velocity to minimize moisture carryover. Heating coils
Plenum Boxes: Air-handling units shall be provided with
shall be selected at or below 3.8 m/s (750 fpm) face
plenum boxes where relief air is discharged from the air-
velocity.
handling unit. Plenum boxes may also be used on the
return side of the unit in lieu of a mixing box. Air-flow
Drains and Drain Pans: Drain pans shall be made of
control dampers shall be mounted on the ductwork
stainless steel, insulated and adequately sloped and
connecting to the plenum box.
trapped to assure drainage. Drains in draw-through
configurations shall have traps with a depth and height
Mixing Boxes: Air-handling units shall be provided with
differential between inlet and outlet equal to the design
mixing boxes where relief air is discharged from the air-
static pressure plus 25 mm (1 inch) minimum.
handling unit. Mixing boxes may also be used on the
return side of the unit in lieu of a plenum box. Air flow
Filter Sections: Filters shall be sized at 2.5 m/s (500 fpm)
control dampers shall be mounted within the mixing box
maximum face velocity. Filter media shall be fabricated so
or on the ductwork connecting to the mixing box.
that fibrous shedding does not exceed levels prescribed by
ASHRAE 52.2. The filter housing and all air-handling
Terminals. VAV terminals shall be certified under the ARI
components downstream shall not be internally lined
Standard 880 Certification Program and shall carry the
with fibrous insulation. Double-wall construction or an
ARI Seal. If fan-powered, the terminals shall be designed,
externally insulated sheet metal housing is acceptable.
built, and tested as a single unit including motor and fan
The filter change-out pressure drop, not the initial clean
assembly, primary air damper assembly and any accessories.
filter rating, must be used in determining fan pressure
VAV terminals shall be pressure-independent type units.
requirements. Differential pressure gauges and sensors
Air leakage from the casing of a VAV box/terminal shall
shall be placed across each filter bank to allow quick and
not exceed 2% of its rated capacity. Units shall have
accurate assessment of filter dust loading as reflected by
BACnet or LONWORKS self-contained controls.
air-pressure loss through the filter, and sensors shall be
Fan-powered terminals: Fan-powered terminals shall have
connected to building automation system.
ECM motors for speed control to allow continuous fan
UVC Emitters/Lamps: Ultraviolet light (C band) emitters/
speed adjustment from maximum to minimum, as a
lamps shall be incorporated downstream of all cooling
means of setting the fan airflow. Units shall have BACnet
coils in an air-handling unit, and above all drain pans
or LONWORKS self-contained controls.
to control airborne and surface microbial growth and
Fan-powered terminals shall be equipped with a ducted
transfer. Applied fixtures/lamps must be specifically
return, featuring a filter/filter rack assembly with the
manufactured for this purpose. Safety interlocks/features
filters having a Minimum Efficiency Reporting Value
shall be provided to limit hazard to operating staff.
(MERV) of 10 (60% - 65% efficient with a maximum
Access Doors: Access doors shall be provided at air-
allowable particle size of 1.0 micron) and covered on all
handling units downstream of each coil, upstream of each
external exposed sides with two inches of insulation.
filter section and adjacent to each drain pan and fan
The return plenum box for fan-powered terminals shall
section. Access doors shall be of sufficient size to allow
be a minimum of 610 mm (24 in) in length and shall be
personnel to enter the unit to inspect and service all
double wall with insulation in-between or contain at least
portions of the equipment components.
one elbow where space allows. Fan-powered terminals
135
MECHANICAL
ENGINEERING
5.8
HVAC Components
Revised March 2005 PBS-P100
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