necessary offsets and mechanical couplings or flanges to permit removal of
heads and tubes.
(b) The floor plans and at least two cross sections shall be drawn at 1:50
(1/4") scale to show clearances and access spaces. The designer shall not
rely on the construction shop drawings to be assured of the adequate
maintenance space.
2.12.13.3 CALCULATIONS: Pump head calculations shall be based on the actual
piping layout and takeoffs. Add an additional 10 percent safety factor to the
total calculated pump head.
inches and larger, the pipe support shall be engineered and all
supports/hanger sizes and locations shall be shown on drawings. In addition,
the interface of the upper attachment of the pipe hangers shall be
coordinated with the structural drawings; auxiliary steel, as required to
support the pipe hangers from the building structure, shall be shown on the
drawings. The designer shall submit complete engineering calculations to the
VA to ensure compliance with this requirement.
2.12.13.5 VARIABLE SPEED DRIVES
(a) Variable/Constant Flow Pumps: With variable flow chilled water systems,
variable speed drive pumps shall be used for the secondary and tertiary
chilled water distribution systems. The designer shall ensure that all
distribution pumps are equipped with the variable speed drive packages rather
than only one or two pumps within the distribution system. This design
feature is essential to ensure that all secondary pumps, while operating in
parallel, run at the same speed and double up the same pumping head.
Otherwise, with one constant speed pump and another variable speed pump, both
connected in parallel, a situation could develop where the check valve of the
variable speed pump may not be able to open, particularly at lower operating
speeds.
(b) Existing Systems: The use of the variable speed drives shall be carefully
evaluated for the existing chilled systems, where three-way automatic control
valves are furnished for the cooling coils. For such retrofit applications,
the existing 3-way valves must also be changed to 2-way automatic control
valves and pressure differential assembly along with variable speed drive for
pumps.
2.13 SMOKE AND FIRE PROTECTION
2.13.1 GENERAL
2.13.1.1 The HVAC systems for the VA facilities shall be designed to meet the
requirements of the National Fire Protection Association codes, NFPA 45, 72E,
90A, 96, 99, and 101, and the additional provisions outlined in this section.
The local building codes, with the provisions in excess of these
requirements, are not legally binding on the VA. The A/E shall, nevertheless,
familiarize himself with these requirements, discuss their stringency and
applicability with the VA, and resolve the need to implement them in the
system design.
HVAC DESIGN MANUAL
2-48
HVAC SYSTEMS AND EQUIPMENT
Previous Page
