After David Mackay

[fivemack]

Every other day, I have a bath.

It is 50cm wide, 130cm long, 15cm deep, say 0.1 cubic metres or a hundred kilos - the water weighs slightly more than I do - and made of water at 40C, heated to that temperature from the 15C at which it arrives in the house.

So that's about ten megajoules - about three kilowatt-hours - of heat that had to be applied to the water. I've got a reasonably modern boiler of say 60% efficiency, the energy content of natural gas is 37 megajoules per cubic metre, so I'm using about half a cubic metre of gas to heat the bath, say twenty moles of methane. I've turned it into twenty moles of CO2 - 880 grams.

So my bathing habit produces 160 kilos of CO2 annually. Easyjet produces 100 grams of CO2 per passenger-kilometre, so my bathing habit is equivalent to an annual return flight to Berlin.

One ton of CO2 emission is equivalent to three hot baths a day for a year - that's a nice human-scale unit.

It doesn't seem unreasonable to hope that, as civilisation progresses, everyone in the world would be able to share my bathing habits. That would be a billion tons of CO2 annually, slightly under 4% of current planetary CO2 output and a little under the present output of the Chinese cement industry; not entirely unreasonable.

It is, however, also three billion cubic metres of natural gas a day, or say a round trillion a year (about 30% of the planetary consumption of 2.819Tm^3/year from reserves of about 200Tm^3); if the water was heated electrically, it's thirty petajoules a day - a third of a terawatt, three times the output of all the nuclear power stations in France, or the power produced by covering Luxembourg in solar panels.

This sounds as if the world can have a bath every other day in an entirely sustainable fashion for an infrastructure input of around fifty billion dollars a year (nuclear power stations costing $3 per watt and lasting twenty years); large but doable. I'm glad of this, I didn't know at the start of the calculation whether my ablutory habits alone would be enough to make my lifestyle unsustainable on planetary scale.

Comments

[ex-robhu.livejournal.com]

But you can get compact fluroescents that use far less energy. I have 3 150 watt equivalents that use approximately 100 watts total when all turned on at once.

[bohemiancoast.livejournal.com]

Except that they don't appear to provide light that my eyes find useful for ordinary tasks such as cooking, reading, or, indeed, bathing. My bedroom is lit by 3 '60 watt equivalents' that between them provide a sort of dim glow, a little like a nightlight. And these are the 'modern' lights that we're supposed to find adequate.

I can only conclude that I am not fooled by whatever trick the compact fluorescents pull; a 12 watt '60 watt equivalent' appears to me to be about as bright as, well, a 12 watt bulb.

Plus they are green and flash on and off, which I find rather disagreeable. And I despise turning a light on and having to wait for a second or two before it comes on. I fear that it is the thin end of the wedge; they have gone from being instantly available, like a PDA, to awaking about as slowly as a Mac laptop. The next generation of domestic lighting will no doubt be dimmer still, and take as long as a Windows laptop to boot.

I appreciate that as a child, I laughed at the stories of people who insisted on sticking with gaslight years after it had been completely overtaken by electricity. I think my current predicament is merely karma.

[ex-robhu.livejournal.com]

My experience of compact fluroescents has been the same as yours, but not with these current ones.

The current ones I have are not dim at all - they're blinding in fact - I had to get those chinese paper ball things to cover them to diffuse the light as guests would complain that they were being blinded by them.

They do still 'warm up' to go to full brightness, but are immediately as bright as a 100w bulb, and within about 1 minute are very close to their full brightness.

Your comments about the light not looking right may be due to you using 2400K fluroescents. The ones I have are 6400K, and look perfectly fine (in fact the colour reproduction of things is noticeably better as the light is whiter than the lightly yellow light I had before).

You should probably get one and try it out: http://www.ecofriendlylightbulbs.co.uk/product.php?productid=16180&cat=278&page=1

Oh, and about your mac comment - my macbook takes about a quarter of a second to wake :P

[bohemiancoast.livejournal.com]

OK, I have ordered two of the 30w daylight spirals. I'm hoping they're fab.

[ex-robhu.livejournal.com]

I look forward to a full review :->

[naath.livejournal.com]

LED lighting is on the edge of possible-for-houses these days (as in, you can get but it costs lots); almost certainly going to be masses better than fluorescents. So a brighter but also more efficient future there.

I also prefer showers to baths (for speed) - I find that putting the plug in when taking a shower (our shower is over the bath) gets me a bath with maybe 2 inches of lukewarm water in it; compared to taking a bath which gets me a bath almost entirely full of very hot water. So I'm confident that showers use less water than baths.

Showers that do their own heating (with electricity) are possibly bad, because gas water/heating is more efficient; because electricity generation is done by heating water with gas and has inefficiencies. Except that if you want to move away from using *any* gas then electrically heating water is better (because electricity can come from wind farms and nuclear power).

The passive solar heating idea is probably the best bet for water-heating efficiently. But it's a bit expensive.

[ex-robhu.livejournal.com]

LED lights are suitable for spotlights now, but not very good for generally lighting your home as it's hard to make them anything other than spotlights.

They are narrow band light sources, with poor correlated colour temperatures (CCT) which means if you light your whole home with LEDs, (for most people) the 'quality' of the light will look bad. This was a problem on older compact fluroescents too, but modern ones come with 'daylight' (6400K) CCTs.

Of course LEDs are very efficient. The ones I have in my home are 2 watt GU10s, being equivalent to about 20 watt incandesents.

[naath.livejournal.com]

I have trouble believing that you can't un-spot a spot-light by careful use of defusing filters and mirrors. Possibly expensive though.

Normal lightbulbs aren't "daylight" though, you have to pay extra. At least LEDs don't flicker. I'm not sure what's so great about "daylight" bulbs (and I don't pay for them).

[ex-robhu.livejournal.com]

Probably expensive and bulky I'd imagine.

You do have to pay extra for 6000K+ compact fluorescents, but not that much more (http://www.ecofriendlylightbulbs.co.uk/product.php?productid=16180&cat=278&page=1), particularly when you consider you're going to be saving an enormous amount compared to an ordinary incandescent.

Older compact fluorescents flickered quite badly. Modern ones don't so much. Ones with a modern electronic ballast flicker at about 30,000Hz, which is too high for people to detect.

I've tried both 2000K and 6400K compact fluorescents out, and the difference in colour quality is really quite obvious, not just in looking at the bulb but in looking at the lit room. I'd never go back to a 2000K fluorescent now.