Recently, a number of small capacity thermally driven chillers have entered on the market, opening up promising possibilities for solar heating and cooling also in the small power range. For the single architect, engineer, installer or planner, it is however difficult to decide in an early planning stage, whether solar heating and cooling is feasible in a specific case.

In order to support this pre-planning process, a virtual case study is being prepared within the project SolarCombi+. The virtual case study is a comparative approach, to provide annual performance data of a solar combi plus system, achieved from simulation calculations. The approach is as follows:

• Three locations will be selected, representing climatic conditions for broad regions in Europe. Currently, the sites Strasbourg, Napoli and Toulouse are considered
• Two types of buildings are considered: an office building and a residential building. For these representative buildings, the heating and cooling loads are calculated at the selected sites and climates; the calculated load files are used as demand files in the solar cooling system simula¬tion calculations
• Two basic system configurations of the solar cooling system are considered (Figure 1). How¬ever, each configuration is split again into sub-configurations with different chiller types, heat rejection (wet, dry) systems and their appropriate control strategy, and using either flat-plate collectors or vacuum tube collectors.
  

The chiller types, considered in the virtual case study, are ranging from 4.5 kW up to 15 kW rated chilling capacity. Simulation models are applied for the Rotartica, ClimateWell, Sunin¬verse and EAW chiller (absorption chillers), and for the Sortech chiller (adsorption chiller). Although some of the ma¬chines allow heat pump operation in winter as well, this option is not considered in the simulation stu¬dy. In each sub-configuration, the collector area is va¬ried in a certain range to identify an optimum in solar thermal contribution and system efficiency.

The virtual case study aims for identification of most promising application fields of the dif-ferent sys¬tem configurations and equipment types. Thus, the results are presented based on a set of evalu¬ation figures, including primary energy savings and avoidance of CO2 emissions in comparison to a refe¬rence system calculation with conventional heating and cooling tech¬nology.

The results of the virtual case study will be made available online at the project web page. Additio¬nal¬ly, the provision of a post-evaluation tool is foreseen in order to adjust e.g. cost figures according to actual energy and system cost.

Figure 1. Solar cooling systems show in general a higher complexity in the hydraulic scheme than other solar thermal applications. From the multitude of possible schemes, two basic configurations were finally selected and implemented in the simulation models. In each configuration, variations are made with respect to the collector size and type, to the chiller model and to the type of heat rejection (wet or dry re-cooling). The system control is adapted to the applied chiller type. The chilled water storage is small and serves mainly as hydraulic switch in the simulations. The configuration with the auxiliary heat source (e.g. boiler) always bypassing the solar heat storage tank as shown in the upper figure, is designed according to the installation requirements in Spain.