Calculating Heat Load for Cooling Tower...
Calculating Heat Load for Cooling Tower...
(OP)
I am replacing a Cooling Tower. I would like to calculate our current cooling load (heat load). This is the info that I have...
Temp in is 85DegF
Temp out is 74DegF
Flow is 2800GPM
...through a 10 inch pipe ( I don't think U need this info though.
I would like to know the BTUs?
or whould it have to be BTUs per minute???
I know 1 BTU is the amount of heat to raise the temp of 1 pound of water by 1 degF.
How is this calculated?
Temp in is 85DegF
Temp out is 74DegF
Flow is 2800GPM
...through a 10 inch pipe ( I don't think U need this info though.
I would like to know the BTUs?
or whould it have to be BTUs per minute???
I know 1 BTU is the amount of heat to raise the temp of 1 pound of water by 1 degF.
How is this calculated?





RE: Calculating Heat Load for Cooling Tower...
You have the heat capacity and the temperature change of the water. This is a simplified number as a portion of the incoming water evaporates to provide the cooling but it will give you a close number for your cooling load.
About 15.4 MMBTU/hr is my rough estimate.
RE: Calculating Heat Load for Cooling Tower...
RE: Calculating Heat Load for Cooling Tower...
2,800 X 500 X 11 = 15,400,000 BTU/hr, which is the same as TD2K's number.
RE: Calculating Heat Load for Cooling Tower...
heh heh, couldn't resist, sorry.
RE: Calculating Heat Load for Cooling Tower...
RE: Calculating Heat Load for Cooling Tower...
Use the formula Q = mCpdT. (excuse me all. I know you already did it
But Iam getting 15,474,921.97 Btu/Hr. This may be because I converted the values first to SI units and then reconverted back. (if so what will be the error?)
(2800gpm/60sec)*(3.785lit/gal)*4.2kJ/Kg. degC*(85-74)*5/9Deg.C = 4533.58 kW*(56.89btu/min/kW)*60 = the above figure.
The above figure is equal to 1289.57 TR (1TR = 12000BTU/HR)
This tower is a pretty big one. What is the application?
Regards,
RE: Calculating Heat Load for Cooling Tower...
Tell me if I am reading this thing right...
I measure the actual pump head (psi x2.31 = ft head).
now I go to the pump curve and move right across the graph until I hit the appropriate curve.
then I go down to the bottom of the graph from that point to see the flow rate at that head pressure! Right?
Now is the pump curve still accurate when reading way over to the right of the graph?
maybe I can email this curve to someone so you could confirm this?
RE: Calculating Heat Load for Cooling Tower...
RE: Calculating Heat Load for Cooling Tower...
First, you say "until I hit the appropriate curve." Unless this is a variable speed pump, there is only one curve that applies to your pump. If the info you have shows multiple curves, you are probably looking at different curves for different impeller diameters. Look at your pump nameplate to get the impeller diameter for your pump, and this will lead you to the right curve.
Also, you want to measure the head developed by the pump, so to be accurate, you need to take a pressure reading at the pump suction as well as the pump discharge. The head difference between the two will be the head developed by the pump.
And since you are an electrical type, you can verify your operating point by taking motor amperage, calculating BHP, and seeing if it matches the BHP curve at your calculated operating point.
---KenRad
RE: Calculating Heat Load for Cooling Tower...
The pump curve should be accurate for the range shown by the vendor. If you have to start extrapolating the curve past those end of curve points (BTDT), you can have problems. On one pump I remember, I was out more than 20% on flow from the curve versus what I got with a portable ultrasonic meter (trying to remember the exact numbers, might have been higher). When I talked to the rotating equipment engineer, he wasn't surprised at the difference given where the pump was operating (and he wasn't happy with its operating point).
RE: Calculating Heat Load for Cooling Tower...
Or maybe I am not thinking straight. Just my 2 cents.
RE: Calculating Heat Load for Cooling Tower...