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Carrier Infinity air conditionerIf you’re wondering what features to look for in a central A/C, you’re not alone, especially here in Florida. Central air conditioning remains the gold standard for home cooling in the Sunshine State. Eighty-six percent of existing homes utilize a split-system central unit compared to the national average of 60 percent. This preference looms large in energy consumption figures as well: While the nation at large expends an average of only 6 percent of residential energy to run air conditioners, Florida residents devote more than four times that amount — a whopping 27 percent. Clearly, comfort and energy efficiency will therefore be high on the list of features to look for in a central A/C here in the Sarasota and Bradenton area.

Why a Central System?

There are good reasons why central air conditioning continues to dominate the residential cooling market, both in new construction and upgrades to existing homes.

  • Greater efficiency: Running a single central A/C provides more cooling for less energy than the same amount of cooling provided by multiple room air conditioners.
  • More power: In a residential system of average size, the airflow generated by a central A/C disperses about 1,400 cubic feet per minute of cool air throughout the entire house.
  • Less noise: Because the noisy parts like the compressor and condenser fan are located outdoors behind the home, central cooling is quieter than window units that incorporate all components within a single indoor unit.
  • Improved indoor air quality: In addition to cooling, a central system continuously filters air as it circulates through the ductwork. The entire air volume of the home is filtered multiple times per day in normal operation.
  • Better humidity control: Humidity extraction is as important as cooling for a comfortable indoor environment, especially here in Florida. The evaporator coil of a central air conditioner may remove over 20 gallons of water from your indoor air everyday.

Start With Sizing

One of the features to look for in a central A/C will affect efficiency and performance for as long as the unit’s installed: the right size. No, this doesn’t mean a specification in feet and inches. In HVAC terminology, “size” refers to a central air conditioner’s capacity, or the amount of BTUs of heat it can remove from the interior of the house. Sizing means matching a unit’s capacity to the home’s cooling load, or the amount of heat that must be removed to maintain a comfortable indoor temperature of around 75 degrees on a typical hot day. Cooling loads vary according to square footage of the house and thermal characteristics like amount of sun exposure, number of windows, quality of insulation and other factors.

To determine the proper capacity specification of the central air conditioner you buy, your home’s exact cooling load must be calculated by a qualified HVAC contractor using industry standard software. Both over- and undersized air conditioners are energy wasters, boosting operating costs and under-performing as far as cooling and humidity reduction, too. Once the home’s cooling load has been accurately determined, your contractor has the information needed to specify an air conditioner with the BTU capacity range that’s an appropriate match for your home.

Efficiency Issues

Energy efficiency simply means how well a particular unit converts electricity input into a desired output, and in this case, cool comfort. For central units, the standard for expressing efficiency is the seasonal energy efficiency ratio (SEER). The SEER rating is one of the important features to look for in a central A/C. It can be found prominently displayed on the yellow Department of Energy EnergyGuide sticker attached to every new unit, as well as listed in the manufacturer’s specs.

The SEER rating expresses the ratio between the amount of electricity consumed in watts and the BTUs of heat energy extracted from the air over a given period. In laboratory tests, calculations are performed across a wide range of simulated outdoor temperatures from 75 degrees to over 100 degrees, then averaged to reach a final SEER figure.

The current federal minimum SEER for split-system central air conditioners sold in the southern region of the United States including Florida is 14. Generally speaking, the higher the SEER rating, the less electricity the unit will consume and the lower monthly cooling costs will be.

When considering features to look for in a central air conditioner, a few important caveats apply to SEER ratings.

  • Central air conditioners with SEER ratings above 20 are available. However, higher efficiency in this range also comes with a commensurately higher upfront purchase price.
  • Lower operating costs associated with a high SEER rating will begin paying back the steeper sticker price from day one of operation.
  • Whether the payback time span is acceptable depends upon individual circumstances, including how many hours per day you run the A/C, the overall efficiency of the house, the length of the average cooling season, and how long you plan to continue living in the home. Your HVAC contractor can advise you on these factors and help you make the best compromise.

Improved Technology

Central air conditioning technology has probably leaped forward since the last time you purchased a new unit. Not only have SEER ratings soared in recent years, but a number of other advancements have also been incorporated that enhance comfort, efficiency or both. To familiarize yourself with the latest features to look for in a central A/C, here are a few available perks and options you probably didn’t get on your old existing system.

Variable-Speed Air Handler

Until relatively recently, central A/C air handlers incorporated old-style permanent split capacitor (PSC) blower motors that operated solely in on/off, single-speed mode. When the unit turns on, the blower delivers 100 percent air output. When it turns off, air circulation ceases entirely. The downsides of this full blast-or-nothing approach include noticeable temperature swings in the house as the unit cycles on and off and high operating costs. A typical PSC blower consumes over 500 watts of electricity in cooling mode.

Programmable electronically commutated motor (ECM) technology incorporated in new variable-speed air handlers regulates blower output across a range of speeds. Beginning at 50 percent output for a few minutes, the program gradually increases blower speed to full output to achieve the thermostat setting, then slowly ratchets the speed down to a continuous, whisper-quiet output that maintains indoor temperature to very accurate tolerance and consistency.

In addition to better comfort control, the brushless DC motor in a variable-speed air handler consumes 80 percent less electricity than single-speed PSC motors. Other features to look for in a central A/C like indoor air quality also improve: Because air circulation is consistent instead of on/off, air filtration is more sustained. Lower output also means more effective humidity reduction at the evaporator coil, too.

Two-Stage Compressor

A standard central A/C compressor pressurizes the refrigerant flow at a single fixed output. Unfortunately, this output is engineered to accommodate maximum expected cooling load. Approximately 80 percent of the time, however, cooling load on the house is less than maximum and full compressor output, and the excess electrical consumption that goes along with it isn’t required. A two-stage compressor senses the changes in your home’s cooling load and, when appropriate, automatically defaults to a lower 65 percent output that cuts electricity consumption while still meeting the demands of the cooling load.

Thermal Expansion Valve

Also known as a TXV, this item is now standard on most new units. A TXV reacts to changes in the home’s cooling load and meters the flow of refrigerant through the evaporator and condenser coils and the compressor. In older systems, excess refrigerant in the liquid state could flood the compressor, potentially causing damage to this expensive component. Alternatively, if refrigerant levels are too low, the compressor can be starved of vital lubricant and incur severe damage. A TXV valve protects the compressor by continuously adjusting the refrigerant flow as the amount of heat inside the home varies.

For more information on the features to look for in a central A/C, check out Aqua Plumbing & Air’s air conditioning solutions or call (941) 306-3715.

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