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  1. #53
    Join Date
    Nov 2004
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    SW FL
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    6,271
    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

  2. #54
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    I just got my LP bill from the last refill last week. I took 266.6 gallons to top off the tank, and the cost was $833.49. So that works out to $3. 13 per gallon...

    They have not ordered the XC95m yet, so if it makes better sense to match the outdoor 4ton XL20i with a TAM8A0C48 air handler, I can still get that changed.

    Would the cost of a TAM8 be less than the combined cost of the 100,000 BTU XC95m and the 4ton comfort coil I have now? I have radiant floor heat in the basement and master bath, and also a gas fire place in the living room that I can use for extreme low temps (which I have not seen in this area for at least 10 years).

    At what outdoor temp does a XL20i heat pump approach a COP of 1.0?

  3. #55
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Here are the load calcs they did for my house:

    The page shows the first floor and basement:



    So if we take out the basement, which is heated via radiant floor heat (and only turned on when I entertain), it looks like I only need 43,481 BTU for heating the first floor. The original furnace was 120,000 BTU. Perhaps it was sized that way originally with the expectation that the basement, if ever finished, would be heated from that source as well?

    Here are the calcs for the 2nd floor:


  4. #56
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,187
    You raise an interesting question about whether to go with a high eff air handler versus the XC95 mod furnace.

    Is there any likelihood that your location will ever have nat gas service?

    What other appliances if any in your home use propane fuel?

    The way you will be using your dual fuel system makes a furnace a very expensive air handler. Simply because you will want to stay off propane as much as possible for the cost savings.

    Anyone in your home object to HP heating?

    This may be a tough call.

    And why are you topping off your propane tank?

    IMO

  5. #57
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    My 10 year old 94% efficient Polaris water heater uses propane. This is what does the radiant floor heat in the master bath as well as the basement when used. My range is also gas powered. Finally, I got a 15kw backup generator that is also plumbed to the 500 gallon in ground tank.

    Natural gas service is not likely to ever happen due to how rural my area is.

    I'm on a schedule with the gas company where they just come and fill it automatically a few times a year based on historical use. I like to keep it on the full side in case of major storms/outages where I need fuel on hand for the generator.

    No one has objected yet to HP heating as it is a definite improvement not having a furnace at all for a couple of week while we waited for the new one to be installed.

  6. #58
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,187
    Well I think you answered your question. Stay with the mod furnace.

    Good Luck!
    IMO

  7. #59
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,271
    Quote Originally Posted by pclausen View Post
    I just got my LP bill from the last refill last week. I took 266.6 gallons to top off the tank, and the cost was $833.49. So that works out to $3. 13 per gallon...

    Would the cost of a TAM8 be less than the combined cost of the 100,000 BTU XC95m and the 4ton comfort coil I have now?
    I have radiant floor heat in the basement and master bath, and also a
    gas fire place in the living room that I can use for extreme low temps
    (which I have not seen in this area for at least 10 years).

    At what outdoor temp does a XL20i heat pump
    approach a COP of 1.0?
    About -15'F theoretically.

    Defrost cycle may be quite significant at +10'F.

    Design Temp seems low at +5'F.
    Does it go below +15'F >150 hours per year?
    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

  8. #60
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,271
    Quote Originally Posted by pclausen View Post
    The page shows the first floor and basement:



    So if we take out the basement, which is heated via radiant floor heat (and only turned on when I entertain),
    it looks like I only need 43,481 BTU for heating the first floor. The original furnace was 120,000 BTU.
    How was the Load Calc actually used in sizing the equipment?
    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

  9. #61
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,187
    I am not disagreeing with previous post but it should be mentioned that it is unlikely the new HP can maintain inside temp comfort at very low temps. This is called temperature balance point where the heat loss is equal to heat gain. Probably your dealer has not made that calculation for you. If you can get down to the low 20s that would be great. Through trial and error, you can find that outside changeover temp that works best for you. Obviously, if inside temp begins to drop, then you are past that point.

    IMO

  10. #62
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    I will obviously want to keep my 500 gallon in-ground tank to supply the water heater, range and backup generator, but I don't see why that would necessarily make it an obvious choice to stay with the mod furnace as opposed to consider a TAM8 air handler?

    Quote Originally Posted by dan sw fl View Post
    Does it go below +15'F >150 hours per year?
    I would say no.

    Here's the historical weather data for my area:



    So it rarely gets below freezing. The record lows are as follows:

    Jan -10F was set in 1994
    Feb 1F was set in 1996
    Mar 10F was set in 1996
    Apr 21F was set in 1950
    Oct 26F was set in 1972
    Nov 10F was set in 1950
    Dec -3F was set in 1983

    So they all took place more than 16 years ago. Looking back over the last few years, would that is it rare for there to be temps consistently below 25 degrees for days, let alone below 15.

  11. #63
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Quote Originally Posted by dan sw fl View Post
    How was the Load Calc actually used in sizing the equipment?
    For cooling, the above calc shows needing 3.5 ton, so I think the 2/4 ton XL20i is the proper size.

    For heating, the model currently installed is 80,000 BTU, but dual stage, so the first stage is 49,500 BTU, which is likely all that would ever be needed. The smallest XV95 furnace is 37,700/58,000 BTU, the the fan is only designed to move enough air to support a 3 ton outdoor unit. At least that is what the guy told me was the reason for going with the TUH2B080A9V4VA furnace model.

    On the modulating furnace, the only model that supports a 4 ton outdoor unit, is the 100,000 BTU model.

    On the TAM8, I noticed there is an option to add a hydronic heat kit. I wonder if that would be a good combo with my 94% efficient Polaris water heater which is sitting right next to the furnace anyway?

  12. #64
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,187
    The reason I think it's obvious is because even with the air handler as opposed to mod furnace, you will still need the propane fuel and the tank.

    I would want to see the operational BTU cost of the propane versus electric heat strips.

    IMO

  13. #65
    Join Date
    Jul 2007
    Location
    Delaware
    Posts
    3,824
    I to thought five degrees was low as a design temp.
    Always here

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