Engineering news
In Mumbai, about 40% of the city’s energy use goes on air conditioning. In the USA, it’s around 6% - but that’s equivalent to total electricity consumption of the whole of Africa. The same is true in many hot countries, and as developing economies develop a taste for cool air in their homes and offices, it could become a big problem. In China, sales of air conditioners have doubled over the last five years, for example.
Analysts are predicting a 33x increase in the amount of power consumed by air conditioners by 2100, and by the middle of the century, we’ll use more energy for cooling than heating. If we’re burning fossil fuels to generate that electricity, we risk a vicious cycle – cooling our homes could make the planet warmer. But maybe engineering can help.
Nano-coatings
One company are using nanotechnology which could make air conditioning more efficient. “At Oxford nanoSystems, we’ve developed a coating method which allows us to coat the internal surfaces of fully manufactured surfaces,” explains Alexander Reip, who is being supported by the Royal Academy of Engineering Enterprise Hub’s SME Leaders Programme.
That breakthrough has allowed them to develop technology that can rapidly increase the rate at which bubbles form on a surface, by increasing the number of points – effectively by making the surface much rougher.
It takes about an hour and a half to coat a heat exchanger, which is one of the key parts of an air conditioner, and in January the company will launch its first product aimed third-world refrigeration systems.
The company are working with the manufacturers of air conditioning systems for buildings, and with their suppliers. “With the coating, we can significantly reduce the size of these heat exchangers,” Reip tells Professional Engineering. “If we can get the size down by 50%, we’re looking at a 10% energy saving.”
Reducing leakage
Oxford Nanosystems aren’t the only company trying to make the heat exchanger more efficient. US company Optimised Thermal Systems is working on an advanced heat exchanger that minimises the number of joints, where refrigerants can leak out. “Approximately 50-80% of air conditioners and heat pumps are undercharged and leak as much as 10% of their refrigerant annually, which can release greenhouse gases into the atmosphere and reduce system efficiency,” write the creators, who have created tubing with aluminium fins that can be pushed together to leave no room for leaks.
Water cooling
Some are working on new systems that work in a different way to traditional air conditioning. Dais Analyticsin Florida are working with the Oak Ridge National Laboratory on a ‘membrane-based’ rooftop air conditioner that would use water as a refrigerant instead of chemicals. It would work by transferring water molecules through a nanostructured polymer membrane, allowing people to control temperature and humidity independently without resorting to potentially environment-damaging CFCs. The aim of the project is to reduce energy consumption for cooling by 30 to 50%.
Smart windows
Others are taking a different approach entirely. At the Grand Global Challenges Summit in Washington, DC earlier this year, a group of students from China presented their technology – smart windows. These coated sheets of glass are designed to adjust to the temperature, allowing heat in when it’s cold, and blocking it out when it’s warm inside for an electricity-free form of air conditioning.
There’s also ongoing work at the UK’s Centre for Process Innovation, which is working with solar photovoltaic glass manufacturer Polysolar, and materials developer Merck to create transparent windows that can both generate power and control temperature. The technology is still at the prototype stage, but could be commercially available as early as 2019.
Beaming heat into space
One out-of-this-world solution could use no electricity whatsoever. It sounds crazy, but scientists at Stanford University think we could actually beam excess heat into space which, at just a few degrees over absolute zero, is the perfect heat sink. Aaswanth Raman and colleagues developed a thin material that reflects 97% of sunlight, and tweaked its reflectivity so that it responded to the frequency that most easily allowed infra-red light to escape from earth into outer space. They tested their photonic sheet in the California desert, and found that it was almost five degrees cooler than the surrounding environment. This would only work for parts of the building with a clear view of the sky, so it couldn’t replace air conditioning, but it could be one weapon in the fight to keep both our buildings and the planet at the perfect temperature.