The packaged air handling unit (AHU) shall be factory assembled units in factory fabricated casings. Each unit shall be complete with aerofoil centrifugal blowers, motors, drives and guards, cooling coil and drain pans, air filters, structural mountings, vibration isolators and all other necessary accessories. The units shall be tested, rated and constructed in accordance with relevant ARI standard, ASHRAE Standard and America Safety Code B91. The blowers and cooling coils of the units shall have the specifications and capacity ratings as states in the technical schedule.
Air Handling Unit
AHU Casing
The casing shall be fabricated from the best quality corrosion resistance electron-galvanized sheet steel and finished externally with oven-baked-on paint. It shall be properly reinforced and braced for rigidly with steel angle. The casing shall be made up in sections to accommodate the fan, the coil, condensate tray and the filters. Mating joints shall be flanged and bolted together with 1/8” thick gaskets to form a continuous air tight seal. Housing shall be supported from floor or ceiling as indicated in the drawings. The casing shall be double-skinned lined internally with corrosion resistance GI sheet to prevent condensation and control noise emission. Insulation material sandwiched between the doubled skinned panel shall be either 2 inches, 24 kg/m3 fibreglass or equivalent injected (thermal and acoustically) foam having a spread of flame index not greater than 0 and a smoked developed index not greater than 3 when tested on exposed face in accordance with AS 1530.3. Prior to the fixing of insulation all casing shall be treated with an approved anti-corrosive treatment. Condensation on any external parts of the casings will not be permitted. Install insulation in such a manner as not to be disturbed if panels are removed. Secure insulation to the casing surfaces and framework with adhesive over the entire surface. Cover insulation with inner casing wall. Neoprene coated fabric shall be used to connect the unit to the ductwork. Each unit shall be mounted on spring isolators. Ceiling hung units shall be mounted on a rigid steel channel or angle frame with shall then be suspended from hanger rods through spring isolators. External galvanised sheet steel shall be of 1.6mm (16 gauge) thick and the internal wall shall be constructed of galvanised sheet steel of 0.6mm (24 gauge) thickness. Fully gasket individual unit sections between flanged joints and fasten together with lock boilers, nuts and bolts to produce an airtight assembly.
Blower and Blower Sections of Air Handling Unit
The blowers of each air-handling unit shall be double width, double inlet and of centrifugal airfoil type. The whole blower, shaft and motor assembly shall be statically and dynamically balanced to ISO quality grade G6.3 and complete with matching housing, Bearings shall be heavy duty self-aligning ball type amply sized for the loads with factory-sealed lubrication and with provisions for re-lubrication externally thru grease nipples. The ball bearing shall be designed for a life not less than 50,000 hours. (ISO B10, 90 survival). The blowers shall be vee-belt driven (minimum 2 belts) by a squirrel-cage type high efficiency A.C induction motor. The vee-belt shall be able to withstand 1.5 times the duty requirement. Motors must be constructed with totally enclosed fan cooling. Motors shall be suitable for 415 volts, 3-phase, 50 cycle supply and 1450 rpm designed for continuous operation. Appropriate starter to comply with TNB Regulation shall be used to limit the in-rush starting current. A method of motor mounting giving full belt adjustment shall be incorporated. The maximum outlet velocity of the blowers shall not exceed 2200 fpm. The blower section shall be manufactured of heavy gauge galvanised steel or aluminium angle members securely bolted and braced with galvanised steel panels. The panels shall be double-skinned insulated with 50mm minimum thickness of neoprene coated fibreglass insulation with a density of not less than 2.0 1b/ft3 and faced with perforated mate face. The casing and all accessories shall be given a protective enamel finish. All metal parts of the units shall be chemically cleaned, phosphatised and coated with oven-baked enamel finish.
Cooling Coils and Coil Sections
The cooling coils of each air-handling unit shall be of cartridge type, removable from either side of casing and supported the entire length in tracks. All coils of more than one row deep should be provided with staggered tube pattern. The coils shall constructed of copper tubes and have a minimum outside diameter of 5/8 ins. tubing shall be individually finned with corrugated aluminium or copper ins warrant under tension and having not less than fins per inch and not more than 12 fin per inch. There shall be minimum of 6 rows of interlaced copper tube to cool and dehumidify the total air-flow. Fin design shall be suitable for operation up to 600 fpm face velocities without moisture carrying over. The maximum design face velocity shall be 550 fpm or less. The coils fitted with the headers shall have a suitable distribution network designed to provide uniform distribution of chilled water over the face of the coils. All coil tube joints must utilize high-temperature brazing alloys. The coils shall be designed for a maximum working condition of 300 psig for cooling. Coil section shall be manufactured the same as the fan section. Coil section with cooling coils shall have drain pan constructed of heavy gauge stainless steel sloped towards centre and with drain connection on the side. The exterior of pan shall be adequately insulated to prevent condensation being formed on the outside.
Face and Bypass Damper
Face and bypass dampers shall be fitted to the all Cinemas AHUs. The damper blades shall be opposed acting type with damper contact rod rotating on nylon bushes and mounted in a rigid galvanised steel damper frame. Each of the Face and Bypass damper shall consist of two sets of dampers, the face damper and the bypass damper. The face damper shall be located directly in front of the cooling coil and the bypass damper shall be located above the coil. This arrangement permits air to bypass the cooling coil for part load control. When one of the dampers is fully opened the other should be fully closed. The bypass arrangement reduces the capacity of the coil by decreasing the amount of air passing over the coil. However, as air flow through the coil is decreased, the remaining fan CFM passes through the bypass to maintain a constant air volume to the air distribution system. This face and bypass damper shall be from the AHU manufacturer. Dampers assembly must be approved by the Consultant before manufacturer to ensure they air of heavy duty type and withstand the operating condition. On application employing face and bypass section, the fan selection and air distribution system must be designed for an air quantity 10% above design dehumidified air volume. This additional air quantity compensates for leakage through a fully closed bypass damper and for air quantity variations when the dampers are in intermediate positions. Dependable heavy duty motorized damper motor shall be installed which shall be activated by a temperature controller installed at the returned end. An off-coil temperature sensor shall be installed after the coil to maintain a constant off-coil temperate by modulating the proposed two-way control valve. The operation shall be Proportional and Integral for optimum control of room temperature and humidity.
Air Handling Unit Filters
Pre-filters and secondary filters shall have an A.F.I dust extraction efficiency of not less than 75% and 95% respectively. Pre-filters shall be of the washable type while secondary filters may be of the disposable or washable type. They shall be arranged in sufficient numbers to operate at the correct manufacturer’s rating. The filters shall be supported on both sides by 12 gauge wire mesh or not more than 4 ins. square in a filter frame of rust proof construction of 18 gauge steel. The filter frame shall consist of an outer section and a quick release removable gate section from which the filter only can be removed for changeover and/or washing. Each A.H.U. shall have 2 stage filter located before the coil.
Vibration Isolators
Factory engineered spring isolators shall be provided with neoprene in double deflection with the optimum deflection for the loading. Suitable mounting channels shall be provided for floor mounting use with the vibration isolators.
Insulation
The blower and cooling coil sections shall be internally insulated and vapour sealed with mastic compound or equivalent.
Condensate – Drip Tray
A suitable designed durable rust proof stainless steel drip tray shall be provided with each air-handling unit. It shall be insulated with sufficiency designed thick PE insulated sheet to prevent condensation and sweating. The drip tray shall be graded to a drain pipe extended throw the unit casing. The drain pipe shall be minimum 32 mm the trapped drain design shall ensure correct condensate drainage and maintain a water seal during unit start-up and operation. Calculation shall be submitted to substantiate the water seal properties.
Technical Submittal Requirements
The following information is to be included and shall form the basis of the shop drawing submittal.
The listed information is to be provided for each unit type and size:
- Detailed construction specification sheets.
- Manufacturer’s latest published data for dimensions, materials, accessories and installation details.
- Full technical rating data based on tests in accordance with current AMCA standards. Include manufacturer’s certified fan performance curves, and certified sound power ratings. Correct all ratings and curves for altitude and temperature.
- Factory test reports initiated by technician who performed test.
- Certified fan performance curves indicating volume- pressure-speed-horsepower characteristics from shut off the free delivery.
- Certified sound power ratings with octave band analysis.
- The type and size of fans being provided.
- The fan motor kW and electrical power characteristics.
- The fan brake kW per unit at:
- 100% flow
- Specified conditions
- 80% flow (maintaining external static)
- 60% flow (maintaining external static)
- Minimum flow (state minimum air flow as % of specified flow)
- Technical data for the motor, including manufacturer’s name and location.
- Plans, elevations and sections of the unit, dimensioned in inches and in millimetres showing clearance required on each side and top of unit as well as the location and access to the following components:
- Fan motor drive, belts, bearings
- Cooling coils
- Filters
- Construction of access panels and method of fastening.
- Unit control diagrams.
- Operating, maintenance, and service instruction and manuals.
- Single line electrical diagrams of all wiring internal to unit.
Quality Assurance
Construct units in compliance with all requirements of the latest edition of the Air Movement and Control Association’s (AMCA) certified rating standards for air moving equipment.
Test, rate and certify unit’s performance characteristics, including cooling coils.
Filters shall be U.L. listed.
Rate filter efficiency, as measured by the Atmospheric Dust Spot Efficiency Test, weight arrestance and dust holding capacity in accordance with the test procedures of ASHRAE Standard 52.
All components shall comply with Fire for flame spread and smoke develop characteristics.
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Site Execution of Air Handling Unit
Installation
Install as per manufacturer’s recommendations and as shown on drawings. Follow SMACNA recommended procedures.
Manufacturer shall provide supervisory, testing, and start-up personnel as required.
Provide flexible connections to prevent separation of equipment from ductwork and to prevent metal to metal contact.
Install air handling units with proper support and vibration isolation as specified in section entitled ‘Vibration Isolation’.
Provide sufficient clearance around equipment for access and servicing of equipment and its components. Install equipment such that fans, coils, valves, access doors, filter, electrical components, etc. are readily accessible and unobstructed.
Bump start fans to check that fan wheel rotation is correct. For fans not rotating in proper direction, correct them.
Tighten and align belts, taking into account design of drive. Do not over tension belts.
Check all belts and fasteners to ensure proper tightness.
Check bearings and motor for lubrication; do not over lubricate. Use lubricants recommended by manufacturer.
Connect all chilled water and drain piping to unit in approved way and in accordance with drawings.
Acoustical Acceptance Test
General
Air handling unit shall be subject to a full scale mock-up test demonstration, witnessed by Employer’s representatives. The Manufacturer must demonstrate, as per the following specification, that the specified sound level as defined in the ‘Schedule of the Noise level of the Designated Room’ is achieved.
The test set-up shall be conducted at the manufacturer plant or at the project building, which will be constructed by the Contractor. Delivery and set up of the AHU, including ductwork construction inside of the fan room, electrical connections, and any other necessary work, shall be conducted by the Manufacturer or its designated representatives.
Air Handling Unit
The test unit shall be standard manufactured equipment, able to deliver the design air flow against the design external static pressure and shall be shown in the schedules in the design drawings, satisfying all specified requirements explained elsewhere in this specification. The unit must be tested with a temporary 50Hz power source, 415 Volts, arranged by the Contractor.
The variable speed control device, fan motor, and all related electrical components, shall be identical models, and shall be mounted in the cabinet exactly as units shall be sent for the project. Substitution or remote placement of any such components for the purpose of the test shall not be acceptable. Provide 19mm thick waffled neoprene pad isolators to be installed beneath the structural supports.
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Ductwork Construction Inside of Fan Room
The Contractor shall supply ductwork connection from the AHU discharge to the point where the duct exist the fan room. Supply ductwork out of the fan room shall be constructed and shall be shown on the design drawing, to provide optimum airflow conditions and sound attenuation. The supply ductwork shall be constructed per SMACNA standards.
Internal acoustical lining should be provided in ductwork. In the AHU supply plenum, acoustical duct lining as specified in “Casings” should be used; and the remainder of the ductwork is to be lined with 25mm thick, mat faced, 24 kg/m3 (1½ lb/ft3) fibreglass duct liner. The manufacturer shall submit drawings showing the fan room layout, with the intended AHU and ductwork configuration, for review by the Employer and the Consultant.
Test Procedures for Air Handling Unit
- The manufacturer shall furnish qualified technicians and the approved Acoustical Consultant appointed by the Contractor to assist the Employer and the E.R Acoustical performance tests shall be conducted as follows:-
- Test unit shall be balanced to deliver design air quantities at design discharge pressures.
- Air quantities shall be verified by taking air velocity traverses across ductwork.
- Motor amperage draw and fan RPM shall be recorded for verification of fan performance with the fan curve.
- Noise measurements in the test rooms shall be performed by the approved Acoustical Consultant appointed by the Contractor who will search for the peak sound pressure levels and establish a reasonable average at each octave bank frequency.
- The test air handling unit will then the throttled back by means of the unit’s variable volume control device to deliver 80% and 60% of full air flow. While maintaining the same discharge duct static pressure. (Downstream damper positions will be varied to provide the necessary resistance at the various airflow conditions). Intermediate steps in the fan speed will be subjectively evaluated to verify that the fan noise does not exhibit any “tonal” characteristics at any fan operating speed.
- Repeat steps (2) through (4) at each air quantity setting.
- Test measurements will be plotted on Noise Criterion curves to establish the test unit’s acoustical performance based on Noise Criterion ratings.
Acceptance Criteria for Air Handling Unit
Manufacturers are encouraged to design and construct their equipment to perform with the lowest Noise Criterion levels, when tested in accordance with procedures specified herein. Suitable internal design features and optimum discharge duct configuration should be incorporated to minimise noise transmitted to the test rooms.
If the manufacturer’s unit performs with noise levels measured in the test room exceeding the designed sound level pressure levels for the office area served.
Conclusion
In conclusion, the specified packaged air handling unit (AHUs) are designed for optimal performance, durability, and efficiency. Each unit is factory-assembled with high-quality materials, including corrosion-resistant steel and advanced insulation, to prevent condensation and reduce noise. Components such as centrifugal blowers and cooling coils are meticulously tested and rated to meet industry standards. The inclusion of face and bypass dampers, high-efficiency filters, vibration isolators, and condensate drip trays ensures effective air control and high air quality. The detailed technical and quality assurance requirements, along with rigorous acoustical testing, guarantee that the AHUs will perform reliably while maintaining compliance with all operational and safety standards, making them a valuable addition to any HVAC system.
About The Author
Omprakash Ramagiri; as the Founder of HVAC Technocrats, I bring over 18 years of experience as a Mechanical Engineer specializing in HVAC (Central Air-conditioning) for commercial, cleanrooms, data centers, and Petrochemical industries. Throughout my career, I’ve held pivotal roles at companies like TATA Consulting Engineers, MW Zander (for Cleanroom solutions), Bluestar Malaysia, and ETA in Dubai. I’ve managed international HVAC projects and gained valuable exposure in dynamic markets like Dubai and Saudi Arabia. With a passion for excellence and a commitment to innovative solutions, I specialize in designing Class 10K & 100K Cleanrooms for various industries. Connect with me to explore collaborations in HVAC design, project sales, and consultancy. Click to visit the Author’s Linkedin page
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