melting – ARCHITERIALS https://www.architerials.com Materials matter. Tue, 28 Feb 2012 18:12:44 +0000 en-US hourly 1 https://wordpress.org/?v=4.9.4 The Wicked Walls of the West https://www.architerials.com/2010/02/guess-whats-melting-the-wicked-walls-of-the-west/ https://www.architerials.com/2010/02/guess-whats-melting-the-wicked-walls-of-the-west/#respond Thu, 04 Feb 2010 22:32:56 +0000 http://www.architerials.com/?p=232 When they poured water on the Wicked Witch of the West in The Wizard of Oz, she started to shrink, screetching, “I’m melting! I’m melting!” and it seemed like a really unpleasant experience for her.  Another way to describe the conversion from evil green lady to a pile of black clothing might be to say that the Wicked Witch of the West underwent a phase change, although “I’m phase changing! I’m phase changing!” doesn’t really have the same ring to it so I respect the script writer’s choice of words.  We benefit from the phenomenon of phase change on a daily basis: anytime water goes from a solid (ice) to a liquid (er … water) a phase change occurs that absorbs nearby heat energy and things like your coke or your spiked watermelon cool down.  It’s just science, people.  It’s just science.*

Image courtesy foo.ca

Phase-change materials add thermal mass to lightweight building materials without the need for all that pesky mass.  Historically, if you wanted to use passive cooling techniques in your buildings you built them in the desert with two-foot thick walls.  Since it would take all day for the heat to make its way through the massive walls, the rooms would stay cool.  At night when the temperature dropped precipitously (as it is wont to do in the desert), the heat that had finally managed to come through the walls would take all night to escape out again, and the rooms would be warm.  But most of us aren’t priviledged to live in the desert, and thick walls can be expensive to put up. 

Since the 1950s, several companies have tried and failed to develop passive cooling systems that take advantage of phase-change materials because incorporating them into common construction materials has been less than easy (Bourzac).  In consequence, we continue to see widespread use of lightweight construction materials that don’t store heat, leading to wild fluctuations in temperature that we use HVAC systems to overcome.

In light of all this I think you’ll be glad to know that “chemical giant” BASF has developed wax capsules that can be incorporated into lightweight construction materials such as gypsum drywall, ceiling panels, or aerated concrete blocks.  The capsules contain “paraffin waxes that melt at around room temperature, enabling them to keep the temperature of a room constant throughout the day. The waxes work best in climates that cool down at night, allowing the materials inside the capsules to solidify and release the heat they’ve stored during the day” (Bourzac).  The desert wins the “best passive cooling building site award” yet again!   

Image credit Peter Schossig

 The process for making these capsules is complicated but it’s predicated on the fact that wax and water find each other repulsive.  When BASF researchers beat melted wax into hot water, they wind up with small droplets of wax similar to what you might see an ill-mixed salad dressing (not that I recommend putting wax in salad dressing).  Acrylic precursors coat the droplets and then a catalyst is added to form an acrylic polymer shell around the wax.  At this point you can add the mix to gypsum to make drywall or you can dry it and add it to concrete or plaster (Bourzac).   

While it seems dicey to add highly flammable (or if you prefer, inflammable) wax to a building material, North Carolina – based National Gypsum “is working with the National Renewable Energy Laboratory and California’s Emerging Technologies Coordinating Council to field-test its heat-absorbing panels, which will be marketed under the name Thermalcore” (Bourzac).  The company plans to test the panels for a year to find out how they perform across all four seasons, the ideal wax capsule ratio, and how much energy they can possibly save.

WU XING:

The phase-change aspect of the material caused me to assign it to the water category, although it edged into fire due to the thermal aspect of things.  I also threw it into earth because it can be incorporated into concrete mixtures. 

*And since I am in no way a licensed scientist I probably didn’t explain that correctly.  Oops!

Cited:

Bourzac, Katherine.  “‘Melting’ Drywall Keeps Rooms Cool.”  TechnologyReview.com 02/04/10.  Accessed 02/04/10.  URL.

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