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Singapore researchers see breakthrough in separating cooling, dehumidifying

Mechanical engineers at the National University of Singapore have developed what they claim is a versatile cooling system that does not employ mechanical compression or chemical refrigerants.

Most of us, when we think of air conditioning, probably imagine two thermodynamic principles: a vapor-expansion/compression cycle (RVEC) or evaporative cooling.

Direct expansion (DX) equipment, heat pumps, and chillers all use RVEC, and most of the energy is consumed by a motor-driven compressor that is generally electric.

RVEC cooling also requires chemical refrigerants, most of which are not particularly friendly to the environment. In extremely dry, desert-like climates, evaporative cooling reduces the sensible heat of the air and increases the latent heat, so that the dry bulb temperature is lower and the relative humidity is higher. These so-called swamp coolers do not rely on compressors or chemical refrigerants, but their effectiveness is very climate-limited.

Now, researchers at the National University of Singapore (NUS) have developed what they claim is a cooling system – suitable for any climate – which does not employ mechanical compression or chemical refrigerants. According to the team’s leader, Associate Prof. Ernest Chua in NUS’ Dept. of Mechanical Engineering, the system can be competitively produced and will consume approximately 40% less energy than typical DX equipment. With its energy efficiency and water-based cooling, it represents a significantly more sustainable, environmentally-friendly technology than RVEC systems. And adding to its sustainability, the system will produce potable water as part of its process.

Team + Prototype: (clockwise from bottom right) Prof. Chua, Dr. Md. Raisul Islam, Dr. M. Kum Ja, and Dr. Bui Duc Thuan.

According to Prof. Chua: “For buildings located in the tropics, more than 40% of the building’s energy consumption is attributed to air-conditioning. We expect this rate to increase dramatically, adding an extra punch to global warming. First invented by Willis Carrier in 1902, vapor compression air-conditioning is the most widely used air-conditioning technology today. This approach is very energy-intensive and environmentally harmful. In contrast, our novel membrane and water-based cooling technology is very eco-friendly – it can provide cool and dry air without using a compressor and chemical refrigerants. This is a new starting point for the next generation of air-conditioners, and our technology has immense potential to disrupt how air-conditioning has traditionally been provided.”

The apparent key to the new technology is the separation of the cooling and dehumidification processes. The first system uses membrane technology to dehumidify the incoming air, which is then cooled by dew-point cooling using water as the cooling medium. Rather than discharging heated air to the outside environment, the discharged air is cool and dry, and the recovered moisture is collected as potable water.

Prof. Chua has indicated that the technology can be adapted to any climate, ranging from tropical to arid, and can also be used in mobile applications. His team is presently seeking industry partners to scale up and bring the technology to the commercial market.

A regular contributor to HPAC Engineering and a member of its editorial advisory board, the author is a principal at Sustainable Performance Solutions LLC, a south Florida-based engineering firm focusing on energy and sustainability. He can be reached at [email protected]

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