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← ↑ → Air, the substance that completely surrounds us, has many forms and properties. It can be hot, cold, humid, dry, polluted, clear, or it can be found with all of these conditions. We’re able to live in just about all of these conditions. However, the most healthful and comfortable form of air occurs in only a very narrow range of these conditions. There is a comfort zone in which we are the most comfortable. It’s generally considered to be between 74 and 77 F with a relative humidity between 40 to 60 percent. POLLUTANTS Each of the pollutants in the atmosphere presents a different kind of problem, such as the following: 1. Allergens such as pollen, dust, and molds make breathing difficult for those who are allergic to them. 2. Bacteria and other airborne microorganisms are a health menace. 3. Flammable and toxic gases in large enough quantities can be dangerous. 4. Odors from many different sources are unpleasant, such as those that come from food preparation, evaporating-type chemicals, or unclean bodies. 5. Solid particles, such as soot and fly ash, in addition to irritating the eyes and nose, are also hard on clothes. 6. Radioactive air contaminants are active in very low concentrations. To reduce the concentration of these pollutants requires an enclosed space with proper air circulation, filters to clean the air, fans to circulate the air, humidifiers to add moisture to the air, and dehumidifiers to remove moisture from the air. Some of these pollutants, such as bacteria, require special equipment to reduce their concentration to acceptable levels. These are controlled through the use of special filters or germicidal lamps. When odors are a problem, charcoal filters (activated carbon) are usually used. It’s usually better to dilute the odors with fresh, clean air. If these pollutants were controlled at the source rather than after they entered the atmosphere, it would be much simpler for all of us. Air conditioning for the removal of the pollutants would not be necessary and we would all be healthier because of it. AIR MOVEMENT Air moves naturally from a high-pressure area to a low-pressure area, or from a high-temperature area to a low- temperature area. The greater the difference in either the pressure or the temperature, the faster is the air flow. This is the natural way we are provided with fresh, clean air. However, when an air conditioning system is used, the air is forced with a blower from a high-pressure area, the blower section, to a low-pressure area, the conditioned space. Air movement in this manner is achieved through the use of two types of fans: the axial-flow type and the squirrel cage (centrifugal) type. The axial-flow fan is the type that is used to set around and blow air directly on a person or something to be cooled. The air flow is in the direction that the fan is pointing, in the direction that the shaft of the motor is pointing. The centrifugal type is a series of blades that are placed into a circle. The air is drawn into the center of the wheel and is forced out through the housing at some point that will concentrate the volume of air. The air is discharged at a 90° angle from that in which it entered the blower wheel. These types of fans are used in ducted systems because they can create sufficient pressure to overcome the resistance of the ductwork. Centrifugal fans are generally used in forced- air systems, forced-air combustion furnaces, and forced-air combustion clothes dryers. The amount of air that can be moved will depend on the size of the motor and the capacity of the fan. Domestic refrigerators use a small 4-inch diameter axial-flow fan with a small 1/150-hp motor. The fan used in central air-conditioning applications may have a 10- or 12-inch diameter centrifugal blower driven by a 1/3 or 1/2-hp motor. The amount of air to be delivered will determine the sizes of the fan and motor. The velocity of the air movement will determine, to a great extent, the comfort of the occupants in the room. The number of air changes per hour will determine the freshness of the air plus the personal comfort of the occupants. A slow air movement will cause a stagnant, stuffy feeling, while a high volume of air will cause drafts and discomfort. Generally, 15 cubic feet per minute is the minimum and 65 feet per minute is the maximum for human comfort. In most instances velocities around 25 to 35 feet per minute are the most desirable. The number of air changes per hour in a room will vary depending on the use of the room. If there are a lot of people with heavy smoking, more air changes per hour will be required than if there are only one or two people with little activity and no smoking. Usually 11 air changes per hour is the minimum. Sometimes a lack of air changes per hour can be temporarily solved by the use of ceiling fans which have several speeds and air volumes. AIR FILTERING Air is filtered to remove dust, smoke, and pollen from the air as it passes through the air-conditioning equipment or the air-filtering system. The filter is generally placed in the air stream ahead of the air-conditioning equipment. There are of two types of filters: the filter type and the electronic ionizing type. 1. In the air-filtering type, the air is forced through a filter made of one of several different types of filter media. This medium may be fiberglass, aluminum, sponge rubber, or some other type of material that will collect dust particles as the air flows through it. Some types of media have a coating that helps to collect the dust and pollen. Some of these filters can be cleaned, while others are discarded and new ones installed. These filters should be replaced or cleaned at least once each month, or whenever they become dirty enough to reduce the air flow through them. 2. In the electronic ionizing type, the air passes through an electronically charged field which removes the particles electronically. These filters have positively and negatively charged plates that charge and collect the dust particles as they pass through the ionized area. These plates are charged to about 20,000 volts dc. The ionizing plates are cleaned periodically according to the manufacturer’s recommendations. Be sure to follow the manufacturer’s recommendations completely when cleaning this type of filter. GERMICIDAL AND OZONE LAMPS Airborne bacteria and mold spores are generally controlled through the use of germicidal lamps. Undesirable odors are removed through the use of ozone lamps. In some instances both odors and bacteria can be removed with a single lamp. Ozone lamps are popular in clothes dryers, range hoods, washrooms, and in smaller air-filtering systems. These lamps must be located so that their output rays won’t come into contact with the eyes and skin to prevent burning them. They should be installed in an air flow so that the ozone will be mixed thoroughly with the air. These are special lamps that operate on 10.5 volts using 350 milliamps of power, ac or dc. The operation of this lamp is due to its ability to arc. In order to arc, it must have a minimum of 28 volts, and it must have a ballast that is either inductive on ac or resistive on ac or dc voltage. The ballast must limit the current flow to the bulb. In some installations a 40-watt, 120-volt incandescent lamp may be used. Germicidal lamps are sometimes placed in the duct work of an air-conditioning system to kill any bacteria and other undesirable pathogens. In most installations they are placed after the filter and before the humidification equipment. There should also be a service access door for these lamps. To kill any microorganisms in the air, germicidal lamps are often used. Their effectiveness is in direct relation to the intensity of the exposure and the length of time exposed. The ultraviolet energy at a 2537 angstrom wave length will react to the skin and eyes much the same as the direct rays of sunlight. Therefore, precautions must be taken to protect the eyes and skin from excessive radiation. In most cases the light fixture is designed to direct the light rays at the ceiling or high on a wall. When installed in this manner, the rays are allowed to bounce around the room with little or no contact with the occupants. QUIZ: 1. What are pollen, dust, and molds known as? 2. When should pollutants be controlled? 3. Name the two types of fans used to circulate air. 4. In any type of installation, what determines the amount of air that can be moved? 5. In an air conditioned building, what determines the freshness of the air and the personal comfort of the occupants? 6. What process is used to remove the dust, smoke, and pollen from the air passing through an air conditioning unit? 7. How are airborne bacteria and mold spores generally controlled? 8. Where are germicide lamps sometimes used? 9. Name two types of air conditioning filters. 10. What is used to kill microorganisms? Home top of page |