Why buy a portable AC, what to look for?

If you don’t want the hassle of a window air conditioner, the best portable air conditioners can be a great alternative. But be aware that they are not rated by ENERGY STAR, efficiency ratings are typically lower than window air conditioners, and they are not truly portable in the way you might expect.

Let’s start with the basics of how portable air conditioners work.

Types of portable air conditioners

There are two types of portable air conditioners:



Condenser-based portable air conditioners such as the one pictured at left operate like a window air conditioner, with a refrigeration cycle that cools indoor air and exhausts the heat to the outside, usually through a window vent that attaches to any window. Condenser-based portable air conditioners remove moisture from the air as well, as dry air feels cooler than moist air. These air conditioners are typically not as efficient as window air conditioners – the one at left has an Energy Efficiency Ratio (EER) of 8.0, while a decent window air conditioner can achieve an EER of 10.7 or higher (the minimum allowed EER for a window air conditioner is 9.7).

 



The most efficient portable air conditioners are evaporative portable air conditioners such as the one pictured right. They use evaporation to cool the air. They draw outside air over water, causing some of the water to evaporate. Since evaporation is a cooling process, the moist air coming out of the air conditioner is cooler (and a bit more humid) than the dry air coming in from outside.

Evaporative portable air conditioners are ideal for very dry hot weather such as in the US southwest, Australia, or the dry season in tropical countries. They are 2-3 times more efficient than condenser-based portable air conditioners, but only in dry weather. You really don’t want to use one of these if you’re trying to cool a room in very humid weather; it won’t cool much, and it will make the humidity worse.

Evaporative air conditioners tend to be much cheaper than condenser-based portable air conditioners because there is no refrigerant or condenser pump. Most are available for under $200, just make sure an evaporative unit makes sense for your local humidity level. There are no EER ratings for evaporative air conditioners.

I won’t cover evaporative air conditioners below this section. Here are a few units you might want to look more closely at:

Convenience of portable air conditioners


In terms of convenience, the best portable air conditioners are ones that are easy to set up, easy to to move around, and give you the option of not having to empty the water container. Condenser-based air conditioners pull humidity out of the indoor air, which condenses on the cooler’s condenser coils. Most units try to blow some or all of that condensed moisture out the window exhaust vent to the outside, but this evaporation takes additional energy so reduces the efficiency of the unit.

Look for a unit that has a tank to capture the water, and switches to exhaust mode when the tank is full. This way, when you remember to empty the tank yourself, you’re saving more energy, and when you don’t, you at least have the convenience of not worrying about it shutting off when the tank fills up.

You can definitely save by buying the most efficient portable air conditioner and using it to provide cool air wherever you are. In just a few minutes you can unhook the unit from one window and hook it up to another, so you can keep your bedroom cool at night, your home office cool during the day, your kitchen cool in the evening. Most of them come with wheels to make them easy to move around.



Another convenient feature of the best portable air conditioners is the ability to heat as well as cool. Those with condenser-based refrigeration cycles can run the cycle backwards, which extracts heat from the cool outside air and pumps it indoors. Heat pump units are more efficient than electric heaters, as long as temperatures are above about 50F or 10C. (More recent vintage dedicated heat pump systems can achieve better performance than electric heaters at temperatures as low as 25F-30F or about -3C, but I would not expect portable air conditioners that also operate as heat pumps to achieve efficient operation at those low temperatures.)

Notice that I said “in just a few minutes” above. I don’t want to oversell the convenience of portable air conditioners. Most such units come with a window kit that fits at the base of a sash window – essentially, a rectangle that can stretch to different widths in order to accommodate different window widths, with a hole in the center that you use to attach the exhaust hose. It’s certainly more convenient to remove the kit from one window, move the kit, hose, and portable air conditioner to another sash window, and place the kit in the other window, than it is to drag a regular window air conditioner from one window to another. But if you don’t have sash windows, you’re out of luck, you can’t use these on casement windows. And if you were thinking you could just drag the unit itself from room to room, it is a little more involved than that. (Mind you, you can’t use window air conditioners on sash windows either.)

Efficiency of portable air conditioners



The best portable air conditioners have an Energy Efficiency Ratio (EER) above 9.9. Although portable air conditioners do not seem to be covered by either US or Canadian energy efficiency standards, we can use regular room air conditioner ratings to guess at what the best portable AC should be able to achieve.

Unfortunately many portable air conditioners do not even have an EER rating (or none is easily found online). However I went through most of the best portable air conditioners that can be purchased from Amazon, and looked up the EER on each, and the energy efficient portable air conditioners featured in this article all fell in the high end of the EER range.

ENERGY STAR rated room air conditioners have an EER of about 10.7 or higher below 20,000 BTU, and 9.4 or better above 20,000 BTU. So look for EER ratings in that range to get the best portable air conditioner in terms of efficiency.

The best portable air conditioners have two hoses, one to draw air into the house and one to exhaust heated air out. The indoor air is drawn across the evaporator coils, while outdoor air is used to draw heat away from the condenser. However many units have only a single hose to vent exhaust heat. This means the units are effectively drawing already cooled, dehumidified indoor air out of the room and pumping it outside, thus reducing the efficiency of the unit.

Unfortunately, for lower BTU portable air conditioners in the 8,000 to 10,000 BTU range, it is hard to find anything over EER 8.9, and many units have EERs of 8.0 or lower. Some of the best portable AC units that fit the bill in the 10,000 BTU and under range are the Soleus KY-80, Whynter ARC-10WB, and Commercial Cool portable air conditioners:

The best portable air conditioners in the 10,000-12,000 BTU range are:

The best portable air conditioners in the 13,000-14,000 BTU range are:

All of the above seven air conditioners get good customer reviews and combine high efficiency with decent convenience. I especially recommend those that can heat as well as cool, as heat pump heating is usually more energy efficient than heating with gas, oil, or electricity when temperatures are cool but above freezing. Finally you might notice a lot of Whynter portable air conditioners in the list above – I recommend Whynter as a brand, because they have a good reputation for quality and we should reward them for having the best overall energy efficiency of their portable air conditioner product line, among all manufacturers.

6 replies
  1. Brian Garland
    Brian Garland says:

    I need a portable AC in my bedroom but it will be on the same circuit as a large screen TV and other A/V equipment. So I assume I need a unit with as high an EER ratings as possible in order to avoid breaker trips. Is that true?

    Reply
  2. nostrildamus
    nostrildamus says:

    It has a lot more to do with your homes electrical system. You could contact an electrician if you are unsure of system let them give you a home electrical evaluation.

    Reply
  3. Pfram
    Pfram says:

    This is good advice with the exception of the phrase “the exhaust hose”. Any decent portable AC (including most of the models you recommend), should have TWO hoses, one to let in outside air to cool the hot coil, and another to let the heated air back out. Whatever its ratings, a single hose model relies on leaks in your windows and doors to replenish the air is sends out, so it will inevitably add some heat to your house that can be effectively subtracted from its rated output. If your house is perfectly sealed, a single hose unit will not work at all.

    Reply
    • Robin
      Robin says:

      Thanks for pointing this out, you’re right that a dual hose system is more efficient because you aren’t exhausting already cooled, dehumidified air from the indoors out the window. I’ve added a paragraph on this topic near the bottom of the article.

      Reply
  4. Gregory Whitchurch
    Gregory Whitchurch says:

    Hi. As a passivhaus owner/advocate I’d like to recommend that you re-research the efficiency (COP) of heat pumps at various outside temps. Few consumers understand the concepts of heat pumps & COP; this could be a place where they learn something valuable that would benefit the environment.

    Reply
    • Robin
      Robin says:

      It appears that the COP (coefficient of performance) of built-in heat pumps has improved substantially over the past few years, with some units being able to heat a home more efficiently than electrical heating even when the outdoor temperature is well below freezing. However I don’t imagine these portable air conditioners can handle outdoor air temperatures that low, and one should bear in mind that the window attachment for venting the hose is likely a major source of heat leakage.

      Reply

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