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The adsorption chiller test facility in the laboratory: The complete cycle can be seen with the adsorber (in the foreground) and the evaporator/condenser unit in the background.
© ITW, Universität Stuttgart
Utilising adsorption chillers in vehicles

During the journey, exhaust heat evaporates the water from the adsorber and feeds it into the evaporator. When the entire water supply is in the vaporiser, the valve closes and the cooling system is ready.

Schematic showing the structure of the test facility.

Exhaust heat cools lorry cab

Time for a break! The driver stops his lorry at the truck stop. To ensure that the cabin also remains cool even in summer, the engine also continues idling when the lorry is parked, often for hours. This produces noise and wastes fuel. However, researchers at the University of Stuttgart have now demonstrated that pleasant temperatures can still be reached even when the engine is switched off and there are no additional energy inputs. They have developed a special adsorption chiller. This utilises the exhaust heat produced while driving for air-conditioning the parked vehicle.

The new device operates quietly and is emission-free. It only uses water, exhaust heat and zeolite, a volcanic material that can store large amounts of water vapour. Unlike conventional air conditioners, the adsorption chiller requires neither compressors, cooling units nor coolants. It requires little maintenance and works without any moving parts subject to wear.

Dr Henner Kerskes, research group leader at the Institute for Thermodynamics and Thermal Engineering (ITW) at the University of Stuttgart, explains: "The starting point for our development is that the conventional stationary cooling used for lorry cabins is still based on more or less climate polluting refrigerants, and is still frequently operated by the engine when it is idling. Around four litres of fuel are used per hour – mostly diesel".

Since the beginning of the year, the researchers in Stuttgart have been testing a prototype of the refrigeration unit. Its cooling capacity amounts to around five to six kilowatt-hours. It is designed for an output of 1.1 kW for the first hour and about 600 watts for a further seven hours. Depending on the cooling requirements, the target temperature can be maintained over this period. The Stuttgart-based researchers are now working on improving the temperature control. In the next step they want to enhance the performance and make the device more compact to facilitate its integration into vehicles.

Exhaust heat regenerates the zeolite storage system

The adsorption refrigeration process does not require any additional energy because it uses waste heat:
During the journey, hot engine exhaust gases heat the water-saturated zeolite. During this desorption process, the water is vaporised and expelled from the zeolite. It liquefies in the condenser and flows into the water tank. The system is now charged. A valve separates the zeolite from the water tank.

If the cabin air needs to be cooled while stationary, the valve opens. At low pressure, the water evaporates and is adsorbed by the zeolite. The latent heat of evaporation cools the supply air for the lorry cab via a heat exchanger. After the driver's break, the system recharges during the rest of the journey. The zeolite and water can be used as often as required for the adsorption and desorption.

The stationary air-conditioning requires no additional energy. It can be integrated into existing air-conditioning systems or retrofitted as a standalone system. The Stuttgart scientists have developed the stationary air-conditioning systems on behalf of the Happich company which equips commercial vehicles. The project has been supported with research funding provided by North-Rhine Westphalia's Ministry of Science. A patent is pending for the method.

The newly developed device for air-conditioning lorry cabs uses the adsorption refrigeration process based on zeolite and water. For example, sorption heat storage systems and domestic air-conditioning systems work according to this principle.

Energy efficient air-conditioning in the home and under way

Together with companies, researchers at ITW have already investigated several uses for adsorption processes in the building sector. For example, in the SolSpaces project they equipped a research building with a new solar heating system. The key components include a sorption thermal storage system for seasonal thermal storage, an evacuated tube air collector with a 26 square metre collector area and a heat exchanger for heat recovery.

In another project for the stationary air-conditioning of lorries, researchers have developed an on-board power supply with a high-temperature fuel cell system as a more environmentally friendly alternative to idling the lorry engine. When the lorry is stationary at a truck stop, the fuel cell generates the electrical energy for the air-conditioning, communications equipment, lighting, electric kettle and fridge.



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Development of the cooling unit
Universität Stuttgart, ITW

Client for the stationary air-conditioning unit


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