Where to place portable A/C for best effect?

[DaveC426913]

TL;DR Summary

I have a portable unit that vents out the window of my large walk-in closet. I want to know where I should place the unit for best efficiency.

I have an attic bedroom with no windows. The only window is in the closet half of the attic.
I have a portable A/C in the bedroom that vents out the closet window.

The closet is quite warm - partly because it's poorly insulated (no soffit-venting), and partly because the A/C unit's vent hose (which is 10 feet long) gives off a lot of heat into the closet. The sun beats down on the roof just inches overhead.

The A/C labours to keep the bedroom cool, even at night.

Currently, I have no barrier between the warm closet and the cool bedroom, so the air can easily mix.

I plan to install a curtain in the doorway to discourage airflow.

Where do I want that curtain? (Actually, where do I want to place the A/C relative to the curtain)? Do I want the A/C to draw in warm closet air? Or do I want it to draw in cool bedroom air?

(The arrows are airflow, not pointers.)

 

[Drakkith]

You want the AC to draw in the cooler bedroom air on the cooling side of the unit, but you want the 'hot' side to pull in the warm air from the warm closet and vent that warm air outside.

If you can't do that then I'm not sure where to place it.

 

[Lnewqban]

What model is your portable unit?
Is the envelope of the cool bedroom insulated?
Can you insulate that curtain and run a make-up air duct?

 

[hutchphd]

I think @Drakkith is correct which means diagram 2 in my experience. Also seal/insulate the partition and the duct. If the closet still gets hotter than the outside then a small circulating window fan in the closet window might help also particularly at night. Fans are cheap and cheap to run.

 

[rbelli1]

The best is to go with a dual duct system. Is the condenser inlet isolated from the evaporator inlet? If so then you need to get another duct and somehow attach one end to the condenser inlet and put the other end outside.

Both the evaporator inlet and outlet should be on the cool side.

On this unit there are separate inlet filters. This probably means that the air flow paths are isolated. The botom rectangular grate is the condenser inlet. The goal would be to have this draw air through a vent from the window. Alternately keep the bottom one on the hot side of the curtain and the top one on the cool side. Don't try to operate it in any orientation except "This Way UP". Operating it in any other orientation will damage it.

BoB

 

[DaveC426913]

Yup. Mine's pretty much identical to that.

It would require a bit of fancy footwork to get the bottom inlet on the warm side of the curtain - while still allowing easy access to the closet. I've considered moving the unit out of the doorway and into wall. (I did all the reno - the closet side is unfinished studs anyway, so there's only 1/4" wallboard to cut a hole in.)

 

[Tom.G]

Those portable air conditioners come in two styles. The effective ones have either two hoses or a single siamese hose for the outside air. The condenser air is drawn from the outside and exhausted to the outside.

The cheaper ones exhaust condeser air but actually draw it from the room. This, of course, is counter-productive because outside air is drawn in which then has to be cooled! Many people are happy with this because they still get a cool breeze out of the unit.

So, if your unit doesn't both draw and exhaust the condenser air, get rid of of it and get a 'real' one! You will get much better results.

Cheers,
Tom

 

[DaveC426913]

The cheaper ones exhaust condeser air but actually draw it from the room. This, of course, is counter-productive because outside air is drawn in which then has to be cooled!

I'm sorry, I don't follow.
Does it draw it from the room? Or from outside?

Mine only has an exhaust to outside, so...

 

[Drakkith]

I'm sorry, I don't follow.
Does it draw it from the room? Or from outside?

Mine only has an exhaust to outside, so...

If you have only one hose then the unit takes cool air from inside the room, blows it over the heat exchanger, and then dumps it outside. This air has to be replaced, so warm air from outside the room flows in through cracks in the door, window, etc. This warm air then has to be cooled. Which is counter productive since you normally want the cool air to stay inside the room, not get dumped outside.

 

[Lnewqban]

I'm sorry, I don't follow.
Does it draw it from the room? Or from outside?

Mine only has an exhaust to outside, so...

That exhaust hose only carries hot air outdoors.
The make up air for cooling the compressor and condenser comes from around the unit (via one of the body's filter-grilles).
Since the unit is standing inside the room to be cooled, the same volume of air must leak into the room somehow.

A room without windows or doors, like yours, will restrict the amount of that make up air, which will reduce the efficiency and capacity of the unit, since the condenser remains too hot.

Please, see:
https://learn.allergyandair.com/portable-air-single-hose-vs-dual-hose/

https://portableairconditioner.reviewstobuy.net/single-hose-vs-dual-hose-portable-air-conditioner/

 

[DaveC426913]

Ah. Of course.

The most convenient culprit is air coming up the stairs from the main floor library. (There is no door at the top of the stairs, though there is a door into the library). That's cool already so it should be OK.

99% of the heating problem is because the bedroom is a reno'd attic, with only 6 inches from paint to shingle (4" insulation, 2" soffits). And it has a roof ridge vent. But the sun beats down mercilessly. You can feel the heat on the ceiling panels.

 

[Drakkith]

99% of the heating problem is because the bedroom is a reno'd attic, with only 6 inches from paint to shingle (4" insulation, 2" soffits). And it has a roof ridge vent. But the sun beats down mercilessly. You can feel the heat on the ceiling panels.

I wonder if pinning something like a sheet up across the ceiling would help. Perhaps not the prettiest solution, but it might be better than paying every month for the extra power the AC uses.

 

[Spinnor]

Do you run the unit 24/7, if not that would help? I have thought that it would be great if there was a safe, inexpensive, and easy way to upgrade a living spaces insulation from the inside but there seems to be all kind of difficult hurdles to do this. There are so many older homes with inadequate insulation. The insulation can't burn, can't trap moisture, should not be too expensive, should be easy to install, should not interfere with power outlets, should not be hideous looking, ect..

A good night's sleep is pretty important for good mental and physical performance the next day, good luck.

 

[rbelli1]

The insulation can't burn, ... should not be hideous looking,

So you don't want your house to be hideous or a death trap? You'll get one or the other and like it!

BoB

 

[hutchphd]

Is there any way to get a reflective barrier on the hot side of the insulation? I have seen a product that is aluminized mylar "chaff" to put on the open insulated floor of an uninsulated attic...but it doesn't sound like you have access to the top ( hot) side. Radiant barrier wonderful when you can do it Can you somehow augment the airflow up the rafter to the ridge (maybe pressurize behind a knee wall slightly or more soffit vents?)
Winter is coming...none too soon.