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Survival-of-the-fittest programming leads to more efficient air-conditioning

September 3, 2013 - A survival-of-the-fittest programming method adapted by researchers at the National Institute of Standards and Technology (NIST in the U.S.) has led to the design of a more efficient rooftop air-conditioning system.


September 4, 2013
By Anthony Capkun

“What we’re doing is identifying the best possible route through the heat exchanger for the refrigerant to follow so that it achieves the highest efficiency,” explained David Yashar. “Given that the unit we studied has 144 tubes, the number of possible routes determined by a sequence of tube connections is astronomical… impossible for a human to explore using traditional methods.”

The NIST approach optimizes the connections among refrigerant-containing tubes so that maximum cooling occurs. This entails matching characteristics of incoming air—especially its temperature and velocity—with the temperature and other characteristics of the refrigerant.

“The objective is to optimally pair air and refrigerant at every location in the heat exchanger,” Yashar explained. That kind of matchmaking can be extraordinarily difficult, he says, largely because the flow of air over the winding circuitry often is very uneven.

The proof-of-concept experiment with a custom rooftop unit demonstrated the practical utility of the NIST approach of combining principles of engineering with those of natural evolution.

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Yashar and colleague Sunil Lee first used a laser-based method to map how much and how fast air flows over the original refrigerant circuitry. This data became fodder for a NIST computer model that simulates heat-exchanger performance. The team used this model with an algorithm that mimics the laws of evolution. The algorithm develops a population of tubing arrangements and the model evaluates the performance of each design in the population. The best potential tubing circuitries from one population served as the starting set for the next generation. After the number-crunching for several hundred generations of circuitry options was completed, a top choice emerged.

The ultimate solution was a circuitry design that increased the heat exchanger’s potential cooling capacity by 8% and, when used to replace the existing design, boosted the entire system’s energy efficiency by 3%.

That amount of improvement could be enough for a manufacturer to achieve compliance with increasingly stringent energy efficiency standards, say researchers. It also could translate into material savings: a reduction in the amount of copper tubing in a heat exchanger without sacrificing performance.