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Posted by Dave on January 12, 2006 at 15:02:35:
In Reply to: Re: Programable thermostats - do they save money? posted by Heatpro on January 08, 2006 at 21:10:13:
This is a great reference, HeatPro.
I've experimented quite a bit with the amount of setback programmed in for various zones in my house. The problem is complicated a little since I have three zones on two levels, two of which are baseboard radiant and one of which is staple-up radiant.
I've monitored the time required to re-heat the house on a weekend morning using a few different schemes. My tests are far from definitive, though, as there are variables such as outside temperature that are hard to compensate for.
Of course, as HeatPro mentions, I can't give any exact recommended values since each house is different.
But, in general:
- I only setback my underfloor radiant a few degrees, since the floor mass "holds on to" heat and, likewise, takes more energy to heat it back up
- For the same reason, I keep the lowest setback temp in adjacent zones the same or higher; otherwise, the radiant zone would be losing heat the neighboring zone
- More setback is possible for my baseboard zones, since they heat up faster; the better insulated the house, the more the setback temp difference can be increased
- Likewise, I have the faster-heating zones resume heating 15-30 minutes before other zones; this way, they are helping out these other zones a little (rather than the hard-to-heat zones doing the opposite)
- Since my house isn't well-insulated, I don't reheat in the morning before I go to work; in other words, it's not worth reheating for just 60-minutes are so as I'm getting ready
- The colder the weather, the more energy it takes to heat the house back up after setback; when it's really cold, I use less setback (again, this depends on how well insulated the house is)
- Also, you can use the sun to your advantage be starting having your thermostat programs start back up after 2-pm in the winter (if you use setback during the work day); this can be significant if you have a lot of southern windows; this way, your house gets a jump start from the sun
- At night, don't start your setback at the same time you go to sleep - start it 30- to 60-minutes before; your house won't cool off that fast, and you'll cut back on one or two firing cycles
This is all pretty qualitative, but it's a complicated question. To me, it's not a question of using setback or not - it's a question of how much setback, when to program the setback and reheat intervals, and in what order to reheat zones in my house. You just have to think it through and set your alarm clock on a couple Sat and Sun mornings to watch how much your boiler is firing for a couple different setback scenarios. Do I need a life, or what?
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