Energy audit advice
To complete an energy audit you can either call in an expert or buy one of the many devices available to measure your energy use. If you opt to do the job yourself, take the time to read up on energy usage first, as there are a few potential areas where you could trip up, particularly when measuring devices such as printers and computers. Their energy usage alters depending on the jobs they’re running so, for example, computers use more energy when they’re doing number crunching tasks, and laser printers will use more energy when they’re printing. If your device has a sleep mode, measure this too: you’ll be surprised at the amount of energy a device can use in a low-power sleep mode.
Once you’ve measured every device, you need to calculate their consumption in kilowatt-hours (kh). It’s most effective to calculate yearly usage – that way you can really get an idea of how much a device costs to run. For example, an item costing £2 a week in energy usage might sound reasonable, however, the calculation of £104 over a year is a little more thought provoking.
To calculate the consumption of an electrical appliance in kWh you will need your electrical appliances’ usage in watts, the number of hours that the appliance is in use per day and the number of days per year when the appliance is in use. Once you have these figures to hand, apply them to the following formula:
[hours] x [days] x ([watts] / 1,000) = number of kWh.
So, if your device uses 6 watts and is on 7 hours a day for 250 days a year, your kWh calculation will be: [7] x [250] x ([6] / 1,000) = 10.5 kWh.
While this calculation provides you with direct energy costs, there are other indirect costs that will not be on the list and also need factoring in. One of the indirect costs is cooling. Computers use energy and produce heat as a by-product. In the winter, this probably reduces your heating bills but in the summer it can add to your energy bills from the additional costs incurred to power air conditioning units.
Unfortunately, if you identify a high-usage device, there’s very little you can do to reduce the power consumption other than replace it or ensure that it’s switched off when not in use. Replacing the heavy energy users will, however, save you money in the long run. Plus, if the equipment is still functioning, you may be able to recoup some of the costs through selling the device.
Most electrical devices supply energy consumption figures – white goods such as fridges and freezers also give efficiency ratings – so when you’re choosing a new device check these figures first. The best place to look is on the product data sheet or on the manufacturer’s website. With desktops and monitors, the data sheet will quote three figures for usage – typical usage, maximum usage and a power-saving usage. Remember that the smaller the number, the better the power saving. While the power save mode is useful, the important figure is the typical usage figure.
