Glossary
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Glossary
A-B
Apparent power A value of power for AC circuits
that is calculated as the product of RMS current
times RMS voltage, without taking the power factor
into account.
ASHRAE Standard 52-76 Industry standard for
air filtration efficiency set forth by the American
Society of Heating, Refrigerating, and
Air-Conditioning Engineers, Inc.
ASL Above sea level.
Btu/h The abbreviation for British thermal units.
The amount of heat required to raise one pound of
water one degree fahrenheit per hour, a common
measure of heat transfer rate.
C-D
CompactPCI The newest specification for
PCI-based industrial computers is called
CompactPCI. It is electrically a superset of desktop
PCI with a different physical form factor. See
http://www.picmg.org/compactpci.stm for details.
CFM The abbreviation for cubic feet per minute,
commonly used to measure the rate of air flow in an
air conditioning system.
Chilled water system A type of air conditioning
system that has no refrigerant in the unit itself. The
refrigerant is contained in a chiller, which is located
remotely. The chiller cools water, which is piped to
the air conditioner to cool the space.
Dehumidification The process of removing
moisture from the air within a critical space.
Derate To lower the rated capability of an electrical
or mechanical apparatus.
Downflow Refers to a type of air conditioning
system that discharges air downward, directly
beneath a raised floor, commonly found in computer
rooms and modern office spaces.
E-K
EIA unit The Electronic Industries Association
(EIA) defines this unit of measurement to be 1.75
inches in height. So then, 1U equals 1.75 inches (1U
equals 44.45 mm).
Hot Pluggable An item is hot pluggable if it can be
added to or removed from a chassis while the chassis
remains operational, but requires software
intervention to do the operation. An example of
hot-pluggable items are server blades. These items
are hot pluggable to the extent that OS and
hardware support is present. Also see hot swappable
below.
Hot Swappable An item is hot swappable if it can
be added to or removed from a chassis while the
chassis remains operational, and requires no
software intervention. Examples of hot-swappable
items are power supplies and fans. These items are
hot swappable assuming their removal does not
create an N-1 situation (for example, if a chassis’s
power status is n+1 then a power supply can be
removed without affecting the operation of the
chassis). Also see hot pluggable above.
Humidification The process of adding moisture to
the air within a critical space.
IA-32 Intel Architecture; 32-bit
IDE acronym for Integrated Device Electronics
Inrush current The peak current flowing into a
power supply the instant AC power is applied. This
peak is usually much higher than the typical input
current due to the charging of the input filter
capacitors. When switching power supplies are first
turned on, they present high initial currents as a
result of filter capacitor impedance. These large
filter capacitors act like a short circuit, producing an
immediate inrush surge current with a fast rise
time. The peak inrush current can be several orders
of magnitude greater than the supply's typical
current.
KVA Abbreviation for kilovolt-amperes. (1000 x
volt-amperes)
