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  1. #1
    Join Date
    Oct 2007
    Posts
    21

    Bryant Evolution - balance point help

    I recently had a Bryant Evolution Hybrid system installed in my home it seems like a great system. I am looking for advice on what a good balance point would be. The system is set at the factory defaults and when I went into the heat pump lockout, it was set to no lockout. I set it to <40 for now but would like to put it at a good point for the winter. Any advice will be greatly appreciated. Thanks!


    Furnace- Bryant 355BAV-080 80,000 BTU, 95% efficiency
    Heat Pump- Bryant 286-036, 3 ton, 15+ SEER
    Thermostat- Bryant Evolution Control
    Location- Sterling Heights, MI
    Home Size- 2000 sq. ft.

  2. #2
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,189
    ADAM

    If you have a calculated balance point frpm your dealer, I recommend taking that number and increasing by 10%.

    for ex,
    a calculated balance point of 30, I suggest a setting of 33.

    However, I assume you just don't know. Then I would set changover at 35 degrees and adjust accordingly up or down based on your home's comfort and if thermostat setting is being maintained without outside unit running constantly.

    IMO

  3. #3
    Join Date
    Oct 2007
    Posts
    21

    Wink

    Thanks for the advice and you are correct that I don't know what to set the balance point to. My installer has not been very helpful yet in this area so I have set it to 35 deg as you suggested. My installer is going to try to see if there is a software program available to help in deciding on a good balance point.

    I was surprised that the default setting said "None" when I went into the advanced settings of the Evolution controller under heat pump lockout temp. I am assuming that this is where the balance point is set? I change the setting to <35 deg.

  4. #4
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    Call your electric company and see if they have a suggestion as what the balance point should be. I think that if you set it at 35 you blowing the whole reason for having a heat pump. We run ours to 12 - 15 degrees in Nebraska. This gets the most possible out of the heat pump.

    Remember that the colder you run the heat pump the cooler the supply air temps will be. Your body temp is 98.6 or so and you may only be getting 95 degrees out of the registers. This may seem cool but is still heating your house.

    You bought the heat pump to save energy so run it down to lower than 35.
    Its a good Life!

  5. #5
    Join Date
    Mar 2003
    Posts
    1,234
    You have a good system. Mine is similar and I set the lockout at 25 last winter and may lower it to 20 this year. Then again I live in a very moderate desert climate. Set it and see how comfortable you are then adjust as needed.

  6. #6
    Join Date
    Dec 2000
    Location
    NW Ohio
    Posts
    516
    What you are looking for on a duel fuel system is the economic balance point.
    That is at what temperature does the furnace operate cheaper than the heat pump? You will need to know what the cost is for your gas and your electric. If your dealer cannot do this for you then have them contact bryant. Looks like you will have a very efficient system when it is setup correctly.

  7. #7
    Join Date
    May 2007
    Location
    Upstate SC
    Posts
    188
    -LONG- sorry!-

    You don't really need a computer program, but I wrote an Excel spreadsheet for mine.

    You basically take the corrected COP for an outdoor temp for the heat pump- that number is roughly the amount of heat the HP makes versus the amount of energy required to produce it (no, it's not creating energy like the definition of COP sounds like, it's just a function of a heat/refrigeration cycle). You can find this exact number in a technical specification from the manuifaturer, but I found my spec manual on the web.. generally NOT a consumer document I have discovered.

    So with the COP number, if your home loses 40,000 BTU/hr of heat during the arbitrary outdoor temp you chose the COP for, then you know you need to add that amount from your HP. With a COP of 3 (for example), you know if you require 40,000 BTU/hr of heat, you need to input about 13,333 BTU/hr of electricity. Divide the 13,333 BTU/hr by 3415 and you get 3.9 KW. Assume this outdoor temp you arbitrarily chose will last 10 hours. Therefore you will need 39 KWh. If you pay $0.10 per KWh, then your power bill that night for the HP alone will be $3.90.

    If you have a gas furnace with 90&#37; AFUE rating, you know it will produce approximately 0.9 BTU/hr of heat for every 1 BTU/hr of gas it burns. If you need 40,000 BTU/hr of heat for your home at that temp you picked, then you need 44,444 BTU/hr of gas into the furnace. Since you pay gas by the therm, convert 44,444 BTU of gas into therms by dividing by 100,000. Therefore you need 0.44 therms per hour, or 4.4 therms for the 10-hr you will be at that cold temp. If you pay $1.25 per therm, then the gas furnace for that 10 hrs will cost you $5.50. You would save, 5.50 - 3.90, or $1.60 if you used the HP at that utdoor temp for that 10 hr period.

    Now, your values will be different. Your equipment will be different, your house temp and heat load loss at that temp will be different. Your equipment will operate with different efficiencies at that indoor and outdoor temp differently, and you pay a different amount for utilities than the example. But you get the idea. From my little experience with my single installation, my installer did not provide me with the technical specification manuals for me to get effiicies at differenty outdoor and indoor temps. I found those on the web somewhere. But you can find general numbers from your manuifacturer's website... like AFUE 92.5 % for a furnace and COP of 2.9 or something for your HP. While a heat loss at each temperature (indoor and out) is nice to figure out exact costs, you can use an arbitrary heat loss (or the design heat loss calc your vendor provided you with) if you just want to see which is cheaper.

    Odds are good at very, very low temps, your HP may not provide enough heat, or it will feel like a cold draft when running. If it can't provide enough heat to maintain the tstat setpoint, your backup heat will come on. The sheer SIMPLE method of figuring out a balance point, is just try it out at different temps (within the manufacturer's accepted temperature ranges, of course) and see what you and your family are comfy with. The math methods I used above is way too simplified, especially if you get similar costs for each heat source to really call it real creditable. In general, if you have the manufacturer spec book, you will see a HP losing ground to a gas furnace as outside temperatures drop. My calcs for a Trane 3-ton XL16i and XV90 furnance showed this to be between 2 and 15&#176; F depending on if you were looking at stage 1 or stage 2 COP values. But my heat pump won't provide enough heat at 2&#176;F, nor will my wife like the 'cool draft' feel of the house if it could.

    Just remember, a heat pump can produce 2-3 times (or better, called COP) worth of heat at a given temperature versus every unit of heat (in the form of electricity) it is provided with. It gets this heat from outside and transfer it inside using the little bit of electricity you provided. A 90.0 AFUE furnace's COP is generally approximately 0.9 at all temps.

  8. #8
    Join Date
    Mar 2005
    Posts
    56

    software? spreadsheet?.....

    Balance point is the point where the heat pump's output becomes equal to the heat loss of the structure. With a proper heat loss calc and performance ratings of the equipment, this can be plotted in graph form on a piece of paper. The outdoor temperature at which your decreasing HP output line and increasing heat loss line meet is the balance point.

  9. #9
    Join Date
    Dec 2000
    Location
    NW Ohio
    Posts
    516
    Quote Originally Posted by stopro1 View Post
    Balance point is the point where the heat pump's output becomes equal to the heat loss of the structure. With a proper heat loss calc and performance ratings of the equipment, this can be plotted in graph form on a piece of paper. The outdoor temperature at which your decreasing HP output line and increasing heat loss line meet is the balance point.
    Don't confuse the thermal balance point of a heatpump with electric backup with the economic balance point of a dual fuel system. What you are describing is the ability of the heatpump to heat the structure at a given temperature. The economic balance point is the temperature that the fossal fuel furnace begins to operate at a lower cost than the heatpump.

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274

    Thumbs up Kiss

    Quote Originally Posted by adamsdp View Post
    My installer has not been very helpful yet in this area so I have set it to 35 deg as you suggested.
    The sheer SIMPLE method of figuring out a balance point, is just try it out at different temps (within the manufacturer's accepted temperature ranges, of course) and see what you and your family are comfy with.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #11
    Join Date
    Mar 2005
    Posts
    56

    Confusion

    Don't confuse the thermal balance point of a heatpump with electric backup with the economic balance point of a dual fuel system. What you are describing is the ability of the heatpump to heat the structure at a given temperature. The economic balance point is the temperature that the fossal fuel furnace begins to operate at a lower cost than the heatpump.
    There is no reasonable economic balance point where the fossil fuel furnace is more efficient than the heat pump, until it's about -10F outside, when the heat pump's COP is at .95 (equal to the furnace). Balance point is and always will be the point where there the heat pump can no longer satisfy the heating demand alone. When the room temp falls below the setpoint, you have fallen below the balance point, and will require back-up heating to maintain the same setpoint.

  12. #12
    Join Date
    Oct 2007
    Posts
    21
    Thanks to everyone for their helpful replies. I am looking for the best economic balance point. From some of the replies it sounds maybe I should go back to the default setting of no heat pump lockout temperature and just allow the furnace to come on when the heat pumpt cannot keep up with the heating demands? Will I be risking any damage to my heat pump if I have the system setup in this fashion?

    I am going to pursue trying to figure out at what temperature the furnace will become more economical to run than the heat pump. It sounds an approximation might be the best one can do, but I still think it will be useful information. Thanks.

  13. #13
    Join Date
    May 2007
    Location
    Upstate SC
    Posts
    188
    Credit for the quote would have been nice

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