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Heat Exchanger

A device used to transfer heat energy from one medium to another. Common uses of heat exchangers are water to air heat exchangers in air handling units, plate and frame heat exchangers in economizers, etc.

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Harmonic distortion

Distortion in the line voltage waveform. Any cyclical waveform can be described as the sum of sine waves of various magnitudes which are integer multiples of the root frequency (60 Hz, 120 Hz, 180 Hz, etc.). Harmonics are often the result of the non-linear loading of the power distribution system due to the nature of solid state power supplies. Harmonics are detrimental to the efficiency and capacity of power delivery equipment and rotating equipment due to increased eddy current losses and non-fundamental frequency torques.

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Gateway

A network element interconnecting two otherwise incompatible networks, network nodes, subnetworks or devices. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.

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Flywheel UPS

A flywheel is a heavy shaft-mounted rotating disc that absorbs and stores twisting or spinning motion and then releases it as rotational kinetic energy to provide motion to a stationary, or nearly stationary object.

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Firewall

The primary method for keeping a computer secure from intruders. A firewall allows or blocks traffic into and out of a private network or the user’s computer. Firewalls are widely used to give users secure access to the Internet as well as to separate a company’s public Web server from its internal network. Firewalls are also used to keep internal network segments secure; for example, the accounting network might be vulnerable to snooping from within the enterprise.

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Entrance Facility (EF)

An entrance to a building for both public and private network service cables (including wireless) including the entrance point of the building and continuing to the entrance room or space. (569)

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Economization

A way of utilizing the local environment around the data center to aid in cooling of the IT load by natural means rather than use more energy. There are two common types of economization, Airside Economization and Waterside Economization; sometimes referred to as LINK. Economization is a great benefit to those who can take advantage of it due to the large energy saving opportunity.

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Duct Bank

An arrangement of conduits, used to transport electrical, telecommunications cabling or data cabling inside or outside of a data center facility arranged in an array.

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Dry-Bulb Temperature

The temperature of the air measured using a dry-bulb thermometer such that evaporative cooling has no effect. Typically taken in conjunction with a wet-bulb reading which does include the evaporative cooling effect in order to determine relative humidity.

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Dry Cooler

A liquid-to-air heat exchanger that is a radiator over which air is blown via fans. Typically used as the heat rejection device for water or glycol cooled condensers, may also be used as the heat rejection device for liquid cooled coils in an AHU under proper environmental conditions.

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Distribution Frame

A structure with terminations for connecting the cabling of a facility in such a manner that interconnection or cross-connections may be readily made.

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Direct Current (DC)

A non-time varying method of delivering power. While slightly more efficient then AC if utilized between the DC portion of the UPS and the power supplies in IT equipment, it has not won wide acceptance in modern data centers.

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