The highest degree in flexibility and precision offer open architecture tools. As the source code of the program modules which reflect the model components is open in these tools, the source can be modified or self written components may be added because of individual requirements. For example, advanced models for thermally driven chiller cycles /7/ could be integrated into the programme library of the simulation environment. The time step in the system simulation is in general adjustable, enabling thereby the user to implement and test more sophisticated control strategies in the modelled system. A detailed energy flow study including the part-load behaviour is possible with simulation tools of this type.

As a disadvantage in the use of these open simulation platforms it should be mentioned that the setup of a desired system model requires much more effort compared to the programs, presented in the previous sections. Beside the development of the system model and of the energetic and economic performance evaluation strategy, the testing of the model can be considerably time consuming. Three types of these tools will be mentioned here, although more software tools may have the potential to be used for thermal system simulation.

A worldwide well known computing software is Matlab, developed in 1984. This technical computing environment can be coupled with the graphical modular simulation surface Simulink. Several tool boxes for different research topics can be purchased for Simulink, one of them is the tool box CARNOT /8/, developed at the Aachen University of applied sciences, which provides components for heating systems and solar thermal collector systems. Additional components for cooling equipment may be added using the standard Simulink procedure for the implementation of self written code (C-language).

Primarily designed for solar thermal and HVAC systems with their controllers, the simulation environment ColSim (Collector Simulation) provides improved numeric algorithms in the program’s solver to allow precise simulation also in small time steps down to a few seconds, a requirement especially in the development of control algorithms /9/. ColSim uses the plug flow model in tracing the mass flow through a hydraulic network. This approach allows a mass flow and energy balance in every time step, representing one of the main features in ColSim’s error detection routine.

Currently, the platform Linux is used. The programme is available for free, and due to several users in different projects, the number of available system component models grows continuously. Public domain software is used for the graphical design of a desired system as well as in the visualisation of online results.

TRNSYS /10/, commercially available since 1975, disposes of a large set of models for standard hydraulic components, solar collectors and other HVAC equipment. The subroutines, containing a certain component of the hydraulic system, are called ‘types’ in TRNSYS. The arrangement of the required types into a hydraulic system to be simulated is called simulation ‘deck’. While the hydraulic system may be composed and configurated using either the graphical surface or a text editor provided with TRNSYS, a special building editor (PREBID) is used to specify a desired building, in order to allow the calculation of heating / cooling loads in TRNSYS.

To give an example for the application of TRNSYS, an additional type for a desiccant cooling system was developed at Fraunhofer ISE. This type contains the models for a desiccant wheel, heat recovery unit, humidifier, heat exchanger, fan and the like. In combination with a control and operation type for the desiccant cooling system, this type can be implemented into the hydraulic scheme of a TRNSYS deck. TRNSYS simulations using these additional components of a desiccant cooling system were applied in the design phase of the first solar autonomous air-conditioning system in Germany /11/.

TRNSYS was also used in the simulation of the solar assisted cooling system of the new federal environment agency building in Dessau, Germany /12/. In this application, an adsorption chiller will be implemented for chilled water supply in order to cool mainly computer rooms. Cooling is required due to the high internal loads throughout the year, but in the cold season, the cooling load can be covered by direct evaporative cooling via the cooling tower. Beside a parametric study investigating different solar collector areas and storage sizes, the most promising system configuration was intensively studied by varying control parameters and the type of the solar thermal collector. For the adsorption chiller, cooling tower and for the system control, self written types were applied in the simulation calculations.

3 Summary

Solar assisted air-conditioning is a growing application and provides the attractive opportunity in saving primary energy and peak-power demand in electricity. To date, most of the existing plants (approx. 50 installations in Europe) have been installed in the frame of demonstration and research projects and thus with very high effort during system design and planning. Actually, a lack of knowledge and experience in design and planning on the commercial side has to be overcome by measures to support the planning of the systems. Rules, guidelines and tools have been created for this reason in the course of numerous projects, with the capability in assisting the planning of a solar air-conditioning system on different levels. A selection of this measures was briefly discussed in this paper. The application of these or similar planning support measures is useful, since the integration of a renewable energy system with the property of fluctuating energy supply complicates the appropriate design and configuration of the system. Fundamental design errors may be avoided and the achievement of target values, e. g. of primary energy savings, can be ensured.