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  1. #14
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,722
    Quote Originally Posted by tedkidd View Post
    I was led to believe these things understood defrost based upon temperature. Given the source of the contradiction, I had to dig. I guess pressure increase does not trigger defrost. What does is really not very clear to me but probably will be to you:

    Ideal Defrost / Intelligent Defrost - (I have the Carrier VNA service training manual)




    What is not clear is it somehow knows how long defrost takes, and based upon that sets the next defrost run interval.

    This thing is pretty amazing. The controller can manage refrigerant charging check, pump down, tells suction pressure, compressor rpm, suction temp, superheat, exv position, airflow, lbs of refrigerant to add or subtract based on lineset length...



    And in a mild climate where the btu cost of propane has a snowballs chance in hell of approaching the cost of high cop heat pump, having a few btu of electric resistance combined with the heat pump for a few hours a winter is going to be WAY WAY cheaper than paying the incremental on the furnace. Paying the additional cost of burning propane particularly when you factor the heat pump CAN run with the resistance (like an additional stage) and the propane CAN NOT.

    I simply have not heard of 50c kwh electric, if it exists it's very rare, and that's still cheaper than propane at most temps.

    Forward energy view is electric will become more and more closely tied to natural gas. The only source that can hold a candle to the btu cost of these high COP heat pumps is Natural Gas, and that requires some pretty cold temperatures. This is very likely to remain true for a long time.
    On demand defrost uses the temp difference between the air and the liquid line to determine if there is ice/frost on the coil to a point that it needs to be defrosted. After the outdoor temp drops below X degrees(varies with manufacturer) they won't go into defrost except for once every 6 hours of compressor run time to make sure the outdoor coil doesn't become oil logged.

    Carrier tries to mimic the efficiencies of on demand defrost. But misses the boat a bit. Its better then just time and temp defrost, but still activated by only coil temp and compressor run time(with respect to outdoor temp being under 50). But when its 10 degrees outside, Carriers Ideal will still do needless defrost cycles. On Demand won't.
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  2. #15
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,699
    Who has demand defrost on their units?
    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.

  3. #16
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    I'd do standard electric backup. I don't see the additional costs of the LP furnace having a reasonable payback time.

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,722
    Quote Originally Posted by tedkidd View Post
    Who has demand defrost on their units?
    York, Lennox, Rheem(although they send time and temp replacement boards), ICP(at least they did in the early 2000s). Not sure who else.
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  5. #18
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
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    7,281
    Quote Originally Posted by beenthere View Post
    York, Lennox, Rheem(although they send time and temp replacement boards), ICP(at least they did in the early 2000s). Not sure who else.
    Trane

  6. #19
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,699
    Thanks BT. Not likely ever going to reach the point I don't have oceans to learn from you.

    Quote Originally Posted by Chris_Worthington View Post
    Trane
    Awesome, that's great to know! Thanks Chris!

    (I've moved over to AS as preferred brand. Anxiously awaiting inverter split. I guess mini's are coming in spring.)
    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.

  7. #20
    Join Date
    Sep 2011
    Location
    Nj and Delaware
    Posts
    75
    Thanks for all the insight, folks.

    I will be having a re-quote done on a 2 stage 10KW electric backup, removing the propane furnace. I suspect the capital cost will be pretty close as I will need to run a 60A service about 80' from the garage to the crawl space for the strips.

    As pointed out, this will make the heat staging a little more complex as I will want to be able to stage Y, Y2, W and W2. Would the EcoBee EB-STAT-02 be a good candidate for this?

  8. #21
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,699
    Quote Originally Posted by pendetim View Post
    Thanks for all the insight, folks.

    I will be having a re-quote done on a 2 stage 10KW electric backup, removing the propane furnace. I suspect the capital cost will be pretty close as I will need to run a 60A service about 80' from the garage to the crawl space for the strips.

    As pointed out, this will make the heat staging a little more complex as I will want to be able to stage Y, Y2, W and W2. Would the EcoBee EB-STAT-02 be a good candidate for this?
    I believe it would. I'm having great fun with mine. Putting 2 more in this weekend.

    That said, the ability to truly communicate with the equipment is like the difference between a 1999 motorola flip phone and a droid razr maxx.

    So if you get communicating equipment (ie Carrier or American Standard), get the manufacturers communicating thermostat.
    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.

  9. #22
    Join Date
    Aug 2001
    Location
    Pavilion, NY
    Posts
    2,108
    Assuming equal cost,,, I would rather have a toaster oven with resistance heaters that last forever and a relatively simple control board in a unit that requires essentially no maintenance over a unit that has multiple pressure switches, gas valves, condensate drains, inducer motor, and igniters to fail and requires far more service. If you factor a 20yr lifespan my money says you will have far less invested in your system with electric backup.
    ...

  10. #23
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,923
    Quote Originally Posted by kangaroogod View Post
    Assuming equal cost,,, I would rather have a toaster oven with resistance heaters that last forever and a relatively simple control board in a unit that requires essentially no maintenance over a unit that has multiple pressure switches, gas valves, condensate drains, inducer motor, and igniters to fail and requires far more service. If you factor a 20yr lifespan my money says you will have far less invested in your system with electric backup.
    Is there anywhere in the U.S. where you can get a Btu of heat from an electric heater for the same cost in energy as a Btu of heat from a gas furnace would cost?

    Ass-u-me?
    Government is a disease...
    ...masquerading as its own cure…
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  11. #24
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,240
    Quote Originally Posted by RoBoTeq View Post
    Is there anywhere in the U.S. where you can get a Btu of heat from an electric heater for the same cost in energy as a Btu of heat from a gas furnace would cost?

    Ass-u-me?
    ((((((((( I would guess Kansas City might be close with extremely low electric rate.
    Designer Dan
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  12. #25
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    Quote Originally Posted by RoBoTeq View Post
    Is there anywhere in the U.S. where you can get a Btu of heat from an electric heater for the same cost in energy as a Btu of heat from a gas furnace would cost?

    Ass-u-me?
    He was using propane as backup. Electric resistance and propane are comparable in our area. Natural gas is of course the clear winner for fuel cost, but also remember to factor in the meter fees.

  13. #26
    Join Date
    Aug 2001
    Location
    Pavilion, NY
    Posts
    2,108
    Given his choices of propane or electric and using the rates provided it would be $3.13 a therm for propane and $3.22 a therm for electric. Based in the fact that the balance point is 30 degrees he will be using essentially all propane below 30 but with the heat pump he will be able to run the unit down to the design temp of 15 degrees with a cop of 2.75 (21200 but output) and supplement the balance of 12800 btus at essentially the same cost of propane. The big difference is that he will only need to heat 12800 btus at $3.22 and the 21200 btus at a bonus of $1.17 a therm instead of 34000
    Btus at $3.13........If my math is correct......$1.09 per hour on propane and $.67 an hour on heatpump with electric backup. No brainier for me. Ass-u-me??? The verdict is still out
    Last edited by kangaroogod; 10-17-2012 at 09:38 PM.
    ...

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