The simulation period is one year with a time step of three minutes; weather data from Zurich is used. A single family house with a heating demand of 60 kWh/m2a is simulated. The maximum power of the burner is set to 10 kW and the set temperature of the auxiliary volume of the store is 63°C. A collector area of 20 m2 and a 1 m3 store is chosen.

3.2. Compared values and comparison of results of the different modelling methods

The comparison of the results is done by comparing yearly values of energy delivered to and taken from the store by the several loops (collector, domestic hot water, space heating, auxiliary heating), the resulting energy balance as well as the fractional thermal energy savings (fsav, therm) of the system defined as the auxiliary energy consumption of the solar thermal system (Esoi) compared to the final energy consumption of a reference system (Eref):

The results show that the deviation of the compared values caused by the interfaces and different component order is negligible. The difference between the above named yearly values of the two systems is less than 1 %. This is also according to a simulation test made with only one controller component of the collector loop connected directly to the tank instead of the interfaces in the subsystem model in SIMULATION STUDIO. This also causes little effect compared to simulations where this component is connected via the interfaces only. Because it is only one component, in this case the difference of the compared values is less than 0.03 %.

2. Conclusion

The use of the new implemented subsystem based structure level in SIMULATION STUDIO — the graphical user interface of TRNSYS 16 — helps to improve the graphical representation of complex models as well as achieving a possibility to replace subsystems in a simple way. Regarding the educational field, the new feature leads to a shorter training time and simplified construction of models and permits students to work on projects using and maintaining complex systems, because they are not forced to get familiar with the ASCII input file. In recent simulation projects the new modular

approach was already applied. A comparison with a standard model representation via manually implemented text file showed negligible deviation, namely less than 1 %, comparing yearly values of the energy balance of the store and the fractional thermal energy savings of a solar thermal system for hot water preparation and space heating support used in the IEA-SHC Task 32. This is most likely caused by the additional EQUATIONS used as interfaces of the subsystems. Nevertheless, the new implemented feature should only be a first approach to get a new structure level to the graphical user interface of TRNSYS. It is worth striving for an integration of it in some way in newer versions of SIMULATION STUDIO without the use of extra equations as interfaces. In the future a database of subsystems could be generated like the TRNSYS component database and the subsystems could then also be linked to each other in the common TRNSYS way.

References

[1] S. A. Klein et al, (2005). TRNSYS 16 — A Transient Simulation System. Solar Energy Laboratory, Wisconsin-Madison University.

[2] W. Weiss et al, (2003). Solar Heating Systems for Houses — A Design Handbook for Solar Combisystems, International Energy Agency, Solar Heating & Cooling Programme — Task 26.

[3] R. Heimrath, M. Haller, (2007). IEA-SHC-Task 32 — Project Report of Subtask A2 of Subtask A: The Reference Building, the Reference Heating System. Institute of Thermal Engineering, Graz University.

[1] Each with ideal pump dimensioning and operating at design point.

[2] Simulation Environment

In order to evaluate and optimise thermosiphon solar hot water systems, a simulation model in the Matlab/Simulink environment [3] was developed. In addition, the Simulink-based CARNOT

# Current address: Institut fur Solartechnik SPF, Rapperswil, Switzerland

[4] For example, air flow velocity > 2 m/s for even distribution and < 3.5 m/s (otherwise pressure drop too

high) [2]

[6] Fortran source code of the model can be downloaded from the TRNSYS website. http://sel. me. wisc. edu/trnsys/tmlib/ASHRAE_secondary_toolkit/heat_and_mass_trnsfr/1223NEW. for

[7] American Society of Heating, Refrigerating and Air-Conditioning Engineers

[8] Considering of condensation is of importance for the mentioned application in Bishkek, Kyrgyzstan as the dew point temperature often exceeds the water inlet temperature of 12°C.

[9] For example, the heat transfer coefficient calculated from (overall heat transfer) measurement data is lower if the heat exchanger is considered as a counter flow heat exchanger (the assumption valid for high number of tubes in air flow direction, e. g. [6]) than that for a cross-counter flow heat exchanger (e. g. [7-13])

’ Fanning factor is defined as the ratio of wall shear stress to the flow kinetic energy per unit volume [18]

[11] Thermal efficiency of a collector where ambient temperature equals the collector working temperature (i. e. no heat losses)

[12] This is necessary to be able to use time dependent values, e. g. temperatures, within equations.