Re: OT - Geothermal Heat issue...?

On Mon, 26 Nov 2007 17:58:20 -0600, dpb <none@xxxxxxx>
wrote:

Robatoy wrote:
On Nov 26, 6:48 pm, Kenneth <use...@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Howdy,

This is way OT...(again), but:

We heat and cool our home geothermally (water to air
system.)

We would, of course, like to decrease our costs further if
we can, and so have explored the benefits of setting our
thermostat lower at those times when the house (or parts of
it) are not occupied.

The folks who designed the heating system say that with
these systems, it is best to leave the set temp unchanged.

Of course, I have asked "why", but when I do, it seems that
smoke starts to come out of the phone. In essence, they say
that it is "best" but seem unable to say why.

Might any of you know what would be best in this regard ,
and particularly whether the issue of thermostat setback is
actually any different for geothermal systems?

Sincere thanks,
--
Kenneth

If you email... Please remove the "SPAMLESS."

Cycling a building in and out of extremes will bring into play the
building's phase.
The lower extremes may force the auxiliary heating to start up (maybe
electric?).
It might be cheaper to keep things at a low wick rather than replacing
lost heat with expensive heat.

The need for the aux heat should be minimal at most for an
adequately-sized geothermal system. Some t-stats may demand it if the
temperature differential from setpoint gets too large, though, so it
should be ensured the rampup doesn't force that.

In general, the same rules apply -- a setback at night, for example,
will result in a lower average temperature so the effect is still there.

As a side note, had a ground-loop geothermal system in TN and liked it a
bunch. Am considering it for a replacement here...

Hello again,

Your reasoning is similar to mine...

We do not have any auxiliary source of heat: Our (9 ton
rated) heat pumps are more than sufficient to do the deed
even at 20 below.

For the life of me, I can't understand why the folks who
design the system say it is best (that is, less costly) to
keep the temp constant.

One possibility that I have thought of:

The cooler the water in the well, the lower the efficiency
of (and thus, the higher the costs of running) the system.

Suppose that each night, we allow the temp of the house to
drop, say, 10 degrees F.

Then, in the morning, lots of energy would have to be
extracted from the well in order to rapidly bring the house
up those ten degrees.

That would (obviously) cool the well, thus decreasing the
efficiency of the system, until the house warmed up. As a
result, the costs per BTU would go up during that period of
(relatively rapidly) re-heating the house.

Assuming that reasoning to be correct, the issue boils down
to whether the cost of that loss of efficiency is greater or
less than the savings to be had with the lower overnight
temperatures.

Thanks for any further thoughts,
--
Kenneth

If you email... Please remove the "SPAMLESS."
.

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