Solid sorption heat pumps

Like liquid absorption systems, solid sorption systems belong to the family of trithermal sorption systems. They are thermotransformers that produce cold or heat from two heat sources: one at high temperature and the other at ambient temperature. The case of sorption systems, which supply heat at the higher temperature, is not covered in this article.

In both cases, the driving force is high-temperature heat. In the case of refrigeration production, the sum of the heat from the hot source and the cold produced is rejected to a heat sink at intermediate temperature (ambient air, subsoil or water). In the case of heat pumps, on the other hand, it is the heat produced that is valorized, with an amplification effect, since the useful heat is the sum of that supplied by the hot source and that from the free heat source (air, subsoil, thermal discharge, etc.). These processes are also suitable for cold or hot storage.

In a context of energy savings and the fight against the greenhouse effect, these solid sorption processes are enjoying renewed interest. The refrigerants used have a zero global warming potential (GWP) and therefore make no direct contribution to the greenhouse effect.

These systems are currently the focus of a great deal of R&&&&D, resulting in the emergence of innovative products, some of which are expected to find a large market in the near future. The building and transport sectors are among those showing the greatest interest.

Air conditioning using low-temperature heat (waste heat, solar energy, etc.) is currently one of the strongest points of these systems. Their advantage over liquid absorption systems is that they can operate at lower hot-source temperatures, which is invaluable for air-conditioning using waste heat. As free heat is involved, the low COP coefficient of performance is not a major obstacle. On the other hand, weight, volume and cost are currently holding back the development of these systems.

Recent research into innovative adsorbent materials (notably MOF organometallic networks) is opening up new prospects for more efficient, lighter and less expensive equipment. If these developments come to fruition, there is no doubt that the market for these systems will grow in zero-energy and positive-energy buildings, as well as in the transport sector.

In this article, the various solid sorption systems are analyzed and their operation and performance are discussed. The focus is on hermetic systems; however, open air-conditioning and dehumidification cycles are also discussed. The main products on the market and their claimed performance are presented. Lastly, R&&&&D efforts and prospects are briefly outlined....