Background article

Air-conditioning with natural

Interview with Thomas Spänich, member of the Board at eurammon, the European initiative for natural refrigerants

Mr. Spänich, according to the German Energy Agency, the operation of ventilation and air-conditioning systems accounts for around 20 percent of all energy consumed by commercial buildings. How do you see the situation?

Thomas Spänich: During the summer months, modern buildings with glass facades heat up in some cases considerably. The use of IT systems and office automation also make buildings heat up, so that in this day and age, air-conditioning of commercial buildings has become almost essential, even in our part of the world. In the context of constantly increasing energy prices, the use of natural refrigerants offers the possibility of energy-efficient, environment-friendly air-conditioning for such premises.

Which natural refrigerants are suitable for use in commercial buildings?

Thomas Spänich: Basically all natural refrigerants, i.e. ammonia (NH3), carbon dioxide (CO2) and hydrocarbons, can be used in building air-conditioning systems. For a long time now, these substances have played a successful role in industrial refrigeration, but have not been used to such a great extent hitherto in air-conditioning systems. However, numerous examples from recent years show that natural refrigerants are ideal for these projects.

Where are natural refrigerants used for air-conditioning today?

Thomas Spänich: The main focus in Central Europe is on the air-conditioning of larger building complexes. These include for example exhibition halls, congress centres or airport terminals, where ammonia-operated water chillers are frequently used. The liquid chilling units are available with smaller refrigerating capacities from about 30 kilowatt. The air is conditioned by a distributor circuit using water or another secondary refrigerant. Large capacities exceeding 2,000 kilowatt can be achieved among others using several chilling units equipped with screw compressors. For example, ammonia chillers have been used since 2004 for the air-conditioning in Terminal 3 of Stuttgart airport.

What is the situation with smaller capacity ranges?

Thomas Spänich: Ammonia and CO2 are best suited to these applications which are used among others for office air-conditioning. However, at the moment, components for systems with smaller capacity are still being produced in relatively small quantities which makes them about 20 percent more expensive than systems with synthetic refrigerants. On the other hand, the higher costs are offset by good energy efficiency, so that as a rule, the additional costs can be recovered within about two to three years. Hydrocarbons can also be used as refrigerants in company IT and server rooms. Greenpeace's IT and office rooms in Vienna for example are cooled with propane. Statutory filling restrictions apply to hydrocarbons on account of their flammability, so that up to now it has only been possible to use them on a smaller scale. However, it would be better if the restriction were made dependent on the conditions prevailing in each particular case, allowing larger filling quantities for example if a system is erected outside a building.

CO2 has not been used for very long in air-conditioning. Can you tell us why?

Thomas Spänich: For a long time it was not possible to use CO2 in air-conditioning because the components, which have to be rated for the higher pressures in operation with carbon dioxide, were simply not available. Moreover, CO2 solutions were deemed to be less energy-efficient than applications with synthetic refrigerants. Meanwhile, economical solutions are
now also available for office buildings with capacities between 50 and 340 kilowatt. Carbon dioxide is used for example to cool the computing centre at the ABM Amro Bank in London.
In the long term, carbon dioxide will see increasing use in systems with smaller capacities of up to 500 kilowatt. CO2 is not flammable and is chemically inactive, giving it the broadest
acceptance in the general public of all natural alternatives in unsupervised small and mini systems. But further development work is necessary here, as at present no suppliers manufacture the components in larger quantities, which would generate competitive prices. Research is currently also looking increasingly at the use of CO2 in heat pumps: the corresponding results could also be significant for future air-conditioning solutions.

Mr. Spänich, eurammon has been advocating the use of natural refrigerants for 15 years now. Which particular advantages do they offer?

Thomas Spänich: On the one hand, natural refrigerants are inexpensive, readily available raw materials. The differences in price to synthetic refrigerants already make themselves felt for example when filling a system for the first time, and also particularly where leakage losses are concerned. Furthermore, natural refrigerants are extremely energy-efficient. Ammonia as refrigerant has verifiably the best thermodynamic properties and needs only relatively little effort to generate refrigerating capacity. While the efficiency of an air-conditioning system depends more on its overall concept than on the particular refrigerant being used, a number of current projects indicate that systems are particularly efficient and environmentally friendly when operating with natural refrigerants. In addition, natural refrigerants do not contribute to depleting the ozone layer and have no or only negligible influence on the greenhouse effect. They are therefore absolutely unrivalled in terms of the climate.

What has to happen to make sure that natural refrigerants are used more frequently in air-conditioning systems in future?

Thomas Spänich: While the use of applications with natural refrigerants is on the increase, these systems are still not self-evident. Already the planning and also the implementation, operation and maintenance of air-conditioning systems using natural refrigerants must be accompanied by an intensified exchange of knowledge about the properties and possible uses of natural refrigerants and the handling of their corresponding systems. This also includes bringing technological know-how in the form of example projects to less developed countries where natural refrigerants have scarcely been used up to now.

Do you see any applications with natural refrigerants as playing a particularly seminal role in future?

Thomas Spänich: Heat pump applications with natural refrigerants are particularly in trend, with heating systems making further use of the waste heat produced by industrial refrigeration systems and computing centres or the purified wastewater from sewage treatment plants. Little energy is consumed by the actual heating-up process on account of the heat that is already available. It is meanwhile possible to reach temperatures of up to 80°C in this way. This technology has also been discovered by larger energy companies that use large-scale heat pumps to supply whole urban districts with hot water.