Trane TRG-TRC014-EN Glossary, parallel fan-poweredterminal unit A fan-poweredVAV terminal unit

Glossary

fan speed control Method of supply-fan modulation that affects the capacity of a fan by varying the speed of rotation—commonly accomplished using a variable-speed drive on the fan motor.

fan-powered terminal unit Type of single-duct VAV terminal unit that can provide heating for a space by mixing warm plenum air with the cool primary air, using a small terminal fan.

inlet vanes Method of supply-fan modulation that affects the capacity of a fan by “pre- swirling” the air in the direction of fan wheel rotation before it enters the wheel. The inlet vanes lessen the ability of the fan wheel to “bite” the air, reducing its airflow capacity.

interior space A conditioned space that is surrounded by other conditioned spaces, with no perimeter walls or windows. Typically requires some degree of cooling all year long to overcome the heat generated by people, lighting, and so forth.

occupied mode Typical daytime operating mode of the system. The building must be ventilated and the comfort cooling or heating temperature set points must be maintained in all occupied spaces.

optimized static-pressure control Optimized method of VAV system static- pressure control that uses the benefit of DDC control, to continuously reset the static pressure set point of the system so that the VAV terminal requiring the highest inlet pressure is nearly wide open.

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.

perimeter space A conditioned space with walls and windows that are exposed to the outdoors. In most climates these spaces would require seasonal cooling and heating.

pneumatic control Method of terminal unit control using pressurized air to operate the airflow modulation-device actuator. The actuator consists of an inflatable bladder and a return spring.

pressure-dependentVAV control scheme that uses the space temperature sensor to directly control the position of the modulating device. The actual airflow delivered to the space is a by-product of this position and depends on the duct-system static pressure at the inlet of the terminal unit.

pressure-independentVAV control scheme that directly controls the actual volume of primary air that flows to the space. The position of the modulation device is not directly controlled and is basically a by-product of regulating the airflow through the unit. Because the airflow delivered to the space is directly controlled, it is independent of inlet static pressure.

primary air Conditioned air delivered by a central supply fan to a terminal unit.

series fan-powered terminal unit A fan-powered VAV terminal unit

consisting of a primary airflow modulation device and a small, integral

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