Air Conditioner Exhaust: Open or Closed?

Discussion in 'The Chatterbox' started by Christopher Powell, Jul 20, 2017.

  1. Christopher Powell

    Christopher Powell Well-Known Member

    I have a window AC unit that has an Exhaust switch. My question is what does this switch do and what position should it be in for maximum cooling?
  2. AGHisBBS

    AGHisBBS Well-Known Member

    The exhaust switch is to let some outside air in, if you wanted to exhaust stale indoor air. Leave it closed mostly.
  3. RyX

    RyX DoH! Staff Member

    Big part of the AC effect is dehumidifying. Good chances it's more humid outside that you like. The unit will be more efficient if you don't keep bringing in humid outside air.
    Ever hear you parents say,"Close the door! I don't want to pay to (Heat or Cool) the outside!" There ya go.
  4. Jorvaljr

    Jorvaljr Operation Daytona 8000

    Not to kidnap the thread but I wanted to buy a portable ac unit, but notice it has a vent hose. Do i need to vent it? What happens if you don't?
    jimjo1031 likes this.
  5. jimjo1031

    jimjo1031 never bloomed myself

    It's purpose is to remove the hot air from the room and should be used. If not, the hot air will just be recirculated back into the room.
    Jorvaljr and RaZorBurn123 like this.
  6. mikewood

    mikewood Well-Known Member

    If you do buy a portable room AC unit look for one that does not collect the humidity from the air in a tank that must be drained.

    Sent from my iPhone using Tapatalk Pro
    RyX, Bama Samurai and Jorvaljr like this.
  7. Bama Samurai

    Bama Samurai with Laser-like Focus Staff Member

    Are you possibly referring to the tube that drains water condensate from the coils? Typically you would have to position that to drain to the earth outside somehow.
    RyX likes this.
  8. Bama Samurai

    Bama Samurai with Laser-like Focus Staff Member

    Closed all day. Open to refresh air at night when temps drop. This is the most efficient setting.
    Zykris likes this.
  9. Zykris

    Zykris Well-Known Member

    I wish I remembered how A/C's work but I've given those up. Haven't used one in about three years.
  10. RyX

    RyX DoH! Staff Member

    That was my question. Just like your car that makes a puddle when the AC is running, or central AC in a house there will be condensation. The way a cold drink gets wet on the outside, the AC unit draws humidity out of the air. That water need to go somewhere. Typically with a window air conditioner the unit sits level or tipped slightly down on the outer end so the water drips outside on the ground.
  11. Christopher Powell

    Christopher Powell Well-Known Member

    So here is what I have experienced. When the exhaust is open the air coming from the AC is cooler than it is when the exhaust is closed. However, there is better blowing power when the exhaust is closed.
  12. mittynuke

    mittynuke New Member

    Most modern window ACs are designed to be installed almost completely level and not on a slant - they have a reservoir/pan that is shaped such that condensate water collects in the back/outside part, and the condenser fan blade (the outdoor fan) is shaped such that it sprays or “slings” this water into the hot condenser coils, helping to cool them down better than with air alone while also evaporating the condensate. This greatly increases the efficiency of the unit because the AC is essentially getting back the energy used to condense the water in the first place (which can be significant, sometimes half the compressor’s power) and also mostly prevents water dripping out the back — Depending on the specific AC model and both the indoor and outdoor temperature and humidity conditions, some water may still drip, if it’s so humid outside and/or so much humidity is removed from indoors that the pan fills up and overflows. Some people drill a hole in the bottom of the AC to prevent this because it makes a somewhat loud spraying/“swishing” noise due to the water spraying at the coils and metal housing, and because it also causes the coils, the bottom part especially, to corrode faster since the water can have a corrosive effect over time. However the efficiency gained is not insignificant (plus no stains on the house/pavement below) — it’s basically a stripped down version of what’s commonly seen in cooling towers on top of large commercial or industrial buildings, and is the basis of how swamp coolers (used in less humid environments) work. Installing an AC on a slant may be recommended for very old ACs that don’t have the water slinger feature, where pooling up water could leak inside, but for anything made since the mid-2000s or so, it’s best to install it level and let it work as designed.

    As for portable ACs, modern ones use a slightly modified/improved version of this, since the design of the unit doesn’t really permit the fan to spray the water, they contain a pump that pumps the water from the bucket over the coils to evaporate it through the air that goes out the exhaust tube. This feature not only improves efficiency as explained before, but evaporates most if not all of the collected water (since the bucket capacity is much greater vs the pan of a window unit), meaning you almost never have to empty the bucket. This is the type of unit you’re talking about.

    If you leave the exhaust tube of a portable AC inside, not only will you heat up the room (as the heat coming out the exhaust tube exceeds the cooling power provided by the unit, in the amount of the electrical power consumed — an 8k BTU unit will essentially function as a 750 watt space heater if you vent it indoors) and you will not provide any dehumidification either. One exception is if you have a smaller, isolated space like a server room or closet you want to keep cool, at the expense of heating and humidifying the surrounding area. On units with a pickup hose for the pump, you can plug this tube or otherwise prevent it from sucking up the condensate water in the bucket, and take off the exhaust air hose/let it blow indoors, and the unit will be functionally equivalent to a dehumidifier provided you empty the bucket or allow the condensate water to drain outdoors or into a floor/sink/shower drain.

    The biggest issue with portable ACs, specifically with the one-hose models, is that they use indoor air to blow through the condenser coils and outdoors through the exhaust hose. This creates negative pressure indoors, and allows hot, humid, outdoor air to find its way back indoors, greatly reducing the effectiveness of the AC. That’s why you need to use a more powerful portable unit vs a window unit for the same size room. Two-hose models are more expensive because they need separate condenser (hot side) and evaporator (cold side) fans, but will not fight themselves by blowing freshly conditioned indoor air outside. Sadly, even on some two-hose models, there are vents to allow indoor air to be sucked through the condenser, essentially meaning (my guess at least) the intake hose is undersized. Using a two-hose model and blocking these vents, and insulating the hot exhaust hose (the hose itself functions as a radiant heater - why you want as short of a hose as possible), will allow a portable AC to be almost as efficient as a window unit.

    Tl;dr: install modern window ACs level, not slanted and don’t drill a hole in the water pan.
    Portable ACs: use two-hose portable ACs if possible, and enable/allow the water to be evaporated/don’t drain the bucket it awa the bucket is filling up (due to the inconvenience caused by emptying the bucket)
    RyX likes this.

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