F)

Giving us a cooling capacity of 8,533,364BTU/h. see full calculations below.

For more information, please visit Kehong.

Related Resources: calculators

Net Refrigeration Capacity Equations and Calculator

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Per. MIL-PRF-32017

To calculate the RU(Refrigeration Unit) capacity the heat leakage coefficient and setup from 4.3.1 shall be used. The capacity for the (Refrigeration Unit) RU unit shall be verified to be no less than 3,000 Btu/hr using the method described below. Recorded data shall be required and shall include all specified temperature readings, electrical heat input, suction and discharge pressures, and complete calculations. All panels and doors of the ADR system shall be in the normally closed position.

a. All accessories and appurtenances shall be in their proper place.

b. Thermocouples, shielded from radiant heat, shall be installed in the air streams entering the evaporator and leaving the evaporator section.

c. Shielded thermocouples shall be located at the approximate center of four equal areas of the condenser face. The condenser inlet temperature will be taken as an average of these four temperatures.

d. Recording pressure gages shall be used for the compressor suction and discharge pressures.

f. The RU shall then be operated with air surrounding and entering the condenser section at 110°F ± 2°F, and sufficient steady, non-varying heat shall be added to the interior of the IC to maintain 0°F temperature of air entering the evaporator ± 1°F. A watt-hour meter with scale increments of 0.1 kilowatt-hour or less shall be used to indicate the quantity of electrical energy added. Air velocity shall not exceed 100 feet per minute (FPM) any point 3 feet from the ADR system.

g. The test shall be considered concluded when eight consecutive half-hourly readings indicate that:

1. The average surrounding ambient temperature T , has been maintained at a steady state of 3 110°± 2°F.
2. Return air temperature entering the evaporator, T , has been maintained at 0°F ± 1F°. 4
3. The net refrigeration capacity shall be considered as the sum of the electrical energy in Btu/hr added during this test plus the heat leakage gain in Btu/hr as calculated from the calibration specified in The Heat Leakage Test and Calculations.

The net refrigeration capacity is given by:

Q = U (T3 - T4) + H2

Preview: Net Refrigeration Capacity System Design Calculator (Membership Required: Premium).

Q = Net refrigeration capacity (Btu/hr)
U = Overall heat leakage coefficient (Btu/hr/°F)
T3 = Average ambient temperature (°F) surrounding the RU
T4 = Return air temperature (°F) entering the evaporator
H2 = Sum of all heat energy added to the IC (Btu/hr)

Note: this is a military specification, commercial application requirements can be different.

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