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Old 01-28-14, 10:12 AM   #121
AC_Hacker
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Quote:
Originally Posted by Daox View Post
I'd recommend more of you guys try setting your temperature back farther at night. Even if its just a few degrees more, it isn't costing you anything but a minute or two to reprogram your thermostat.
Great idea there.

I usually let my heating go completely off at night and let the house drift down until morning.

But during the Arctic Vortex I, I left the oven in my gas kitchen stove on 'warm' (that is lower than 'low') to reduce the viciousness of the night cold. That was the only night heat in the house during the most frigid days of this cold snap. It was enough to give me morning temps of just under 50.

My 3/4 Ton mini-split pulled the load during the days. There were days (13F) when it was really struggling to put out 65F of the 68F it was set for, so it ran continuously.

My Degree Days data:
HDD 68F = 5293
CDD 78F = 198

My house is small at 750 sq. ft. I don't directly heat the whole house, just the living room where I spend most of my time, and I let the 'secondary heat' supply the rest of the house.

My upstairs bedrooms are completely unheated, except for what 'leaks up' from the living room.

I do use a mattress pad to pre-heat the bed and then I switch it off when I crawl in under two layers of down comforters. I leave a window open on all but the most viciously cold nights. On nights that are just slightly cold, I put a fan in the window, too. I sleep very well.

I have also started putting a miniature oil-filled heater in the mini-loo (which is also insulated on all sides) as an homage to civilization for when my girl friend comes over for a visit.


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Originally Posted by warmwxrules View Post
...One problem we do have is the amount of baths that are taken every day. Seems like several a day are becoming common this time of year (kids are like fish)...

Hey, I don't think it's a problem at all. I mean kids are not just fish... they are tropical fish! I was taking more showers during that time, it felt great!! Maybe you should follow your kid's example, you might like it.

I think that in the evolutionary sense of things our deep ancestors were tropical dwellers, and beneath our clothes and thermal systems, we're not so different.


Best,

-AC

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Old 02-06-14, 09:05 PM   #122
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I use 58F at home and awake, turn heater off at night or away from home. I did set it to 45F the lowest possible setting when I was worried about getting freezing temperatures inside at night.
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Old 02-07-14, 07:41 AM   #123
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That is pretty chilly ppd! Also, welcome to the site.
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Old 02-07-14, 08:30 AM   #124
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I leave my heat at the same temperature night & day , my theory for doing so is that the house would need to fight extra hard in the morning to bring the colder walls / ceilings and floors back up to temperature, with excessive heater run times.

Using this technique has netted me a average electric bill (baseboard heaters) of just $80 a month in a 2,000sqft split level home of which I only heat the 1000 sq-ft upstairs.
My low electric bill would suggest this technique has merit, I have been doing this for 9-10 yrs.

I almost forgot, my temperature preference is 68 degrees.

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Old 02-07-14, 09:05 AM   #125
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Excessive heater run times increasing bills is typically a myth (only exception is heat pumps that kick on resistance heater backup). Lowering the temp at night and while you're away will net you more savings. A cooler house = less heat loss. When your heaters are on, they are at 100% efficiency, so you don't even have cycling losses as some of the people with forced air have. Try setting it back when you're gone and I bet you'll see some decent savings.
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Old 02-07-14, 09:26 AM   #126
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Quote:
Originally Posted by Daox View Post
Excessive heater run times increasing bills is typically a myth (only exception is heat pumps that kick on resistance heater backup). Lowering the temp at night and while you're away will net you more savings. A cooler house = less heat loss. When your heaters are on, they are at 100% efficiency, so you don't even have cycling losses as some of the people with forced air have. Try setting it back when you're gone and I bet you'll see some decent savings.

I think this is only partially true. If the house has a lot of thermal mass, I would guess that it is probably better to leave the temperature the same, or only fluctuate the thermostat <2 degrees. For example, my parents have a 1000 sq ft ICF home with a small 1.2 ton GSHP. They went out on vacation and wanted me to house sit. They had upped the temperature by about 4-5 degrees to around 78 F in summer (74 is comfortable to me). Since I ended up sleeping there, I had to knock it back down to a more comfortable level. It took about 3-4 hours for the house to cool down, with the GSHP running the whole time.

I may be completely wrong, but I just don't know if changing the thermostat applies to high thermal mass, tight homes. I would have to look at a complete system analysis to really know and understand.
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Old 02-07-14, 09:36 AM   #127
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At this point I am going to wait till I get a heat pump as old habits have become a way of life.. My house is a split level, with a open stairway and the front door entrance is split between the two floors.
I am spoiled , I like having my house up to temperature at night as like today I'm up at 5 in the morning, tomorrow could be 7:00, i may stay up till 11:00 I may stay up till 2 either way my house will be warm. I do concede / understand how the heat loss increases with higher temperatures or in short its takes much more energy to heat a few degrees when battling the cold then it does to back it off a few..
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Old 02-07-14, 12:32 PM   #128
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Natethebrown

Set back thermostats work well when there is minimal thermal mass. My last home had some 100 tons of concrete in the thermal envelope and the decay curve was very slow.

I tested this by heating the house to 70F on a night when it was frigid and without wind. Turned off the heat pumps and recorded the exponential curve as the home cooled down that night.

Got only an 8F decay in temp. With this situation, a set back doesn't work well, especially with a geothermal heat pump.

On a customer's recent house analysis, I got almost a 25 F decay in 12 hours. Virtually no thermal mass in the home.

Recording the decay curve is part of my assessment along with blower door tests and evaluating fuel use consumption data. It has shown me where insulation is present and not.

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Old 02-07-14, 08:01 PM   #129
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There are multiple factors to using setbacks.

If you have a heating system based on an inverter heat pump, you'll be at a lower efficiency when it is running at full capacity versus coasting along. If using a standard heat pump and not using heat strips its a bit of a wash. If you've got heat strips you are really losing out.

If your heat capacity closely matches design load and you are close to the design load you need to balance the setback depth to the time that you set the thermostat to restore your temperature prior to getting home. If you are heating with natural gas or propane you are most likely a great candidate for setback because these systems are almost always oversized because of their size increments being in 20k differences and the smallest 95+% condensing furnace is a 40k unit and even that is enough for a fairly deep setback. I have a furnace with a 57k output and I can recover 12 degrees in an hour even when it is -10 degrees F outside, my heat load at -13f is 17k and my house is 2100 square feet, I'm at a definite oversize. I'd be comfortable with a 20 degree setback set to a 2 hour recovery with a 40k furnace with a 2 hour recovery and I'd be at within 5 degrees of my setpoint and I'm okay with that. I'd use a 2.5-3 hour recovery if I wasn't. I work 12 hour shifts and am away from home for 13 hours at a time so I'm willing to drop the temp and my furnace doesn't run when I'm not home at all as I don't lose heat down to the 'safe against freezing setpoint' that I use. With a heat pump of any kind, if sized very closely to the heat load of the house, your setback potential is reduced.

Thermal mass is tricky and if you are using in slab heat through the a high mass concrete floor, you are limited to your setback options but if you are well insulated and use solar water heat, you get the benefit of not losing too much temperature overnight and supplemental heat needs on a well designed solar gain house are far reduced. If you don't have a high solar gain design, I think you are better off not going with high thermal mass, I'm just not seeing the advantage to it without trying to capture external heat.

"On a customer's recent house analysis, I got almost a 25 F decay in 12 hours. Virtually no thermal mass in the home."

Don't forget that the 25f decay in 12 hours is also largely a factor of insulation and infiltration. Even if you have very low mass you can reduce the heat loss and cut this down. A house that loses 25f in 12 hours isn't going to save energy being high mass but at least if they are off to work for 8-12 hours a day they can slip in a setback to reduce the temperature difference to the outside and inside to not lose as many valuable BTUs to the outside.

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Old 02-09-14, 10:50 AM   #130
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We're stuck with keeping the house at temp all the time, i did experiment with a small 2C setback and it takes 1.5 days to get the house back up to temp.

Using a very small (cheap and nasty) ASHP which can just about manage down to freezing.
We've been very lucky so far this winter and only experienced -2C for a few hours at most.
Must do a white up sometime of how much hassle it's been to get working efficiently.

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