New absorption chiller and control strategy for the solar assisted cooling system at the German federal environment agency

• Energy efficiency is increased considerably by a new developed absorption chiller.
• Electricity and spray water consumption is reduced by more than 35%.
• Despite variable solar driving temperature chilled water temperature is kept constant.
• Minimum operating cost is achieved by control of hot and cooling water.

Typically the cooling capacity of absorption chillers is controlled by adjusting the driving hot water temperature according to the load. Meanwhile the cooling water temperature is controlled to a constant set value. In order to increase the solar cooling fraction and/or to decrease the operating costs of solar assisted cooling systems (SAC-systems) a new control strategy has been developed which controls hot and cooling water temperature simultaneously. Hereby the specific cost of cold – generated from solar or conventional heat – can be reduced. The basic concept of the strategy is explained and results are shown for the SAC-system at the Federal Environment Agency in Dessau, Germany. Here a recently developed absorption chiller is now used instead of a former adsorption chiller. With the new absorption chiller and the control strategy the seasonal energy efficiency ratio SEER is above 0.75, electric efficiency is 35% higher and water consumption is reduced by 70%.