# looking for help with a design question

• 04-19-2012, 10:03 PM
rockwrangler
looking for help with a design question
Hey Guys, I am looking for some help here. My situation is I have a 120g geo storage tank, a 60,000btu water to water geo unit and a 16gpm circulator in between. I need to drop the temperature of the tank 40 degrees F. What I need to know how long will it take to cool that down. What I'm actually looking for is an equation or formula to figure this out. With an explanation if possible. Thank you in advance for any help.
• 04-21-2012, 10:50 AM
terawatt
Formula for how long will it take? Water weighs ~8.33 lbs. per gallon. A BTU is the energy needed to change the temp. of 1 lb. of water by one degree F.

heat (Btu/hr) = Flow Rate (GPM) x 500 x Temperature Difference (degrees F).

The“500” accounts for water at 8.33 lbs. per gallon x 60 min/hr. You still have a few missing variables unique to your application, more details including your environmental data and application goals would be needed to get a really accurate answer.
• 06-02-2012, 05:05 PM
hcong
I never looked into this before but like what terawatt mentioned, if seems like a conversion problem.

That 60,000 btu is actually btu per hour (btuh or btu/hr).

So...

60,000 = 16 X 500 X delta_T

delta_T = 7.5 F

Pump = 120gal X min/16 gal = 7.5 minutes

So 7.5 minutes to cool the 120 gallons of water 7.5 F or 1 min per 1 F.

Assuming you can bring down the water the same amount every run, and not taking account heat added from pump or other devices. I say 40 minutes.