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High electric bills and unexpectedly low COP with Carrier heat pump

Folks,

I'm wondering if it's cost effective to investigate why I'm getting unexpectedly low efficiency from my Carrier heat pump.

I have a heat pump + electric backup system that has always been expensive to operate. I recently did some experiments, on days with near freezing temperatures and no wind, running with electric only and running both the HP and electric heat. Running the heat pump only reduced power consumption for heating to 77% of what it was with electric heat only, which looks to me like a system-wide COP of 1.23.

Carrier's published COP rating for this heat pump and air handler, at this air temperature, is 1.6.

At these temperatures, the heat pump does not need much help from the electric backup except when recovering from night setback.

Would it be worth-while to ask a HVAC contractor to have a look at this (e.g. to check refrigerant charge levels) or is this the expected real-world performance for this kind of equipment?

The air filters, condenser coil, and evaporator coil are clean.

Thanks for any input.

Comments

  • GW
    GW Member Posts: 4,691
    I’m kind of stating the obvious, but refrigeration charges crucial. Let’s run with the assumption for one moment that the charge is a off. One of two things, the installer did not commission the job properly, or, he needs to come back in the spring charge it in AC mode, or perhaps there’s a leak. Another factor is airflow, little bit difficult to guess over the keyboard. Properly size? Ductwork? Sealed and insulated? This could go on and on

    What model heat pump? Inverter? You did not go to any details about installation and if that contractor is still in the mix, that’s a whole different conversation.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
    EdTheHeaterMan
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,840
    How old is this thing? Modern heat pumps have COPs >3 at those temps
    EdTheHeaterMan
  • ratio
    ratio Member Posts: 3,623
    I view COPs like I do MPGs. You can expect to meet them with new equip sitting on an engineers desk in a well-lit office. Out in the field, a few weeks after install…
    EdTheHeaterManWMno57
  • pecmsg
    pecmsg Member Posts: 4,838
    edited January 2022
    As outdoor temps drop so does the COP but a heat pump is almost always more efficient than straight electric.
    Age of equipment, Has the charge been pulled and weighed? Setbacks are not advised with heat pumps, set it and forget it.
    EdTheHeaterManSuperTech
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,817
    edited January 2022
    Your test method has a flaw. If you did the test and used a night setback during the test, then you are operating the back up electric resistance heater for a longer amount of time during the test cycle. If you do not use a night setback, then there will be less electric resistance heat used.  

    Although your test will still be somewhat incorrect, you should find the number to be closer to the ratings listed.  Any use of auxiliary resistance heat will lower the COP.   Electric resistance back up heat is not part of the COP Calculation. Including the amount of electricity used for electric resistance auxiliary or back up heat will yield an incorrect number

    For this test to be most accurate, compare heat pump only operation with electric resistance he disconnected to electric resistance only for the same time frame and degree day.  This is nearly impossible since no two consecutive days or weeks or whatever timeframe you select, will have identical degree days.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • PC7060
    PC7060 Member Posts: 1,156
    As @GW mentioned there is lots to consider.  Leaking ducts in unconditioned spaces have a huge impact on performance.   Not only do you loose the heated air; cold outside air is pulled in through the envelope.  
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,513
    And this is what we all have to look forward to when fossil fuels are shut down
    SuperTech
  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    They won't be shut down all at once Ed. It will take decades. The places a lot of folks here don't agree with politically will lead the way. That will drive demand so that manufacturers keep improving heat pumps for all climates (global warming is helping with that problem).

    Then as that technology improves and becomes more attractive, more people will like the way heat pumps cost and work regardless of their politics or personal feelings.

    It won't be a continuous curve either necessarily. Reduced use of fossil fuels on the consumer market will cause prices to fall which will spur localized increases for new installs of fossil fuel technology.

    Some people who just really love to burn things will keep installing even coal systems for quite awhile (I've even thought about the possibility of installing a coal boiler in a future home). Coal and gas and oil will remain legal for new installations in plenty of states that don't care about their air quality, or who value personal freedom to harm their descendants.

    So don't cry for fossil fuels...they'll be around, just like vinyl audio today, for collectors and the nostalgia-minded.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    edited January 2022
    For what it's worth, @ethicalpaul , I wouldn't mind a bit having a heat pump instead of Cedric when it comes time to replace him (he's only 16, so that's going to be a while yet). And, possibly, by the time he needs to be replaced, there will be such a thing. At the moment, there isn't. Period. It doesn't exist. Not that it can't, but it doesn't. And when it is available (if ever), it won't be as reliable as Cedric. I won't be able to power it with a generator when I have a week at 0 and no sunshine or wind because I won't be allowed to own a generator.

    Nor will I be able to afford to buy it.

    And I'm very fortunate in that I have enough woodland to keep my fireplaces going, and a daughter and son-in-law who are young enough to do that work. My ancestors lived that way, so we can too.

    But no one seems to give two hoots and a loud yell for the average working stiff on a half acre lot with an existing home in a village. And that is where I get upset. If the process and change could go the way you seem to hope -- costumer driven -- it would be fine. But it won't. But that's a political problem.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    Hi Jamie-- I think you and we will be able to have a gas generator for the next 50 years no problem. And no politician will be able to harm the people in every state who live rural lives--they don't want to, and they can't afford to.

    Heck, even today rural folks are burning their trash and their wood pellets and no one is going to make them stop doing that certainly not within our lifetimes.

    I care about these people too. They're who I was raised by and with although today I'm an "urban elite". They'll be fine.

    These regulations as I mentioned will come in very slowly and the harmful heating methods will likely be priced out of existence, replaced by more affordable replacements (I know you are pessimistic about this and I respect that) rather than be mandated out. Heck today about 30% of people think coal is clean and that the government should be subsidizing its production. That's a lot of votes that need pandering for!
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
    Canucker