19 December 2013

Measuring Energy

Not sure why the picture shows cost in £. The device is
equally happy to display cost in our native R.
One of the best birthday presents I've ever received was an Energy Monitor given to me by one of my sons this year. Electrical Energy Monitor, to be more accurate, since I hardly see it measuring the other myriad forms of energy. It's one of those that plugs in to the AC supply, and in turn provides a plug for some appliance, allowing you to measure the consumption of that specific device.

As part of the Solar Project, I know to within a gnat's pubic hair width how much electrical energy we consume overall on a month to month, season to season basis, but nailing down the detailed usage of specific appliances has long been a problem – just not a high enough priority to justify running out to buy a monitor. But having been given one,... well, now I'm measuring every electrical device in sight.

I started, predictably, with my PC. My PC is switched on pretty much all day, every day, since it's a Work Device, and although I have been quite conscious about buying lower-power motherboards that actively manage fans and power to the various components, a more efficient (and probably not coincidentally a much quieter) Power Supply, energy efficient CPU and so on, but have nevertheless remained quite in the dark about exactly how much power this beastie draws. I am not so terribly interested in the specific consumption of something like the motherboard or the disks, but of the entire cluster of equipment; the PC box and all it contains, the monitor, all those trickle drain devices hanging off various USB hubs... they're all on at once, and that's what I most needed to get a handle on.

Amazingly, it turns out that my estimates were surprisingly accurate. At a "quiet" level of operation – the stuff we do most of the time: reading emails, browsing the web, typing blog posts and so on – the entire cluster draws around 105W. That's surprisingly little for what is, I confess, quite a decently powerful machine. Well,... it serves me perfectly doing some reasonably heavyweight software development, running the usual array of server applications, development tools and debuggers. I have, of course, avoided getting any sort of serious graphics cards. For a start I have little to no interest or skill in graphic work, and for another I'm not into any level of seriously graphic intensive gaming. (I could probably get into that world quite easily, but I fear – with some justification – getting sucked into a black-hole for time.) So: pleasant to find that my energy conservation efforts were not entirely in vain.

Power draw does surge up as high as about 150 to 170W in times of more intensive CPU use, but those are pretty transient events. Stuff like my Development Environment starting up and doing a whole bunch of work for perhaps ten or fifteen seconds. I also note that the consumption increases in proportion with the ambient temperature in the office – fans have to work a little harder to cool the electronics when the weather is hot. Some day any decade now I shall get around to installing the long planned for Solar Chimney in the roof as part of the the Whole House Passive Cooling System.

What is disturbing is that the Computer Cluster, much to my consternation, unexpectedly draw around 4.5W when it is "off". What the hell is that? I surmise that it is some parts of the motherboard sitting quietly waiting to be awakened by the ring of the telephone, or some incoming network packets, these all being pretty stock features of most motherboards. I have a Raspberry Pi computer currently doing service as a household network server that only draws 3W at peak, so 4.5W when allegedly "off" is atrocious and unacceptable. I believe I will install a master power switch somewhere on the desk so that I can completely sever the electricity connection at night, thus solving the problem. I need, in any case to do this as part of my Lightning Mitigation Strategy; currently (forgive the pun) I run around unplugging all devices when ever a thunderstorm rolls to near. I've lost many thousands of Rands-worth of kit over the years to lightning induced surges.

So it's been great fun, and quite educational, using the Power Monitor so far. I plan on monitoring the computer for about a week to give me a good estimate of its power use, then I'll move on to the other part of the Compute Centre, the DSL Router, RasPi and associated wall-warts and supporting devices. I don't expect their consumption to amount to very much, but they have the attribute of being always on which is an important factor when sizing the battery pack for a PV Solar setup.

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