We may look back in wonder at the myopia of our times. Energy efficiency technologies are often expensive and untested compared to today’s cheap (heavily subsidized) and proven solutions. A strong economic case can be built for sticking with today’s lowest cost materials and technologies if we accept a social discount rate (the percentage that discounts the value of future benefits to people) that gives short shrift to the future. Governments usually peg this at about 5% or more on a good day.
But science is advancing so quickly--or just applying old principles in new ways--that some conventional technologies don’t really make sense anymore. Take walls.
For decades, we have been using mined gypsum pressed between two cardboard sheets for the drywall hanging in most homes and offices. Now a construction material incorporating phase change materials (PCM), a polymer-encapsulated wax in this case, can store five times the thermal energy of conventional gypsum with just a bit more thickness, say scientists at Spain’s Polytechnic University Madrid.
Using these augmented gypsum boards, which may contain as much as 45 percent PCM (compared to just half that when the material entered the market in the 1980s), rooms can be kept a comfortable 20 to 30ºC without air conditioning. The system pays for itself within one to two years.
It works because phase change materials store and release large amounts of energy as they transition from one physical state to another--usually solid to liquid and back again. Heat captured during the day ("melting" the wax) is released slowly during the evening, while the night’s cooler temperatures, stored in the more congealed physical structure of the walls, buffers the daytime heat.
This kind of PCM board has already been used in the 2007 Solar Decathlon eco-house competition in Washington, D.C., but it’s starting to enter the mainstream construction trade: A similar product made by National Gypsum in North America called ThermalCORE is on the market.
In the future, look out for those melting homes.