Does placing air handler in attic reduce system cooling effeciency?

[Dukes]

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)

[smokin68]

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"?

[emcoasthvacr]

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.




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"?

[Shophound]

A quote from an FSEC study at this link:

http://www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/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.

[Dukes]

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)

[Airmechanical]

the effeciency of anyone who has to service it will go way down.

aint that the truith!



.

[cem-bsee]

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

[Carnak]

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.

[mchild]

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.

[Dukes]

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

[mchild]

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!!

[Shophound]

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 (http://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. :cool:

I'd be curious how this affects your present system's performance...maybe knocking off enough load that it is now oversized?

[BigJon3475]

it's like "great stuffing" your attic.

[Carnak]

How is the humidity in the attic mchild?

Foam on the underside of the roof pitch was my second choice, I ended up externally insulating my roof.

[coolmen]

how about a roof attic fan

[cem-bsee]

MCHILD: how's shrinkage on that product? - after 5y

Icycene seems to have good specs, no shrinkage

[mchild]

With it 95 still outside? That's impressive. :cool:

I'd be curious how this affects your present system's performance...maybe knocking off enough load that it is now oversized?

Temps have dropped since it was 95* that day but it looks like it is going to be as they stated. The next day it was in the uppper 80's and it was only 87.1 in the attic/79* in the living.

Yes, the second floor sytem will be or is oversized. It was oversised before I had this done. On days in which it is 3-4 degrees over a design day (90*) it would not run an entire hour without stopping for 5-8 minutes. It doesn't run non-stop until the outdor temp is up to 100* - ten degrees over a design day. It is like a lot of resi systems - oversized. I have had several local companies tell me that they design for 99/75.

I currently have 5.5 tons of cooling and according to my run on the load calc I can cool the home with about 3.5 tons (two 2 ton multi stage systems). Of course, this is after the improvments that I am making with the insulation. In addition to the attic I am going to have the crawl space closed and foamed and make it conditioned. This will help with overall humidity and it will help a lot on the heating side of the equation. We have lots of infiltration through the crawl.

Same thing on the heat side. Currently have the 3 ton heat pump in the attic and a 96K net output oil furance on the first floor. Load calc calls for about 70K total.

Since I can't wait to replace the attic heat pump with the not yet released Nordyne system I will use a two stage unit for that. Hopefully, within the next year, when I replace the heating/cooling on the first floor, I can use the Nordyne equipment and size more for the heat side.

[mchild]

MCHILD: how's shrinkage on that product? - after 5y

Icycene seems to have good specs, no shrinkage

It is supposedly guaranteed not to shrink or fail in any manner for as long as I own this home. We'll see.