SECTION 15662 DIRECT FIRED MAKE-UP AIR UNITS
PART 1 - GENERAL
1.1 SUMMARY
A. Section Includes
1. Direct-fired make-up air units.
2. Controls.
1.2 SUBMITTALS
A. Submit shop drawings in accordance with the General Conditions and Division 1.
PART 2 - PRODUCTS
2.1 GENERAL
A. The direct gas fired make-up air units shall be manufactured by Greenheck, or Modine.
1. Horizontal Units shall be equivalent to Greenheck DGX model
2. Vertical Units shall be equivalent to Greenheck VSU model
3. Assembled, wired and fire tested prior to shipment, with the capacity and configuration shown and listed on the plan.
B. Unit Casing: The unit casing and accessories shall be heavy gauge galvanized steel. The unit casing is to be suitably reinforced to ensure rigidity and is to be supplied with a formed steel base or stand depending on configuration.
1. The unit casing is to be airtight, insulated, weatherproof and constructed of double wall construction with insulation layer.
2. An observation port shall be located to provide a view of the pilot and main flame.
3. Hinged double wall access panels shall be supplied to allow physical entry to the fan, blower and burner section and the electrical and piping control section.
C. Blower Section: The unit shall be supplied with an AMCA rated forward curved, double inlet, statically and dynamically balanced centrifugal fan assembly.
1. The fan is to be mounted on a heavy duty, tuned, ground and polished steel shaft designed with its maximum operating speed not exceeding 75 percent of its first critical speed.
2. The bearings are to be of the heavy duty, prelubricated type. V-belt drives are to be sized with a capacity 25% greater than motor horsepower.
D. Burner Section: The unit shall be supplied with a field adjustable burner baffles with modulating turndown ratio of 25:1. Adjustable profile plates shall be supplied. The unit shall have an electronic flame supervision feature with timed prepurge. The burner assembly and gas manifold shall be prepiped and factory test fired and shall include:
1. Maxitrol electronic modulating valve.
2. Motorized safety shut-off valve.
3. Manual firing valve.
4. Manifold pressure test plug.
5. Main manual shut-off valve.
6. Pilot manual shut-off valve.
7. Pilot regulator.
8. Pilot solenoid valve.
E. Control Enclosure: The unit shall be supplied with an insulated hinged control enclosure. All controls are to be mounted in the control enclosure and wired to a numbered terminal strip. All wiring shall be color-coded to match the circuit diagram supplied with the unit.
F. Controls: The control systems shall include the following components required to provide automatic operation.
1. Fan motor starters and overload relays.
2. Control circuit fuses.
3. High temperature limit switch.
4. Supply fan air proving differential switch.
5. Flame safeguard relay with alarm contacts.
6. Ignition transformer.
7. Pilot automatic valve.
8. Main gas automatic safety shut-off valve.
9. Maxitrol electronic modulating system.
G. The following accessories shall also be provided:
1. Internal motor and blower neoprene vibration isolation.
2. Remote operating stations.
3. Room Override Thermostats: Provide where indicated on Equipment Schedule and where shown on Plans.
a. Class 1 Division 1 or 2 classification spaces served by room override thermostats shall have the thermostats remote mounted in non rated adjacent space and have remote sensing bulb located in the rated space. Remote sensing bulb must also be suitable for use in corrosive environment.
b. High Moisture/ Wet environment spaces served by room override thermostat shall utilize thermostat suitable for use in that type of environment.
4. Motorized inlet damper or discharge damper(s) as indicated on plans. Sizes shall be coordinated with ductwork dimensions shown on drawings. Damper materials shall be stainless steel and Actuators shall be rated for type of environment they are located in. Dampers shall be wired to interlock with unit operation.
5. Filter box with permanent filters.
6. Insulated double wall unit casing.
7. Single speed motors as indicated in equipment schedule located on plan. Single speed fan motors to have TE enclosure.
8. Ambient outside temperature heating lockout sensor – adjustable setpoint
9. Structural supports stand when shown on drawings or indicated on schedule. Support Stand shall be fabricated of standard structural steel shapes and be furnished primed and painted. Color to match unit.
H. Remote Control Panel: Provide Remote control panel of NEMA type required for environment in which panel will be located. NOTE: Panels mounted outside shall be housed within a NEMA 4X rated enclosure.
I. In General, provide controls outlined below. Control applications may vary depending particular unit application. Coordinate controls provided with each unit with control sequences outlined in Section 15971.
1. Provide with standard interface. “ON-OFF” switch single speed units, Outdoor air temperature Sensor w/ setpoint control (to lock out heating if O.A. Temp is
above preset value), indicating lights for supply fan, pilot operation, burner operation, and clogged filter indication. Provide room temperature override thermostat where indicated and of a type suitable for its location (Note: Some locations are Class 1, Division 1 and will require Room override thermostat with remote sensing bulb which is also corrosion resistant). Low limit freezestat control. Provide discharge sensor on discharge, and low outdoor ambient sensor control for field mounting in discharge duct. All set points to be adjustable. Mount panel where indicated on drawings. Panels shall be NEMA rated for actual mounting locations.
a. With the main switch in the “on” position, the unit shall engage. With the main switch in the “off” position, the unit shall be off. If the switch is in the “Auto” position, then the unit shall operate based on automatic control, either time clock or other if outlined as such.
2. Interlocks: Unit shall be constant volume operating based on room occupancy. Burner to modulate as required to maintain duct discharge temperature set point. Provide one set of additional control interlock contacts for remote equipment operation.
3. Safety Controls: Sense correct airflow before energizing pilot and sense pilot ignition before activating main gas valve.
4. Manual Reset Low and High Limit Controls: Maintain supply air temperature between set points and shut fan down if temperatures are exceeded.
5. Purge Period Timer: Automatically delays burner ignition and bypasses low limit control.
6. Provide remote Status indication for Interface with SCADA communication connection. Status shall indicate unit Run/Fail status.
PART 3 - EXECUTION
3.1 INSTALLATION
A. Install in accordance with manufacturer’s instructions and applicable state or regulatory code requirements.
B. Mount unit as indicated on plans, either on support stand or on concrete housekeeping plan as applicable.
1. Coordinate size of concrete equipment pad with General Contractor.
2. Support Stand Installation: Shim support stand legs as required to achieve level installation. Anchor stand to floor or housekeeping pad as applicable.
C. Provide factory authorized startup of unit.
END OF SECTION
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