explosion proof air conditioning 

PURPOSE:

The Birdwell internal relief pressurization systems were designed for meeting the National Fire Protection Association, Inc. 496 standard for purged control rooms in Class I (II) locations and are listed by ETL Testing Laboratories, Inc..

CONSTRUCTION:

Unit cabinets are manufactured using 16 gauge (.062) galvanized paint grip(optional stainless) steel. They are prime coated, then given two coats of polyurethane enamel for corrosive atmosphere protection.

The internal relief damper is made of type 304 stainless steel. The hinge is the continuous type, constructed of stainless steel.

The units are equipped with direct drive, axial flow aluminum blade fans for spark proof operation. The motors are suitable for the Class I (II) location specified on the unit nameplate.

The filter grilles are of the straight through egg crate design for low air pressure drop. The grilles are made of extruded anodized aluminum, hinged for easy filter replacement. The filters are the high velocity, low air pressure drop type.

A gas detection power relay may be provided as an option in the unit to deactivate the pressurization fan in the event of gas detection. The gas detection equipment and the electrical connections between the two items are to be provided by the customer.

A standard sized bolt ring flange is located on the top rear for mounting a matching ring flange fresh air stack. The stack is an optional item available in stainless or galvanized steel.

CONTROLS:

The pressure gauge is the Magnehelic type. Pressure range is 0.0 to 0.5 inches w.c. with an accuracy of two percent of full scale at 70 degrees F.

The explosion proof pressure switch operating range is .07 to .15 inches w.c.. An alternate explosion proof pressure switch with an operating range of 0.4 to 1.6 inches w.c. is used for some Class II applications.

Time delay relays are the solid state type.

The optional gas detection relay is single pole double throw 24 or 115 volt plug in type. The optional remote alarm relay is single pole double throw 115 volt plug in type. The optional local alarm bell is explosion proof and suitable for 115-1-60 power.

If the system is ordered for standard Class I, Division I (type "X" purging) duty, the off/on switch, the indicator lights, time delay relays, control relay, and optional relays are installed in an explosion proof NEMA 7 enclosure. In addition, the explosion proof motor is wired using mineral insulated cable.

If the system is ordered for standard Class I, Division II (type "Z" purging) duty, the motor is wired using liquid tight conduit and fittings.

INSTALLATION:

Provide an opening through an outside wall approximately 3/8" larger than the height and width of the unit to provide clearance (opening must be squared). See dimensional drawings for size.

We recommend that the unit be installed as close to the normal building passage door as possible so that when the door is opened, the pressurization air does not sweep through the building removing an excessive amount of heated or cooled air.

Also, when locating the unit, make sure there are no obstructions where the fresh air stack will be located, and that the stack will clear the roof overhang, if any.

Run a bead of silicone rubber caulking along the bottom of the opening, then carefully set the unit in the opening with the front of the unit approximately flush with the inside wall, then caulk completely around the unit.

Next, attach the mounting angles to the unit sides and to the building wall. It may be necessary to provide an angle iron shelf bracket to provide full support, especially if the unit must support a vertical stack.

Screws may be inserted through the unit case inside the fan compartment into the framed wall opening if desired.

After installation, carefully silicone rubber caulk between the unit and the wall opening to prevent water or air leakage.

Attach 1/4" stainless steel aircraft type cables to the attach points near the fresh air stack cap. Apply silicone rubber caulking to the unit flanged stack ring, then lift stack in position and bolt the matching flange rings together. Be sure the stack is plumb, then secure the guy wires.

CAUTION: Before making any electrical connections or performing any maintenance, make sure all power switches pertaining to this equipment are turned off and locked. In addition to the danger of electrical shock, the fan motors may have internal overload protection that could restart a fan without warning and cause serious injury! Also, before energizing any of the electrical equipment or making the initial start up of the pressurization system, make certain the ambient atmosphere is safe (non-hazardous). Although the pressurization system is suitable for the hazardous environment, other electrical equipment in the conditioned space may have arc making devices (relays, contactors, switches, etc.) that could ignite a flammable gas. This procedure should be observed any time the system has been off and must be restarted.

Field wiring must comply with the latest applicable articles of the National Electrical Code and the requirements of the United States Coast Guard in the case of offshore drilling/producing platforms or oceangoing vessel use. Wiring should be performed only by a qualified electrician.

In hazardous locations install and pour seals between the unit and all connecting conduit. Refer to articles 500 and 501 in the National Electrical Code for specific requirements.

Size conductors using the data supplied on the nameplate. Use only stranded copper conductors. Be certain the available voltage matches the data on the nameplate. A disconnecting means must be within sight and readily accessible from the unit.

The unit must be securely grounded to the grounding lug provided.

NOTE: Properly ground unit power supply conduit.

Provide power to the unit as indicated on the wiring schematic. The unit voltage and amperage requirements are noted on the nameplate.

After the power to the unit has been connected and tested, turn the pressurization controller system switch to the on position. If the building is not immediately pressurized (with all openings such as windows and doors closed), check the rotation of the pressurization fan (if 3 phase power).

OPERATION:

The pressure switch is preset to meet the National Fire Protection Association's 496 code requirement of .1" w.c..

With power applied to the unit, the system on/off switch may be turned to the on position for indefinite purge time. In this position, possibly hazardous gasses will be purged from the building.

If the building pressure is at, or above, the predetermined pressure set point, the green light will be energized to indicate normal pressure.

If the building pressure is not at the desired level, adjust the pressure control knob (located on the front of the unit) using the reference arrows for rotation direction for an increase or decrease in pressure.

With clean air ducted (free of hazardous concentrations of flammable vapors and gases, contaminants and any other foreign matter) to the fresh air inlet of the Birdwell pressurization unit, the fan will introduce only enough air into the building (with all doors closed) to provide a positive pressure while making up for normal leakage around doors, etc.

Should this leakage suddenly increase (as when a door is opened), the internal relief damper will close, thereby causing the full air volume to be directed into the building to maintain a high air flow through the open door. This minimizes the possibility of contaminated (possibly explosive) air from entering the building. Simultaneously, the red warning light is energized to indicate building pressure loss.

Should the door remain open, or for any other reason the building lose the predetermined pressure level for a time period of 20 seconds, the optional alarm bell will be sounded or optional relay contacts closed for user's remote alarm system (type "Z" purging). Or, in case of type "X" purging, the contacts may be used to terminate power to the control room.

MAINTENANCE:

The Birdwell pressurization units are practically maintenance free since the motors are lifetime lubricated and the fans are direct drive. However, the filter must be kept in a clean condition in order that it not impede air flow to the extent that the required air velocities are not met (NFPA 496 standard requires 60 fpm velocity through all openings capable of being opened).

We recommend that the filter be checked on a weekly basis until the rate of filter loading has been determined.

CAUTION: Since the filter is very close to the operating fan, the unit must be turned off before opening the filter grille.

Also, the motor may have automatic overload protection, and could start without warning, so be sure the main power has been disconnected before working on any part of the unit.

If any problem is encountered that is not covered in these instructions, or for any questions that might arise, call The Birdwell Company in Houston, Texas (281) 492-1786.