Most people have a central air conditioning system. We all know the air comes out of vents that are in different rooms in a house. Most of us know that there's an air filter somewhere in the house that needs to be changed once in awhile. There are some other things about the airflow in a central air system that may be of interest to people. Did you know the air conditioning vents are located in precise places? Did you wonder why the thermostat is located in that hallway, or why two story houses usually have two air conditioning units? These questions and others are easily answered, and can empower people with some of the basic knowledge necessary to maximize the life of their central air unit.
The vents located in each room of a house are usually placed where they are for a reason - to maximize airflow in the room and to keep the air circulating throughout the entire room. These vents have baffles, or fins, on them that direct airflow in certain directions. If you look around your home, you may notice that some of the vents are one-directional, while others are multi-directional. The object of the multi-directional vents is to cover as much area as possible in a room and to keep a room from having 'hot spots'.
The thermostat in your home is probably located in a hallway. This is the spot where the temperature most resembles that of the rest of the house. In other words, the temperature where the thermostat is located is the average temperature of the home. For this reason, the thermostat is usually located in a central point in the home. After all, you don't want the air conditioner or heater to kick on when part of the house is freezing, while another part is just right.
Air circulation is critical in a home air system. As each vent, or register, discharges a certain amount of air, there needs to be someplace for that air to go. If there were nowhere for the air to go, it would cause positive pressure to build up in the home. The efficiency of the unit would be drastically reduced too, as it struggles to force more air into a positively pressured environment. The good thing about positive pressure in your home would be that no airborne particles would be able to enter your home since they would be forced away by the pressure escaping the dwelling. The cost outweighs the benefit though, as the high electric bill and shortened life of the unit will cost substantial money in the long run.
To make sure the unit works as efficiently as possible, there is a return air grill, which usually houses the air filter. This return air grill is located in a place where all the circulating air of the home is able to be cycled through it. The air is then cleaned, cycled through the evaporator coil located in the air handler, and redistributed throughout the house. As this is done repeatedly, cooler air is recycled, so that the unit brings the temperature to its desired setting quicker, and the change in temperature from air going into the return and coming out of the return gets smaller. This allows the unit to maintain the temperature of the home by running for relatively short cycles periodically. Then we can enjoy our lower electric bill.
Larger houses typically have different zones fed by more than one air system. When a house is on a horizontal plane, as a single story dwelling is, it's easier to regulate the temperature throughout the home. There's typically a problem with two story and taller dwellings though, which makes it harder for the temperature to be regulated. In warmer seasons, the air conditioner is used. In colder seasons, the heater is used. As we all know, heat rises, so in the winter, the heat all goes upstairs. But in the summer, the colder air all goes downstairs. It's a tough problem to solve. This can be done if you block off the two zones. This can be done by closing the doors to each bedroom. Another way to do it is to close the vents downstairs in the summer and upstairs in the winter. Neither option is very effective, so most people just live with the discomfort.
As you can see, your central air system has a little more to it than random airholes in the ceilings. Not all contractors are trained to design systems, so extra care should be taken to hire an experienced HVAC contractor to perform your new construction design... or while you are having your plans drawn up, have a mechanical engineer design the air conditioning system. It may cost a little more, but it's well worth it to keep your house as comfortable as possible.
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