For Coffee Drinkers…
Interesting result here:
Dutch study (pdf in english) on the life cycle impacts of reusable vs disposable cups for coffee service found that hand-washed ceramic coffee cups are the most impactful way of consuming coffee, machine-washed porcelain coffee cups are the second-most impactful, and disposable single-use paper cups are the least impactful, with the notable exception of very high ozone depletion potential due to chemicals used in paper cup production. Polystyrene was middle-of-the-road. But read on…
Looking closer, the assumptions of the study are a little eye-opening. In particular, the study assumes the reusable cups are washed after every use, and that hand-washing uses an always-on under-sink electrical water heater. In this case, the environmental effects of the ceramic-mug system are “virtually entirely the result of using electricity” (46). Electricity is also the culprit in dishwasher-cleaned porcelain mugs, although dishwashers are more energy efficient than standby electric water heaters. Finally, the non-electricity-caused environmental impacts of the reusable systems come from eutrophication from detergents; non-phosphate detergents would mitigate this effect.
Most of these issues are considered in the sensitivity analysis (they didn’t talk about phosphate-free detergents). All you coffee drinkers should be relieved to know that simply by washing your mug with cold water (which the study calls “hygienically questionable”), ceramic-mug drops to rock-bottom in terms of impact. Even under their high-impact assumptions, washing with hot water is ok as long as you only wash after 4.5 or more uses.
The moral is that before you sneer at people drinking from disposable coffee cups (as I often do), you must first ask yourself, “are these the type of people who leave the hot water running when they do dishes and/or use a fresh cup every morning?” If they are, maybe you should thank them for using disposables instead.
Now, back to work…
REPLY))
Thanks for the link – I’m one of those people who needles anyone who reaches for the disposable (styrofoam!) cup at work. I wonder how the efficiency of an American-style automatic dishwasher compares?
Also, how does the energy consumption of a typical American-style hot shower compare to other energy uses? I bet it’s huge. (How many miles driving is equivalent to a 20-minute hot shower, etc?)
How does electric water heating compare to gas heating? I’m rather aghast at the concept of electric heating, since (I think!) conversion of fuel to heat can be nearly 100% efficient, but converting fuel to power to heat is limited by the carnot efficiency (etc).
REPLY))
@ Tobin Fricke
sigh…
hot showers are my one pernicious indulgence. well, hot showers and sleeping in. and today I had a hamburger..
So I have many indulgences.
Anecdotally, gas-fired heaters are about 80% efficient (heat loss out the exhaust). Electric heaters are themselves 100% efficient, although as you say, electricity generation is only maybe 35%. Generally, electricity should not be used for heat unless it’s running a heat pump, which can multiply efficiency by 2 or 3 (or more) as long as it’s not too cold out. [heat pumps basically air-condition the outside].
Gas-powered water heaters are a different story, since instead of just making heat they have to transfer the heat to the water. If the water is stored in a tank, then it basically just fritters away energy. Again anecdotally, tank gas water heaters are about 50% efficient. Tankless (on-demand) models are more like 75%.
If we back-of-the-envelope it, say a gas water heater is 50% efficient, the temperature change of the water is 40C, the flow is 2.5gpm or 9.5 liters per minute … and this isn’t a proper life-cycle assessment, of course … just the heating of the water would take about 3.2 MJ worth of natural gas per minute of shower, not counting the energy to pump the water in from Colorado.
In contrast, driving a car (well, my car) at 70mph I get 30mpg or 4.3 MJ of gasoline per mile.
That gives an equivalency of the better part of a mile of driving per minute of shower.
REPLY))
@brandon
I used this for my anecdotal numbers:
http://www.standardsasap.org/documents/WH_Q&A_Aug_2009_final.pdf
It seems like “Energy Factor” or E.F. that they use to rate water heaters is the efficiency of transferring heat to the water; but the linked document discusses energy efficiency at the point of use and says it’s more like 43% for most water heaters.