Team of engineers invents low-cost solar energy/natural gas-powered DEVap cooling system.

The US Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) has announced that it has invented a new air conditioning process with the potential of using 50% to 90% less energy than today’s top-of-the-line units.

The DEVap, which stands for desiccant-enhanced evaporative air conditioner, uses membrane technology to combine the efficiency of evaporative cooling and the drying potential of liquid desiccant salt solutions. 

According to the announcement, the idea is to revolutionise cooling, while removing millions of metric tonnes of carbon from the air. Engineers from NREL, who have been working with membranes, evaporative coolers, and desiccants, reportedly observed an opportunity to combine them into a single device for a product with unique capabilities. 

The press release further elucidated the process: Evaporative coolers are a low-cost alternative to air conditioners in places with dry climates (for example, Rustaq and Nizwa). But in humid climates (for example, Muscat, Salalh, Sohar and Sur), adding water to the air creates a hot and sticky building environment. Furthermore, the air cannot absorb enough water to become cold. Therefore, evaporative cooling or desert cooling is not useful. So, refrigeration-based air conditioning is the preferred way of keeping cool and it consumes significant amount of energy. The DEVap solves this problem by relying on the desiccants’ capacity to create dry air using heat and evaporative coolers’ capacity to take dry air and make cold air. 

According to HVAC news, the kind of desiccants that NREL uses are syrupy liquids – highly concentrated aqueous salt solutions of lithium chloride or calcium chloride. They have a high affinity for water vapour, and can thus create very dry air. Because of the complexity of desiccant cooling systems, they have traditionally only been used in industrial drying processes.

To solve the problem of easy installation and maintenance, the NREL device uses thin membranes that simplify the process of integrating airflow, desiccants, and evaporative cooling. These result in an air conditioning system that is said to provide superior comfort and humidity control. 

The membranes in the DEVap air conditioner are hydrophobic, which means water tends to bead up rather than soak through the membranes. This property, reportedly, allows the membranes to control the liquid flows within the cooling core and keeps the water and the desiccant separated from the air stream. In this technology, water and liquid desiccant are brought into DEVap’s heat-mass exchanger core. The desiccant and evaporative cooling effect work together to create cold-dry air. The air is cooled and dried from a hot-humid condition, to a cold and dry condition, all in one step. It is claimed that this happens in a fraction of a second, as air flows through the DEVap air conditioner. The result, evidently, is an air conditioner that controls both thermal and humidity loads.

Because the DEVap uses salt solutions rather than refrigerants, it eliminates greenhouse gas concerns. Also, traditional air conditioners use a significant amount of electricity to run the refrigeration cycle, but DEVap is said to replace the refrigeration cycle with an absorption cycle that is thermally activated. It can be powered by natural gas or solar energy and uses very little electricity. 

NREL has patented the DEVap concept and engineers from the organisation expect that over the next couple of years, they will be working on making the device smaller and simpler and perfecting the heat transfer to make DEVap more cost-effective. NREL will eventually license the technology to industry.