Calculating the GPM to Cool a 250,000 BTU Coil

Assume that the water leaving the coil is 60F giving you a delta T of 10F. Divide btu/hr by 500 and by the 10F delta, or divide btu/hr by 5000.

1 BTU is the energy required to raise 1 pound of water 1 degree F.

The GPM will be dependant upon the heat transfer efficiency of your chilled water cooling process, and can't be known by someone in this forum without much more information or empirical data.

I assume you mean you have a coil from which you wish to remove 250,000 Btu/hr. Such a rating has to be based on some temperature difference between the media inside and outside as well as a heat transfer coefficient.

Any consistent set of units can be used. I use english units below.

The formulas you need are as follows:

Q=M*Cp*dT = U*A*dT2

M*Cp*dT is the energy transferred into the heat transfer media. You can trade-off flow for dT and achieve the same heat transfer.

U*A*dT is essentialy states the capacity of the heat transfer surface to move heat form one side to the other.

Q = heat flow (Btu/hr)

M = mass flow of heat transfer media (#/hr)

Cp = heat capacity (Btu/# F)

dT = entering temp - leaving temp

U = overall heat transfer coefficient (Btu/hr ft2 F)

A = heat transfer area (ft2)

dT2 = inside coil temp - outside could temp (use an average or log mean)

1/U = 1/hi = 1/ ho

hi = inside heat transfer coefficient

ho = outside heat transfer coefficient.

values for U, hi and ho can be estimated from relevant tables, empirically measured, or calculated. To calculate, I woudl start with the Seider Tate equation which you can find on-line.

What brand of coil? Website? Books on shelf? Tables will tell pump size h.p. & g.p.m. have you people ever heard of K.I.S.S. principle. If you don't know some of the info., compare sizes, passes, etc. to Trane coil of same. They have great literature to source.