Central Air Conditioner Brattleboro VT
Greenfield , MA
East Dorset , VT
Greenfield , MA
Colchester , VT
Central Air Conditioner or Room Air Conditioner
Room air conditioners have their advantages: They are relatively inexpensive and easy to install, and they can effectively dehumidify a room. They are noisier than central air, however, and generally not as energy efficient.
Central air costs more to install A three-ton central system (one ton equals 12,000 BTUs per hour) is suitable for a typical 2,000- to 3,000-square-foot house and is likely to cost about $4,000 installed. In contrast, a two-ton room unit, the largest commonly available, costs about $900. In many cases, you can install the room AC yourself. Providing electrical service will represent a significant portion of the installation cost for larger room AC units, since most one-ton units and larger ones use 240 volts. However, some higher-efficiency units of up to 16,000 BTUs run on 120 volts. Room AC units come in sizes ranging from about 5,000 to 24,000 BTUs. Depending on the size and layout of your house, it may be possible to provide cooling throughout the entire space with two or three room AC units. Central air is generally more energy efficient Most central systems have a seasonal energy efficiency ratio (SEER) - the measure of efficiency for central air - in the 10 to 13 range. The efficiency measure for room AC units is the energy efficiency ratio; most room units are in the eight to 10 range, comparable to SEER ratings of nine to 11. However, the efficiency of the central system can be reduced by the duct system through heat losses, air leakage or restricted air flow. The room AC, of course, has no losses from a duct system. Surprisingly, many central AC systems actually operate at lower efficiency than the room AC because of duct losses. There are several steps you can take to ensure that your central air system ducts will perform efficiently.
First, require the contractor to fabricate the duct connections and seams with mastic and embedded fiberglass mesh. Foil duct tape is more likely to experience adhesive failure, especially in hot attic applications. Cloth duct tape should never be used for duct fabrication, since the tape adhesive remains effective for several months or perhaps a few years at most. The mastic with embedded fiberglass mesh should produce airtight duct seals that last the life of the building. Even better, have the duct system installed within the conditioned space - in dropped ceiling areas, soffits or other arrangements. By locating the ducts within the conditioned space, air leakage is largely eliminated. Central air systems are generally quiet That's because the compressor unit is outdoors and the air handler blower is separated generally from the occupied space by lengthy duct runs. Note, however, that some air handlers are noisy, and a metal duct will carry the blower sound farther than flexible or fibrous board duct. In contrast, nearly all room AC units are noisy, and the noise is often the greatest drawback of this type of system. The higher noise levels occur because the compressor unit is located within the AC unit, often just a few feet from the room occupants. Furthermore, there is no duct system to diminish noise generated by the blower. While surveying room AC units in stores, I found many units with names like Quiet Breeze or Whisper Cool, implying quieter operation. However, they have no noise ratings, which would be a big help to the consumer. Room AC is a mixed bag for dehumidifying Room AC units can effectively dehumidify a room. That's because their coils are often undersized relative to central units, and therefore operate at colder temperatures: the colder the coil, the greater portion of cooling devoted to moisture removal. There is, however, one feature of room AC units that often creates poor dehumidification performance under normal operating conditions: continuous fan operation.
In most room AC units, the blower is set to operate continuously, while the compressor cycles on and off in response to the on-board thermostat. The thermostat temperature sensor is located typically just behind the return grill, between the filter and cooling coil. When the room air drops to the thermostat setting, the compressor shuts off while the blower keeps running. Why is this a problem? Within a minute of the compressor shutting off, the coil warms to a temperature above the dew point temperature, and moisture begins to evaporate off the coil. Depending upon how frequently the compressor cycles on and off, a substantial fraction of the moisture collected by the cold coil during compressor on cycles evaporates, sending moisture back into the room. Central AC, on the other hand, has two fan settings - auto or on. In nearly all cases, it should operate in the auto position, for four reasons. First, the air handler blower consumes several hundred watts of electricity, which you pay for when the fan runs needlessly. Second, the operation of the blower adds heat to the house, which must be removed by the air conditioning system. Third, air flowing through the duct system picks up heat through the walls of the ducts and by means of duct leakage. Fourth, the system will not dehumidify effectively in the fan-on setting.
Most central units will dehumidify reasonably well. The question remains: Can a room AC unit achieve good humidity control? The answer is yes, in three instances. First, even if the blower operates continuously, it can dehumidify well if the unit is turned on intermittently, because during the first hour or more of operation, while pulling down the room temperature, it will effectively dehumidify the room. Second, if you install an external thermostat that turns the unit on and off (including the fan), it will most likely dehumidify well. Third, there are some units that allow the blower to cycle on and off with the compressor, which will most likely dehumidify well. The fundamental question when it comes to a cooling strategy is this: How much of the year do you need to cool your house? If you live in the southeastern United States, where summers are hot, humid and long, you may need to air condition six months or more each year. If you live in Wisconsin, on the other hand, there may be only a few weeks each summer when you feel the need for cooling. In general, the shorter your cooling season, the more likely you are to trade the inconveniences of room AC units - noise, less than ideal temperature control, and having only a portion of the house cooled - for the lower cost.