There is some confusion when people talk about a portable air conditioner with an exhaust hose as to just exactly what one is and how it works.
To help clear things up in some way, I have put this information document together to explain how the exhaust aspect of an AC unit operates and why it is needed.
To get the ball rolling along, let's first look at what I mean by an exhaust hose in relation to a portable AC unit. If you own one of these or have been checking them out at the stores with a view to making a purchase to help keep you cool indoors during the summer months, then you'll already be familiar with how the unit looks and what the vent hose looks like.
For those that don't, below is a picture of a typical vented portable unit deploying the hose connected to a window kit.
Venting a Portable Air Conditioner Out of a Window
You'll see the hose connected up to a custom fixing on the window itself and if this is your first time seeing one, you're probably thinking about how ugly and overly conspicuous it looks.
You'd be quite right in thinking that, because to all intents and purposes, it is a truly out-of-pace, unsightly and unwelcome addition to any habitable room in your home!
You're probably also thinking that it would be better to do away with the venting contraption altogether. It is quite normal to want to have the portability and convenience of one of these devices to cool a room in your home without the encumbrance of the flexible hose dangling off a window!
The reality is that while an un-tethered unit would be much more pleasing to the eye, it would not be much use as a cooling device since what comes out of that vent hose is hot air. A lot of hot air!
Venting the Hot Air
That hot air needs to go someplace other than inside the room the unit is trying to cool down. It may now seem patently obvious that if the unit is pumping out cold air from the front but hot air from the back, the net result would be a room no cooler than it started out being.
The actual way this works is there would actually be a net heat increase because the typical free standing AC unit produces more heat than cool. That is because of the way it creates the cold air inside its internal mechanisms.
In a similar way that a domestic refrigerator cools the air inside itself, an AC uses a compressor to compress a refrigerant gas inside a latticework of narrow pipes (similar to a kind of radiator) that chill the air being forced across them.
Because the compressor is mechanical and quite hefty, it produces a lot of heat during its operation. Similarly, there is a heat-exchange process operating inside the unit where a comparable volume of hot air is created as a by-product of producing the volume of chilled air that is fanned into the room to cool the air.
At the same time, the chilling process dries the air, effectively taking a lot of moisture out of it which is mixed with the hot air (evaporated into water vapor), which is exhausted out the back of the unit through the vent hose and out of the building through a suitable outlet in an external wall or convenient window.
If the hot, moist air is not vented out of the building, it would overcome any cooling effect and produce a net heating and humidifying of the air in the room, making it even more uncomfortable than it was to begin with.
AC Window Fixing Kit
To make it fairly easy to vent the hot, moist air out of the room, portable AC units come with a flexible hose and a window fixing kit. These attachments allow the hose to be connected to a window opening to let the hot air out and no allow it to come back in.
Of course not all window configurations are suitable for a simple flat fixing kit to fit to, but that is the subject of another info article as it would make this one rather longer than it ought to be to make it easy to read. I'll cover that subject separately.
Likewise, there are other options for venting a portable AC, such as modifying a window pane with an opening to accept the hose end, or creating a vent in an external wall so the hose can connect directly to the wall and not be such an eyesore hanging from a window!
Ventless Portable Air Conditioning Unit
Lastly, I would like to make an important point about those advertisements that try to get you to believe that you can buy a portable air conditioner without an exhaust vent hose at all. What they are talking about are not true air conditioners (see: https://ventlessportableairconditioner.intervalinc.com/air-conditioning/), but are in fact evaporative coolers (swamp coolers).
This type of cooling device operates in a completely different way to standard air conditioning as we have become so accustomed to.
These units do not employ a refrigeration process to produce chilled air. Instead they rely on the evaporation process in a similar way that your skin cools itself by perspiring and the breeze evaporating that perspiration creating a cooling effect. You can read about swamp coolers by clicking that link to the document I created on that very subject here on this website.
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