Solar Air Powered Air Conditioning Comes To Dubai

Saturday, August 14, 2010

Solar Air Powered Air Conditioning Comes To Dubai

by Lloyd Alter

Doesn't look like much from the top; ESAB building, from Construtionweekonline

One of the reasons we have been so dubious about Dubai is the energy consumption required to keep people cool there; they even air condition the beaches. But if there is one thing they have lots of, it is sunlight; that's why we have always considered solar powered air conditioning the holy grail that will make places from Dubai to Phoenix sustainable.

Now ClimateWell of Sweden has installed a working solar air conditioning system at the ESAB offices and warehouse in Dubai. ESAB is a worldwide welding equipment and supply company, and the building is considered by Construction Week to be one of the Middle East's five best green buildings.

Most solar air conditioning ideas we have shown were used ammonia based adsorption systems, which predate conventional air conditioning. ClimateWell developed a "Triple-State absorption technology using salt and water."

If you follow the animation a few times it becomes clear that hygroscopic salts absorb a lot of water vapour, which absorbs a lot of heat when changing state from liquid to gas. Then it takes heat to get the salt to give up the water, where the solar comes in, to cycle the water back so that it can evaporate again. In case I got that wrong, here is their more technical writing:

A chemical heat pump is based on the principles that water molecules bind more efficiently to certain hygroscopic salts than to other water molecules. As a consequence, when using two separate bowls - one containing water (evaporator), and the other containing hygroscopic salt (reactor) - in a confined space, water will evaporate to the salt that absorbs the water. When the confined space is in a state of vacuum the water transport will be so high that the water will start boiling in order to produce vapour at the same speed as it is absorbed by the salt. Such evaporation requires energy. If the energy is not supplied from outside the system it will be taken from the water itself, which as a consequence gets colder. In essence the evaporation process transports thermal energy (heat) from the water to the salt. The temperature difference increases until a maximum difference (∆T), at which the salt is no longer able to absorb more water.

There is more than enough solar energy to meet all of the cooling and heating needs, of either a house or an office building.

Thomas Bohlen, chief technical officer at the Middle East Centre for Sustainable Development (MECSD) in Dubai says in ConstructionWeek:

"The best bit is the building's solar thermal cooling system, which uses a roof-mounted solar tube collectors to provide hot water to six absorption units, that in turn provide cold water to air handling units on the roof. Cold air is then circulated through the concrete pre-cast, hollow core ceiling slabs of the office, providing cool air and radiant cooling. The way this system is woven into the building structure is a great example of how early commitment by the stakeholders to sustainability can make for a great building.....This project has proven that even industrial buildings in the Middle East can be designed, constructed, and operated to the highest current standards of sustainability.""

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