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Ever since I got my portable AC, I've been wondering how I can make this hunk of junk more efficient because till this day, I have never been able to drop the temperature lower than 25° C.

This week I was making a few modifications to my room and realized the amount of air being sucked into the room but no wind was blowing in the corridor. It hit me right there that this portable AC is venting air but I never considered where the air was coming from. This leads me to the conclusion that because it's pulling air from outside at 30°C and lowering it to 25°C and it repeats this process. The door is on the opposite side of the room to the AC and the AC vents out a nearby window.

My question: Is there a proper way that the room is to be setup to allow this AC to pull air through the room efficiently.

Any suggestion would be accepted at this point, because my room is basically a construction site to me. I'll add a diagram soon to better aid in seeing the air flow that is happening.

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    a shorter tube will increase efficiency. you can't really do much about the intake/outtake; you have to push that hot air outside, and new air must come from somewhere to replace it. This is why such units aren't that good, a mini split is much better.
    – dandavis
    Jan 12 at 4:53
  • There are portable units with 2 hoses. Which avoid this issue of under-pressuring the room. Jan 12 at 11:14
  • I agree with Dan, they work but are less efficient than a window air conditioner because the window unit cools the condensing coil with 100% outside air, single hose units have to draw in warm air to exhaust the hot air.
    – Ed Beal
    Jan 12 at 15:04
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I had this issue in an old office of mine which which was a room we subleased from an architect who apparently didn’t believe in air conditioning.

As you have observed, single pipe portable AC units create negative pressure in a room because they use the conditioned air from the room to cool the condensing coil which is then expelled from the room.

I identified the grill on the unit that was pulling in the conditioned air to cool the condensing coil and made a plenum out of cardboard which I taped to the unit, and ran a duct from this plenum to pull air from outside the room, which balanced the pressure.

If you do this, make sure that your intake is below your exhaust so that you’re not pulling the hot exhaust back into the unit.

After the first day of using my modified 2 pipe system, the temperature of my office dropped 15°F!

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  • Wow, Thanks Jack! I'll give this modification a try, I can definitely see already how this would help out. Once it works out I'll let you know with the green tick :). Jan 12 at 15:47
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    I tried it out and it really works great! I cut some cardboard and duct taped it around the intake filters and fitted a vent hose to it, the one I have is 4" but I'll go get a 6" eventually to match the 6" exhaust hose. But wow, already there's a difference in the room and I was able to turn off the AC and have the room remain cold for nearly an hour. Thanks so much for the suggestion! Jan 14 at 15:24
  • @ForeverLearningJP glad it worked out! Nice to have my theory proven by someone else! Jan 14 at 19:18

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