Hurt your brain Question

[dreamingmuscle]

OK this is hypothetical question. I have no plans to do this but I am wondering how well if it will work if at all.

If you have a shop with lets say 13' walls and a 20' roof peak with open rafters and a ridge vent the full length of the roof.

The question is. If you put lets say two large A/C window units in the rafters.

(I know if you put window unit in the middle of a room the heat from the exhaust will cancel any cool air it might generate.)

But if you could mount them high in the rafters of a tall building with decent ventilation. Shouldn't the cool air fall from the a/c units cool the building while the heat from the condenser goes up and out of the vents?

 

[RECox286]

This is a trick question, no ?

Uncle Bob

 

[nehog]

WTF?

Gotta be a trick question... As who has windows in their rafters?

 

[dreamingmuscle]

hypothetical question Gentlemen

 

[Falcon67]

The heat will radiate downward and any going out will carry some good air with it. The part of the shop with a uninsulated ceiling and good venting runs mid 90s and the insulate ceiling part runs mid 80s.

 

[nehog]

Are you simply asking if it is feasible to mount the outlets at ceiling height vs mid-wall height? (Ignoring the fact there would be no windows there...) Then the answer is probably not very efficient. I think you would be much happier with the AC units at mid-wall (say 4-6 ft) level.

 

[shoot summ]

Think about what AC is actually doing, it isn't really "cooling" the air, it is dehumidifying it. So you are not isolating the exhaust(and moisture) from the shop as if you had the units through a wall. You might cool the shop, but not nearly as efficiently as if you had mounted them properly.

It's not really a hurt your brain question...

 

[dreamingmuscle]

OK this started out with my kid wanting to plug in a window unit we had sitting in the floor while we worked on the window.

He thought it would still cool the room just because of the nature of the machine. I had to explain to him the way a A/C unit worked by exchanging the heat through the condenser and evaporator. (forgot about the humidity factor)

That got me thinking that if you had a high enough ceiling the heat from the exaust could go up and the cool air would drop. Thus maybe defeating the need to have it exhaust outside.

I never thought it would work just had a passing h'mmm. Why shouldn't it work hot air goes up and cool air drops. It would in no way be efficient but in weak theory it should work somewhat.

 

[Grumpy365]

Think about what AC is actually doing, it isn't really "cooling" the air, it is dehumidifying it. So you are not isolating the exhaust(and moisture) from the shop as if you had the units through a wall. You might cool the shop, but not nearly as efficiently as if you had mounted them properly.

It's not really a hurt your brain question...

Please explain this.

If you would say the AC isn't "cooling" the air it is transferring the heat from your evaporator ( the coil inside) to the condenser ( the coil usually located outside), I could go along, OR if you extrapolated that, this heat transffer cycle all happens within 18" within a window unit and you would effectively accomplish nothing with just letting this air commingle in the same space, I could see your point, ,but I am not seeing your dehumidifier logic.

The AC is removing the heat from the air. The AC dehumidifies BECAUSE the air is cooled and no longer has the capacity to hold moisture. In the process of cooling the air the moisture is condensed on the evaporator and is run out the drain.

So, is my understanding jacked up?

Edit: I would go one step further. The unit will dehumidify and you will see a drop in Humidity. The moisture will condense on the coil and run out the drain, even with this unorthodox setup.

 

[mrobins297aaa]

pretty much like grumpy said, the normal temperature drop across the evaporator on a residentail furnace is between 15 and 18 deg.
so if the return air is 85 deg than the supply air would be around 70 deg, as the house cools and the return air drops so will the supply air temp drop.

to the op, that idea wouldn't work at all imo, the cool air would be warmed by the rising hot air from below long before you'd ever notice it.

 

[hughfree]

I will throw my two cents into this discussion...in manufacturing and warehouse installation I have utilized window units for spot cooling application. You must have high bay space and the AC unit needs to be located so that the condenser exhaust high enough that the work area is not effected. The high bay must have ridge vents or mechanical exhaust. This application will require that the evaporator discharge be ducted to the work area.

 

[Alchymist]

Please explain this.

If you would say the AC isn't "cooling" the air it is transferring the heat from your evaporator ( the coil inside) to the condenser ( the coil usually located outside), I could go along, OR if you extrapolated that, this heat transffer cycle all happens within 18" within a window unit and you would effectively accomplish nothing with just letting this air commingle in the same space, I could see your point, ,but I am not seeing your dehumidifier logic.

The AC is removing the heat from the air. The AC dehumidifies BECAUSE the air is cooled and no longer has the capacity to hold moisture. In the process of cooling the air the moisture is condensed on the evaporator and is run out the drain.

So, is my understanding jacked up?

Edit: I would go one step further. The unit will dehumidify and you will see a drop in Humidity. The moisture will condense on the coil and run out the drain, even with this unorthodox setup.

This is the way dehumidifiers work.

 

[pseudorealityx]

This is the way dehumidifiers work.

A DX dehumidifier is just a A/C that rejects it's heat back into the air stream. In goes warm wet air and out comes hot drier air. They just put the condenser inline right after the evaporator.

 

[pseudorealityx]

Going back to the original question...

The cold air will start to fall. The problem is, as it falls, it's cooling off... or you could say, it's being heated by the air its falling through. So it would never get down to a useful level anyway.

And due to the nature of physics, you can't have a 100% efficient piece of equipment. You throw more heat than you cool. Running a window A/C 'inside' is called a dehumidifier. You'll be able to pull moisture out of the air, but it will only heat up the space.

 

[Falcon67]

It could work with an open bay in the rafters, with the back side of the units in sealed attic space. You could use a ceiling fan to move the air down. Not real efficient IMHO.

>Think about what AC is actually doing, it isn't really "cooling" the air
Yes, it is. The working fluid (R12, R22, R2D2, etc) is compressed which heats it. The condenser remove the heat from the fluid. The expansion valve drops the pressure and turns it into a gas - when it does that, the fluid temp drops real quick. That cold working gas is run through the evaporator and cools the air. Same thing a refrigerator does. Pretty simple concept, really.