Air Extractor Automatically Gives AC A Boost

Portable air conditioning units are a great way to cool off a space during the hot summer months, but they require some place to blow the heat they’ve removed from your room. [VincentMakes] got a portable AC unit for his home, but he found that the place he wanted to put it was too far from the only window he could use to dump the hot air. Having too long of a duct on the hot air exhaust increases the back pressure on the fan which could cause it to prematurely fail, so [Vincent] used an extractor fan to automatically give is AC unit’s exhaust a boost on its way to the window.

Because his AC can operate at low, medium, and high speeds, he chose an extractor fan that also supported multiple speeds and took care to match the airflow of the AC and extractor fan to avoid putting too much strain on either fan. He designed a system to automatically set the speed of the boosting fan to match that of the AC using a Hall effect current sensor to measure the AC unit’s power draw and an Arduino Nano for control. A custom PCB interfaces the Nano to the Hall Sensor and control relays, and we have to applaud [Vincent] for keeping the +5V DC and 230V AC far, far away from each other. In addition to this fine electronics work, [Vincent] also built an enclosure for the fan controller that allows the fan to be mounted on top at an angle, which helps avoid having hard bends in the exhaust duct.

If this has you thinking about smart air conditioners to keep cool this summer, check out this ESP8266-powered smart AC system, or this Raspberry Pi-based system that controls both AC and blinds!

37 thoughts on “Air Extractor Automatically Gives AC A Boost

    1. just gonna say as a HVAC technician Technology connections hit it right on the nose. and window shakers (through the window) are not bad if anything they are the most cost effective, efficient way to do zone cooling. given you properly sealed the gaps around the window and keep that room’s door closed and your heat load is less then your BTU rating on the unit . but if you are up for doing a Arduino control and associated wiring I am sure you can figure out how to install a mini-split system I see absolute morons do it all the time. Also no ill will here just sharing my perspective!

      1. Yep, I can confirm, and I really enjoy Technology Connections. He’s not always 100% technically correct about stuff but he’s trying to explain HVAC to normal folks so I can forgive him for overgeneralizing or the like.

      2. If you’re renting you probably can’t install a mini-split, and lots of shitty apartment complexes won’t let you use your own window unit; you have to rent their garbage at insane monthly rates. Violating your lease with a portable unit is by far the most sensible option.

      3. In the UK window units aren’t really a thing and with rentals I can’t change the window or install ‘proper’ AC so portable is the only real option.

        But as long as I close the other windows and do a proper seal on the open window, it works pretty well for the dozen or so days we actually need it

  1. The ones with an outside air intake hose are a lot better because they don’t pull air in from the room they’re cooling to blow through the condenser, heat it back up, then blow it outside.

      1. The single tube ones are great for being frivolously wasteful on a hot Florida summer afternoon/night. Sit out on the patio with an adult beverage in hand, air conditioning the outside. You pretty much have to sit in the path of the cool air output. Dont even have to attach the hose, the hot air just blows straight out the back away from you =)

        1. – Those don’t draw hot humid air into your house though – the inside is (more or less) closed loop air circulation – with heat exchange done via refrigerant through the lineset form inside to outside your house. These blow hot air past evap and then outside, from inside your house. That air volume inside your house being sucked out needs to be made up for / replaced, which is done by drawing more hot/humid air into your house through various routes/leaks – which again needs to be cooled.

      2. They’re the only form of portable/plugged air conditioner available in the UK which is really disappointing. My next project is converting a single hose unit to dual hose without altering the unit itself since it’s still in warranty, advice welcome!

        1. Without modding the unit, your best bet is probably to fashion a box that fits over the intake grill over the condenser and tape it on with hvac tape (the aluminized foil stuff, not duck tape, which sucks at duct work) and run dryer hose from that to the window. You can probably get away with cutting a hole in the window panel of the old unit and keep your warranty on the base unit, but if you’re not comfortable with that, I’d get some acrylic sheet and make a dual pane sheet out of that and some double sided foam tape. And if you’ve got a decent length hose run, try to insulate the hoses if possible, too. It’ll keep you cooler and be better for the unit’s longevity.

          Good luck!

        2. Based on this photo (first one): https://fccid.io/2ANDE-COOL100/Internal-Photos/Internal-Photos-3562854

          You can see that there are two compartments and two fans (2nd fan in 2nd photo). The upper compartment houses the evaporator, which the indoor air blows through to cool. The lower compartment houses the condenser (and also the compressor). Air is pulled across it and then blown outside.

          In this unit, you can plainly see the input vents for the condenser chamber on the right side. You’d want to attach a hose feeding outside air to these. You’d have to make an adapter that the hose can attach to that will then encompass all this vent area.

        3. I made a box from cardboard and tape that fits the intake to the compressor and then hose from the box to the outside. The AC performs better. A more stylish option is to unscrew the plastic shield over the intake on the AC and replace it with a 3D-printed hose adapter plate. There are a few such designs on Thingiverse.

      3. I’m pretty sure they just blow room air out the tube. It goes across the coils so you get some cooling, but it ends up sucking in air to replace that somewhere.

    1. you can also wrap a gold/silver thermal blanket around the hose, silber side around the hose, I just used some wire to fix it. It radiates nearly no heat(luke warm after hours vs. 65°C) after that.

    1. Its not always an option. For instance in my apartment we’re not legally allowed to have a unit in our living room window because it would block the fire escape, so our only option is to use a portable unit.

      1. you put it on the wall, then the unit outside on the wall. I did my partment years ago that way – and yes it tool a bit of work to get the unti loutside up 4 stores, but then it just bolted to the brick wall. Small hole in the bricks for the pipes going in to the head unit (and I filled the whole with insulating foam goo) and then you’re golden.

        So as long as you have an external wall you can do it.

        You can also put the outside uit NOT next to the internal one ie put the unit on the outside wall, run the pipes up into the ceiling eight, through you ceiling cavity to the head unit on an internal wall. You need a small pub to exit the water from the head unit..

        Of course, if you aren’t allowed to put an outside unit up at all you’re stuffed. Then it’s time to take over the body corporate…

    2. In many parts of Europe the single-hose versions is the only version of portable AC for sale to consumers. Window units are not available. Split units with a wall/ground mounted outside part is often not permitted when renting an apartment. Sad but true.

      1. It’s not just Europe. Cost cutting by manufacturers is screwing everyone, and because of the ignorance of how these things work, there’s not much push to go back to two hose units. My suggestion would be to contact your government representatives and demand that two hoses be required on new portable air conditioners. It’s not a great option, but it’s one that might be feasible.

    3. I know this is not ideal but I use this mobile AC only temporarily during heat waves. For context, I live in Switzerland where permanent ACs are not so much the norm like in the US. Additionally, the house comes with an energy-saving/ecological certification label which prevents me to make holes through the insulation or to use a permanent AC. I believe the approved cooling system to keep the certification would be the geo-cooling/heat exchanger one. Overall the insulation + double flow ventilation system works very well, especially in winter where the house stays warm at low cost but the downside are those heatwaves.

    1. Sounds like you’re talking about mini split systems. This is about portable units, which are similar to a window unit, but sit on the floor and use hoses (or sadly, in most cases these days, just one hose) to direct the air through the condenser.

  2. The solution in the UK is pretty simple. Yes, it does get hot sometimes. There’s cold beer in the fridge for that week of the year. Bring on global warming (not really), 2 weeks of beer would be great!

  3. Two other modifications for portable AC units that I’d like to see:
    1. Noise reductions for the compressor. Could we even take out the compressor and place it in another room where noise is not a problem?
    2. similar extension hoses but for the cold are output. Which can also be a workaround for the noise problem by placing the unit further away from the area you want cool air in.

    1. > Could we [relocate] the compressor?

      That’s called a mini-split system.

      While you could theoretically modify an existing A/C to separate the components, it would involve first safely removing (and hopefully recapturing) the refrigerant gas, then doing extensive re-plumbing, then properly adding back a new amount of refrigerant (that will likely be larger due to more piping). This would require various specialized tools (manifold gauges, vacuum pumps, etc.) and training. It’s not the kind of hack for just anybody.

  4. Those things are horrible, even the 2 hose system is horrible. I even insulated the hoses, but the compressor is a 1KW heater….in the space its cooling. I had a 14000 BTU unit in my “data center”. It used as much energy as my central air. I installed a 25 SEER mini split, and its amazing. I don’t even see it on my energy bill.

    Honestly, I’d rather see a dual hose outdoor unit where it would pull indoor air over an insulated condenser and back to the house. Then all the hot parts and energy consumers would be outside, not in. The losses would be from esccaping the hose and the outdoor condenser. Yes, theft could be an issue….but how many people are putting boards in their windows for these portable or even window units? It also wouldn’t work well for a second story window, it would still be nice if it was an option! I considered attempting to modify the data center unit to be like this. I never bothered because of how well the mini split worked!

  5. +1 for the minisplit systems, though they can have their own challenges. My house has a hip roof and on top of that the two bedrooms on the second floor have rooms behind them so each bedroom has one exterior wall that is full of windows, and one wall that starts tilting inward about 5′ off the ground, one wall that faces to the inside of the house and one wall that is common with the room behind it. The only place I can put a minisplit in my place is on that last wall, it is one of the two full height walls and the other one does not have room for the air handler. So, I need to go through one wall, across a room, through the outside wall and down at least some. There is also the issue of the condensate drain line that needs to slope downwards it’s entire run. Ideally I would like the unit mounted a comfortable working height off the ground. High enough to mow under, low enough to not need a ladder to work on it. There are specs for the length of the lineset with the initial included charge and limits on the maximum lineset length, as well as limits on how high above the compressor the air handler can be. It is amazing how many times people do not follow these. Ditto with the positioning of the air handler in the house, and the compressor as far as clearances go. I have tried multiple times to get different eBay sellers to send me a link to the install manual to make sure if I buy a unit I will be able to comply with all of it’s install specs and it seems all they wanna so is cash your check. I suspect if you have a problem after the install it is totally on you.

    As far as using a window rattler goes, in my last house, I was going to do my bedroom but my plan was to mount a big old 14KBTW window rattler in the attic eave over the room on the other side of the house. I used that as an office. The rattle in there would not bother me at night. The idea was to do what you wanna do, but duct the cold air into my bedroom so I would get the cooling but not as much of the noise.

    Or, you could do what they did in a place I used to work. It was a historic brick building so they installed window AC’s in the exec’s offices that vented out onto the shop floor. Nothing nicer that a 100degree day with 95% rh and having hot air blown on you so the execs could stay cool.

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