Dear Jim: We have central air-conditioning. It seems wasteful to cool the entire house when just we two are home. Is using a portable air conditioner in various rooms more efficient overall? — Sean K.
Dear Sean: Natural ventilation is the most efficient cooling. In many climates though, such as hot/dry or humid areas, it is just too uncomfortable without some type of cooling. A swamp cooler, which relies on evaporative cooling, is the most economical cooling source in hot, dry climates. In most other regions, a standard refrigeration-cycle air conditioner design is typically used.
Using a portable or window air conditioner is a good idea, especially when you and your wife are going to be in the same room for an extended time. This is effective even with central air conditioning. Even though the SEER efficiency of a central air conditioner is generally higher than the EER efficiency of a portable or window model, using them can save money overall.
Run the portable or window air conditioner to cool just a frequently used room or two to the temperature you desire. Raise the temperature setting on the wall thermostat for the central air conditioner 4 or 5 degrees higher than normal. Doing this significantly reduces the amount of electricity consumed as compared to trying to keep the entire house comfortably cool.
Portable air conditioners are particularly convenient to use because you can roll one from room to room. With this feature, one portable air conditioner can be used to keep different rooms cool depending upon which room you are using. Most portable air conditioner are relatively heavy, so they don't carry one up and down stairs easily. It is better to have one for each floor of a two-story house.
Portable heat pumps, which look identical and operate similarly to a portable air conditioner, also provide heating during cold weather. This efficient heating source can produce up to 12,000 Btuh from a 120-volt electrical outlet. Most electric space heaters produce only 5,100 Btuh. The thermostat is built into the handheld remote control so it senses the temperature precisely where you are sitting. I use one year-round in my study.
A flat adapter panel is used to connect the portable air conditioner or heat pump to a window with one or two 5-inch-diameter flexible and collapsible ducts. This is where the heat pulled from the room air is exhausted outdoors. The window adapter and ducts, which must be moved along with the portable air conditioner, fit most easily in single- or double-hung or slider windows.
Two-duct models are the most efficient because already-cooled room air is not drawn outdoors.