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  1. #1
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    897

    Frown 1st foam house - seem to be undersized ?

    Just started up 3 ton Rheem on open cell foam new construction. Foam on outside walls and roof rafters. Was 96 in house yesterday when I started unit, ran all night, checked at 7 am this morning, only pulled down to 83 inside.

    This is giving me a bad feeling in my stomach if you know what I mean.

    House is 2600 sq. ft. It also has been extremely hot here. 106 and 107 day after day. The design temp for this area is 97.

    Question , how should I handle the ceiling load calc when the insulation is up on the roof rafters. Now the whole attic space is being cooled .
    I may be ripping this system out and going larger.

  2. #2
    Join Date
    Aug 2011
    Posts
    568

    Confused

    Quote Originally Posted by Timber View Post
    Just started up 3 ton Rheem on open cell foam new construction. Foam on outside walls and roof rafters. Was 96 in house yesterday when I started unit, ran all night, checked at 7 am this morning, only pulled down to 83 inside.

    This is giving me a bad feeling in my stomach if you know what I mean.

    House is 2600 sq. ft. It also has been extremely hot here. 106 and 107 day after day. The design temp for this area is 97.

    Question , how should I handle the ceiling load calc when the insulation is up on the roof rafters. Now the whole attic space is being cooled .
    I may be ripping this system out and going larger.
    tell the customer all the humidity you're taking out of the air!

  3. #3
    Join Date
    Sep 2005
    Location
    Texas
    Posts
    2,793
    You could install return ducts into the living space ceiling, add insulation so you dont have the attic load to the house.
    Do you have a heatload calculation?

  4. #4
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    897
    Quote Originally Posted by air2spare View Post
    You could install return ducts into the living space ceiling, add insulation so you dont have the attic load to the house.
    Do you have a heatload calculation?
    I used wrightsoft. But maybe my data entered was off for the ceiling load.

    I was thinking about insulation above the ceiling to remove or lessen the ceiling load.

    Just talked with another local contractor a they are sizing the units the same regardless of the type of insulation used. That being said this would have been a 4 ton unit.

    Air2spare when u say add returns in ceiling, you would also tie them into the return plenum at unit. Right.

  5. #5
    Join Date
    May 2009
    Location
    In the Hudson Valley of New York
    Posts
    1,898
    Done a few foam houses, I always size the same as non foam as well.

  6. #6
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    897
    Quote Originally Posted by EugeneTheJeep View Post
    Done a few foam houses, I always size the same as non foam as well.
    Well I think I screwed up. Makes me want to say some cuss words .....

  7. #7
    Join Date
    Aug 2011
    Posts
    568

    Confused

    Quote Originally Posted by Timber View Post
    Well I think I screwed up. Makes me want to say some cuss words .....
    hey timber, wow, where i come from, we call that a money loser!!!
    i feel for you. these days i don't do any new installs, i do repair,replacement,service, no money$ in installations, any way good luck, really, been there done that! again good luck!

  8. #8
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,372
    You have a few things to check before going off the deep end. The refrigerant change and air flow over the cooling coil are the starters. Over charge or undercharge will reduce btus moved. The coil temp should be 25^F below the return air temp. Lower coil temp improves latent removal and but slows sensible cooling. In your case, to improve the sensible cooling, you could start with -20^F coil temp.
    What is the situation on fresh air ventilation? Limit the fresh air to 70 cfm when occupied.
    Also, are all of the blinds and window covers inplace? Solar gain is a killer that can be slowed with shade, blinds, or other ways.
    More info on the temp/%RH, coil temp, and superheat/subcool. Is the outside condenser clear of obstructions and free air flow.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  9. #9
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    897
    Quote Originally Posted by teddy bear View Post
    You have a few things to check before going off the deep end. The refrigerant change and air flow over the cooling coil are the starters. Over charge or undercharge will reduce btus moved. The coil temp should be 25^F below the return air temp. Lower coil temp improves latent removal and but slows sensible cooling. In your case, to improve the sensible cooling, you could start with -20^F coil temp.
    What is the situation on fresh air ventilation? Limit the fresh air to 70 cfm when occupied.
    Also, are all of the blinds and window covers inplace? Solar gain is a killer that can be slowed with shade, blinds, or other ways.
    More info on the temp/%RH, coil temp, and superheat/subcool. Is the outside condenser clear of obstructions and free air flow.
    Regards TB
    I will check the charge this afternoon. This unit is coupled with 90 % furnace running on Hi for cooling. Probably not going to get anymore Sensible out of that.
    ERV is not hooked up yet.

  10. #10
    Join Date
    Aug 2011
    Posts
    568

    Hmm

    Quote Originally Posted by Timber View Post
    I will check the charge this afternoon. This unit is coupled with 90 % furnace running on Hi for cooling. Probably not going to get anymore Sensible out of that.
    ERV is not hooked up yet.
    hey timber, what's the delta over the coil? got enough return coming back to the furnace? you pprobably ck'd already, but trying to give you moral support!

  11. #11
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,090
    Around here, a 2600 sq ft house would usually have a 3 ton even with R11 walls and some blown in the attic. We just came off a stretch of upper 90s and very high humidity and people did just fine.

    I'm with the rest, give the place a chance to cool down & dry off and see how it does.

    I remember my foaming buddy telling me of a job where the HVAC sub oversized the equipment since he didn't believe the size the calc called for. HO had lots of humidity issues.

  12. #12
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    897
    Quote Originally Posted by BaldLoonie View Post
    Around here, a 2600 sq ft house would usually have a 3 ton even with R11 walls and some blown in the attic. We just came off a stretch of upper 90s and very high humidity and people did just fine.

    I'm with the rest, give the place a chance to cool down & dry off and see how it does.

    I remember my foaming buddy telling me of a job where the HVAC sub oversized the equipment since he didn't believe the size the calc called for. HO had lots of humidity issues.
    Sounds good, our summer here has broken all the records, wish these 100+ days would break. We have had like 45 days over 100 so far. a couple of weeks ago it hit 110. Its like Arizona but in the pineywoods of East Texas.

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,372
    Another thought. Make sure you do not have a kink in the suction line going back to the compressor. Also extra long suction line without upsizing. Both really kill capacity.
    Good luck
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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