Hacking Portable Air Conditioners
pmarks.net
pmarks.net
> Seriously, either we need to get more awareness of how dumb single-hose portable A/C units are, or we need to just use window units whenever possible. While I know that there are times a portable unit is the only option (remember, I’m in that boat), it seems that only very high capacity, premium machines have the facility to use two hoses. Which is frankly stupid but then again that’s what I’m trying to tell you now.
Yes, you "shouldn't like them," unless it's you're only option, like in his case.
In the video, the guy says he owns two portable AC's. So there's that.
Also, don't forget the ever-popular "apartment building doesn't allow anything protruding from the windows" rule.
Of course it would take up more space and be louder than a regular window unit, but at least it wouldn't require hoses. Plus it could drip condensation out the window through a short tube.
For anyone reading this, presumably because windows are thin and walls are thick, window ACs are expected to stick out and thus have vents on the sides, whereas wall ACs have vents only on the back surface.
So as long as you figure out drainage (so condensation doesn't just land on the windowsill), you can install a wall AC in a window and have it not protrude.
The compressor and radiator are outside. A section a couple inches tall contains the pipes, wiring, and braces. The fan, blower, filter and thermostat are in the front bit. Your window panes (hopefully double glazed or better?) and a couple inches of foam provide the sound dampening. The lowest displacement model claims 47dB with the fan and compressor at full bore.
We received funds but the funds were not enough to retrofit a 600-unit building with central A/C. However, the city of SF will not permit wall-mounted mini-split units nor window units in the building, since that’s a change to the facade. So we’re stuck with portable units...
https://aepronet.org/california-supreme-court-rules-against-...
https://law.justia.com/cases/california/supreme-court/2014/s...
But I created a wedge-shaped mount for the hose ports that fits in the triangular window gap exactly, so the room is still relatively sealed. When summer is over, the mount is disassembled and stored flat.
I've never seen anyone else do this. I've always hated the look of hoses dangling out of open apartment windows and of course that's terribly inefficient. Every time I see our windows from the outside I'm rather jazzed at how great-looking the solution is.
Typically we get just a few days where it stays over 80 °F with high humidity, so I guess it isn't particularly adaptation.
I once went hiking. I checked the forecast and the maximum was 72. Great! I almost had a heat stroke - very bad day. I confirmed later that the temperature was not higher. And I've hiked at warmer temperatures just fine.
This is why when I buy a car, I want to make sure it's trivial for me to adjust both the flow of air and the level of cool/heat independent of each other, and not rely on the temperature setting. Almost all cars let you do that these days, but there was a period where some cars did not let you do that. Having a thermostat and letting you maintain a temperature is really not much of a feature if the variance in the "right" temperature is too large.
The content might be interesting, but it's way too long. The guy goes on way too many tangents and adds way too much filler. You probably can boil the whole video down to a few bullet points, yet it's 16 minutes long.
Seems to be unique
Watching his videos reminds me of university and being in a really high quality lecture or lab session.
... if you ignore the energy consumption, which is the whole point of the video.
Noisy and inefficient is a good description. Granted, it had to run off a regular 15A outlet so it was never going to be as powerful as the one in the attic. But it made sleeping possible by getting the temperature below 85F (30C).
Anyone else know of other companies in this vein?
Each has just straight up sent me a new unit or full replacement part when the previous one failed with no rma or warranty check - none of that nonsense just great service. Dyson support even sent me full factory service manual for the unit 5 years after it was discontinued (and 7+ out of warranty) since I wanted to troubleshoot a power supply issue which ended up working fine after resoldering the main power cord to the power board.
These companies are increasingly rare.
Interesting! My AM11 fan started screeching and making a strange noise so I called in and my warranty had expired just a month ago and all they could do is replace my unit with a refurbished one.
Sounded fine to me, especially because it was out of warranty, officially, but the unit that came was a different color and cosmetically in horrible condition, much worse than the one I sent in.
At least it didn't squeak or screech and I suppose the fact they even helped out outside of the warranty period is nice.
Even more so as the existing one are moving away from it, the logitech of today seem significantly worse than the logitech of 10-15 years ago for instance.
That's not really true from a design perspective. You really want to know what sort of problems your customers are having in the field. And you don't know really unless you talk to them.
You want people to install the stuff and have it just work. 'connected to the internet' is something that fails all the time.
One you leave software as an exploitative service or the customer is the product, which most of the stuff people here work on. And enter the world of hardware that solves peoples real problems you want the customer to install the stuff, have it do what they expected and thus NEVER CALL YOU.
The problems identified in the article are such low hanging fruit. Everywhere you look in residential housing there's huge efficieny gains to be made, but very little effort is going in to making them.
I'd love to find ways we can use technology to make housing more efficient. We need to - it's such a crucial pillar in dealing with climate change, and the vast majority of housing is so comically inefficient. The single tube air conditioners mentioned in the article are just the icing on the cake of all these massive energy wastes we accept because they're marginally more convenient. Does anyone know how to fix this?
There's honestly a lot happening and changing. Obviously you won't see it by buying "HVAC" junk from a box store. What this person should have done is paid an actual HVAC tech to install a ductless mini-split [0]. It would have been a heck of a lot more efficient. He states his one unit is drawing 10 amps (110 volt I assume). Whereas my american standard 4 ton (48,000 btu) unit draws 10 amps as well (240 volt) and cools a 2200 square ft house in 100+ degree texas weather with an electric bill usually not higher than $120 per month (1200 - 1400 kwh or so).
By comparison, at my old house (which was half the size, 1100 sq ft) with a much older 12 Seer unit, my electric bill was regularly over $200. I measured that unit at drawing 18 amps (at 240 volt) and it was only a 3 ton 36,000 btu out door unit. The latest and greatest 21/22 seer units are even more efficient than my current one mentioned above (which is probably only 17 seer).
[0]: https://www.americanstandardair.com/products/heating-and-coo...
You can't say what somebody "should have done" without knowing a lot more details about their life.
Installation will no doubt be more expensive in the US, but there is no reason for AC itself to be (if anything, most kinds of hardware seem to generally be cheaper in US than in Europe).
I suppose it's hard to complain too much. HVAC installers need to have some decent technical background, troubleshooting skills, and their bodies tend to get injured/broken by the time they're in their late 40s like most manual labor trades. A HVAC installer/tech can make $80K or more a year, which makes it one of the few jobs still out there where you can make a decent middle class income without tons of schooling.
Installing a mini split is nowhere the difficulty of an HVAC though, assuming your have the electrical circuit (which I'd guess would be an electrician's job not HVAC) it's a few hours' work, at least for a simple case and if the installer knows what they're doing: pierce the wall, mount the external unit, mount the internal unit, connect the two, charge[0], done.
By "simple" I mean a 1:1 setup with both units mounted on the same wall (and a wall-mounted indoor unit). Obviously a more complicated setup (multi-zone, slim duct, more distance between the two units) would take more time and be more expensive.
I can see $2000 for a non-trivial multi-zone setup.
[0] if you're handy there are mini-splits sold specifically for DIY installations which come pre-charged, though that means the pipes won't exactly fit the distance I guess
In addition, running the electrical is usually done by the HVAC company and setting up the mounting pad for the outdoor unit.
I completely agree that it isn't rocket science, and it's well within the realm of a skilled DIYer with about $250 in specialized tools. However, I can see why an HVAC company charges as much as they do. For an average install (not dead simple), it's probably 5-6 hours of labor, they have to pay for the company equipment, vehicles, health insurance, permits (my township requires one for a mini), taxes, etc.
Given the orders of magnitude less work required to find a product and click "Buy", it'd greatly benefit society for portable A/C manufacturers to compete on efficiency.
Obviously only you know your situation, but just in case any other readers are considering a mini-split: it doesn't have to be this way and it typically isn't.
From firsthand experience installing Mitsubishi mini-splits in multi-unit buildings in very regulated cities, a typical condo installation takes 2 days, including running power from an electrical panel that's not in the unit. A reasonable HOA can often answer in a week or two unless you're the first person to install a mini-split in the building. Larger buildings often recommend specific HVAC contractors. Your contractor will apply for HVAC and/or electrical permits online with very basic drawings; they're often issued immediately ("over-the-counter"), subject to field inspection. There's generally one inspection after it's installed. A good contractor will handle almost all of this.
Basically, it can be complicated but it doesn't need to take a ton of calendar time. Other than cost and needing outdoor space for the condenser, the hardest challenges you & your contractor will encounter are running new electrical circuits from the panel and draining condensate from the indoor head.
Why is this needed? Is it because the electricity in the US is at 120V? Over here (Europe) you can just plug the cable from the indoor unit into the electrical outlet.
Regardless, ac draws enough power that you want it on a dedicated circuit no matter where you are. Sharing that outlets with anything else is likely to result in annoying breaker trips when you overload the circuit.
At least in the US, many systems power the indoor unit(s) from the outdoor unit. My guess is that since a control wire is required anyway (for central control of fan speed and direction), the manufacturers think it’s easier to power everything from one run.
The AC would not have been planned for when designing the original circuits, so you would need to add a 240V circuit for it unless you put it in a room which already had one.
As the others have noted, since it's a high-power unit anyway you'd really want to have it on its own circuit to avoid adding too much load on the circuit. So even in europe you probably want a circuit exclusive to the AC, meaning you may have to run a new one unless an AC circuit had originally been run "just in case" (and even then it might not have been run to the room you wanted it in e.g. maybe the original builders put the circuit for an eventual AC in the living room but you want it in the bedroom you converted to a study).
Split systems are the norm on my continent, and most can be installed in well under a day. Many installers can do multiple per day into existing dwellings, code compliant, filled, sealed, and on a proper circuit. Units/Apartments are likely to take longer.
Many people don't understand the world of stupid they've joined when they buy an HOA property. Although I have to deal with the psychic trauma of a neighbor who doesn't mow often, living in a reasonable city on a normal block means that permitting nightmares and other bullshit don't really exist. :)
At best they achieve a local maximum nowhere near the potential, while costing a mint in fees and preventing one from doing anything crazy like planting native plants in the front instead of grass or not painting your house the right shade of beige.
Mount it like a TV, cut a hole in the wall, hook up electricity. No architectural designs needed. I'm not sure who told you that, but there are dozens of DIY youtubers who must have gotten free split units, because there is a flood of videos of people installing a precharged version with only themselves and a helper.
I don't approve of the above, but that is how it is.
Yah done goofed.
In general if you bought a condo, you goofed.
Building code for electrics is probably your largest problem. But then some places you can't even change a damn light bulb.
Mini-spits have an outdoor unit and an indoor unit connected by two hoses. The indoor unit basically screws to the wall. You do need a hole through the wall for the hoses but that's it. As a result they are cheap to and quick to install. They are also very efficient.
That's what they're pointing out. It's not a huge hole but it's still a hole going through the wall, and if they rent and buy the unit with their own money they'd be leaving with it, leaving that hole in the exterior wall. 3" is probably on the upper bound of what you need but it's not wrong. And it's not like the landlord would be much happier with a 2" hole.
Builders spend money on things that make them profit and home buyers don't particularly evaluate efficiency.
After that you figure out how to spend public money on lower efficiency structures. Fraught, but spend money where it's likely to pay off and it probably works out okay.
I'm using one of those portable units because I live in a rented apartment. There is nothing convenient about it compared to a much more efficient real (split) AC, but I have no other options.
Even if the landlord was OK with allowing it, "green" laws intentionally make it incredibly tedious and expensive to get the permits to install an AC, so people swarm to the option they can get without paperwork.
Also who in their right minds in Europe decided to rate single hose AC at A+, or A efficiency levels; the same as a good split AC? Single hose portables should all start with an F to educate a potential customer as to how dumb this device design is.
https://www.galaxus.ch/en/s2/producttype/air-conditioners-28...
edit: loud like air-whooshing loud, not like vibrating compressor loud.
Non-summary version:
In the office, the sun bakes the roof to make our rooms a good bit hotter than outside, open windows or no. I was there for my interview on one of the hotter days that year and decided right then and there that either the company was going to buy an AC or I was. It ended up being the company, but I was fairly insistent about needing one so the money was kind of spent for me. If it had been my money, I'd have considered it a sunk cost and good lesson.
It took about one day of using the device for me to start to wonder about its working principles. I mean, I roughly knew: I own a fridge after all. One side gets hot and you cool it with air that is then blown outside; the other side is cold and you use it to cool air that is then blown into the room. But I hadn't really thought about it until after we owned one:
How can this thing have only one hose? What is the air that it blows out replaced by?
I asked that question out loud in the office and, yeah, given that it only blows hot air out, it must be creating negative pressure in the room and basically sucking that hot outside air back into the room. It's nonsensical. I even sketched out for a friend how it should work instead because they didn't get my issue. Turns out I reinvented the dual host system (which I never heard of until today).
To make matters worse, the ground floor apartment I moved into at the same time as starting to work there is amazing: it remains 22-24°C during the summer, also after 2 weeks of 35+°C outside (thick walls and shaded from the sun; no air conditioning involved at all). I didn't know that was possible.
If I had known that it would be fine to work from home for a few weeks per year and that my apartment would be super cool (literally and figuratively), I would never have insisted on some kind of air conditioning to try and counteract 20kW of sunlight[1] hitting the office windows and roof. I could have saved a ton of power/CO2 and quite a bit of money. To make matters worse, we didn't use to be under the roof, we used to have only morning sun through the windows. It was only slightly cooler than the new place, but this unit could actually manage to cool the room down.
But now we've chosen this course and I feel too guilty to say that we should just consider it a sunk cost, I'm not going to use it, it's so loud I can hardly concentrate, and I'll just work elsewhere during the hottest weeks. Can't do it. Recently, one of our smaller windows was replaced with some insulated plates with a hole cut out exactly for the AC hose in an attempt to make it work better. I think it does work better because it's less leaky than the flexible thing we had before to put in the window crack, but it's still a huge waste and we keep sinking money into this shitty "solution".
I don't even get it. Like, how hard is it to put a horizontal piece of foam in the hose and have the dual hose system in one hose? Make sure the hot side is on top and put fins at the end of the top half to make the hot air be blown upwards. May not be as efficient as having them be in separate hoses, but wouldn't that be a lot better? It's also not as if you'd be putting cold air next to hot air: it's about the already-hot outside air that would be running alongside the slightly hotter waste-heat air.
[1] https://hypertextbook.com/facts/1998/ManicaPiputbundit.shtml 1.4kW/m² multiplied by an estimate of window and roof surface area of the single room that the AC is in.
I keep it that I can find no difference between operating in with one or two hoses myself https://news.ycombinator.com/item?id=24025482 .
Essentially what I'm aiming for is this: https://www.cruisencomfortusa.com/hd-series
which is a perfect product, except that it costs $4000 and still uses 20% more power than some of the smallest window units. It's ridiculous that the major difference between this $4000 unit and a $150 window AC is that the $4k version has a rubber hose connecting the compressor to the condenser coils instead of the typical thin copper pipe. I am sure there are other differences - it uses better components that are more suited to a moving vehicle with shocks and vibrations, has a strong compressor to deal with the longer hose length, and is already adapted to run off of 12V. But a $3850 price difference is ridiculous.
As the fellow on Youtube has shown (it's been in his camper van for years without a problem) there's really no reason the components from a $150 window unit won't work.
Whenever I finally do a camper van build I'm going to find an HVAC tech who can help me with a couple steps (mostly removing and then re-adding refrigerant) and convert the copper pipes to PTFE lined stainless braided hoses attached to SAE fittings. It may not work, and I've heard finding an HVAC tech to work on weird projects is very difficult, but I want to give it a try.
That said, refrigerant removal and reinsertion is regulated now and it's somewhat of a pain to do properly even with the right equipment.
Some newer passengers cars and maybe some vans use electric motors to drive the compressor. And EV's tend do that as well. In the EV case no mods are probably needed. Electric vans though are just becoming a thing and have low range and high price tag.
Surely the 3000W unit will use 3000W when running full tilt and will cool significantly more and faster than a 450W window unit, and would achieve the same cooling as the 450W unit by only running about 15% of the time? (or at 15% power if it's an inverter AC).
Up front cost is higher, but the efficiency gains are huge, and they can cool/heat much faster.
Is it because HVAC is so common it usually makes sense to plug the AC in the HVAC, and the rest of the market is basically leftovers which get to have window units or crappy portable air conditioners?
In the northeast where buildings are generally the oldest in the country, window units are common - especially in rental units, because the tenant typically provides the AC themselves. One less thing for the landlord to maintain.
The northwest, for the most part, doesn’t use AC much with their climate. Many homes don’t have AC at all.
Mini-splits are becoming more and more common in big cities here now, but only if you’re lucky enough to own a place and you don’t have landmarked facade problems. I’d love to use one instead of my window units, but I rent a street-facing apartment in a landmarked building. Even if I could get my landlord to approve me paying for a mini-split to be installed, I couldn’t put anything outside. The commercial tenants in my building have mini-splits, but they have access to a side of the building which doesn’t front onto the public street, so no landmark concerns.
(The fact that many landmarked facades have a random collection of window ACs hanging off the front seems much uglier to me than a bunch of professionally-installed identical mini-splits compressors would be, but, c'est la vie...)
It's the the large horizontal vents protruding from the wall you see in pretty much every low-rise (2-3 floors) residential buildings ("apaato"), or if you go to the back of the building you can see each flat's external unit, generally wall-mounted next to or below a window.
They're almost all reversible heat pumps, though their heating capacity tends to be lower than their cooling capacity.
Note that mini splits can also use a more discrete slim duct (as the link notes), but in my experience the wall mount is by far the most common, as that's way simpler and more convenient for multi-unit buildings.
The only place in this wide world I’ve seen anything other than split units is North America, so “Euro style” seems an odd description.
I was using "Euro" only to help people picture the things, it's a common way I've heard them described.
The insulated hose is something I'm exploring myself. There's insulated ducting like this: https://www.homedepot.com/p/Speedi-Products-6-in-x-12-ft-Ins... but it looks terrible. I'm kind of worried about having fiberglass being in my living space like that, the PPE is significant https://homeguides.sfgate.com/safe-ways-handle-fiberglass-in... and I'm pretty sure my cats would shred it up. I'm leaning toward adding reflectix sleeves with gaps so that the hose is flexible.
Window air conditioners work great, but if you can't have that, consider an evaporative cooler if you can get one at a decent price. Do make sure you get one with a decent air flow as well as a decent sized tank (e.g. one where you can run it all night without the water running out in the middle).
Probably won't work well in humid Midwest or South/East.
For me, they're great in practice. And I don't live in a dry climate.
I'll do anything to avoid living in a humid place, though. I can take very hot temperatures, but not hot and humid. At least when it's hot and dry I can still enjoy the outdoors.
Pros:
- You can (and are supposed to) keep the windows open for air flow. No worrying about closing everything off.
- They're rated for way more square footage than window or portable A/C units (although they are pretty directional). For example, mine is spec'd for 1600 sqft.
- Cost.
Cons:
- Requires cleaning. Not as much work as maintaining a fish tank, but it reminds me of that :)
It's funny how when you search the Internet, everyone says "It's useless in Seattle because it rains so much and is never dry."
And yet...
I'm not sure I agree with all your pros, though. I think good brand new ones are quite pricey, and you can easily find used window A/Cs for much cheaper. In my experience, window A/C units work better at cooling, and handle more square footage, but perhaps you simply got a bigger/more powerful evaporative cooler than I have. No way would mine handle 1600 sqft. I assume yours is not portable...?
I grew up on window A/Cs[1] and I think they're the best, to be frank. They cool a room down much better than a central A/C. If you have a decent size house, a central A/C is probably more economical from an utility bill standpoint if you want to cool the whole house. But if I want it as cool as I'd like it, and only want to do 1-2 rooms, nothing beats a window A/C.
But if you want a portable unit, I think an evaporative cooler is much better than a portable A/C. The latter are crap.
[1] They were "window" A/Cs, but were installed in the walls. Unfortunately, few houses are designed with this in mind, and US society has a weird aversion to window A/C's (many HOAs ban them)
It is portable, if a bit large.
The thing about price is: what are you paying to cover a certain square footage? To cover 1600 sqft with a window A/C, you need a 25,000+ BTU unit for $900+. The A/C units in the price range of that evaporative cooler only cover 450–550 sqft.
(Speaking to my situation, I live in a loft that's one big room, and only skylights instead of windows. Thank goodness for the swamp cooler, because even if I made a custom adapter to run a duct up to the skylights, no portable A/C would be able to handle the footage!)
In societies that rely heavily on window A/Cs, people usually have one per room, and the goal is to cool only that room, so a high BTU unit is not needed. They also couple it with a ceiling fan to get an even temperature.
Used window A/Cs are cheap. I'm trying to sell mine for $75 and no one is buying.
It seems like the design of your living space won't allow for it, though.
It got so boring when we rebuilt with proper falso floors ceilings and real racks.
However, the more I use the thing the more I realize that there's nothing wrong with it. Since the rest of the house isn't air conditioned there are open windows and fans throughout. Air is more likely to be drawn in from the rest of the house than through the cracks to the outdoors. Might be an issue in a sealed studio apt, but in our leaky shoebox of a ranch style home, it's hardly the biggest inefficiency.
Connecting to the Nest was probably easier than turning an ESP32 into a proper thermostat.
The hardest part of the whole project was figuring out how to read a clean signal from a photodiode.
One thing I've long wanted to try with mine is use 'heating mode' as a quieter version of cooling mode. They work the same - the unit just runs backwards, with the cold air coming out of the tube instead of the vents - so in theory you can cool your bedroom without having the noisy aircon in the same room. But the thermostat doesn't work properly in this case, because it thinks it's trying to raise the temperature of whatever room you put it in, not cool the other end of the tube, so for this to work properly you need to hack the control board.
In the US, I think the EPA would not let you...
...not that it stops people all that much, as a YouTube search for "DIY AC" will show.
In Canada, you need to be a licensed something-or-other to purchase or own compressed CO2 canisters. This put SodaStream in an awkward position when entering the Canadian market, since their whole business model is built on selling people CO2. But they figured out a workaround: in Canada, you don't buy their CO2 canisters; instead, you "join a club" that allows you to borrow CO2 canisters (and/or refills the ones you have), and then charges servicing fees for "their" canister equipment. (Sort of like how a catering company would rent a helium tank.)
I wonder if something similar could be done for refrigerant-supply licensing in the US.
I even get it filled up at the corner store lol.
Paintball guns run on CO2. You don’t need a special permit to own a paintball gun. You can pick up a paintball tank on eBay and run down to Canadian Tire or any paintball field and they’ll happily fill it up for you. Or at least they used to — it’s been a while for me.
Interestingly, in their tests, they didn't find dual-hose models to work much better than single-hose, unless it's extremely hot.
I chanced it and figured I could return it if I got a lemon. On specs alone it’s clearly the most compelling portable on the market right now, and it has turned out to be a really great machine. The past few weeks have been brutally hot in NYC and it has kept our entire apartment very comfortable. With the variable compressor it can run super quietly, and it uses about as much electricity as the two window units it replaced. Freeing up two windows also means we can leave it off more often, which I prefer anyway.
> The usual "smart" stuff that Nest provides
Reminder: https://michaelblume.tumblr.com/post/169525456166/tech-enthu...
> Tech Enthusiasts: Everything in my house is wired to the Internet of Things! I control it all from my smartphone! My smart-house is bluetooth enabled and I can give it voice commands via alexa! I love the future!
> Programmers / Engineers: The most recent piece of technology I own is a printer from 2004 and I keep a loaded gun ready to shoot it if it ever makes an unexpected noise.
> Security technicians: takes a deep swig of whiskey I wish I had been born in the neolithic.
I did find a big improvement in getting duct insulation and wrapping the exhaust hose in that. For the window portion, I cut out an insulating foam board to mount the hoses, and taped the outside edge with reflecting tape. It's keeping my large bedroom around 76, unless it gets above 95 and will start creeping to low 80s.
https://www.youtube.com/watch?v=0NELPBxrgsE
Wonder why there's no "n" designs for obstructive light. Regardless, there's no reason for portable AC, even duo hose ones due to length limitations on hose before inefficiencies. More effort into easy to install window / split units please.
(In my area, the herds would move between valley floor, mid-mountain, and alps. Most people would move between valley floor and mid-mountain. Peasant banking started here when everyone sent their cows up to the same alp, and the resulting cheese had to be divvied up between the owners and the alp crew.)
I paid extra for a dual hose unit and find myself almost never using the second hose at all. The effect is negligible and not worth the small effort of picking up the second duct from the closet.
And on my unit (trotec) you _can_ close the intake vents with a simple switch if you install the 2nd hose, so its not like all manufacturers are idiots.
How did you determine that the effect is negligible? A single-hose A/C should actually blow colder air locally, because it's using cool interior air to cool its condenser. The problem is, it's also throwing cool interior air out the window, which is thermodynamically insane. Every unit of air it expels must be replaced by hot air somewhere else in the building.
> e.g. not all the compressor's heat being vented outside
This is an engineering problem; the compressor should be well-insulated from the room (thermally and acoustically), and cooled using outdoor air.
> How did you determine that the effect is negligible?
The power bill measures overall how much time the compressor spent running for the same preset, and there's little difference between two hose and one hose mode. I'd presume this is the most effective efficiency measurement I have.
> A single-hose A/C should actually blow colder air locally, because it's using cool interior air to cool its condenser.
Usually it feels as if the air _around_ the ducts/behind the compressor is warmest, rather than around the room's ventilation grills which is where I suspect you would notice warmness if there was a significant negative pressure issue (yes, this is modern France building so I'm forced to keep an aperture to the outside for air renewal, even though otherwise the isolation is topnotch).
> the compressor should be well-insulated from the room (thermally and acoustically),
This obviously makes sense, but it is much easier said that done. People still want to carry the thing between rooms (and/or carry it themselves to their homes) which is why it is a mobile air conditioner in the first place.
Still curious about the diy potential here though...
Edit: It occurs to me you might be suggesting that it would be better to rip out the guts of a freezer than to use an air-conditioner... which does make a certain amount of sense.
I think some manufacturer names were mentioned? There are units now with with variable compressors, so you run them constantly at low current instead of full blast. If you want to build your own fridge, just to build one, I'd maybe look at those.
The efficiency of a heat pump is relative to the delta-T you're trying to push. If you are trying to hit 40° sitting in a 72° room? You could probably repurpose a portable unit for that, sure. If you're trying to bring ambient down to 40° for a cabin? I think you're right to be concerned if it's up for it.
There's also the defrost functionality which you won't have.
If you go to a convention, like Adam is fond of doing, you're gonna be suited up for hours, without support crew. So it's gonna be tricky, and he makes money doing videos about tricky things...
That said, he did start with a surplus EVA (or was it fighter pilot?) base layer with the cooling tubes built in.
In theory, you could build an insulated box with a mini-split or window/wall unit, but they're probably all optimized for cooling a large space, not freezing a small space.
Tech Ingredients made a DIY fridge (and a freezer in later videos) using peltier coolers: https://www.youtube.com/watch?v=YWUhwmmZa7A
People used to turn portable A/Cs into PC coolers, which was pretty... cool.
To attach equipment, you can connect a 24VAC-friendly load between (e.g.) Y<->C or W<->C.
Problem with attaching a load is that if you want to build a standalone unit with the nest, you’ll need some type of inverter when powered off DC, or perhaps a simple sine wave generator? I’m more of a digital, DC power guy.
There might be a way to trick the Nest into running on something closer to DC, but I could only guess.
Even a poor mini split will outperform these in terms of efficiency and silence - and they can be wired directly to a nest or simple thermostat.
The difference between the loud portable unit and the blessed silence and efficiency of the mini-split is chalk and cheese. There really is no comparison.
The mini-split cools the shed down to 72, where I have to increase the temperature to stay comfortable, in about 4 minutes. It's even silent outside, and these units will provide 12k BTU of heating or cooling, so it'll be useful in winter too.
I think the boxes were like $40, but they looked like electrical junction boxes. Clearly meant to be buried in a wall cavity.