Alexander Thür Compact Solar Combisystem High Efficiency by Minimizing Temperatures DANMARKS TEKNISKE UNIVERSITET PhD Thesis BYG·DTU Rapport R-160 2007 ISSN 1601-2917 ISBN 97-88778-772-343 Alexander Thür Compact Solar Combisystem High Efficiency by Minimizing Temperatures Solar Store Unit Technical Unit Space Heating HW M S Domestic Hot Water CW M Radiators S Floor Heating M Boiler Solar Store Unit Technical Unit Space Heating Collector HW S (V5) M Loop S 4 Domestic Hot Water (P6) (P4) CW M (V4) Radiators (V3) 1 S Floor Heating (V2) M 2 (P3) Boiler 3 5 (P1) (P2) Collector S Loop (V1) 2007 R-160 ISSN 1601-2917 ISBN 9-78877-877-2343 Compact Solar Combisystem High Efficiency by Minimizing Temperatures Ph.d.-Thesis Alexander Thür BYG•DTU - Department of Civil Engineering Technical University of Denmark February 2007 Compact Solar Combisystem - High Efficiency by Minimizing Temperatures Copyright (c), Alexander Thür, 2007 Printed by DTU-Tryk Department of Civil Engineering Technical University of Denmark ISBN 9-78877-877-2343 ISSN 1601-2917 Preface This work has been financed by Nordic Energy Research and the Technical University of Denmark and the main industry partner METRO THERM A/S as sponsor of the prototypes. This thesis is part of the result of the project REBUS – Competitive Solar Heating Systems for Residential Buildings. It was a great honour for me to work within this project and I like to thank all partners for the good co-operation. Naturally, the co- operation with some persons was much closer than others, therefore I like to thank especially the following: First of all I like to thank my supervisor Simon Furbo, who was available for discussions and support at any time. Further, I like to thank Frank Fiedler who was the main partner for fruitful discussions and exchange of experience, especially during the important period of laboratory tests. I also like to thank Dan Kristoffersen, Torben Schifter-Holm and their chief Kurt Rasmussen from METRO THERM A/S for the good co-operation. Very special thanks to Frede Schmidt for his great personal effort. He supported the controller development even when being in hospital. I also like to thank Otto Schäffer and his family for the possibility to get the first experience in practice with the demonstration system in their house. Thank you for almost adopting me in the family and for the perfect support with superb food all the time when I was working in the basement. I also like to thank for the important contribution from Katrin Zaβ, Daniel Barandalla and Anneli Carlqvist, who carried out very valuable master thesis projects within this project. All my colleagues in the solar group I like to thank for being good and friendly company for the last three years with a lot of interesting and fruitful discussions as well. The proof readers, Simon Furbo, Anne Rasmussen and Walter Meusburger, I like to thank for the time consuming and great job they did to improve the English of this thesis significantly. Last but not least, never forget the past. In Austria I also like to thank all my former colleagues at AEE INTEC, where during eight years of joint work I learned the basics about solar heating systems, which was important background knowledge for this work. Further, I like to thank Manfred Oelsch and his family who also gave me the possibility to learn a lot about solar combisystems in practice in their own house. iii iv Abstract Compact Solar Combisystem - High Efficiency by Minimizing Temperatures Alexander Thür Department of Civil Engineering, Technical University of Denmark Solar heating systems are getting increasingly popular in many European countries, mainly focused on solar domestic hot water systems. But so-called solar combisystems, which supply heat for both domestic hot water and space heating, are still only really noticable in Sweden, Germany, Switzerland and Austria. Reasons for that, beside others, might be not sufficiently attractive energy savings, too big space requirement and too much effort and risks for installers due to the complexity of many system concepts and products available on the market. Based on elaborated knowledge in international research projects within IEA-SHC Task 26 and the ALTENER project “Solar Combisystems”, a new solar combisystem concept was developed. Therefore the focus was concentrated on minimizing the temperature in the system with the goal to reduce system heat losses and to increase the efficiency of the condensing natural gas boiler and the solar collector. The major task was to enable high domestic hot water comfort at any time, independent of the auxiliary set temperature in the solar tank. For a condensing natural gas boiler in combination with a flat plate heat exchanger hot water unit, a hydraulic and control concept could be developed, which ensures the required hot water comfort without the need of high temperature in the solar tank. As a consequence it is possible to use the auxiliary volume in the solar tank at any low temperature level required by the actual space heating demand. This strongly improves the operating conditions for a condensing natural gas boiler and reduces the heat losses of the tank and, most important of all, the pipes within the system. The compactness of the total hydraulic system, which is installed in a closed 60 x 60 cm cabinet as a technical unit, leads to further reduction of heat losses, the possibility to use heat recovery effects, and several practical advantages like attractive appearance, easy transport and simple and fast installation. Due to the concentration of all technical parts in the technical unit, it is possible to combine it easily with standard tanks of any size in order to achieve the requested energy savings. The hydraulic and control concept was designed to be used with great advantage in combination with condensing natural gas boilers, but it can be also combined with pellet-, wood- or oil boilers just by adjusting some control parameters. Theoretical investigations including system simulations with TRNSYS showed for this new solar combisystem concept a potential of up to 80% more energy savings compared to existing, conventionally controlled solar combisystems. After development and test of the first prototype in the laboratory, a demonstration system was built which replaced an old conventional natural gas heating system in a one- family house. Measurements in practice showed how this new natural gas - solar heating concept performs in comparison with the old one. Keywords: Solar Heating, Solar Combisystem, Heat Loss, Efficiency, Condensation v vi Resumé Kompakt kombianlæg - Høj effektivitet ved lavere temperaturer Alexander Thür BYG•DTU, Danmarks Tekniske Universitet Solvarmeanlæg bliver mere og mere populære i mange europæiske lande; hovedsagelig solvarmeanlæg til brugsvandsopvarmning. Dog er brugen af solvarmeanlæg til kombineret brugsvands- og rumopvarmning faktisk kun værd at bemærke i Sverige, Tyskland, Schweiz og Østrig. Nogle af grundene til det kunne være: ikke tilstrækkeligt fordelagtige energibesparelser, for stort pladsbehov og for meget besvær, og for store risici for installatører på grund af den kompleksitet der er ved mange anlægskoncepter og produkter på markedet. Baseret på detaljeret viden om internationale forskningsprojekter inden for IEA-SHC Task 26 og ALTENER projektet “Solvarmeanlæg til kombineret brugsvands- og rumopvarmning”, er der udviklet en teknisk unit inklusive en kondenserende naturgaskedel og en lagerunit med solvarmeanlæggets varmelager. Der blev fokuseret på at minimere temperaturen i anlægget med det mål at reducere varmetabene og øge effektiviteten for den kondenserende naturgaskedel og solfangeren. Hovedopgaven var at muliggøre en høj brugsvandskomfort til enhver tid, uafhængigt af temperaturen i solvarmebeholderen. For en kondenserende naturgaskedel kombineret med en pladevarmeveksler til opvarmning af brugsvandet kunne der udvikles et hydraulik- og kontrolkoncept, der sikrer den fornødne varmtvandskomfort uden brug af høj temperatur i solvarmebeholderen. Følgelig er det muligt at bruge det supplerende volumen i solvarmebeholderen på et hvilket som helst lavt temperaturniveau der kræves af rumopvarmningsbehovet. Dette forbedrer driftsbetingelserne for en kondenserende naturgaskedel betydeligt og reducerer varmetabet fra beholderen og, vigtigst af alt, fra anlæggets rør. Den tekniske unit, som er indbygget i et lukket 60 x 60 cm kabinet har et lavt varmetab, mulighed for at bruge varmegenvinding, flere fordele som attraktivt udseende, nem transport, og enkel og hurtig installation. På grund af koncentrationen af alle tekniske dele i den tekniske unit, er det muligt nemt at kombinere den med standardbeholdere af enhver størrelse for at opnå de ønskede energibeparelser. Konceptet blev konstrueret til med stor fordel at kunne anvendes i kombination med en kondenserende naturgaskedel, men det kan også kombineres med pille-, træ- eller oliefyr bare ved indstilling af nogle kontrolparametre. Teoretiske undersøgelser, inklusive simuleringer med TRNSYS, viste et potentiale på op til 80% større energibesparelser for dette nye kombianlægkoncept, sammenlignet med eksisterende, konventionelle kombianlæg. Efter at den første prototype var udviklet og afprøvet i laboratoriet, blev der bygget et demonstrationsanlæg der erstattede et gammelt konventionelt naturgasanlæg i et enfamiliehus. Målinger i praksis viste hvordan dette nye naturgas- solvarmekoncept fungerer sammenlignet med det gamle energianlæg. Stikord: Solvarme, kombianlæg til kombineret