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.
Pete
