On Oct 30, 8:26*pm, Joseph Gwinn wrote:
...
Well, when this issue was hot some years ago, I measured the thermal
time constant of my then house, which was built in 1896. *The test is
simple: *

In the winter, heat house to 90 F, turn the boiler off, and record the
declining temperature periodically. *The time constant (to 1/e of temp
difference between 90 and outside ambient temperature) was an hour or
two, if memory serves. *

So, for my then house, it made sense to reduce the temperature if one
would be away for more than about 5 hours.

It turned out that the temperature decline curve was well described by a
simple exponential curve, plotting as a straight line on log-linear
paper. *This implies that the thermal mass of the wall and ceiling
plaster and to a lesser degree the wood floors dominated, and these
swamped all the other thermal storage mechanisms.

Joe Gwinn- Hide quoted text -

- Show quoted text -

If you read my Google Groups posting you'll see I did the same and
found a cooldown rate of 2% - 3% of the in-out difference per hour,
another way to state the exponential nature of Newton's Law of
Cooling. I've also measured the heating rate, and I think that those
two rates are enough to predict the likely savings for setback
routines and let you select a good one before making lengthy
measurements.

I don't have a multichannel temperature datalogger yet and recording
only 10PM and 6AM temperatures doesn't catch a rapid temperature drop
outside until clouds form and stop it, or how long the stove burns.
During the day solar gain is an unknown. For my house I think it's
equivalent to adding 10 - 15F to the outside air temperature.

Pyotr, you can reduce electric water heating cost with a tempering
tank that effectively uses your main heating system to bring cold
water to room temperature, or by shutting off the lower element to do
the same internally. On my tank the non-adjustable upper quick-
recovery thermostat heats to the right temp for a shower with no cold
mixed in. My sink-spray shower hose limits demand enough that the
element can keep up. Last month I used 33 KWH for showers and laundry
(no solar hot water).

jsw