Environmental Engineering Reference
In-Depth Information
Home space heating is accomplished primarily by the use of modular,
freestanding, unvented natural gas or kerosene space heaters in the warmer
regions of the U.S. and in countries such as Japan and Australia. These
devices are designed to emit only limited quantities of carbon monoxide
(CO) and do not pose an asphyxiation hazard. They may cause significant
indoor air contamination with a variety of combustion by-products (see
Chapter 3). Such space heaters are commonly used to “spot heat” individual
rooms to reduce energy costs.
Electrical devices or systems are often used for home space heating in
the U.S. These include cable heat, with elements in the ceiling, or electric
heat pumps. In the latter case, energy is extracted from outside air or ground-
water, with a heating coil supplement during very cold weather. Electric
heating devices do not produce any combustion by-products and do not, in
theory, pose any indoor air contamination risks.
Indoor space heating can be provided by central systems which forcibly
or passively distribute heat from a combustion or electrical appliance to
attain and maintain desired thermal conditions. Such systems heat all spaces,
including those that are unoccupied. In forced air systems, heat is distributed
through duct systems. In radiant heat systems, hot water is pumped to
radiators distributed in various parts of the house.
In forced air systems, a fan draws air through a filter into the appliance,
where it is heated and then delivered through ducts to building spaces
through supply air registers. Air is returned to the furnace to be reheated
through a second duct system described as a cold air return.
Duct systems in residences can cause or contribute to indoor air con-
tamination problems. Historically, ducts (both supply and return) were con-
structed of galvanized steel. Increasingly, ducts are being fabricated from
fiberglass materials. These include duct board, which is fashioned into sup-
ply and return air trunklines on-site, with polyethylene-lined, fiberglass-
insulated flex duct serving to deliver conditioned air to supply air registers.
Duct board may release contaminants such as methylamine, which is both
an odorant and an irritant. Porous surfaces of duct board are deposition sites
for organic dust, which may serve as a medium for mold growth and sub-
sequent indoor air contamination.
Return air ductwork, which is under a high negative pressure, is typi-
cally located in attic, crawlspace, or basement areas, or attached garages.
Wet crawlspaces and basements are often heavily contaminated with mold,
and the usually leaky ductwork located in these spaces serves as a conduit
for mold spores, moisture, and even radon into living spaces.
In many dwellings, cooling is provided either by window or whole-
house systems that are integrated into heating systems.
12. Plumbing
Most houses have plumbing systems that carry water into them, then heat
(and in many cases soften) it and distribute it to kitchen and bathroom sinks,
