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  1. #1
    Join Date
    Jun 2007
    Location
    Southeren Oregon
    Posts
    3

    Smile Does placing air handler in attic reduce system cooling effeciency?

    Hello, I am having a 2 ton heat pump system installed in a single story 1000 sq. foot home addition. There are physical advantages to putting the air handler in the attic as opposed to taking up living space. I understand that cooling systems have fixed limits of cooling capability, that is if the outside air is 100 degrees the system can only cool a difference of 30 degrees resulting in 70 degrees inside. If I have the air handler put in the attice which is at least 30 degrees warmer than the living space am I losing cooling potential in the living space? Thanks Bill, (Dukes)

  2. #2
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    If it's sealed/insulated well you'll lose very little, however the effeciency of anyone who has to service it will go way down. I avoid attic installs if possible, what do you lose, 10 sq ft of "living area"?
    If everything was always done "by the book"....the book would never change.

  3. #3
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681

    Angry amen on that

    I see a lot of AHU's in Georgia, and they are a PITA to service.

    I had a couple of nice shocks because the temp is so high in the attic during the summer, your sweat rolls down your fingers when doing electrical testing -- this creates a path for current to flow. Same applies to the outdoor unit when servicing -- be carefull about sweat rolling down your fingers during the hot Summer.

    I wear wrists bands so my sweat doesn't flow -- but technicians need to be aware that sweat rolling off your fingers creates a current path.

    I see some codes changing in florida about AHU's in the attic, but the codes in Georgia up to 1998 or so allowed AHU's in the attic -- the kind that need servicing....lol.



    Quote Originally Posted by smokin68 View Post
    If it's sealed/insulated well you'll lose very little, however the effeciency of anyone who has to service it will go way down. I avoid attic installs if possible, what do you lose, 10 sq ft of "living area"?

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,347
    A quote from an FSEC study at this link:

    http://www.fsec.ucf.edu/en/publicati...1-00/index.htm


    The air handler is both poorly insulated with the greatest temperature difference (the evaporator) of any location of the cooling system. It also has the greatest negative pressures so that some leakage into the unit is inevitable. Evidence for this influence is contained in a monitoring study of sub-metered air conditioning energy in 48 Central Florida homes conducted by Cummings (1991) which found that homes with the air handlers located in the attic used 30% more space cooling energy than those with the air handlers located in garages or elsewhere.
    If you have a choice, leave it out of the attic, IMO.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Jun 2007
    Location
    Southeren Oregon
    Posts
    3

    Smile

    Thanks, that was really fast response, and much appreciated. The 30% number of cooling loss is what I was worried about. Is it also conversely true that it would actually improve heating effeciency? If so maybe they will cancel each other out over a year. I will be framing the platform in the attic over the next week, and will endeavor to make it as easy access and comfortable place to work as I can. The point about the effeciency of the service tech having to work in the heat is well taken. It is a 6/12 pitch so the headroom is pretty good. We put a ridge vent all along the ridge, but perhaps I should add a spot vent immediately above the air handler location. I guess I am rationalizing the 10 sq. feet of lost living space as worth about $1000 in construction costs here in Southern Oregon. Thanks again, Bill (Dukes)

  6. #6
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by smokin68 View Post
    the effeciency of anyone who has to service it will go way down.
    aint that the truith!



    .

  7. #7
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    since your attic is not sealed, the a/h will be surrounded by almost Outside temp -- maybe much hotter in the summer --
    about the same in the winter

    PIA for service men
    losses thru sheet metal

    remember, construction costs are one time --
    energy is lost from a/h when the unit is running

    so, build a closet up there?
    foam the outside of the a/h
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  8. #8
    Join Date
    Apr 2002
    Posts
    11,808
    You place an air handler and duct work in an unconditioned attic and go 'please do not do what you naturally want to do' and then get dissapointed when it ends up sweating.

    Placing the air handler in the attic is harder on the air handler and on the guy who services it.

    The ductwork and air handler in the attic will probably pick lose 10% of their sensible cooling capacity vs the air handler and ducts being in the conditioned space.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  9. #9
    Join Date
    Sep 2006
    Posts
    1,253
    I just wrote the check for having my attic cathedralized by using spray foam on the under side of the roof deck, all the way down to cover the soffet, and then on to cover the top plate of the outside wall. Gable ends are sealed up too. It took an entire day. They use a steam sytem to spray it on. So in addition to our current 95* the steam was coming out at 240*. It got mightly hot up there as they were working and it is still hot up there, but the installer said the temps should be about 5 - 10 above the living area temps once stabilized. We normally keep it at 79* on the second floor so I'm looking forward to the attic not being more than 89*. A much less hostile environment for not only the air handler but the people who have to work on it.

  10. #10
    Join Date
    Jun 2007
    Location
    Southeren Oregon
    Posts
    3

    Smile

    Interesting. That might be cheaper than building an attic "closet" around the air handler. What is the foam product's name?

  11. #11
    Join Date
    Sep 2006
    Posts
    1,253
    There are a few different ones on the market but I wanted something that did not off gas anything hazardous. It is called BioBased: www.biobased.net.

    I just took a reading in my attic. It is 79* on the second floor and 87.1* in the attic. Sccchhweeeet!!

  12. #12
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,347
    Quote Originally Posted by mchild View Post
    There are a few different ones on the market but I wanted something that did not off gas anything hazardous. It is called BioBased: www.biobased.net.

    I just took a reading in my attic. It is 79* on the second floor and 87.1* in the attic. Sccchhweeeet!!
    With it 95 still outside? That's impressive.

    I'd be curious how this affects your present system's performance...maybe knocking off enough load that it is now oversized?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #13
    Join Date
    Apr 2007
    Posts
    6,285
    it's like "great stuffing" your attic.

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