On Dec 8, 6:57 pm, Doug Winterburn wrote:
Kenneth wrote:

Hello to all (again),

Well, I am the OP on this "Will I save if I use a thermostat
setback on my geothermal system" thread, and I believe that
I now have an answer:

Part of the hassle I faced in experimenting with this was
that for some reason, I kept thinking only of my house. We
have a number of electrical appliances there that are used
(essentially) randomly, and their use would certainly throw
off any comparisons that I could make over a relatively
short period of time.

I commented on that to my wife, and she said "So do the
experiment in the barn." (She did not actually say "So do
the experiment in the barn, you idiot", but that is what I
heard.)

Our office-barn is heated with exactly the same system as is
our house (water to air geo with no backup resistance heat)
and there is no variability of electrical consumption other
than the heating system for most of each day.

So, with that information, I did a very simple experiment. I
have run it only for six days but, as you will see, the
pattern seems quite clear:

I set the programmable thermostat to drop the "call heat"
temperature by 10 degrees F for 12 hours on alternating
nights.

Each morning, at the same time, I read the barn's electric
meter.

Finally, I got the degree days, and wind speed, from a
weather service site.

With that, I could calculate the ratio of KWH to Degree Day.
I have also included in the table below the reported max
wind speed for the day.

KWH/DD WS

Day 1: 1.2 (setback) 14

Day 2: 1.6 (no setback) 17

Day 3: 1.0 (setback) 8

Day 4: 1.3 (no setback) 0

Day 5: 1.0 (setback) 12

Day 6: 1.2 (no setback) 3

So, on the days with setback, the mean KWH/DD was 1.06. On
the days with no setback, that mean was 1.36.

The resulting savings are approximately 22%.

I do remain baffled by the reasons the geothermal folks
(installers, designers, sellers) seem to be consistent in
suggesting that such setbacks are not of value.

All the best,

I'm wondering if your savings aren't as great as you think. The reason
is that on a setback day, you have zero electrical usage as the house
coasts down to the setback temp. The next day's usage gets nailed with
the recovery time usage. Perhaps week long vs day long alternating
periods might mitigate some of this effect?

So long as he reads the meter after his house i swarmed up,
it doesn't matter. But it should be well after it has warmed up
as lingering cold spots away from the thermostat will have the
effect you suggest. It would be better to read the meter at the
same time every night, right before the setback.


--

FF