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  1. #1
    Join Date
    Dec 2019
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    Help with Friedrich Heat Pump PTAC (Using lots of power)

    Hi!

    The main heating source in my NYC apartment is a Friedrich PTAC (AC/Heat pump).

    Model: PDH12K3SG
    The forum won't let me post links to product but it can be found on AJ Madison or by googling model number along with the manual and specs, etc.

    I ran some tests looking at power consumption over a few hours and it appears my heat pump is using too much power during normal extended running. According to the documentation the resistance heating element uses 3450 watts when it is turned on. The manual states the inefficient electric heat (resistance) is only utilized when
    1: the unit is first turned on to quickly warm up space
    2: the temp drops more than 5 degrees below the set temperature
    3: the heat pump cannot adequately heat up the room and needs a boost
    4: Dip switch 1 is flipped to on position (aka emergency heat) in which case electric heat is ALWAYS used.

    Based on how much power my unit is using EVERY time it cycles on over the course of a number of hours I am concluding it is always using the electric heat which doesn't make sense to me. Is there something I am misunderstanding? Every single time the unit runs it uses the equivalent of 3350 watts/hr for the amount of time it is on. (i.e., uses 1.675 kWh if on for 30 minutes, 0.8375 kWh if on for 15 minutes which is normal cycle length).

    The documentation says the heat pump uses roughly 900 watts during extended run time which is clearly much more efficient than the electric heat and the entire point of having the heat pump. Friedrich sells a unit with just the resistance heat but that is the PDE model and not the PDH. Am I not getting the efficiency of the actual heat pump? My unit is operating like a PDE12k that was mislabeled as a PDH12k.

    Background information:

    Set temp: 67 degrees F
    Outside temp during testing: 38 degrees
    Average cycles per hour:2 (no strain)
    Average cycle time: 15-20 minutes
    Temperature never dropped more than 1.8 degrees below set temperature.
    Unit's air filter is clean
    Dip switch 1 is set to off (emergency heat is OFF)
    Unit is less than 2 years old
    12000 BTU rated output
    650 sq foot apartment in new construction building 2 years old.

    Please any help would be appreciated. Right now my power bills are through the roof and I have to keep heat off as much as possible just so my power bill isn't over $300 in a 640 sq ft apartment using one freaking heater.

  2. #2
    Join Date
    Sep 2007
    Location
    edmonds wa
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    Sounds like a tech visit is in order to verify compressor working. Any chance they have a spare unit to swap with?
    UA Local 32 retired as of Jan 2020

  3. #3
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    Dec 2019
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    Thread Starter
    I think I may need to call a tech as well. I don't think building has any spare parts lying around.

    So, I'm not crazy in thinking that it appears to be using the resistance heating element instead of the heat pump?

    There is one other identical heater in the apartment that I rarely use because it is in the bedroom and way over powered. 12000 BTU for 120 sq ft (lol). But I may run some tests on that and see if I get similar numbers. I highly doubt both compressors are messed up but it might help me figure it out either way.

    My other theory is the unit is calculating that it can't heat the room appropriately without the resistance heat based on the outside temp and the set temp, but it just isn't that cold out so I'm not sold on that idea.

  4. #4
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    It also runs straight electric heat based on outdoor temp.

    It cannon run both at the same time.

    Sounds like your setup to not use the heat pump.
    I’ve set them up that way on purpose, due to customer requirements.


    Are you using a wall thermostat or are you using the onboard display?

  5. #5
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
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    The manual indicates that when switch #! is in ON position, the unit is in EMERGENCY HEAT, your electric heat is the only heat operating.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  6. #6
    Join Date
    Dec 2007
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    Quote Originally Posted by dandyme View Post
    The manual indicates that when switch #! is in ON position, the unit is in EMERGENCY HEAT, your electric heat is the only heat operating.
    He stated that and that it was off.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  7. #7
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    I'm with vegas. Too much weather in the low to mid 30s or less causing the compressor to shut off. These suckers don't defrost like mini splits and conventional units. All they can do is stop the compressor. I think GE PTHPs are the only of their breed that can even run comp & strips together if warm enough and backup is called for.

  8. #8
    Join Date
    Sep 2007
    Location
    edmonds wa
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    If both of your units are the same model number, it should be easy to swap the chassis around and see if operation changes.
    UA Local 32 retired as of Jan 2020

  9. #9
    Join Date
    Dec 2019
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    Thread Starter
    Quote Originally Posted by hvacvegas View Post
    It also runs straight electric heat based on outdoor temp.

    It cannon run both at the same time.

    Sounds like your setup to not use the heat pump.
    I’ve set them up that way on purpose, due to customer requirements.


    Are you using a wall thermostat or are you using the onboard display?
    This is what I am suspecting and would honestly suck because in NYC most winter days are lower 30's/ upper 20's. In the manual it says:

    "When the outdoor coil temperature falls below 30° F for more than 2 minutes the unit will operate the resistance heaters and not the compressor. When the outdoor coil temperature reaches 45° F the compressor will be
    allowed to operate again."

    I don't know enough about heat pump coils but seems this could be forcing the unit to use electric. Does outside coil normally drop below freezing when temperature is upper 30's? Or is this something that normally happens but is quickly remedied by running electric for a few minutes?

    To answer a few of the other questions:

    *I am not using different thermostat. I am using onboard system.
    *DIP switch 1 is confirmed off. That was first thing I checked.
    *Both units are the same model number. I haven't run any tests on bedroom unit yet to compare power usage.

    With heat pumps is the compressor running or the auxiliary heat running but not both? As far as I can tell from the documentation the only way to force resistance heat is with dip switch so if that is turned off either my compressor is broken which i actually strongly believe is not the case or the unit itself is running resistance heat due to outside temperature. Running resistance heat in the mid 30's in NYC is essentially useless as a heat pump since most days are below that if that is the case.

  10. #10
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
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    Quote Originally Posted by pacnw View Post
    He stated that and that it was off.
    thought they stated #1 is on, oh well.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  11. #11
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
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    Yes.
    It sounds like your unit is running as designed.

    Not that I feel it’s the best product for your application, but that it’s operating as intended.

    Just an FYI for the new few questions, the heat strips are before the coil. Meaning that it can’t run simultaneously.

    It also has no defrost board.

  12. #12
    Join Date
    Dec 2019
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    9
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    Thread Starter
    Quote Originally Posted by hvacvegas View Post
    Yes.
    It sounds like your unit is running as designed.

    Not that I feel it’s the best product for your application, but that it’s operating as intended.

    Just an FYI for the new few questions, the heat strips are before the coil. Meaning that it can’t run simultaneously.

    It also has no defrost board.
    I ran some more experiments today because temperature was warmer. 46 F instead of mid 30's. I ran my unit for an hour and the heater was on and blowing for 30 minutes out of that hour. Except this time it only used about 291 Watts in that hr for an equivalent power usage of ~600W if it was on for the entire hour. Obviously this is far superior to the ~3,400W/hr the heater was using when I wrote my first post.

    I think you were right in that the cooler temperature (below 40F) is just forcing the resistance heat and there is nothing I can do about it which sucks because rarely is it above 40F. I honestly could not run the heat at all when it is 45 outside and ambient building heat will keep my apartment around 66.

    Oh well. Thanks for the help guys. The unit seems to be running fine. The builders should have put in a unit that isn't so sensitive to the cold outdoor temps.

  13. #13
    Join Date
    Dec 2019
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    Thread Starter
    Possible Solution

    Wow. Interesting development.

    The temperature in NYC yesterday was around 47F during the day. (I also unplugged the unit for 15 minutes while I was messing with it. Didn't change anything though). Either of these may have triggered the outside coil to read above 45 degrees which is the requirement for compressor to run after falling to below 30 degrees.

    The temperature dropped back down to mid 30's (same as first experiment) with a windchill that was freezing (about 31F) and the heat pump performed perfectly all afternoon and all evening! It never used more than 225W/hour which blows my mind!

    It seems the key is getting the unit reset somehow after temperatures dip below 30 degrees or resistance / aux heat will be used indefinitely until temps go back to 45F.

    Check out the difference in power usage from before and after (below img). During the worst of my tests the heater was pulling 0.8kW in a 15 minute time period not really shown in image cause I dialed it back out of frustration lol. The low consistent power usage is proper functioning of the heat pump.


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