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  1. #27
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    21,135
    Quote Originally Posted by Kyhusker80 View Post
    Gary,
    Courtesy of "beenthere" in 2010, this was what prompted me to start this thread. Hope this isn't a no no:

    Using a blanket 1 hour heating requirement of 51,195 BTUs.

    A heat pump with staged 20 KW of strip heaters. With the first stage being 10 KW. And the heat pump outputting 17,065 BTUs at a COP of 1.5.

    With only 10 KW of strip on. The heat pump and strip would use a combined total of 13.33KWs.
    Both the heat pump and 10 KW of strip ran for 1 hour(60 minutes).

    Not staging the strips. The heat pump and strip both on during the full heating call. The combine total KW usage would be 13.61KWs. With the run time being .5834 of an hour(35 minutes).

    The loss of the heat from the heat pumps 1 hour of run time. Makes the strip heaters have to provide more of the heat for the load. Then if the heat pump ran for an hour.

    If the heat loss remained the same for 24 hours. The unstaged system would use 6.704KWs more a day.
    Or, 201.12 KWs more in a 30 day period of the same heat loss.

    The above doesn’t take into consideration the additional heat loss through the duct work due to a higher air temp. And greater duct work heat loss.

    This is based on a low COP of 1.5, at temps where the heat pumps COP is higher. The unstaged method would increase the cost difference between the 2 methods even more.
    Quote Originally Posted by garyed View Post
    Those numbers are assuming the heat strips are always running along with the heat pump which is not the case in real world usage.
    The heat strips are mainly used to keep the temperature from dropping in the house when the outside temp gets below the balance point which is when the HP can no longer maintain the temperature by itself. Therefore using the requirement of 51,195 btus with the HP only putting out 17,065 btu's the HP would run continuously for an hour regardless of whether 10kw or 20kw strips were running as auxiliary(back up) heat. So in theory the 20kw strips would run for 30 minutes out of the hour but the HP would still run the full hour so you are not losing any benefit of the COP of the HP. Remember the heat pump is first stage heat and the heat strips are second stage and beyond. The only time staging the strips really matters is when the out side temp is well above the balance point and you left the heat turned down really cold and want to bring it back up. Then you would get the benefit of the HP running longer with staged strips.
    Quote Originally Posted by Kyhusker80 View Post
    I see what you mean. So would you say you can't really oversize the heat strip then? Why not just go with the largest heat strip if it fits your budget?
    Might want to add one more thing in here: Run time. Short run times tend to not distribute the heated (or cooled) air evenly... thus a less comfortable experience for the occupants of the structure. Sadly... this can be mis-interpreted as 'it does not heat (cool) as well as it should'... which of course is not true. Perception... one of those messy things.

    Bottom line: A happy customer is the goal, as they produce referrals. Best to offer them options to make the structure feel comfortable.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  2. #28
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,217
    Quote Originally Posted by Kyhusker80 View Post
    I see what you mean. So would you say you can't really oversize the heat strip then? Why not just go with the largest heat strip if it fits your budget?
    That is a partially true statement but not absolutely true.
    There are added installation costs and added load to the whole house electrical panel.
    Also grossly over sized heat strips can have the effect that GA-HVAC-Tech talked about.
    If you're talking just rule of thumb, I'd say bigger is better.
    Control wiring is my specialty but I've never staged my heat strips in 30 years and have never had a complaint because of it.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  3. #29
    So...the install didn't go well in regards to my visionpro iaq. They weren't familiar with the eim. Disappointed since I asked about it beforehand. He clearly felt more comfortable installing the trane 803 and I agreed since he offered it his cost supposedly and I didnt feel comfortable with him installing the iaq. Very frustrating but my system is working quite well. Live and learn but I had really done a ton of research and felt good about my installer. Highly recommended, trane dealers, high survey feedback, yada yada.

  4. #30
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,032
    The "equipment interface module" is nothing too special, don't understand why they couldn't have figured it out.

  5. #31
    I know but once I got some hesitancy I didn't feel confident in the install so I went with what they knew. Didn't feel like following up constantly if it wasn't set up right. If I had known going in it was a problem I would have continued shopping around. Heck I went three weeks in June and July without air thinking I made the right choice. Does the top of the line trane 900 (I think that's the one) not have an eim? They had talked about that one...

  6. #32
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,064
    Quote Originally Posted by garyed View Post
    Those numbers are assuming the heat strips are always running along with the heat pump which is not the case in real world usage.
    The heat strips are mainly used to keep the temperature from dropping in the house when the outside temp gets below the balance point which is when the HP can no longer maintain the temperature by itself. Therefore using the requirement of 51,195 btus with the HP only putting out 17,065 btu's the HP would run continuously for an hour regardless of whether 10kw or 20kw strips were running as auxiliary(back up) heat. So in theory the 20kw strips would run for 30 minutes out of the hour but the HP would still run the full hour so you are not losing any benefit of the COP of the HP. Remember the heat pump is first stage heat and the heat strips are second stage and beyond. The only time staging the strips really matters is when the out side temp is well above the balance point and you left the heat turned down really cold and want to bring it back up. Then you would get the benefit of the HP running longer with staged strips.
    Many digital thermostats will keep the aux heat in until the set temp of the thermostat is satisfied. Staging does help to reduce heating cost. The IAQ brings on aux heat, when it determines that the home is at 90% of the heat pumps capacity.

    This is evident in colder climates then yours, so you may not notice it much.
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  7. #33
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,064
    Quote Originally Posted by Kyhusker80 View Post
    So...the install didn't go well in regards to my visionpro iaq. They weren't familiar with the eim. Disappointed since I asked about it beforehand. He clearly felt more comfortable installing the trane 803 and I agreed since he offered it his cost supposedly and I didnt feel comfortable with him installing the iaq. Very frustrating but my system is working quite well. Live and learn but I had really done a ton of research and felt good about my installer. Highly recommended, trane dealers, high survey feedback, yada yada.
    Too bad, the IAQ is a much better thermostat.
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  8. #34
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,195
    The IAQ is a nicer thermostat than the 803. Since though you are getting a HP with air handler, the major feature you lose with the 803 is dehumidify on demand. Still the 803 is a good choice.

    BTW, what did you decide on the heat strip?

    Good luck with new system.

    IMO

  9. #35
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,064
    Quote Originally Posted by tigerdunes View Post
    The IAQ is a nicer thermostat than the 803. Since though you are getting a HP with air handler, the major feature you lose with the 803 is dehumidify on demand. Still the 803 is a good choice.

    BTW, what did you decide on the heat strip?

    Good luck with new system.

    IMO
    The IAQ would also slow his blower to help keep the RH down in his house.
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  10. #36
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,195

    Confused

    Quote Originally Posted by beenthere View Post
    The IAQ would also slow his blower to help keep the RH down in his house.
    Isn't that "dehumidify on demand" that I mentioned?

    IMO

  11. #37
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,064
    Quote Originally Posted by tigerdunes View Post
    Isn't that "dehumidify on demand" that I mentioned?

    IMO
    No, the 803 can do DOD. Its just that all it does is over cool by up to 3 degrees. The IAQ can over cool, if need be, plus slow the blower on a cool to dehumidify call. And it will also slow the blower during a regular cooling call if the humidity gets above set point.
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  12. #38
    I went with 10 kw heat strip. Does anyone know if the comfort link stat has an eim? That was the top of the line one my installer offered. Letting it go now. I am more comfortable than I've ever been in the five years I've owned this home. Thanks for everyone's advice--now please come set up shop in kentucky and hook this stat up for me

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