This method Statement shall cover the Supply, Installation, testing and commissioning of VAV Variable Air Volume System in line with project requirements as indicated in the approved HVAC shop drawings, specifications and VAV manufacturer’s instructions.
Arrange following tools before starting the VAV installation and testing activities:
- Mechanical Tool Box
- Electric Drill Machine
- Step Ladders
- Threading Machine
- Solvent Cement
- Electric welding machine. (if required)
- Pipe Cutting Machine
- Grinding Machine
- Pressure Gauge
- Mobile Scaffolds
- Staging Platforms
General Installation Procedure for Variable Air Volume
The terminal shall have a round duct connection and a rectangular discharge suitable for flanged duct connection.
Terminal casing shall be minimum 20 gauge and or based on the duct size galvanized steel internally lined with non-porous.
The casing shall be designed for hanging by sheet metal straps.
Terminals with internal actuator mounting or linkage connection must include gasketed access panel removable without disturbing ductworks.
All pneumatic tubing shall be “UL” listed fix retardant type.
Note: HVAC System Ducting & Connection shall be as per the project Specification as mentioned below:
The main supply & return trunk ducts should be internally lined with acoustic glass fibre insulation.
Main supply trunk duct includes ductwork up to the branches leading to the VAV boxes.
Insulation should be between 24-48 kg per cubic meter, and be at least 25 mm thick.
The insulation shall be produced from strong resilient glass fibre firmly bounded together with a thermosetting resin.
Facing shall be made of stable woven glass fibre promoting no fibre migration.
VAV Boxes and diffusers should be selected to achieve maximum NC rating of 25.
The ducting from the VAV box to the diffuser should be lined with acoustic insulation, at least 25 mm thick.
Ducting to supply air diffusers or VAV boxes should be straight and unobstructed for at least 4 duct diameters upstream of the diffuser.
The supply ducting should not include a damper within at least 4 duct diameters upstream of a supply diffuser.
All ducting in mechanical rooms shall be externally covered with 50 mm of glass fibre insulation and lagged with limp coating having a surface density of at least 20kg/ml.
Flexible duct connections should be provided between all fans and ductwork.
Resilient thrust restraints should be incorporated into the flexible connections to eliminate loading of the flexible connection. The restraints should be steel spring isolators having a static deflection of at least 19mm.
Wall or floor duct penetrations should allow for a 13mm clearance around the duct.
The gap should be stuffed with glass fibre insulation and sealed with non-hardening caulking. The duct should be supported on both sides of the wall.
Variable Air Volume units should be mounted as high in the ceiling space as possible, at least 2m away from any return air opening.
Final Installation Requirements
The VAV’s shall be installed using at least two support brackets with anti-vibration rubber under the terminal.
Ensure that each of the brackets shall be fixed with two threaded rods to ceiling or slab above.
VAV’s shall prevent the body of the VAV terminal from high mechanical tension, which could damage the construction and performance of the terminal.
Ensure to provide some flexibility to the final location of the VAV Terminals.
Use at least 1 x diagonal straight duct length before the VAV inlet.
Ensure that additional manual volume control dampers before the inlet are not required/ recommended.
Ensure that all connections are thermally isolated.
Pressure sensing tubes or air flow sensor shall not be “kinked” or otherwise obstructed by the external duct insulation.
Place the factory installed/ calibrated VAV controller on the VAV terminal by placing the opening of the actuator over the damper shaft extended from the box.
Ensure that terminal ends of the enclosure are over a flat area of the box or mounting bracket must be used.
Electrical Connection to VAV Terminals
The VAV must be electrically supplied to the required power as recommended by the manufacturer.
Locate the terminals on the outside edge of the VAV terminal strip and connect to the power source.
Do not supply power with any other power requirement other than what is required. Connect power to the VAV by connecting wires from the transformer to Terminals.
The terminals are labelled on the edge of the VAV. The red indicator LED under the board clam shell cover will illuminate when the power is properly connected.
For connections to the VAV, strip the wire back approximately 3/16 inches and insert into the terminal block.
Back out the screw on the terminal block until the bare wire inserts fully, and turn the screw back down until there is firm tension on the wire.
Ensure that the clamp secures the stripped portion of the wire and that no insulation is under the clamp.
It is recommended that zones or specific areas are powered in groups, and that not all controllers within the system are powered from a single transformer.
All communication wiring must be connected such that the plus (+) terminal is wired to a plus terminal and the minus (-) is wired to a minus terminal.
Do not install communication cables near power cables or in power conduits. Isolate all communications wiring from large motors, fluorescent lighting fixtures or other sources of high intensity electromagnetic interference.
Ensure that each controller must have a unique address setting for proper operation.
The VAV provides predetermined analogue & digital inputs for variable air volume terminal control. Connect all sensors and output cable drain wires to earth ground.
Connect the room sensor:
The room sensor monitors the space ambient temperature, as well as optional setpoint adjustment and system override function.
In addition, the sensor can be provided a jack, which allows connection to the individual controller with a laptop through the room sensor.
Connect the duct sensor:
The duct sensor monitors the incoming supply air temperature and allows the reverse operation of the damper upon a high entering duct temperature.
Mount the sensor upstream from the VAV box in the branch duct according to the manufacturer’s installation instructions.
Make sure that the sensor is in a straight section of the duct, and install at least 5 duct diameters ahead of box and away from elbows.
Connect the digital outputs:
Take note that the maximum current for each digital output is 1 amp at 24 V (AC or DC).
The digital outputs on the VAV are for low voltage, pilot duty switching.
Do not attempt to switch line voltage (120V or higher) through the digital outputs, serious damage may be done to the VAV controller.
Pre-Commissioning Procedure for VAVs / CAVs
Ensure that the VAVs / CAVs installation is complete & mechanical completion is approved.
Make sure that the VAVs with 12 point flow cross type of averaging air flow sensor installed as per approved drawings.
Ensure that no damage occurs between mechanical completion & pre-commissioning. Ensure that proper access is available for VAVs & CAVs. Repair all damages to the equipment galvanizing finish.
Check VAVs / CAVs are installed as per the approved shop drawings and manufacturer’s instructions. Check the sensing grids tubing connection from the grids to the transducer is correct & secure.
Make sure the proper mounting of the actuator on the body of the VAV / CAV.
Check that the thermostats as per approved material submittal are fixed.
Also check duct connections and grilles as per approved shop drawing and respective method statement & are cleaned internally & externally.
Check all VCDs, BDs and fire dampers are open.
Check for proper electrical power, control and earthing connections as per manufacturer’s recommendations. Field wiring to be pre-tested for continuity and insulation resistance.
Ensure that VAVs & CAVs are interfaced with the BMS system.
Ensure the precommissioning & commissioning of AHUs is complete in line with the approved procedure.
Check & ensure that the thermostat LCD display features are in line with the approved material submittal.
- Visual inspection to ensure that all DDC panels, sensors, actuators and other system devices are installed as per the approved point list, schematic drawings and specifications.
- Check the wiring of field devices with DDC panel is correct & completed
- Set the MAC address in Controller using DIP switch.
- Supply the power to the DDC controller.
- Connect the DDC controllers to the MSTP net work.
- Assigning the software addresses to the DDC controllers
- Save the DDC controllers & their properties to the Configuring Database.
Commissioning Procedure for VAVs / CAVs
Ensure that all the precommissioning checks are carried out successfully.
- Configure the input/output settings in the DDC program.
- Download the DDC program to the DDC controller.
- Check the space temperature and set point through thermostat.
- Check the modulating action of the VAV damper actuator as per the required cooling set point of temperature.
- Check communication of all the VAVs from the Building Management System Supplier-end and it should be able to access all the data points of each VAV controller through BMS graphics.
Ensure that the AHU is operating & sufficient air flow is obtained at the suction of the VAV/CAV.
Check for proper suction & discharge of air through the VAV / CAV.
Change the thermostat setting & check for the modulation of the damper in the VAV/CAV.
Check for proper operation of the actuators.
Check the entry of air through the induction port using a rotating vane anemometer.
Measure & record the value due to changes in the thermostat setting in form.
Check for any undue vibrations / noise.
Complete air balancing of the entire HVAC system shall be carried out in line with the approved procedure.
During air balancing the VAV flow rate shall also be measured & recorded in the performance record sheet.