Cool strategies for cooling buildings

Researchers at the National Renewable Energy Laboratory credit ancient architecture and developing world cooling strategies for their outside-the-box thinking that led to an air cooler that just might revolutionize air conditioning. NREL’s Desiccant Enhanced Evaporative, or DEVAP, system won an R&D 100 Award this year.

The idea was born when Ron Judkoff was a young Peace Corps volunteer in Kedougou, Senegal, one of the warmest places on Earth. “That’s where I really saw the effectiveness of evaporative cooling,” said Judkoff, principal program manager for building technologies at NREL.

“The Senegalese would make these clay pots to keep water in,” he recalled. “The pots didn’t feel wet on the outside, but they were semi-permeable. There was enough porousness in the clay that there was evaporation taking place. You could take a nice drink of cold water — and the water would stay cold in the pot.”

That semi-porous clay operated in a similar way as the high-tech membranes operate in NREL’s DEVAP system. DEVAP works in any climate and achieves comfortable cooling while saving 40 to 80 percent of the energy use of a conventional air conditioning system.

During his Peace Corps tenure, Judkoff also noted how indigenous people in Saharan and sub-Saharan climes would effectively cool their buildings with the clever use of spray from fountains and transpiration from plants. He went on to study architecture under James Marston Fitch, a pioneer in bio-climatic architecture at Columbia University, and gained a greater appreciation for the ways ancient peoples and modern indigenous people achieved cooling. They could even make ice in deserts using night sky radiation. They fabricated wind scoops to channel soothing natural ventilation into otherwise stifling buildings. Later he researched desiccants — materials with the capacity to dry out moist air, which are a must if air conditioning is to be comfortable in a hot, humid climate.

“I had this notion that if we could only combine desiccant and evaporative cooling we might be able to come up with something really important,” Judkoff said. “But it was just a notion, because with the materials available at that time, the cost, the weight, the volume — it just didn’t look like it would pan out.”

Still, Judkoff never completely let go of the idea, and in his early days at NREL he oversaw the first full-scale leap into evaporative cooling at NREL’s second building, the Solar Energy Research Facility. In Colorado’s dry climate, evaporative cooling by itself can achieve comfortable indoor climates. But it doesn’t work in vast stretches of the United States and the world where the air is too humid.

Next page: Improving on the elephant in the room