Dear Jim: I like to use natural ventilation, but sometimes I need to air-condition. Since it is just my husband and I here now, we need to cool only a room or two. Would a portable air conditioner make sense for us? -- Joan C.
Dear Joan: Natural ventilation is obviously the most energy-efficient form of cooling, but it is not always enough. In many climates, such as hot dry areas or very humid areas, it is just too uncomfortable without some type of cooling. In dry climates, a swamp cooler, which relies on evaporative cooling, is the most economical cooling source. In most other climates, a standard refrigeration cycle type of air conditioner is best.
If both you and your husband are typically in the same room together, then using a portable or window air conditioner does make sense. This is true even if you have central air-conditioning. Even though the SEER efficiency of a central air conditioner is generally much higher than the efficiency of a window or portable model, you can still save money.
Set the wall thermostat for the central air conditioner five degrees higher than you normally would for comfort. This will dramatically reduce the amount of electricity consumed. Run the portable or window air conditioner to cool just a room or two to the temperature you like.
Overall, less electricity will be used than 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 conditioners are relatively heavy, so most people would not typically 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 to a portable air conditioner, also provide heat during cold weather. This is a very efficient heating source which can produce up to 12,000 Btuh from a 120-volt electrical outlet. Most standard electric heaters can produce only about 5,100 Btuh. I use a Soleus heat pump year-round in my study.
A portable air conditioner or heat pump is connected to a window adapter with one or two ducts. This is where the heat which is 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. All of the air that is drawn through the condenser comes in one duct, flows through the hot condenser coils, and is exhausted out the other duct. Some models also exhaust the condensate from the cooling coils; otherwise you have to empty a small water tank when it is full.
The following companies offer portable air conditioner/heat pumps: Fedders, (609) 662-5300, www.fedders.com; Soleus Air, (513) 985-1211, www.soleusair.com; Sunpentown, (800) 330-0388, www.sunpentown.com; Toyotomi, (203) 775-1909, www.toyotomiusa.com; and Windchaser, (800) 405-2943, www.windchaserproducts.com.