Programable Thermostats and Radiators
coffeymaker
| Posted in Energy, Heating & Insulation on
I have hot water heat (cast iron radiators) throughout my house. In an effort to keep energy cost down, I installed a programmable thermostat, the idea being I could lower the heat setting when no one was home. The problem is, the house takes so long to heat up (and I have my “at home” setting at a miserly 65 degrees) that I’m ready to go to bed by the time the house gets to the target temp. Is the programable thermostat doing any good? Am I better off keeping the house at a constant temp?
I’ve done all the routine maintenance on the system, and I’m pretty confident in the house’s insulation.
Replies
Some of the better one has adaptive or smart setbacks that adjust the time so that the temperature changes start early so that they reach desired temp at the scheduled time. Cheap one start the change at the scheduled time.
And some have setup switch or program mode for hot water heating. So if yours has that make sure that it is set.
Now if the house also has a slow cool down period yes you can save money.
But you probably need to play with the settings.
Say if you get home at 6 pm then start the warm up at maybe 3 or 4 pm. And then if you go to bed at 11 pm set the cool down period at maybe 9 pm.
William the Geezer, the sequel to Billy the Kid - Shoe
In my experience the 'adaptive' setback stats didn't work. 15+ years ago, I bought a Honeywell Chronotherm III which supposedly had adaptive intelligence to turn it on at the right time. It seemed like it was always coming on at 2 am to start its thing early enough to be up to temp ... fine as long as by 6 it was at temp just in time to shut off, but it would shut off after like 45 minutes! ... meaning it reached setpoint WAY to early ... so I dissabled that and simply had it come on at the time I thought it would take to reach setpoint when I wanted to get up (e.g. 5:00 or 5:30).
Maybe I didn't give it a chance to learn, but I would figure it would learn pretty fast ... starting by coming up a bit short rather than long. Either way it didn't seem to do its thing right. I tend to be a a bit of a skeptic. Maybe the newer ones are better. The Chronotherm was supposed to be the best at the time. I liked it otherwise .... easy to operate.
Maybe I didn't give it a chance to learn, but I would figure it would learn pretty fast ... Either way it didn't seem to do its thing right.
Be wary of artificial intelligence (an oxymoron?). Remember what happened with HAL?
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Yup ... I remember. It should be generally fairly simple sequence of gathering some simple information. Things are always simple in concept.
I have a similar setup except I have hot water baseboards instead of cast iron radiators. I installed programmable thermostats and played around with cycling the temps. Target home temp is 68 oF, setback for sleep and work is 63 oF. I found that I have to program the heat to ramp up about 1-2 hours before I want the target temp. I tried larger setbacks than 5 degrees but it took too long to warm up. However, even with the 2 hour warmup period it is still quite a bit more efficient to cycle the house temp. Typically I see 0.21 CCF/HDD using the cycling protocol, and 0.28 CCF/HDD if I just leave the thermostat at 68. I have a 95 y.o. house and I'm hoping that if I can insulate the walls one day the cycling protocol would be even more efficient.
Generally that is a bad idea with a system like you've got. Those thermostats work better with quick responding systems like fin tube radiators. You've got too much water and too much mass to heat up.
If you have adequate radiators, I find it more economical to lower the water temperature from the boiler and let it circulate almost continuously, rather than trying to use a setback thermostat.
I just responded to another similar question from someone with a similar system. He was having the same problem that you have.
You cannot let (maybe hundreds) of gallons of water cool off and then expect it to heat up right away when you want heat.
Thermostat set-back, whether manual or programmed, does not offer much savings with high-mass buildings or high-mass heaters, such as cast iron radiators or radiant concrete slabs.
The additional heat required to bring the space back up to temperature is the same as the heat saved during cool-down, so the only savings is during the "plateau" time between cool-down and warm-up cycles.
If the building takes long to cool and long to warm, then there's very little savings in between when the delta-T is lower.
For the typical low-mass home, the savings are approximately 1% per °F per 8-hour set-back.
Solar & Super-Insulated Healthy Homes
Check out the Honeywell programmables with Adaptive Intelligent Recovery. Over the course of a few days it "learns" how your system performs and starts the recovery period at the right time so you reach the set point at whatever time you desire. In other words, you set the time you want the recovery to be complete, not when it starts.
I have CI radiators and a programmable thermostat. Setting the temp back works for me, but then my house takes about an hour to warm up. The "smart" thermostat sounds great, but I use a low tech method of programming my thermostat to kick up the heat about an hour before I need it, and shut it down about an hour before I go to bed or leave for work or whatever. Low tech but it works.
I've got a 100 year old house with HW rads and I have been turning the boiler off and on depending on time of day etc. Last month my bill was about $300. I have another building with a similar heating system that used to cost about 5% less to heat but last month it cost about $500. So I figure I saved about $200 by turning the boiler off and on. The electric bill is down as well and I expect my circulator pumps to last longer.
Another vote for the Honeywell stats that "learn" how long it takes the house to heat up. I find it takes about a week or to get it right. The only thing you need to experiment with is the sleep time, since you can tell it to sleep early if the house will hold heat for a while.
Pete
Edited 12/17/2008 10:52 pm ET by PeteBradley
The problem is...with a system like his, the fancy thermostat will soon learn that it has to kick up the heat shortly after it gets shut down because it will take that long to heat the place back up again.
Of course, all of this depends on a lot of things....insulation, boiler efficiency, heating mass etc. etc.
The same principle applies with the Wirsbo radiant heat thermostats. They work very well to help control temperatures with high mass systems.
One more for the Honeywell "smart" thermostat.
Also...what is your low setting? You said it only needs to kick up to 65.....but from where?
A drastic change in temps will end up using more energy than leaving it at a constant setting.
J. D. Reynolds
Home Improvements
I don't think it is correct to say that a drastic change in temperature uses more energy than maintaining a constant setting. I think what actually happens is that you may not reduce your energy use as much as you might think by having a really low cool setting in comparison to your warm setting. Even though the heating system has to run longer to bring the temperature back up from a low cool setting (as compared to a moderate cool setting), that also means it remains idle longer as the temperature is falling down to the cool setting. So it's a wash, in that regard.This very subject became a debate the other day among some friends, me among them. We never reached a consensus :)
Yeah....its' been debated here many times over the years as well....without consensus also.
Wanna talk roof venting?
{G,D & R}
J. D. Reynolds
Home Improvements
Talk about roof venting?Actually, someday, yes! :)My 1890 house has no ridge vent or soffit vents. It's got a regular DH window in the gable on the front of the house and two knee high fixed sash windows in the gable on the back side of the house. Years ago someone created venting by replacing the top sash in the front window and one of the back windows with louvers and screens. The attic floor is filled in with blown in cellulose and covered with tongue and groove flooring. No insulation in the rafter bays.I want to believe that if I could get that attic better insulated and closed off that I'd save a lot of heat. But then I figure I'd rot my roof with all the moisture that couldn't go anywhere.
Edited 12/18/2008 11:20 am ET by JohnPJackson
It depends on whether you can make use of the stored energy at the end of the warm cycle or not..
William the Geezer, the sequel to Billy the Kid - Shoe
If your thermostat intelligently stops the heating system at the correct time before the temperature is programmed to drop to the low setting then there wouldn't be any excess stored energy left in the system, correct?
"If your thermostat intelligently stops the heating system at the correct time before the temperature is programmed to drop to the low setting then there wouldn't be any excess stored energy left in the system, correct?"Yes.But I have been thinking I don't know if they are adaptive on the set back or not. I don't think that mine is, but not sure.But mine is about 3 generations old.I had a POS Hunter. First it had a 2-3 degree dead band. But the setback seemed to work OK in the fall when the room temp might drop back to only 68 (62 setpoint). But then when it got cold I would wake up in the morning and the temp might be 66.Replaced it with a Honeywell adaptive and with the same settings it would be back to temp when I got up..
William the Geezer, the sequel to Billy the Kid - Shoe
"A drastic change in temps will end up using more energy than leaving it at a constant setting."
Not true. The greater the setback the greater the savings, as long as the mass of the building doesn't prevent several hours of "idle" time between cooling and re-heating. The savings comes entirely from the lower delta-T during the "idle" phase.
http://apps1.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12720
A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 12/18/2008 11:35 am ET by Riversong
Actually, since the vast majority of existing homes have wildly oversized heat sources, I would say that not only are they not "working harder", setback recovery might be the only time such heat sources achieve anywhere near their expected, rated efficiency.Also not true in high mass heating systems. But for conventional frame, medium level insulation, un-sized heat sources, setback could be the best thing since sliced bread.In tight, high mass, well insulated, high efficiency, well sized systems... waste of time.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Just curious if your heating system has a circulator pump. I had good success several years back with the Honeywell t'stat, but only after I added a cicrulating pump to the boiler.