“Hybrid” Application of IFC and NFPA Most local governing bodies will require major repair garages to meet the most stringent requirement, which requires the ventilation system to be sized for 5 ACH. However, it is essential to ensure that at the 5-ACH ven tilation rate the building design and construction do not potentially hinder effective air changes in the ceiling zone. Mechanical ventilation strategies should be reviewed in advance with the AHJ to ensure that effective ventilation is achieved in the ceiling zone. Ventilation Strategies Figure 8. Roof-mounted upblast fan.
Photo courtesy of Gladstein, Neandross & Associates, NREL 44698 The applicable codes do not specifically address how the ventilation is to be achieved. Most facilities rely on exhaust fans to move air out of the facility. In this case, make-up air is provided via natural draft through openings such as doors and louvers, or by mechanical means such as make-up air units. Facilities that were not designed with rooftop exhaust fans instead feed make-up air into the space with interlocked electronically actu ated gravity vents in the ceiling to maintain proper air balance.
The codes require that the exhaust be through the roof of the structure and that makeup air be provided from near floor level. can pull air through exhaust ductwork serving specific areas of the ceiling zone as shown in Figure 10. Most existing maintenance facilities are equipped with roof-mounted fans, some of which may be rated for use in Class I, Division 2 areas. In some cases, existing roof- mounted fans can be used with minimal modifications for compliance with CNG vehicle maintenance facility requirements. Roof-mounted fans require certain charac teristics to be suitable for use in a CNG vehicle mainte nance facility.
For example, the fan blades and shrouds must be constructed from non-sparking materials A variety of approaches are available, each with advan tages or disadvantages based on factors such as 1) the local governing body’s decision regarding applicable code, 2) the design and construction of the existing facil ity and its ability to accommodate modifications, 3) the climate in which the facility is located (i.e., warm weather versus cold weather and related air-tempering energy costs), 4) ease of operation, and 5) cost. Ventilation approaches are based on factors such as: 1. The local governing body’s decision regarding applicable code Figure 9. Direct fan intake with louvers.
Photo courtesy of Gladstein, Neandross & Associates, NREL 44700 2. The design and construction of the existing facility and its ability to accommodate modifications 3. The climate in which the facility is located 4. Ease of operation 5. Cost. The most common form of facility ventilation is a roof- mounted upblast fan that vents into the atmosphere (Figure 8). These exhaust fans can pull air directly from the space via the fan inlet as shown in Figure 9, or they Figure 10. Intake ducting used to evacuate air from specific areas. Photo courtesy of Gladstein, Neandross & Associates, NREL 44701 COMPRESSED NATURAL GAS VEHICLE MAINTENANCE FACILITY MODIFICATION HANDBOOK 12