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Work Cell

The area of a rack and the related area immediately in front of and behind the rack. If a rack is 2 feet wide and 4 feet deep. Standard aisles are 4 feet wide front and back, so half of that space is workspace for a given rack. This results in a standard work cell of 32 square feet 2′ W x 4′ D x 2′ Front x 2′ Back. Actual work cell size varies with data center design.

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Wet-Bulb Temperature

The temperature of the air measured using a wet-bulb thermometer, that is, the temperature to which a wet surface can be cooled by evaporation. This temperature is affected by both the dry bulb temperature and the dew point of the air. Dryer air has a lower wet bulb temperature. This is a design constraint when utilizing cooling towers or evaporative pads in the cooling process.

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Watts per Cabinet

Usually based in Kilo Watts (KW) per cabinet is a unit of power density with in cabinet in the data center. This is a design parameter for total capacity for power load within a cabinet and the ability of the cooling plant to cool this load. At times the capabilities of the power installed within a cabinet may exceed the ability to cool the load which caused the KW per cabinet to be derated.

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Watt per Square Foot (WPSF)

A unit of power density. In a data center this is a bulk term that refers to the total load in a particular space divided by the total area of that space. This is a design parameter for total capacity of the cooling and power systems and is used in conjunction with point load (the amount of load in a small space such as a rack). In higher density data centers most operators refer to Kilo Watts per cabinet as measurement of capacity.

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Watt (W)

A unit of power, commonly used in electrical discussion, watts are the product of potential (volts, see V) and current (amps, see A). If the current and voltage are AC, the relationship between watts, volts and amps includes power factor (see PF), watts = volts x amps x PF.

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Water-side economizers

Use cold air to cool an exterior water tower. The chilled water from the tower is then used in the air conditioners inside the data center instead of mechanically-chilled water, reducing energy costs. Water-side economizers often operate during nighttime to take advantage of cooler ambient temperatures. Economizers can save data center operators substantial operating costs. According to GreenerComputing.org, economization has the potential to reduce the annual cost of a data center’s energy consumption by more than 60 percent. Use of cooler external environmental temperatures to preserve hardware is an important component in sustainable green computing practices in general. Unfortunately, economizers are only useful for data centers located in cooler climates.

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Water Usage Effectiveness (WUE)

A sustainability metric defined by The Green Grid, which is a measure of the water used on-site for data center operations including humidification and on-site evaporation for cooling or energy production. WUE is calculated by dividing ‘annual water usage’ by the ‘energy consumption of the IT computing equipment’ The units of WUE are liters/kilowatt-hour (L/kWh).

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Volt-Amp (VA)

A unit of apparent power. In AC circuits, the magnitude of the voltage across a circuit times the current through the circuit is the apparent power. Including a representation of the angle between the two waveforms in the form of power factor (see PF) yields the real power.

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Uninterruptible Power Supply (UPS)

A device placed in series with the supply of power from the utility which contains energy storage such that the supply of power from the UPS is continuous even when the utility supply is removed. While battery-based energy storage is the most common, flywheel-based energy storage is gaining in popularity due to the reduced maintenance cost. UPS is used to hold the load until either the generator turns on to handle the load or the utility power is restored. Battery based UPS systems have a finite time that they can handle the load, usually less than 10 minutes. Flywheel-based energy storage is usually less than 5 minutes depending on the design.

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