Question: How Does VAV System Work?

What are VAV boxes used for?

These terminal units, commonly referred to as VAV boxes, are used to control the volume and, sometimes, the temperature of air entering a designated space.

There are a few different types of terminal units used in today’s developments: single duct, parallel fan-powered, and series fan-powered..

What is VAV terminal load?

Variable air volume (VAV) systems control the dry bulb temperature inside a zone by varying the supply air volume instead of the air temperature. At full cooling the VAV terminal unit damper is fully open supplying the specified maximum design air flow rate.

How does a fan powered VAV box work?

With a parallel fan-powered variable air volume (VAV) system, each zone is conditioned by a box with a small fan that draws-in plenum return air and mixes it with supply air from a primary system. … If the primary air is at minimum flow and heat is required, the fan is started, introducing warm plenum air to the zone.

What are VAV fans called?

Axial fans are used in VAV applications, but the use of centrifugal fans is more common.

What is bypass VAV?

Bypass VAV system responds to changing cooling or heating requirements by varying the quantity or volume of air delivered to each zone. An HVAC unit delivers a constant volume of air to the system. … A Bypass VAV box provides constant or variable airflow depending on the temperature demands of the space.

How do I choose a VAV box?

electing the inlet size of a variable air volume (VAV) terminal box requires the consideration of five factors: (1) pressure drop across the box; (2) ability of the VAV box controller to measure and control the desired minimum and maximum airflow setpoints; (3) first costs of the VAV box, its installation, and controls …

How does a HVAC damper work?

HVAC dampers work by being situated closer to the mouth of the distribution pipe and will push or hold air from that point as needed. The pressure in the pipe will then redistribute the airflow to whatever zone requires regulating at that time.

How does VAV reheat work?

Typical VAV with Reheat System The supply air temperature is held constant at 55°F. When a zone falls below its set point, the damper closes and reheat is enabled. When a zone is above its set point, the damper opens fully to allow as much 55°F air as possible into the zone to cool the space quickly.

Where are VAV systems used?

Traditionally, single-zone VAV has been used for larger, densely occupied zones that have variable cooling loads. Common examples include gymnasiums, cafeterias, lecture halls, auditoriums, large meeting rooms, churches, and arenas.

How does pressure independent VAV work?

The pressure independent control is achieved with the addition of a flow sensor and flow controller to the VAV box. The controller maintains a preset volume by measuring the flow through the inlet and modulating the damper in response to the flow signal.

What is difference between AHU and FCU?

In simple terms, an air handling unit (AHU) is a component of an HVAC system that cools and distributes air into the space through a duct. A fan coil unit (FCU) is a standalone system that circulates the existing air in a small space, but it can also be a part of an HVAC system.

What does Cav mean in HVAC?

Constant air volumeConstant air volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC) system. In a simple CAV system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space.

What is a FCU in HVAC?

A fan coil unit (FCU) is a device that uses a coil and a fan to heat or cool a room without connecting to ductwork. Indoor air moves over the coil, which heats or cools the air before pushing it back out into the room.

What is a VAV system?

Variable Air Volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. … Because the supply air temperature, in this simplest of VAV systems, is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served.

What is difference between VAV and CAV?

Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant temperature.

How many types of VAV are there?

twoThere are two primary types of VAV systems—single-duct and dual-duct.

How do you balance a VAV system?

Start balancing the VAV boxes closest to the discharge of the supply fan. Set the box to a call for full cooling. Measure actual air volume and compare to the BAS system indicated air volume. If not the same adjust the VAV box flow coefficient until actual and indicated air volume is the same.

What is the purpose of a reheat coil?

The coil is supplied with hot water or steam, or in some cases might use an electric resistance heater. The reheat coil acts as a shim, a backup in case the designer’s load estimate isn’t exact. Occupant comfort and humidity control still can be achieved through judicious use of reheat.