Chiller cooling output calculation in KW
I have water-cooled chiller, I need to calculate its cooling output in KW. I have chilled water flow in GPM and supply & return temperature in C.
You need to have very precise thermometer to calculate correctly cooling output.
Since dT is usually around 5K your imprecise temperature reading could lead to 30% (or even more) error.
m=mass of water
c=specific heat capacity of water
You can estimate cooling output in British Thermal Units per Hour (BTUH) via:
500 x GPM x deltaT = BTUH
Keep your units consistent. If you know the Gallons Per Minute, use Fahrenheit for the temperature scale.
Once you determine the BTUH, divide that number by 12,000 to get tonnage.
To get kilowatts consumed per ton, you measure what the machine is using in kilowatts to deliver the measured tonnage.
Example: process chiller flowing about 50 GPM with a 10 degree split between return and supply water...
500 x 50 x 10 = 250,000 BTUH
250,000/12,000 = 20 tons
Assume machine is drawing 12 kilowatts to achieve this output:
12 kilowatts/20 tons = .6 kilowatts per ton
Remember that there are 3.413 BTUs per watt, 3413 BTUs per kilowatt. So, on a one to one basis, you would need about 3.515 kilowatts per ton (12,000 BTU), but we can achieve a ton of refrigeration with less kilowatts per ton consumed than that, by far.
- Electricity makes refrigeration happen.
- Refrigeration makes the HVAC psychrometric process happen.
- HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.
A building is NOT beautiful unless it is also comfortable.
The formula for KW of refrigeration is L/s x Delta T(*C) x 4.19kj/kg (for Water)
To convert GPM to L/s GPM (div by) 60= GPS
GPS x 3.785= L/s
60 seconds in a minute
3.785 litres in a US Gallon
I have it as 3.415 BTU/ Watt
Originally Posted by shophound
Good calculations. Please clarify what is the '500' used for? I mean what does it denote?
Originally Posted by chad_nc
I know it is a constant. What I want to know is that how is it derived? it is just not a number which is assumed.
500 is a constant for water. The reason I believe is, you are dealing in GPM(minutes) and BTU/HR (hours)
60 Min. in an hour and the weight of 1 US gallon of water 8.31 lbs.
60 x 8.31 = 498.6
rounded to 500.
Process system with glycol depends on weight of 1 gall of dilluted glycol.
Thanks Bertoh, I got my answer.
Originally Posted by bertoh