Słownik pojęć technicznych w branży Data Center (A-E) – część 1 z 3

Słownik pojęć technicznych w branży Data Center (A-E) – część 1 z 3

Kontynuujemy prezentację pojęć technicznych używanych w branży Data Center. Jak już pisaliśmy, naszym zdaniem coraz częściej pojawiające się zwroty przeniesione z języka angielskiego wymuszają potrzebę szybkiego i jednolitego sposobu komunikacji. Kluczem jest prawidłowe zrozumienie znaczenia definicji i prawidłowa ich interpretacja. W celu ułatwienia poniżej przygotowaliśmy słownik pojęć technicznych używanych w branży.

Poniższa lista przedstawia pierwszą część z ponad 320 definicji używanych w branży Data Center. W naszej opinii jest to kompletna lista. Jednakże każda norma, freamework, wytyczne, standardy mogą zawierać inne unikalne i użyteczne propozycje.

Mając na uwadze, że większość dokumentacji jest prezentowana w języku angielskim, a szereg sformułowań nie posiada odpowiednika w języku polskim pozostawiliśmy słownik bez tłumaczenia.

Jednakże jak sygnalizowaliśmy już wcześniej prowadzimy z kolegami pracę nad polskim słownikiem i definicjami dla branży Data Center (w języku polskim Centrów Przetwarzania Danych). Mamy nadzieje, że już niedługo będziemy mogli zaprezentować naszą wspólną pracę. Zapraszamy do współpracy w tym zakresie każdą zainteresowaną osobę. Każdy może pomóc nam w poprawnym przygotowaniu tego materiału.

W przypadku zainteresowania prosimy o kontakt na email biuro@bcagroup.pl .

Poniżej przedstawiamy pierwszą część słownika zawierających ponad 110 pozycji zaczynających się od litery A kończąc na literze E.

Życzymy miłej lektury.

Technical Dictionary in the Data Center (A-E) – Part 1 of 3

We continue to present technical concepts used in the Data Center industry. As we have already written, in our opinion, more and more frequently occurring phrases transferred from English force the need for fast and uniform communication. The key is to properly understand the meaning of definitions and correct their interpretation. In order to facilitate below we have prepared a glossary of technical terms used in the industry.

The following list outlines the first of more than 320 definitions used in the Data Center industry. In our opinion this is a complete list. However, each norm, freamework, guidelines, standards may contain other unique and useful suggestions.

Bearing in mind that most of the documentation is presented in English, and a number of wording is not equivalent in Polish, we have left the dictionary without translation.

However, as we have already signaled, we are working with colleagues on a Polish dictionary and definitions for the Data Center industry. We hope that we will be able to present our work together soon. We invite you to cooperate in this field with every interested person. Anyone can help us with the proper preparation of this material.

If you are interested, please contact us at biuro@bcagroup.pl.

Below is the first part of the dictionary containing more than 110 entries starting with the letter A ending with the letter E.

We wish you a pleasant read.

Pojęcie Definicja
Air Plenum or Floor Void An area created by the installation of a raised access floor used to allow the distribution of air created by a down flow air conditioning system.
Air changes per hour (ACH) The number of times per hour that the volume of a specific room or building is supplied or removed from that space by mechanical and natural ventilation.
Absolute Humidity Absolute humidity is the mass of water vapor in a given volume of air or gas, usually measured in grams per cubic meter. It may also be measured as the partial pressure of the water vapor. See Relative Humidity.
Access Block A single access switch or group of switches sharing one trunk/uplink – or set of redundant uplinks – to the distribution layer. Generally confined to one telecommunications room (TR). In a large TR, it is possible to have more than one access block.
Access Floor A system consisting of completely removable and interchangeable floor panels that are supported on adjustable pedestals or stingers (or both) to allow access to the area beneath.
Access Layer First layer of the three-layer hierarchical model. The Access layer is the point at which local end users are allowed into the network. In the LAN environment, this connection point is typically a switched Ethernet port that is assigned to a VLAN.
Access Provider The operator of any facility that is used to convey telecommunications signals to and from a customer premises.
Air handler, or air handling unit (AHU) Central unit consisting of a blower, heating and cooling elements, filter racks or chamber, dampers, humidifier, and other central equipment in direct contact with the airflow. This does not include the ductwork through the building.
Adapter A device that enables any or all of the following: (1) different sizes or types of plugs to mate with one another or to fit into a telecommunications outlet, (2) the rearrangement of leads, (3) large cables with numerous conductors to fan out into smaller groups of conductors, and (4) interconnection between cables.
Administration The method for labelling, identification, documentation and usage needed to implement moves, additions and changes of the telecommunications infrastructure
Alarm A visual and audible signal indicating the presence of heat, smoke or other products of combustion within the facility.
Asset Defined as any physical, technological or intellectual possession.
Attenuation The decrease in magnitude of transmission signal strength between points, expressed in dB as the ratio of output to input signal level.
Availability A ratio of uptime to mission time — usually expressed as a percentage — as applied to a component or system. For example, a system with 8759 hours of uptime in a year would have an approximate annual availability of 99.99% (8760 hours per year). The availability of a system is equal to the lowest availability of the components that comprise the system. Note: „Availability” does not tell us enough about the quality of service, since the same availability number can represent either 100 outages of one minute or one outage of 100 minutes.
AMF (Automatic Mains Fail over) Switch used in conjunction with a generator designed to monitor the condition of the electrical supply to your centre. The unit automatically switches between electricity board generated power and generator power to provide constant and stable power to your environment
Argonite An inert gas used in fire suppression Systems, consisting of 50% Nitrogen and 50% Argon.
Arrester A lightning arrester is a device used on electrical power systems to protect the insulation on the system from the damaging effect of lightning. Metal oxide varistors (MOVs) have been used for power system protection since the mid-1970s. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth.
Atmospheric Pressure Atmospheric pressure is the pressure caused by the weight of air above any area in the Earth’s atmosphere. Standard atmospheric pressure (atm) is discussed below. As elevation increases, fewer air molecules are present. Therefore, atmospheric pressure always decreases with increasing height. For example, a column of air, 1 square inch in cross section, measured from sea level to the top of the atmosphere would weigh approximately 14.7 Ib. A 1 m2 column of air would weigh about 10 tones. See density of air. STANDARD ATMOSPHERIC PRESSURE Standard atmospheric pressure or „the standard atmosphere” (1 atm) is defined as 101,325 pascals = 101.325 kPa. (see also Standard temperature and pressure) This can also be stated as: 29.92 inches or 760 mm of mercury 1013.25 millibars (mb) 14.7 psia or 0 psig 0,967838490064855 at (metric atmospheric pressure). This „standard pressure” is a purely arbitrary representative value for pressure at sea level. Real atmospheric pressures vary from place to place and moment to moment everywhere in the world.
Backboard Backboard generally refers to the A-C, fire-retardant, plywood sheeting lining the walls of the telecommunications facilities. Backboards may also refer to the entire wall-mounted assembly, including wire management and termination frames.
Backbone / Backbone Cable 1) Afacility (e.g., pathway, cable or conductors) between any of the following spaces: telecommunications rooms, common telecommunications rooms, floor serving terminals, entrance facilities, equipment rooms, and common equipment rooms. 2) In a data centre, a facility (e.g. Pathway, cable or conductors) between any of the following spaces: entrance rooms or spaces, main distribution areas, horizontal distribution areas, telecommunications rooms.
Barrier A fabricated or natural obstacle used to control access to something, or the movement of people, animals, vehicles or any material-in-motion.
Battery A battery is a type of linear power supply that offers benefits that traditional line-operated power supplies lack: mobility, portability, and reliability. A battery consists of multiple electrochemical cells connected to provide the voltage desired. Three Main Types: ■    Flooded Cell ■    Sealed Lead Acid ■    Nickel Cadmium The most common batter in a Data centre is the valve regulated lead-acid (VRLA) storage battery. This battery is rechargeable; it consists of lead and lead/dioxide electrodes which are immersed in sulfuric acid. When fully charged, this type of battery has a 2.06 – 2.14 V potential. During discharge, the lead is converted to lead sulfate and the sulfuric acid is converted to water. When the battery is charging, the lead sulfate is converted back to lead and lead dioxide.
Bonding The permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.
Blank Panel (Or Filier Panel) A panel, per the dimension requirements of CEA–E, which may be plastic or finished metal and which is not integral to any discreet electronic component or system. Used to block open U spaces in a rack to prevent or minimize by-pass air.
Break Before Make Transfer Switch A break before make transfer switch breaks contact with one source of power before it makes contact with another. It prevents back feeding from an emergency generator back into the utility line, for example. One example is an open transition automatic transfer switch (ATS). During the split second of the power transfer the flow of electricity is interrupted. Another example is a manual three position Circuit breaker, with utility power on one side, the generator on the other, and „off in the middle, which requires the user to switch through the full disconnect „off’ position before making the next connection.
Breaker Panel A breaker panel is a mounting enclosure for multiple electrical Circuit breakers. These are generally placed in two rows. Distribution boards are typically found in central locations inside buildings and often serve as the point at which electricity is distributed within a building.
Building Systems The architectural, mechanical, electrical. and control system along with their respective subsystems, equipment, and components.
Building Commissioning In the broadest sense, a process for achieving, verifying, and documenting that the performance of a building and its various systems meet design intent and the owner and occupants’ operational needs. The process ideally extends through all phases of a project. from concept to occupancy and operations
BREEAM Building Research Establishment Environmental Assessment Method (BREEAM) is a voluntary measurement rating for green buildings that was established in the UK in 1990 by the BRE (Building Research Establishment). Since its inception it has since grown in scope and geographically reach, being exported in various guises across the world. It is somewhat equivalent to LEED in North America and Green Star, in Australia. See LEED
British thermal unit (BTU) Any of several units of energy (heat) in the HVAC industry, each slightly more than 1 kJ. One BTU is the energy required to raise one pound of water one degree Fahrenheit. In the United States the power of HVAC systems (the rate of cooling and dehumidifying or heating) is sometimes expressed in BTU/hour instead of watts. The conversion to the metric unit kWh is: 1 kWh = 3412Btu/h or 1 BTU = 1055.05585 joules. 1 watt is approximately 3.413 BTU/h 1000 BTU/h is approximately 293 W 1 horsepower is approximately 2,544 BTU/h 1 „ton of cooling”, a common unit in North American refrigeration and air conditioning applications, is 12,000 BTU/h. It is the amount of power needed to melt one short ton of ice in 24 hours, and is approximately 3.51 kW.
Cabinet A Container that may enclose connection devices, terminations, apparatus, wiring, and equipment.
Cabinet (Telecomms) An enclosure with a hinged cover used for terminating telecommunications cables, wiring and connection devices.
Cable An assembly of one or more insulated conductors or optical fibers, within an enveloping sheath.
Cabling A combination of all cables, jumpers, cords, and connecting hardware.
Cable Management Physical structures attached to and/or within cabinets and racks to provide horizontal and vertical pathways for guiding and managing cabling infrastructure. Similar to pathways as defined in ANSI/TIA/EIA-A standards, horizontal and vertical pathways within cabinets and racks guide cabling infrastructure in an engineered and orderly fashion when connecting to equipment and connectivity housed within the racks and/or cabinets.
Cable Plant Cable, conduit raceways, vaults, junction/pull boxes, rooms, racks, equipment, patch bays/blocks, and other infrastructure required to provide physical, electrical, optical connectivity between buildings on the Owner.
Cable Rack Hardware designed and manufactured for horizontal pathway distribution of cable and inside wiring inside the MDF, TR, or TR rooms.
Cable Sheath A covering over the optical fiber or conductor assembly that may include one or more metallic members, strength members, or jackets.
Cable Tray A ladder, trough, spline, solid-bottom or channel raceway system intended for, but not limited to, the support of telecommunications cable.
Cali centre An environment specifically designed to support Staff and technologies required to deliver high volume effective and efficient Communications to an organizations internal and/or external customers
Campus A building or collection of buildings located within a limited geographic area – typically one contiguous piece of property.
CATV Cable Antenna Television system.
Centralized Cabling A cabling configuration from the work area to a centralized cross-connect using pull through cables, an interconnect, or splice in the telecommunications room.
CFM Based on the simplified heat transfer eauation of CFM = 1.76W/CT – (W = Watts and CT = temperature rise in Celsius). This equation describes the conditions wherein the chilled air delivered through a access floor tile in front of a higher density cabinet is consumed by the bottom half of the cabinet and the rest of the equipment in the upper portion of the cabinet pulls in ambient make-up air from the room. That make-up air will be mixed with the exhaust air from the hot aisle and as it is heated by the equipment, it will come out hotter and continue that re-cycling pattern, continuing to get hotter each cycle. That is the source of hot spots and the source of the conventional wisdom regarding the 6 kW ceiling. By removing all heated exhaust air from the room, and pumping a little extra chilled air into the room to effectively pressurize the data centre, you remove that dynamic of warmed ambient air and you can effectively have one constant air temperature throughout the entire data centre.
Change Of State A change from the normal operating stance of a system, whether required by maintenance or a failure, resulting from an automatic or a manual response to some form of system input or response.
Channel The end-to-end transmission path between two points at which application specific equipment is connected.
Chiller A device that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This cooled liquid flows through pipes in a building and passes through coils in air handlers, fan-coil units, or other systems, cooling and usually dehumidifying the air in the building. Chillers are of two types: (1) air-cooled or (2) water-cooled. Air-cooled chillers are usually outside and consist of condenser coils cooled by fan-driven air. Water-cooled chillers are usually inside a building, and heat from these chillers is carried by recirculating water to outdoor cooling towers.
Coil Equipment that performs heat transfer when mounted inside an Air Handling unit or ductwork. It is heated or cooled by electrical means or by circulating liquid or steam within it. Air flowing across it is heated or cooled.
Cold Aisle Containment Cold Aisle Containment augments its predecessor’s (hot aisle/cold aisle) arrangement by enclosing the cold aisle. The aisle then becomes a room unto itself, sealed with barriers made of metal, plastic, or plexiglass. Even at minor heat loads, there are challenges associated with hot aisle, cold aisle. Some of them include: Bypass Air the volume of cold supply air that enters the room but does not directly enter the IT equipment” – limiting the precise delivery of cold air at the server intake. Hot air where exhaust heat enters the cold aisle, either over the tops of racks or recirculation through open rack spaces, ensures that the cooling infrastructure must throw colder air at the equipment to offset this mixing. Hot air prohibits the air handlers from receiving the warmest possible exhaust air, contamination rendering their operation less efficient. Hot spots may persist as a result of all of the above Due to the open architecture of the data centre room, hot aisle/cold aisle cannot attain complete air separation. With the cold aisle encased, the cold air, delivered from under the floor, stays where it’s needed at the server intake. The roof and walls of the containment ensure that the only place this air can exit is through the rack mount equipment. The exhaust air, because of the boundaries, routes back to the air handlers only, eliminating the previous concerns of hot air contamination and hot air recirculation. If there is adequate capacity in the central plant, cold aisle containment can harness that capacity to support higher density cabinet installations. With mixing out of the equation, the system can focus on cooling the load instead of the entire room. As a result, data centre professionals have a more predictable system—a consistent server inlet temperature. Cold aisle containment ensures that server exhaust air is not unnecessarily cooled before it returns to the air handlers. By improving the heat exchange across the coils, the containment maximizes the capacity of the entire air conditioner. See also Hot Aisle/Cold Aisle Containment.
Condenser A component in the base refrigeration cycle that ejects or removes heat from the system. The condenser is the hot side of an air conditioner or heat pump. Condensers are heat exchangers, and can transfer heat to air or to an intermediate fluid (such as water or an aqueous solution of ethylene glycol) to carry heat to a distant sink, such as ground (earth sink), a body of water, or air (as with cooling towers).
Constant air volume (CAV) A system designed to provide a constant air volume per unit time. This term is applied to HVAC systems that have variable supply-air temperature but constant air flow rates. Most residential forced-air systems are small CAV systems with on/off control.
Controller A device that Controls the operation of part or all of a system. It may simply turn a device on and off, or it may more subtly modulate burners, compressors, pumps, valves, fans, dampers, and the like. Most controllers are automatic but have user input such as temperature set points, e.g. a thermostat. Controls may be analog, or digital, or pneumatic, or a combination of these.
Clear Zone An area separating an outdoor barrier from buildings or any form of natural or fabricated concealment.
Closed Transition A change or State or transfer where the electrical Circuit connection is maintained during the transfer. This is also known as “make before break”.
Commissioning Authority The qualified person, company or agency that plans, coordinates, and oversees the entire commissioning process. The Commissioning Authority may also be known as the Commissioning Agent.
Common Mode Noise (CMN) CMN is caused due the voltage imbalance between Ground & Neutral and is created by the ground and neutral currents. CMN is a major source of EMI in power supplies and can significantly damage computing equipment and cause permanent data loss. To protect the IT Load, bonding of N-G is required, and attenuation via a multi-shielded isolation transformer (K-13 or higher) must be done, combined with a TVSS to suppress transient surges.
Commissioning Plan The document prepared for each project that describes all aspects of the commissioning process including schedules, responsibilities, documentation requirements, and functional performance test requirements.
Commissioning Test Plan The document that details the pre-functional performance test, functional performance test, and the necessary information for carrying out the testing process for each system, piece of equipment, or energy efficiency measure.
Common Equipment Room (Telecommunications) An enclosed space used for equipment and backbone interconnections for more than one tenant in a building or campus.
Compartmentalization The isolation or segregation of assets from threats using architectural design or countermeasures, including physical barriers.
Component Redundancy A configuration designed into a system to increase the likelihood of continuous function despite the failure of a component. We achieve component redundancy by designing and deploying a secondary component so that it replaces an associated primary component when the primary component fails.
Computer Room An architectural space whose primary function is to accommodate data processing equipment.
Concurrently Maintainable & Operable A configuration where system components may be removed from service for maintenance or may fail in a manner transparent to the load. There will be some form of State change and redundancy will be lost while a component or system is out of commission. This is also known as a Tier 3 facility.
Conduit (1) A raceway of circular cross-section. (2) A structure containing one or more ducts.
Connecting Hardware A device providing mechanical cable terminations.
Connectivity Patch panels, cabling, connectors, and cable management used to create and maintain electrical and optical circuits.
Consolidation Point A location for interconnection between horizontal cables extending from building pathways and horizontal cables extending into furniture pathways.
Construction Manager An organization whose role is to manage the construction team and various contractors to build and test the building systems for the project.
Core Layer Within the three-layer hierarchical model, the Core layer is the high-speed switching backbone of the network. Its primary purpose is to allow the Distribution layer access to critical enterprise computing resources by switching packets as fast as possible.
CRAC A Computer Room Air Conditioner includes an internal compressor, using the direct expansion of refrigerant to remove heat from the data centre. This technology – often referred to as precision air conditioning – require outdoor heat rejection source. CRAC units are traditionally connected to remote condensers.
CRAH A Computer Room Air Handler includes only fans and a cooling coil, often using chilled water to remove heat from the data centre. This technology – often referred to as precision air conditioning – require outdoor heat rejection source. CRAH units are traditionally connected to chiller systems.
Critical Distribution Board A power distribution board that feeds IT loads. The CDB consists of individually mounted, molded-case Circuit breakers with shunt trip coils. The shunt trip coils are activated by the EPO system.
Cross-Connect A facility enabling the termination of cable elements and their interconnection or cross-connection.
Cross-Connection A connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers that attach to connecting hardware on each end.
Countermeasures The procedures, technologies, devices or organisms (dogs, humans) put into place to deter, delay or detect damage from a threat.
Cali centre An environment specifically designed to support Staff and technologies required to deliver high volume effective and efficient Communications to an organizations internal and/or external customers
Cat5E Cabling standard used for local area desktop data and voice networks. Bandwidth 100MHz
Cat6 Cabling standard used for local area desktop data and voice network. Bandwidth 250MHz
Classification of Data Centers (Tier 1 – Tier 4). The Telecommunication Industry Association (TIA) has published the TIA-942 standard for classification of data centre capabilities. Tier 1 – Basic: 99.671% Availability Susceptible to disruptions from both planned and unplanned activity Single path for power and cooling distribution, no redundant components (N) May or may not have a raised floor, UPS, or generator Takes 3 months to implement Annual downtime of 28.8 hours Must be shut down completely for perform preventive maintenance Tier 2 – Redundant Components: 99.741% Availability Less susceptible to disruption from both planned and unplanned activity Single path for power and cooling direction, includes redundant components (N+1) Includes raised floor, UPS, generator Takes 3 to 6 months to implement Annual downtime of 22.0 hours Maintenance of power path and other parts of the infrastructure require a Processing shutdown Tier 3 – Concurrently Maintainable: 99.982% Availability Enables planned activity without disrupting Computer hardware operation, but unplanned events will still cause disruption Multiple power and cooling distribution paths but with only one path active, includes redundant components (N+1) Takes 15 to 20 months to implement Annual downtime of 1.6 hours Includes raised floor sufficient capacity and distribution to carry load on one path while performing maintenance on the other. Tier 4 – Fault Tolerant: 99.995% Availability Planned activity does not disrupt critical load and data centre can sustain at least one worst-case unplanned event with no critical load impact Multiple active power and cooling distribution paths, includes redundant components (2 (N+1), i.e. 2 UPS each with N+1 redundancy) Takes 15 to 20 months to implement Annual downtime of 0.4 hours.
Cloud Computing (and Storage). Cloud computing is a style of computing in which dynamically scalable and often virtualized resources are provided as a service over the Internet.
Comfort Cooling Air Conditioning units that provide cooling and heating of air typically within an office/call centre environment. Usually ceiling or wall mounted
Computer Room A room designed to provide stable environmental operating conditions in to which IT equipment is installed
Condenser The heat exchange unit for an air conditioning system which is installed outside the building, usually on the roof, external wall or secure area adjacent to the building
Conditioned Supply Usually used in connection with the supply of electricity, it refers to a power supply which has been filter and cleaned to provide a high quality source of power
Contact centre An environment specifically designed to support Staff and technologies required to deliver high volume effective and efficient sales Communications to an organizations internal and/or external customers
CTI (Computer Telephony Integration) The functional integration of business software and telephone based com
Data centre A data centre is a purpose built facility for housing Computer systems and related electronic equipment and other associated components, such as telecommunications and storage systems. It generally includes a large Computer room, including peripheral rooms such as operations bridge, plant rooms, a comms room, and printer rooms with redundant or backup power supplies, redundant data Communications connections, environmental Controls (e.g., air conditioning, humidity Controls, fire suppression, chilled water), and a Security Post and special security devices. A bank for example may have a data centre where all its mainframes, servers, credit card Processing systems etc. live. It can occupy one room of a building, one or more floors, or up to the whole building. They are designed to run 24 hours a day all year round. A co-location centre is a type of data centre.
Damper A plate or gate placed in a duet to control air flow by introducing a constriction in the duet.
Delta T Delta T is a reference to a temperature difference. It is used to describe the difference in temperature of a heating or cooling fluid as it enters and as it leaves a heat transfer device. This term is used in the calculation of coil efficiency.
DCIE Data centre infrastructure efficiency (DCIE) is a metric used to determine the energy efficiency of a data centre. The metric, which is expressed as a percentage, is calculated by dividing IT equipment power by total facility power. DCIE was developed by members of the Green Grid, an industry group focused on data centre energy efficiency. How to Determine DCIE: 1.    Take a measurement of energy use at or near the facility utility’s meter. If the data centre is in a mixed-use facility or Office building, take a measurement only at the meter that is powering the data centre. If the data centre is not on a separate utility meter, estimate the amount of power being consumed by the non-data centre portion of the building and remove it from the equation. 2.    Measure the IT equipment load, which should be measured after power conversion, switching, and conditioning is completed. According to The Green Grid, the most likely measurement point would be at the output of the Computer room power distribution units (PDUs). This measurement should represent the total power delivered to the server racks in the data centre. PUE, the reciprocal of DCIE, is calculated by dividing total facility power by IT equipment power. According to the Uptime Institute, the typical data centre has an average PUE of 2.5. This means that for every 2.5 watts „in” at the utility meter, only one watt is delivered out to the IT load. Uptime estimates most facilities could achieve 1.6 PUE by using the most efficient equipment and best practices.
Dielectric A dielectric is a non conducting substance, i.e. an insulator. Although „dielectric” and „insulator” are generally considered synonymous, the term „dielectric” is more often used to describe materials where the dielectric polarization is important, such as the insulating material between the metallic plates of a capacitor, while „insulator” is more often used when the material is being used to prevent a current flow across it.
Dew Point The dew point or dew point of a given parcel of air is the temperature to which the parcel must be cooled, keeping barometric pressure constant, for it to become saturated with water vapor. At this temperature condensation will begin if conditions are suitable (presence of a solid surface or other condensation nuclei; otherwise called supersaturation) — water vapor then condenses into liquid water called dew. When the dew point temperature falls below freezing it is called the frost point, instead creating frost or hoar frost by deposition. Note that warmer air can hold a great deal more water vapor than can cold air. The dew point determines relative humidity. When the relative humidity is high, the dew point is closer to the current air temperature. If the relative humidity is 100%, the dew point will be equal to the current temperature. As relative humidity falls, the dew point becomes lower, given the same air temperature.
Down flow Air Conditioning Air Conditioning system designed to supply air at Iow level. I.e. through a raised floor void
Dark Fiber Unused installed fiber optic cable. When it is carrying a light signal, it is referred to as „lit” fiber.
Demarc Demarcation point between carrier equipment and CPE.
Demarcation Point A point where the operational control or ownership changes.
Design Document The record that details the design intent.
Design Efficiency The ratio of the KW required to serve the load divided by the total installed KW for that system. For example, if 2 MW of UPS power is required to serve the load and the Tier rating demands that a total of 3 MW of UPS power be installed, the design efficiency is .66 or 66%.
Design Intent Design intent is a detailed technical description of the ideas, concepts, and criteria defined by the building owner to be important
Designation Strips Paper or plastic strips, usually contained in a elear or color tinted plastic carrier, designated for insertion into a termination frame. Designation strips are usually imprinted with the adjacent terminal number and are used to aid in locating a specific pair, group of pairs, or information outlet inserted into the termination frame, or for delineating a termination field.
DNS Domain Name System. System used on the Internet for translating names of network nodes into addresses.
Domain A portion of the naming hierarchy tree that refers to general groupings of networks based on organization type or geography.
Double Ended A switchboard with two inputs, with an interposing tie breaker between the sources, where either end of the switchboard can supply 100% of the load. The double-ended system constitutes an N+1 or 2N system. This type of system may be used for dual utility systems, a single utility system split into redundant feeds, and may possess the Circuit breaker transfer system with the generator.
Earthing See grounding
Ecaro-25 Fire suppression gas which can be used as a direct replacement for Halon 1301. Otherwise known as Dupont FE-25
Electromagnetic Interference (EMI) Radiated or conducted electromagnetic energy that has an undesirable effect on electronic equipment or signal transmissions.
Energy Efficiency Measure Any equipment, system, or control strategy installed in a building for the purpose of reducing energy consumption and enhancing building performance.
EMS (Environmental Monitoring Systems) System used to actively monitor the status of environmental systems within a technology room and report alert messages.
Entrance Conduit Conduit that connects the Owners underground infrastructure with the building’s entrance room
Entrance Facility (T telecommunications) 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.
Entrance Point (Telecommunications) The point of emergence for telecommunications cabling through an exterior wall, a floor, or from a conduit.
Entrance Room Or Space (Telecomms) A space in which the joining of inter or intra building telecommunications backbone facilities takes place.
Equipment Cable; Cord A cable or cable assembly used to connect telecommunications equipment to horizontal or backbone cabling.
Equipment Distribution Area The Computer room space occupied by equipment racks or cabinets.
Equipment Room (T telecommunications) An environmentally controlled centralized space for telecommunications equipment that usually houses a main or intermediate cross-connect.
Event Typically, a message generated by a device for informational or error purposes.
Evaporator A component in the basic refrigeration cycle (in CRACs or CRAH) that absorbs or adds heat to the system. Evaporators can be used to absorb heat from air (by reducing temperature and by removing water) or from a liquid. The evaporator is the cold side of an air conditioner or heat pump.



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