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setback thermostats

Started by bobby s, October 30, 2014, 04:29:09 PM

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bobby s

Does anyone out there use a setback t-stat with your owb? If you do, have you noticed a difference in your wood consumption?
I'm always hearing and reading how everyone should have one and they save you money, but a few H.V.A.C professionals I've spoken to say it takes the same amount of energy to bring a room back up to temp. as it would have taken to maintain a constant temp. Is this just manufacturers trying to sell products in the name of being "green"?
I know there's many knowledgeable F.F. members out there who can give me a good explanation.
Thanks in advance.

WmFritz

What are you using for heat emitter's; i.e. radiant slab, baseboard, etc?
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

woodmills1

Did you ever notice how much wood you burn if you let the water get down around 100 degrees?
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

Dave Shepard

Where I used to work I went through a few episodes of the "turn the thermostat down at night" routine. I agree that it takes as much, or more to recover than it does to maintain. We kept the shop at 55 during the day, and the Modine unit barely ran during the day. Maybe every two hours for a little while. If we turned it down as low as it would go, maybe 40-45, the Modine would run from 8:00 until early afternoon. The part that really ticked me off was having to listen to the thing blowing all day, and having cold steel tools to handle in the morning. Timber framing tools are hard to use with winter gloves on. Finally, after several conversations with different heating contractors, the thermostat was left alone. Fuel consumption at the end of the year was about the same. If you were going to be gone for longer periods of time, like for the week, and you were only going to be around on the weekend, then it would probably save a little bit of fuel.
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thecfarm

We do turn ours down at night. Not to save on wood,but we both like it cooler to sleep. As soon as I get up,the heat goes up.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Al_Smith

My first wife ,bless her heart in spite of being a college graduate had no idea how a thermostat worked .If she was cold she cranked it wide open .Then she was hot,shut it off and opened the windows and doors . ::)

WmFritz

Quote from: Al_Smith on October 30, 2014, 09:31:23 PM
My first wife ,bless her heart in spite of being a college graduate had no idea how a thermostat worked .If she was cold she cranked it wide open .Then she was hot,shut it off and opened the windows and doors . ::)


Al, save yourself the grief . Remove the t-stat and replace with a single pole toggle switch. :D


edit: I missed the first wife part.
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

WmFritz

bobby s, are you talking about a programmable t-stat or an outdoor temperature reset something like this?


http://tekmarcontrols.com/solutions/browsesolutions/energy-savings.html


~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

Compensation

Quote from: Al_Smith on October 30, 2014, 09:31:23 PM
My first wife ,bless her heart in spite of being a college graduate had no idea how a thermostat worked .If she was cold she cranked it wide open .Then she was hot,shut it off and opened the windows and doors . ::)

Haha. I charge $30 for a dummy t-stat and $45 for a digital dummy t-stat.

Your best bet is to maintain temperature. Its not just the air temp but the temp of everything inside the house. I have a top of the line touch screen programable thermostat, I only use it in manual mode. I get about a 10% increase in energy consumption when its in program mode.
D4D caterpillar, lt10 Woodmizer, 8x12 solar kiln, enough Stihl's to make my garages smell like their factory :) Ohh and built Ford tough baby!

bobby s

The thermostat we have is a 7 day programmable t-stat that controls the main portion of our house.
The heat type is forced hot water baseboard.
We do have one section of the house that is hot water/radiant, but I know enough to leave that t-stat set at one constant temp.
Like many others, the two upstairs zones controlling the bedrooms are kept much lower, usually around 62, and only get turned up when it's very cold out.


JSNH

I have setback thermostats and an outdoor boiler. It helps to save wood if you can turn the temp down for more than a few hours. When both my wife and myself had the same schedule we went thru 10% or more less in wood than now. We would have the heat drop at 9 pm and start at 5am, it would turn off at 7an and on again at 3pm. When you heat the house you are adding heat to it and it looses the heat to the outside. no house can be so well insulated that it can hold all the heat in. Setting your house temp down reduces the heat loss the closer you get the inside to the outside temp the less heat loss or delta T. If its 30 degrees out side and 70 inside the delta T is 40. If you drop the inside temp to 60 your delta T is now 30. That's a 25% reduction in heat loss at that point. Yep it helps.

jdonovan

Quote from: bobby s on October 30, 2014, 04:29:09 PM
I'm always hearing and reading how everyone should have one and they save you money, but a few H.V.A.C professionals I've spoken to say it takes the same amount of energy to bring a room back up to temp. as it would have taken to maintain a constant temp. Is this just manufacturers trying to sell products in the name of being "green"?

The rate of something changing temperature is based on the difference between the two objects. So if you let the inside of the house get cooler, it will loose heat to the outside less rapidly.

So while you are in cooler than normal, you will loose less heat.

The premise of the setables is that not only will you set it to a lower temp when you are away from the house, but you'll also set it to a lower temp when you are not active... i.e. at night. So you can save some money by adjusting the temps.

As some others have indicated when you try big overnight swings, everything in the place gets cold, and turns into a cold sink. When you ask the furnace to warm things up, the air comes to temp fairly quickly, but everything else in the house is still cold. I discovered it was no fun to sit down on a 55 degree couch. And it took HOURS to get everything in the house warmed back up.

This made the family unhappy, and the setback thermostat was declared evil.

Next year we tried a new plan.

What I found made the biggest difference was to set a new 'baseline' temp that was about 6 lower than we used to run the house. Then set the morning wake, and the evening home to about 2 warmer than our old baseline.

old way - 24 hours at 68
new way 8 hours at 70,( 2 am hours, 6 pm ) 16 hours at 62.

So my new 'average' on a 24 hour basis temp was 64.5 degrees. The awake time temp's were higher, family was more comfortable, and net-net my average thermostat setting was down 3.5 degrees. Don't save a ton of money, but this plan actually increased comfort, and saved money. win-win.




doctorb

Interesting discussion.

We use programmable thermostats and, like many, turn down the temp at night because we like it cooler for sleeping.

What's interesting to me in this discussion is the concern for "using" more wood with your OWB when purposefully creating temperature swings within the house.  The greatest advantage of an OWB is cheap fuel.  I don't worry about saving wood in this respect because I do not think that the difference in wood use would be so great that it would change the way we regulate temperatures in the house.  It is the freedom to do whatever you want to do with the house environment that is one of the major benefits of heating with an OWB.  If I use an extra 1/2 cord or so for the winter, so be it.  I am not one the throw away money or the effort it takes to prepare my wood pile for winter heating, but the advantages of having a little extra seasoned wood  far outweigh any increase in fuel consumed, IMO.
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

beenthere

I'm along the same thought as Drb, and removed the three setback thermostats to went back to the straight "set it and forget it" ones. For the sleeping area, that temp is lower and stays the same (68°). For the wifes' living area, that stays the same (72°). For my "office" area (71°). Want to be warmer, go stand next to the wood boiler.  ;D

If I were on gas, might be different. But I burn wood dried 2-3 years and enjoy having a steady temp that is comfortable in the house, day in and day out.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

pineywoods

My first experience with setback thermostats was in a mobile home with a propane furnace. Took about an hour for interior temp to drop down to night time setting and another hour in the morning to get back up to day time temps. All in all, it worked well. Then I moved into a house built on a concrete slab with ceramic tile floor covering. In additon, one wall in the open living area is exposed brick. Installed my setback thermotat and fired up the gas furnace. The poor furnace tried, but with that much thermal mass, getting a temp swing from night to day setting could take as much as 18 hours.. In short, if you have lots of thermal mass, you won't like a set back thermostat..Set it and forget it..
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
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jfaulring

I leared pretty quickly that there's no benefit to setting the temperature back on a daily basis with my radiant floor setup. During the coldest part of the winter it would almost take it as long to come back up to temp just to set it back again.  If we're heading out of town for a few days I'll set it back and there's quite a savings in wood - the WiFi thermostats I have make it really nice to turn the set point back up remotely from my phone when we're headed home so we walk into a nice toasty warm home.

stumper

Wow, back to elementary Thermodynamics.  The rate of heat loss increases as the temperature differential increases.  So  if you lower the temperature setting for a significant period then you will loose less heat.  Now there are a couple of variables in this.  Will the time period of lower temp be long enough for the home to reach equilibrium, and is there a loss of efficiency at the boiler for either the long idle period or the wide open period during the reheat. 

For most there will be a savings with these thermostats. 

The real questions are.  Is the savings significant?  Will it pay for the new thermostats?  How long will the pay back be?  Is there additional benefit or cost of comfort and livability.

For me and my family the benefits did not out weight the costs.  Maybe if it were just my wife and I and we had nice predictable schedules the answer might change.

xalexjx

house set at 72 and shop set at 65 (radiant) heating with an Outdoor wood boiler
Logging and Processed Firewood

sharp edge

All homes have air coming and going, which is a big factory in heating them. At one temp. their is less. My .02

SE
The stroke of a pen is mighter than the stroke of a sword, but we like pictures.
91' escort powered A-14 belsaw, JD 350-c cat with jamer and dray, 12" powermatic planer

bandmiller2

Outside furnaces get a bad rap from starting and stopping and the resulting smoke cloud. I think the most efficient burn would be a smaller fire constantly burning in a masonry fire box to keep the combustion temp. up. High temp is where clean burn and economy comes from. Many folks have too large a outside furnace, better is a smaller unit fed more often. My own feelings are setbacks will only create more problems than they will solve. Frank C.
A man armed with common sense is packing a big piece

LittleJohn

I agree with STUMPER,
Quote from: stumper on November 01, 2014, 04:42:47 PM
The real questions are.  Is the savings significant?  Will it pay for the new thermostats?  How long will the pay back be?  Is there additional benefit or cost of comfort and livability.

With in-slab radiant and the slow reaction times, I do not see any benefit to setback.  However, if you have a low-mass (under-subfloor) type stytem and and larger afternoon solar gain (LIKE I DO, in my living room) I would maybe consider it to help reduce some of the overshoot in the afternoon hours

tractorman44

Quote from: LittleJohn on November 04, 2014, 02:22:43 PM
I agree with STUMPER,
Quote from: stumper on November 01, 2014, 04:42:47 PM
The real questions are.  Is the savings significant?  Will it pay for the new thermostats?  How long will the pay back be?  Is there additional benefit or cost of comfort and livability.

With in-slab radiant and the slow reaction times, I do not see any benefit to setback.  However, if you have a low-mass (under-subfloor) type stytem and and larger afternoon solar gain (LIKE I DO, in my living room) I would maybe consider it to help reduce some of the overshoot in the afternoon hours

In response to the original poster, set back thermostats are not usually installed with boilers whether they be commercial steam, hot water, residential steam or hot water or outdoor wood fired for many of the above mentioned reasons.

For standard manufactured gas or electric boilers a controller called a "reset control" is the most energy saving device.  The reset control adjusts the boiler water temperature porportionately up or down based on outdoor air temperature. 

If you needed 180 degree water to satisfy the heat loss to your structure at zero degrees, that same structure could be satisfied easily with 140 degree water at 35 degrees.  Therebycutting the amount of time the fossil fueled or electric boiler operates to maintain that lower loop temperature.

I'm sure a reset controller could be installed on an OWB, but don't know if it's recommended or not.  When a gas, oil or electric boiler is shut off, there is no fuel consumption....what happens to an OWB when the space temp is met ..?? The combustion air fan and/or damper is shut off or closed to minimim but the fire is still there, though snuffed down and smoldering somewhat producing heat primarily that's not doing anything but going up the chimney  ??  Well, depending on your control scheme, its still maintaining loop temperature or at least boiler reservoir temp.

I'm not sure a set back thermostat or a reset controller is a good idea.....on an OWB.

LittleJohn, without knowing anything about your situation at all, it kinda sounds like a zone control valve and separate thermostat for the glassed in room (if economically feasible) would be a step in the right direction to solve your delimma.


Compensation

I was talking to a guy I know about this topic. He sells and installs natures comfort, he told me they are not worth it. Not trying to bash it just repeating what I was told, hoping there would have been a better answer I could have got.
D4D caterpillar, lt10 Woodmizer, 8x12 solar kiln, enough Stihl's to make my garages smell like their factory :) Ohh and built Ford tough baby!

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