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  1. #14
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,390

    Exclamation Set-back

    Originally posted by doorz
    Currently I set the temperature back 4 to 5 degrees during the day, and 6 to 8 degrees at night.
    Try 3 dgrees
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  2. #15
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,390

    WHY

    Originally posted by thorton
    Originally posted by doorz
    Currently I set the temperature back 4 to 5 degrees during the day, and 6 to 8 degrees at night.
    I have the Carrier thermidistat and have my aux heat locked out to 5 degrees F. This lock-out temperature has allowed my heat pump, alone, to heat my house all winter, except for the odd day most of the winter so far.


    I have also locked out the defrost heat too!

    Thorton
    Would Defrost Heat be locked out too?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #16
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,222

    Re: WHY

    Originally posted by dan sw fl
    Originally posted by thorton
    Originally posted by doorz
    Currently I set the temperature back 4 to 5 degrees during the day, and 6 to 8 degrees at night.
    I have the Carrier thermidistat and have my aux heat locked out to 5 degrees F. This lock-out temperature has allowed my heat pump, alone, to heat my house all winter, except for the odd day most of the winter so far.


    I have also locked out the defrost heat too!

    Thorton
    Would Defrost Heat be locked out too?
    Don't know what you mean?

    Thorton

  4. #17
    Join Date
    Jan 2006
    Posts
    20
    That may be what has been happening, is that the heat pump has been going into defrost mode. In monitoring things yesterday, the temerature was colder 38 degrees, and the heat pump ran much longer than say 15 minutes, and it the heat pump completed it's cycle without the furnace coming on.


    As I mentioned before it's a hard thing to monitor, as I have to pay attention to when the system cuts on, and then how long it runs to see if or when the furnace cuts on. My system runs VERY quite, which makes things even more difficult.


    The thing with the thermostat changing by .6 degrees I dont think applies, because my thermostat unless it's in a setback mode ALWAYS reads 68 degress, which is what I have it set too.



    I suppose I need to keep monitoring it, and see if the system seems to kick the furnace in when I think it shouldn't and then walk outside to look at the outdoor unit.

    Would the heat the heat pump need to go into a defrost cycles after only running for say 15 minutes though? I would think it would run longer before needing to go into a defrost cycle, unless maybe the previous runtime left it in an almost frosted state?


  5. #18
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,222
    Originally posted by doorz
    That may be what has been happening, is that the heat pump has been going into defrost mode. In monitoring things yesterday, the temerature was colder 38 degrees, and the heat pump ran much longer than say 15 minutes, and it the heat pump completed it's cycle without the furnace coming on.


    As I mentioned before it's a hard thing to monitor, as I have to pay attention to when the system cuts on, and then how long it runs to see if or when the furnace cuts on. My system runs VERY quite, which makes things even more difficult.


    The thing with the thermostat changing by .6 degrees I dont think applies, because my thermostat unless it's in a setback mode ALWAYS reads 68 degress, which is what I have it set too.



    I suppose I need to keep monitoring it, and see if the system seems to kick the furnace in when I think it shouldn't and then walk outside to look at the outdoor unit.

    Would the heat the heat pump need to go into a defrost cycles after only running for say 15 minutes though? I would think it would run longer before needing to go into a defrost cycle, unless maybe the previous runtime left it in an almost frosted state?

    Sure a heat pump can go into a defrost mode after 15 minutes. Mine shuts off if the thermistat is satisfied just before a defrost cycle is set to begin. Then the next time the stat calls for heat the heat pump may run only a few minutes and then goes into a defrost.

    Thorton

  6. #19
    Join Date
    Mar 2004
    Posts
    1,042
    The other way to know it's gone into defrost is to listen for a characteristic "Whoosh!" sound from the outdoor unit at the beginning and end of each defrost cycle.

    It decides when to defrost based on running time; the standard setting is that it will defrost after 90 minutes of accumulated run time, provided that it's cold enough out for frost to have formed at all. As such it can be the case that the heat pump starts up and almost immediately hits the 90th minute, and so starts defrosting.

    I have the same setup and have found that the only way to really maximize what you get out of the heat pump, and minimize your use of the furnace, is to use no setbacks at all. That won't make you defrost any less often, but since the furnace always finishes the entire call for heat after a defrost cycle with this setup, it makes sure that it won't take long to get there. Otherwise you end up starting to try to recover several degrees, almost certainly go into a defrost before you recover, and then the furnace has to run a long time to finish the cycle. If you maintain a steady temperature, the cycles are typically shorter, so when the cycle comes that does actually require a defrost, the furnace can satisfy the (smaller) demand for heat quickly. Then a few minutes later you'll need another heating cycle, and the heat pump can pick up again.

  7. #20
    Join Date
    Jan 2006
    Posts
    20
    It's such a hard thing to determine what to do maximize my savings. Before I had my old gas furnace replaced, I know that I was saving by using a setback. My old thermostat has an energy buttion that gave hours & minutes of system run time. When I used the setbacks, the system ran less time than when I left it set at the same temperature all day long.

    With the new system I had to replace the thermostat since it wouldn't work with the multi-stage equipment. Since temperatures fluctuate so much, and now I have gas & electricity involved, it makes it more difficult to determine what my optimum setting should be.


    I certainly have to use much less gas than I did before, as my new 80% furnace has to be more efficient than the old furnace. The gas doesn't seem to have to be used as much, as it appears that it's only used when the heat pump goes into defrost mode, and when the system is recovering from a setback.

    It's only been a month since my system was replaced, and haven't gone through a complete billing cycle, I will have to see where things stand when I get my bill next month. Electricity around here is much cheaper than gas, so hopefully my electric bill won't skyrocket & outweigh my gas savings.

    I have been keeping track of all my energy use age since I moved in the house almost 2 years ago, so if my electric bill seems out of line, then maybe I will have to try to leave the thermostat set at a constant temperature and see where things stand for that next month.

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