Central Air Conditioner Systems

Heat Pump Condenser The central air conditioner system is the single greatest energy consumer in homes located in moderate to warm climates.  It may consist of central air conditioner and a furnace or a heat pump with supplemental electric heat strips or gas heat.

In older homes or those located in cooler climates, one or more room air conditioners may be all that is used for cooling.  Heating in these locations is generally done with a gas or fuel oil furnace.

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The programmable thermostat is best tool for managing the electrical load on your central air conditioner system.  These devices allow you to adjust the temperature automatically to fit your lifestyle and schedule.

Program the temperature you want for different periods of the day which include sleep, awake, leave and return. Units can be set up for different schedules throughout the week and some can even be programmed remotely via the Internet.

Central Air Conditioner vs. Heat Pump - What is the Difference?
A central air conditioner system circulates refrigerant through a condenser coil and an evaporator coil using a compressor.  A heat pump does the same thing to cool but reverses the flow of refrigerant to heat.  Here's a closer look at how each of these cycles work...


The Cooling Cycle
Heat Pump Cooling Cycle

In the cooling cycle warm, pressurized refrigerant vapor leaves the compressor and is routed through the condenser coil. Outside air is pulled through the condenser coil with a condenser fan to cool the warm refrigerant vapor.  As the vapor cools, it condenses into a liquid and releases the heat outdoors into the condenser fan air stream.

The liquid refrigerant from the condenser is then routed through a thermostatic expansion valve or TXV.  As the liquid passes through the TXV the pressure drop causes some of the refrigerant to return to a vapor.  This partial vaporization causes the temperature of the refrigerant to cool immediately.

The cool mixture of liquid and vapor circulates through the evaporator coil which is located in an indoor plenum.  Warm inside air driven by an air handler fan blows across the fins in this coil.  As the warm air comes in contact with the cool evaporator coil, it releases some of its heat and returns to the interior living space at a lower temperature.

As the refrigerant absorbs the heat from the inside air, the remaining liquid vaporizes.  When the refrigerant leaves the evaporator coil it is fully vaporized and returns to the compressor.  The compressor repressurizes the vapor and sends it to the condenser and the cycle repeats.  In a central air conditioner this is the entire process.

A heat pump, on the other hand, can reverse the flow of refrigerant to create a heating cycle...


The Heating Cycle
Heat Pump Heating Cycle

The heating cycle is accomplished by simply reversing the direction of refrigerant flow through a reversing valve.  The outdoor condenser coil becomes the evaporator and the indoor evaporator coil becomes the condenser.

As warm pressurized refrigerant vapor leaves the compressor it is piped to the indoor "condenser coil" where the indoor air circulates across it.   The inside air absorbs heat from the coil and carries it to the living space.   This release of heat causes the refrigerant vapor to cool and condense.

This liquid refrigerant is routed through the outdoor "evaporator" coil and where it absorbs heat from the outside air.  As heat is absorbed, the refrigerant vaporizes and returns to the compressor and the cycle repeats.

Surprisingly, on a cold day there is still heat to absorb from the outside air, even when the temperature is below freezing.  However, the rate at which heat is absorbed is much slower at these low temperatures so supplemental heat strips are used to augment comfort.

The compressor, the condenser fan and the air handler fan(s) all contribute to the heating and cooling load.  When the supplemental heat strips are energized in cold weather, they can more than double the electrical load of the entire system.

Thus, a trade-off emerges.  Is it more economical to run the heat pump longer and leave the heat strips off, or turn the heat strips on to reduce heat pump run time?  At what temperature should the heat strips come on?  The real answer is that it varies. It varies by the square footage and insulation level in your home, the size and type of heat pump and the winter temperature pattern where you live.

To find the most energy efficient setting for your home you will need to invest in an outdoor thermostat and put your home energy monitor to work.   Here's the strategy we recommend.

Another important feature to check on your central air conditioner or heat pump system is the Seasonal Energy Efficiency Rating or SEER.   If your unit is more than ten years old, you may be able to reduce energy cost significantly by upgrading to a newer, more efficient one.   Click here and we'll walk you through the steps you'll need to make a good decision.

For additional energy saving ideas for HVAC equipment, please visit the following:

Outdoor Thermostats  l   SEER Rating  l   Programmable Thermostats  l   AFUE Rating





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