Retrofitting Domestic Hot Water Tanks for Solar Thermal Collectors. A Theoretical Analysis

Luís Ricardo Bernardo
Energy and Building Design, Lund Technical University, Lund, Sweden

Henrik Davidsson
Energy and Building Design, Lund Technical University, Lund, Sweden

Björn Karlsson
Mälardalen University, Västerås, Sweden

Ladda ner artikelhttp://dx.doi.org/10.3384/ecp110573765

Ingår i: World Renewable Energy Congress - Sweden; 8-13 May; 2011; Linköping; Sweden

Linköping Electronic Conference Proceedings 57:13, s. 3765-3772

Visa mer +

Publicerad: 2011-11-03

ISBN: 978-91-7393-070-3

ISSN: 1650-3686 (tryckt), 1650-3740 (online)


One of the most expensive components of a solar thermal system is the storage tank. Retrofitting conventional domestic hot water heaters when installing a new solar hot water system can decrease the total investment cost. In this study; retrofitting of existing water heaters using forced circulation flow was investigated. A comparison with a standard solar thermal system is also presented. Four simulation models of different system configurations were created and tested for the climate in Lund; Sweden. The results from the simulations indicate that the best configuration consists on connecting the collectors to the existing heater throughout an external heat exchanger and adding a small heater storage in series. For this retrofitted system; preliminary results show that an annual solar fraction of 53% is achieved. In addition; a conventional solar thermal system using a standard solar tank achieves a comparable performance for the same storage volume and collector area. Hence; it is worth to further investigate and test in practice this retrofitting. Furthermore; using the same system configuration; solar collectors can also be combined with new standard domestic hot water tanks at new installations; accessing a world-wide developed and spread industry.


Solar thermal; Storage tank; Water heater; Retrofit; Domestic hot water


[1] Swedish Energy Agency; Energy statistics for one- and two- dwelling buildings in 2008; 2009.

[2] Cruickshank; C. and Harrison; S.; Analysis of a Modular Thermal Storage for Solar Heating Systems; Proceedings of Canadian Solar Buildings Conference; 2004.

[3] Lin; Q.; Analysis; Modelling and Optimum Design of Solar Domestic Hot Water Systems; Ph.D. thesis; 1998; ISBN 87-7877-023-8.

[4] Fraser; K. F.; Hollands; K. G. T. And Brunger; A. P.; An Empirical Model for Natural Convection Heat Exchangers in SDHW Systems; Solar Energy 55(2); 1995; pp. 75-84. doi: 10.1016/0038-092X(95)00029-Q.

[5] Liu; W. and Davidson; J.; Comparison of Natural Convention Heat Exchangers for Solar Water Heating Systems; Proceedings of American Solar Energy Society Conference; 1995.

[6] Klein; S. et al.; TRNSYS; a Transient System Simulation Program; University of Wisconsin; Madison; 1999.

[7] Swedish Building Regulation; Regelsamling för byggande; BBR 2008; ISBN 978-91-86045-03-6.

[8] Widén; J.; Lundh; M.; Vassileva; I.; Dahlquist; E.; Ellegård; K. and Wäckelgård; E.; Constructing load profiles for household electricity and hot water from time-use data—Modelling approach and validation; Energy and Buildings 41(7); 2009; pp. 753-768. doi: 10.1016/j.enbuild.2009.02.013.

[9] Stengård; L.; Mätning av kall- och varmevattenanvändning i 44 hushåll; 2009.

[10] Swedish Energy Agency; FEBY – Krav Specifikation för Minienergihus; 2009.

[11] Statistics Sweden; Boende och boendeutgifter 2006; BO 23 SM 0801; 2006.

[12] Hausner; R. and Fink; C.; Stagnation behaviour of solar thermal systems; IEA SHC; task 26; 2002.

[13] Nordlander S. and Bales C.; TRNSYS type 221; distributed by the Solar Energy Research Centre; Sweden; 2007.

Citeringar i Crossref