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  1. #27
    Join Date
    Jan 2004
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    Lancaster PA
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    That could be caused by sun shine, if its not mounted in a shaded area, or on the North side of your home. Can also happen if its near a sofit vent.

    Not unusual for an air port to have one temp, and a mile or 2 a way have another temp, a couple degrees cooler or warmer.

    But jumping that much. Sounds a bit out of line. Does it seem to do it more when its windy outside.
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  2. #28
    Join Date
    Nov 2009
    Location
    West Coast of Canada - Home of the 2010 Winter Olympics
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    56
    I know other factors can influence it, but I've got a "weather station" the Kids bought me a couple years ago that communicates via radio telemetry, which is just around the corner and far more stable in temperature. The sky was quite dark (late afternoon) with no direct sun. It's also tucked in close to the house behind 2 fences out of the wind, rain, sun, etc. (It grows great moss there - and not much else.)

  3. #29
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    Jan 2004
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    Lancaster PA
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    Quote Originally Posted by -Jim- View Post
    It's also tucked in close to the house behind 2 fences out of the wind, rain, sun, etc. (It grows great moss there - and not much else.)
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  4. #30
    Join Date
    Oct 2009
    Location
    Vancouver, BC
    Posts
    12
    The installers previously had the sensor in the electrical box that feeds the heat pump. I advised the installer I was getting intermittent readings that were off about 5 degrees.

    The installer removed the sensor from the inside of the electrical box and exposed it to the outside air. Its better now but when the heat pump is on its out about 1.5 degrees.

    I have to get the installer to move it to a better location.

    Where is your sensor located?

  5. #31
    Join Date
    Apr 2009
    Posts
    523
    That sensor is pretty basic. The thermostat is measuring resistance of the sensor. Needless to say there is a LOT of things that can effect it that arent related to temperature and location at all. Things like the wire condition, solid or stranded, electromagnetic interference from high voltage wiring or from anything for that matter, the length of run, etc etc

    My example is my house, obviously I would do it the BEST to my ability. I have a standard isolated two wire run from the control to the thermostat and the sensor soldered to the wire. It avoids ALL wiring low and high voltage and is mounted in a very good location. I'll still see more then a 1.5 degree difference then it really is sometimes. PLUS how accurate is that thing your kids bought you seriously? If we are talking a 900 dollar whether station I would assume it right but I doubt its that nice of a device...

    Cause you will have a cool/warm breeze blowing off nearby objects or heat trapped in what its mounted too, uv reflecting off of something distant. etc etc

    Basically what I'm saying is it might be as good as its going to get. The efficiency difference between a 1.5 CONSTANT difference in outdoor temp sensor will be minimal to the point I be willing to say incalculable....

  6. #32
    Join Date
    Dec 2007
    Posts
    4,690
    I believe the sensor for that thermostat requires its own wire and it should be shielded and possibly stranded.

    check the install pamphlet that comes with that sensor.

    we installed some with and without and some do and some do not show issues.

    I have one in my house that is connected to the regular run of stat wire, no issues.

  7. #33
    Join Date
    Nov 2009
    Location
    West Coast of Canada - Home of the 2010 Winter Olympics
    Posts
    56

    Cool

    Thanks for the input Gents. Now that the New Year is here and I've gotten most of the Holiday stuff out of the way, I'm going to call the contractor and ask them about it.

    I recently walk by the thermostat and it said the outside was 38 F and the Aux Heat (Gas Furnace) was on. (The Heat Pump should be on.) By the time I got a camera to take a photo (15 seconds later) it was 35 F. Daffy !

  8. #34
    Join Date
    Nov 2009
    Location
    West Coast of Canada - Home of the 2010 Winter Olympics
    Posts
    56

    Cool

    Folks,


    I've been pondering the following:

    The incremental energy costs here for Natural Gas is $ 10.02 per GJ, whereas Electricity is $24.48 per GJ (8.8 cents / kWh) => in Canadian Dollars once I include all taxes, levies, etc., converting at 1 GJ = 278 kWh.

    According to BC Hydro (the local Electricity Utility) air at -5 C contains 85% of the heat in air at 20 C, and Heat pumps can operate effectively down to -5 C. Below -5 C all heat must come from a secondary source.

    According to the contractor a Heat Pump operates in concert (simultaneously) with supplimental back up electric heat. (Like my Brother in laws system.)

    Does it follow that down to -5C that electric heat only makes up 15% of the heat energy required with the Heat Pump providing the rest? If so using Natural Gas in Metro Vancouver for supplimental heat may not be the bargain I was told it was.

    Perhaps one of you Guru types know if I'm on the right track here.

    Thanks for the assist!

  9. #35
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    Jan 2004
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    Lancaster PA
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    As the outdoor temp gets lower. The heat pumps COP drops off.
    So at -5C(23F) you need to lnow what the heat pumps COP is.

    At your posted rates. When your heat pumps COP drops below 2.5. Gas heat at 95% efficiency is cheaper then the heat pump, let alone electric aux.

    With an 80% furnace, gas becomes cheaper then the heat pump at a COP less then 2.1

    So gas aux is cheaper.
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  10. #36
    Join Date
    Nov 2009
    Location
    West Coast of Canada - Home of the 2010 Winter Olympics
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    Cool

    Beenthere,

    Thanks for the comment. I understand the COP of the Heat Pump decreasing as outside temperature drops (in a linear manner - following the Balance Point Graph?).

    The new G61 MPV Furnace has an AFUE rating of 95% so that also would have to be factored into the analysis.

    I found a site where it states:

    "Energy Efficiency Ratio

    The efficiencies of air conditioners and heat pumps sold in the United States are often stated in terms of an energy efficiency ratio (EER):



    This peculiar ratio can be compared to the more straightforward coefficient of performance by converting BTU/hr to watts:



    Therefore CP = EER x 0.292. The range of EER's for air conditioners is typically about 5.5 to 10.5 with those units for which EER>7.5 being classified as "high efficiency" units. This is a range of 1.6 to 3.1 in CP."

    The certified EER (AHRI Certificate) for my system is 12.00 which then gives a CP of 3.504 but isn't this in a cooling mode, or can this be used for heating as well?

    I'm a bit confused on how to apply all of this to see which source => Gas or Electric => is the correct choice for supplimental heating. My wife thinks I'm daft as the system is all installed and there is nothing to be gained by figuring this out now; but the mental excercise will help me sleep better at night as well as corroborate the recomendation of the Contractors.

  11. #37
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    Jan 2004
    Location
    Lancaster PA
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    EER is not a constant. As outdoor temp changes, so does the EER.

    Since we're talking heating. Use factory COP ratings. Since you may have a hard time finding the EER rating for heating.

    If you only have the COP for 47 and 17 outdoor temp. Plot a chart, and see where it drops below a COP of 2.5
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  12. #38
    Join Date
    Nov 2009
    Location
    West Coast of Canada - Home of the 2010 Winter Olympics
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    56

    Cool

    Beenthere,

    I found some more helpful data / equations:

    "Since 1 BTU = 1055 J, and 1 watt-hour = 3600 J, the seasonally-averaged COP is given by:

    Avg COP = Heat transferred / electrical energy supplied = HSPF * 1055 J/BTU / 3600 J/watt-hour = 0.293 HSPF.

    Thus, a system which delivers an HSPF of 7.7 will transfer 2.25 times as much heat as electricity consumed over a season."

    Therefore following this logic, my system which has an HSPF of 8.7 will transfer 2.55 times as much heat as electricity consumed over a (heating) season.

    I'm amazed I can't seem to find the COP at the Lennox Site (temperature dependant => or seasonally averaged) or even in my documentation. All that would be needed is the operating power input to the Heat Pump at the various outside temperatures, or an equation defining the slope of the curve if it's close to a linear relationship.

    I'm thinking if I could document the actual COP versus outside temperature, I could figure out which energy source (mathematically) should be the back up heat supply.


    You commented: "At your posted rates. When your heat pumps COP drops below 2.5. Gas heat at 95% efficiency is cheaper then the heat pump, let alone electric aux." How did you figure this out?

    If the calculation above is correct (Seasonally Averaged COP = 2.55) then there isn't much room for degradation to your 2.5 value.


    Is this on the right track or is there a better / simpler way to do this?

  13. #39
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    Jan 2004
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    Lancaster PA
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    I used the rates you posted.
    On the electric. I just kept dividing the cost for a gj by COPs, until I came to the point that gas was cheaper.

    24.48/=9.79
    24.48/2.4=10.20

    At a COP of 2.5, with a heat pump you are getting 2.5 times as much heat as you would if you were using electric resistance heat.
    So you just divide the gj cost by 2.5, or what ever COP you want to know if its cheaper then gas at its gj rate.

    Depending how new your heat pump is. You can find the COP for 47 and 17 on the AHRI website.
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