Transient analysis and energy optimization of solar heating and cooling systems in various configurations

In this paper, a transient simulation model of solar-assisted heating and cooling systems (SHC) is presented. A detailed case study is also discussed, in which three different configurations are considered. In all cases, the SHC system is based on the coupling of evacuated solar collectors with a single-stage LiBr–H2O absorption chiller, and a gas-fired boiler is also included for auxiliary heating, only during the winter season. In the first configuration, the cooling capacity of the absorption chiller and the solar collector area are designed on the basis of the maximum cooling load, and an electric chiller is used as the auxiliary cooling system. The second layout is similar to the first one, but, in this case, the absorption chiller and the solar collector area are sized in order to balance only a fraction of the maximum cooling load. Finally, in the third configuration, there is no electric chiller, and the auxiliary gas-fired boiler is also used in summer to feed the absorption chiller, in case of scarce solar irradiation. The simulation model was developed using the TRNSYS software, and included the analysis of the dynamic behaviour of the building in which the SHC systems were supposed to be installed. The building was simulated using a single-lumped capacitance model. An economic model was also developed, in order to assess the operating and capital costs of the systems under analysis. Furthermore, a mixed heuristic-deterministic optimization algorithm was implemented, in order to determine the set of the synthesis/design variables that maximize the energy efficiency of each configuration under analysis. The results of the case study were analyzed on monthly and weekly basis, paying special attention to the energy and monetary flows of the standard and optimized configurations. The results are encouraging as for the potential of energy saving. On the contrary, the SHC systems appear still far from the economic profitability: however, this is notoriously true for the great majority of renewable energy systems.

[1]  Vice President,et al.  AMERICAN SOCIETY OF HEATING, REFRIGERATION AND AIR CONDITIONING ENGINEERS INC. , 2007 .

[2]  W. Beckman,et al.  A design procedure for solar heating systems , 1976 .

[3]  W. R. McIntire.  Factored approximations for biaxial incident angle modifiers , 1982 .

[4]  Georgios A. Florides,et al.  Modelling and simulation of an absorption solar cooling system for Cyprus , 2002 .

[5]  Nesreen Ghaddar,et al.  Modeling and simulation of solar absorption system performance in Beirut , 1997 .

[6]  S. Kakaç,et al.  Heat Exchangers: Selection, Rating, and Thermal Design , 1997 .

[7]  William A. Beckman,et al.  Solar transmittance characteristics of evacuated tubular collectors with diffuse back reflectors , 1985 .

[8]  Georgios A. Florides,et al.  Modelling, simulation and warming impact assessment of a domestic-size absorption solar cooling system , 2002 .

[9]  Francesco Calise,et al.  Simulation Model and Analysis of a Small Solar-Assisted Refrigeration System: Dynamic Simulation and Optimization , 2008 .

[10]  Ibrahim Atmaca,et al.  Simulation of solar-powered absorption cooling system , 2003 .

[11]  Mahmoud Hammad,et al.  Performance of a second generation solar cooling unit , 1998 .

[12]  Khalid A. Joudi,et al.  Development of design charts for solar cooling systems. Part I: computer simulation for a solar cooling system and development of solar cooling design charts , 2003 .

[13]  Soteris A. Kalogirou,et al.  Simulation and optimization of a LiBr solar absorption cooling system with evacuated tube collectors , 2005 .

[14]  Jeffrey M. Gordon,et al.  HIGH-EFFICIENCY SOLAR COOLING , 2000 .

[15]  Mehdi Shahrestani,et al.  Energy simulation of solar assisted absorption system and examination of clearness index effects on auxiliary heating , 2007 .

[16]  Robert Hooke,et al.  `` Direct Search'' Solution of Numerical and Statistical Problems , 1961, JACM.

[17]  Khalid A. Joudi,et al.  Development of design charts for solar cooling systems. Part II: Application of the cooling f-chart , 2003 .