Dietetic Equipment
Refer to PG-18-6
Sterilizers and Washers
Refer to PG-18-6
Laundry Presses and Ironers
860 kPa (125 PSI)
Terminal Humidifiers (Duct
105 kPa (15 PSI)
Mounted)
2.9.4 PRESSURE REDUCING VALVES (PRV) AND PRV STATIONS
2.9.4.1 Pressure Services: Provide PRVs for each of the following:
(a) Radiators and Convectors: For the heating system involving radiators and
convectors, the steam pressure reduction shall be in two (2) stages: from HPS
to 206 kPa (30 Psig), and from 206 kPa (30 Psig) to 34 kPa (5 Psig).
(b) For air handling units and related equipment, that is, heating coils,
unit heaters, heat exchangers, central humidifiers, domestic hot water
heaters, and dietetic equipment, covert HPS or MPS to 206 kPa (30 Psig). Use
local 2nd stage PRV station for equipment, which require less than 206 kPa
(30 Psig) steam.
(c) Usually 413 kPa (60 PSIG) steam is required for sterilizing and
laboratory equipment. Refer to Equipment Reference Manual, PG-18-6. Use
second Stage PRV Station for equipment that requires less than 413 kPa (60
Psig) steam.
domestic hot water, humidification, and equipment (process) load. For
equipment load, use 100 percent steam consumption of the largest single user
plus 25 percent steam consumption of all other users.
2.9.4.3 Where a single PRV would exceed 102 mm (4-inch) size or the turn-down
ratio (maximum load/minimum load) is greater than 10, provide two PRVs in
parallel, approximately 1/3 plus 2/3 with a single by-pass. Where the steam
service includes capacity for future expansion, size all PRV station
components for the future capacity. Size the PRVs for the present load only.
Show globe valves to by-pass the main shut-off valves.
2.9.4.4 Size the PRV by-pass valve and the safety valve according to National
Board Inspection Code of the National Board of Boiler and Pressure Vessel
Inspectors (Columbus, Ohio). Size the safety valve to handle the maximum flow
of the largest PRV or the by-pass. Verify that the by-pass valve capacity
does not exceed the capacity of the safety valve.
2.9.4.5 Mechanical Equipment Rooms: The rooms in which PRV stations, pumps,
converters, heat exchangers, etc., are located, shall be of suitable size to
permit easy access for maintenance. If duplex condensate pump is installed in
a pit, the starter, disconnect switch, and alternator are to be located
outside the pump pit. See VA Standard Detail 15705-27.
2.9.5 STEAM PIPING
2.9.5.1 Size steam piping according to ASHRAE Guide and Data Books. See
Master Specifications, Section 15705, "HVAC PIPING SYSTEMS" for piping
materials.
HVAC DESIGN MANUAL
2-22
HVAC SYSTEMS AND EQUIPMENT
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