Specifications
7
V = volts pf = power factor
A = amperes
kVA = kilovolt-amperes BTU/hr = British Thermal Units per hour (heat output)
kW = kilowatts Kcal/hr = kilocalories per hour (heat output)
System Sizing
Sizing a critical power system to meet present and future
needsis a fundamental requirement.
Present Requirements
Estimating the present system size in kilovolt
amperes (kVA) is done in a number of ways. Typical
sources include computer site planning manuals,
equipment nameplate data, and electrical service
data. kVA and kW requirements are estimated using
any of the following formulas:
After the present kVA requirement has been
determined, the anticipated growth and the special
characteristics of the load must be considered.
G
rowth Requirements
The critical power system should be sized to anticipate
growth. Growth rates associated with data processing
centers double power requirements in a short time.
Therefore it is reasonable to size the system for twice
the present kVA load. Even in a minimum growth
environment, the power system should be sized for
125% of the estimated kVA load.
Special Load Characteristics
For special load characteristics, factory application
engineers should be consulted for recommended
system sizing.
System Grounding Considerations
The grounding of any power conditioning system is
critical to its performance. The National Electrical Code
provides for a safe electrical system. The ground path
req
uired by the NEC for safety should be enhanced
or improved for system performance, never defeated
or eliminated.
1. Power profile of equipment. (This is the most reliable
base from which to estimate present kVA loading.)
2. Kilowatts (kW) and Power Factor (pf).
(If pf is not given, assume 0.8).
For three-phase systems For single-phase equipment
kVA = V • A (1.73) kVA= V • A
1000 1000
3. Am
pe
r
e s
pecifications for the electrical service
feeding the site (for three-phase systems).
4. BTU/hr or Kcal/hr specifications:
(if pf is not known, assume 0.8).
kVA = BTU/(hr) = kcal/(hr)
3413
860
A = kVA /V/(1.73)• 1000
kVA = kW
pf
kVA = kW
pf