and well-being), building design and management principles must be applied throughout each of the four stages of a building's life cycle: (1) preconstruction period, (2) construction period, (3) long-term occupancy, and (4) adaptive reuse and eventual demolition (NRC, 1987b). These principles apply to both commercial and residential buildings.

Two basic strategies for controlling occupant exposure to allergens can be identified: source control, which can eliminate occupant exposure, and exposure control, which can minimize but not eliminate occupant exposures by methods of dilution or air cleaning. A simple, one-compartment model of a control system for a uniformly mixed occupied space, shown in Figure 7-1, illustrates the interrelationship that exists among the variables that affect air quality (Woods, 1991; Woods and Rask, 1988). In this model, Ci is the indoor concentration, and Vr is the recirculation airflow rate. The dilution rate, Vo, represents infiltration, natural ventilation, or mechanical ventilation with outdoor air. In terms of controlling airborne allergens, the removal rate, E, represents the capacity of air conditioners, filters, and other such removal devices. The efficiency of the removal device, e, is defined in terms of the contaminant being removed. Exposure to allergens can be controlled by removing or minimizing the sources, i.e., by reducing the net

FIGURE 7-1 One-compartment, uniformly mixed, steady state model for indoor air quality control. In steady state, an energy or mass balance for the model can be expressed as Ci - Co = N - E / Vo where:

Co = concentration of contaminant in outside makeup air,

Ci = concentration of contaminant indoors (occupied space),

Cu = concentration of the contaminant upstream of the air cleaner,

Cd = concentration of the contaminant downstream of the air cleaner,

Vo = dilution rate (i.e., infiltration, natural or mechanical ventilation rates),

Vr = air flow rate through air cleaner,

e = efficiency of the air cleaner,

N = net generation rate, and

E = removal rate.

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