Supply and Exhaust Fans

Exterior wall and roof-mounted supply or exhaust fans should be avoided; connect interior fans with ductwork and louvers.

Except for interior wall-mounted propeller units, all fans should be centrifugal type and connected directly to weatherproof louvers or roof vents via ductwork.

• Fans larger than 2000 CFM (944 1/s) should be provided with V-belt drives.

• Care should be taken to prevent the noise level generated by exhaust fans and
associated relief louvers from being transmitted to the exterior of the building.
Any in-line fans located outside the main mechanical and electrical areas should
be provided with acoustical enclosures to inhibit noise transmission to the adjoin­
ing occupied spaces, depending on occupant use.

Where possible, exhaust fans in all buildings in housing, recreational, hospital, and administrative areas should be of the centrifugal type, discharging through louvers in the side wall of the building using ductwork, as necessary. Roof-mounted fans of the low-silhouette type may be used.

Centrifugal type roof exhausters should be used in shop, flight line, or ware­house areas. Where exhaust ventilating fans or intakes are provided in buildings, a positive means (gravity dampers are not acceptable) of closing the fan housing or ducts should be provided to prevent heat loss in cold weather, except as prohibited by NFPA Standard 96.

7.16.2 General Items

Incorporate the following:

• Ventilation for VAV systems will ensure proper ventilation rates at low and high
system airflow.

• Year-round supply (makeup) air should be provided to equal the total quantity
of all exhaust hoods.

• Where desirable, incorporate a purge mode into system design. This mode could
be used, for example, to purge the building with outside air during off-hours or
to purge the affected zone during building maintenance, such as painting.

• The toilet rooms and janitor closet should be exhausted at a rate of 2 CFM/ft²
(10 1/s/m²) by insulated in-line fans to maintain a negative room pressure. The
required makeup air for the exhaust system should be from undercut doors or, if
necessary, through door grilles. Exhaust registers, in lieu of grilles, should be pro­
vided in areas with rigid ceilings.

• Shower areas have a 2.5 CFM/ft² (131/s/m²) exhaust rate to maintain a negative
room pressure.

• Where practical, photocopiers, laser printers, and print equipment should be
located in a separate room. Copy rooms with photocopiers and laser printers
should not be directly conditioned, but should be maintained at a negative pres­
sure relative to adjacent areas by exhausting air from these adjacent areas directly
to the outdoors. All conditioned supply air to the room should be exhausted and
not returned to the air-handling unit system due to contaminants.

• Mechanical and electrical equipment rooms should be ventilated and cooled with
outside air by thermostatically controlled fans set to operate when the tempera­
ture exceeds 85°F (29°C).

• The boiler room should be ventilated and cooled with outside air at a minimum
rate of 20 air changes/h by a thermostatically controlled supply or exhaust fan set
to operate when temperature exceeds 85°F (29°C). Supply fans should be used
when atmospheric burners are permitted.

The fire protection room should be ventilated and cooled with outside air by

a thermostatically controlled fan set to operate when the temperature exceeds

85°F (29°C).

Provide exhaust fans in laundry rooms sized for a minimum of 3-min air changes.

Automotive maintenance shops must be provided with a suitable engine exhaust

ventilating system. General ventilation should be provided at 1.5 CFM/ft²

(81/s/m²) of outside air.

Battery rooms should be ventilated at a rate of four air changes per hour.

Дата добавления: 2015-11-16