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  1. #1
    Join Date
    Jan 2010
    Posts
    6

    Time delay heating with heat pump

    Hello everyone,

    Hoping someone can help with a problem I have. I have a geothermal heating and airconditioning system with a Robert Shaw 9000i series thermostat. I have a air handler for forced hot air through ducts.

    Is there a way to set a time delay for turning on the blower for heating to allow the heat exchanger to heat up before the fan turns on? It takes about 6 minutes from when the thermostat calls for heat to when hot air starts coming out of the ducts. The bedrooms get pretty chilly when cold air is blowing from the ducts. A better solution would be a temperature probe to turn on the fan when the heat exchanger reaches a setpoint.

    In air conditioning mode, I do not need any delay.

    Thank you for your help!
    David

  2. #2
    Join Date
    Apr 2005
    Posts
    498
    how old is that t-stat?....not even on there site....but have tech install a new programmable stat, a good one will have built in time delay funtion for heat only, some of them you can even set the delay to diffrent times. some of the old furnaces would bring on fan thru temp but i think they got away from that due to higher failure rate, and make sure he sets up the stat to delay fan shut off after call for heat ends so you can maxamize effciency
    Jason J Saylor
    Pinellas County Schools
    HVAC Tech/Part Time HVAC Instructor Fortis College
    Pinellas County Florida

    "You will encounter many distractions and many temptations to put your goals aside: The security of a job, a wife who wants kids, Whatever. But if you hang in there, always following your vision, I have no doubt you will succeed.
    Larry Flynt quote

  3. #3
    Join Date
    Jan 2010
    Posts
    6
    I should have been more specific. It is model 9920i and is the Deluxe Programmable Thermostat. I figured it would have such a function also since it is pretty new, but I called the company and they said it does not have that function. I did not see it in the manual, but maybe it still has it??

  4. #4
    Join Date
    Jul 2008
    Posts
    551
    Is that even controllable through the t-stat? That seems like a function that would be adjustable at the air handler because the air handler is going to start the fan when it sees the call for heat and not wait for a call for fan.

  5. #5
    Join Date
    Jan 2010
    Posts
    6
    I have two terminals on the thermostat - one for the fan relay to turn on the fan and another for the heat relay to trun on my heat pump compressor. So I think technically the thermostat could turn on the heat pump and wait to turn on the fan....

  6. #6
    Join Date
    Jan 2010
    Posts
    6
    I saw devices called "Fan Limit Switch" which seems to be used exaclty for this. However I don't think it works for heat pumps, only furnaces. And not sure how to make it delay only in heating mode and not in air conditioning mode.

  7. #7
    Join Date
    Apr 2005
    Posts
    498
    you right i looked thru paperwork on that stat and no delay option, so you just call your local tech and have them bring a 24volt time delay and install it on the fan you want him to put a delay on/delay off relay they have adjustable ones and set value ones he can pick up at local HVAC house. if you want it to only happen in cooling he will have to know what he doing to wire it up.
    Jason J Saylor
    Pinellas County Schools
    HVAC Tech/Part Time HVAC Instructor Fortis College
    Pinellas County Florida

    "You will encounter many distractions and many temptations to put your goals aside: The security of a job, a wife who wants kids, Whatever. But if you hang in there, always following your vision, I have no doubt you will succeed.
    Larry Flynt quote

  8. #8
    Join Date
    Jun 2003
    Location
    Hell Hole Swamp
    Posts
    4,180
    Delaying the fan turning on more than 10 seconds or so would cause a high pressure condition and a safety trip, you cant warm up a heat pump coil like you can a gas furnace

  9. #9
    Join Date
    Jan 2010
    Posts
    6
    So I can't put a time on delay starting the fan until the coil heats up?

  10. #10
    Join Date
    Apr 2005
    Posts
    498
    NO YOU CANT.....But a tech can



    not common, but he using Geotherm, i think he could get away with a short 5-7 second time delay, a tech would have to watch pressures and do it right, and instlling HPS would protech compressor. i dont think it is impossible to do....
    Jason J Saylor
    Pinellas County Schools
    HVAC Tech/Part Time HVAC Instructor Fortis College
    Pinellas County Florida

    "You will encounter many distractions and many temptations to put your goals aside: The security of a job, a wife who wants kids, Whatever. But if you hang in there, always following your vision, I have no doubt you will succeed.
    Larry Flynt quote

  11. #11
    Join Date
    Jan 2010
    Posts
    6
    I need 5 minutes though! Will that be possible?

  12. #12
    Join Date
    Apr 2005
    Posts
    498
    5 MINS>.....no way////... your internal gas pressure will cause compressor to go out on internal bypass and you will have even more issues. but a very short delay on/off will give you some better effciency a good tech can set that up., may want to insulatat your attic more if your duct is up there and getting that cold.
    Jason J Saylor
    Pinellas County Schools
    HVAC Tech/Part Time HVAC Instructor Fortis College
    Pinellas County Florida

    "You will encounter many distractions and many temptations to put your goals aside: The security of a job, a wife who wants kids, Whatever. But if you hang in there, always following your vision, I have no doubt you will succeed.
    Larry Flynt quote

  13. #13
    Join Date
    Nov 2008
    Location
    Chapel Hill, NC
    Posts
    1,070
    With most (electric) heatpumps, the thermostat controls the fan while with most gas furnaces, the furnace controls the fan. No sure how your geothermal setup would work but I think it would be the same as an electric air-to-air heatpump. In any event, I'm not aware of any thermostats that have this delay - maybe some of the pros on this forum will know.

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