Variable Speed Means More Savings with Room Air Conditioners
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Summary
When it’s hot out, you probably don’t think much about how your room air conditioner (room AC) works or if it is working efficiently; you just want to stay cool.
When it’s hot out, you probably don’t think much about how your room air conditioner (room AC) works or if it is working efficiently; you just want to stay cool. Choosing an ENERGY STAR certified model, which uses 20-35% less energy than a standard model, means you can be confident that you will be comfortable, while saving energy and money. But how do ENERGY STAR models save energy, and what advancements have been made in air conditioner technology?
How has air conditioner technology changed?
Room ACs cool by pulling in warm, humid air from the room and passing it over a cooling coil to transfers its heat to the extremely cold refrigerant contained inside. This heat, captured in the now hot refrigerant, is transferred to outdoor air through the condensing coil in the back of the unit. As the humid indoor air loses heat and drops in temperature, the moisture condenses out, leading to the water that drips from AC units onto the sidewalk below. The result is cool, dry air blown back into the room.
One of the big advancements in AC technology has been the increased use of variable speed compressors, present in most ENERGY STAR certified models. In a conventional room AC, the compressor works like an on/off switch; it is either “on” at maximum capacity when the room thermostat calls for cooling, or “off” when the desired temperature has been achieved, alternating between on and off to maintain temperature. In room ACs with variable speed compressors, the speed of the compressor motor and the fan can fluctuate in response to the cooling needs of the room, reducing their speed when weather conditions are moderate and ramping them up when it’s hot out. This allows a variable speed unit to maintain room temperature with greater energy efficiency and operate more quietly than a single-speed unit when there is less of a cooling load. This means that on most days, keeping your variable speed room AC on can often be more efficient than turning it on and off periodically throughout the day. By maintaining the temperature of the room, the unit operates consistently at a lower, less-energy intensive speed, without the big jumps in cooling demand that come with turning it on after allowing the temperature of the room to increase significantly. This technology can greatly improve the user’s comfort throughout the day while simultaneously saving them money.
Another important change to room AC technology is the use of refrigerants with lower global warming potential (GWP). Many room AC models now use lower-GWP refrigerants such as R-32 (HFC-32), R-454B, and R-290. These room ACs have a reduced impact on the climate compared to earlier models using higher-GWP refrigerants, such as R-134a.
What features should you consider when choosing a room air conditioner?
- Design. Manufacturers offer different designs for room AC units. Newer designs, like the u-shaped or saddle-style, bracket the window or windowsill rather than fitting between the windowsill and window. These designs allow you to fully open and close the window where conventional unit design does not, and typically provide quieter operation because the compressor is more isolated in the outdoor side of the unit.
- Smart. Many room AC models now offer smart or connected features that provide sophisticated control through a web or mobile app. Certain apps include features such as allowing you to set a schedule or adjust temperatures remotely, geo-fencing that automatically adjusts to home or away settings when your phone leaves or enters a certain distance from your home, and “sleep curve” schedules that automatically increase the room temperature while you sleep, and cool off towards your wakeup time. Many integrate with voice-activated home assistants. By choosing a model with connected capabilities, you may also be able to take advantage of additional savings through “smart-grid” programs offered by local utilities.
- Additional settings. Depending on where you live, you might want an AC model that offers controls for additional dehumidification or fan operation without cooling. Models can also provide “eco mode” for consumers looking to further reduce their energy use.
What size air conditioner do you need?
Choosing the right sized model is crucial. Correct sizing is all about matching the cooling needs of a room size to the AC’s cooling capabilities (often described as its capacity). A unit that is too big will have no issues meeting the desired room temperature, but it will cost more to operate and less effectively maintain comfortable room conditions, especially when humidity is a concern. Often, an oversized unit will cool the air before it has a chance to remove the humidity, making the room feel damp and clammy.
An undersized unit may be unable to meet the cooling needs of a room, making it impossible to reach the desired temperature, especially if it’s a particularly hot day. If a variable speed unit is undersized, it will run continuously at full speed, as though it were a single-speed model, unable to take advantage of its energy saving technology.
To choose an appropriately sized room AC, measure the square footage of your room and use the chart here to determine the necessary cooling capacity (BTUs/hour) of a unit. Room Air Conditioners | ENERGY STAR
What does the future of these products look like?
Room AC models of the past tended to be noisy and unattractive, often used as a quick fix to meet additional cooling needs. Now, many innovative new models are quiet, leverage significantly more efficient technology, offer useful features, and complement a room with sleek designs.
Some manufacturers have begun offering room ACs with heating options. These models are capable of both cooling and heating by operating the AC cycle in reverse-- capturing heat from the outside air as it blows over the extremely cold (much colder than the outdoor temperature) refrigerant and transferring it to the indoor air. Models with a heating mode are currently convenient for providing supplemental heat in the spring and fall, but future models, capable of providing heat in the winter, are in development.
Where can you find an ENERGY STAR certified room air conditioner?
Ready to start looking for the best room AC model for your home? Use the ENERGY STAR Product Finder to find and compare certified models from a wide variety of manufacturers and identify any rebates available in your area.