Study Sites
Study Sites
Ventilation-system characteristics of the buildings studied are summarized in Table 4.1. The Norton Simon Museum and the Scott Gallery are modern buildings with custom-engineered heat- ing, ventilation, and air-conditioning (HVAC) systems (Fig. 4.1, p. 78). At the Norton Simon
Museum, make-up air from outdoors passes through a fibrous mat filter (F A1 ), and an activated carbon filter (F A2 ) before being blended with return air that has been passed through a fibrous mat filter (F A3 ). The air mixture is then conditioned for proper temperature and humidity, and distrib- uted to the building. The make-up airflow rate (Q F ) is lower than the original design value, because the supply-air blower (P A1 ) has been shut off to improve temperature control. At the Scott Gallery, the building was originally operated with 25% make-up air, which was blended with the return air, passed through a fibrous filter, conditioned, and then distributed to the building (Nazaroff and Cass 1986). Recently, an activated-carbon filter was added to the system for ozone removal, and the flow rate of make-up air was reduced effectively to zero by closing the intake dampers (again to improve thermal control). At the time of the particular experiments discussed here, air-exchange between indoors and outdoors at the Scott Gallery occurred entirely due to infiltration through cracks in the building shell and through door openings.
Concentration and Fate of Airborne Particles in Museums
Sepulveda House Dimensions
Norton Simon Museum
Scott Gallery
Number of floors 2 1 2 Floor area (m 2 )
330 Wall area (m 2 )
1050 Volume (m 3 )
Ventilation a
Outdoor air exchange (h -1 ) 0.37 b 0.28 ± 0.01 3.6 ± 1.4 Recirculation (h -1 )
Monitoring period
Start date
March 30, 1988 Start time
April 6, 1988 c April 24, 1988
a. Flow rate divided by building volume; mean ± one standard deviation of measurements for 24-hour period. b. Based on hot-wire anemometry measurements of outdoor airflow rate into mechanical ventilation system.
Tracer gas decay yielded 0.40 h -1 with 90% confidence bounds of 0.37–0.44 h -1 . c. Boundary layer flow and temperature differences measured for 24 hours, commencing at 1200 PDT on April 4, 1988.
Table. 4.1. Characteristics of the study sites.
The Sepulveda House is an historical museum with no system for regulating the air temperature, humidity, or ventilation rate. Air exchange is provided by infiltration through rel- atively large openings in the building shell. When the building is open to the public (10 a.m.–3 p.m. daily, except Sunday) and the weather is warm, two downstairs doors are kept open.
At each site, one wall was selected for investigation of boundary-layer airflows and temperature gradients that influence particle-deposition rates. Measurements of particle- deposition rate, reported in Chapter 2, were made on the same walls. Briefly, an interior wall with a painted drywall surface was selected for investigation at the Norton Simon Museum; a painted plywood panel mounted on an interior wall with furring strips was selected at the Scott Gallery; and an outer brick wall with a painted, irregular plaster surface was chosen at the Sepulveda House.
Because these experiments would have been disruptive to normal museum operation, measurements at the Norton Simon Museum and at the Scott Gallery were conducted
Concentration and Fate of Airborne Particles in Museums
while the buildings were closed to the public (although the museum staff was present). Conse- quently, this study does not fully incorporate the effects of occupancy on airborne particle prop- erties. The Sepulveda House was open to the public as usual, from 10 a.m. to 3 p.m., on the day of monitoring.
Measurement and Modeling Results: Aerosol Size Distribution and Chemical Composition