Conserving energy in an automated home

In the same way that the saying “you’ve got to spend money to make money” works, sometimes it’s also necessary to spend energy to save energy. An automated home may have more gadgetry than normal homes, but if set up correctly these little power-consumers can help to save energy. While the debate about whether the apparent global warming trend is the result of our actions, it can’t hurt to try to reduce energy use (or rather, conversion) as much as possible.

For years computers have had the ability to reduce their power use by shutting down hard drives or going to sleep automatically. Since then advancements have been made to further reduce power use. Some motherboards and processors support reducing the speed of the CPU when it’s not in high demand, and some motherboards even let the entire computer go into a low power ‘semi-conscious’ state suitable if you’ve got something that needs downloading. So if you combine all these features, you can save a good deal of power even for computers that must stay on most of the time (e.g. media centres, servers, home automation control systems).

Another way to improve the efficiency of a machine is to use solid-state memory. Generally this technology emits less heat than a hard drive, consumes much less power and operates much faster. The downside is the expense, the current relatively limited capacity, and their failure time (limited by number of write operations) for those that are based on Flash memory. However they are still suitable as system drives. Normally system drives never get the chance to go to sleep because they are needed for operations at the kernel level, and if you have virtual memory enabled they are also by default used as swap disks. SSDs don’t need to go to sleep because they only consume power when being written to and read from.

For systems that shouldn’t be on all the time the easiest thing is to make them go to sleep. The amount of power needed to keep a computer in sleep mode is significantly less than almost any other power saving mode. A small amount of current is used to maintain the system state in RAM. The best mode of all is hibernation because then the machine’s state is completely saved to hard drive so that the computer can be completely unplugged. I believe that Windows Vista uses a hybrid hibernation-sleep mode, which saves the state to disk before putting the computer into a normal sleep state (corrections welcome).

Embedded devices use relatively tiny amounts of power, so things such as the Media MVP should be preferred over their more power-hungry counterparts – in this case a media centre PC – where appropriate. Several companies are starting to produce really tiny PCs, based on embedded/solid state technology. These function like normal PCs, albeit at a slower speed, so can run standard PC operating systems, but at a fraction of the power. Some are even so light-weight that they can run solely off of a single roll-up solar panel. Since these are still quite new to the market, their price is relatively high compared to standard desktops, but prices will drop as demand increases. As a side benefit, since embedded systems are generally quite small, they use less resources and therefore I suspect they take much less energy to be produced.

So far I’ve not touched on what home automation can do. As most home automators will be aware, there are a number of products that allow remote control of lights and sockets within a house. Combine this with sensors around the home, and a connection to the alarm system, and you have something that can reduce your power use by turning things off that aren’t needed. When you leave the house, for example, as soon as you set the alarm all the TVs in the house could be switched off at the wall and any lights extinguished. To balance this with security, lights could be switched on/off to provide the illusion of occupancy at night. This can still save energy compared to just leaving a bunch of lights on, by using one or two normally then occaisionally switching a few more on/off to give the impression of someone moving about the house. To prevent lights being left on in the day time, light sensors could be placed around the house to detect when a room is bright enough to cope without having the light on.

Other sensors could monitor energy usage. At the moment there are a few commercial sensors available that display energy consumption on a remote display. These work by surrounding the incoming phase(s) of the house with what’s known as a current transformer. There’s no direct electrical connection, so an electrician is not needed for the installation – although care must be taken to avoid touching any exposed connections! However, as far as I’m aware there are no similar products that can connect to an IP-based network and interface with a computer. A product like this could allow people to track their use over time, and perhaps even partake in competitions to see who can reduce their power usage the most.

Thus far I’ve got the hard-drive standby mode sorted on the main fileserver in the house (boron) and now I’m starting to look at the other ways of reducing power. This will help reduce our electricity bills and of course reduce the burden on the national grid. The system drive for boron may be replaced with an SSD, since space isn’t really an issue for a server. The touchscreen controllers around the house will probably be based upon embedded devices, or at the very least low-power machines.

Once we have got all the rooms decorated and decided on light fittings, I will be able to retro-fit some power control technology (most likely X10 because of it’s cheapness, abundance and suitability for retro-fitting) and light sensors. Lights with energy saving bulbs can’t (generally) be dimmed, so these lights will have to use appliance switches. Incandescent lights, while rare in the house, can be dimmed so dimmer switches can be installed.

I’m also going to attempt to modify a commercially available current meter to connect to a network, then both record the results and use the live data to predict and reduce consumption within the house.

When the whole-house audio system is not in use, it will be switched off using the APC MasterSwitch remote power switch that is in my rack cabinet.

One of the ultimate dreams is to have a micro-generation facility. There are only really 2 choices for this – solar or wind (the local river isn’t large enough or close enough for hydro-electric). We have a very long (~100m) garden which would be suitable for a wind turbine, but I’m not sure about whether the wind is constant enough around here. Solar is more expensive per watt, and the panels would have to be mounted only on the rear of the house, if planning permission is granted at all. Our roof is fairly well exposed, so being able to bathe in the sun shouldn’t be a problem.

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