Optimisation of primary energy consumption of solar (thermal) cooling plants by means of efficient technology and innovative control strategies

The R&D Project „Optimisation of primary energy consumption of solar (thermal) cooling plants by means of efficient technology and innovative control strategies“ (SolarCoolingOpt) aimed to find out the optimized configurations and control strategies for solar thermal cooling plants regarding primary energy balance.

A first step was the development of two improved simulation models on the TRNSYS platform, based on detailed measures: a type for a speed dependent sorption wheel and another one for an absorption machine with dynamic behavior. One of the key aspects of the project was the investigation of several solar cooling systems and configurations with different control strategies by means of improved simulation models, to find out the most appropriate and efficient optimizations which could be implemented in existing or planned systems.

For the following solar assisted cooling systems simulations were carried out:

a) Systems with desiccant-evaporative-cooling (DEC)-technology for air conditioning in offices and hotels
b) Small-scale systems with absorption machine (19 kW) for office cooling
c) Large-scale systems with absorption machine (1,45 MW) for pre-cooling and base-load cooling

For each type of technology a „standard configuration“ was compared to several configurations with modified components and control strategies in terms of non-renewable primary energy consumption. All investigated variations were compared also to a reference system with conventional cooling (compression chiller). For air conditioning with DEC-technology, particularly with climate conditions of Central-Europe, the importance of the sorption wheel to recover the indoor humidity in heating season was pointed out. In the system with small-scale absorption machine, dynamic power control and abandonment of cold water storage and thermal Back-Up lead to very good performance indicators. Large-scale systems (> 1000kW), for pre- and base-load-cooling are able to realize non-renewable primary energy savings of >50% in comparison to a reference system, if the components are optimally designed and simple but appropriate control strategies are implemented. Solar assisted cooling systems in this size and with optimized configurations can reach at least electrical “Seasonal Performance Factor“ SPF_el > 12.

The developed optimizations were implemented and tested successfully in some selected realized systems.

Life Cycle Analyses for two simulated systems with absorption machine (standard and optimized configuration) have shown that solar thermal cooling systems with optimized operation are able to compensate the higher expenses for production and disposal by means of primary energy saving during their use phase. Considering the whole life cycle, the reduction potential of green-house-emissions and non-renewable primary energy demand for the investigated optimized systems amounts to 35% bis 50% in cooling operation.

Furthermore an experimental Set-Up for a cost-efficient cooling tower (26 kW recooling power) was developed and tested, with focus on better water hygiene, reduced energy consumption and use of low-cost serial components.