An Indirect-fired gas heating and ventilating unit(s), as indicated on the drawings shall be furnished. Orientation shall be Horizontal (Down) (Side) (Up) discharge. Unit(s) shall be factory assembled, tested and shipped as a complete packaged assembly, for indoor or outdoor mounting, consisting of the following:
|Unit(s) assembly shall be tested in accordance with Standard, ANSI Z83.8-2006 and CSA 2.6-2006 and shall bear the ETL label. The duct furnace shall be certified by the American Gas Association and approved by the Canadian Gas Association.|
Unit housing shall be constructed of 20 Gauge G-90 galvanized steel. The wall panels and roof panels shall be fabricated by forming double-standing, self-locking seams that require no additional support. The floor and wall panels shall be caulked air tight with a silicone caulk. All casing panels shall be attached with sheet-metal screws or rivets, which can be removed to field service large components. The unit base shall be suitable for curb or flat mount. The base shall be constructed of galvanized steel for improved rigidity. Base shall be structurally reinforced to accommodate the blower assembly and burner. Housing construction should be suitable for outdoor or indoor installation.
All doors and at least one side of every sheet metal surface of the unit separating two air-masses of different air temperatures shall be faced with properly secured 1" aluminum-faced insulation for condensation prevention.
The discharge of the unit (Down/Side/Up) shall be internal to the heating module containing the furnaces.
All electrical controls on the control board shall be mounted in an isolated, fully enclosed and insulated vestibule, completely separated from any combustion air, but accessible for servicing needs.
All furnace exhaust flues shall be of double-wall construction. All furnace exhaust flue connections and roof-penetration seams shall be sealed with High-Temp Fire-Barrier 2000+ type silicone caulking.
All unit housings, sizes 1-3, shall be equipped with Internal Air Distribution Screens on the upstream side of each furnace heat-exchanger.
All gas valves and electrical safety-limits shall be mounted within the burner vestibule; wiring to these components shall be properly secured and away from all high temperature metal surfaces. The burner vestibule shall be an integral part of the unit and not extend outside the exterior casing of the unit and not exposed to the main air stream.
If an outdoor unit, high wind rain caps shall be installed at the termination of the furnace discharge flues.
The vestibule full-size door shall provide easy access to controls and gas-train components. Blower door shall provide easy access to blower, motor and drives. Access doors shall be provided on both front and back side of unit providing full access to every part of the unit.
Wheels shall be balanced in two planes. The wheel blades shall be aerodynamically designed to minimize turbulence, increase efficiency and reduce noise. The wheel blades shall be securely attached to the wheel inlet ring. The wheel shall be firmly attached to the fan shaft with set screws and keys. The blower assembly shall be isolated from the fan structure with vibration isolators.
Blower capacity shall be _____ CFM at 70 degrees F standard air, ____ external static press.
External Static: The sum of duct loss plus duct component static- Example: louvers, diffusers. All blowers shall be tested and set at rated speed after being installed in the factory-assembled unit.
Blower(s) shall be forward-curved, centrifugal, Class I or II (depending on requirements of the application), double width, double inlet, constructed G-90 galvanized steel. Unit shall have a heavy-duty, solid-steel shaft.
Direct drive blower assembly shall consist of a centrifugal backward inclined, non-overloading wheel secured directly to a heavy duty, ball bearing type motor via two set screws. The motor and wheel assembly shall be mounted to a heavy gauge galvanized steel frame. The motor shall be controlled by a variable frequency drive, allowing for variable airflow without the need of belts and pulleys.
Motor & Motor Compartment
Motors shall be heavy duty ball bearing type and furnished at the specified voltage, phase and enclosure. Motor mounting plate shall be constructed of heavy gauge galvanized steel and shall be designed to provide easy adjustment of belt tension. Blower motor shall be suitable for operation on _______ volts, _______ cycle, _____ phase power. Blower motor shall be a ___________________________ HP motor, Open Drip Proof.
Shaft & Bearings
Shafts shall be precision ground and polished. Heavy duty, pre-lubricated bearings shall be selected for a minimum (L50) life in excess of 200,000 hours of operation at maximum cataloged operating speed. They shall be designed for, and individually tested specifically for use in air handling applications.
Belts & Drives (Belt Drive Units Only)
Belts shall be oil and heat resistant, non-static, grip-notch type. Drives shall be cast type, precision machined and keyed and secured attached to the fan and motor shafts. Fan operating speed shall be factory set using adjustable pitch motor pulleys; motors over 3 HP will come standard with double groove pulleys.
Burner & Heat Exchanger
The gas burner shall be an indirect-fired, push-through type, sized to provide an output of ________ BTU/hr using (natural) (LP) gas at an inlet-supply pressure to the unit of _____ inches water column (7" w.c. minimum Nat. Gas, 11" w.c. minimum LP Gas).
The burner shall be capable of heating the entire air supply from _____F° to _____F° (______ degrees F temperature rise). Burner shall be a tubular in-shot fired design capable of using natural or LP type gas. Each burner ignition shall be of the direct-spark design with remote flame sensing at inlet of the last firing tube of the gas manifold. Each burner ignition module shall be pre-programmed with an ignition sequence comprised of a 1 minute pre-purge, 1 min inter-purge, 2 minute post-purge, 15 second ignition, 3 trials for ignition, and 60 min lockout.
Direct-sparking sequence shall last through the complete during of the trial for ignition period for guaranteed light-off. Burner shall always be lit at maximum gas flow and combustion airflow for guaranteed light-off. Each burner ignition module shall have LED indicators for troubleshooting and a set of exposed prongs for testing flame indication signal.
All furnaces shall be controlled by an electronic vernier-type fully modulating control system capable of achieving 80% combustion efficiency over the entire gas firing range of the unit.
Each furnace shall have:
Each furnace module gas inlet shall be equipped with a 0-35"w.c. gas pressure gauge. A 0-10"w.c. gas pressure gauge shall be installed on the gas manifold of each furnace.
All gas equipment shall conform to local-Code requirements
All gas manifold components shall be piped and wired at the factory.
High Gas Pressure Regulator
TEMPERATURE CONTROL SYSTEMS
HMI Control: One HMI or Human-Machine Interface to be provided standard. Space HMI or room sensor shall be provided for temperature control utilizing space temperature. Additional HMIs or room sensors can be provided for space averaging. Cat5 connections shall be utilized between all HMIs. All settings and set points shall be able to be controlled at any HMI.
Activate Based on: Shall have the ability to activate heating/cooling based on the following.
Tempering Mode: Shall have the ability to control heating/cooling based on the following.
Scheduling (Optional): Shall have the ability for 7 day scheduling.
Re-Circulating Control Options
Manual/0-10V Control: The dampers can be manually controlled from the HMI in the unit or from a remote HMI to any position from 0% to 100% fresh air to match building ventilation requirements.
Field Wired Control (Two Position): The dampers can be controlled by a two position switch (field supplied switch device) to open the fresh air to 100%.
Outdoor Air Percentage: The dampers can be controlled from the HMI in the unit or from a remote HMI to any position from 0% to 100%. The IBT board utilizes an algorithm to alter its 0-10V output to the mixing box damper to maintain an exact outdoor air percentage based on entering and leaving temperatures.
Static Pressure Control (Photohelic): The dampers can be controlled by a building static pressure control. This controller will sense the difference between pressure inside the building and pressure outside the building, and position the dampers to maintain the pressure setting on the controller.
Building Automation System (BAS) Control: The supply and return dampers will modulate based on a 0-10 VDC signal from a building automation system.
Schedule Control: The supply and return damper will change based on the schedule; the unit will maintain the appropriate outdoor air percentage based on the schedule state.
VAV (Static Pressure Control): A factory-supplied field wired VFD is provided which varies the speed of the blower wheel. The VFD is controlled by a field wired Static Pressure Controller which measures building pressure and uses auxiliary inputs on the IBT control board to accelerate of decelerate the blower speed to maintain the building pressure set on the Static Pressure Controller.
VAV (Manual): A factory-supplied field wired VFD is provided which varies the speed of the blower wheel. The VFD is controlled by a preset speed on the IBT control board.
VAV (Preset Speeds): A factory-supplied field wired VFD is provided which varies the speed of the blower wheel. The VFD is controlled using auxiliary pins on the IBT control board to switch between preset speeds.
VAV (0-10VDC): A factory-supplied field wired VFD is provided which varies the speed of the blower wheel. The VFD is controlled using external 0-10VDC signal to vary blower speed.
WIRING AND ELECTRICAL
Unit(s) shall be operated, tested and set at the factory using job-site conditions for electrical and gas input. All operating and safety controls shall be tested and set at the factory. Adjustable, or fixed sheaves shall be set for proper RPM at specified conditions. Gas-pressure regulator shall be set for specified burning rate at specified inlet pressure.
SERVICE AND PARTS
The supplier shall furnish gas piping schematics, as built wiring connection and control-circuit diagrams, dimension sheets and a full description of the unit(s). Service manuals, showing service and maintenance requirements, shall be provided with each unit.