----- Forwarded message from Jae Kwon <[email protected]> ----- Date: Tue, 3 Jul 2012 21:29:21 -0700 From: Jae Kwon <[email protected]> To: Kragen Javier Sitaker <[email protected]> Cc: [email protected] Subject: Re: washing machines don't have to use energy to heat water X-Mailer: Apple Mail (2.1084)
Maybe your heated shower water can be stored for use with a washer. Maybe your clothes get washed while you shower. We should be wearing togas anyways. It's way sexier. On Jul 3, 2012, at 4:24 PM, Kragen Javier Sitaker wrote: > I recently saw an article that claims that heating water to 40° for washing > laundry consumes around 5–10kWh per load. > > However, it turns out that heating up water doesn't consume energy. You need > energy to do it, to be sure — but that energy is still in the water after you > heat it up. The Carnot limit prevents you from recycling most of that heat > into exergy to, say, drive the washing machine motor, but nothing is > preventing > you from transferring that heat from dirty water into clean water, or into a > heat reservoir that holds it until your next wash. > > First, is such a reservoir possible? Most definitely. You can buy > fractionated paraffin wax that melts at more or less whatever temperature you > want, to a few degrees of precision, with a heat of fusion near that of water > ice. A big Thermos inside the washing machine, full of paraffin or another > phase-change material, could hold a laundry load's full of heat for several > days, if not a week. But how to get the heat into it? > > The key is a clever little machine called a "countercurrent heat exchanger": > in > its simplest form, two parallel long pipes that have been welded together, > with > water, or some other fluid, flowing in opposite directions through them. As > the hot water flows in one direction, it loses heat to the cold water flowing > in the other direction — and the cold water, you might say, loses its cold to > the hot water. When the formerly hot water exits, it's just a little warmer > than the cold water going in, and similarly, the formerly cold water exits > just > a little cooler than the hot water was originally. > > The countercurrent heat exchanger is part of many animals (a nose is a variant > that needs only one tube, which acts as a heat reservoir, and the reason you > don't get hypothermia just from breathing) and its use in human engineering > goes back decades, if not centuries. And indeed devices like cement kilns and > Passivhausen use CCHE to reduce heat loss to manageable levels. > > So why doesn't your washing machine use one? Maybe because 5-10kWh per load > is > maybe a dollar at residential electricity prices, and saving US$30 a year > isn't > worth the extra machinery, fragile glass, and extra space. > > Essentially any process that heats something up to a high temperature, then > cools it back down, can have its efficiency improved by the same principle. > Firing pottery, making glass, casting metal, powder-coating metal, baking > bread, sterilizing water, making cement (as mentioned above), and so on. Many > of these processes are not inherently energy-consuming, or inherently consume > only a tiny fraction of the energy that we currently spend on them. > > Kragen > -- > To unsubscribe: http://lists.canonical.org/mailman/listinfo/kragen-tol ----- End forwarded message ----- -- To unsubscribe: http://lists.canonical.org/mailman/listinfo/kragen-discuss
