Power use and Heat

Posted Jun 5, 2008 9:06 UTC (Thu) by tialaramex (subscriber, #21167)
In reply to: Power use and Heat by zlynx
Parent article: Fedora harnesses the power of idle computers with Nightlife

Still a few caveats...

I used to think this way but then I spent more time pondering it. If you do have electric
heating it will usually be optimised to heat spaces where people live and work. Heating any
part of the house when it's empty (ignoring frost protection), or the closet with a household
server in it, or a spare bedroom, or even a living room when everyone's asleep upstairs, is
still mostly useless because no people benefit.

It's true in principle that you can find situations where the power isn't "wasted" by turning
it into heat, but they're rarer than might first appear. Maybe $100 spent running a PC
translates to $10 of "free" heating for some people, and even more for a few, but that's still
a poor reason to leave all that hardware running when energy prices are rising.

Power use and Heat

Posted Jun 5, 2008 17:01 UTC (Thu) by nix (subscriber, #2304) [Link] (5 responses)

I don't know about you, but in the UK we have a wide choice of heating: we 
can heat the whole house on a thermostat or we can heat none of it at all.

So the `heating unoccupied rooms' thing is irrelevant at best, because the 
standard central heating heats *all* rooms, including all the unoccupied 
ones.

Power use and Heat

Posted Jun 6, 2008 0:44 UTC (Fri) by wookey (guest, #5501) [Link] (2 responses)

whilst systems this dumb are indeed very common, things are steadily improving as people get
programmable room stats, TRVs, boiler managers, and even fancy linux-controlled home-autoation
systems. As eneergy prices rise the benefits of having a more flexible control system
increase.

I agree with your fundamental point that exactly how usefully your computers do or do not
contribute to house heating depends on the control system installed.

Power use and Heat

Posted Jun 6, 2008 18:08 UTC (Fri) by giraffedata (guest, #1954) [Link] (1 responses)

I believe central electric heating is rare in the US, because it's cheaper and more useful to put a separate electric heater in every room. In contrast, gas/coal/oil systems are centralized because it isn't practical to put a burner in every room. Or even a thermostat.

I've seen central electric (forced air is worth paying more for for many people), just not very much.

I don't know why that would differ between the UK and the US, though.

Power use and Heat

Posted Jun 6, 2008 19:09 UTC (Fri) by nix (subscriber, #2304) [Link]

Central heating in towns and cities in the UK is pretty universally 
natural gas-based. Outlying regions might use oil-based heating, storage 
heaters, or stranger systems, and places with broken or very old central 
heating or bad insulation might choose to stick electrical heaters in some 
rooms. Pure house-wide electricity-based systems are unheard of (by me at 
least): even heating your water with electricity is an emergency fallback 
for when the gas or boiler goes out. (It's also pretty much a historical 
curiosity: in thirty years I've never seen a built-in electrical immersion 
heater used, but they're still widely fitted).

Power use and Heat

Posted Jun 6, 2008 18:50 UTC (Fri) by tialaramex (subscriber, #21167) [Link] (1 responses)

So fine, I live in the UK too. If you have a whole house on a single thermostat that usually
means you're using gas central heating. In which case heating your house by leaving a PC
turned on is already horribly inefficient because of the price difference between gas and
electricity. You also live in a temperate country, where the house doesn't need to be heated
for most of the year (and indeed may be uncomfortably hot for a month or two each summer).

Any radiators installed since the popularity of home central heating in the UK really began
will have bypass valves so that you can disable radiators in unused parts of the house (e.g. a
spare bedroom) or add a cheap local thermostat (included in newer installations) which
bypasses when that room is above a certain temperature. Most installers will skip rooms that
are rarely occupied and can be heated by conduction or convection from elsewhere, such as
closets.

Any installation that's less than 30 years old will have a timer as well as the thermostat and
manual control, and newer ones will have a seven day variable timer. Typically this means you
only heat the house for a few hours every day, usually when you wake up (it's not nice to wake
in a cold house, and the timer may also control production of stored hot water for the
bathroom) and for a while in the afternoon or evening. There's no need to heat the house while
you're asleep, you will be comfortable at a lower temperature and the bedding insulates you
anyway.

The idea that all heat energy released by inefficient use is "free heating" in some way just
doesn't work out in reality. Unless you've got an electric element or fan heater next to the
PC that you leave switched on all the time, chances are that turning the PC off is a
significant net saving (I tend to work to £1 per watt as a rule of thumb).

Power use and Heat

Posted Jun 6, 2008 18:59 UTC (Fri) by tialaramex (subscriber, #21167) [Link]

Sorry, that should be £1 per watt _per annum_ of course, ie over a year's usage switching off
something that wastes 100 watts saves you about £100. If it wastes 100 watts for 6 hours per
day, that's £25. It's a rule of thumb, so your specific tariffs may be rather different
depending on the mixture of fixed versus variable costs, but probably not by an order of
magnitude.