Page 1 of 3 123 LastLast
Results 1 to 13 of 33
  1. #1

    Ideal Night Setback

    For a non-modulating furnace, what is the ideal temperature differential for energy savings during night setback? At what temperature differential, does night time energy savings equal morning warm up energy usage?

    Thanks,
    ACResearcher

  2. #2
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    typically most Energy companies will tell you to not set back your stat more than 6*, and if one is using a HP for heating you shouldn't really set-back your stat at all. The savings for set-back can be significant for most HO's unless you home leaks like a sieve then of course there's no benefit. It's shouldn't matter if you have a mod furnace or not to set-back your stat unless your running a single stage furnace then a set back wouldn't benefit a HO much.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    On gas or oil systems. I tell most people 1 for every 2 hours of set back.
    Since the savings is based on how long the house is at the lower temp setting. And it takes a fair amount of time for most houses to drop several degrees of temp.

    Set back temp is a balance of how cool you like it when you go to bed, and how warm you like it when you get up in the morning to get ready for work.
    Some what the same for setting temp back while your at work. With the exception, that its how warm you want it to be when you get home. Or how long your willing to wait for it to get warm while your at home.

    A few years backs. I started turning my heat off during the day(I was gone for 14 hours or more). It saved a lot of money on the heating bill. I just wasn't warm/comfortable for the first 5 hours(some days it dropped 20+) of recovery(recovery time depended on outdoor temp).
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Quote Originally Posted by DanW13 View Post
    typically most Energy companies will tell you to not set back your stat more than 6*, and if one is using a HP for heating you shouldn't really set-back your stat at all. The savings for set-back can be significant for most HO's unless you home leaks like a sieve then of course there's no benefit.

    Why wouldn't there be a benefit of not heating the outside for 8 hours or so?


    It's shouldn't matter if you have a mod furnace or not to set-back your stat unless your running a single stage furnace then a set back wouldn't benefit a HO much.
    Set back benefits people weather they have a single stage, 2 stage, 3 stage, or mod furnace.

    People have been setting back oil furnaces since the energy crisis of the 70's.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    Since the savings is based on how long the house is at the lower temp setting. And it takes a fair amount of time for most houses to drop several degrees of temp.
    That doesn't make sense to me - heat loss declines as soon as the temperature drops below the normal setpoint.

    While the amount of energy required to recover is equal to what's lost as the space cools down, it will always be less than what would have been used to maintain a constant temp. (savings don't only occur when the equipment starts cycling again during the setback period)

    You can confirm this by graphing heat loss (based on temperature differential) and looking at the area under the curve; the surface area under the portion where the temp goes down (and the equipment doesn't operate) is proportional to the amount of energy required to recover.*

    *Energy use (surface area) will always lower than that of maintaining a constant setpoint during the same period of time.

    This does not apply to heatpumps with electric backup, of course.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Quote Originally Posted by amd View Post
    That doesn't make sense to me - heat loss declines as soon as the temperature drops below the normal setpoint.
    You won't see any notable savings if you leave it drop 5 degrees and then bring the temp up as soon as it has dropped 5 degrees(as a setback).

    You will if your thermostat has that as a differential though. And does that every heat or cooling call.

    You can plot graphs all you want(I plot lots of them). Real world will not follow the graph close enough to save what the graph will show when used as a setback if it doesn't have time at teh setback temp. Takes time at the set back temp to get the savings.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    Jul 2008
    Posts
    551
    Go as low as you can sleep well if you have a smart recovery type of t-stat that will get it back to where you want it by morning. The more, the better when you have a furnace.

  8. #8
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    Quote Originally Posted by beenthere View Post
    You won't see any notable savings if you leave it drop 5 degrees and then bring the temp up as soon as it has dropped 5 degrees(as a setback).

    You will if your thermostat has that as a differential though. And does that every heat or cooling call.

    You can plot graphs all you want(I plot lots of them). Real world will not follow the graph close enough to save what the graph will show when used as a setback if it doesn't have time at teh setback temp. Takes time at the set back temp to get the savings.
    I wonder if any studies have been done to demonstrate that, because it defies everything I know about heat transfer. (I know of this one - https://www03.cmhc-schl.gc.ca/b2c/b2...00450000000009, large 6C/11F drop saved more than 4C/5F drop in an energy efficient house)

    A graph can only represent a hypothetical scenerio obviously, but it doesn't change the fact that heat loss drops off as soon as the temperature starts declining. Provided that the conditioned space spends a lot of time at a lower temp than the normal setpoint (Energy use proportional to delta-t x time), I'm convinced that large setbacks save, whether it gets cold enough for the equipment to start cycling or not.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    A large set back will save. If it stays at that temp for some time.

    But if the stat determines that it has to go into recovery as soon as the house reaches that setback temp. You won't have saved anything worth mentioning. Over having used a set back half as much.

    What good is setting the temp back to 10 degrees if the furnace starts a 6 hour recovery on time as soon as the temp drops 10.
    A 6 set back would probably save as much or more.

    If however,. It stay at the 10 setback temp for 2 or 3 hours. Yes it would save.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    What good is setting the temp back to 10 degrees if the furnace starts a 6 hour recovery on time as soon as the temp drops 10.
    A 6 set back would probably save as much or more.
    Assuming that the furnace is properly sized, on a cold morning a good chunk of the energy used (at least 50%-60%) during a 2-6 hour recovery is used to offset heat loss (during the time period in question) to begin with. (would have been used anyway)
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    You can use your own house. And conduct a test.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #12
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    A HO will only benefit if say you set back the temp 5* at say 10 pm and have the furnace bring the temp back up to 70* at 5 am and within that 6-7 hour period your furnace doesn't kick in to maintain the 65* fro more than a 1 hr your saving money. However if you set-back and the furnace is kicking in 2-3-hrs later to maintain set point there's no use in have the stat set for set back your not going to save anything.

  13. #13
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    Quote Originally Posted by DanW13 View Post
    A HO will only benefit if say you set back the temp 5* at say 10 pm and have the furnace bring the temp back up to 70* at 5 am and within that 6-7 hour period your furnace doesn't kick in to maintain the 65* fro more than a 1 hr your saving money. However if you set-back and the furnace is kicking in 2-3-hrs later to maintain set point there's no use in have the stat set for set back your not going to save anything.
    That doesn't make much sense to me either - lower delta-t = lower heat loss, resulting in less run time during the setback period.*

    *If that wasn't the case, maintaining a more modest setpoint (ex: 66F vs 72 in the winter) in general wouldn't save any energy. (...and we all know that doing so reduces operating costs)
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event