5.10 Primary Heating Systems
Also, the use of steam for HVAC applications shall be
limited to the conversion of steam heat to hot water heat
and for use in providing humidification. Steam shall not
be used as a heating medium for distribution throughout
GSA prefers low-temperature hot-water heating systems;
a building to terminal units, air-handling units, perimeter
207 kPa (30 psi) working pressure and maximum
heating units, coils, or any other form of heat transfer
temperature limitation of 93.3C (200F). Supply
where steam is converted to a source of heat for use in
temperatures and the corresponding temperature drops
space comfort control or environmental temperature
for space heating hot water systems must be set to best
control.
suit the equipment being served. Total system temperature
drop shall not exceed 16.7C (30F). The temperature
Steam delivered from any source other than a clean steam
drop for terminal unit heating coils shall be 11.1C (20F).
generation system shall be prohibited from use in
Design water velocity in piping shall not exceed 2.4 m/s
providing humidification. Steam delivered from a central
(8 fps) or design pressure friction loss in piping systems
plant, a district steam system, steam boilers, or any
shall not exceed 0.4 kPa/m (4 ft per 100 ft), whichever is
equipment where chemicals are delivered into the
larger, and not less than 1.2 m/s (4 fps).
medium resulting in the final product of steam shall not
be used for the purpose of providing humidification to
District Steam Heating
the HVAC system or occupied spaces.
GSA buildings are built for the long-term; therefore, it is
Hot Water Heating Systems
prudent for GSA to provide the building heating system.
District steam heating, if available, may be considered
The use of electric resistance and/or electric boilers as
if determined to have long-term reliability and can be
the primary heating source for the building is prohibited.
economically justified through a life cycle cost analysis.
Design and layout of hydronic heating systems shall
In the event District steam heating is utilized, appropriate
follow the principles outlined in the latest edition of the
space must be provided to allow GSA to install boilers and
ASHRAE Systems and Equipment Handbook.
associated equipment at a later date. If steam is furnished
to the building, such as under a district heating plan, it
Boilers. Boilers for hydronic hot water heating
shall be converted to hot water with a heat exchanger in
applications shall be dual fuel (natural gas and No. 2 fuel
the mechanical room near the entrance into the building.
oil) low pressure, with a working pressure and maximum
If steam heating is used, the designer shall investigate the
temperature limitation as previously stated, and shall
use of district steam condensate for pre-heating of
be installed in a dedicated mechanical room with all
domestic hot water. Steam heating is not permitted inside
provisions made for breaching, flue stack and combustion
the building other than conversion of steam-to-hot water
air. For northern climates, a minimum of three equally
in the mechanical room.
sized units shall be provided. Each of the three units shall
141
MECHANICAL
ENGINEERING
5.10
Primary Heating Systems
Revised March 2005 PBS-P100
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