Frequently Asked Questions - FAQs

This section provides answers to commonly asked questions regarding both product and organizational capabilities. If your question is not addressed in this section, feel free to submit your own questions to "information at purcellsystems dot com"

Questions and answers on outdoor enclosures

Q: What types of thermal management systems does Purcell Systems provide?

A: Outdoor enclosures and cabinets commonly deploy four main types of thermal management technologies - Direct Air Cooling (DAC), Air Conditioning (A/C), Air-to-Air Heat Exchange (HEX), and Thermoelectric Cooling (TEC).

Direct Air Cooling (DAC) –A combination of vents, fans, and filters, DAC uses natural thermal efficiencies of ambient air while simultaneously lowering your system costs.  DAC Systems can utilize inexpensive mesh filters, or hydrophobic filters to prevent moisture entry into the enclosure.  Poor environmental conditions may dictate frequent filter changes.

Heat Exchanger (HEX) - A heat exchanger is a closed loop cooling system designed for efficient heat transfer from one medium to another. The air flow within the HEX is separated by a solid wall, so that air flows never mix, and an air-tight seal can be maintained within the enclosure. HEX prevents air contamination, dust and humidity issues caused by outside environments.

Air Conditioner (A/C) - A/C is a closed loop cooling system that dehumidifies and extracts heat from the enclosure interior. A/C uses a compressor-based refrigeration cycle. In a refrigeration cycle, a heat pump transfers heat from a lower-temperature heat source into a higher-temperature heat sink. The most common refrigeration cycle uses an electric motor to drive a compressor. 

Thermoelectric Cooler (TEC) – A thermoelectric cooler uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier device is a solid-state active heat pump which transfers heat from one side of the device to the other, with the consumption of electrical energy, depending on the direction of the current.  When direct current runs through the Peltier device , heat is moved from one side to the other. Therefore a TEC can be used either for heating or cooling by reversing the current with an intelligent controller.

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Q: Can all enclosures offered by Purcell Systems be fully cooled by their thermal management systems?

A: Some manufacturers may offer a specific enclosure size that may not be adequately cooled by the single thermal system once the equipment is installed.  The surface area on a single door face may not accommodate an adequate thermal system.  Purcell Systems offers a wide selection of thermal systems that can adequately cool and heat specified enclosure configurations without stranding any Rack Unit (RU) capacity within the enclosure. In the event of suboptimal pairing of enclosures and thermal systems, Purcell Systems offers custom thermal systems to optimize the operational performance of the enclosure.

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Q: What is zone cooling?

A: The enclosure, and all its affiliated accessories, can accommodate multiple temperature zones, with each zone capable of being independently equipped with any thermal system technology .  This enables the enclosure to keep one horizontal zone at a different temperature than another.  By grouping equipment into different operating temperature ranges, zones can be designed to maintain each group of equipment within the recommended temperature ranges, while reducing operating costs.  Variable speed fan control reduces the energy consumption, and reduces the acoustic emissions to the surroundings.   This capability is especially useful for enclosures that house both batteries and electronics.

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Q: How does Purcell Systems support field upgrades of the thermal management systems?

A: The recommended mounting scheme for thermal systems is externally mounted, typically on the front and/or back doors.  The mounting mechanism and interior venting accommodates upgrades within a family of thermal systems (i.e., a medium HEX to large HEX), as well changing to different thermal systems (upgrade medium HEX to large A/C).  Field upgrades of thermal systems are accomplished by exchanging doors which have dissimilar thermal systems.  This exchange can be accomplished in minutes by a standard craft person.  By standardizing on the common doors, interchangeable hardware (hinges, latches, handles), and thermal systems for Purcell System’s entire product line of enclosures, field upgrades are cost effective and time efficient without having to take the enclosure out of service.

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Q: Does Purcell Systems allow vertical stacking or horizontal line-up for expansion or large installations?

A: Purcell Systems allows the operator to standardize on one enclosure brand and model, while also providing flexibility for the different equipment configurations and deployment challenges presented by different environments.  Shorter enclosures offer vertical stacking features or mounting on a raised plinth for easier access.  If multiple enclosures are to be stacked, the top and bottom of the enclosure provide aligned bolt patterns to enable joining.  Note that these bolt holes should are only accessible from the interior of the joined enclosures to prevent tampering.  Another key consideration is meeting seismic zone requirements when enclosures are stacked.

The enclosure architecture also accommodates horizontal stacking of enclosures, typically called a line-up.  This enables expansion, while utilizing the power terminated in the first enclosure.  For larger openings between chambers, features that enable horizontal expansion include aligned bolt patterns and cable entries for mechanical joining of the adjacent walls.  For basic routing cables among chambers, the alignment of knockouts on adjacent walls and cables seals are required.

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Q: What features are offered to provide security?

A: Security is a critical concern for any network operator.  Unauthorized access to equipment can quickly lead to network downtime, which results in poor service levels and unhappy subscribers.  Enclosures and cabinets from Purcell Systems have numerous features that provide uncompromising security.

Interior Door Hinges - Hinges on all access doors should be only accessible from inside the enclosure, and reside inside the exterior gasket area of the enclosure so they are protected from exposure to the elements. The hinge should not be accessible when the door is closed.  Unlike interior hinges, exterior hinges can be easily knocked off the enclosure, thus allowing the removal of the door and access to the enclosure interior. Exterior piano hinges can easily be defeated with a hacksaw, allowing door removal and access to the enclosure interior as well.

Door Latches and Frame – All exterior doors should be locked with a multi-point latching mechanism to ensure that all door corners and edges are secured.  Any latching mechanism for the door should be in the enclosure interior.  The latching system should also be captive such that when the handle is in the locked position, the latches effectively bond the door to the cabinet. Latches that aren’t captive can easily be defeated with a crowbar.  The door latching hardware and mechanism should be capable of withstanding torque levels, typically 400 in-lbs, without any physical distortion or loss of functionality.  In the event that the exterior handle is compromised, the latching mechanism should not be accessible to external tampering, and stays in the locked position.

Unauthorized intrusion can be accomplished by prying the door open with a crowbar.  When closed and locked, the door should be flush with the enclosure frame and provide no more than a 3 mm gap for any prying tools. In addition, the interior of the door frame has a flange perpendicular to the enclosure wall that ensures no narrow tools can access to the enclosure interior.  

Firearms Resistance – Any penetration of the enclosure wall provides enough access to compromise the enclosed electronics.  Purcell Systems GR-487 certified enclosures meet industry standards that specify that enclosures must be capable of withstanding a point blank 12-gauge shotgun blast without penetration of the cabinet wall by any pellets. 

Intrusion Alarms - Intrusion alarms provide signaling to a centralized alarm monitoring center of an unauthorized or unscheduled opening of the door.Alarms operate with all main chamber doors, as well as the side chamber.  This is an optional feature

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Q: Does Purcell Systems offer staging or integration services?

A: The operator may wish to outsource the integration of the installed equipment to the enclosure manufacturer.  Purcell Systems will design the enclosure with all of the equipment taken into consideration, and does offer staging services to simplify the installation process. Issues that are addressed during staging by Purcell Systems include; 1) the order the equipment is stacked for best thermal performance, 2) enabling easy access for service by best positioning the equipment mounting ears (i.e. front to back), and 3) pre-wiring for equipment, service lights, battery heaters, and laptop trays.  Purcell Systems does accept electronic equipment (as customer-supplied inventory, on consignment, or purchased directly from the manufacturer), and completes the entire installation of equipment and accessories prior to final installation in the field.  This staging and integration service is more efficient and cost effective if performed by Purcell Systems, and ensures the enclosure is architected for maximum efficiency and utilization.

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Q: How does Purcell Systems minimize acoustic emissions?

A: Purcell Systems uses numerous techniques to minimize acoustic emissions.  1) Sound-absorbing material can be installed around the air plenums and vents within the cooling systems and the enclosure. In addition, Purcell engineering will design the air flow path to also minimize the acoustic emissions.  2) Vibration decoupling is a structural principle applied to any moving parts.  Vibration decoupling means that any moving or rotating part is mounted to a fixture which is firmly attached to the enclosure base or foundation.  As an example, vibration decoupling discourages having a first fan mounted to the base of a second fan.  3) Variable speed fans are used to minimize oscillations and subsequent noise emissions (as well as power consumption).  4) Multiple vents will reduce noise emissions by diffusing the noise in multiple directions rather than maximizing the noise emissions along just one plane.  Purcell Systems can customize \enclosure configurations to meet specific acoustic thresholds.

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Q: What considerations and capabilities are affiliated with side chambers?

A: Critical features to be considered are the availability of side chambers for both sides of the enclosure, physical dimensions, NEMA Ratings (3R minimum recommended), the degree of Ingress Protection (IP) rating, cable entry seals and glands, three-point locking mechanisms, options for a secondary grounding bar, door activated lights, and intrusion alarm.

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Q: What are the common terms and phrases used to describe features for enclosures and cabinets?

A: Common terms and phrases for features of enclosures and cabinets