Using A Plugin Power Meter

>_When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science._
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>William Thompson, Lord Kelvin (1821-1907) – Popular Lectures and Addresses [1891-1894]

If you want to reduce your electricity consumption, you first need to understand where and how you’re using power around your home. You could keep running out to your power meter and reading it while turning various appliances on and off, but a power meter is a much more convenient way to measure it.

Broadly speaking, there are two types of power meters.

The first measures the incoming mains power to your house, and presents it in a more readable format (and usually somewhere inside the house, for added convenience). This gives a snapshot view of how much power you are consuming at any given time, and you can turn appliances on or off to see how they affect it. While this is useful, it’s limited in what it can tell you – for example, fridges and freezers cut in and out periodically, so you can’t easily tell how much power they use per day.

The second type of power meter looks like a timer switch or double adapter, and plugs into a power point. You then plug a device into it and use it normally, and the meter will measure how much electricity it consumes. It can measure both instantaneous (i.e. real-time) consumption and cumulative (i.e. total over a period of time) consumption.

This article will focus on the second type.

So, what can you use a plug-in power meter for?

Most obviously, you can measure the real-time power being drawn by an appliance. So you can walk around the house and see that your kettle draws 2200 W, your floor lamp draws 60 W, and so on. This gives you a good idea of which appliances draw lots of power and which only draw a small amount. It’s a good idea to minimise the use of the high-draw appliances.

You can measure peak power drawn by an appliance such as a washing machine that goes through various stages in its cycle, or a fridge that has a high start-up load. This is mainly handy for people running their house or caravan off batteries or generators, where you want to avoid overloading and tripping out the inverter.

Measuring the cumulative daily usage of always-on appliances like fridges, freezers and air conditioners takes into account their stopping and starting at various times throughout the day. You can then adjust your usage of those appliances (e.g. by changing thermostat settings) and measure the impact it makes.

Using the power meter in cumulative mode is also useful to measure the total power used by a full ‘run’ of an appliance like a washing machine, dishwasher or breadmaker. You can play with the different modes (e.g. economy mode vs normal mode vs heavy duty mode on a washing machine) to see how much different the various settings make. Sometimes the difference can be quite significant.

You could also make comparisons between different appliances with similar uses. For example, is it better to bake bread in the breadmaker or in the oven? Does it use less energy to steam vegies in the microwave or in an electric steamer? Does the old CRT TV or the new LCD flatscreen use less power?

An interesting thing to measure is the power drawn by your various appliances in standby mode, when they are not being used but still have power connected. Many older TVs, videos, stereos and even washing machines will draw power all day long – it is estimated that between 3% and 10% of average household power consumption is used by this ‘phantom power’. If your appliances are not well-behaved, you may need to get in the habit of turning them off at the wall.

If you have variable metering (i.e. different electricity costs at different times of the day), some meters will allow you to program in those costs and times so you can measure the actual daily cost of operating an appliance. You might discover that you can save considerable money by running them at specific times of the day, for example putting your dishwasher and washing machine on at night before you go to bed, when electricity is the cheapest, instead of during the day, when it is most expensive.

It takes a lot of fiddling around, but going through these exercises will give you a really good understanding of the power use of all your appliances. Once you understand that, you can change your habits to minimise the power you use each day. And when the time comes to replace appliances, you’ll be much more aware of the potential running costs and power use of the various options.

Probably the most common and best value power meter on the Australian market at the moment is the MS6115, available from Jaycar and other outlets. You can read my [MS6115 review](http://green-change.com/2008/11/27/ms6115-mains-power-meter-review/) for details.

You might also discover, like I did, that your ancient beer fridge in the garage is using 2.5 kWh/day all by itself! That energy use alone could justify the cost of a new, smaller, more efficient fridge.