North American Network Operators Group

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Re: rack power question

  • From: Petri Helenius
  • Date: Wed Mar 26 09:24:25 2008

Dorn Hetzel wrote:
I believe some of the calculations for hole/trench sizing per ton used for geothermal exchange heating/cooling applications rely on the seasonal nature of heating/cooling.

I have heard that if you either heat or cool on a continuous permanent basis, year-round, then you need to allow for more hole or trench since the cold/heat doesn't have an off-season to equalize from the surrounding earth.

I don't have hard facts on hand, but it might be a factor worth verifying.
That is definitely a factor. I do know that you can run such systems 24/7 for multiple months but whether the number is 3, 6 or 8 with the regular sizing I don't know. Obviously it also depends on what's the target temperature for incoming air, if you shoot for 12-13'C the warming of the hole cannot be more than a few degrees but for 17-20'C one would have double the margin to play with. It's also (depending on your kWh cost) economically feasible to combine geothermal pre-cooling with "traditional" chillers to take the outside air first from 40'C to 25'C and then chill it further more expensively. This also works the other way around for us in the colder climates where you actually need to heat up the inbound air. That way you'll also accelerate the cooling of the hole.

I'm sure somebody on the list has the necessary math to work out how many joules one can push into a hole for one degree temperature rise.