Use a dedicated 100-percent outdoor air ventilation
point drops below 2.8C (37F), the unit shall have the
distribution system ducted through an air flow control
capacity to maintain neutral pressure in the perimeter
device (air flow measuring station) to the return side
zones with respect to the outdoors.
of the floor-by-floor air handling units. In this case, the
Floor-by-floor Air-Handling Units. The building shall
system shall be provided with a means of bypassing the
have multiple, horizontally zoned, recirculating, Variable
floor-by-floor air-handling unit during unoccupied hours.
Air Volume (VAV) air-handling units. The air-handling
The dedicated 100-percent outdoor air ventilation
units shall provide all of the required conditioning for
systems shall be completely independent of any other air
the spaces they serve, and shall deliver conditioned supply
distribution system. Building exhaust air heat recovery
air to the perimeter and interior heating and cooling
shall be provided to precondition the outdoor air.
systems. Floor-by-floor air-handling units shall utilize
VAV terminals or fan-powered VAV terminals.
When determining the capacity of the dedicated 100-
percent outdoor air ventilation system, the designer must
The VAV supply fan shall be designed for the largest block
consider diversity in the calculation of ventilation
load, not the sum of the individual peaks. The air-handling
demand. In addition, the designer must provide building
unit and associated VAV terminals or fan-powered
air balance calculations (including: outdoor air, supply air,
terminals shall have self-contained microprocessor
return air, and exhaust air) verifying that the largest of
controls capable of connecting to and interoperating with
the two DOAVS sizing requirements (ventilation or
a BACnet or LONWORKS Direct Digital Control (DDC)
pressurization) has been met.
Building Automated System.
Supply air dew point leaving the air-handling unit shall
All underfloor air distribution air-handling units and
be maintained at 10.0C (50F) and the supply air dry
systems shall be designed in accordance with the GSA
bulb temperature leaving the air-handling unit shall be
PBS Guidelines for Raised Floor Systems, with and without
a minimum of 12.8C (55 F) and not greater than 25.6C
Underfloor Air Distribution (RF/UFAD Guidelines). Any
(78 F) during occupied hours. During occupied hours,
design parameters or design criteria contained in the
this unit shall operate to deliver conditioned ventilation
RF/UFAD Guidelines supersede those herein.
air directly to the occupied spaces to both supply the
required ventilation air flow rates and to maintain
Perimeter and Interior Heating and Cooling Systems.
positive pressure in the perimeter zones with respect to
Perimeter and interior zones shall have a baseline
outdoor air pressure. During unoccupied hours, the
perimeter heating and cooling system selected from one
DOAVS air-handling unit shall run at reduced capacity
of the following four options depending on the specific
(the minimum of either 30-40% of supply capacity or
application and building configuration:
as required by calculation) to provide conditioned air at
Use a ducted overhead variable air volume (VAV) air
10.0C (50 F) dew point and at least 21.1C (70F) to
distribution system with VAV terminals with hot water
maintain positive pressure in the perimeter zones with
heating coils for cooling and heating, supplemented
respect to outdoor air pressure. When the outdoor air dew
(where required) with hot water finned-tube radiation, or
126 F A C I L I T I E S S T A N D A R D S
FOR THE
PUBLIC
BUILDINGS
SERVICE
5.4 HVAC Baseline System
Revised March 2005 PBS-P100
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