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Venting of portable aircon units

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Venting of portable aircon units

Old 24th Jun 2020, 16:26
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Venting of portable aircon units

Not sure if JB is appropriate for a random tech question but here goes:

Thinking of buying a portable air con unit for ad hoc domestic use. Can the exhaust hose just be dangled out of a window or must a window adaptor unit be fitted (which I realise is more efficient)? Trying to avoid window surgery if poss.

Thanks for info.
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Old 24th Jun 2020, 16:59
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It will work, but the outflow air is quite hot, so any finding its way back in will defeat the cooling. Ideally the exhaust hose should be as short as possible (reduces radiated and conducted heat in to the room from the hose) and the 'hole' in the window should be sealed as best as possible.

However, this leads to the very serious shortcoming of all 'single circuit' (which portable units are...). As you are expelling hot air, and quite a considerable flow of such air, there must be an equal flow of outside (warm / hot) air back into the room. Thus you're drawing warm / hot air back in, massively reducing the overall cooling effect. Sure, standing next to the cold, dry air at the vent feels very cold, especially due to evaporation of sweat in the dry air, but this masks to inflowing hot air which is undoubtedly hotter than the ambient room air.

To see how serious the drawing in of hot outside air really is, try to make your room a well sealed as you can, including wrapping towels around the exhaust hose, whilst the unit is off. Then watch the towels being sucked into the room when you turn the unit on, as they try to hold back the inevitable leakage of warm / hot outside air back in to replace the exhaust air.

Using approximate temperatures for today's 30 degrees C outside. Say your room is 25 degrees. When the unit is on, it is likely to be blowing 10 degree cooled and dried air which feels great. It is cooling some room (25 degree) air down by around 15 degrees. In doing so, it is expelling room (originally 25 degree) air heated up to around 40 degrees. Even if you let NONE of this leak back into the room, you'd still be drawing in the same volume of 30 degree outside air back in to the room. So it is 3 steps forwards, 2 steps back. Of course, if you let the heated 40 degree air back in, it is 3 steps forward and 3 steps back, as the air conditioner is likely drawing close to 1kW of electrical energy which is pure heating - and completely surplus to requirements in this instance!

Hence you'll never make the room much cooler overall, but it will feel good being near to the cool air flow whilst it is on. Any cooling of the room will be short lived once the unit is turned off. Hence the best air conditioners are the dual circuit ones, which recirculate cooled air inside, and which have a separate circuit of outside air to take away the heat to outside.

Hope this helps.
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Old 24th Jun 2020, 20:14
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We had one for a time, and found that dangling the hose out of a window was pretty ineffective. The problem is that the fan that blows the exhaust air out also draws in room air, so when it's hot outside warm air gets pulled back in through the open window that the hose is dangling out. The fix that sort of worked was to cut a bit of plywood that could be wedged into an open window frame, with the hose outlet fitting screwed to it. The thing still draws in outside air, but with care you can open a window where the air outside is a bit cooler, so not having such a big impact on performance. We found that the unit we had wasn't that effective, and made a lot of noise, and overall we were a bit disappointed with it. I opted to fit proper air conditioning when we built this house, a decision I have never had cause to regret (especially today, when it was well over 30 deg outside, yet a pleasant 22 deg indoors).
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Old 24th Jun 2020, 20:18
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As VP said, you can, but you don’t want to. I have two portable units, and find them acceptable if you can’t get anything better. They are much more expensive/BTU than other types, pretty noisy, and take up space, but they do work. You will need to seal up the window around the discharge hose, either with the factory adaptor or some other means.
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Old 24th Jun 2020, 20:59
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If you are just dangling it, god forbid the hose falls back into the room. You will awake, as I did, a few hours later inside the centre of the Sun.
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Old 24th Jun 2020, 21:17
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Agreed that these are inherently inefficient. In the USA mfr are required to include effective BTU as well as rated BTU. A 12000 BTU portable unit we have has a ~8500 effective btu rating.

This did work well for an occasional use studio in an attached garage, when cooling we left a door to the main house open so the makeup air was cool air from our centrally AC cooled house.
Still not great for efficiency but was a quick fix. (Eventually had a heat pump installed to provide heat as well as cooling, a great solution.

There are a few (more expensive of course) dual hose portable units that work similar to a standard AC but can be rolled around room to room.
If handy with duct tape you could probably convert a single hose unit to dual hose model.
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Old 25th Jun 2020, 00:24
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The unit should have come with a window fitting. Ours did, but we have sliding windows.
The fitting we have would not work with casement, double hung, louvre, awning or bigfold
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Old 25th Jun 2020, 00:59
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However, this leads to the very serious shortcoming of all 'single circuit' (which portable units are...). As you are expelling hot air, and quite a considerable flow of such air, there must be an equal flow of outside (warm / hot) air back into the room. Thus you're drawing warm / hot air back in, massively reducing the overall cooling effect. Sure, standing next to the cold, dry air at the vent feels very cold, especially due to evaporation of sweat in the dry air, but this masks to inflowing hot air which is undoubtedly hotter than the ambient room air.
Well what's the difference with other more common air conditioners. Don't they all suck from the same source?

Could the difference be that the common window type hangs its hot compressor outside the window?
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Old 25th Jun 2020, 04:06
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As said, single hose units are inherently inefficient. Hot air used in heat exchanging at the condenser and vented outside must be replaced by air drawn into the room from somewhere else. Thus you are constantly replacing air you have already expensively cooled with non-cooled air, and blowing some of it (a lot!) outside. Some units come as dual hose units, with appropriate window fittings. They separate the evaporator (air cooling) and condenser (air heating) circuits. Thus external air is drawn in, heated through the condenser, and then exhausted back outside. The evaporator side will then just be recirculating and recooling already cooled air from the room. Much more efficient, and how most aircons work.
Single hose units can be MacGyvered to be dual hose units. I've done it to mine, and it works considerably better.
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Old 25th Jun 2020, 07:39
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Originally Posted by lomapaseo View Post
Well what's the difference with other more common air conditioners. Don't they all suck from the same source?

Could the difference be that the common window type hangs its hot compressor outside the window?
Split air con units have an external unit that sucks in outside air, blows it over the external heat exchanger and vents the air outside. There is no air flow from inside to outside, or vice versa. The heat is pumped via the two gas lines that run inside to the internal unit(s). The internal unit is just another heat exchanger with a fan, that draws warm room air in, cools it using the expansion of the refrigerant from liquid to gas through another heat exchanger and blows cooled room air out. As the unit works, the room air steadily gets cooler, as it is recirculated through the internal unit, being cooled more with each pass, until the thermostat is satisfied. We keep our bedroom aircon set at 18 deg C through the day at this time of the year, turning it off overnight, and that's enough to ensure the bedroom remains cool overnight (it had risen to about 21 deg by this morning). We could leave the thing on overnight, as it's very quiet, as the compressor (which is the thing that makes most of the noise) is in the external wall mounted unit.
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Old 25th Jun 2020, 07:50
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We have one,

Came with a bent spout that goes out the window, then we tape some plastic bags across the resulting gaps, looks a little heath robinson, but works like a dream.

The best effect is the dehumidifying, noisy buggers though, and you only get 1 cold room, but that room can get properly cold in comparison to the rest of the house.

has to be on for a good 12 hours to start with to suck the heat out of the fabric of the house, once the walls are cold, youíre away.

oh, take it apart and wash all the insides with dettol etc when you put it away, otherwise itíll smell next year.
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Old 25th Jun 2020, 08:33
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Portable. The in-thing this summer in Japan, with the only venting being the cooled air itself. Not sure if these are available outside Japan, but here is a random ad.
N.B. I have no axe to grind, as I have not yet bought one from anyone, but will admit to looking at getting one of these.
https://www.amazon.co.jp/-/en/A500/dp/B088TNBS4K

Looks economical where electricity is not cheap. Not sure if these are available outside Japan, but just throwing this into the pot.
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Old 25th Jun 2020, 08:35
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Originally Posted by lomapaseo View Post
Could the difference be that the common window type hangs its hot compressor outside the window?
The "rattlers" sort of work that way. It doesn't matter where the compressor is if it is using room air to cool it while it performs its function. The condenser circuit (bit that makes the air hot) is outside, and the evaporator circuit (bit that makes the air cold) sucks air from the room through one part of the face plate grill, over the evaporator coils, and blows the cooled air back into the room through another part of the face plate grill. The "box", ie all of the workings, sits outside the window to take up less room inside. You just need two separate air paths, which they all have, but you don't want the air source to be the same.

Last edited by Traffic_Is_Er_Was; 25th Jun 2020 at 08:45.
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Old 25th Jun 2020, 08:43
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Not air conditioning but a silent ceiling fan for small rooms. We have them in each bedroom with the associated remote control. So far, we are very satisfied.

https://www.amazon.co.uk/Westinghouse-Turbo-Swirl-Ceiling-Fan/dp/B0016KUYAO/ref=sr_1_6?crid=XEPWRFPF48GQ&dchild=1&keywords=westinghouse+ceiling+fan&qid=1593074451&sprefix=westinghouse%2Caps%2C152&sr=8-6 https://www.amazon.co.uk/Westinghouse-Turbo-Swirl-Ceiling-Fan/dp/B0016KUYAO/ref=sr_1_6?crid=XEPWRFPF48GQ&dchild=1&keywords=westinghouse+ceiling+fan&qid=1593074451&sprefix=westinghouse%2Caps%2C152&sr=8-6
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Old 25th Jun 2020, 08:47
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FWIW, I installed a Toshiba split aircon unit myself last year. Took me less than a day to fit, the hardest part being fitting the external unit, which weighs over 20kg, on to brackets on the wall. The rest was easy, drill a ~70mm hole through the wall, run the two pre-insulated and terminated refrigerant pipes through the wall (one 1/4" the other 3/8" flexible copper), together with a 3/4" flexible condensate drain pipe. The indoor unit was very light, and just clipped on to a bracket screwed high up on the wall. Commissioning was just connecting a vacuum pump to the pipework, leak testing it all, leave it pumped down at vacuum for half an hour, then close off the service valves and open the valves in the outdoor unit. The latter came pre-gassed, so there was no need to mess around with refrigerant, although even if there had it's easy enough, as you can buy cans a bit like aerosols for refilling aircon systems.

The total cost, including the purchase of the vacuum pump and test gauge set, plus all the ancillaries, like ducting for the pipe work, cables, spray foam insulation for the hole in the wall, etc, came to about £800. A lot more expensive than the portable unit, but massively more effective and extremely quiet. When running in "silent" mode, the noise inside the house in imperceptible, certainly not enough to keep us awake at night, on the few times we've run it overnight. If we have it in normal mode and leave the bedroom door open, it does a pretty good job of cooling the whole house, as cool air seems to just flow out and down the hall.
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Old 25th Jun 2020, 09:55
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I have a portable air conditioner and use it in some of the bedrooms, it draws the cooler air from the hallway and expels through the window vent.
The difference is noticeable in 10 mins.
However the biggest change I made was putting small vents between the felt in the roof.
This allows the warm air to be taken out of the slate roof by the breeze and in the winter it stops a condition known as Christmas Damp.
This is condensation caused in the winter from heat rising up through the ceiling and condensing on the underside of the felt, rafters and slate.
It is called Christmas damp as it is usually discovered when people enter the loft to get the Christmas decorations.
I fixed the problem for £30.
https://www.lbsbmonline.co.uk/mantho...SABEgJiqPD_BwE
Next year I intend to replace the felt with a breathable membrane and add a couple of electric Velux windows to vent the roof on warm evenings.
Hope this helps.
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Old 25th Jun 2020, 12:24
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Originally Posted by Spunky Monkey View Post
I have a portable air conditioner and use it in some of the bedrooms, it draws the cooler air from the hallway and expels through the window vent.
The difference is noticeable in 10 mins.
However the biggest change I made was putting small vents between the felt in the roof.
This allows the warm air to be taken out of the slate roof by the breeze and in the winter it stops a condition known as Christmas Damp.
This is condensation caused in the winter from heat rising up through the ceiling and condensing on the underside of the felt, rafters and slate.
It is called Christmas damp as it is usually discovered when people enter the loft to get the Christmas decorations.
I fixed the problem for £30.
https://www.lbsbmonline.co.uk/mantho...SABEgJiqPD_BwE
Next year I intend to replace the felt with a breathable membrane and add a couple of electric Velux windows to vent the roof on warm evenings.
Hope this helps.
I did something very similar at our old house. We had condensation on the underside of the felt in winter, after having installed more loft insulation, so making the loft a lot colder. I had some offcuts of 1 1/2" PVC waste pipe, so cut it into short lengths and wedged it in the joins in the felt. Made a very noticeable difference, just from improving the ventilation. Cheap, too, as the bits of pipe were just left overs from when I refurbished the bathroom and kitchen.
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Old 25th Jun 2020, 12:41
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FWIW, I installed a Toshiba split aircon unit myself last year.
Good for you. Illegal in Australia unfortunately. Another example of our "protection of vested interests" statutes.
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Old 25th Jun 2020, 12:52
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Originally Posted by jolihokistix View Post
Portable. The in-thing this summer in Japan, with the only venting being the cooled air itself. Not sure if these are available outside Japan, but here is a random ad.
N.B. I have no axe to grind, as I have not yet bought one from anyone, but will admit to looking at getting one of these.
https://www.amazon.co.jp/-/en/A500/dp/B088TNBS4K

Looks economical where electricity is not cheap. Not sure if these are available outside Japan, but just throwing this into the pot.
That looks like an evaporative cooler (albeit a USB powered desk top one). Mains powered ones are readily available here in Aus. It will cool to some extent, but no where nearly as effectively as a refrigerated type. They also don't work too well if it is really humid, as they rely on evaporation to work (hence the name). Just remember that they are basically blowing water vapour into your room. Also, you need to keep adding that water, because if the tank runs dry, they don't cool. They just become a fan.
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Old 25th Jun 2020, 12:55
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Originally Posted by Traffic_Is_Er_Was View Post
Good for you. Illegal in Australia unfortunately. Another example of our "protection of vested interests" statutes.
Technically it's a breach of building regulations here, but the only impact in reality is on the warranty. If the unit is installed by a Toshiba approved, building regs compliant person, with an F gas ticket, then the warranty is 3 years instead of 1 year. However, the cheapest quote I had to supply and install this same unit was over £1,700, and there was no way I was paying someone ~£900 for something that would, for them, be less than a days work. If I could fit one in a day, with zero experience, I'm pretty sure a skilled person could fit one in a lot less time, maybe even half a day.
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