PDA

View Full Version : Calculating Heating Output of A Hydronic Heating System

DerekCutler
01-31-2008, 08:06 AM
Hello All,

This is my first post on this forum and am hoping that somebody may be able to shed some light on my question. Hopefully this is the right place to post this. I am a controls technician and have worked in the HVAC/R for 8 yrs. This is the first time I have come up against this. I have a project where the engineer wants me to calculate the heat output (energy consumption) of the heating system in Btu/H. I do have a calculation to solve this but am unsure if it is providing the correct info. The formula is Btu/H = (HWR-HWS)* Flow(Gpm)*500.

My question is: Is this formula using degC or degF for the Hot Water temps?

I believe that it is looking for degC, from what I have been able to find. The project that I am working on is all degF, so I need to know what the formula would be for this. The 500 in the equation I believe is the Specific Heat Factor for water, I can only assume that this would be different if the calculation was using degF temperatures. If anybody can shed some light on this for me it would be greatly appreciated. Thanks.

DCSCO
01-31-2008, 09:52 AM
One BTU will raise one pound of water one degree. Find delta T and multiply by flow in GPM. Multiply by 60 minutes, multiply by pounds per gallon (8.3?) equals BTU/H. That's the way I've done it. Their are many configurations of this formula, they all give the same answer.

rich pickering
01-31-2008, 10:03 AM
temp is f. gpm is us gallons. specific heat depends on fluid.

jayguy
01-31-2008, 05:39 PM
I have a project where the engineer wants me to calculate the heat output (energy consumption) of the heating system in Btu/H. I do have a calculation to solve this but am unsure if it is providing the correct info. The formula is Btu/H = (HWR-HWS)* Flow(Gpm)*500.

these formulas are the amount of heat being absorbed or released by the fluid not the amount of energy consumption it took to get it there. are you just looking for the heat transfer of the fluid or the amount of heat it took to get it there?

good luck.

supertek65
01-31-2008, 07:10 PM
just go clock the meter?

airdata870
01-31-2008, 11:15 PM
btuh=gpm x 500 x deltaT deg f

8.333lbs/gal x 60 mins=500lbs/hr

water sp.ht.=1.0 btu
air sp.ht. =.24 btu/lb.

DerekCutler
02-01-2008, 01:50 PM
Thanks guys for the help. The equation that I was using was in degF so my calculation was right. The engineer should be happy to see the btu/h of heat transfer. This should indicate a basic energy consumption value. More btus/hr means that they are burning more fuel because of the increased heating output. It should give him a good indication of how high the heating demand was. The spec is very vague so I guess unless he has a better calculation this will have to do. Thanks Again.

supertek65
02-01-2008, 08:23 PM
once the thing is installed.
run it for 6 minutes and read the gas meter.
times the usage x 10

djken
02-01-2008, 08:25 PM
BTU/HR = 1.08 x CFM x ΔT
or
CFM = (BTU/HR) / (1.08 x ΔT)
or
ΔT = (BTU/HR) / (1.08 x CFM)

airdata870
02-02-2008, 12:11 AM
BTU/HR = 1.08 x CFM x ΔT
or
CFM = (BTU/HR) / (1.08 x ΔT)
or
ΔT = (BTU/HR) / (1.08 x CFM)

those are formula's for air.