Specifications

GF-2030 Benchmark Series Boilers
TAG-0047_0G Gas Supply Design Guide
PR1 10/04/13 AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, New York 10913 • Phone: [phone] Page 3 of 10
GENERAL
AERCO Benchmark Low NOx gas fired boilers are modulating input devices that require an adequate volume of natural
gas at constant pressure for proper operation. The gas requirements specified in this document must be satisfied to
ensure efficient combustion. Designers and installers must adhere to the AERCO specifications and those of the local
authorities having jurisdiction. A thorough understanding and knowledge of these guidelines is required for the
successful design and installation of Benchmark Low NOx series boilers.
Gas Train Components
AERCO Benchmark gas-fired boilers are equipped with standard UL approved/FM compliant gas trains. These gas
trains are factory tested and fired, with a minimum number of modular components. The gas train components have
been designed to operate at high combustion efficiencies by closely controlling both the volume and air/fuel mixture to
the burner. The major internal gas train components are:
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SAFETY SHUT OFF VALVE (SSOV) With BUILT-IN SUPPLY GAS REGULATOR - An electro-hydraulic gas valve,
containing a proof of closure switch, is utilized to stop fuel from flowing into the gas train of the boiler. This is a 100%
tight shutoff device with a visible window indicator showing valve position. Reliable, and a standard industry
component, this valve is factory piped with a low gas pressure switch on the inlet side of the valve which monitors the
manifold pressure for minimum supply conditions. There is also a high gas pressure switch installed on the outlet side
of the gas valve, which shuts down the boiler if gas manifold pressures exceed maximum conditions. On all BMK750
to BMK 3000 models, the actuator has a built-in regulator that replaces the need for an external supply regulator for
installations that have supply pressure of up to 14.0” W.C. This does not apply to the BMK 6000 units, which have a
minimum supply pressure of 14” W.C. For installations that have supply pressure greater than 14.0” W.C., see the
“Gas Pressure Requirements” section.
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AIR/FUEL VALVE - The air/fuel valve controls the volume and mixture of air and fuel in perfect proportion throughout
the entire modulation range of the boiler. The valve utilizes one common shaft to simultaneously vary the gas port
area and air volume. The gas portion of the valve is a slide port type valve with linear proportion-to-position
characteristics. The air side uses a butterfly type valve for adjusting the air volume. The driver of the valve shaft is a
precision stepping motor which provides continuous positioning from full input to minimum fire. The air/fuel valve also
contains two proof-of-position switches.
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CAST ALUMINUM BLOWER ASSEMBLY - A cast aluminum pre-mix blower ensures the precise mixing of air and
fuel prior to entering the burner thereby providing controlled combustion.
* LOW NOx BURNER – The burner provides the actual point of air/fuel contact and combustion into the cylindrical
combustion/heat exchanger. Fabricated from metal fiber mesh covering a stainless steel body, the burner is stable
throughout the entire input range of the boiler. The spark igniter and flame detector for the combustion supervision
system are part of this assembly. The burner is easily removable from the boiler.
GAS PRESSURE REQUIREMENTS
AERCO Benchmark Low NOx series boilers require a stable natural gas and propane input pressure. For Benchmark
Models BMK 750 through BMK 3000, the nominal inlet supply pressure to the boiler is 7.0” W.C. The allowable gas
inlet pressure range is 4.0” W.C. (min.) to 14.0” W.C. (max.) when firing at maximum input, except for the BMK 750
and BMK 1000 when operating with propane, in which case the minimum propane inlet pressure is 7.0” W.C.
for the BMK 750 and 10.0” W.C. for the BMK 1000. A low supply gas pressure switch in each gas train prevents the
boiler from operating without sufficient pressure. Maximum allowable gas pressure is 14.0” W.C. for BMK 750 through
BMK 3000 boiler sizes. Gas pressure should be measured when the unit is in operation (firing). Measure the gas
pressure with a manometer at the 1/8” NPT ball valve provided at the SSOV inlet. In a multiple boiler installation, gas
pressure should initially be set for single boiler operation, and then the remaining boilers should be staged on at full
fire, to insure gas pressures never fall below the supply gas pressure when the single unit was firing.
The Benchmark BMK 6000 Model requires a minimum stable gas pressure of 14” W.C. The maximum allowable gas
pressure for the BMK 6000 is 2.0 psig. As with all other BMK sizes, a low supply gas pressure switch is provided in the
gas train to prevent operation without sufficient gas pressure.