Control Techniques

The basic control techniques to improve the quality of indoor air are source removal, ventilation, isolation, and air cleaners.

Source Removal

This technique involves removing or modifying the source of pollution and replacing it with a low-pollution substi-

tute. Asbestos pipe insulation should be encased securely or replaced by nonasbestos pipe insulation if possible. Limiting the use of formaldehyde insulation, particle boards, carpets, fabric, or furniture containing formaldehyde can limit exposure to formaldehyde. Replacing kerosene and gas space heaters with electric space heaters can eliminate exposure to carbon dioxide, carbon monoxide, and nitrogen oxide. Biological contaminants and VOCs can be controlled by source removal.

Ventilation

Increasing ventilation can remove the offending pollutants, such as VOCs, and dilute the remaining pollution to a safer concentration. For example, gas stoves can be fitted with range hoods and exhaust fans that draw the air and effluent in over the cooking surface and blow carbon dioxide, carbon monoxide, and nitrogen oxides outdoors. However, range hoods that use charcoal filters to clean the air and then revent it to the room are ineffective in controlling carbon dioxide, carbon monoxide, and nitrogen oxides. One solution is to open a window near the stove and fit it with a fan to blow out the pollutants.

Forced ventilation with window fans works the same as natural ventilation but insures a steadier and more reliable ventilation rate. Figure 5.28.8 shows heat exchangers that are the basis of a heat-recovery ventilation system.

One way to measure the success of a ventilation system is to use a monitor that detects carbon dioxide (a gas that causes drowsiness in excess amounts). If carbon dioxide levels are high, other pollutants are also likely to be present in excessive amounts. Monitors are available that trigger a ventilation system to bring in more fresh air when needed (Soviero 1992).

FIG. 5.28.8 Heat exchangers for heat-recovery ventilator. A heat-exchange element is the basis of a heat-recovery ventilator. Fresh outdoor air (1) is warmed as it passes through the exchanger and enters the house (2). Stale indoor air (3) leaving the house is cooled as it transfers heat to the exchanger and is vented outside (4). In the fixed-plate type, heat is transferred through plastic, metal, or paper partitions. The turning wheel of the rotary type picks up heat as it passes through the warm air path and surrenders heat to the cold air stream half a rotation later. Liquid refrigerant in the pipes of the heat-pipe type evaporates at the warm end and condenses at the cold end, transferring heat to the cold air.

FIG. 5.28.8 Heat exchangers for heat-recovery ventilator. A heat-exchange element is the basis of a heat-recovery ventilator. Fresh outdoor air (1) is warmed as it passes through the exchanger and enters the house (2). Stale indoor air (3) leaving the house is cooled as it transfers heat to the exchanger and is vented outside (4). In the fixed-plate type, heat is transferred through plastic, metal, or paper partitions. The turning wheel of the rotary type picks up heat as it passes through the warm air path and surrenders heat to the cold air stream half a rotation later. Liquid refrigerant in the pipes of the heat-pipe type evaporates at the warm end and condenses at the cold end, transferring heat to the cold air.

Isolation

Isolating certain sources of pollution and preventing their emissions from entering the indoor environment is best. Formaldehyde outgassing from urea-formaldehyde foam insulation can also be partially controlled by vapor barriers; wallpaper or low-permeability paint applied to interior walls; and plywood coated with shellac, varnish, polymeric coatings, or other low-diffusion barriers. These barriers contain the formaldehyde outgasses, which are seemingly reabsorbed by their source rather than released into the home.

Air Cleaners

The air cleaners for residential purposes are based on filtration, adsorption, and electrostatic precipitation as follows:

Filters made of charcoal, glass fibers, and synthetic materials are used to remove particles. Pollen or lint, which are relatively large particles, are easily trapped by most filters. High-efficiency particulate air (HEPA) filters can remove particles larger than 0.3 am, which include bacteria and spores, but not viruses.

Whereas filters trap larger particles, adsorbents react with the molecules. Three common adsorbents are activated charcoal, activated alumina, and silica gel. Adsorbents remove gases, such as formaldehyde, and ammonia.

FIG. 5.28.9 Two-step precipitator.

Electrostatic air cleaners work by charging airborne particles with either a negative or positive electric charge. These charged particles gravitate to oppositely charged, special collector plates within the air cleaner. The technique is effective against dust, smoke particles, and some allergens. Figure 5.28.9 shows the operation principles of a two-step precipitator.

The National Aeronautics and Space Administration (NASA) studies have long indicated another simpler way to handle pollutants: household plants which absorb some toxins. The spider plant and philodendron, for example, remove formaldehyde and carbon dioxide from indoor air (Soviero 1992).

DIY Battery Repair

DIY Battery Repair

You can now recondition your old batteries at home and bring them back to 100 percent of their working condition. This guide will enable you to revive All NiCd batteries regardless of brand and battery volt. It will give you the required information on how to re-energize and revive your NiCd batteries through the RVD process, charging method and charging guidelines.

Get My Free Ebook


Post a comment