central Air conditioners & Home energy improvements

Central ducted air conditioners are complex systems, difficult to size and to tune-up and improve.

Before choosing and installing a central AC system, consider carefully the various alternatives. Central AC is expensive to buy, install, maintain and run. They rarely make sense in energy efficient homes.

- Prefer two/multi-stage AC air conditioners with a SEER of more than 15.
- Prefer a Energy Star unit
- Consider carefully the Humidity Coefficient of the equipment.
- Choose a unit with a quiet condenser, that is, with a sound level of 75 decibels or less.
- Consider other alternatives to central AC.
Is central AC very expensive?
The equipment may cost $3.000 or $4.000. But the installation and the ductwork may double or triple the cost... This - and the running and maintenance costs - can make central AC costs hight. Central AC is not a good choice for low-energy buildings.

If you are building a new home, consider low-energy consumption strategies and the various alternatives to central AC..

Central AC unit, from LennoxSee: AC Alternatives

Advanced features

If you do need a central AC system, that is, if you have large air conditioning requirements and your home isn't energy efficient enough, consider advanced features: a multi-speed unit with a dual-compressor and zoning ability; and a unit with a high SEER (energy coefficient) and a proper humidity factor (SHF).

And do not forget the importance of proper sizing and installation.

Sizing and installation

Do not overvalue the brand issue; consider a good brand, or stay with the brand you trust, but do not forget the importance of installation and sizing.

Only a knowledge contractor will be able to correctly size your equipment and ensure a proper installation, able to prevent drafts and exorbitant consumption and common AC problems.

The concept behind central air conditioning is rather faulty, to say the least: to cool a whole house consistently with a single-stage unit and a single thermostat it's a hard task, close to the impossible; only a knowledgeable contractor can do a decent job and get some home energy improvements.

If you are planning home energy improvements involving windows, insulation and air sealing, make them before buying and installing your new AC system. Otherwise you will end up with an oversized equipment.

SEER: energy Efficiency

Central AC units energy efficiency are rated by their SEER (Seasonal Energy Efficiency Ratio).

Prefer a unit with a high SEER, namely in dry climates. Do not forget: a unit with a SEER of 18, compared to an old unit with a SEER of 9, will use half the energy.

Humidity factor

The ability of AC units at removing moisture - a critical feature for comfort, and to prevent mold, mildew and fungi - is measured by their SHF (Sensible Heat Factor).

There are two types of ducted AC systems: the packaged and the ducted split-system. In the packaged type all the main parts of the AC system are located outdoors, in a box than contains the evaporator but also the condenser and the compressor. In the ducted split-system the air evaporator coil is installed in an indoor cabinet or in the main supply duct of a furnace or heat pump.
The SHF is a decimal number, between 0.5 and 1.0; the higher the SHF the less moisture the unit will remove; the lower the SHF the more moisture it will remove.

A higher SHF is advantageous in dry and mild climates: air conditioners with a high SHF can be more energy-efficient. In other climates a lower SHF is more advantageous: a unit with a SHF between  0,67 and 0.77 can be a good choice.

See: AC Efficiency and Humidity Removal

Multi-Speed blower motors and dual speed compressors

The improvements in efficiency and flexibility of modern air conditioners are largely based on dual/multi-speed blower motors and dual speed compressors.

Prefer units with these two features. Multi-speed units will cost you a lot more (30% or so) but will prevent temperature fluctuations, or excess wear problems. And it allows energy-saving strategies otherwise impossible, namely temperature zoning (room-by-room cooling).

The SEER (Seasonal Energy-Efficiency Rating) is a measure of the energy-efficiency of central AC units and ranges from 13 to 23. A SEER of 13 instead of 10, means a 30% improvement in energy consumption and savings.

The noise issue Improvement

Look for a qualified Energy Star (or UE eco-labeling...) unit with a quiet condenser: a sound level of 75 decibels or less.




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