Whole House/Attic Fan for metal barn question.

[Lear60man]

S Florida, 40X60 with 18' vertical walls metal barn. I currently have a 5 ton AC unit and 2" foam board on walls with 1/4" bubble style insulation blanket on the ceiling. BlueTex insulation on the roll up doors. The AC duct is suspended about 2' down the spine of the ceiling. One 100" Parrot uncle fan in the center. Summer is here and Im trying to keep this as cool as possible but im only getting mid 80s inside during the day. 75 would be optimal. Inside temp around human height is mid 80's, but 110-120 'upstairs'.

Since the AC unit is suspended from the ceiling, its sucking in a ton of hot air so im thinking of installing a whole house fan and mounting it onto one of the windows which are near the top of the walls. My thought process is to expel out the hot air towards the ceiling so that the AC unit ***** in cooler air. Backup plan is to install two 2 ton mini splits to help take the load off of the 5 ton.

The Attic fan is a cheap, easy investment compared to the mini splits. And yes I know the roof needs better insulation. Insulation would run about $2500 and take up a few days of my time. 2 mini splits would be just a few bucks more but I could throw them up in a day.

https://imgur.com/a/XFb3Y6T

 

[jack stand]

The bubble foam is a big zero (joke, ripoff, snake oil). There's a very slight radiant plus if it's got the "foil".
It's a very week link in your insulation and in an area where it counts with your sunshine.
Sorry, but don't feel too bad as you're not alone with this con job. I'm no scientist but I'd think the metal roof would provide plenty of radiant protection over a thin mylar layer might offer underneath it on the bubble wrap.

 

[driftpin]

Where are you in So. FL? I have a BNIB attic fan, I cleared out a storage garage, and this was one of the things that didn't get recycled/tossed, as it's new. If you're interested, I'll take pics as it's in storage away from the house. PM me.

 

[dscheidt]

Trying to cool an uninsulated building is not going to work any better with a fan than it does without one. Insulation will pay for itself pretty quickly, throwing money at added cooling will not.

 

[mm08822]

Adding ceiling fans is secondary w/18' ceilings.

Stopping the heat gain is your best money spent.

Adding more cooling just shreds more cash faster.

 

[Lear60man]

Thanks for the replies, lots to chew on. I agree with all of the comments on the roof 'insulation' or lack there of. I would like to use it over this summer/fall without stroking out. I have more money than time right now so a mini split makes sense until I figure out a permanent solution to the ceiling insulation next winter. Working on a skyjack by myself in 120 heat is not on the menu.

Where are you in So. FL? I have a BNIB attic fan, I cleared out a storage garage, and this was one of the things that didn't get recycled/tossed, as it's new. If you're interested, I'll take pics as it's in storage away from the house. PM me.

Thanks for the offer, but in on the Gulf Coast.

 

[Jackfre]

Not sure if this will handle what you want to do as it is a newer product by them, but they make excellent equipment. Worth a look.

D-Strat Compact, High Velocity Destratification Ceiling Fans - Tjernlund Products, Inc.

The Problem: Stratification in high ceiling warehouse and commercial spaces creates huge temperature differentials between the ceiling and the occupied floor level. It is typical for a differential of 20 degrees or more to exist. The Solution: D-STRAT™ 30 watt, 540 CFM high velocity fans can...

tjernlund.com

 

[rust in the eye]

I can't speak to how it would effect a large building as yours but will share that the WH fan in my home moves a LOT of air.
While it will pull hot air out your A/C air handler may not be able to keep up with cool air so you'll be throwing the baby out with the bath water.
Do you need all that ceiling height everywhere?(dumb question?) A false ceiling and introducing the cooled air below it would certainly help.
Agreed about the bubble stuff being worthless, especially on a tin roof. Good luck, you've got a challenge.

 

[racecougar]

Since the AC unit is suspended from the ceiling, its sucking in a ton of hot air so im thinking of installing a whole house fan and mounting it onto one of the windows which are near the top of the walls. My thought process is to expel out the hot air towards the ceiling so that the AC unit ***** in cooler air. Backup plan is to install two 2 ton mini splits to help take the load off of the 5 ton.

Where will the makeup air come from?

Adding more cooling instead of more insulation doesn't compute whatsoever.

 

[mm08822]

Buy a couple big Walmart floor fans or go with 2 permanent pendant fans. These should get you through til winter.

 

[manwithtools]

Since the AC unit is suspended from the ceiling, its sucking in a ton of hot air so im thinking of installing a whole house fan and mounting it onto one of the windows which are near the top of the walls.

How about extending the air return duct for the AC unit down closer to floor level. That way it's intake is "cooler" air than it currently receives up near the ceiling. Let the warm air stay up high and the cooler settle to the human height.

I agree with others, more insulation is always better.

 

[bluedog225]

The foil on a radiant barrier, whether it’s bubble or not, works. Don’t let anyone tell you it doesn’t. It has to have about a half inch to three-quarter inch gap on one side or the other (emissivity/reflectivity). Similarly, painting your roof with Henry’s cool roof elastomeric also works.

Another vote for more installation. With the florida sun you’re picking up all kinds of heat off that roof.

 

[Lear60man]

How about extending the air return duct for the AC unit down closer to floor level. That way it's intake is "cooler" air than it currently receives up near the ceiling. Let the warm air stay up high and the cooler settle to the human height.

I agree with others, more insulation is always better.

Ive thought of this as well....drawing in cooler air will result in less work to cool it further. Thanks for reaffirming that thought.

 

[Shiftless]

I have a whole house fan in my house but no A/C. It’s mounted in the ceiling of my hallway.
Whole house fans have been around for MANY years. The idea is to expel stale hot air from a building and draw in outside cooler air. I use mine when the outside temp falls in late afternoon to draw cool air into the house and push it into my attic which forces hotter air out the attic vents.
If you install such a fan in your big shop building, it will draw out air from near the ceiling but also air that you have paid to cool from the rest of the shop. But worse, the fan will draw in hot humid outside air. If your fan expels 2000 cubic feet per minute for example, 2000 cubic feet of hot humid outside air will come in. If such a fan was installed in a super tight building, the fan would create a very slight vacuum and then stop expelling air.

Just get more fans to stir air around your shop and plan to add (a lot more) more ceiling insulation later on.

 

[racecougar]

Yep. Exactly why I was inquiring as to where the makeup air would come from. I have a whole house fan in my house and my shop, and they are great under specific circumstances (pulling in outdoor air that is at comfortable temp/humidity). Running the fan while also running the AC doesn't compute, unless you really like wasting electricity.

 

[toplessHO]

If you have good water perhaps try a mister at roof peak
It shouldnt need to keep it wet,just experiment with a thermometer inside

 

[Shiftless]

If you have good water perhaps try a mister at roof peak
It shouldnt need to keep it wet,just experiment with a thermometer inside

Misters cool air and metal roofs by evaporative heat loss. They work great in dry climates. South Florida maybe not so well.

 

[dscheidt]

The foil on a radiant barrier, whether it’s bubble or not, works. Don’t let anyone tell you it doesn’t. It has to have about a half inch to three-quarter inch gap on one side or the other (emissivity/reflectivity). Similarly, painting your roof with Henry’s cool roof elastomeric also works.

if the science supported an internal radiant barrier, it would be a requirement in the IECC for zones it makes sense in. It's not, because it doesn't work. The problem with an internal radiant barrier is that it's inside, and the heat is already in the envelope. the space between the roof deck and the barrier gets heated by conduction, and that conducts to the barrier, and then into the conditioned space. An exterior radiant barrier, like a shiny roof or the various coatings, really does work -- because it's rejecting heat to the sky, which is generally outside the building. If the radiant barrier is air sealed properly, and the gap is ventilated, there isn't as much conduction, so there's less heat transfer. But if you have a standard insulation layer that's air sealed, there's little conduction either, and the amount of heat that's actually radiated by the roof is lower than you think, because it's simply not that hot (in thermodynamic terms, even if it's hot enough to fry an egg on).