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VAV Terminals


Variable Air Volume (VAV) Terminals

Variable air volume (VAV) devices are duct-mounted terminal units which modulate the amount of conditioned air that enters the space. A damper located in the supply airstream modulates the amount of conditioned air that enters the space in response to space thermostat requirements.

VAV boxes may be broadly classified into two types: pressure independent and pressure-dependent. Both pressure-independent and pressure-dependent VAV boxes modulate the amount of air delivered to the space based on requirements from the space thermostat. By allowing the airflow quantity to vary, in proportion to the cooling load in the space, large savings in fan energy can be realized since most systems rarely operate at their maximum capacity for more than a few hours each year.

A pressure-independent box delivers a constant amount of air regardless of pressure fluctuations inside the ductwork. On the other hand, airflow quantity fluctuates along with duct pressure for a pressure-dependent VAV box. Hence, the higher the duct pressure, the higher the airflow quantity for a pressure-dependent VAV box. Pressure-dependent VAV boxes do not control to a specific air volume quantity, instead they modulate a primary air damper inside the VAV box in response to the amount of cooling or heating required in the space. Pressure-dependent boxes are generally less expensive than pressure-independent boxes and should not be used on systems with widely varying duct pressures.

VAV boxes usually have an adjustable minimum position damper to allow the minimum acceptable airflow quantity to be defined while some boxes "shut-off" completely.

Various types of control systems are available and range from pneumatic or electric and may be either system-powered (from duct pressure) or from an external electric power source. In order to modulate the quantity of air delivered from the central station air handler, special fan controls are required including inlet guide vanes, variable speed drives, variable frequency drives, fan discharge dampers and variable pitch controls. Sophisticated direct digital (DDC) controls available today allow the actual airflow quantity to be controlled at each VAV box. This information can then be used to monitor and record space operating conditions such as total airflow rate, ventilation rate, temperature and relative humidity.

35D Single Duct VAV Terminals

The 35D single duct variable air volume (VAV) unit provides cooling only or cooling with reheat to meet all your application needs. The 35D is offered in 11 sizes covering an air delivery range from 45 to 4000 cfm.

37HS Moduline VAV Terminals

Carrier's 37HS Moduline terminals offer: heating and cooling distribution from the same terminal with automatic changeover and control, a full range of system (duct pressure) powered controls which offer both volume and temperature control without separate energy control supply. Integral linear slot diffusers available with one-way and 2-way direction, multiple slots, and heating/cooling options.

37HC Moduline VAV Terminals with Product Integrated Control (PIC)

Carrier's 37HC Moduline terminals offer: heating and cooling distribution from the same terminal with direct digital (DDC), automatic changeover control, a full range of system (duct pressure) powered controls which offer both volume and temperature control with a direct digital communication link to the central station air handler. Integral linear slot diffusers available with one-way and 2-way direction, multiple slots, and heating/cooling options.

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