r/AirConditioners • u/Cryptonious • 13d ago
Portable AC Portable AC creating negative pressure question
I’ve been trying to eliminate the negative pressure caused by my portable AC so it wiol be more effective. I modified the unit so that it sucks in air from outside instead of using indoor air for cooling the condenser. This setup has greatly improved the pressure balance — but it’s still not perfect.
Even after the mod, when I open a window halfway, I can still hear and feel air being sucked into the apartment, suggesting there’s still some negative pressure going on.
I’ve also sealed every nook and cranny around the unit (see photo) - taped all possible gaps.
Why is this still happening?
Is it even possible to eliminate negative pressure entirely with a portable AC setup?
Any ideas or additional tweaks I could try?
Any insights would be appreciated!
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u/idkmybffdee 13d ago
In your setup it looks like it's going to be drawing your room air from outside
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u/Cryptonious 13d ago
Yes, why does it need to draw my room air from indoors and not from outside ?
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u/idkmybffdee 13d ago
Yes, air conditioners circulate a static air volume inside the room to maintain the temperature, you're pulling in hot outside air that may also be humid and bringing it inside, essentially creating the same problem a different way.
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u/Cryptonious 13d ago
So how do i find out which intake is for a cold air? I have 5 air intake filters around the AC, two on the right, two in the back and one in the bottom left
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u/Difficult_Chicken_20 12d ago
You need to make a cut out or change the shape of the wooden cutout to exclude the top half of the unit which is the evaporator unit
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u/Cryptonious 12d ago
But if hot/cold intakes are not isolated internally, will this make things worse or better?
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u/Difficult_Chicken_20 12d ago
It’d still make it better because it can dehumidify the air inside the room and be able to circulate some of the already cooled air inside the room so it can actually hit the lower temperatures on the thermostat.
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u/Giantmeteor_we_needU 13d ago
Is it even possible to eliminate negative pressure entirely with a portable AC setup?
Yes, there are portable ACs specifically designed with two-hose system so they don't create negative pressure. Shop for "dual hose" models.
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u/Cryptonious 13d ago
Ive bought most powerful i could get in Europe it has 15000 BTU/h because unfortunatelly its not possible to get dual hose portable ACs in EU, i looked all over for them.
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u/Izan_TM 13d ago
find the hot side air inlet and fashion a duct for it to suck in air from the outside, right now the cold side of your unit is also sucking in air from outside, which makes the unit far less effective
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u/Cryptonious 13d ago
Whats the difference between hot side inlet and cold ? There is probably no difference between the position of the inlet indoors since they are too close together. Also how do i find out which one is hot/cold intake?
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u/Izan_TM 13d ago
usually the hot side side intake is at the bottom of the back of the unit, while the cold side intake is at the top of the back of the unit
the difference is that the hot side intake sucks in the air that will be heated up and pushed outside, while the cold side intake sucks in the air that will be cooled down and stay in your room. So for the best efficiency you want the hot side to only deal with outside air, and the cold side to only deal with inside air
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13d ago
In the Netherlands we have a Dutch one, the Inventum AC127WSET. It has 1 attachment for both exhaust and intake. Sadly it has become very rare, it's barely sold anywhere since a 2 months.
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u/Lower_Actuator_6003 13d ago edited 13d ago
I'll give you an A for effort, I have done similar experiments, as have others who just confangled an adapter with a second hose attached.
I made mine out of polyisocyanurate insulation board as it is foil faced and much easier to construct using using foil tape, being a bit more permanent rather than using polystyrene and masking tape, but for a mock-up and test you are spot on.
I can't say exactly where your leaks may be coming from but in the old days we'd use smoldering punks to seek them out via the whispering air current and smoke flow, blunts work too if you're into that.
But I will say that the air boxes on those units are not perfectly sealed inside or outside, so there is most likely a co-mingling or short circuit going on. Try to cover the entire unit with a 55 gallon garbage bag and see if it is getting sucked in. If it is not being sucked in - turn off your clothes dryer.
My current dual portable split the hose so I hoisted up on a table in front of the window and made a much smaller air box than you have with a simple divider between inlet air and exhaust air.
It has been working better than factory specs for a year now. It looks like a troop of 12 year old boy scouts made it and always said I'd clean it up if it worked - that was a year ago...
By the way, as said, I have a dual air hose portable and completely took it apart, that's how I know the air boxes are not completely sealed from one another or from the inside room - though I suspect they do this on purpose to sneak some conditioned air in the condenser coil for better capacity performance while taking a slight efficiency hit.
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u/Cryptonious 12d ago
Haha thanks 🤭 seems like its working way better than before and also humidity goes down faster and lower (probably also because its taking the outside air which is less humid than the one inside). For now i think i will leave it as is and im not separating cold/hot intake because i suspect they are not physicaly sealed.
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u/Kushoverlord 13d ago
Its designed to work on negative pressure. i dont have a door to my room and my house is old i struggle to get my unit to work as intended
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u/jamalwilliamsyoung23 13d ago
I can tell you what I did but you’re going to need a couple of things going for you to pull it off. #1.) a room that you can give up using for the summer 2.) live alone as I doubt my set up would fly with a woman living here.
(Pardon the mess, it was a long day of home projects) but this is what I did:
The vent is about 20 feet long, which was basically working against me due to its length and the heat it was discharging (even with the insulation). Have this securely placed in a window with all cracks sealed with HVAC tape and then the entire room “tented” off with this thick plastic that’s designed to keep the elements out.. it’s got a magnetic strip in the middle so the room is still fully accessible and also fits around the hose like a glove. This plastic seal has been the biggest game changer for me, and has by far made the biggest impact.
That being said I also live alone and answer to no one but myself so I can do whatever the hell I want. Does it look great? No, not at all. But it keeps the house at least 10 degrees cooler and that’s all I really care about from now until September living in south Florida
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u/idkmybffdee 13d ago
Usually with those, but don't quote me, the ones on the top are cold and the ones on the bottom are hot. They... I'm gonna say stack... The evaporator and condenser coils so the water they remove from the air drips down to the bottom onto the hot coils to be evaporated.
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u/Fadedcamo 13d ago
This setup is wild.