Are there any advantages to a one-hose (portable) air-conditioner?

[hmmm27]

TL;DR Summary

The only thing I can imagine is that a mfr can advertise a higher BTU/hr figure.

So, I picked up a used single-hose portable a/c (window is better than portable of course - and cheaper - but my back is shot and for some reason the super takes a dim view of window units on the 20th floor).

It was 31C for a few days, earlier in the week : this normally means I'm screwed without a cold sink on hand (yes, it's on the laundry list of medical issues I'm currently trying to have addressed). I was prepared for the advertised 8,500BTU/hr to be around 5k net instead : it's not a large room(12x 12'?) and should be doable.

On the one hand, the room went from 90F down to 80F, but I was looking for the ability to drop it down to 65F, or so (enough wiggle room that I can count on 70F : a comfortable sleeping temperature for yours truly).

It's not (or at least doesn't appear to be) a faulty unit - the air coming out of the vent is cold enough - but, the fact that the damned thing is actively exhausting warmed room air to the outside at about the same rate it's providing cold air is pretty annoying. Also, within context of an apartment building, 5/6 sides of the room are non-radiative into nighttime relative coolth.

I'm going to DIY the thing into a two-hose for the obvious reason, having the requisite amount of cardboard and duct-tape on hand to build a plenum for the short length of 5" hose I'm going to use. It does appear to have two inlets for air (two grills; one has a filter, behind it). But, that's probably next week's post.

Meanwhile, the mystery I'd like to solve is "Which idiot designed this thing ? and in what context would it actually be useful ?"


Thanks

 

[bob012345]

It's not clear what you mean. Is this an evaporative cooler? Can't you just vent the warm air out the window?

 

[hmmm27]

The pic is similar to the unit I have. That's an actual air-conditioner, not a swamp (evaporative) cooler.

With the two-hose models, outside air is inletted, warmed and exhausted to the outside ; inside air is cooled.

With the one-hose models, the inside air is used to dump heat to the outside, thus only one hose is necessary.

Comparison

I'm honestly trying to figure out how the one-hose a/c's got past design quality-control.

 

[russ_watters]

It's not clear what you mean. Is this an evaporative cooler? Can't you just vent the warm air out the window?

The problem is that if you exhaust the hot air to outside, you need to bring in make-up air from somewhere, otherwise you will deflate the room. So yeah, they're not great.

 

[bob012345]

The problem is that if you exhaust the hot air to outside, you need to bring in make-up air from somewhere, otherwise you will deflate the room. So yeah, they're not great.

That makes sense. Thanks. So I presume window units reject the heat using already outside air just like my AC compressor at my house. Now I get what hmmm27 is planning to do, to turn a one hose into a two hose.

 

[russ_watters]

That makes sense. Thanks. So I presume window units reject the heat using already outside air just like my AC compressor at my house. I suppose you could bring in outside air, run it over the coils and send it back outside to reject heat. Is that what's going on here?
https://www.physicsforums.com/attachments/284317

Yep, you got it!

 

[bob012345]

I'm interested in this problem because I live in Dallas and it's been humid. I keep my house on the warmer side as it is to limit stress on the AC system. I just bought a dehumidifier to dry out the air inside. One thing I noticed is that is rejects warm (not hot) air into the room. Sure, it's dryer air but I still need to compensate for it with the central air. I wasn't expecting that yet I suppose I should have.

So basically this dehumidifier is similar to an AC unit. My theory is that is cools the air (a lot) to condense out the water (three gallons so far in less than 24 hours!) then mixes that cool air back with the hot air to attempt to be neutral. The extent the air is warm is a measure of the slight mismatch between hot and cold air due to basic inefficiencies.

I conclude its still worth it since the dryer air will feel cooler and will actually cool more efficiently in the central AC.

 

[DaveC426913]

My one-hose portable unit pulls air from the room, cools it (dehumidifying it in the process), then uses the heat to evaporate the collected water, and ejects it outside. I never have to dump the water.

 

[bob012345]

My one-hose portable unit pulls air from the room, cools it (dehumidifying it in the process), then uses the heat to evaporate the collected water, and ejects it outside. I never have to dump the water.

So you're saying it recycles the room air and only rejects the water vapor?

 

[hmmm27]

My one-hose cportable unit pulls air from the room, cools it (dehumidifying it in the process), then uses the heat to evaporate the collected water, and ejects it outside. I never have to dump the water.

That's what I thought (as a sole advantage) until I read where a two-hose unit does the same thing. I thought that the exhaust would be extremely hot (to minimize blowing out inside-air) but it's just warm.

[OT'ically ; I remember your thread regarding that; how did it turn out ?]

Back to 1 vs 2 hose, I suppose a one-hose could be used parasitically in a domicile that already has central A/C, but one room isn't cool enough for its purpose... and simply sticking a fan in the (house HVAC) vent to increase flow wouldn't occur to everybody.

 

[DaveC426913]

So you're saying it recycles the room air and only rejects the water vapor?

No, sorry, it ejects hot air as well. The exhaust hose is quite warm (and - at 20 feet long, running the length of my closet - rather inefficient).

No, that does not mean my closet is 20 feet long...

Also, whatever happened to the font size options in messages?

 

[DaveC426913]

[OT'ically ; I remember your thread regarding that; how did it turn out ?]

Er. I don't. What was I doing?

 

[hmmm27]

Er. I don't. What was I doing?

Well, somebody was going on about trying to configure a one-hose portable in their attic. I'd a fleeting thought of lending a spare dehumidifier I had, but (I don't think) the thread continued long enough to get to that stage.

Alternate universe, mebbe.

 

[DaveC426913]

Well, somebody was going on about trying to configure a one-hose portable in their attic. I'd a fleeting thought of lending a spare dehumidifier I had, but (I don't think) the thread continued long enough to get to that stage.

Alternate universe, mebbe.

I was, and I did, and I vaguely remember asking about it. Oh yeah. I was trying to figure out where to place it in relation to my BR/closet doorway for best efficiency.

I finally cut an 8" hole in the wall between the two rooms so I could run the hose into the BR and not have the AC sitting in the doorway where someone* would trip and fall down the stairs.

*inevitably my wife

 

[hmmm27]

Well, in your case it might actually work reasonably well, considering that - from childhood memory - the upper floor is still broiler hot long after the sun's gone down : useful thermal mass in the winter, not so much in the summer.

I'm interested in this problem because I live in Dallas and it's been humid. I keep my house on the warmer side as it is to limit stress on the AC system. I just bought a dehumidifier to dry out the air inside. One thing I noticed is that is rejects warm (not hot) air into the room. Sure, it's dryer air but I still need to compensate for it with the central air. I wasn't expecting that yet I suppose I should have.

A dehumidifier in a closed system (ie: not venting to or from the outside) will heat the air a little... but "at least it's a dry heat". I put one in my niece's condo basement ; it cleared things right up and almost completely ditched the musty smell. You'll have taken a load off the regular A/C by using it.

 

[DaveC426913]

Well, in your case it might actually work reasonably well, considering that - from childhood memory - the upper floor is still broiler hot long after the sun's gone down : useful thermal mass in the winter, not so much in the summer.

This is an attic, converted by an amateur, for his own occasional visit. There was 2 inches of air gap - and nothing else - between drywall and shingle.

I once measured the room temp to be 107F before I got the AC in.

I had 10" candles in 4" holders. They had melted and fallen over till they touched the table.

 

[russ_watters]

I'm interested in this problem because I live in Dallas and it's been humid. I keep my house on the warmer side as it is to limit stress on the AC system. I just bought a dehumidifier to dry out the air inside. One thing I noticed is that is rejects warm (not hot) air into the room. Sure, it's dryer air but I still need to compensate for it with the central air. I wasn't expecting that yet I suppose I should have.

So basically this dehumidifier is similar to an AC unit.

You are correct - an AC unit and dehumidifier are basically the same device. So if you need cooling, it is best to locate the condensing unit outside (a normal split system air conditioner), so it isn't rejecting the heat into the room.

I conclude its still worth it since the dryer air will feel cooler and will actually cool more efficiently in the central AC.

This is unlikely. Yes, it's probably more efficient than an AC unit in a certain way of measuring (heat movement at the coils), but the heat rejection into the room means you need another way to cool the room otherwise the overall feel will be hotter. In other words, the cycle itself is more efficient if you use the same equations, but the math doesn't "know" the heat is being rejected into the room. If you instead measure efficiency based on heat movement for the room, the efficiency of the dehumidifier is negative. It's heating the room instead of cooling it, and it is unlikely to even "feel" cooler for being dehumidified.

 

[Dullard]

I have a '1 hose' unit that I use during Hurricane power outages (my generator will carry it). One of the 'sneaky' problems with these units is that the latent heat (moisture) of the air that is drawn into the room to make up for the air used to expel the heat/condensate is typically high. Condensing water 'uses up' a whole lot of what would (otherwise) be cooling capacity. As a result, BTU comparisons between Conventional AC systems and '1-hose' units are not apples-apples.

 

[bob012345]

You are correct - an AC unit and dehumidifier are basically the same device. So if you need cooling, it is best to locate the condensing unit outside (a normal split system air conditioner), so it isn't rejecting the heat into the room.

This is unlikely. Yes, it's probably more efficient than an AC unit in a certain way of measuring (heat movement at the coils), but the heat rejection into the room means you need another way to cool the room otherwise the overall feel will be hotter. In other words, the cycle itself is more efficient if you use the same equations, but the math doesn't "know" the heat is being rejected into the room. If you instead measure efficiency based on heat movement for the room, the efficiency of the dehumidifier is negative. It's heating the room instead of cooling it, and it is unlikely to even "feel" cooler for being dehumidified.

Buying the dehumidifier was an experiment. I can see good uses for it such as removing a large amount of humidity in a basement to prevent mold and not caring too much about temperature since it tends to be cool in basements anyway.

My goal was to have dry cool air in the house without having to have the central AC on all the time to dehumidify. I figured it would be easier and cheaper to cool the house with central air if the air was dry even if I had to run it a little bit more to make up for the extra rejected heat. It took about 3 gallons of water out of the air in 24 hours. I doubt that would go on forever once things even out.

Alternatively, I could buy a supplemental window AC unit which would help dehumidify the house air while cooling it somewhat without rejecting the heat inside. Maybe I should have just done that instead?