have equal capacities such that the combined capacity of
appliances and equipment shall be delivered outdoor
the three boilers shall satisfy 120 percent of the total peak
of the building through the use of breaching, vent, stack
load of heating and humidification requirements. For
and chimney systems. breaching connecting fuel-fired
southern climates, a minimum of two equally sized units
equipment to vents, stacks and chimneys shall generally
at 60 percent of the peak capacity (each) shall be
be horizontal and shall comply with NFPA 54. Vents,
provided. The units shall be packaged, with all
stacks and chimneys shall generally be vertical and shall
components and controls factory preassembled. Controls
comply with NFPA 54 and 211. breaching, vent, stack, and
and relief valves to limit pressure and temperature must
chimney systems may operate under negative, neutral, or
be specified separately. Burner control shall be return
positive pressure and shall be designed relative to the flue
water temperature actuated, and control sequences, such
gas temperature and dew point, length and configuration
as modulating burner control and outdoor air reset, shall
of the system, and the value of the insulation techniques
be utilized to maximum efficiency and performance.
applied to the vent. Venting materials may be factory
Multiple closet type condensing boilers shall be utilized, if
fabricated and assembled in the field and may be double
or single wall systems depending on the distance from
controls capable of connecting to and interoperating with
adjacent combustible or noncombustible materials.
a BACnet or LONWORKS Direct Digital Control (DDC)
Material types, ratings and distances to adjacent building
Building Automated System. Boilers shall have a
materials shall comply with NFPA 54 and 211.
minimum efficiency of 80 percent as per ASHRAE
Hot Water Pumps. Pumps shall be of a centrifugal type
Individual boilers with ratings higher than 29 MW (99
and shall generally be selected to operate at 1750 RPM.
million Btu/hour) or boiler plants with ratings higher
Both partial load and full load must fall on the pump
than 75 MW (256 million Btu/hour) are subject to review
curve. The number of primary hot water pumps shall
by the Environmental Protection Agency.
correspond to the number of boilers, and a stand-by
pump shall be designed for each hot water circuit.
Boilers shall be piped to a common heating water header
Variable volume pumping systems shall be considered
with provisions to sequence boilers on-line to match the
for all secondary piping systems with pump horsepower
load requirements. All units shall have adequate valving to
greater than 11.2 kW (15 hp). The specified pump motors
provide isolation of off-line units without interruption of
shall not overload throughout the entire range of the
service. All required auxiliaries for the boiler systems shall
pump curve. Each boiler group pumps shall be arranged
be provided with expansion tanks, heat exchangers, water
with piping, valves, and controls to allow each boiler
treatment and air separators, as required.
group to operate independently of the other boiler
Gas Trains: Boiler gas trains shall be in accordance with
International Risk Insurance (IRI) standards.
Freeze Protection. Propylene glycol manufactured
Automatic Valve Actuators: Gas valve actuators shall not
specifically for HVAC systems shall be used to protect
contain NaK (sodium-potassium) elements since these
hot water systems from freezing, where extensive runs
pose a danger to maintenance personnel.
142 F A C I L I T I E S S T A N D A R D S
Revised March 2005 PBS-P100