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  1. #1
    Join Date
    Mar 2004
    Posts
    33
    Well I have limited data but I am starting to swear by setback thermostats, even though we have a heat pump. Live in southeast PA.

    Set back settings 70 day and 66 overnight, recovery occurred at 6AM. My data from Nov, Dec and Jan showed approximately average 67 kwH per day with highs of 95 kwH on the coldest days during that period. Single digits for day and night temps on those cold days.

    I just swithched to keeping the temp at a constant 70 which feels comfortable I doubt we could lower it. And for the first two days with temps similar to the coldest days I am comparing it to last month. The weather conditions and other appliance use being the same over those days. Our electric has been 126 and 152 kwh each day respectively. That is almost 1.5X as much electric used to keep the house at 70 overnight. I am going to give it about a week so the outside temps vary but at this rate there is no one that can convince me setback is bad with a heat pump.

    We had 1 evenings and highs of 10 for a few days in a row when we were using set back settings and the highest 24 hour reading I had was 95 kwh during that period.
    We have not used the oven or dryer so I could make an accurate comparison. The dishwasher and hot water heater were not used any differently over these day as compared to those days.

  2. #2
    Join Date
    Nov 2002
    Location
    emerald city, sc
    Posts
    1,469
    you have to figure in more than the outdoor temps highs and lows. how long was the low temp for, how long was the high temp for, what was the wind speed and direction, cloudy or clear.
    the only way to know is to install a watt meter on the heat system, and compare degree days. even then there are variables.
    the main thing to remember is, are you comfortable?
    i wanted to put a picture here

  3. #3
    Join Date
    Mar 2004
    Posts
    33
    I appreciate those variables. I feel I have taken a good amount of that into consideration. I might expect 10% -15% difference even if it appeared to be similar conditions with my limited abilities.

    But to see a 50% increase with very similar and very low temps I tend to want to draw the conclusion I did. I can't believe wind direction on a 5 night makes more then a 10% difference in heat requirements.

    I am going to continue my data collection but if it continues to be this lopsided then I will go back to using a set back.

    I only bring this up, because of all the people, on here and elswhere that have said there is no way setting back a heat pump can use less electric then holding it at a steady temp.

  4. #4
    Join Date
    Oct 2003
    Location
    west chester pa
    Posts
    343
    Setback is good on heatpumps when done through a programable t-stat that brings the temp back up slowly so you don't rely on the electric heat. Most people turned down at night then just turn it back up in the morning using a manual t-stat but that causes the electric heaters to run wasting the saved energy at night.

  5. #5
    Join Date
    Sep 2004
    Posts
    265
    I'll agree with pipe. Most people with heatpumps do not understand that once you set the t-stat 2-3 degrees pass the set temp that the electric heat will also go on.
    During cold spells I set my heatpump back at night and it is programmed to raise the temp in two degree increments so the house is warm when I get up in the morning.

  6. #6
    Join Date
    Feb 2005
    Posts
    9
    Heatpumps --

    Despite what is commonly mentioned in this forum, I agree 100% with your conclusion regarding setting back thermostat for heatpumps. However, as was mentioned in this thread, people that crank up the thermostat in the morning will negate the savings due to aux heat kicking in. To avoid this, I keep aux heat off at breakers. Thus, in the morning, when I crank up the heatpump, only the heatpump will run until thermostat is satisfied. I have only a basic 2-stage manual thermostst. I do realize that I am losing some heat during defrost, however, I have learned to live with that. The savings is tremendous as you mentioned.

    I would be very interested to know your fan speed (cfm). I am running off a Trane variable speed air handler with matching heatpump, and my temperatures are not nearly as high as yours during heatpump-only operation. Maybe my speed needs to be lowered, which is easy to do.

    Any recommendations on a reliable thermostat that will bring up the temperature gradually in 2-3 degree increments?

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,350

    marca

    Any recommendations on a reliable thermostat that will bring up the temperature gradually in 2-3 degree increments?
    Consider a digital programmable from Honeywell that has Adaptive Intelligent Recovery (AIR). The VisionPro has this feature, with the ability to enable/disable it if you discover a conventional recovery actually works better. The AIR works well from my experience...it ramps up or down to the desired temperature you've selected at a given time. If you like to wake up to a warm house at 6 AM, the AIR will begin ramping up over time the temperature (slowly extending run times each cycle) until the temperature is at the higher setpoint. Works great and saves energy.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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