generation rate (N), by increasing the rate of removal of allergens from air (E), or by diluting airborne allergens (Vo). For some allergens, which are airborne only sporadically and in association with specific human activities (e.g., house dust mite allergens), source control is the best option. For others (e.g., outdoor allergens such as pollen) removal by filtration (E) is the usual method.

The physical causes usually associated with problem buildings include two basic inadequacies: (1) design inadequacies, which include system and equipment problems, and (2) operational inadequacies, which consist of inappropriate control strategies, lack of maintenance and housekeeping, and ineffective load management of building systems (Cone and Hodgson, 1989; EPA, 1991a; Molhave, 1987; Morey, 1984, 1988; Morey and Singh, 1991; NRC, 1987b; Robertson, 1988; Stolwijk, 1984; Woods, 1988, 1989a, 1989b, 1991). Table 7-1 summarizes some of the data on the physical causes of problem buildings.

The remainder of this section on principles and strategies discusses various source and exposure control strategies as they relate to building design, HVAC system design, building operation, and remediation. This is followed by a section that summarizes some practical control strategies in general, and as they apply to residential and commercial buildings. The chapter ends with conclusions and recommendations.

TABLE 7-1 Frequencies of Occurrence of Physical Causes of Problem Buildings Reported by Two Independent Investigative Teams

 

 

Frequencies (%) of Occurrence

Problem Category

Physical Cause

Woods

Robertson

Design

System problems

 

 

 

Inadequate outdoor air

75

64

 

Inadequate air distribution to occupied spaces (supply and return device)

75

46

 

Equipment problems

 

 

 

Inadequate filtration of supply air

65

57

 

Inadequate drain lines and drain pans

60

63

 

Contaminated duct work or duct linings

45

38

 

Malfunctioning humidifiers

20

16

Operations

Inappropriate control strategies

90

NA*

 

Inadequate maintenance

75

NA

 

Thermal and contaminant load charges

60

NA

* NA, not available.

SOURCES: Woods, 1989a; Robertson, 1988.



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