2.12.2.5 ADDITIONAL DESIGN CONSIDERATIONS
(a) New Construction: A designated reserve space shall be provided, and shown
on the drawings, for a future chiller equal in size to the largest machine
being furnished. The space planning shall also include space for circulating
pumps, cooling tower, electrical starter, etc. associated with future
chiller. The chilled and condenser water mains and the chilled water
distribution loop shall be sized, valved, and arranged to accommodate the
future chiller.
(b) Chiller/Accessories Arrangement:
(1) The piping arrangement shall be such that each chiller shall have a
dedicated condenser water pump, cooling tower fan and a primary chilled water
pump. When the chiller is not in operation, its dedicated condenser and
chilled water pumps and the cooling tower fan shall also be inoperative.
(2) Chilled water and condenser water circuits shall be piped for complete
functional flexibility. Provide cross connections for the chilled water pumps
and condenser water pumps, suctions and discharges, and condenser inlets and
outlets, and cooling tower cells to increase flexibility. Provide automatic
on/off valves, where necessary, to avoid pumping through an inoperative
chiller and cooling tower. Investigate the need to provide primary/secondary
piping-pumping arrangement as described below.
(3) Primary/Secondary Arrangement: The chilled water flow through the
evaporators shall be kept constant. The chilled water flow through the
cooling coils, however, shall be variable with automatic, two-way, modulating
control valves controlling the flow. A primary/secondary piping arrangement,
shown in Central Chilled Water Plant Flow Diagram 2.12.3, shall be used to
ensure hydronic separation between primary and secondary loops.
(4) Tertiary Arrangement: For a campus type of facility where multiple
buildings are served by the central chilled water plant, or where all cooling
load is not scheduled to be activated at the same time, tertiary
piping/pumping arrangement shall be provided, as shown in Secondary
Distribution Interface Flow Diagram 2.12.5. Tertiary systems shall also be
considered where the secondary pumping head could become excessive without
tertiary pumps or where the chilled water temperature entering the system
need to be higher than the chilled water temperature leaving the chiller(s).
(5) Chilled Water Temperature Differential: The chilled water temperature
differential across the chiller be optimized but shall not be less than 12
degrees C (10 degrees F) Consider the impact of piping, pumping cost, cooling
coil performance, and chilled water piping arrangement in order to optimize
the chilled water differential.
(6) Chilled Water Filter: A cartridge type of water filters shall be provided
across pumps per VA Standard Detail 15705.16. The filter capacity shall not
be more than 1 percent of the total flow in circulation.
(7) Cooling Tower Water Treatment: Water treatment for the cooling towers
shall be provided and the equipment location shall be shown on the drawings.
The equipment location shall make an allowance for the chemical drums (in use
and spares) and their movement in and out of the chilled water plant. If the
chemicals feed pump is interlocked with the cooling tower flow, the treatment
HVAC DESIGN MANUAL
2-40
HVAC SYSTEMS AND EQUIPMENT
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