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GLOSSARY OF AC TERMS AND EXPLANATIONS OF EQUIPMENT FOR THE HOMEOWNER
CONDENSING UNIT: This is the outdoor unit on your home, and holds the compressor, outdoor coils and a condenser fan motor. People mistakenly refer to it as the compressor, but that would be like calling your car a motor. This is the unit that generates the cooling ability of your unit and is sized in “tons”, each ton being the equivalent of 12,000 BTUH in capacity. (British Thermal Units per Hour)
EVAPORATOR COIL: This is the indoor portion of the cooling side of your system. When the compressor is running, this coil will get cold, just above freezing, and the indoor blower will blow air across it to cool the air. In a gas heat application, the coil is separate from the furnace, and in an electric heat system, the coil, blower and heat elements are in one enclosure. This coil will be cased like a box, and if cube shaped is called a box coil, and if long and thinner it is called a slab coil. The coil general is installed in the airflow after the gas furnace.
FURNACE: Although some people call units with electric heat an “electric furnace” we generally call a natural gas or propane fired heater a furnace. These can be in an attic, horizontal or vertical, or in a closet space in a hall or mechanical room. An allowance must be made for combustion air to serve the burners, and to safely dispose of the burnt gases, similar to the exhaust on your car. An improper installation can result in poisonous gases in your home, or may create a fire hazard.
AIR HANDLER: Generally refers to any blower assembly that moves the indoor air, but for residential applications will be a unit that uses electric heat strips instead of gas to provide heat to the home. Although this is a less expensive system to buy and install than gas heat, it uses frightful amounts of power when heating. Usually 2-3 times more than your AC unit in summer. Luckily, in South Texas the winter is light enough to get away with it, but still it is the most expensive way to heat your home. Typically, the air handler will house the evaporator coil for cooling, the blower, and the heat strips all in one box. The gas furnace, on the other hand, always has a separate coil.
SEER RATING: This is a term for rating the operating efficiency of an AC system. It is a general rating at certain design conditions, with certain combinations of equipment. The label that comes with the outdoor condensing unit may say 16 seer, but it is a general rating that may make 16 with only certain combinations of air handler, coils or furnaces. Not all combinations are tested, so it’s really just a guideline. Currently in Texas the minimum Seer rating allowed is 14. Not long ago it was 10, then12, then 13. The power rating of it is relative. That is a 20 seer unit uses half the power of a 10 seer, and a 15 seer would use 3/4 the power of a 20 seer. Keep in mind, the Seer rating conditions are not tested near the 95-100 outdoor temperatures we experience so the actual operating efficiencies will be lower. Sort of like rated MPG in a new car. Also, like a car, as mileage accumulates on an AC unit, it loses efficiency. Another reason you may not wait for it to die before replacing.
AFUE: The rating system for gas furnaces. Generally a percentage of heat that makes it into the home versus heat up the vent pipe to the outdoors. Around here we generally use 80% afue furnaces, which lose 20% of the heat outside. They make condensing furnaces that make up to 96% efficiency, but the additional; equipment cost and installation cost just will not pay out reasonable in our “warm” winter climate.
VARIABLE SPEED: This title can be a little confusing, because it is used to describe two totally different items.
There is a variable speed blower, that moves the air, and it will slowly ram up and down to correct operating speed very quietly and may be different for heat, cool or 2 stage operation. These blowers operate quieter and with less power than a conventional PSC “on-off” blower motor. This affects the air circulation only.
There is also a variable speed compressor which is a newer technology that has a compressor that varies speed according to the actual refrigeration load requirements, so the unit never runs harder than it has to, and is much more efficient. This technology is called variable refrigerant flow or VFR. It does involve complex electronics, and electronic flow valves, but all these have proven to be very reliable. Most manufactures are now offering a version of this technology as their top line, and also require training of the personal who install and service these units.