If you are serious about the energy efficiency of your buildings, there's a game-changing term you'd better get to know: phase change.
Phase-change materials, or PCMs, are being applied to building products at a rapidly accelerating pace. The substances can store and release huge loads of energy as they turn solid or liquid. No, don't worry; your building won't melt. The trick is using natural PCMs such as wool insulation, paraffin and clay finishes, which store energy to heat or cool structures a tiny bit across large surface areas. Even better, use super-duper engineered PCMs in concentrated doses within novel building products.
Another term to describe this material effect class is latent heat storage, or LHS.
These fortunately fickle PCMs have been applied to concrete, plaster, ceramics and glass. The latest advance is gypsum board invented by researchers at Polytechnic University (Universidad Politécnica de Madrid) in Spain. The patented drywall boards, made with a waxy coating of paraffin microcapsules, store thermal energy. Of course.
Tests show the new Spanish gypsum board can slash building energy consumption by up to 40 percent, mainly by holding five times the heat of conventional boards. That means a room will stay comfortable longer, with less air conditioning needed.
The Madrid team estimates a payback of less than two years, thanks to energy savings alone. (I think that's on installed cost.)
Spray-applied phase change
Last fall, we heard from researchers at University of Nottingham in Ningpo, China, who unveiled a heat-regulating material that will also cut building HVAC costs. It could be made as a fluid, to be added to wall paints or even sprayed onto the exteriors of existing buildings.
Readers of The Astute Architect often stop me here: If I can't spec it today, Chris, please don't bother me with these uppity science projects. Well, we have good news: Lots of phase-changer products are ready for your use on buildings right now.
First, spec interior walls with paraffin and ceilings with salt hydrate, just as the Solar Decathlon-winning German team did with surPLUShome a couple of years back. And just last year, the team from Appalachian State University used a hot-water system with phase-change substances to keep temps even, as well as a PCM-based wall cavity insulation to store daytime heat and release it at night.
This delayed heat transfer is the benefit behind RavenWindow and RavenSkin, the temperature-regulating building panels made by RavenBrick.
Your father's insulation is democratic, blocking all heat equally. The RavenBrick products are engineered for climates where releasing stored heat selectively, such as at night, is helpful. (It calls to mind the few times I've camped out in the desert -- PCM sleeping bags, anyone?)
RavenSkin and its sister windows use an outer layer that reflects heat when outdoor temperatures are above a certain threshold. Behind it is an air gap and then glass, creating a greenhouse effect in the void. Behind that is a downconverter material, which turns solar rays into infrared energy before it enters a PCM layer, to be held for use when conditions are right.
The bottom line: These full-wall solutions have a quick ROI and can cover an entire office building or school, with HVAC savings approaching 100%.
PCMs on the market today
The fact is that many manufacturers are using PCMs in their product formulations and assemblies, just like RavenBrick. But it would help if they use the term more, so awareness goes up.
The R&D scene is bubbling with activity in game-changing phase-changers. One of my favorite ways to look for better architectural solutions is in non-architecture magazines like Product Design & Development. (Alternatively, an architect could subscribe to the hundreds of technical and scientific journals that PD&D follows, such as Advanced Energy Materials or the stirring quarterly, the International Journal of Fatigue.)
For example, an MIT team came out with a cool-roof/hot-roof concept recently that even advertises its phase change prowess. The prototype roof tiles are black when it's cold out, absorbing heat, and then slowly turn white as they heat up, to reflect heat away. A polymer gel inside the roof panels is what makes the switch, activated by temperature.
The color-changing roofing tiles are a cool product idea that has a hot name: Thermeleon, which rhymes nicely with chameleon.
Great news, but here's a slight bummer: PCMs are being applied more to coffee warmers, cell phones and other consumer junk. Not building products or roadways or such -- huge surface areas where the impact could be truly earth-changing.
Yes, I know. It's just pure economics: PCMs follow the money too.
But the real future of PCMs is at the scale of the wall, the building, the city.