How „bumble bee“ and „bee“ generate cooling in the desert

Absorption-based cooling system "bee"

Exhibited absorption-based cooling system “bee” at the Environment Week. Photo: Stephanie Stühler/IKI

In the Jordanian desert city Petra, the sun is shining seven to ten hours a day on average with temperatures above 40°C. Therefore, the region has an extremely high demand of air conditioning systems and cooling solutions. The IKI project Industrial and commercial solar cooling in Jordan makes use of these climate conditions by profiting from solar energy to generate cooling. For this purpose, absorption chillers are deployed, the so called “bumble bee” and its little sister “bee”. In cooperation with the Jordan environmental ministry, the TU Berlin and the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) are jointly implementing the project in Jordan.
The project presented itself at the Environment Week (Woche der Umwelt) at the castle park of Bellevue in Berlin on the 7th and 8th of June 2016. There, we met Marion Geiss, who advises as GIZ-consultant the project Industrial and commercial solar cooling and Christopher Paitazoglou, research associate at TU Berlin, and we asked about their experiences with the project.

Solar cooling sounds like a contradiction in terms. The IKI-funded project aims to achieve a zero-carbon cooling process by using solar energy to drive the system. How does this work?

Foto von Christopher PaitazoglouC. Paitazoglou: Our motto at Environment Week is ‘Heat to Cool’. An absorption-based cooling system takes up heat at high temperature and uses this energy to generate cold. This is a specific type of heat transfer process that essentially operates according to the heat pump principle. It uses solar energy, which is available at high temperature, to ‘pump’ heat from a low to an intermediate temperature level. The extraction of heat from the lower temperature level generates the cold that is the useful energy in this system. At the same time, the absorption heat pump can also supply useful heat at the intermediate level; this can be used for space heating or hot water production, for example. In contrast to a conventional refrigerator or compression-based cooling system (which is effectively an electric heat pump), an absorption-based cooling system uses a thermal compressor and thus saves the electrical energy that conventional systems use to drive the compressor.

The Bee, as you call the absorption system, consists of two yellow-painted vessels mounted on top of each other and connected by several tubes. What is happening inside this system?

C. Paitazoglou: The vessels contain a natural refrigerant – namely water – and a salt. The process harnesses the salt’s hygroscopic property. In a concentrated state, the saline solution can absorb refrigerant vapour in the low-pressure vessel. Heat is released during absorption, so the absorber needs to be cooled. The refrigerant absorbed in the solution evaporates in the evaporator, and in so doing it withdraws heat from an external circuit where it causes a drop in temperature. The solution diluted with refrigerant is conveyed to the high-pressure vessel by means of a small circulation pump, which consumes a fraction of the electricity required by electrically-powered cooling systems. In that vessel, the solution is regenerated by the input of high-temperature heat – solar heat! The concentrated saline solution can now be used again to absorb refrigerant. The gaseous refrigerant released in the high-pressure vessel is liquefied by external cooling and is thus made available again as pure, liquid refrigerant in the low-pressure section of the system. Unlike a compression-based cooling system, this is a continuous process.

Jordanian and German partners are cooperating on this project. The Jordanian partner is the Ministry of Environment, while GIZ and TU Berlin are involved on the German side. How is cooperation progressing?

Photo of Marion GeissM. Geiss: IKI is providing the funding, of course. GIZ set up the project in consultation with the Jordanian Ministry of Environment within the wider context of Montreal Protocol negotiations. The German Environment Ministry commissioned the project in 2012, whereupon we immediately began to look for the various technology partners. We performed a technical appraisal with support from HEAT, a technical consultancy, and thus hit upon TU Berlin. Technical experts held talks with TU Berlin in the initial phase of the project to find out whether there is any interest in bringing this type of pilot plant to Jordan. One of the project’s aspirations is that technology transfer should be cooperative. This means that on the Jordanian side the technology partner, Millennium Energy Industries, takes up the know-how and rolls it out across the MENA region through follow-up projects.

Why was Jordan chosen?

M. Geiss: Jordan had proved to be a highly committed partner in the international negotiations. Jordan approached IKI several times to explore where we could provide support in the refrigeration sector in order to meet the great demand for cooling across the country, especially during the very hot periods in summer. The goal is to find alternative, low-carbon solutions. It must be kept in mind that Jordan itself has no major resources: it has no oil or  gas deposits, it imports and heavily subsidises fossil fuels, and its energy prices depend to a large extent on the current level of political stability in the country, which is influenced by events across the entire region. Using solar energy for cooling is therefore the most attractive solution: this would cut energy costs, contribute to climate change mitigation and boost the economy. Jordan is particularly well suited for solar thermal technology and solar energy in general, as it enjoys very high levels of solar irradiation throughout the year.

Here at Environment Week, many exhibitors are presenting novel ideas in the environmental and energy sectors. What makes your project particularly innovative?

C. Paitazoglou: All the components of the Bumblebee system utilise state-of-the-art structural engineering, process design and process and system control based on a characteristic equation. The specific space and material requirements of this absorber system are much more favourable than reference absorption-type cooling systems, as the configuration of heat exchanger surfaces within the unit is extremely efficient and makes very sparing use of materials. Combined with internal sensors and actuators, system operation is much better and safer, notably in operational states beyond classic parameters, for instance at high cooling water temperatures at which conventional plant manufacturers would prohibit operation. Bumblebee-type units permit this because process monitoring and design have been so greatly refined that special operating states can be handled better, with less risk of failure.

Group photo in front of "bee"

A hotel in Jordan is one of four pilot projects deploying the new technology. What has been the experience here to date?

C. Paitazoglou: We have gathered a great deal of positive experience throughout. Many of the concerns raised beforehand have proved unfounded. The cooperating planning consultancy, which is responsible for the entire planning and implementation of the solar cooling systems, is highly competent. Our partner, Millennium Energy Industries, is very well positioned internationally and has excellent knowledge of the business thanks to various successfully completed solar projects, both large and small. There was of course a need for advice and support on the integration of solar cooling into existing refrigeration or solar energy systems. This applied equally to new-build solar cooling systems like the one in Petra. We met this need by offering in-depth and intensive workshops at the Technical University in Berlin and by engaging in close cooperation and frequent exchange throughout the planning and implementation process. We thus succeeded in engaging in active knowledge and technology transfer. The way in which all participants shared their knowledge on equal terms, in a constructive and targeted manner, made this a very positive experience for me.

M. Geiss: Yes, we are keen that activities should continue beyond the pilots and technology transfer should not remain restricted to a small number of partners. A technical committee in which all the major universities and engineering faculties are represented is an integral part of the project’s design. This ensures replication via the universities’ curricula, thus mainstreaming solar cooling as an alternative technology. It is also important that the project’s outcomes are fed into international forums and gain a high profile there, which will hopefully ensure that they are replicated to an adequate extent.

What results has the project delivered up to now?

C. Paitazoglou: Last year, plant operation in the German Jordan University was very stable throughout the summer. The plant was in operation across the whole range of ambient temperatures, which can exceed 40°C. Despite sup-optimal performance of a pre-existing collector field, the newly installed absorption cooling system provided high operational availability and a high utilisation factor. Electrical efficiency, which is the ratio between cold output and electricity input, ranged between 15 and 25 for the solar cooling system in Petra Guest House during the first weeks of operation in early May. This means that this system can generate up to 25 units of cold with one unit of electricity. The relatively favourable ambient temperatures around 30°C helped to achieve the high electrical efficiency. We expect electrical efficiency to drop in the hot summer months due to increased consumption for recooling in that period. The plant’s CO2 emissions per unit cold output were about one quarter to one fifth of a compression-type cooling system in this operational phase. Those are really quite good results for the start of the year.

What would the preconditions be for broad-scale deployment of this technology?

C. Paitazoglou: Broad-scale deployment depends above all upon the technology’s economic viability. The capital costs of an absorption-type cooling plant are still above those of a conventional electrically-powered refrigeration system. In economic terms, solar thermal cooling makes most sense in refrigeration systems with medium to high cooling capacity, less in the low capacity range of approx. 2 to 50 KW. This is due to the relatively high specific production costs of small components. Overall, solar thermal cooling makes sense in combination with the utilisation of solar heat in winter, which of course delivers economic benefits. The solar-powered system then generates dual benefits in winter and summer. For the technology to penetrate the market, it has to be economically viable in addition to offering environmental and energy management benefits. What’s more, we are working in Jordan to demonstrate that absorption-type cooling systems yield good operational results even with dry recooling and high cooling water temperatures – something thought impossible in the industry up to now.

Interview/Photos: Stephanie Stühler and Elena Metz (IKI)

Castle Bellevue