greenStation Power Consumption

Posted April 26, 2009

Raw Values

The following values for a greenStation system with 320GB hard disk, CD/DVD drive and D-Link 803.11G wireless adapter were measured during recent testing. Values are listed in both watts (for EPA Energy Star testing purposes) and volt-amps (for off-grid users).

System State Watts Volt-Amps
Off 1.562 mW 8.22 mVA
Standby 6.96 W 7.327 VA
Idle 36.02 W 37.13 VA
greenStation, WiFi, CD/DVD, 320GB

Energy Star TEC

Energy Star 5.0, category "B" desktop computer values:

ETEC = 8760 / 1000 * (0.55 * POff + 0.05 * PSleep + 0.40 * PIdle)

Substituting the actual values above, the annual power consumption, in kilowatts-hours, is

ETEC = 8.76 * (0.55 * 0.001562 + 0.05 * 6.96 + 0.40 * 36.02)
ETEC = 8.76 kilo-hours per year * 14.76 watts
ETEC = 129.3 KWH / year

Allowable power, excluding adjustments for additional hard drives and the 945G dedicated GPU, is 175 KWH / year.

Off-Grid TEC

The following values are calculated using the volt-amp values to reflect apparent power, rather than real power, for off-grid users.

ETEC = 24 * (0.55 * VAOff + 0.05 * VASleep + 0.040 * VAIdle)

Substituting the actual values above, the daily apparent power consumption, in volt-amp hours, is

ETEC = 24 * (0.55 * 0.00822VA + 0.05 * 7.327VA + 0.40 * 37.13VA)
ETEC = 24 hours per day * 15.22 volt-amps
ETEC = 365.4 volt-amp hours / day

Please be sure to divide by battery and inverter conversion efficiencies when calculating storage and production requirements for off-grid use.

The idle state amperage load value for a 120 VAC system using 12 VDC battery power is 3.1 amps. Please include conversion losses for the DC-to-AC inverter stage, as well as battery capacity (amp-hour) reduction due to discharge rate, when sizing battery storage and UPS size. See your battery manufacturer for capacity values at expected rates of discharge. See your UPS manufacturer for inverter efficiency values.



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