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I think some have said that the setback thermostats
don't save much energy, not that the setback doesn't (but perhaps I missed a
post or two). One reason setback thermostats don't save as much as is often
predicted is that those who buy, install, and program setback thermostats in
many cases would have set back the temperature manually without the programmable
thermostat. The savings come from the set back itself, not from the
PT. So while a PT may make things easier, those already practicing manual
set back often won't see big savings from a PT.
It does take more energy to warm a space with high
mass, but that doesn't mean setback isn't a good idea. The amount of heat
a space loses--i.e., the amount of heat you pay to create in the space--is
proportional to the temperature difference inside/outside. The lower the
temperature difference, the lower your heat loss. You will
require energy to warm the space back up, but it will be less energy than
it would have taken to keep the space warm. With a large amount of mass,
recovery might also take a long time. This lag is what makes setback more
difficult with high mass hydronic radiant systems. If you need to warm the
space on a moment's notice with such a high mass system, you're out of
luck. But if the space's use is more predictable you can use setback and
see savings.
I don't know if this answers your
question.
--Mike
Several responders noted that they saved
no energy from setting back their nighttime temperatures (in
contradiction to your opener that it will almost always save
energy). Care to hazard a guess as to why?
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