| Absorption cooling is heating up around the world. Today in Japan, for example, more than half of total installed cooling tonnage is handled by absorption cooling equipment such as absorption chillers. While the growing use of absorption chillers may be a new trend, absorption cooling technology is nothing new; the first absorption chillers were developed in the 1800s. Despite the long history of absorption cooling, the 20th century had been dominated by electrically-powered, compressor-driven cooling systems. However, due to recent developments, absorption chillers are now considered viable alternatives to electric chillers for many applications.
Environmental Concerns
One main reason for the growing use of absorption chillers has to do with the fact that fluorocarbon-based refrigerants like CFCs (Chlorofluorocarbons), which are used in compressor-driven chillers, are harmful to Earth's ozone layer.
The Montreal Protocol, established in 1987 and signed by forty-three nations, set in motion the phase-out of CFCs, thus accelerating the movement to find environmentally-safe alternatives. HCFCs (Hydrochlorofluorocarbons) were widely accepted as suitable replacements. However in 1990 HCFCs were added to the list of compounds to be phased out. Another alternative, HFCs (Hydroflourocarbons) are considered benign with respect to ozone depletion but HFCs have been identified as 'green-house' gasses and their use is coming under increased international pressure.
The bottom line is that virtually all refrigerants used in electric cooling systems are either targeted for phase-out or are under increased scrutiny, with more stringent regulations and harsher penalties for improper use and disposal. Absorption chillers, which use natural gas to drive a process where water is the refrigerant, use no ozone-destroying substances and are is said to have less impact on global warming.
Electricity Costs
Electricity prices are the second main reason for the growing popularity of absorption cooling and indeed for the growing use of natural gas-powered cooling (gas cooling) technology in general. Firstly, electricity prices can fluctuate wildly, making it difficult to manage an electric chiller's operating costs. Secondly, the prices of electricity are highest during the warmer months when cooling is needed most. Absorption chillers, which are powered by natural gas burners, are less costly to operate during these peak times, and natural gas prices are generally more stable than electricity prices.
Disadvantages
While absorption cooling has some significant advantages it also has some disadvantages. Absorption chillers are inherently less efficient than compressor-driven chillers, primarily because water is a less efficient refrigerant than fluorocarbon-based refrigerants. This lower efficiency necessitates larger components making absorption cooling systems larger than electric chiller systems of equal capacity. Also, absorption chillers have a higher first cost than electric chillers. A recent innovation that is improving efficiency is the two-stage absorption process. Two-stage absorption chillers effectively use a given quantity of heat energy twice in the absorption cycle, making them up to 45% more efficient than chillers from just a few years ago.
Cooling and Heating in One
Another factor that should make absorption chillers more attractive is that an absorption chiller can provide both chilled and heated water. Thus, a properly sized absorption chiller can supply both a building's cooling and heating requirements, eliminating the need for a separate boiler. It is also possible to configure an absorption chiller to supply both chilled and heated water simultaneously for process applications.
Hybrid Systems
Recognizing the specific advantages of electric chillers and absorption chillers has lead to the creation of hybrid systems. In a hybrid system an electric chiller is employed for base load requirements and an absorption chiller comes online during peak load requirements. This allows building owners and managers to retain an existing electric chiller while taking advantage of the absorption chiller's lower operating costs during periods of peak electrical demand. Having two chillers also adds redundancy, which is beneficial if one chiller fails.
An Absorbing Future?
Will absorption cooling ever supersede electric cooling? Only time will tell, but with the growing international movement against fluorocarbon-based refrigerants, unstable electricity prices, and the increasing use of natural gas as an alternative to electric power, demand for absorption cooling is definitely rising. How ironic that the dominant cooling technology of the hi-tech 21st century may be one that utilizes an intrinsically low-tech process invented back in the 19th century.
To learn how absorption chillers work, click here .
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