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  1. #1

    Newer heat pumps turn on aux heat too soon

    I do home inspections in the charlotte nc area and have been noticing this for a few years on all of the new heat pumps.
    I don't see it as a defect but am wondering why these nice R410 units would have a programmed design that wastes energy.
    Is it done to reduce what may be perceived as nuisance callbacks from home owners that don't like heat pumps due to long past issues?

    If the set point is raised just one degree, the aux heat usually comes on and is displayed as such.
    I say "usually" because the actual amount of difference between the room temperature and the set point is displayed without the benefit of knowing the tenths of a degree that is used internally to the t-stat. With 2 degrees set it always comes on. As we all know, the aux heat uses about 3 times the power per btu than the heat pump.

    I see mostly Carrier or Lennox heat pumps that use Honeywell t-stats.
    Typical t-stats: Honewell TH6320R1004 and RTH3100C1002/A

    Anyone know why they have designed these to not take advantage of heat pump technology any better than this?
    Since the manufacturer will not take calls from anyone other than you guy's could someone look into this for me please?

    thanks!

  2. #2
    Join Date
    May 2000
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    Indianapolis, IN, USA
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    34,158
    Probably because many customers want instant comfort. So they want the house to go up that 1 degree immediately and not wait for the heat pump to do it, which in very cold weather, could be a long time. White-Rodgers can be set for a delay in bringing on backup and many upper end stats have the option of outdoor sensors to lock out backup in mild weather.

  3. #3
    Join Date
    Jul 2008
    Location
    Rochester NY
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    Because the energy bill is the homeowners problem, while the unpaid complaint call from goofy and doofus is food off the installers table at hay making season.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    7,032
    Outdoor sensors is the best way to remedy this problem but lots of customers or builders want it done cheap therefore they get lower end model thermostats as you described. Most customers don't understand how heat pumps work and would call a contractor to come look at there unit if it didn't come up to temp rapidly costing them more in a wasted service call than running the strip heat a little more to make them satisfied and comfortable. The more informed consumer will usually opt for a better thermostat with an outdoor sensor that locks the strip heat out until necessary to keep up with the heat loss of the structure and be economical/most efficient.

  5. #5
    Join Date
    Jul 2008
    Location
    Rochester NY
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    Quote Originally Posted by jtrammel View Post
    Most customers don't understand how heat pumps work and would call a contractor to come look at there unit if it didn't come up to temp rapidly costing them more in a wasted service call than running the strip heat a little more to make them satisfied and comfortable.
    Maybe we should start a campaign against the dogma that "setback saves," then this problem goes away.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,064
    Its not the heat pump. Its the thermostat. Thermostats designed to maintain a tight temp tolerance will bring on aux quicker then ones designed more for economy.
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  7. #7
    Join Date
    Jan 2004
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    Lancaster PA
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    Quote Originally Posted by tedkidd View Post
    Maybe we should start a campaign against the dogma that "setback saves," then this problem goes away.
    You should start a thread in tech to Tech, or the Pro forums to talk about this.
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  8. #8
    Join Date
    Dec 2012
    Location
    Lancaster County, Pennsylvania
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    What's a good tstat that allows me to control when the aux heat comes in?

    I have not been a fan of tstats that bring the strip heat in every time the house is in recovery from a setback and don't give me any control of how and when. I maintain systems in group homes and we have about 50 geo units. Those things will heat no matter what and yet the strip heat gets called. Our dual fuel units with the Honeywell 8000 series tstats and outdoor reset enabled will let me lock out the aux by temperature, but a geo unit doesn't care about OA. We do use a night setback in some situations because with single zone dwellings, if the person(s) prefer to sleep in a cooler temp, say 65 to 68 and daytime heat is 72, they have to pay for that extra electric. I've shut off most of the strip heat in those places and hope that a compressor or circulator doesn't quit during a cold snap when I'm out of cell phone range.

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    Even the DOE has backed away frmo the table a little on setbacks. I think thre's is a comment on energy start site abotu not using setbacks with heat pumps in particular.

    THe big problem with setbacks is they reduce comfrot which causes you to keep it warmer most of the time and they require you to have oversized equipemnt which is less efficient and more exensive to isntall... which engates the energy that might be saved in the first place.

    Most homeowners and contractors will be shocked at how small equipment actually needs to be when properly installed on a properly constructed home to maintain temperature in design conditions. I think one homeowner that visited here said that after sealin, insulating his home and right sizing the equipment their energy bill statistically was I think 58% of the average of similar sized home in his area.

  10. #10
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    Quote Originally Posted by motoguy128 View Post
    THe big problem with setbacks is they reduce comfrot which causes you to keep it warmer most of the time and they require you to have oversized equipemnt which is less efficient and more exensive to isntall... which engates the energy that might be saved in the first place.

    Most homeowners and contractors will be shocked at how small equipment actually needs to be when properly installed on a properly constructed home to maintain temperature in design conditions. I think one homeowner that visited here said that after sealin, insulating his home and right sizing the equipment their energy bill statistically was I think 58% of the average of similar sized home in his area.
    I think your second statement is even bigger part of the problem than the first:

    It might be arguable that with over sized equipment setback DOES save (due to reduced cycling losses and steady state efficiency gains).

    But going from 8 mpg to 12 mpg is missed opportunity if it COULD have been taken to 30 mpg.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  11. #11
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    Lancaster PA
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    68,064
    Quote Originally Posted by motoguy128 View Post
    Even the DOE has backed away frmo the table a little on setbacks. I think thre's is a comment on energy start site abotu not using setbacks with heat pumps in particular.

    THe big problem with setbacks is they reduce comfrot which causes you to keep it warmer most of the time

    Why would a night set back cause someone to set their temp higher.

    and they require you to have oversized equipemnt

    Does't require you to have over sized equipment, thats just a myth.

    which is less efficient and more exensive to isntall... which engates the energy that might be saved in the first place.

    Most homeowners and contractors will be shocked at how small equipment actually needs to be when properly installed on a properly constructed home to maintain temperature in design conditions. I think one homeowner that visited here said that after sealin, insulating his home and right sizing the equipment their energy bill statistically was I think 58% of the average of similar sized home in his area.

    One method of reducing energy cost shouldn't be trampled on to promote another.
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    How many times must one fix something before it is fixed?

  12. #12
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    Rochester NY
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    Because mean radiant swings behind air temp. Air temp settings tend to be either "comfortable" or "minimum bearable" depending on occupant. Either way, lower mean radiant (and rh) means higher air setting required. Check the link in my sig.

    By definition the ability to recover means more output required than needed to maintain. Expectation of recovery is most certainly one major factor that has hvac guys and acca (?) factoring what, .77 fudge?

    Cycling losses are a big unmeasured cost that, when I aggressively downsize and install equipment that NEVER shuts off, seems to be the only thing that can account for extraordinary savings people are experiencing. But a side effect is, while maintaining is not a problem, they can't achieve any kind of acceptable recovery at temps ANYWHERE NEAR DESIGN.

    So yes, bloodletting and leaches must be put to bed for us to move into this next era. You've taught me so much, if I can share perspective here that helps you that would be very gratifying.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  13. #13
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    As Ted said, radiant lags air temp. So while the stat reads 70 after a recovery the walls, floors, furniture are still much cooler for a few hours.

    Setback doesnt work when properly sized because in cooler weather it lacks reserve capacity the recover. Although with manual j sizing a little extra is built in. Even then, 3 to 4f is all you'll get. Doesn't seem worth it to cut heat loads by what 2 or 3% over a 24 hour period.

    Sent from my DROID RAZR using Tapatalk 2

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