Page 2 of 2 FirstFirst 12
Results 14 to 20 of 20
  1. #14
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,373
    Your heat calc assume tight ducts and you are guessing at the infiltration rate.
    For the sake of learning.
    Question: infiltration rate; is this referring to the house or duct system?

    I was playing with some numbers and your load could be reduced by 3k to 5k btu depending on infiltration and duct gains and losses. My guess is that your house is leaky by the age of the house and the ducts located in the attic.
    Question: infiltration; is this referring to the duct system or the building?
    Question: duct gains & losses; is this referring to insulation or infiltration?

    Question: Heat Calcs; does this figure out a duct system to be air/water tight? or is there a % leakage rate entered automatically?

    I'm just curious, i'm still learning!

  2. #15
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    The infiltration rates are usually in a default setting, you can over ride them and/or create defaults for different situations. With proper training the load calc can be one of your most usefull tools on abid. Use a program that is ASHRAE and or ACCA approved. Infiltration can occur in the return duct if it is located outside the conditioned envelope ( conditioned space) through the walls, windows, doors, duct penetrations into the home,(gaps around boot holes ect). Range hood ducts w/ no back draft damper, fireplaces, wood stoves, bath fans with no dampers. Infiltration adds to the design load in winter and summer. Sealing the duct with mastic and caulking boot cut ins help, but the building must be looked at, including the color of the roof and if the attic is vented or non vented, vented/leaky crawl ect. An excellent load calc program is WRIGHT SOFT MAN J reidential load calc program.
    Genius = The guy who can do anything...except make a living!

  3. #16
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    Just a few things I'll add.

    First, you'll be using your heat twice as much as your a/c, 3328 degree days to 1651 degree days. Second, I question your numbers. At 93 degrees outside with a 1400 sq ft house and a 72 inside temp, 13,381 btu's heat gain doesn't seem right to me with r-19 /r-11 insulation, you might want to double check the numbers. Third, at 16 degrees outside, your 2 ton heatpump will need it's heatstrips on constantly to keep up with the 25,355 heat loss.

    I'd re-check the numbers and in this case look into a manual s for sizing the equipment.....the colder it gets, the lower the heatpumps's capacity. You might be alot better off with a 3-3 1/2 ton two stage heatpump, where you get more heating capacity and can lower the cooling capacity to control humidity. This is JMO and something to ask your contractors.
    If everything was always done "by the book"....the book would never change.

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    In my area a 1400 SQ FT would usually have a 2 to 2.5 ton HP with 10 KW of strip.
    We over 5000 HDD.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #18
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    Quote Originally Posted by beenthere View Post
    In my area a 1400 SQ FT would usually have a 2 to 2.5 ton HP with 10 KW of strip.
    We over 5000 HDD.
    With r-19/11 insulation? Wouldn't a larger heatpump sized for the heating load with the capability of lowering its output for cooling be better?
    If everything was always done "by the book"....the book would never change.

  6. #19
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    I have a 2000 sq ft house in Myrtle Beach, SC. I have only a 2-ton heat pump to do the whole thing. It includes 8 KW strip. It is 2 stage with a Variable Speed blower and I love it!!! ( of course I have better insulation than you)

    Your load sounds like 1.5 ton, assuming no major mistakes. A 2-ton two stage would make a lot of sense. Sounds like the 2 ton guy knows better. It sounds like he did a load calc also.

    Stay away from the 2.5 ton guys, they are just guessing.
    Remember, Air Conditioning begins with AIR.

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,069
    [QUOTE=smokin68;1713770]With r-19/11 insulation? Wouldn't a larger heatpump sized for the heating load with the capability of lowering its output for cooling be better?


    If his house needs 2 tons for cooling. And you put in a 3 ton 2 stage HP with first stage at 60% capacity.
    Your still at 1.8 tons, with a possible high SHR. Making the HO lower stat set point in the summer to feel comfortable. Losing a lot of the energy savings you tried to gain by over sizing. ( And possibly losing comfort in the summer )

    If the HO ever tries to improve his envelope later down the road, it becomes an even worse situation.

    IMO:
    Better off selecting an equipment match that has a higher COP, then just increasing system size for heating.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

Page 2 of 2 FirstFirst 12

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event