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# Difference between revisions of "How to do an electrical energy audit"

## What

A home energy audit is a tally of all of the heat and electricity use in your house. This describes an electrical energy audit, in which you assess the electrical energy demand of the appliances in your home or work in order to find ways to reduce. Often this is done using a spreadsheet and an energy meter such as a KillAWatt.

## Why

Many conserve water by turning off faucets while brushing teeth and fixing leaks, but electricity is hard to see. An electrical home energy audit can help you understand your usage, conserve and even fix some leaks.

## Definitions

Before we start, here are some definitions. See Electricity basics for more.

Voltage (V)
Charge pressure measured in volts (V)
Current (I)
Flow of charge measured in amps (A)
Power (P)
Electrical power measured in watts (W)
Energy (E)
Electrical energy measured in watthours (Wh)
Usually seen in kilowatt-hours (kWh) or (kW-hrs), 1000 watthours.
Any electrical device plugged into the wall.
Truly frightening beasts that suck energy even when devices are ‘’off’’’.

## How

The basic idea of an electrical energy audit is to analyze the amount of electrical energy used by every device/appliance/load. This spreadsheet will help you complete your electrical energy audit.

Some loads in your home are easy to estimate. For example, light bulbs come with a specific power rating such as 25W. This power rating is the average power draw of the light bulb when it is on. To find the energy use of that bulb you would only need to multiply by the time it was used for. A 25W light bulb on for 4 hours per day would be 100Wh/day (25W*4h/day).

Some loads are more variable. For example, a computer might be rated at 200W, but will only consume that high rate when the computer is working hard (e.g. playing a new video game or rendering 3D). To work around this, you can (a) do the audit assuming the maximum power, (b) look up some average power values online, or (c) use an energy monitor (like a KillAWatt) to find the real average power for your computer and use. Then to find the energy use, simply multiply that average power by the hours that load is used.

Some loads have variable states. For example, a refrigerator will have a few possible states the maximum power is when the compressor is running (and might be 500W), whereas some states are quite low (e.g. 50W). To find the energy use, you can (a) find the average energy values online or maybe even still stuck on your refrigerator from energystar (these values will often annual in the form of kWh/year), (b) use an energy monitor and leave it plugged in for at least 24 hours to find an average daily value. For loads like this in the spreadsheet you will skip all of the power and hours cells and just enter the average Wh/day value in energy cell.

Some loads might not show the power rating in Watts. For most household devices you can instead multiply the input voltage and current ratings to find the input power (because in an ohmic circuit Power = Voltage * Current).

Similar to doing a water audit you will need to take your various power ratings and multiply them by the amount of time each load is utilized. It is often simpler to estimate the amount of time you use a load per day, and then how many days per week. For more intense audits you can use a form next to devices to track their usage.