5.7 Mechanical and Service
air-cooled condensers or recirculating water-cooled
condensers connected to a cooling tower or evaporative-
cooled condenser. Water-side free cooling shall be utilized
For cooling loads greater than 281 kW (80 tons), chilled
A minimum of 4 percent of each floor's gross floor
water air-handling systems shall be considered in a life
area shall be provided on that floor for air-handling
cycle cost analysis. A dedicated chiller(s) is preferred,
equipment. Where additional equipment is required,
unless other parts of the building also require 24-hour
additional space on that floor shall be provided as needed.
cooling. The dedicated chiller plant shall provide some
A minimum of 1 percent of the building's gross area shall
means of redundant backup, either by multiple machines
be provided for the central heating and cooling plant
or connection to the facility's larger chilled water plant.
(location to be agreed upon during preparation of
concept submission). All mechanical equipment rooms
In large computer installations [areas of 465 m2 (5,000 sq.
shall be a minimum of 3.7m (12 ft.) in height. Space
ft.)] it is recommended to segregate cooling of the sensible
requirements of mechanical and electrical equipment
load (computer load) and control of the outdoor air
rooms shall be based upon the layout of required
ventilation and space relative humidity by using two
equipment drawn to scale within each room.
separate air-handling systems. In this design, one unit
recirculates and cools room air without dehumidification
Service Access. Space shall be provided around all HVAC
capability. This unit is regulated by a room thermostat.
system equipment as recommended by the manufacturer
The second unit handles the outdoor air load, provides
and in compliance with local code requirements for
the required number of air changes and humidifies/
routine maintenance. Access doors or panels shall be
dehumidifies in response to a humidistat. This scheme
provided in ventilation equipment, ductwork and
avoids the common problem of simultaneously
plenums as required for in-site inspection and cleaning.
humidifying and dehumidifying the air.
Equipment access doors or panels shall be readily
These systems shall be provided with an alternative
operable and sized to allow full access. Large central
power source, connected to emergency generators, if the
equipment shall be situated to facilitate its replacement.
computer room houses critical components. Consult
The HVAC design engineer shall be cognizant of the
GSA's Office of the Chief Information Officer to
necessity to provide for the replacement of major
determine which computer rooms meet this requirement.
equipment over the life of the building and shall insure
that provisions are made to remove and replace, without
Vehicle Garages. Vehicle garage exhaust fans
damage to the structure, the largest and heaviest
generally be activated based upon carbon monoxide
component that cannot be further broken down.
sensors within the garage. Carbon monoxide sensors shall
In addition, adequate methods of access shall be included
also be located in all floor areas where vertical shafts
for items such as: chillers, boilers, air-handling units, heat
penetrate the garage areas.
exchangers, cooling towers, reheat coils, VAV terminals,
pumps, water heaters and all devices that have
maintenance service requirements.
Mechanical and Service Space Requirements
Revised March 2005 PBS-P100