5.8 HVAC Components
If ventilation air is delivered through the VAV terminal,
the minimum volume setting of the VAV terminal shall
equal the larger of the following:
Air-Handling Units (AHU). All air-handling units,
Use 30 percent of the peak supply volume, or
including dedicated outdoor air ventilation units,
Use 2 L/s per m2 (0.4 cfm/sq.ft.) of conditioned zone
dedicated perimeter pressurization units, floor-by-floor
area, or
air-handling units, and air-handling units serving special
Use a minimum outdoor airflow to satisfy ASHRAE
areas, shall be sized to not exceed 11,800 L/s (25,000 cfm).
Standard 62 ventilation requirements.
Smaller units are encouraged to facilitate flexible zone
Supply, Return and Relief Air Fans: Centrifugal double-
control, particularly for spaces that involve off-hour or
width double-inlet forward curved and airfoil fans are
high-load operating conditions. To the extent possible,
preferable for VAV AHUs. All fans shall bear the AMCA
"plug-n-play" AHU configurations shall be considered,
seal and performance shall be based on tests made in
facilitating easy future adaptations to space-load changes.
accordance with AMCA Standard 210. Fans shall be
Psychrometric process charts shall be prepared for each
selected on the basis of required horsepower as well as
air-handling unit application, characterizing full and part
sound power level ratings at full load and at part load
load operating conditions. Air-handling unit/coil designs
conditions. Fan motors shall be sized so they do not run
shall assure that conditioned space temperatures and
at overload anywhere on their operating curve. Fan
humidity levels are within an acceptable range, per
operating characteristics must be checked for the entire
programmed requirements, Table 5.1, and ASHRAE
range of flow conditions, particularly for forward curved
Standard 62.
fans. Fan drives shall be selected for a 1.5 service factor
and fan shafts shall be selected to operate below the first
Depending on sensible heat ratio characteristics, effective
critical speed. Thrust arrestors shall be designed for
moisture control may require cooling coil air discharge
horizontal discharge fans operating at high static pressure.
dew point temperatures as low as 10.0C (50F). As
required, provide face-by-pass or heat recovery features to
Coils: Individual finned tube coils shall generally be
re-heat cooling coil discharge temperatures for acceptable
between six and eight rows with at least 2.1 mm between
space entry. Provide a direct form of re-heat and/or
fins (12 fins per inch) to ensure that the coils can be
humidification only if space conditions require tight
effectively and efficiently cleaned. Dehumidifying coils
environmental control, or if recurring day-long periods
shall be selected for no more than negligible water droplet
of unacceptable humidity levels would otherwise result.
carryover beyond the drain pan at design conditions. All
hot water heating and chilled water cooling coils shall
Particular attention shall be given to the volume control.
be copper tube and copper finned materials. Equipment
Zone loads must be calculated accurately to avoid
and other obstructions in the air stream shall be located
excessive throttling of air flow due to oversized fans and
sufficiently downstream of the coil so that it will not
terminal units. Diffusers shall be high entrainment type
come in contact with the water droplet carryover. Cooling
(3:1 minimum) to maximize air velocity at low flow rates.
coils shall be selected at or below 2.5 m/s (500 fpm) face
134 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
5.8 HVAC Components
Revised March 2005 PBS-P100
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