ERAS

Environmental Resource Assesments

| | |

Room Air Conditioners

Introduction. Although less efficient than central air conditioners, room air conditioners are often advantageous due to their ability to isolate cooling areas, thus reducing the energy needed for cooling. If most of our time indoors is spent in a single room, perhaps an office, than it makes sense to cool just that room and not the bathrooms, hallways, etc., which would require a central air conditioning system. However, there is a limit to the number of room cooling units one should use in a single building. If a number of units are being used in the same locality of the building, then a more efficient central air conditioning system may be a better choice. Before buying or replacing a system look at ways to reduce the cooling load as much as possible. This often allows much smaller units to be installed, or in some cases may even reduce the need for air conditioning altogether. Have a qualified air conditioning technician or energy auditor size the unit needed in accordance to thorough analysis. Be sure the analysis includes local climate information, calculations of heat gain through windows and walls, and any of the initial conservation efforts made.

Selection. If considering room air conditioners, a decision needs to be made between window-mounted units and those that are built into walls. Wall-mounted units are often the better choice, both for aesthetic and practical reasons. They will often cost more since an opening has to be cut into the wall, however, window air conditioners are harder to seal, they block views and light, and they prevent the use of the window for natural or forced ventilation.

Choosing an inefficient model will lock you into high electric bills for years to come, thus an efficient unit is just as important as is a correctly sized unit. The efficiency of room air conditioners is measured by the energy efficiency rating (EER), which is the ratio of the cooling output (in BTU) divided by the energy consumption (in watt-hours). Consider a room air conditioner with an EER greater than 9 to be efficient, and a model with an EER over 9.5 to be very efficient. High-efficiency units generally cost more, but in hot climates (where the air conditioner runs for more than 300 hours per year) more efficient units pay for themselves over a few years through reduced electricity bills.

Other features to look for include an automatic delay fan switch to turn the fan off a few minutes after the compressor turns off; a filter check light to remind checking the filter after a pre-determined number of operating hours; and a fan only switch, which enables using the unit for nighttime ventilation, substantially reducing air conditioning costs. Also, try listening to different models in operation before purchasing, since room air conditioners often vary in the amount of noise they generate.

Installation. To maximize efficiency the outside portion, or compressor, should be located in a cool, shaded place. It would be ideal to mount the unit in a northern facing wall under a canopy of trees or tall shrubs. However, the unit should not be choked with vegetation. The compressor needs unimpeded air flow around it to dump waste heat effectively. Mounting the unit on a south facing wall is second best, but be sure the unit will be shaded during the high noon summer sun. A room air conditioner should never be placed in an east or west facing wall unless it is completely shielded from the summer sun, because sunlight shining on it will heat it up and reduce its efficiency at dumping heat. Operation. In order to perform at peak efficiency, a number of maintenance procedures should be performed. The air filters should be cleaned monthly, and the condenser should be cleaned by a professional every other year. During service of a unit, its refrigerant may need recharging. A 10% undercharged system can operate at 20% lower efficiency, but overcharged systems can have drastically reduced lifetimes. Thus units need to be charged correctly by licensed professionals. It is very important that the refrigerant not be allowed to leak into the environment, where the potential exists for further damage to the ozone layer. It is also a good idea to unplug the unit, or flip the circuit breaker if a switch does not exist, during the winter months.