What is a Variable Air Volume System ?

• VAV systems supply constant temperature and vary the volume of air as against a conventional system which supplies a constant volume and varies the air temperature.
• Operating costs are greatly reduced by using less fan energy and less refrigeration energy.
• VAV systems also cut initial cost by taking advantage of building diversity.
• VAV systems gives the owner the flexibility to adapt to changes during or after construction of the building.
• With today’s energy conservation and efficiency requirements, Model ZVAV4 to ZVAV40 are designed for and adaptable to any VAV requirements.
• The latest in control components and options provide maximum flexibility with a wide scope for cost effective innovation.

SALIENT FEATURES

• Available in ZVAV4 to ZVAV40 unit sizes to handle from 400 to 4000 cfm.
• 18 ga. G.I. Opposed balde damper with seals. Damper leakage is less than 2 % of nominal flow.
• 18 ga. G.I. casing, mechanically sealed, low leakage construction.
• Rectangular discharge with slip and drive cleat / TDF Flange duct connection.
• Dual density insulation maximizes acoustical and thermal performance. 33 Kg/cu mtr density.
• Compact low profile design to accommodate tight ceiling spaces. Maximum unit height is only 14” (355) for sizes 4 through 40 upto 4000 cfm (1900 l/s).
• Gauge tapes provided for field calibration and balancing.
• Multi-point averaging Diamond Flow Sensor for pressure independent applications.
• Single point electrical connection.

VAV FOR ‘IAQ’ SENSITIVE APPLICATIONS

• Zeco offers several options for Variable Air Volume applications where the maintenance of an extremely high indoor Air Quality is highly critical or a primary concern. Specific ‘IAQ’ lining are designed to address issue of fiberglass insulation eroding and entering the airstream.
• Zeco’s Fiber-Free lining is thick, closed cell electrometric foam. The lining has excellent insulating characteristics and provide acoustical attenuation also.
• The foam does not absorb water, reducing the likelihood of mole or bacterial growth.
• The Fibre-Free lining surface is smooth, so that dirt and debris won’t accumulate.

VARIABLE VOLUME BOXES-TYPES
All of the VAV boxes described below have some common components :

• Corrosion resistant zinc coated steel casing.
• Sound absorbing internal insulation.
• Erosion resistant facing and a throttling damper to control conditioned air.
• Associated controls-Analog or Electronic.

SINGLE INLET / SINGLE OUTLET TYPE
Operation : The VAV box reset s the volume (variable air volume) of conditioned air delivery to the spac in response to the room thermostat. The Box can handle hot or cold air.

BYPASS VAV BOX TYPE
Operation : the VAV box delivers conditioned air to the space during periods of maximum cooling requirements ( as determined and signaled by the room thermostat). As cooling demands diminish, the unit damper is modulated to bypass increasing amounts of conditioned air to the ceiling plenum. The result is a variable volume air supply to the space while a relatively constant volume of air is maintained across the central system air handling unit.

PRESSUE INDEPENDENT
A device is said to be pressure independent when the flow rate passing through it is maintained constant regardless of variations in systems inlet pressure.

The pressure independent control is achieved with the condition of 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. The preset volume can be varied between calibrated minimum or the maximum limits by the thermostat output.

The logarithmic graph illustrates pressure independent boxes typical airflow settings and characteristics, the vertical lines 1a -1b and 3a-3b represent the calibrated minimum and maximum airflow settings respectively, that are adjusted at the flow controller. Line 2a-2b represents any intermediate airflow settings maintained by the flow controller in response to thermostat demand. The damper will modulate (open and close) as required to hold the airflow setting constant up and down this vertical line regardless of upstream static pressure variations. Airflow will only change when the thermostat signal (demand) changes. The vertical lines are cut off by diagonal line 1a-3a, which represents the minimum operating static pressure requirement of the terminal unit for the given airflow – the pressure drop across the Box with the damper in the fully open position.

Pressure independence assures the proper distribution of air of the conditional space as required and allows the engineer to know that the design limits specified will be maintained. Maximum and minimum airflow limits are important for maintaining proper air distribution.

• Maximum airflow limits prevent over-cooling and excess noise in the occupied area.
• Minimum airflow limits assure that proper ventilation is maintained.