February 06, 2010
Phase Change Material Could Cool Houses
MIT's Technology Review reports on paraffin wax capsules could use the cold of evening to cool rooms in the day.
Building materials that absorb heat during the day and release it at night, eliminating the need for air-conditioning in some climates, will soon be on the market in the United States. The North Carolina company National Gypsum is testing drywall sheets--the plaster panels that make up the walls in most new buildings--containing capsules that absorb heat to passively cool a building. The capsules, made by chemical giant BASF, can be incorporated into a range of construction materials and are already found in some products in Europe.
This won't help much so much where the difference in day and night temperatures is small. But desert areas get very cool at night. So this approach would work well for these areas. What I wonder: Does the paraffin increase the flammability of the walls in a fire?
One could also use a similar approach to make use of lower night rates for electricity. Run an air conditioner or ground sink heat pump at night and use it to cool a compound from liquid to solid phase at night. Then blow home air over the solid during the day to cool it.
Pricing of electricity by time of day and even by level of demand would provide more incentive to implement storage systems for heat and cool. Changes in utility regulatory policies to change electricity pricing based on supply and demand would encourage greater use of materials for storing cool and heat.
This goes straight back to efforts publicized in the 70's (and even earlier things written up by Farrington Daniels). Yes, wax-impregnated wallboard will burn if it gets hot enough to release the wax (fuel is fuel). I'd lean more toward phase-change salts if they can be isolated and kept from separating beyond re-dissolution.
If they tax/credit electric (and plug-in hybrid) cars to a significant level of use, the night electricity underuseage that guided the night discounts will disappear.
Engineers seem to go for the easy solutions: Hot during the day, cold at night. Most of the the 'green' solutions are designed for extreme temperature swing environments. Now try temperate or tropical environments, where it's hot and humid during the day AND night. If you can solve this with phase-change materials, I'll give you a gold star.
They did this for our building when I worked at Hughes Aircraft in the 80s. They used Glaubers salt in plastic bricks (like the blue ice things in your freezer) with circulating water. Have no idea how successful it was.
Large institutions -- Stanford University for one -- are employing your suggested strategy of using cheap night-time electricity to effect a phase change in a material, then blowing air over it during the heat of the day to cool the air without requiring significant electricity then. The miracle phase-change substance? Water!
We use a phase-changing material to cool our house right now, and it works extremely well. It's called HFC's, but it used to be called Freon. Very cool stuff.
Ummm... Adobe? (no not the company but the building material)
Thanks , Kevin for the most enlightened comment I have seen in months:
"We use a phase-changing material to cool our house right now, and it works extremely well. It's called HFC's, but it used to be called Freon. Very cool stuff."
Amazing what will come from innovation and most of what has already happened didn't need GOVERNMENT. Let the markets/economics do their thing.
You're doing this all on the inside (insulated cell) of the house. Are we even thinking about putting it in the thermal mass? What happens in winter, when you're paying to jack up that heat sink--does it all come back when the thermostat trips? Let's petition to repeal the laws of thermodynamics. They're just getting in the way.
So, paraffin (careful, that's British for kerosene) isn't quite flammable enough to encapsulate in my drywall.
Candles are made of paraffin: I wonder, will it burn? No, we're boldly going ahead into research on...loblolly sap. With enough tax and R&D incentives, it's sure to work.
Atlas Shrugged is a thousand pages long, yet I keep getting the feeling there's a chapter she left out. Just for you.
Barack Obama salt based phase change material video
Shows how phase change material works and how it can be applied. It also is naturally fire retardant.
It looks like the next solution to energy conservation.