Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

80 Chapter 3 Introduction to Engineering Design

The air flow patterns in and around a building will also affect the indoor air quality. The air

flow pattern inside the building is normally created by the HVAC system. However, the outside

air flow around a building envelope that is dictated by wind patterns could also affect the air flow

pattern within the building as well. When looking at air flow patterns, the important concept to

keep in mind is that air will always move from a high-pressure region to a low-pressure region.

Methods to Manage Contaminants

There are several ways to control the level of contaminants: (1) source elimination or removal,

(2) source substitution, (3) proper ventilation, (4) exposure control, and (5) air cleaning.

A good example of source elimination is not allowing people to smoke inside the building

or not allowing a car engine to run idle near a building’s outdoor air intake. In other words,

eliminate the source before it spreads out! It is important for engineers to keep that idea in

mind when designing the HVAC systems for a building — avoiding placing the outdoor air

intakes near loading docks or dumpsters, for example. A good example of source substitution

is to use a gentle cleaning product rather than a product that gives off harmful vapors when

cleaning bathrooms and kitchens. Local exhaust control means removing the sources of pollu-

tants before they can be spread through the air distribution system into other areas of a build-

ing. Everyday examples include use of an exhaust fan in restrooms to force out harmful

contaminants. Fume hoods are another example of local exhaust removal in many laboratories.

Clean outdoor air can also be mixed with the inside air to dilute the contaminated air. The

American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has

established a set of codes and standards for how much fresh outside air must be introduced for

various applications. Air cleaning means removing harmful particulate and gases from the air

TABLE 3.9Typical Sources of Indoor Air Pollutants

Outside Sources Building Equipment Component /Furnishings Other Indoor Sources

Polluted outdoor air HVAC equipment Components Science laboratories, copy and

Pollen, dust, fungal Microbiological growth in Microbiological growth on print areas, food preparation

spores, industrial drip pans, ductwork, coils, soiled or water-damaged areas, smoking lounges,

emissions and vehicle and humidifiers, improper materials, dry traps that allow cleaning materials, emission

emissions venting of combustion the passage of sewer gas, from trash, pesticides,

products, and dust or materials containing volatile odors and volatile organic

Nearby sources debris in ductwork organic compounds, compounds from paint, chalk,

Loading docks, odors from inorganic compounds, and adhesives, occupants with

dumpsters, unsanitary Non-HVAC equipment damaged asbestos, and communicable diseases, dry-

debris or building Emissions from office materials that produce erase markers and similar

exhausts near outdoor equipment, and emissions particles (dust) pens, insects and other pests,

air intakes from shops, labs and personal hygiene products

cleaning processes Furnishings

Underground sources Emissions from new

Radon, pesticides, and furnishings and floorings

leakage from underground and microbiological growth

storage tanks on or in soiled or water-

damaged furnishings

Source:EPA Fact sheets, EPA-402-F-96-004, October 1996

Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀