The Times they are a Changin'

Solar Powered Air Conditioning Under Development


The consumer-grade absorption chiller under development by UC3M uses the heat of the sun to cool water. (Source: Universidad Carlos III of Madrid)The sun will keep you cool in just a few seasons.

The Montreal Protocol, crafted in 1987 and signed by 191 countries as of 2007, put the hot iron to the cooling industry. It has seen several revisions since 1987 and some of its strictures affect industry as a whole while others involve mainly cooling and refrigeration.
The ultimate goal of the protocol is to reduce the amount of several ozone-depleting chemicals used by industrialized nations to zero. Most CFCs (chlorofluorocarbons) were to be phased out of use by 1996; other less dangerous CFCs and chemicals are to be phased out by 2010; HCFCs (hydrochlorofluorocarbons) are on a longer leash, and have cease and desist date of 2030, 2020 in developed nations.

Unfortunately for the air-conditioning and refrigeration industries, this means an industry-wide change in practice, as HCFCs are commonly used as refrigerants in modern cooling machines. There are several technologies that cool without the use of these refrigerants, but until recently, they have been utilized mostly only in large-scale applications. Absorption chillers are used in many industries, from commercial to machinery cooling.

Absorption chilling differs from standard mechanical air conditioning in that it doesn't use an active force, such as a compressor, to condense the coolant chemical, but rather uses heat to drive a circulatory system. Many absorption chillers are utilized in areas where ample amounts of waste heat are available (turbine power or water heating systems are common sources). This allows them to make use of waste heat for a secondary purpose, thereby making the entire system more efficient and cost-effective.

This nearly century-old technology has not been widely used in consumer arenas like home cooling as the heat needed to power the system would cost more than the typical compressor-driven air-conditioning unit and there are not usually readily available sources of waste heat powerful enough to harness. Professor Marcelo Izquierdo of the Universidad Carlos III of Madrid and his group of researchers are aiming to put this technology into homes, however, with a little help from a very large furnace – the sun.

Izquierdo's team built an absorption chiller unit that closely resembles a typical exterior air-conditioning unit, and it works by capturing solar energy and residual heat to provide the impetus for the system's circulation. The device uses a refined lithium bromide-based coolant process – most absorption chillers use either an ammonia, hydrogen and water or a lithium bromide solution and water system – and is capable of cooling water to a temperature of 7C to 18C with an ambient temperature of 33 to 43C. The machine can produce enough chilled water to cool a 120 cubic meter area via a water-to-air heat exchanger.

Neither the lithium-bromide solution nor the more common ammonia and hydrogen systems are ozone depleting. This makes them a viable alternative to the HCFC refrigerants used in modern compression systems. In the very near future, consumer-grade absorption chiller units could become common in many regions that experience high temperatures during one or many seasons. Using the Big Heater in the Sky itself to power the cooling units is an ironic twist and one definitely worthy of more research.


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