LIGHTING AND APPLIANCES: Air Circulation

Questions:

• Will a ceiling fan help save energy?
  
• Can you tell me the difference between an attic fan and a whole-house fan?
  
• What should I consider before purchasing a whole-house fan?
  

Will a ceiling fan help save energy?
A ceiling fan saves energy primarily by enhancing comfort in the summer. The amount saved will depend on how much less an air conditioner is used. A fan creates air movement that can help the room feel cooler at higher air temperatures.

Research has shown that moving air can compensate for a four-degree increase in air temperature with no perceived loss of comfort.This means someone can be as comfortable at 82 degrees with a fan moving air, as someone would be at 78 degrees with no air movement.

For each degree increased on the thermostat setting in the summer, expect to save three to four percent on the cooling bill. So, if someone operates a ceiling fan and raises the thermostat setting four degrees, 12 to 16 percent will be saved.

Keep in mind the thermostat must be kept at the higher setting to achieve the expected savings. And, in order to be comfortable, a fan may be needed in each room of the house. Install a ceiling fan in the most frequently occupied room, such as the family room, and use several portable fans to move air between rooms. Any type of fan can enhance comfort in summer, not just a ceiling fan.

In the winter, ceiling fans recirculate warm air from the ceiling to the floor, but the energy savings is not significant, especially in homes with forced-air heat or ceilings lower than 12 feet. When a ceiling fan operates in winter, the air movement, even when directed upward, often causes discomfort, so the thermostat may need to be turned up.
Therefore, don't operate the ceiling fan in winter.

Can you tell me the difference between an attic fan and a whole-house fan?
An attic fan ventilates only the attic by drawing in air through the attic vents. It is installed in the roof or gable. It turns on whenever the attic temperature reaches a high temperature.

Research shows that any savings in air-conditioning costs because of an attic fan generally are offset by the cost to operate the fan.

A whole-house fan ventilates the house and uses the attic vents only for discharging the air. The fan is located in the ceiling between the occupied space and the attic. It cools the house by pulling in cool outside air through open windows.

A whole-house fan can save a significant amount of energy by reducing the need for air conditioning when outside temperatures and relative humidities are in the comfort range.

What should I consider before purchasing a whole-house fan?
Several factors must be considered before making such a purchase. First, make sure a whole-house fan is appropriate for the lifestyle and climatic location.

Cooling with ventilation works best in climates with large day-night temperature differences and relatively low humidity. This type of climate is more characteristic of western Kansas than eastern Kansas. Also, be willing to use the fan on a regular basis in lieu of air conditioning to achieve a significant savings.

If a whole-house fan still makes sense, determine the size of fan the house needs. For a whole-house fan to ventilate effectively, it should make 40 air changes an hour. This means it must move two-thirds of the house volume in one minute.

Determine the volume of the house by multiplying floor area by ceiling height. Then, select a fan that has a CFM (cubic feet per minute) rating of two-thirds the house's volume. If the house is large with several floors, consider sizing the fan for just one floor.

Second, determine where to install the fan. Whole-house fans are usually mounted horizontally in the ceiling between the attic and the top floor. If the model chosen discharges through the attic, allow enough vent area for the air to escape without building up pressure. It is recommended to have one square foot of open vent area for every 750 CFM of the fan's rated air-moving capacity.

For example, a fan rated at 4,500 CFM needs six square feet of open vent area. Remember that most attic vents have insect screening, which cuts the effective area by about 50 percent.

Whole-house fans are available in direct-drive and belt-drive models. Direct-drive models have the fan mounted directly on the motor shaft. They are usually quieter and require less maintenance than belt-drive models.

Belt-drive models often use less energy per CFM of capacity than do direct-drive because the fan motor is matched more closely to the optimum fan speed. Also, belt-drive models are usually available in larger sizes.

When installing a whole-house fan, consider a variable-speed controller and a timer. The variable speed controller allows operation of the fan at different speeds, depending on outdoor temperature. The timer allows someone to turn on the fan in the evening, and then set it to automatically shut off after a certain time.

Finally, seal off the fan during the winter months to eliminate the significant amount of heated air that can be lost through the fan louvers. The simplest method is to install a whole-house fan weatherization kit available at many hardware and discount stores. The kit provides a heavy clear plastic cover and self-adhesive plastic channels to hold the plastic. The channels and plastic are applied to the house side of the fan, making seasonal installation and removal convenient.