Download Applications Engineering Manual - Chilled

Glossary
optimal start. An optimized morning warm-up routine that determines the
length of time required to bring the zone from its current temperature to the
occupied setpoint temperature, and then waits as long as possible before
staring the system, so the zone reaches the occupied setpoint just in time for
scheduled occupancy.
optimal stop. An optimized system shutdown routine that determines how
early heating and cooling can be shut off for each zone, so that the indoor
temperature drifts only a few degrees from occupied setpoint by the end of
the scheduled occupied period.
outdoor air. Air brought into the building from outside, either by a
ventilation system or through openings provided for natural ventilation.
parallel fan-powered terminal unit. A fan-powered VAV terminal unit
consisting of a primary airflow modulation device and a small, integral
constant-volume fan packaged to provide parallel airflow paths.
PCO. Photocatalytic oxidation. An air cleaning technology that uses
ultraviolet light shining on the surface of a catalyst to adsorb gaseous
contaminants (such as VOCs) and inactivate biological contaminants.
perimeter zone. A conditioned space with walls and windows that are
exposed to the outdoors. In most climates these spaces would require
seasonal cooling and heating.
plenum. The space between the ceiling and the roof or the floor above.
plenum fan. A fan assembly consisting of a single inlet impeller, mounted
perpendicular to airflow, which pressurizes a plenum chamber in the air
distribution system.
population diversity. The ratio of the actual system population to the sum
of the peak zone populations.
pressure-dependent. VAV control method that uses the zone temperature
sensor to directly control the position of the air-modulation damper. The
actual airflow delivered to the zone is a by-product of this position and
depends on the static pressure inside the duct at the inlet to the terminal unit.
pressure-independent. VAV control method that directly controls the actual
volume of primary air that flows to the zone. The position of the airmodulation damper is not directly controlled and is simply a by-product of
regulating the airflow through the unit. Since the airflow delivered to the
zone is directly controlled, it is independent of inlet duct static pressure.
primary air. Conditioned air delivered by a central supply fan to a terminal
unit.
psychrometric chart. A tool used to graphically display the properties of
moist air.
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Chilled-Water VAV Systems
SYS-APM008-EN