General: Make-up air unit shall be as manufactured by Greenheck or approved equal provided all specifications are met. Greenheck Model DGX equipment is used as the basis of design. Performance to be as scheduled on plans. Make-up air unit shall be ETL listed to ANSI Z83.4 -1999, CSA 3.7 - M99 (for 100% outdoor air) or ANSI Z83.18-2000 (for recirculation).
Gas Train and Controls: Direct gas-fired system shall have a draw through design and field adjustable burner baffles. Gas trains up to 400,000 Btu/hr shall include a direct spark ignition system. Gas trains greater than 400,000 Btu/hr shall include a pilot ignition system and shall have digital coded fault indicator capability. Fault indicator shall provide service history by storing codes for the last five faults. Dual safety shutoff valves shall be industrial duty and use 120 VAC control signals. Temperature control shall incorporate a Maxitrol electronic modulation control system.
Unit Casing and Frames: Unit shall be of internal frame type construction of galvanized steel. All frames and panels shall be G90 galvanized steel. Where top panels are joined there shall be a standing seam to insure positive weather protection. All metal-to-metal surfaces exposed to the weather shall be sealed, requiring no caulking at job site. All components shall be easily accessible through removable doors.
Insulation: Unit casing to be lined with 1 inch fiberglass insulation where specified. Insulation shall be in accordance with NFPA 90A and tested to meet UL 181 erosion requirements. Double wall shall be provided where specified.
Fan Section: Centrifugal fans shall be double width, double inlet. Fan and motor shall be mounted on a common base and shall be internally isolated. All blower wheels shall be balanced. Ground and polished steel fan shafts shall be mounted in permanently lubricated ball bearings or ball bearing pillow blocks. Bearings shall be selected for a minimum (L10) life in excess of 100,000 hours at maximum cataloged speeds.
Motors and Drives: Motors shall be energy efficient, complying with EPACT standards, for single speed ODP and TE enclosures. Motors shall be permanently lubricated, heavy duty type, matched to the fan load and furnished at the specified voltage, phase and enclosure. Drives shall be sized for a minimum of 150% of driven horsepower. Pulleys shall be cast and have machined surfaces, 15 horse power and less shall be supplied with an adjustable drive pulley.
Electrical: All internal electrical components shall be prewired for single point power connection with exception of the larger evaporative cooling sections. All electrical components shall be UL listed, recognized or classified where applicable and wired in compliance with the National Electrical Code. Control center shall include motor starter, control circuit fusing,
control transformer for 24 VAC circuit, integral disconnect switch and terminal strip. Contactors, Class 20 adjustable overload protection and single phase protection shall be standard.
Filter Section: Filter section shall be designed such that velocities across the filters do not exceed 550 feet per minute. Filters shall be 2-inch washable aluminum mesh or 2-inch disposable.
Weatherhood: Weatherhood shall be constructed of G90 galvanized steel with birdscreen mounted at the intake.
Recirculation (optional): Recirculation airflow shall be controlled by adjustment of return damper position. Input signal for return damper shall be from building pressure sensors, potentiometer, external signal, or manual switch. Recirculated air shall not be permitted to pass across the burner. Return air shall be filtered.
Variable Volume (optional): Volume shall be varied by either a 2-speed motor or variable frequency drive. Input signal for fan speed shall be from building pressure sensors, potentiometer, external signal, or manual switch. A self-adjusting burner bypass damper shall maintain a constant air volume across the burner to ensure proper gas combustion. Bypass damper shall operate automatically without an electronic signal.
Cooling Coil (optional): Direct expansion (DX) or chilled water coil shall be factory tested and rated in accordance with ARI 410. Coils shall have copper tubes with permanently expanded aluminum fins, 12 fpi or less. DX coils shall be equipped with distributors to receive expansion valves at the liquid connections. Drain pans shall extend at least 12 inches downstream of coil and be sloped to drain connection. Cooling coil shall meet UL 1995 specifications for non-protected coil.
Evaporative Cooling Section (optional): Evaporative cooling section shall include a galvanized steel housing with louvered intake, 2 inch aluminum mesh filters and a stainless steel evaporative cooling module all provided by the make-up air unit manufacturer. The louver shall be stationary type with drainable blades, and be designed to withstand wind loads of 25 PSF. Evaporative cooling media shall be 12 inches deep, with a UL 900 class II fire rating for a cooling effectiveness of 90%. Drain and overflow connections shall be piped through the side of the evaporative cooling section.
