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  1. #1

    Heat pump, heat strip settings

    I am trying to determine what is the most efficient thermostat setting for a heat pump / heat strip system. I currently have a thermostat that will only allow me to determine when the heat strips turn on to support the heat pump by time. So currently, I have the heat strips set to turn on 20 minutes after the heat pump turns on in the hope that under normal circumstances the heat pump will do its job in that amount of time and turn off without needing the heat strips but under colder than normal conditions, the heat strips will turn on.

    This seems very limiting. I know many thermostats will use the temperature to determine when to turn on the heat strips. For example, if the set point is 72 and the room temp drops to 3 or 4 degrees below 72 then the strips will turn on to supplement the heat pump. The only downside of this is that if the heat pump is only able to maintain the current temp and not increase the temp than the heat pump will run continuously and not trigger the heat strips, or at least will take several cycles and more time to get to the point of the strips turning on.

    Does anyone have any input on what is the best trigger for turning on the heat strips? Also, I am not sure what the ideal setting is for the time delay option. I chose 20 minutes but if I make it shorter it may run the strips too often and if I make it longer, then when it is very cold out, the heat pump will always be guaranteed to run for that amount of time before turning on the heat strips.

    Thanks for the help.

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Need a Manual J load calculation ,then a Heat Pump Balance point can be determined.

    The balance point is the outdoor temperature that the heat pump will need the strips to maintain the indoor set point.

    Then add an outdoor stat,so strips are locked out until the outdoor temp drrops to that point.

    This is the most economical way to operate the system.

    With some controls,like Carrier's Infinity, you have a built in outdoor stat,and can adjust the setpoit to bring on the strips ,from the indoor stat..

  3. #3
    Join Date
    Jun 2007
    Location
    The Twilight Zone
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    2,964
    Quote Originally Posted by cdub20 View Post
    For example, if the set point is 72 and the room temp drops to 3 or 4 degrees below 72 then the strips will turn on to supplement the heat pump.
    Typically, a digital thermostat will cycle the strips on/off if the heat pump is struggling to maintain setpoint. The room doesn't have to lose 3 or 4 degrees. Old mercury t-stats would kick in the aux if the setpoint temp dropped 2 degrees.

    Remember that the heat pump is your cheapest heat. You want it to run as long as possible before the aux strips are energized.

    Setting the strips by a timer does not help your operating costs.

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,764
    Long run times for the heat pump are preferable to having the aux heat satisfy the thermostat under most circumstances.

    A thermostat like the Honetwell IAQ. Will bring on the aux heat when it determines that the heat pump is working at 90% of it capacity. So it eliminates a lot of needless aux heat use.
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  5. #5

    Setting heat stips on outside temp

    In the 5 years we've been in our house, the only issue we have is when it's 20 degrees outside, the heat pump will run for 2 hours, when the temp finally drops another degree to turn on the strips. What I'm looking in to is setting the strips up where they come on based on outside temperature. It seams like I could run the circuit that turns the heat on through another thermostat that's outside and then to the heat strips. But where could I find a thermostat that I could set at, say, 30 F? This is over simplification, but has anyone done something like this?

  6. #6
    Join Date
    Sep 2003
    Location
    Portland.OR
    Posts
    316

    Dash is correct.. [I hate to say!! joke]

    Yep just upgrade the indoor to a thermostat that can use an outside temp sensor to turn off the heat pump. Depending on many variables, like sizing, insulation, outside temp, heat loss, it will be about 25 to 45 degrees [outdoor temp], then your AuX or EMG heat will be the only source of heat. Then when it warms up to a temp the heat pump can be efficient it will come back on.

  7. #7
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,764
    Quote Originally Posted by redraider View Post
    In the 5 years we've been in our house, the only issue we have is when it's 20 degrees outside, the heat pump will run for 2 hours, when the temp finally drops another degree to turn on the strips. What I'm looking in to is setting the strips up where they come on based on outside temperature. It seams like I could run the circuit that turns the heat on through another thermostat that's outside and then to the heat strips. But where could I find a thermostat that I could set at, say, 30 F? This is over simplification, but has anyone done something like this?
    They make stats that will do that. Of course, if you used one like that, your electric bill will go up.
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