Proposed standard for portable ACs falls short

Yesterday, the US Department of Energy (DOE) proposed what would be the first-ever efficiency standards for portable air conditioners (ACs). While the new standards would be a significant step forward for portable ACs, higher efficiency levels could more than double the savings.

Preliminary DOE estimates indicate that about one million portable ACs are sold each year. Consumer Reports has referred to portable ACs as “the cooling choice of last resort” and found in their tests that portable ACs “barely got a room below sweltering.”

Portable ACs are similar to window AC units, except instead of being mounted in a window, portable ACs sit on the floor and exhaust hot air through a window using a duct. The problem with portable ACs sold today is that much or all of the air flow used to reject heat to the outside is drawn from the room being cooled. This process creates a negative pressure, which results in hot air being drawn in from outside. Making matters worse, portable ACs also add heat to the room due to heat losses through the duct and the unit’s case. DOE tested many portable AC units at typical summer temperatures (95 F) and found that after accounting for these effects, some units actually have negative cooling capacities. That means they are actually heating the room!

While window ACs have been subject to efficiency standards for more than 25 years, portable ACs have never had to meet any efficiency requirements. As a result, their efficiency performance has lagged badly.

DOE estimates that typical portable ACs sold today use about 900 kilowatt-hours (kWh) per year, which is roughly twice what a typical new window AC uses. The proposed standards, which could be met using more-efficient compressors and improved heat exchangers, would reduce energy use by about 25%. But higher cost-effective standards would save even more, cutting energy use by 35-45%.

DOE estimates that with the new standards consumers would save $160 on average over the lifetime of a portable AC unit. Higher standards would boost average lifetime savings to $220-275.  On a national level, the proposed standards would save about 55 billion kWh over 30 years of sales, which is equivalent to the annual electricity use of 5 million US households, and save consumers $2-5 billion. However, DOE’s analysis shows that higher cost-effective levels could more than double national energy savings and increase consumer savings to $4.5-10.5 billion. Setting a standard equivalent to the most-efficient products available today would increase energy savings by 50% relative to the proposed standard.

With standards for portable ACs, consumers would also have much better information for making purchasing decisions. Today, the advertised cooling capacities and efficiencies of portable ACs are not based on a standardized test method, and they often significantly overestimate actual performance. This discrepancy between rated values and actual performance makes it difficult for consumers to compare units. 

DOE is scheduled to publish a final rule for portable ACs later this year, and the new standards would take effect five years later.