MP 227 Fans and Comfort by John Langston

COOPERATIVE EXTENSION SERVICE University of Arkansas, United States Department of Agriculture and County Governments Cooperating Fans and

A provides air movement that results in Table 2. Moderate Activity, Lightly Clothed increased comfort under certain conditions. Fans do not change the temperature or humidity of air, but the air movement causes a person to feel cooler. How much cooler depends on the activity level, the amount of clothing worn, the speed of air movement, and the relative humidity. Most people feel about 4 to 5 degrees cooler when ex­ posed to air velocities greater than 100 feet per minute. Ashrae, 1977 Handbook of Fundamentals, Fanger's Com­ fort Chart Air Movement Means Feeling Cooler — Table 1 Increased air movement, whether the person is shows that the average person at rest will feel com­ active or at rest, allows a person to feel comfort­ fortable at 77.5 degrees Fahrenheit when there is able at 4 degrees to 5 degrees higher temperature. little or no air movement (20 fpm) and the relative humidity is 60 percent. However, when air move­ Lower Humidity Means Feeling Cooler — ment is increased to 100 fpm, that person can feel Assuming little air movement (20 fpm), Table 1 comfortable at a higher temperature, 81.5 degrees shows that the comfort temperature for 80 percent Fahrenheit. Increasing the air movement to 300 relative humidity is 77 degrees. Lowering the fpm (about 3 miles per hour) will allow the person humidity to 40 percent will allow a person to feel to be comfortable at an even higher temperature comfortable at a higher temperature, 78.5 degrees. (83 degrees). A properly sized unit (one that is not too large) does a good job of lowering humid­ ity. It is important to note that using fans in con­ junction with air conditioning can cause high humidity problems in homes where the air con­ ditioner is already oversized. Turning the thermo­ stat up 4 degrees causes the air conditioner to run less resulting in a humidity increase inside the home. Some increase can be tolerated as long as the humidity does not rise above 60 percent. The house then begins to feel “muggy,” and have musty odors. In some cases mildew may appear.

Humidity control can easily mean 2 degrees Table 2 demonstrates that increasing a person’s difference in comfort, because low humidity does activity level causes the need for lower air tempera­ allow a person to feel comfortable at a higher ture. With equal clothing and the same air move­ temperature. ment, a person generally needs a 10-degree cooler temperature to feel comfortable when moderately active as compared to sedentary. This means that John Langston is Extension agricultural engineer, 77.5 degrees may be fine for reading, but running University of Arkansas Cooperative Extension Ser­ the can cause discomfort unless vice, Little Rock. the air temperature is about 67 degrees Fahrenheit. 3

Any fan that moves air at the described veloc­ Several disadvantages come with a whole house ities will have similar comfort effects on the human fan. Installation is more than a minor job. Noise body. Different types of fans have different appli­ can be a nuisance, but this can be minimized if cations, and any fan has advantages and disadvan­ blade speed is kept as slow as possible (preferably tages. Some can be operated at the same time as not over 500 rpm) and if care is taken in locating an air conditioner to gain the benefit of reduced the fan. A great deal of airborne dust and pollen humidity as well as increased air movement. can be pulled into the house. These fans cannot be used with air conditioning. When air conditioning Whole House Cooling Fans — Years ago they is on, the fan must be off. were called attic fans, but now they should not be confused with attic ventilating devices. Whole Window Fans — They normally range from 16 house fans are normally 24 to 36 inches in diam­ to 24 inches in diameter, have multiple speeds, and eter and require from 300 to 700 watts of power are usually reversible. Air can be pulled in or blown to operate a motor that may be as large as 3/4 out. They have the advantage of requiring no spe­ horsepower. The fan may cost as much as $300, cial installation or wiring. They are not considered not including installation. Cost of operation will portable, but can be moved from window to win­ range from 2 1/2 cents to 5 1/2 cents per hour (8 cents dow without too much effort. Cost can be up to per kilowatt hour of electricity). These fans move about $100 for a high quality unit, and most will a great deal of air and are often sized to change the require no more than 200 to 250 watts of power. air in a house as much as once per minute. Correct This costs about 2 cents per hour of operation. fan size in cubic feet per minute (cfm) can be arrived at by the following:

Fan size (cfm) = (Length of house x width of house x ceiling height)

This provides one air change per minute for whole house ventilation. Dividing your answer by two yields a fan sized to change the air in the whole house once every two minutes or once per minute in half the house. This is often done when only a portion of the house will be ventilated.

Box or Circulator Fans — These units are usual­ ly 20 inches in diameter but may vary from 16 to 24 inches. This is probably the most practical fan for many residences. Economy models often cost as little as $25. Power consumption is usually 200 watts or less, meaning about 1 1/2 cents per hour operating cost. The fans are usually multiple speed, require no installation, are lightweight, and highly Air movement can be provided in any part of a portable. The only disadvantages are noise when house depending on how doors and windows are using the high speed and the fact that the fan manipulated. This type of fan will not perform usually sits in the floor where small children may satisfactorily if sufficient openings are not pro­ be tempted to stick things in it. The inexpensive vided to let air out of the attic. Attic opening area models will not offer the long life of some of the amounting to twice the area of the fan frame is a better heavy-duty fans, but an economy model rule of thumb for most fans. may last several summers. 4

Ceiling Fans — Ceiling fans are a proven way of increasing air movement to increase comfort in a room. They are currently sold as decorator items which also serve as energy saving devices. However, there are many misconceptions about ceiling fans. Like other fans, they have their advantages and disadvantages. Ceiling fans normally come in sizes ranging from 36 inches to 52 inches. Cost can run from $75 to over $600. Power requirements, even for the large ones, rarely are over 100 watts which is less than one cent per hour. Most of these fans have enough power to move air in the 200 feet per minute range, so they can give the 4 to 5 degrees Fahrenheit cooling effect discussed earlier. The advantages of ceiling fans are numerous.

1. They are nostalgic and serve as decorator items.

Box Fan 2. The fans are ceiling hung and out of the way.

Table Model Oscillating Fans — The selection is 3. They provide gentle air velocities over a almost endless with sizes ranging from about 6-inch large area rather than high velocities in a diameter fan blades up to 16 inches. These fans concentrated area as with small fans. have been popular for many years. They are very portable and are designed to sweep a large area 4. They use very little power. rather than stay directed in one spot. They require very little energy, usually less than 100 watts (less 5. They can be run in conjunction with an air than one cent per hour) even for the large models. conditioning system. All qualities are available from inexpensive short life models to units that should last a lifetime. 6. They are very quiet.

There are also disadvantages:

1. A separate fan is required for each room. They are not portable.

2. They are expensive compared to other fans.

3. Installation may be fairly involved depend­ ing on the fan weight and wiring require­ ments.

Oscillating Fan 5

Selecting a ceiling fan can be confusing. A 36- movement to allow setting the about 4 inch fan will normally provide enough air move­ or 5 degrees higher. Each one-degree temperature ment for a 12’ by 12’ room. The 52-inch fans will setting on a thermostat may save about 5 percent take care of rooms in the 15’ by 15’range. Larger in air conditioning costs. Some energy is expended rooms will require more than one fan, or locating for the fan, but it is very little. Therefore, energy one fan over the area most often occupied. Energy can definitely be saved if the air conditioning is not much of a consideration in selection because thermostat is set to a higher temperature. Remem­ most require only 50 to 100 watts (not including a ber that this will not work with a whole house fan light kit). Variable speed is a nice feature; although or a window fan, because air will be moved out of two distinct speeds are usually adequate. Some the house faster than the air conditioner can pro­ variable speed fans will not start on low speed cess it. settings. This is a disadvantage because power may be turned on and left on accidentally resulting in Can you afford to buy the fan for the air con­ motor burnout. ditioning savings? Probably so, if an inexpensive fan is purchased and good management is prac­ There is certainly a difference in the quality of ticed. Remember that one ceiling fan will only ceiling fans available. Generally, the more expen­ take care of one room. So it is not unusual for sive fans have better warranties and longer life ex­ ceiling fan advocates to purchase three or four, pectancy. Decorative items can also add to the locating them where they spend the most time. If price of a fan and do not add to life expectancy, you purchase decorator models, you could easily so consider the warranty. invest $1,000 in fans. That this investment would ever be recovered in energy savings is doubtful. However, if you buy the less expensive models, A ceiling fan should be hung by a knowledge­ a 20 percent saving on air conditioning could be able person. They must be properly supported and significant. safely wired. Some weigh as much as 40 pounds and cannot be secured directly to an electrical For example, 20 percent of a $500 seasonal ceiling outlet unless the outlet box is securely cooling bill is $100. In a few years that could pay anchored to a joist or blocking strip. Box anchor­ for several modest fans. ing kits, joist hooks, and swag kits are all available for hanging fans. Some can be wired directly to the wiring provided for a light. Others with multiple Ceiling fans are often sold as winter energy speeds and light attachments may require that savers by blowing hot air off the ceiling. This is of additional wiring be pulled into the outlet boxes. very little significance in most homes. Only those Always follow manufacturers’ instructions for with high ceilings (10- to 12-feet) and little or no hanging and wiring a fan. Be certain your installa­ insulation should have enough heat layering to tion conforms to local building codes. benefit from blowing it down from the ceiling. Well-insulated homes with storm windows and 8-foot ceilings will not benefit from ceiling fans What about energy savings? in the winter. Instead of helping, the cooling effect of the fan will work against trying to stay warm. A ceiling fan or any other fan has the potential Some fans offer a reversing switch for winter oper­ to save energy. Obviously, some days a person can ation to direct air flow away from the occupants. be comfortable with a fan without running his air This does stop the concentrated down draft direct­ conditioner. Air conditioning may cost in the ly under the fan and has merit in the case where range of 8 cents to over 13 cents per hour per ton winter operation is needed. to operate. For example, a 3-ton unit may cost from $4.32 to $7.20 per 24-hour day depending You can also use ceiling fans to distribute heat on the unit efficiency and outdoor temperature. in a room with a wood stove. The fan helps blend (This assumes the compressor is cycling on 75 per­ the air to eliminate hot spots. Use other types of cent of the time and electricity is 8 cents per fans, such as box fans, to move air to other parts kilowatt.) The idea of using a fan along with air of the house. This is not only effective with wood conditioning is to set the thermostat higher, create stoves but also works well with single-room air some air movement, and still be comfortable. As conditioners when cool air needs to be pushed to mentioned earlier, a fan can create enough air other rooms. Issued in furtherance of Cooperative Extension work. Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Dr. W. J. Moline, Director of Extension Service, University of Arkansas Division of Agriculture. The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, sex, or handicap, and is an Equal Employment Opportunity Employer. MP227-7.5M-8-84