01 December 2000

Ab-sorption machines for heating and cooling in future energy systems – Final report

The title of Annex 24, “Ab-sorption machines for heating and cooling in future energy systems” focuses attention on the technology of the known absorption cycles. However, the splitting of the word “absorption” into “ab-sorption” (with a hyphen), emphasises that a broader view is taken, embracing all sorption technologies. The title also spells out the prime functions of the machine (to cool and heat), and of the Annex (to look into the future of this technology). Furthermore, the objectives of the Annex state that an understanding of actual systems is needed to appreciate the market barriers to the adoption of sorption technologies, even when they benefit the environment. Finally, recommendations are made regarding policies and R&D, to enable these technologies to be better assisted by market pull, especially when they offer environmental benefits.

After this Executive Summary and a brief introductory chapter, Chapter 2, Sorption Technologies for Heating and Cooling in Future Energy Systems, reviews the main types of sorption systems. They are summarised in Table 2.4 on page 32. Chapter 3, Market Segmentation, then considers the major segments of the market including residential, commercial/institutional and industrial, and the types of sorption hardware most suitable to each.


The highly important residential and commercial/institutional markets are mostly concerned with air-conditioning of buildings, which is dealt with. More applications are identified and discussed for the industrial market, including refrigeration, food-storage cooling, process cooling, and process heating at various temperature ranges from hot water for hand-washing to high-temperature (greater than 130C).

Heating demand catered for by furnaces is not directly considered, since it has no direct applicability to heat pumping or other absorption technologies due to the very high temperatures involved (several hundred degrees Celsius). The waste heat may, however, be of interest to run absorption chillers, if a suitable cooling demand has to be met. Flue-gas cleaning (which is generally mandatory) is the simplest and most direct method of recovering what would otherwise be waste heat, mostly vented to the atmosphere via cooling towers. Cooling tower water is a source of lower-temperature waste heat which may be of great interest.

Other interesting industrial applications are absorption cooling or heating combined with co-generation, desiccant cooling, gas turbine inlet air cooling, combining absorption chillers with district heating systems, direct-fired absorption heat pumps (AHPs), and a closed greenhouse concept being developed for that economically important sector in the Netherlands. In all such applications of sorption (or any other) technology, it is emphasised that proper system design is essential to reap real benefits.

Industry (including agriculture) accounts on average for 20 – 50% of the total energy consumption in the countries participating in Annex 24, so technologies such as heat pumps in general, and sorption systems using waste heat for cooling in particular, would have great potential for saving primary energy (fossil fuel) and reducing its adverse impact on global warming and environmental pollution.

System suitability

Most of the sorption market at this time comprises direct-fired absorption chillers, or hot water or steam absorption chillers indirectly driven by direct-fired boilers. Throughout the report, this category of absorption chillers is referred to generically as ‘direct-fired’. Absorption chillers constitute most of the sorption market; in addition, this report covers absorption (reversible) heat pumps, absorption heat transformers, compression-absorption heat pumps, and adsorption chillers and heat pumps. Adsorption systems together with desiccant systems are also addressed.

After the review of systems and markets in the earlier chapters, Chapter 4, Factors Affecting the Market, considers economic, environmental and policy issues. The geographical make-up of the world sorption market is then reviewed, followed by a number of practical operating and control considerations. These include vacuum requirements, crystallisation, corrosion, maintenance, health and safety etc. Possible crystallisation and corrosion problems are still major concerns of some users, but with proper attention by producers, system designers, installers and maintainers are shown not to be problematic in practice. The lack of trained maintenance people is a major concern.

A brief survey of R&D activities is given in Chapter 5.

Future opportunities

In Chapter 6, Future Opportunities, an analysis of the market factors shows that the market pull favours sorption technologies in different ways. Direct-fired absorption chillers are installed in areas where there is lack of mains electricity, or restrictions on using it to power electric-driven mechanical compression chillers. A chart has been compiled to illustrate the different market pull factors. It shows, in decreasing order of market pull, the following technologies:

– Direct-fired or boiler-driven absorption chillers; and

– Absorption chillers driven by waste heat, heat recovery or combined heat and power (CHP) systems.

Far less prominent are:

– Absorption heat pumps; then

– Absorption heat transformers; and finally

Adsorption chillers.

The chart shows that environmental benefit is inversely proportional to the market pull and share of sorption technologies. The main market barriers are considered to be the relatively high first costs of absorption plant, and the lack of knowledge of sorption technology by technicians, engineers, and professionals.

In practice, different technologies are found to be most suitable for different countries, mainly depending on their energy infrastructure and particularly on how the country’s electricity is produced. An energy infrastructure based mainly on coal-fired generation should favour sorption or other non-electric systems over compression systems. On the other side of the spectrum are countries that have a more renewable energy basis, which should favour electric-driven systems. The history of generation shows that energy production generally improves over time, which affects the benefits sorption technology can offer. Recommendations are made regarding policies to promote sorption technology (where it is environmentally beneficial), and with regard to future R&D.


In Chapter 7, Conclusions, it is emphasised that the application of sorption technology is not in all cases the best choice for the environment.

Detailed conclusions are that:

– Direct-fired chillers should be phased out slowly, in the short and medium term;

– Encouragement should be given to absorption and adsorption chillers using waste heat, heat recovery or applied heat;

– Sorption chillers applied to CHP systems have an existing market pull, and benefit the environment. However, the overall efficiency has to be relatively high with respect to each nation’s power production, throughout the life of the system;

– Absorption heat pumps (including reversible heat pumps) will be available on the market in the short term, and due to their environmental benefits should be strongly supported, unless electric heat pumps are more beneficial, as occurs in countries with a high proportion of hydroelectricity and even gas energy; and

– Absorption heat transformers and compression-absorption heat pumps offer excellent environmental benefits for industry. However, the latter are likely to have more market pull in the medium or long term.


Chapter 8 concludes the main body of the report with Recommendations for Future Work. Technically, it is suggested that the main emphasis of such work could be on sorption applications of waste heat / heat recovery and process heat, but other factors need equal or greater attention. They include the study of the effect of existing taxes and economic incentives, and formulation of recommendation for such measures; system capital cost reduction studies; the closer study of environmental benefits and new potential markets; and the need to assemble a representative portfolio of Case Studies and Demonstration Projects. Details of future work still have to be resolved regarding objectives, work plan, time-scales, budget and participation.

Seven Appendices conclude the report. Appendices 1 and 2 list National Contacts for the Annex, and Manufacturers of Sorption Equipment. Appendices 3, 4 and 5 briefly review the absorption heat pump cycle; sorption thermodynamics; and competing technology, i.e. the electrically-driven mechanical compression cycle.

Appendix 6 reviews 12 Case Studies, each demonstrating some new technology or novel application(s) of interest. Further information is available in the references indicated. Appendix 7 lists useful website addresses, which are followed by lists of References and Bibliography. Lists of Figures and Tables conclude the report.