Central Cooling
The most common central cooling systems are split systems, which includes an outdoor cabinet containing a condenser coil and compressor, and an indoor evaporator coil, usually installed in conjunction with a furnace or air handler. The compressor pumps a chemical called refrigerant through the system.
How they work
Once warm air inside the building blows across the indoor evaporator coil, its heat energy transfers to the refrigerant inside the coil. That transfer, in turn, "cools" the air. The refrigerant is pumped back to the compressor where the cycle begins again. The heat absorbed by the refrigerant is moved outside the building while cooled air is blown inside. Moisture that contributes to humidity is also condensed out of the air.
A cooling system is usually combined with a central heating system because they share the same ductwork for distributing conditioned air throughout the building.
Central Heating Systems
Central heating systems have a primary heating appliance, such as a furnace, typically located in a basement or garage. All furnaces consist of four main components: 1) burners that deliver and burn fuel, 2) heat exchangers, 3) a blower and 4) a flue that acts as an exhaust for gaseous by-products. Depending on the situation, region and needs, you can choose from heating systems running on either gas or oil as fuel, or a hybrid packaged system that can use both fuel types.
How they work
Combustion gases are generated by the burners in a furnace and passed over a heat exchanger. Air from the building blows across the heat exchanger to be warmed. It is then blown through a system of ducts to distribute throughout the building.
During warm seasons a heating system works with central air conditioning. Air is cooled as it's blown over an air conditioning unit's cooling coil, often attached to the exhaust of the furnace, and then sent over the same air ducts throughout the building.
Heat Pump Systems
A heat pump is an all-in-one heating and cooling system. It heats a building in winter and then cools it in summer. A typical heat pump installation consists of two parts: an indoor unit called an air handler and an outdoor unit similar to a central air conditioner. A compressor circulates refrigerant that absorbs and releases heat as it travels between the indoor and outdoor units.
How they work
What kind of magic does a heat pump perform to both heat and cool the air? Think of a heat pump as a heat juggler. Even in air that's below freezing temperatures, heat energy is present. When it's cold outside a heat pump extracts this outside heat and transfers it inside. When it's warm outside, it reverses directions and acts like an air conditioner, removing heat from the building.
One advantage of a heat pump is that it moves heat instead of generating heat, which is more energy efficienct. Also, it is powered by electricity, so can save substantially on fuel consumption. For example, a Trane XL19i heat pump is among the HVAC industry's most efficient, with a rating up to 17.90 SEER and 8.9 HSPF.
Note that heat pumps are best for moderate climates, keeping buildings warm even when temperatures drop into the low 20s. A supplemental heating source may be needed for lower temperatures.
Packaged Heating & Cooling Systems
Packaged systems offer a more minimalist approach to heating and cooling. The system contains the same components as a typical split-system—the evaporator, condenser, compressor and more—all working together in one space-saving unit. Packaged units are typically installed outdoors at ground level or on the roof, making them versatile for both horizontal or down-flow designs.
How they work
Packaged systems have been carefully engineered to give you all of your heating and cooling equipment in a single cabinet. Depending on the weather situation and energy needs, there are four types of packaged systems to chose from, each working differently:
- Heat pump packaged systems that both heat and cool your home
- Air conditioner packaged systems that offer cooling solutions for warmer climates
- Hybrid fuel packaged systems that work as a heat pump, but can also provide gas heating for greater flexibility
- Gas/electric packaged systems that can switch from electric air conditioning to gas heating to give you more fuel options