AIR HANDLING UNIT
Unit Construction
The following sections describe in detail construction requirements for the unit base, cabinet, access doors, insulation and paint finish. Unit shall be built for outdoor installation.
Unit Base
Each unit shall be constructed on a base fabricated from ASTM A36 welded structural steel channel. Tubular or formed metal channel bases are not acceptable. Channel bases shall be sized as a function of air handling length as follows:
A.H. UNIT / LENGTH / MINIMUM / CHANNEL SIZEUP to 10' / 4" x 1-5/8" / (5.4lbs/Lin.Ft.)
11' to 20' / 6" x 2" / (8.2lbs/Lin.Ft.)
21' to 30' / 8" x 2-1/2" / (11.5lbs/Lin.Ft.)
31' to 50' / 12" x 3" / (20.7lbs/Lin.Ft.)
Heavy removable lifting lugs shall be added to the perimeter channel along the longest length of the unit.
The unit floor shall be fabricated of 16-gauge hot rolled galvanized steel sheets. (Other materials such as aluminum, stainless and tread plates in various thicknesses are available.) The floor shall be supported by structural steel members. Max spacing of floor support shall be 24" centers. These supporting members shall be welded to other members for maximum strength. Floor skin shall be supplied with standing seams and drive cleats to maintain water and airtight seal. The flooring shall be spot welded to the members below -no penetrations thru the floor skin. Welds shall be below the floor and spaced no greater than 6" on center.
Fans, coils and major components shall be supported with structural steel members.
Housing
The unit housing side and roof panels shall be constructed of 16-gauge galvanealed steel, (other materials such as aluminum and stainless in various thickness are available.) and shall utilize a standing seam modular panel type construction. The panels shall be caulked and attached to each other, to the roof, and to the floor using nuts and bolts. Drive screw attachment is not acceptable. All panels shall be removable. All seams shall be sealed with an acrylic latex sealant prior to assembling the panels and after completion of the assembly. All floor openings shall have a steel-frame and 16 gauge flange around the entire perimeter of opening for duct connection.
Minimum sound transmission loss (STL) through unit panels shall be as follows:
2" - 1½ PCF Insulation125 / 250 / 500 / 1K / 2k / 4k / 8k
25 / 29 / 36 / 42 / 47 / 48
4" - 3 PCF Insulation
26 / 36 / 47 / 56 / 57 / 58
Hinged, double wall, insulated, man size access doors shall be provided in all sections requiring access for maintenance or service. Access doors shall be fully gasketed with a closed cell, replaceable neoprene gasket. The gasketing material shall be installed to allow for easy removal and replacement. Access door must not leak more than 25 CFM @ 6" static pressure.
Door hinges and latches shall be easily adjustable, without the use of shims or special tools, to allow for a tight seal between the door and the doorframe as the gasketing material compresses over time. The door hinge design shall allow for field modification of door swing and doors shall be easily removable. Provide door detail drawing with submittal package.
Latches shall utilize phenolic knurled knobs. When required, the latch assembly can incorporate a built-in safety catch to release cabinet operating pressure prior to opening the door.
Doors entering into any section of the air handler that contains rotating fans shall be provided with zinc-plated nuts in lieu of knurled knobs. The nuts shall limit access to personnel with proper tools. Include a 10" x 10" wire reinforced glass view window in each fan access door.
On ETL listed equipment, a door switch shall be interlocked with fan starter to stop the fan before access door is opened.
Insulation
Insulation shall be 2" thick, 1½ lbs per cubic foot density, (other densities are available, 3.0 lbs/ft3 and 6.0 lbs/ft3, 4" thickness is available) neoprene coated fiberglass to cover all walls, ceilings and under floors. Insulation shall meet NFPA-90A smoke and flame spread requirements. There shall be no raw edges of insulation exposed to the airstream. Plenum fan sections shall have a 20 gauge perforated galvanized sheet metal liner covering all wall and ceiling surfaces in the blast area of fan.
Drain Pans
Drain pans shall be constructed from 16-gauge, 304 stainless steel. Galvanized steel drain pans are not acceptable. The drain pan shall be insulated with 2.0", 1½ # density insulation to prevent condensation under the drain pan. Insulation shall be protected with a 20-gauge galvanized steel liner. Drain pans must be sized such that the entire coil, including headers and return bends, are inside the drain pan. Drain pans must slope in two directions so there is no standing water in drain pan. Stainless steel condensate connection shall be provided on one side of the unit. The coil drain pan is designed to prevent immersion of the coil in condensate and allow for complete cleaning of drain pan beneath the coils.
Paint Finish
After final assembly the unit exterior shall be coated with an industrial grade, high solids, and polyurethane paint. In addition, all fan bases, springs and structural steel supports shall be coated with the same finish. The paint system shall meet ASTM B117 Salt spray test for a minimum of 2000 hours in a 5% solution.
- INTERNAL COMPONENTS
A. Fan Assembly
Plenum fan assemblies shall be arrangement one or four. Arrangement three plenum fans are not acceptable because they are less efficient and generate more noise. The air handling unit manufacturer, for the purpose of sole source responsibility, shall manufacture all fan assemblies. Fan wheels supplied shall be in accordance with AMCA standard 210.
Fan performance shall be based on tests run in an AMCA certified laboratory and administered in accordance with AMCA Standard 210. Fan performance tests shall be taken with fans running inside the cabinet to include any affects from the unit cabinet and other internal components. Fans shall bear AMCA seal for air and sound.
Plenum fans shall be configured so that both fan bearings are on the drive side of the wheel with the wheel over hung (Arrangement #1) or direct-coupled to the motor (Arrangement #4). There shall be no obstructions (i.e., bearings or bearing supports, etc.,) at the inlet of the fan. Fan wheel shall be aluminum with aluminum extruded airfoil blades. Fan bearings shall have a minimum L10-200,000 Hr. operating life and be mounted on a structural steel channel or machined surface. On DWDI fans the structure supporting the bearing shall be fabricated from structural steel and be detachable to allow for removal of the fan wheel and shaft as one piece. The fan discharge shall be isolated from the cabinet by means of a neoprene-coated flexible connection. Plenum fans shall be provided with spring or rubber-style thrust restraint.
Each fan shall be sized to perform as indicated on the equipment schedule. The wheel diameter shall not be less than that shown on the equipment schedule. The fan shall be constructed to AMCA Standards for the Class Rating as indicated on the Equipment Schedule.
Provide grease fittings and extend lubrication lines to the motor side of the fan, just inside the access door.
B. Fan Base, Spring Isolation, and Support Framing
Mount fan and motor on an internal, fully welded, rigid structural steel base. Base shall be free-floating at all four corners on spring type isolators with seismic earthquake restraints. The fan assembly shall be isolated from the cabinet by steel springs with minimum deflection of 2.0" or as indicated on the schedule. The spring isolators shall be mounted to structural steel members. All isolators shall be rated for zone 4 seismic requirements. The spring isolators shall be mounted on a waffle pad for vibration isolation.
C. Balancing
The fan shaft shall be sized not to exceed 75% of the first critical speed for the maximum RPM of the fan Class specified. The critical speed will refer to the top of the speed range of the fans' AMCA class. The lateral static deflection shall not exceed 0.003" per foot of the length of the shaft. Fans shall be balanced to ISO standard G6.3.
A copy of the above balance test data for this project showing calculations for deflection and critical speed of the shaft and wheel assembly shall be submitted to the engineer and a copy forwarded to the Owner.
D. Motors and Drive
Furnish premium-efficiency open drip proof, NEMA frame, ball bearing type motors, with grease lubricated bearings and alamite fittings. Horsepower's as shown on the schedule are minimum allowable.
The motor shall be mounted on an adjustable slide rail motor base. The fan motors shall be factory wired to an external junction box with flexible conduit of adequate length so that it will not have any affect on the vibration isolation.
Provide V-belt type, cast-iron sheaves, and reinforced rubber belts. The belts shall be selected for 150% of the motor nameplate horsepower. Drives shall be "Browning" or equal.
E. Coils
Chilled water coils shall be of the plate fin extended surface type. Tubes shall be 5/8" outside diameter seamless copper with a 0.02" minimum wall thickness. Each coil shall have individually replaceable return bends of 0.025 wall thickness on both sides of the coil. Coils incorporating a "hairpin" type design are not acceptable. Tubes shall be expanded into the fin collars to provide a permanent mechanical bond.
The secondary surface shall be formed of 0.006" (0.008", 0.010") aluminum (copper) fins and shall be spaced not closer than 12 fins per inch with integral spacing collars that cover the tube surface. Headers shall be non-ferrous seamless copper, outside the air stream and provided with brazed copper male pipe connections. Drain and vent tubes shall be extended to the exterior of the air handling unit.
All coils shall have counter flow construction with connections left or right hand as shown on the drawings. The use of internal restrictive devices to obtain turbulent flow will not be accepted.
Cooling coil casings shall be of minimum 16-gauge, 304 stainless steel with doubleformed 1-1/4" stacking flanges and 3/4" flanges on the side plates. All other coil casing shall be of 16-gauge galvanized steel. Tube holes with raw sheet metal edges are not acceptable. Reinforcing shall be furnished so that the unsupported length is not over 60". All coil assemblies shall be tested under water at 300-psi and rated for 150-psi working pressure. Headers are to be located inside the cabinet casing with only the pipe connections extending through the casing. All sides of coils shall be carefully blanked off to ensure all air passes through the coil.
Intermediate condensate pans are to be furnished on multiple coil units and single coils greater than 48" high. The pans shall be 16Ga. 304 stainless steel and drain to the main drain pan through copper downspouts.
All water coils shall be rated in accordance with ARI Standard 410.
F. Filters
Filter sections shall be fabricated as part of the air-handling unit. Filters shall be arranged for upstream, downstream, or side loading as shown on the drawings. Provide filter-holding frames to accommodate scheduled filters. Filter frames shall be 16 Ga. 304 stainless steel and shall be welded to reduce leakage of air through corners.
Factory install at each filter bank a Dwyer Magnehelic "Series 2000" pressure gauge complete with static pressure tips, hardware and fittings. Enclose the gauge in a 304 stainless steel protective weatherproof box with a hinged inspection door.
G. Dampers and Louvers
Dampers shall be supplied with low leak extruded aluminum airfoil blades. Blades shall be supplied with rubber edge seals and stainless steel arc end seals. Rubber edge seals shall be backed by the damper blade to assure a positive seal in the closed position. Dampers shall be provided with nylon bearings within extruded openings. Damper leakage shall not exceed 6 cfm/ft2 at 5.0" of static pressure. Leakage testing shall be in accordance with AMCA standard 500 figure 5.5. Test results must be from independent testing laboratory. Provide louvers for outside air and exhaust air for units located outdoors. OSA Louvers shall be sized for a maximum face velocity of 500 fpm based on gross louver face area. Louvers shall have zero water penetration at 600-ft/min air velocities.
Maximum louver pressure drop shall be 0.03" in w. g. at 500 ft/min. Provide test results from independent testing laboratory. Test must be conducted in accordance to AMCA Standard 500 figure 5.5. Louver water carry over must be less than 0.01 oz/ft2 at 1100 ft/min of free louver face area. Test must be conducted by independent testing laboratory per AMCA 500-89 figure 5.6. Hoods may be used instead of louvers where necessary.
H. Economizer / Mixing Box
Economizer section shall include dampers for return air, outside air and exhaust air. Dampers shall be opposed blade type. Dampers shall be sized for not greater than 1200 fpm face velocity based upon gross damper face area. Dampers shall meet above specifications.
I. Air Flow Measuring Stations
Fans shall be supplied with a complete flow measuring system capable of supplying a 4 - 20mA. output signal to the EMS system that is proportional to airflow. The flow measuring station and a flow transmitter shall be factory mounted. The flow measuring station shall consist of pressure taps located in the inlet cone of each fan. Provide a gauge with CFM scale on external side of the fan sections, which indicates the fan volume.
The electronic flow transmitter shall be mounted on the exterior of the fan section. It shall be capable of receiving signals of total and static pressure from a flow element, of amplifying, extracting the square root, and scaling to produce a 4 - 20 mA or 0 - 5 VDC output signal linear and scaled to air volume or velocity. The flow transmitter shall be capable of the following performance and application criteria.
Calibrated spans from 0 - 896 FPM, in eight flow range increments. Output signal 4 -20 mA or 0-5 VDC standard. Integral zeroing means 3-way zeroing valve with manual switch. Temperature effect ± 2.0% of full span from 40° to 120°F.
The transmitter shall not be damaged by over-pressurization up to 200 times greater than span, and shall be furnished with a factory calibrated span and integral zeroing means. The transmitter shall be housed in a NEMA 12 enclosure with external signal tubing, power, and output signal connections.
The electronic differential pressure transmitter shall be Setra Model 264 or equal.
J. Electrical Requirements:
Provide single source power panels (SSPP's) that are constructed according to N.E.C. regulations and carry a U.L.508 listing. The panel shall include a non-fused main disconnect switch, starters, transformer, Hand-Off-Auto switches, relays and pilot lights for complete operation of the unit. The single source power panels shall be factory wired to all factory furnished devices such as motors and interlocks.
The air handling unit manufacturer, for the purpose of sole source responsibility, shall manufacture all electrical panel assemblies supplied for the air handlers. The air handling unit manufacturer shall be a U.L. 508 listed panel shop.
The main control panel shall have access door(s) for direct access to the controls. The panel shall be NEMA type 3R (rainproof) and shall contain a single externally operated, non-fused disconnect, suitable for copper wire up to and including 3" conduit. The electrical contractor shall bring separate power to the single source power panel.
Provide vapor tight marine lights in each access section, factory wired to a single weatherproof switch located on exterior of cabinet. Provide weatherproof, 15 amps, GFIC receptacle near the light switch wired to the lighting circuit. The Electrical Contractor shall bring separate 120/1/60 power to the light switch.
All wiring shall be run in either EMT and flexible UL compliant conduit, raceways are not acceptable.
If the unit requires splits, junction boxes shall be furnished on each section to allow the electrical contractor to make final connections in the field. Wiring shall be clearly labeled to allow ease in final interconnections.
K. Variable Frequency Drive
A drives manufacturer shall provide, coordinate and start-up a variable speed drive system to ensure proper application of equipment to the driven load.
Factory warranty for a period of one year from date of start-up shall apply for both motor and drive.
VFD shall be current rated at 8 kHz carrier frequencies for VFD's 1-75 HP and 4 kHz for VFD's 100-400 HP. All HP ratings shall meet or exceed Table 430-150 of the National Electric Code. Three phase motor full load currents, HP, maximum current, and rated voltage shall appear on the drive nameplate. No derating of the VFD shall be