Implications of the modelling of stratified hot water storage tanks in the simulation of CHP plants

Abstract This paper considers the effect that different hot water storage tank modelling approaches have on the global simulation of residential CHP plants as well as their impact on their economic feasibility. While a simplified assessment of the heat storage is usually considered in the feasibility studies of CHP plants in buildings, this paper deals with three different levels of modelling of the hot water tank: actual stratified model, ideal stratified model and fully mixed model. These three approaches are presented and comparatively evaluated under the same case of study, a cogeneration plant with thermal storage meeting the loads of an urbanisation located in the Bilbao metropolitan area (Spain). The case of study is simulated by TRNSYS for each one of the three modelling cases and the so obtained annual results are analysed from both a First and Second-Law-based viewpoint. While the global energy and exergy efficiencies of the plant for the three modelling cases agree quite well, important differences are found between the economic results of the feasibility study. These results can be predicted by means of an advanced exergy analysis of the storage tank considering the endogenous and exogenous exergy destruction terms caused by the hot water storage tank.

[1]  B. J. Newton,et al.  Modeling of Solar Storage Tanks , 1995 .

[2]  K. Khan,et al.  Energy conservation in buildings: cogeneration and cogeneration coupled with thermal energy storage , 2004 .

[3]  Björn Rolfsman,et al.  Combined heat-and-power plants and district heating in a deregulated electricity market , 2004 .

[4]  Tatiana Morosuk,et al.  Endogenous and Exogenous Exergy Destruction in Thermal Systems , 2006 .

[5]  Richard L. Ottinger,et al.  Compendium of Sustainable Energy Laws: Proposal for a Directive of the European Parliament and of the Council on the Promotion of Cogeneration Based on a Useful Heat Demand in the Internal Energy Market , 2005 .

[6]  D. J. Close,et al.  A design approach for solar processes , 1967 .

[7]  Adrian Bejan,et al.  Second-Law Analysis in Heat Transfer and Thermal Design , 1982 .

[8]  M. G. Abu-Hamdan,et al.  An experimental study of a stratified thermal storage under variable inlet temperature for different inlet designs , 1992 .

[9]  F. C. Lai,et al.  Experimental Study of Stratification in a Liquid Storage Tank With a Porous Manifold , 2004 .

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

[11]  Anders N. Andersen,et al.  Exploration of economical sizing of gas engine and thermal store for combined heat and power plants in the UK , 2008 .

[12]  Jay Burch,et al.  Tool for Generating Realistic Residential Hot Water Event Schedules: Preprint , 2010 .

[13]  H. A. Vielmo,et al.  Comparison between models for the simulation of hot water storage tanks , 2003 .

[14]  A. R. Balakrishnan,et al.  Parametric studies on thermally stratified chilled water storage systems , 1999 .

[15]  Shahab Alizadeh,et al.  An experimental and numerical study of thermal stratification in a horizontal cylindrical solar storage tank , 1999 .

[16]  A. Gómez Moreno,et al.  Simulation of a solar cooling system. , 2010 .

[17]  W. Beckman,et al.  Solar Engineering of Thermal Processes , 1985 .

[18]  Stig-Inge Gustafsson,et al.  Heat accumulators in CHP networks , 1992 .

[19]  Antonio Valero,et al.  Structural theory as standard for thermoeconomics , 1999 .

[20]  Anders N. Andersen,et al.  Feasibility of CHP-plants with thermal stores in the German spot market , 2009 .

[21]  Ruzhu Wang,et al.  Thermal stratification within the water tank , 2009 .