How effective would evaporative cooler be utlized this way? 2

[shane21]

For a 300 sq ft workshop that you'd not want to add humidity into directly with a swamp cooler, what if you made instead a 4" false ceiling of 2x4's on end, covered with thin plastic sheeting of minimal r-value, to blow cooler evaporative air through a serpentine baffle configuration to achieve even contact all along the whole ceiling and plastic.

How effective might that be if that evaporative swamp cooler outside was blowing 70F air into that 4" false ceiling space of 300 sq ft when ceiling air temp inside, just under that plastic, before you turned it on, was 90F?

Let's assume here no heat gain/loss from above the original ceiling, the top of the false ceiling.

Would this setup likely draw much of that 90F ceiling heat off with 1000 cfm evaporative cooler blower 70F?

Any guess what the BTU's cooling total range might be for that 300 sq ft with this setup?

Whatever its effectiveness, would it likely work better just to let hotter air naturally accumulate up at ceiling for largest Delta T, or use some fans to agitate it along underside of ceiling plastic sheeting, even though that might introduce some cooler air from below, lowering Delta T at plastic surface?

Thanks for any thoughts.

 

[MikeHalloran]

It sounds like a firetrap.

I'd likely start with a cheap air conditioner and thick(er) insulation.



Mike Halloran
Pembroke Pines, FL, USA

 

[shane21]

Firetrap? Because of the plastic sheeting overhead? If so, thank you, duly noted, will make provision to minimize risk. If for some other reason, please elaborate.

Structure very well insulated, AC is certainly quick/easy, but for where swamp cooler can work, it's both cheaper to acquire and run, if you've already got free water in a low humidity locale.

I don't know yet, though, if it's even worthwhile fooling with as I'd proposed it above, thus the reason for my inquiry.

 

[LittleInch]

So basically you have a 300 ft2 plate heat exchanger made of plastic film.

Issues I can see are:

Lack of delta T which gets worse the further you get from the inlet

Your blown air might only be a few inches of water column but that's going to tear your thin plastic sheet

If your inside air gets close to 90%humidity at 70 F them you'll start to drip water from the ceiling!

Ditto any water collecting in the void will add to the load on the plastic film.

Better to blow your 70F air at the condensors of an AC unit to improve their performers or somehow have a blown and more efficient compact HX between your 70F air and 90F air.

Something like this

http://www.fantronix.com/acatalog/M...yK8mFF5mCVIYQIWGxofYS-1va8epw9C3DEaAmf98P8HAQ

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[LittleInch]

Also search "indirect evaporative air conditioning" Looks a better bet to me. ..

http://www.climatewizard.com/how-it-works/

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[willard3]

Condensation will cause a lot of problems in the occupied space.

 

[shane21]

LittleInch, Thank you for all the additional potential issues needing to be considered and some options, sort of things I was hoping to get revealed posting it here.

Willard3, yes, condensation rearing it's ugly head could be a deal breaker in itself, thanks for that.

Let me ask this of you both, hypothetically, if there were no issues with condensation or plastic tearing, and this 'plate heat exchanger' could be incorporated and run at little expense, what would Delta T have to be, at a minimum, in your opinion, to make it noticeably effective cooling internal air and worth having?

Yes, I understand AC and cooling it's condenser coils with evaporative cooler and HRV units (which i especially like and am looking closely at) are smart options, just wanting to know what effect, if this could be done right, that a cooler ceiling might have on internal air temps.

 

[Lnewqban]

I see the original investment grow from the original idea:

1) In order to reduce the static pressure inside the cavity, which will make you reinforce the plastic sheeting from underneath, supply and exhaust fans would be needed. If moving in the direction of reducing the flow of cool-humid air to reduce static pressure, then you will have less heat transfer in the film.

2) Even with reduced static pressure, you will have vapor pressure constantly trying to push humid air into the room and up through the ceiling; hence, good vapor barrier should be achieved.

3) Wood of steel within the chamber should be protected/isolated from high humidity air.

4) Ventilation of the workshop, if occupied, is another problem to solve, which might negate the marginal cooling effect of this idea. Even with no forced ventilation, some of the cooler room air will leak out through doors, windows and crevices not meant for air conditioning, being replaced by infiltrated hot air.

5) For increased heat transfer, agitation of the room air, especially closer to the discharge of the supply fan (higher delta T), will greatly increase the heat transfer (removing the insulating film of room air next to the film). Additional fan(s) and energy consumption.

6) You will always have some heat transfer from ceiling surface and elements of the serpentine baffle configuration into the cool-humid air.

7) Useful BTU's cooling total range would depend on all the factors mentioned above, including the ones explained in above posts, on the capacity of your evaporative cooler and on the outdoor relative humidity and temperature. I would also consider the cost of that cooling effect, in fans, in electrical installation, water, materials, work and energy.

Due to economical and practical reasons, I would take the path of indirect evaporative cooling:

https://en.wikipedia.org/wiki/Evaporative_cooler#Indirect_evaporative_cooling

"Where the spirit does not work with the hand, there is no art." - Leonardo da Vinci

 

[LittleInch]

It's not so much the delta T as the air velocity. If you included a centre mount ceiling fan to generate an air movement, 20F is probabky enough. Natural air convection wouldn't be enough but maybe run it along one wall instead?



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[shane21]

Lnewqban, yes, I get too far into the weeds and away from KISS principles and results can get fuzzy and expenses mount.

Bottom Line; I've got low humidity outside and free water and am exploring most efficient and cheapest way to incorporate some evaporative cooling without adding any humidity from it to inside air. I just want the 'coolth' without the moisture as inexpensively and simply as possible, the fewer moving parts, probably the better.

 

[shane21]

LittleInch, agreed, natural air convection probably not enough, always figured fans or blower would be incorporated, maybe even at both ends, pusher & puller.

 

[LittleInch]

If you're going for cheap and cheerful why not try two metal pipes one inside the other and blow cold air on the offside and warm air counter flew on the annulus. Size and length depandant on air flow. The wall idea I think is more effort than its worth.

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[shane21]

LittleInch, I'd thought about that earlier, still am some, like the counterflow efficiencies.
I was wondering, too, if there weren't cheap fins that could be wrapped around pipe to
increase surface area, too, like I've seen added onto on some wood stove flue pipes...

For lack of room, it'd require to be outside and insulated itself, where what got me thinking
about inside with false ceiling here is it'd be easier to slap up some 2X4's and plastic and
already well insulated above it. Still thinking on it...

 

[LittleInch]

or google "DIY air to air heat exchanger"

Dryer ducting looks good!

Gems like this

https://www.wildsnow.com/17884/how-to-build-air-cross-flow-heat-exchanger-budget/

and

http://tomtomheylen.com/categories/DIY/hot_cold_air_heat_exchanger.pdf

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[shane21]

LittleInch, thank you, great articles, digging into now!

- Shane

 

[LittleInch]

I've been thinking if you can knock up a suspended ceiling why not a long thin tube (that thin AL stuff they use for domestic air extract ducting)inside a box with thin ply say twice the OD of the pipie and then blow air counterflow to the "cool" air in the mniddle along the length of your room with outlet at the end. A decent sized extract fan should do the trick and maybe one at the far end to drag the air out.



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[shane21]

LittleInch,

Been thinking of doing something like that, pipe inside pipe counterflow heat exchanger.

I know it would be efficient and help, I'm just wondering if it'd be more effective than the greater surface area of the whole ceiling as originally proposed, I really don't know.

 

[LittleInch]

Moving air is much more efficient. Also much more solid than sheets of plastic. Both will exhaust air which is cooler than ambient but if you don't want humid air in your room then you accept these losses.

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[MikeHalloran]

Star for LittleInch.

I am rather impressed by the HXs described, especially the first one using dryer ducting as the heat exchange surface. The stuff is cheap and easy to work with and has a lot of surface area and roughness. I'm sure you could hack up something like that that would be effective with a swamp cooler for just a few hours work and a little money. ... and it can be much less of a fire hazard than big sheets of poly film, and take up a lot less space.





Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

Don't forget that even a really good HX doesn't get much better than a 7 C difference between one side and another. So your interior cooled air coming out of the HX might only be 60F or higher unless the tube is really long.

Love to know how it turns out!

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