Re: OT - Geothermal Heat issue...?

On Mon, 26 Nov 2007 21:44:01 -0500, Kenneth
<usenet@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Mon, 26 Nov 2007 16:44:48 -0800, "Lew Hodgett"
<lewhodgett@xxxxxxxxxxxxx> wrote:

In a nutshell, thermal inertia.

Once the system is balanced, it requires minimum energy to maintain
the balance.

Change the set point to a lower level, remain there for a while, then
return to the higher level requires a lot of thermal work.

Heat intensive industries such as steel, refineries, etc, run 24/7 for
just this reason.

Lew


Hi Lew,

I don't deny it... I just don't understand it:

(Though there may be parallels to industrial applications,
I'll stick with home heating for my example.)

For a given outside and inside temperature, the house loses
a constant amount of heat per hour, and that amount must be
replaced if we are to keep the internal temperature
constant.

If the internal temperature of the house is allowed to drop,
two things happen. First, there is the direct energy savings
because it takes fewer BTUs to keep the house at the lower
temp; but perhaps less obviously, the rate of heat loss to
the outside environment is decreased. (Because the greater
the temperature differential, the more rapid the rate of
equalization.)

So, for the eight hours or so that the interior temperature
was lowered, there are savings for two reasons: We are
providing less heat to the house, and we are losing less per
hour of what heat we do supply.

When we decide to go back to the original interior
temperature, at every stage (prior to reaching that temp)
the hourly rate of heat loss is something less than it would
be when we reach the desired internal temperature.

Now, of course, heating up the house those 10 degrees will
take a bushel of BTUs, but (unless I am way off here) that
would have to be fewer than those saved.

I well understand that the efficiency of the system goes
down as the well cools, but it seems to me that the
diminished efficiency, though regrettable, is more than
balanced by the savings at the lower temperatures.

With all of this, I may be completely out to lunch, but I'd
love to understand where I am going astray.

Thanks for any further thoughts,

I have a closed loop slinky coils in three trenches as deep as the
backhoe could dig. Covered back with the clay that came out of the
trenches. I think it is a 3 ton unit conditioning 2700 sf, a little
east of Atlanta Ga. No booster heat. Hot water heater option. When it
is extremely cold, ie 10F or extremely hot 100F the unit runs a lot.
It makes lots of hot water when the delta T is enough for the unit to
run more than a few minutes. I think the thermostat is at 74 in the
winter and 78 in the summer. My wife my cycles the thermostat a degree
when she is too cold or too hot. No 68F in the winter that I grew up
with. Warm blooded woman I married.

I have no idea if setback works as she is awake when I sleep. Rolling
the thermostat when you have people living different shifts does not
work so swell.

The neighbor down the road has a couple of geothermal units that they
zoned for the main part of the house they lived in and another zone
and unit for the extra bedrooms. They claimed power bills less than my
house even though their house was much bigger. Makes me mad enough to
finish insulating the concrete walls in my conditioned basement.

I have not thought about how dry the earth might be and how that might
affect the efficiency of the unit. Not a lot of rain over the summer.
I do know I have added dirt to the trenches once in 10 years. I need
to add a few more inches to some of the trenches close to the house as
they have settled. Settled is good suggesting better heat transfer,
maybe.

If you can get the same night to happen back to back read your power
meter. My house seems to do about 1000 kwh a month or about 38-45 kwh
per day average in the coldest of winter days. You could read the
meter before you go to bed on a normal night and read it at 8 am. Next
night assuming same wind conditions, cloud cover and night temps do
the setback and rollup. You might get your answer. Or put an
hour/minute meter on the air handler and get similar results. The
hour/minute meter might be more accurate. You could also attach
thermometers to the two water lines to see the delta T and what if any
measurable influence the setback does to the well temps.
.

Relevant Pages

  • Re: Turn thermostat down?
    ... Imagine for a minute that you have to leave house for a month. ... Factors such as insulation / heat ... proportional to the temperature difference (the exact equation will depend ... water needed to reach a given level. ...
    (rec.crafts.metalworking)
  • Re: Turn thermostat down?
    ... Imagine for a minute that you have to leave house for a month. ... Factors such as insulation / heat ... efficiency homes) it can require a multi day absence to see any savings. ... proportional to the temperature difference (the exact equation will depend ...
    (rec.crafts.metalworking)
  • Re: OT - Geothermal Heat issue...?
    ... the balance. ... For a given outside and inside temperature, ... a constant amount of heat per hour, ... If the internal temperature of the house is allowed to drop, ...
    (rec.woodworking)
  • Re: Turn thermostat down?
    ... Imagine for a minute that you have to leave house for a month. ... Factors such as insulation / heat ... reduction where savings begin, and in some cases (typically high ... with the thermostat set lower will yeild a lower internal temperature, ...
    (rec.crafts.metalworking)
  • Re: Turn thermostat down?
    ... Imagine for a minute that you have to leave house for a month. ... Factors such as insulation / heat ... efficiency homes) it can require a multi day absence to see any savings. ... proportional to the temperature difference (the exact equation will depend ...
    (rec.crafts.metalworking)
Loading