Calculate Energy Usage
A typical green audit calculates energy usage, and makes an assessment on how to reduce energy consumption by recommending power saving methods as well as looking into cooling, and ventilation aspects.
The first step is determining the extent of energy usage by the IT resources. Refer to the wattage, or the maximum power the device draws; this is usually stamped on the bottom or back, or at the nameplate of the appliance. The actual consumption however, may vary depending on the settings. If the device does not specify the wattage, find the current draw in amperes using a tong-tester or any other method, and multiply the same by the voltage used by the appliance. Most IT equipment in the United States uses 120 volts.
Estimate the device’s energy use using the formulae:
Wattage × Hours Used Per Day ÷ 1000 = Daily Kilowatt-hour (kWh) consumption. 1 kilowatt (kW) = 1,000 Watts.
Multiply the resultant figure by the number of days for which the calculation is done. Finally, multiply the resultant figure by the local utility’s energy rate per kWh for the same period.
For instance, a personal computer and monitor with 120 Watts and 150 Watts respectively, in use for 4 hours a day consumes the following energy:
(120 Watts + 150 Watts × 4 hours / 365 days) ÷ 1000 = 394 kWh. Assuming the energy costs 10 cents per kWH, the total annual energy cost is $39.4.
Now, if the personal computer and monitor is replaced by a laptop that consumes only 50 Watts, the annual energy consumption becomes:
(50 x 4 hours x 365 ) / 1000 = 73 KwH, and at 10 cents per KwH costs just $7.3. Switching over to a laptop can result in 39.4 – 7.3 = $ 32.1 savings a year, all other things remaining equal.