Method Statement for Installation of GI Ducts for HVAC System

This mechanical hvac method statement covers the installation of GI ductwork.

Procedure defines the method used to ensure GI ducting installation has been carried out as per contract requirements and best practices.

The method statement gives details of how the work will be carried out and what health and safety issues and controls are involved.

Safety Measures and Precautions

Always schedule and plan the lifting of the hvac ducts.

Only the required capacity materials will be lifted into the platform and number of person working on high will be observed as per requirement.

The main access to the working platforms will be via proprietary stair.

Lifting equipment will be inspected and registered on a time frame.

Inspection must be shown on lifting equipment by color tagging.

Safety measures will be strictly implemented on site while lifting of materials on high.

Roles and Responsibilities

Project manager shall be responsible overall to complete all MEP works as per specifications, budget, time, & quality.

MEP Site Engineers shall be responsible for but not limited to the following  important activities:

a) To ensure that all the preparation and application works are carried out according to the contract specification and manufacturer’s data sheet(s).

b) To ensure that the progressing of works is carried out according to the planned program, and as per the approved method statement.

c) To ensure that all the equipment’s and materials required in executing the works are available according to the planned construction program.

d) To coordinate with the main contractor’s MEP coordinator and safety officer for all safe and proper execution of the work in accordance with the risk assessment.

e)  To coordinate with the civil team for any area preparation, access, clearance.

Foreman shall be responsible for but not limited to the following important activities:

a) To guide and control the tradesmen and charge-hands(s).

b) To ensure that work is done as per the approved shop drawing(s).

c)  To report to the MEP site engineers.

H& S Officer shall be responsible for but not limited to the following important activities:

a.) Ensure health and safety of the site personnel.

b.) Ensuring PPE available with site personnel

c.) Good housekeeping on site

d.) Environmental concerns are addressed.

e.) Responsible for implementation and assurance of the safety and environmental requirements (JSEA).

Quality control engineers shall be responsible for but not limited to the  following important activities:

a) Inspecting the materials on site as per approved materials submittal prior to installation on site.

b) Inspection for the installation as per approved Method Statement, approved drawings and approved test plans and checklists.

c) Preparing test forms for testing on site and updating results

d) Issuing inspection request within 24 hrs before the actual inspection.

e) Responsible for the assurance of Quality control,  method statement and inspection testing plan

f) Controlling the shop drawings flow on site.

Delivery, Handling and Storage of Materials

The duct material and its associated material supplied will be packed for protection against damage during handling, transport, storage   and installation.

Material to be delivered to the site store in self supporting framed units.

The duct material will be stacked as loose with all material parallel (nested).

Material will be stored in clean and closed store for protection and according to the engineers and manufacturer’s recommendation.

Duct material will be stored in closed shaded area and should be stacked properly with allowable height of 2 meters, and covered with PVC sheets.

Material  not complying  with the Material Submittal or unusable/damaged duct or fittings will be placed in a quarantined area and clearly labelled ready for manufacturer to replace.

General Requirements & Method of Ducts Installation

Determine the position of the ductworks support and mark out on the soffit, marking allowance for insulation thickness and cladding where applicable. Marking out and installation of supports will require the operatives to work at height.

Work platforms which are to be used are to be safe and suitable for purpose. Podium steps and mobile tower scaffolds used in the project areas will be below height of 3 meter. Any work over 3 meters will require a heavy duty scaffold.

Heavy duty scaffold will be erected by 3rd party scaffold company; general scaffold will be inspected and green tagged.

Potable electrical equipment’s used at site (power drill, drop saw, grinder and extension leads are all to be 110V and not damaged.

Power drill will be used to make the holes and screw fittings into the soffit and walls.

Personnel using potable electrical equipment shall wear adequate PPE including but not limited to safety glasses hearing protection dust musk and gloves.

Drill the hole in the concrete for the anchor fixing using the appropriate size drill bit as recommended by the anchor fixing manufacturer, and approved calculations.

Fix support in position with accordance with the approved schedule for supports spacing and sizing. Supports and inserts have to be installed prior to lifting of ducts.

Cross-Linked Closed Cell Polyolefin Foam Duct Insulation is installed above the supports to avoid any possibility of the insulation damage.

GI Duct are pre-fabricated and longitudinally pre-assembled to a maximum length of 1.2m at the workshop as per the construction schedule. Preparation/formation of flanges for transverse joints are made at workshop.

GI Duct received at project site shall be joined together on the floor, to form manageable lengths.

Wherever branch take-off collars are to be fixed, suitable cut out shall be made in the ducts.

The size of cut out shall be equal to the duct cross sectional area and secured using Aluminium pop rivets and the joint between collar flange and duct surface shall be sealed with duct sealant.

Pre-insulated Ducting

Ducts are pre-fabricated in the workshop and longitudinally assembled to a maximum length of 4m.

Preparation for the traverse joints including the fixing of the flanges/profiles as applicable as per the construction schedule is carried out at workshop.

HVAC GI Ducts

Branch take-off collars are tap-in glued type and will have shoe configuration at the take-offs.

Wherever branch take-offs are to be made, suitable cut out shall be made on the main duct with 45° angle cutter to form the 45° female part of the joint.

The branch/take-offs with 45° male cut ends are secured to the main duct by the joining glue.

Joint is sealed with duct sealant and finished with self-adhesive aluminium foil tape.

Pre Installation Checks for GI HVAC Duct Installation

A pre-start meeting prior to the commencement of the ducting works will take place with the Site Engineer, H&S Officer, QC Engineer, and Supervisor/Foreman in charge to address the following:

Ensure that notification to start (where as applicable).

Ensure that the area has been surveyed as per approved drawings.

Ensure that the installation area is clean from debris and foreign matter.

Ensure that materials are as per approved Material Submittal and inspected on site.

Ensure that adequate number of tradesmen and proper tools are present.

Ensure that latest approved shop drawing for this installation is present, and all personnel are working off the same drawing.

Ensure that area is safe to carry out the work.

Area for materials preparation / fabrication work shop for ducting installation has been identified and procedures will be in place.

Eye wash area near in the fabrication areas in case of workers skin contamination with resin or other chemicals.

Temporary electrical DBs are provided and inspected regularly by the electrician prior to execution of the works.

Ensure that the related mock-up is accepted /approved by the consultant.

Checking of Ductwork prior to assembly

Check that all the ductwork is tagged and that the correctly tagged sections are available for the job.

Confirm metal duct sheet is as per approved material submittal.

Check that all duct accessories such as stiffners, turning vanes, flanges, dampers, sleeves etc. are in accordance with the correct size and good condition.

The duct metal sheets tolerances will be based on the following SMACNA standard comply with HVAC duct construction standards for fabrication and installation of metal ductwork.

Gauge USG	Thickness [mm]
	Minimum	Maximum	Nominal
18	1.181	1.441	1.311
20	0.906	1.106	1.00
22	0.7534	0.9534	0.90
24	0.6010	0.8010	0.70
26	0.4712	0.6488	0.56

Check dimensions are correct. Where dimensions are shown on the drawing these are internal dimensions.

• Dimensional tolerances are ±2 mm
• Check that the duct sections and fittings are free from any defects or holes
• Check that the ducting is clean. Clean if necessary.
• Check if the smoke extract duct has the correct fire rating
• Check if the stem ducting materials are as per the approved material.

Installation Method for Horizontal HVAC GI Duct

The layout of duct to be installed shall be as per approved drawing.

Position of duct supports shall be marked on the underside of the slab / structural member/vertical approved drawings.

Threaded rod of suitable size shall be fixed to the mechanical anchor fastener / clamps using proper lock nut.

GI angle, cut to required size of duct (to have clearance of 50mm on either side) shall be fixed to the threaded rod suspension and locked in position by suitable nuts and washers.

Assembled, as above, ducts shall be lifted and shall be installed on trapeze.

Pre-insulated ducts are joined either by glue in type male & female joints or with PVC H bayonet cleats for flanged joints as applicable as per the construction schedule.

Duct sealant is applied at the male and female joint and finished by self-adhesive aluminum tape.

On laying the ducts as detailed above to form the required layout, the ducts shall be properly aligned and leveled to maintain B.O.D. and distances as per approved drawing.

Method for Installation of HVAC Riser / Shaft Duct

GI Duct supports shall be taken at each floor / vertical wall as the case may be and shall be as per approved drawings.

Successive ducts shall be installed starting from low level as the successive higher floors are constructed.

The open end of the upper most ducts shall be sealed properly.

The insulation of the flexible ducts shall be rolled up to 100mm from the edges and the flexible duct shall be slipped on to the collar fixed on the main duct and shall be secured firmly using G.I. Straps and clips.

Then the insulation of flexible duct shall be rolled back and fixed firmly on to spigots and adjoining duct surface and finished with self-adhesive aluminium foil tape.

Flexible ducts installed as above shall be supported using 25mm GI strip wound around the duct and suspended from slab if the flexible duct length exceeds 1.5 meter. Suitable plenum box as applicable shall be connected to main duct through pre-insulated flexible ducts.

Manual volume control dampers as approved shall be fixed in the ducting system wherever mentioned in the drawing.

Fire damper shall be installed as per approved drawing / manufacturer installation details.

Access doors shall be provided for fire dampers wherever applicable.

Diffusers plenum/droppers shall be leveled properly to suit false ceiling.

The ducts are identified (service wise) as per approved identification labels (directional arrows).

After the duct installation QC shall inspect the complete installation and offer the same for consultant’s inspection.

On fixation of final fix items like grilles / diffusers etc. consultant’s engineer shall be invited for final inspection and certification.

Fire Rated Duct Work Method Statement

Ducts for fire rated extracts and smoke system are made of 3mm black steel DW172 standard and SMACNA standard.

Duct to be installed at the same dimension and levels as per the approved drawings.

Horizontal ducts to be supported on GI channels anchored to the soffit.

Vertical duct risers to be supported with GI angles spot welded to the duct and angles bolted to the Gl channel frame.

Ducts will be lifted up mechanically with the help of lifting equipment’s adhering to the safety standard.

Access doors will be provided at every 3 m centres for the cleaning.

For horizontal duct runs access door should be installed at on the side of the duct with the underside of the door at least 40mm above the underside of the duct.

On vertical ducts cleaning doors shall be provided at the bottom of the riser.

Fire rated gasket applied at the transverse joint (companion  angle) between two ducts.

Fire rated flexible connector is used to connect the fire rated duct to the fire rated fans and others fire related equipment’s.

Connection to Equipment and Air Outlets

Flexible Duct Connector:

1-  Cut a length of flexible equal to 1.5 times the perimeter  of the ductwork.

2-  Pop – rivet as necessary  in centres of 100 mm.

3-  Seal using duct sealant as necessary.

Ensure that the equipment and the ductwork are aligned. A maximum misalignment of 30 mm is permitted as per ASHRAE tolerances.

Install flexible connectors immediately adjacent to equipment in ducts associated with fans and motorized equipment supported by vibration isolators.

For fans developing static pressures of 1250 Pa and higher, cover flexible connectors with loaded vinyl sheet held in place with metal straps.

Flexible Duct Installation Method

Cut a length of flex duct that fits the installation site with little to none left over. Stretch the flex duct between  the two points of attachment so that the duct doesn’t sag.

Prevent the duct from bending too much, causing the duct’s width to narrow more than the standard width of the duct anywhere along its length.

Attach the flex duct to the duct fitting with at least 1 foot of the duct around the fitting.

Keep the flex duct in place by wrapping duct tape around the connection at least twice.

Place a metal clamp around the connection and apply paste around the edges of the clamp.

Replace  the jacket of the flex duct by pulling its insulation over the connection.

Tape the jacket into place with at least two layers of duct tape.

Connect terminal units to supply ducts directly or with maximum 1500-mm lengths of flexible duct.

Do not use flexible ducts to change directions.

Connect diffusers to low pressure ducts with maximum 1500-mm lengths of flexible duct clamped or strapped in place.

Connect flexible ducts to metal ducts with draw bands.

Installation of Partition Penetrations

Non-Fire-Rated Partition Penetrations:

Where ducts pass through interior partitions and Exterior walls and are exposed to view, conceal spaces between construction openings and ducts or duct insulation with sheet metal flanges of same metal thickness as ducts. Overlap openings on 4 sides by at least 38mm.

Fire-Rated Partition Penetrations:

Where ducts pass through interior partitions and exterior walls, install appropriately rated fire dampers, sleeves, and fire-stopping sealant.

For full details regarding Duct Dampers and accessories refer to the “Dampers and Accessories” method statement.

Installation Method of Access Doors

Install duct access doors to allow for inspecting, adjusting, and maintaining accessories and terminal units as follows:

On both sides of duct coils.

Downstream from volume dampers, turning vanes, and equipment.

Adjacent to fire or smoke dampers, providing access to reset or reinstall fusible

To interior of ducts for cleaning; before and after each change in direction, at maximum 15-m spacing.

On sides of ducts where adequate clearance is available.

Install the following sizes for duct-mounting, rectangular access doors:

• One-Hand or Inspection Access: 200 by 125 mm.
• Two-Hand Access: 300 by 150 mm.
• Head and Hand Access: 460 by 250 mm.
• Head and Shoulders Access: 530 by 355 mm.
• Body Access: 635 by 355 mm.
• Body Plus Ladder  Access: 635 by 430 mm.

Access  for the fire dampers  and  the kitchen  exhaust  ducts must  be in accordance  with the related NFPA.

Pressure relief access doors

Install the following sizes for duct-mounting, pressure relief access doors:

One-Hand or Inspection Access: 175 mm in diameter.

Two-Hand Access: 250 mm in diameter.

Head and Hand Access: 330 mm in diameter.

Head and Shoulders Access: 480 mm in diameter.