Unit Air Conditioners

Unit air conditioners are small, electrically powered K PTACs mounted in windows or exterior walls. The unit air conditioner is the most common piece of mechanical equipment in the United States. They are common in new and existing rooms and buildings. Unit air conditioners are easy to select, install, and service or replace. They provide the option of separate zones for individual apartments or motel rooms. If they are turned on only as needed, they may offer energy savings.

Unit air conditioners (Fig. 25-4) are not as efficient as a larger central unit, however, especially if a fuel other than electricity would power the larger unit. They don't offer energy-conserving options like exchange of waste heat. Unit air conditioners are noisy and, due to high air velocity, can cause drafts. Sometimes the noise is welcome, as it can mask street noise. In moderate climates, air can be circulated either through cold-side or hot-side coils, using the unit as a heat pump to cool in hot weather and heat in cool weather. This doesn't work economically in very cold weather, when there is not enough heat outdoors.

In many homes, a room air-conditioning unit is installed in the window or wall with the compressor located outside. The efficiency of air-conditioning equipment is listed on an EnergyGuide label. Room air conditioners measure energy efficiency with the energy efficiency ratio (EER), which divides the cooling output in

The tight layout for the retail store left only one space for the cash/wrap desk to go, and that turned out to be right next to the old, ugly, and highly visible air-handling unit. Richard thought he could probably tuck the desk into the available space with enough room around it for staff and customers, and covering the unit to improve its appearance wouldn't be too difficult. The tricky parts would be providing access to the unit for repairs and maintenance, and hiding the large air intake grille.

Once Richard had worked out the space planning issues and come up with a finish materials palette, he addressed the air-handling unit. He enclosed the unit in veneer plywood stained to match the adjacent woodwork. The plywood panels were attached with screws that were covered by removable wood plugs, so that the panels could be taken down for major maintenance. They also provided a perfect spot for a sign.

The air intake grille, which was about 2 ft square and near the floor, faced directly out toward the customer side of the desk. Richard designed a counter just to the side of the unit that butted up against the front of the unit. The counter gave the store a spot for impulse and informational items adjacent to where the customers would stand, and the grille was much less visible hidden below the counter. Maintenance personnel could duck under the counter to remove the grill and replace the filter. The solution worked fine and looked great.

Figure 25-4 Unit air conditioner;

Btu by the power consumption. On average, the 1990 standard requires a minimum EER of about 8.6. New room air conditioners, as of October 2000, must have an average EER rating of around 10, and even stricter regulations are under consideration by the federal government.

Window air-conditioning units are also best kept out of direct sun, so east or west windows are to be avoided. The north wall of the house, or possibly the south wall, is a possibility.

Some home air conditioners save energy with a fan-only switch that allows you to use cooler, noncondi-tioned outside air at night. A filter check light reminder for maintenance and an automatic delay fan switch that turns the fan off a few minutes after the compressor shuts off also improve energy efficiency. Quiet operation, which is not usually rated, is a valuable feature, but you will probably have to turn the air conditioner on to check this out. Highly energy-efficient units may not dehumidify as well as less efficient units. Air conditioners must be kept clean and refrigerant must be recharged as needed to keep efficiency up.

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