K. T. Witte1*, J. Albers2, M. Krause3, M. Safarik4, F. Besana1, W. Sparber1

1 European Academy Bolzano, Institute of Renewable Energy, Viale Druso 1, 39100 Bolzano, Italia
2 Technische Universitat Berlin, Institut fur Energietechnik KT-2, Marchstrabe 18, 10587 Berlin, Germany
3 Fraunhofer Institute for Building Physics, Gottschalkstr. 28a, 34127 Kassel, Germany
4 Institute of Air Conditioning and Refrigeration (ILK), Bertolt-Brecht-Allee 20, 01309 Dresden, Germany

* Corresponding Author, kwitte@eurac. edu.

Abstract

In order to propagate the installation of solar cooling systems dimensioning and system design have to be optimised. Although the transient simulation software TRNSYS is well established for this purpose, considerable deviations to measured values are possible, when components are not correctly used or designed for the simulation. For this work two different models (so called Types) are investigated in parallel to simulate the part load behaviour of the absorption chiller EAW Wegracal SE 15. The paper reports on the possi­bilities and application limits for both TRNSYS Types. Their differences in accuracy regarding laboratory test data as well as real time data of a solar cooling system are dis­cussed. The basic methodology as well as the applied modifications to adapt the TRNSYS — Types to the EAW chiller are described. Finally the necessity to improve both models for non-nominal flow rates is shown.

Keywords: Solar cooling, EAW absorption chiller, Simulation, Characteristic Equation

1. Introduction

Solar Combi-Plus systems use solar energy to provide heat for domestic hot water and heating in winter as well as for domestic hot water and cold production in summer. Thus high solar fractions are possible over the year. Moreover such systems contribute to decrease the peak power demand during summer, which is partially caused by the growing number of small electrically driven air­conditioning appliances in the sunny and hot southern countries of Europe [1]. For the optimum design of solar cooling systems computer simulations are essential. To validate these simulations real time data of Solar Combi-Plus systems are required. Therefore, the European Academy (EURAC) in Bolzano is monitoring one of them at the premises of Ebner Solartechnik, using the absorption chiller EAW Wegracal SE 15 [2]. For the simulation of this plant and its utilisation the simulation software TRNSYS [3] is used. In a first step the available component of the ‘standard package’ of TRNSYS Version 16.1 was chosen to simulate the absorption chiller (Type 107). Since the implemented control strategy of this Type as well as the performance data differ from real operation of the EAW Wegracal SE 15 chiller, both the source code and the performance data of Type 107 have been modified. In a second step, another model based on the method of characteristic equations [4] (Type 177) was adapted to the EAW chiller and the simulation results have been compared to the same measurements.

2. Simulation models