June 16, 2008
Disposable or washable nappies?
I’ve been enjoying Slate’s “Green Lantern” feed:
A 1992 study from Franklin Associates estimated that producing a year’s supply of disposables, which are composed largely of plastic, consumes roughly 6,900 megajoules of energy, vs. around 1,400 megajoules for a year’s supply of cloth diapers. Yet the study concluded that cloth ended up being 39 percent more energy-intensive overall, given the electricity needed to wash load after load of dirty diapers.
That conclusion is now woefully outdated, however, given the major advances that have occurred in washing-machine efficiency (PDF). For a washing machine made in 1985, an 11-pound load of cottons washed in warm water used up 1.68 kilowatt hours of electricity and 34 gallons of water; for a machine made two decades later, the relevant figures are just 0.95 kilowatt hours and 12 gallons.
A 2005 study (PDF) by Britain’s Environment Agency took into account some of these technological advances. In making their calculations regarding cloth diapers, the study’s authors used average energy-consumption figures for machines made in 1997. They concluded that there was “no significant difference” between the environmental impact of cloth and disposable diapers. Keeping a child clad in home-laundered cloth diapers for 2.5 years emitted 1,232 pounds of carbon dioxide equivalent, vs. 1,380 pounds for disposable diapers.
So there. Also, are Priuses actually worse for the environment than Hummers? (No: but the source of the urban myth is interesting.) And, are mechanical dishwashers bad for the planet? No they aren’t:
More than 100 Europeans were observed cleaning a dozen full place-settings by hand. The German researchers found that the average hand-washer is quite the wastrel, using 27.2 gallons of water, which requires 2.5 kWh of electricity to heat. (The most careless hand-washers were Spanish and Portuguese, while the most economical were German.) An ultra-efficient machine, by contrast, used only between 3.96 and 5.81 gallons of water, and between 1 and 2 kWh of electricity.Advantage, technology. But if you read the German study carefully, you’ll see that the best hand-washers came close to matching the machine’s performance.
The feed is here.
[…] services really impose the greatest environmental harm — as opposed to speculating about it. Tim Harford reviews some studies suggesting that the outcomes will not be what we think. Others have done the […]
Posted by: CoreEcon » Blog Archive » Will emissions trading stick | June 16th, 2008 at 9:27 am | Report this commentI note that cloth still comes out in front.
However, I think this study still suffers from a flaw present in many other studies like this, which is that it still assumes that the cloth nappies will be laundered in hot water, soaked in chemical sanitising solutions first, and will be tumble dried afterward.
I (and many other cloth nappy users I know) wash nappies in cold water, do not soak in any chemicals and do not tumble dry.
It also assumes the nappies will be made from cotton, when many of the modern cloth nappies available now are made from less resource intensive fibres (hemp, for example).
I was pleased that they have realised that disposable users have been disposing their child’s excrement in landfill (illegally).
I am still waiting for the LCA comparison that shows the data for a user of hemp nappies, washing in cold water, not soaking in chemicals, and not tumble drying.
Posted by: Moospie | June 17th, 2008 at 5:35 am | Report this commentAs well as employing the uber-efficient German ‘two-bowls’ technique, I save water and energy by leaving the dirty plates and pans to build up on the kitchen side-board for as long as possible before attacking them all in one big go…
Posted by: Jobes | June 19th, 2008 at 1:44 pm | Report this comment2.5 KWh (9MJ) of energy is enough to raise 27.2 US gallons (103l) of water by only 21K.
So presumably much of that water is cold, because 21K above the temperature of the rising main is lukewarm at best. But even so, 103l sounds like a lot more water than I use to wash up as much as I can fit in dishwashers I’ve had. The mode in the study was 50-60l, not 100l. Likewise the mode energy use was 1.6-1.8 KWh, compared with mean 2.5KWh, and with 1 or 2 (depending on program) for the machine.
The 80 minutes time taken may be an over-estimate too, since the test methodology did not permit the well-understood hand-washing tactic of “leaving it in cold water until I can be bothered to do it”. Their 140-item test load is more than the two people in my household can reasonably create in one meal. We don’t even own “a dozen full place settings”, so would not be able to run what the study calls a full dishwasher load without first getting a bigger crockery cupboard.
It’s misleading to compare the mean of a broad distribution with the mean of a very narrow one (dishwashers are presumed pretty consistent). The question “should everyone wash up by hand or should everyone use a dishwasher?” is a false dichotomy. To minimise resource use, stingy hand-washers should hand-wash, since I reckon they beat the machine given that the unconsidered factors (better efficiency of gas water heating and the energy cost of manufacture) are in their favour. Wasteful hand-washers should either use a machine or change their technique.
In particular, I’d suggest that those who regularly wash by hand might tend to be better at it, than those who don’t. This suggests that, looking at short term marginal resource use, most people can stick with what they’re doing already and feel like it’s the right thing. How convenient.
Still, it’s interesting that the dishwasher beats all but a small proportion of hand-washers.
Posted by: SteveJ | June 19th, 2008 at 11:43 pm | Report this comment