Ceiling fans only affect the room in which they are installed. They work best when installed with their blades 7-9 feet above the floor and 10 – 12 inches below the ceiling. Larger blades move more air than smaller blades, but blade material has no effect on the amount of air moved. Larger blades provide more cooling in the summer and heat distribution in the winter at a lower velocity, which can be important in a space where a strong breeze would be unwelcome.
During the summer, fans create a wind chill effect, making a room more comfortable. In temperature climates, a combination of ceiling fans and natural ventilation may be enough to keep a space cool without air conditioning. In an air conditioned space, the use of ceiling fans can allow you to increase the set temperature by 4°F with no decrease in comfort.
During the winter, ceiling fans can help make a space feel warmer by redistributing warm air that has risen up to the ceiling back down to where a room’s occupants are. For this purpose, a ceiling fan should be run at low velocity to avoid creating chilling drafts.
A whole house fan pulls air in through open windows, and exhausts it through the attic and roof. They’re useful for cooling a building when outdoor temperatures are in a comfortable range. One of the most common uses of a whole house fan is to drawn in cool night air and exhaust indoor air that has heated up during the course of a day.
Whole House Ventilation
A building which is well insulated and sufficiently air tight to be energy efficient will generally need some kind of ventilation system to provide fresh air and control moisture. In the past, buildings were ventilated through uncontrolled air movement and infiltration through small cracks and holes in the building envelope, but in energy efficient buildings, those small cracks and holes don’t exist. Some ventilation can be achieved by opening windows and doors, especially with the addition of passive solar ventilation, whole house fans and other spot ventilation. When a central heating or cooling system is in use, however, it would be counterproductive to use any of those ventilation strategies, and some form of whole-house ventilation would be more appropriate.
Exhaust Ventilation Systems work by decreasing the air pressure inside of a building, causing indoor air to leave the building, while outside air enters the building through leaks in the building shell and intentional passive vents. These systems are most suitable in cold climates, as warm, moist outdoor air can condense and cause moisture damage inside building walls. These types of systems are relatively inexpensive and easy to install, but cause higher heating and cooling energy costs than energy recovery ventilation systems, as the incoming air is not warmed, cooled, or dehumidified before entering the building.
Supply Ventilation Systems use a fan to force outside air in to a building, causing inside air to leak out through holes in the building shell and intentional ducts and vents. Unlike exhaust ventilation systems, these systems allow control of where air enters a building, and allow outdoor air to be filtered to remove pollutants and moisture. These systems work best in hot or mixed climates; in cool climates, there is a potential for moisture damage as warm interior air leaks out of the building and moisture condenses in colder parts of the exterior wall. These systems lead to higher heating and cooling requirements than energy recovery systems.
Balanced Ventilation Systems exhaust and introduce roughly equal amounts of outdoor and indoor air. Because they directly supply outside air, it can be filtered to remove pollutants and moisture. Such systems are appropriate for all climates, but like the previous two systems, lead to higher heating and cooling costs than energy recovery ventilation systems. They are also more complicated and expensive than exhaust or supply systems.
Energy Recovery Ventilation Systems transfer heat from outgoing air to incoming air in the winter, and from incoming air to outgoing air in the summer, leading to lower heating and cooling requirements. There are several different types of energy recovery ventilation systems, but they all have a heat exchanger, controls, and one or more fans to move air through the machine. Energy recovery ventilation systems are more expensive to install, require more maintenance and require more electricity to run than the previous three types of systems, but can provide significant energy savings in heating and cooling. They provide the most return on investment in climates with relatively extreme winters or summers and where costs of heating and cooling are high.