- HVAC Air Distribution/HVAC Filtration
- HVAC Equipment/Fans
Casings shall be double wall, insulated sandwich panel construction. Outer wall shall be at minimum 0.040″ Aluminum, 22 gauge stainless or galvanized steel. Inner walls shall be .040″ aluminum, 22 gauge 304 stainless steel or 22 gauge galvanized steel. Insulation shall be 2″ polyurethane for walls, floors, and roof having a “U” factor of no more than .066. Fiberglass insulation and insulation utilizing CFC or HCFC blowing agents is not permitted. The floor shall be a minimum of 3/16″ checker plate aluminum or stainless steel for walk-in custom equipment and 18 gauge minimum for all other.
Penetrations shall be insulated, sealed and sandwiched between metal with equivalent materials to the casing construction.
Lab quality AHU’s panel connections shall use aluminum extrusions with a phenolic resin thermal break for no through metal construction. Intersecting extrusions shall be continuously welded to form an airtight seal.
Major components shall be supported from the unit framework, not the casing.
Units shall be specified to require external connection to all coils, drains, electrical, controls, and ducts. All piping connections shall extend 3″ through the panel casing and terminate with either flanges or threaded connections as applicable.
Leakage and deflection requirements
Modular AHU’s leakage shall be less than 0.5 cfm per sft at +/- 5″ w.c or less than 1/2% of design airflow at 1.25 times operating static pressure. For specialty applications utilizing modular AHUs and when welded modules are acceptable, leakage shall be less than 0.232 cfm per sft at +/- 8″ w.c.
Specify air handling units to withstand 8″ w.g. positive or negative internal pressure, or the fan shut off pressure whichever is greater.
For AHUs greater than 40,000 cfm, specify that all units are to be factory and field tested for a maximum of 1% of design cfm allowable leakage at 10″ positive and 10″ negative pressure. All units shall be factory and field tested for deflection based 1/200 of the greatest span at 12″ positive and 12″ negative pressure. The owner has the option to witness all testing. All testing will be performed by the unit supplier.
All pipe and conduit penetrations shall be sealed airtight. After wire is pulled conduit shall be sealed so that air cannot be transferred into or out of the unit.
Doors and Panels
Access doors shall be sized to provide access to each section. Doors shall be wide enough to remove replaceable unit components. Door construction shall match unit casing. Doors shall be perimeter, airtight, double sealing with replaceable ¾” x 5/16″ neoprene gaskets. All doors shall be installed to open against the greater air pressure. Minimum door size shall be 24″ W x 60″ H unless unit height limits the door height. Consideration must be taken to allow for access around UV lights, humidifiers, and other features which block the door opening.
Removable access panels, located at each coil and fan shall be provided to facilitate removal of each coil and fan. Panels shall be constructed the same as access doors and screwed in place on 6″ centers.
Test ports shall be provided in all doors.
AHU door closure hardware shall be metal with the exception modular AHUs may be equipped with plastic handles rated for high pressure applications.
Windows shall be provided in all doors of walk in AHUs. For all other AHUs, windows shall be provided for inspection of UV lights, the fan section, and humidifiers.
An auxiliary drain pan shall be provided under the entire AHU when it’s installed over occupied spaces.
Floor drains shall be provided in all non-drain pan sections of custom walk-in AHUs.
Pre-wired lights shall be provided in each section for all walk in units with a single on/off switch. Equip switch with an illuminated indicator which indicates when the lights are on. All 120V items shall be wired to a junction box.
All wiring to motors shall be in conduit. No exposed wires allowed. Conduit shall be sealed so that air cannot be transferred into or out of the unit.
Power conductors inside the AHU shall be enclosed within conduit.
Provide one VFD per fan motor.
When equipped with motors 20 hp or greater, an integral rail and hoist or other permanent lifting means shall be provided for motor removal.
Differential pressure gauges shall be provided across each filter section, cooling coils and fans. Pressure gauges shall be sized to provide measurement in 1/10 in. w.g. or less increments. Calculated operating point shall be at 50% of full range.
Mount pressure gauges on to the exterior of air handler and specify copper tubing. Gauges shall not be mounted in the AHU casing walls.
Gauges shall be equipped with on-off-vent valves for measurement of static pressure at each probe and differential pressure across the probes.
Specify ultraviolet (UV) lights on the downstream side of chilled water coils. There shall be adequate access for bulb replacement.
UV lamps shall be non-proprietary and available from multiple manufacturers. Submittals must provide a list of alternate bulb manufacturers (two minimum) with equivalent cross-reference lamp model numbers. Bulbs shall have a coating to contain mercury upon accidental bulb breakage. UV lights shall provide 360 degree UV coverage. Fixtures shall be corrosion proof. Specify safety switches and safety stickers on doors on both sides of the cooling coil.
Ballast shall be installed on the exterior of the AHU. Ballast shall have a 5-year warranty.
Control dampers shall be opposed blade type. Prototypical opposed blade dampers shall be RuskinCD50 series or approved equal.
Stratification of cold outside air shall be avoided by premixing the return and outside air streams or providing adequate mixing box depth. Where space limitations result in inadequate mixing, provide parallel-blade control dampers directed at one another or blenders.
Outside air ducting shall be sized for full economizer operation.
Provide a separate minimum outside air and economizer damper when the minimum outside airflow is less than 25% of the economizer airflow.
Flexible connections at fans shall be stretched tight without wrinkles. (to avoid fan system effect)
Field Service and Equipment Startup
A factory-authorized service representative shall inspect the equipment installation, including piping and electrical connections prior to unit startup. A factory-authorized service representative shall perform startup service.
Fan-powered VAV terminal units are allowed only with written approval from the University. The approval request shall include the location of each unit for service.
The minimum flow rates of air terminals shall be specified as 30% of maximum air flow unless the design requires otherwise.
Air terminals shall be equipped with a 10″ x 10″ minimum access door between the damper and reheat coil.
When internal liner is provided, provide liner which is resistant to mechanical damage, resistant to mold, shall not shed fibers, and when cooling coils exist, shall provide full insulation capability even when exposed to water.
Prior to the installation of permanent ID tags, mark air terminals and air valves in a visible location with the equipment identification number using thick black marker or equivalent and 2″ characters. Exception: does not apply for permanently exposed equipment.
The designer must coordinate the location of air terminals on the drawings so that safe ladder access is available without moving fixed and heavy furniture. Also coordinate with lights, sprinkler heads, life-safety devices, etc.
On the design documents, provide a division of work detail for control wiring. Identify controls power wiring to be provided by the mechanical and controls contractor on the mechanical drawings.
Air terminal schedules shall indicate the electrical requirements.
Size reheat coils for 160 °F supply temperature and 140 °F return temperature. Specify a minimum of 2-row reheat coils.
- Coiling coil casings shall be stainless steel.
- Coils shall have a minimum of 0.025″ tube wall thickness.
- Drain pans shall be stainless steel or other corrosion proof materials.
- Equip with 2″ MERV 8 filters.
- Insulation shall be impervious to water, and fiberglass insulation is prohibited.
When installed above ceilings, specify an auxiliary float switch.
Fan coil units and blower coils are not permitted to serve occupied spaces except for (and when approved) renovation projects, housing projects, and equipment rooms. In all cases, a means to dehumidify the building shall be provided.
Fan coils shall not be located above ceilings.
To minimize air-side pressure drops, all cooling units shall remain in operation and shall not be staged.
Individual fans shall be fully independent and shall not share motors or VFDs.
- Buildings serving administrative and classroom functions: 120% of the design airflow.
- Buildings serving laboratories, research, health care functions: 130% of the design airflow.
- Specify the minimum fan wheel size and maximum RPM.
- All belt-driven fans shall have a minimum shaft size of 1-1/8″.
- Each fan shall have means to re-lubricate the fan shaft bearings.
- Where necessary, extend grease fittings to an accessible location.
- Fans shall be checked for balance at all speeds and specified not to exceed manufacturer’s recommended vibration levels.
- Each fan shall have the sheaves aligned by contractor prior to acceptance by the University.
- A spare set of belts for each belt driven fan shall be turned over to University at the end of project.
- Shall have a NEMA rated adjustable motor base with a minimum of two (2) belt tensioning bolts.
When necessary, extend bearing grease lines to an accessible location so that bearings may be lubricated with the fan operating.
Specify long-life bearings. Except for small fans, specify L10 at 80,000 hours. For custom AHUs and major fans and when available, specify L10 200,000 hours.
Ducts shall be aligned within +/- 3/8″ tolerance with fan inlets and outlets.
When available as an option, specify hinged access doors (avoid bolt on access panels when possible).
Designs shall minimize system effect. Avoid inlet swirl. On the outlet side of fans, provide 2.5 straight duct diameters for conditions up to 2500 fpm, and 1 additional duct diameter for each additional 1000 fpm.
Fiberglass fan wheels and housings are prohibited.
Airfoil fans should be used whenever possible to improve efficiency. Forward curve fans should only be used on small fans with low external static pressure.
When equipping AHUs with multiple fans, specify backdraft dampers.