Cool Off (almost) Anywhere

Mar 21, 2001 (Updated Mar 28, 2001)

Popular Products in Air Conditioners
The Bottom Line Portable air conditioners are console units that can be moved from room to room for versatile comfort. However, they cost more than window units and use more energy.

Unlike window air conditioners or central systems, portable air conditioners require minimal installation and are easy for users to move from room to room. Typically they are console units 3 to 4 feet tall and 1 to 2 feet wide, and they roll around on small wheels or casters. They are made by such manufacturers as Delonghi, Fedders, Toyotomi, and Danby. Portable air conditioners offer a very versatile cooling option for those who can't use more conventional air conditioning methods, but they do have limitations that users need to be aware of.

Some people call these "windowless" air conditioners because technically you don't need a window: You can turn them on anywhere and they will produce a breeze of cool air. Used this way, a portable a/c might make you feel a little cooler if you sit right in front of it, but it will not lower the temperature of a room because while cool air blows out the front vents of the unit, hot air blows out the back or side. Air conditioners and other refrigeration appliances do not actually create coolness -- what they do is move heat. Any heat removed from air one place has to be released somewhere else. That's why most air conditioners have both an inside and outside component: They pick up heat inside and let it go outdoors.

Considering this, the way you make a portable a/c work with a degree of effectiveness is by connecting a vent hose (supplied with all models) to the back of the unit and placing the other end up to a slightly open window or door so the hot air can blow out the hose. The hose looks a little like a vent hose for a dryer. Almost all models also come supplied with little panels and other fittings that can make this setup easy and fast.

Once the vent hose is placed up to an opening to the outside (or even into another room as long as you don't mind heating that room up as you cool the other one down) a portable air conditioner will cool the air in the room and reject hot air out the vent hose, working with a degree of effectiveness. Of course, moisture is condensed from the air during the cooling process, and something has to be done with it. Some models have a bucket which needs to be emptied periodically (usually every several hours), while others use a small pump that circulates the condensation water over the unit's condenser where it evaporates and goes out the vent hose with the hot air. This helps both convenience and the efficiency of the unit.

However, there still is one difference between portable units and window or central ones: When a portable unit draws in room air and uses it to cool the unit's condenser coils, and then throws it out the vent hose, there is a level of inefficiency in the cooling process. Cooled room air is being blown outside as the unit operates. It's kind of like putting a fan in your window and using it to blow air outside while you are running a conventional a/c system. How big a problem this is depends entirely on where and how you want to use the unit, and also to some degree on where you live.


Because they exhaust room air as they cool, portable a/c models are not usually going to be anywhere near as efficient as window units of comparable cooling capacity. And depending upon how you use the portable unit, it may or may not work satisfactorily.

As the unit exhausts room air through the vent hose, something else is also happening: It's creating a negative pressure in the room, which is drawing air from adjacent areas in. This means several things:

-Portable air conditioners are very effective in removing stale air, smoke, cooking odors, and other undesirable indoor pollutants from a room. Moreover, use of a portable a/c in a room will essentially guarantee that odors from that room do not go to adjacent areas. This can be a big plus in homes or offices where people smoke. A portable a/c in a smoking area will keep that area at a negative pressure relative to the surrounding areas, keeping smoke and odors from migrating out of the room.

-Portable air conditioners can keep a small area of an un-air conditioned home (such as a bedroom) reasonably comfortable, especially at night when the outside temperature is not extremely high.

-Portable air conditioners are very good to provide supplemental cooling in areas of a home or office that are served by a central system but are chronically too hot. This is because the room's replacement air - which flows in from adjacent areas as room air is exhausted - will be relatively cool.

-The one place where portable air conditioners can be more efficient that conventional models is a room with high "internal heat gain" -- meaning that most of the heat in the room comes from activities taking place in the room itself or from equipment used there. Examples are kitchens of homes or restaurants, offices with copiers and other heat-generating equipment, and computer centers or labs. In these cases the exhausting of room air actually helps rather than hinders the cooling process.


-These units will not work well in very hot environments where no other form of air conditioning is in place. The exhausting of room air and resulting need for replacement air from uncooled areas (such as the outdoors or non-air conditioned areas of the home) will make it very hard for the portable a/c to make much headway as it struggles to reduce the temperature of the room. This just stands to reason: To a degree, it's working against itself as it blows room air out and sucks in ever more hot, uncooled air.

Used in this type of setting, a portable a/c would probably be able to keep a small bedroom more or less bearable throughout the day, and would do a truly good job of cooling it only at night when the outside temperature is not as high.

If you cannot have any other type of air conditioner than this and live in a very hot area, give strong consideration to those models that use a pump to evaporate condensation collected from the room air to aid in the cooling process. Because the water evaporating aids in the transfer of heat, they cool better than those that simply empty this water into a bucket to be discarded. Models of this type will advertise the fact that there are no buckets to empty.

A few units take the use of water one step further and include a water tank that you can fill with tap water, ensuring that there's always plenty of water available to speed cooling. While this is a good idea in principle, in practice I do not like it. I own a six year old portable a/c unit with this "add water" feature and the lime buildup essentially destroyed it. I used the cleaning solution recommended by the manufacturer at intervals they suggest (an expense and hassle in itself), and still had to disassemble it, clean out water lines, scrub off the condenser coils, etc., and it still had a lot of lime in it in places I couldn't get to.

Then last summer a big flake of lime broke off from somewhere and jammed up the water circulating pump, ruining it, and also causing the compressor to overheat and become noisy, indicating that it's on its last leg. This is a big hassle you don't need, and for what you pay for these portable a/c units, they should last a lot longer than six years.

(Lime buildup will not be a problem on units that do not allow you to add water, regardless of whether they pump water over the condenser to cool it or just empty the water into a bucket. The only water ever in them is collected out of the air, so it does not contain mineral deposits as surface water or groundwater does.)

One final point to keep in mind is that btu/hour ratings of portable units are hard to compare to ratings of conventional window units. I do not think portable air conditioners are subject to the same standards of the AHAM (Association of Home Appliance Manufacturers) as are window units, so it may be hard to know what size you need. Generally they are offered in 6,000 to 8,000 btu/hour sizes. These will cool an average bedroom.

Portable air conditioners do offer a cooling option for people who cannot use conventional window or central units. While they are not as energy efficient as window units, and they cost more to purchase, they work well to supplement existing air conditioning systems and can provide some needed relief from the heat to those who have no other cooling possibilities.

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