For the baseline fan power limitation, the pressure drop allowances are defined. I am a bit fuzzy on the definition of "Return/Exhaust Control Devices". A system with a return fan and OA economizer typically has dampers to control the flow of the OA, return/exhaust air streams. Would these dampers qualify as a Return/Exhaust Control Device?
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Christopher Jones, P.Eng.
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Here is an abstract from 90.1 User?s Manual that answers your question:
Pressure Drop Adjustment Devices
This section provides a description of the
types of devices that quality for additional
fan power. ?
???
Return and/or exhaust airflow control devices.
Some types of spaces such as laboratories,
test rooms, or operating rooms require
that an airflow control device be provided
at both the supply air delivery point and at
the exhaust. The exhaust airflow control
device is typically modulated to maintain a
negative or positive space pressure relative
to surrounding spaces. An additional
pressure drop and associated brake
horsepower adjustment is permitted when
this type of device is installed. The credit
may be taken when some spaces served by
an air handler have exhaust airflow devices
and other spaces do not. However, the
credit is taken only for the CFM of air that
is delivered to spaces with a qualifying
exhaust air flow device.
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Maria Karpman LEED AP, BEMP, CEM
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HI Chris,
The base fan power allowance already includes the necessary pressure drop for return/exhaust dampers in the air handler. The adjustment for exhaust/return control devices refers to damper boxes or other devices used to control space pressurization like you would typically find in a laboratory or hospital.
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Michael Tillou, PE, LEED AP BD+C, ASHRAE BEMP
Associate
Atelier Ten
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