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Cooling systems


July 10, 2009
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I don’t have air conditioning (cooling) in my home. Can I add it to my existing furnace?

Yes, you can add air conditioning to a furnace, but you must first consider the furnace blower and the duct, or air-distribution, system. The heating and cooling modes of operation require different air volumes most of the time, and the blower should be able to operate at several speeds. Since the heating and cooling modes have different air-volume requirements, the air ducts must also be the right size to handle the varying air volumes.

How can I tell if the blower in my furnace can handle both the heating and cooling of my home?

Most of the time, you can use the blower that you'll find on the furnace to meet both the heating and cooling airflow requirements. Most furnaces have multi-speed motors that can operate at a higher speed in the cooling mode, and at a lower speed in the heating mode. Multi-speed motors usually have color-coded wires or power leads.The low-speed is the red wire and the high speed is the black wire.Here is a diagram of a two-speed motor:

Three-speed motors also have a medium speed. The blue wire usually takes care of that.

Along with the black, brown and blue wires, there will also be other colored wires coming from the motor. The white wire(which is sometimes yellow)is the common, or neutral, wire, and we use this to complete the electrical circuit. You may also see brown wires,and these will connect to capacitors. Capacitors store electricity, and they can cause an electrical shock even when the power to the furnace is off, so be careful
If the motor has only a black, white and brown wire,the motor is a single-speed motor and is probably not the correct one for both the heating and cooling applications. Here is what a single-speed motor may look like:

So,if there are speed taps or wires (red or blue),chances are that the blower will meet the airflow requirements for both heating and cooling.

I don’t have air conditioning (cooling) in my home, but I do have a hot water (boiler) heating system. How can I add central air conditioning to my home?

You would have to install the central air conditioning system from scratch. Since there is no cooling equipment and no air-distribution system, the cooling system would be completely separate from the existing heating system.

How can I determine if my cooling (air-conditioning) system is tied into my heating system?

There are many options for heating and cooling our homes. For cooling, we can use incremental or individual window or through-the-wall air conditioning units for each of the rooms we want to cool. We can also use a central air-conditioning system to provide comfort cooling to the entire home. Larger homes may require more than one central system, and each system services one portion, or zone, of the home. For example, one zoning strategy uses one system for the upstairs of the home, while the second system services the downstairs areas.
For heating, we can use a furnace or a boiler, as I mentioned earlier.
Quite often, you can accomplish the heating and cooling of a home through the same air distribution or duct system. The most common method for providing comfort cooling along with heating is by setting a cooling coil on top of the furnace. Since there is ductwork on top of the furnace, it is usually very difficult to see the cooling coil. But there are ways to know if there is a cooling coil resting on top of the furnace:
  • look for a PVC or copper condensate drain line leading from the duct to a floor drain or condensate pump.

  • Look for two copper lines coming from the main duct section of the furnace.One of these lines will likely be wrapped in black insulation;the other will be unwrapped.

  • Look for a condensate pump at the foot of the furnace.

With this setup, heating is provided when the heat source is activated and the cooling system is not. Cooling, on the other hand, is provided when the cooling system is activated and the heat source is not. In either mode, the blower in the furnace circulates air from the occupied space across either the heating or cooling heat-transfer surface. When operating in the cooling mode, the blower will turn at high speed. When the system is operating in the heating mode, the blower will turn at low speed.

Another way to provide heating and cooling is to use a boiler in conjunction with the air-handler portion of a cooling system. In the cooling industry, we use the term “air handler” to identify a piece of equipment that contains the blower and the cooling coil. This type of heating system is called a “hydro-coil” system, or a"hydro-air"system. We install a hot-water-heating coil in the supply duct, coming off the air handler, but this is not active when the space is calling for cooling. When the occupied space calls for heat, the boiler cycles on, heats the water, and circulates this heated water through the coil inside the duct. The blower in the air handler circulates air from the occupied space through the hot water coil,heating the air. The heated air is then reintroduced to the occupied space.