408 Energy Project Financing: Resources and Strategies for Success
mass balance calculation (Persily and Dols 1990). However, in many
buildings, CO 2 concentrations never stabilize during a workday because
occupancy and ventilation rates are not stable for a sufficient time pe-
riod. If the CO 2 concentration has not stabilized at its equilibrium value
and the steady-state relationship between CO 2 and ventilation rate is
used to estimate the rate of outside air supply, the estimated outside
air ventilation rate may be substantially in error.
Carbon monoxide (CO) and nitrogen oxides (NOx): Indoor con-
centrations of CO and NOx may be higher than outdoor concentrations
due to indoor unvented combustion (e.g., unvented space heaters),
failures in the combustion exhaust vent systems of vented appliances,
and leakage of air from attached parking garages into the building.
Tobacco smoking can cause a small increase in indoor CO concentra-
tions. Short-term exposures to highly elevated concentrations of CO can
cause brain damage or death (NRC 1981). Lower concentrations can
cause chest pain among people with heart disease (NRC 1981). NO 2
is usually considered to be the most important of the indoor nitrogen
oxides. High concentrations (e.g., 0.5 ppm) of NO 2 can cause respiratory
distress in individuals with asthma and concentrations of approximately
1 ppm cause increased airway resistance in health individuals (NRC
1981). Long term exposure to much lower concentrations of NO 2 may
be associated with increased respiratory illness among children (Vedal
1985).
Volatile organic compounds (VOCs): VOCs are a class of gaseous
pollutants containing carbon. The indoor air typically contains dozens of
VOCs at concentrations that are measurable. VOCs are emitted indoors
by building materials (e.g., paints, pressed wood products, adhesives,
etc.), furniture, equipment (photocopying machines, printers, etc.),
cleaning products, pest control products, and combustion activities
(cooking, unvented space heating, tobacco smoking, indoor vehicle use).
Humans also release VOCs as a consequence of their metabolism and
use of personal products such as perfumes. The outdoor air entering
buildings also contains VOCs. VOCs in contaminated soil adjacent to
the building can also be drawn into buildings.
New building materials and furnishings generally emit VOCs at a
much higher rate than older materials. Emission rates for many VOCs
may decline by an order of magnitude during the first few weeks after
the materials are installed in the building. However, the emission rates
of some VOCs, such as formaldehyde emissions from pressed wood