In article
,
Jim Wilkins wrote:
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 ...
Never touch the stuff
... 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.
The solar bump is noticeable. I could see it in phase stability plots
when I was tracking the electrical length of a cable to picosecond
precision for days. Could also see the boiler cycling on and off in the
night.
One can get the little USB temp loggers for $50 to $100. Here is the
successor to the one I have:
http://www.onsetcomp.com/products/da...s-product_page
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Joe Gwinn