2.Barometric Relief Damper: Building air exhaust shall be accomplished through barometric relief damp- ers installed in the return-air plenum. The dampers open relative to the building pressure. The opening pressure shall be adjustable.
2.On/Off, Fan-Powered Exhaust: A DWDI Class I or II forward-curved centrifugal exhaust fan shall be provided to exhaust building return air to relieve building static pressure. The fans shall be constant volume and operate based on either a building static pressure, or outside air-damper position.
2.Powered Exhaust with Modulating Discharge Damp- er: A DWDI Class I or II forward-curved centrifugal exhaust fan shall be provided to exhaust building return air to relieve building static pressure. The fans shall operate at a constant volume and operate based on building static pressure. Exhaust airflow shall be modulated via a parallel-acting, control damper. The exhaust-air dampers shall be sized for 100% of the exhaust airflow.
2.Powered Exhaust with Variable-Frequency-Drive: A twin DWDI Class I or II forward-curved centrifugal exhaust fan shall be provided to exhaust building return air to relieve building static pressure. Exhaust airflow shall be modulated via a factory-installed and commissioned variable-frequency-drive with the same nameplate horsepower as the supply fan motor.
[FOR POWERED-EXHAUST OPTIONS ABOVE, USE THE FOLLOWING]
3.Fan Motor: Fan motors shall be NEMA design ball- bearing types with electrical characteristics and horsepower as specified. Motors shall be 1750 RPM, ODP [TEFC] open drip-proof type. The mo- tor shall be located within the unit on an adjustable base.
Mountings: Fan and fan motor shall be internally mounted and isolated on a full width isolator sup- port channel using 1-inch [2-inch] springs. The fan discharge shall be connected to the fan cabinet using a flexible connection to insure vibration-free operation.
Bearings and Drives: Fan bearings shall be self- aligning, pillow block or flanged type regreaseable ball bearings and shall be designed for an average life (L50) of at least 200,000 hours. All bearings shall be factory lubricated and equipped with standard hydraulic grease fittings and lube lines extended to the motor side of the fan. Fan drives shall be
selected for a 1.5 service factor and antistatic belts shall be furnished. All drives shall be fixed pitch. Fan shafts shall be selected to operate well below the first critical speed and each shaft shall be fac- tory coated after assembly with an anticorrosion coating.
Filter Section:
[SELECT A FILTER RACK, FILTER MEDIA, AND SWITCH IF DESIRED]
1.Angled Filter Rack: two-inch throwaway filters shall be provided in an angled filter rack.
1.Angled Filter Rack: two-inch carbon media filters shall be provided in an angled filter rack.
1.Angled Filter Rack: two-inch cleanable filters shall be provided in an angled filter rack.
1.Angled Filter Rack: two-inch high-efficiency (30%) pleated filters shall be provided in an angled filter rack.
1.Flat Filter Rack: 60-65% efficient rigid filters with a two-inch, high-efficiency pleated pre-filters shall be provided in a flat filter rack.
1.Flat Filter Rack: 90-95% efficient rigid filters with a two-inch, high-efficiency pleated pre-filters shall be provided in a flat filter rack.
2.Dirty Filter Alarm: A dirty-filter switch shall be pro- vided and wired to the rooftop unit control panel. Upon closure of the switch, the controller shall display a dirty-filter fault. The setting of the switch can be changed manually to close at a specified pressure drop across the filters.
Evaporator Section
1.Cooling Coil: Evaporator coils shall be direct-expan- sion type with intertwined circuiting to assure com- plete coil-face activity during part-load operation. Coil tubes shall be 3/8” OD copper, with internally enhanced tubes. Fins shall be enhanced mechani- cally expanded to bond with the copper tubes. Coil casing shall be fabricated from heavy-gauge galvanized steel. All coils shall be pressure tested at a minimum of 450 PSIG.
2.IAQ Drain Pan: The main coil drain pan shall be double-sloped with a condensate connection through the base rail of the unit. Clearance between the evaporator coil and the drain pan shall allow for easy access to the drain pan for cleaning, and shall be visible for inspection without the removal of components.
3.Intermediate Drain Pan: Coils with finned height greater than 48” shall have an intermediate drain pan extending the entire finned length of the coil.
