Page 1 of 2 12 LastLast
Results 1 to 13 of 20
  1. #1
    Join Date
    Jan 2006
    Posts
    20
    I recently had a Carrier Peformace Line 80% efficency setup installed in my house, and I have a question about the way it opperates.I recently had a Carrier Performance Line 80% efficiency setup installed in my house, and I have a question about the way it operates.


    The system was installed with the Carrier thermostat, and the balance point is currently set at 35. There have been times when the furnace has been running, when I thought the heat pump should be running instead. For example when I got home yesterday it was 45 outside according to the thermostat, which is above the balance point. The heat pump was running for maybe 15 minutes or so, and then the furnace kicked in. During the day I have the thermostat set back, but by this point the system had already meet the elevated temperature of 68 inside the house. I would think the heat pump should be running longer than this.


    According to the thermostat instructions, the thermostat will operate the first stage, and if after 15 minutes the system isn’t making progress the second stage (furnace) will kick in. I could see this applying if you were coming out of a setback mode and it was 66 in the house, but the thermostat was calling for it to be 68. But in this instance it was already 68 in the house, and it was just maintaining 68. In this instance, I would think that the heat pump would have run until the thermostat was satisfied.


    In looking at the thermostat instructions, I can lock out the furnace so it won’t come on until whatever temperature that is above the balance point. I thought this, but not sure if it’s efficient, since during the day & at night I have my thermostat setback. I would think the heat pump would have to run an awfully long time to recover from its setback point to bring the house temperature back up to normal. The old system in my house was gas furnace only, so I have no comparison for what a heat pump can or can’t do.

    I think there have been times when I think the heat pump has run much longer (45 minutes or so), but it has been warmer outside like in the 50’s. It’s just a hard thing to monitor, as I have to keep checking the thermostat to see when the system kicks on, and then have to continue monitoring it to see if the furnace kicks in, or if the heat pump continues. I would have though with the conditions yesterday, the heat pump would have satisfied the demand without the furnace.


    I am going to have the people that installed the system come back to check things out, but wanted some input as to people’s thoughts before they come out. I just want to make sure I am getting the most out of my dual fuel system.


    Thanks


  2. #2
    Join Date
    Mar 2005
    Location
    Indiana
    Posts
    66
    You're on the right track by having the installer come back to take a look. Since we don't know all the details of your house and system layout, it's hard to tell you what temperature to have what operate at. However, in my area, the majority of duel fuel installations, I program the stat to lock the heat pump out anywhere from 25-35. And the furnace is locked out above anywhere from 40-50. It will vary from home to home, based on equipment size vs. heat loss at different temperatures.

    Just explain your concerns and how you think the heat pump should operate and see what they say. You should see some pretty big savings in the form of less gas consumed. Duel fuel is definitely the way to go these days.

  3. #3
    Join Date
    Jan 2006
    Posts
    20
    I am certainly going to have them come back to check out the system. I just want to find out as much information from various people so I know as much about it as possible.


    I am not so concerned about the temperatures, as I realize there are way too many variables to determine the ideal settings. I was mainly using the temperatures as a point of reference so it made more sense to explain.


    My biggest concern is the heat pump running for so such a short period of time (15 minutes) before the furnace kicked in. From what the thermostat manual says if the system isn't making progress after 15 minutes then the second stage kicks in. It would make sense if you were trying to bring the temperature up from 66 to 68, and after 15 minutes it's still 66, then the second stage kicks in.


    Since this is my first heat pump, is it better to have the furnace locked out, unless it falls below a certain temperature?

    If I end up going that route, will the heat pump have issues of bringing the temperature back up after a setback, or would it be better to have the thermostat at a set temperature throughout the day.


    There are some very educated people on this forum, and I am just trying to the maximum savings from my new system.


  4. #4
    "Since this is my first heat pump, is it better to have the furnace locked out, unless it falls below a certain temperature?"

    I think the answer to this question depends on how much of a setback you are planning to use.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,184
    Sounds like it is doing what it is supposed to if that stat brings on backup after 15 minutes. Was this during a warmup? I don't do a setback with my heat pump, just leave it sit all the time. Figure it is cheaper to run the pump than the gas backup to warm up. If you can switch off the gas, I'd shut it off above 30 if you don't do a backup, and maybe 40-45 if you do.

  6. #6
    Join Date
    Jan 2006
    Posts
    20
    Currently I set the temperature back 4 to 5 degrees during the day, and 6 to 8 degrees at night.

  7. #7
    Join Date
    Jan 2006
    Posts
    20
    "Sounds like it is doing what it is supposed to if that stat brings on backup after 15 minutes. Was this during a warmup?"

    This wasn't during a warmup, the 68 degree temperature had already been satisfied about an hour before. I would expect the gas to come on during a warmup.


    Isn't 15 minutes an awefully short period of time for a heat pump to run to maintain a temperature?

  8. #8
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,211
    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 think most of the tech's will agree with me that heat pumps should not be set back to the extent that you are doing. Heat pumps don't recover very well and do better when kept at a more constant temperature. 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

  9. #9
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,184
    I would think the stat should look more at temp diff, not time. My Totaltouch stat has a time feature like that but it can be turned off so it will run the pump for a long time if it feels it is keeping up OK. Apparently your stat doesn't from what I read. It does have a way to shut off backup so I would find a temp as I described above to do so.

  10. #10
    Join Date
    Jan 2006
    Posts
    20
    It certainly seems that the general consensus is to have the furnace locked out until it gets down to a certain temperature. Since the Carrier thermostat doesnt seem to have a way to override or extend the 15 minute interval, locking out the furnace seems to be the only workaround.


    This then brings it to an issue of not using the setback, since a few people seem to indicate dropping the temperature 4 to 8 degrees is too much for the heat pump to handle.


  11. #11
    Join Date
    Mar 2003
    Posts
    1,234
    Just a thought....are you sure the outdoor unit isn't going into defrost? If so, the furnace will come on until the call for heat is satisfied then it will go back to heat pump operation on the next call.

  12. #12
    Join Date
    Jan 2006
    Posts
    20
    This is probably a dumb question, but is there an obviuos way to tell if the heat pump has gone into defrost? Is it the outside unit that frosts up?



    As I mentioned before, this is the first time I have ever had heat pump. Previous house had radiant, and this house had gas furnace before going with dual fuel.

  13. #13
    Join Date
    Feb 2005
    Location
    small island in the Pacific Ocean
    Posts
    558
    yes its the outside unit that ices up and you can tell that it is defrosting because the compressor will be making a low growling noise and the outdoor fan will not be running, then when it shifts out of defrost the fan (outdoor) will start up and a cloud a steam (vapour) will rise up from unit.

    With duel fuel during defrost your gas furnace will come on and finish that call for heat. With electric back up once defrost is complete the heat pump comes back on and the electric heat shuts off.

    I agree with some of the others that you are using too great of a set back at night for heat pump efficiency. If I'm not mistaken the carrier stat will bring on AUX heat if the temp. has not risen .6 of a degree in either 10 or 15 minutes.




Page 1 of 2 12 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