Thesis
Reference
Heat pump systems for multifamily buildings: which resource for what demand?
DE SOUSA FRAGA, Carolina
Abstract
Ce travail vise à analyser, d'un point de vue énergétique, le potentiel et les contraintes de l'utilisation des systèmes de chauffage avec pompe à chaleur (PAC) dans les bâtiments résidentiels collectifs. Il se base sur un retour d'expérience d'un système innovant de PAC avec source froide solaire, implémenté dans un nouveau complexe résidentiel. Par simulation numérique, le potentiel de ce système pour 6 bâtiments résidentiels collectifs différents est analysé, suivi par une analyse comparative des potentiels et contraintes de 6 sources froides différentes, mises en œuvre dans les 6 bâtiments en question. Le travail se termine par une discussion concernant l'impact potentiel, en termes de consommation électrique annuelle et de puissance de pointe (en valeurs journalières), d'un développement généralisé de ce type de systèmes sur le parc résidentiel collectif genevois.
DE SOUSA FRAGA, Carolina. Heat pump systems for multifamily buildings: which resource for what demand? . Thèse de doctorat : Univ. Genève, 2017, no. Sc. 5065
DOI : 10.13097/archive-ouverte/unige:94939 URN : urn:nbn:ch:unige-949392
Available at:
http://archive-ouverte.unige.ch/unige:94939
Disclaimer: layout of this document may differ from the published version.
UNIVERSITÉ DE GENÈVE FACULTÉ DES SCIENCES Section des Sciences de la Terre et de l’Environnement Professeur Bernard Lachal Département F.-A. Forel
des Sciences de l’Environnement et de l’Eau Institut des Sciences de l’Environnement
Heat Pump Systems for Multifamily Buildings:
Which Resource for What Demand?
Long-term in-situ monitoring of an innovative system in Geneva
combined with sensitivity and comparative analysis via numerical simulation
THÈSE
présentée à la Faculté des sciences de l’Université de Genève
pour obtenir le grade de Docteur ès sciences, mention sciences de l’environnement
par
Carolina de Sousa Fraga
de
Rabo de Peixe (Portugal)
Thèse N 5065
À Gustavo, Margarida et Carlos
2“Ergue-te, pois, soldado do Futuro E dos raios de luz do sonho puro, Sonhador, faze espada de combate!”
- Antero de Quental, in "Sonetos"
Remerciements
Cette thèse n'aurait pas été possible sans le soutien, l'aide et l'encouragement de nombreuses personnes et organisa- tions.
Je témoigne tout d’abord beaucoup de reconnaissance à mon co-directeur Pierre Hollmuller pour la confiance qu'il m'a accordée. Ses conseils m'ont aidé tout au long du développement et de l'écriture de cette thèse. Ses connais- sances, sa patience, sa façon méthodique d’aborder les sujets, son expertise et son temps m’ont été indispensables.
Cela m'amène à remercier Urânia Sampaio d'avoir été si compréhensive et d’avoir concédé une partie de son temps avec Pierre, afin que nous puissions progresser avec ce travail.
Mes sincères remerciements vont également à mon directeur de thèse, le Professeur Bernard Lachal, qui m'a si sage- ment conseillé tout au long de ce travail. Ses remarques précises et pertinentes, basées sur sa maîtrise remarquable du domaine, ont été essentielles pour la qualité de ce travail. Je tiens également à souligner que son incroyable capa- cité de gestion du Groupe Systèmes Énergétiques, avec sincérité, respect et ouverture d’esprit, a rendu mon parcours doctoral très agréable.
Je tiens à remercier également Floriane Mermoud d’avoir participé si énergiquement à ce travail. Pour m'avoir enga- gée, pour sa gestion du projet COP5 et pour avoir partagé ses connaissances sur les pompes à chaleur, ainsi que le retour d’expérience, un grand merci.
Merci à Eric Pampaloni, son soutien a été crucial dans la phase de mesures de ce travail. Par ailleurs, sa patience avec mon apprentissage du français ... a été stoïque. Je le remercie pour me faire sentir chez moi tout en étant loin de chez moi.
Je tiens également à remercier les membres du Groupe Systèmes Énergétiques qui ont énormément contribué à mon évolution personnelle et professionnelle à Genève. Ce groupe a été une source d'amitiés ainsi que de bons conseils et de collaboration. Loïc Quiquerez pour avoir été mon partenaire de thèse, pour ses idées claires et nos échanges intel- lectuels fructueux. Jad Khoury pour ses conseils judicieux sur la façon de bien réussir un doctorat, et toutes ses con- naissances sur le parc de bâtiments résidentiels Genevois. Pierre Ineichen pour la source illimitée de café, ses données solaires précieuses et d'excellente qualité, ainsi que ses remarques pointues qui ont fait de l'apprentissage du français un défi si amusant. Jérôme Faessler pour son dynamisme, sa réactivité et ses connaissances, qui sont toujours une source d'inspiration. Fleury de Oliveira, pour ses connaissances pratiques et techniques, et pour apporter au groupe une ambiance de l’hémisphère sud. Zeinab Alameddine pour ses encouragements et son réconfort. Elliot Romano pour son expertise dans le domaine des tarifs de l'électricité, pour ses bonnes risées et surtout pour le chocolat belge et les pâtisseries de sa mère. Daniel Cabrera pour ses connaissances techniques sur la mesure et les économies d'élec- tricité, et pour être si compréhensif. Jean-Luc Bertholet pour sa connaissance en statistique et pour partager avec moi un goût prononcé pour les friandises. Stefan Schneider pour ses connaissances dans le domaine des bases de don- nées, son travail dans le SCCER FEEB&D et pour avoir été si coopératif chaque fois que j'avais besoin de certaines don-
Remerciements
Je suis particulièrement reconnaissante aux Prof. Miguel Brito, Dr. Jakob Rager et Prof. Martin Patel pour avoir promp- tement accepté d’être membres de mon jury de thèse et pour le temps consacré à la lecture et à l’examen de ce ma- nuscrit.
Je voudrais également exprimer ma reconnaissance aux personnes suivantes:
Les nombreux membres du programme de la Tâche 44 du Programme Solar Heating and Cooling de l’AIE.
Leurs contributions et leur expertise lors de nos réunions ont été une excellente source de connaissance;
Les membres du groupe de suivi du projet COP5, pour leurs remarques, observations et expertise ;
ERTE et Suntechnics, les concepteurs et les gestionnaires du système de pompe à chaleur qui fait l’objet de la première partie de cette étude. Nos fréquentes réunions et échanges d’information et de données ont été cruciaux pour ce travail;
les examinateurs des articles de revue publiés dans le cadre de cette thèse. Leurs remarques pertinentes ont permis une amélioration précieuse de ce travail;
Laurent Parisse, de SIG, pour sa disponibilité et pour voir partagé ses connaissances sur les pompes à chaleur.
Ce travail n'aurait pu être mené à bien sans l'aide de différents financeurs : l'Office fédéral de l'énergie (OFEN), les
«Services industriels de Genève» (SIG), l'Office cantonal de l'énergie de l'Etat de Genève (OCEN) et la CTI dans le cadre du projet SCECER FEEB & D (KTI.2014.0119).
Mon séjour à Genève a en grande partie été rendu agréable en raison des nombreux amis qui sont devenus une partie de ma vie. Je suis également reconnaissant pour l'hospitalité de Monique Bornand lors de mon arrivée à Genève.
Enfin, je remercie mon cher époux Gustavo Sousa pour son soutien calme et apaisant, sa patience éternelle, ses re- marques pertinentes et son enthousiasme contagieux à l’égard de mes travaux, comme de la vie en général. Notre couple a grandi en même temps que mon projet scientifique, le premier servant de socle solide à l'épanouissement du second. Je suis reconnaissant à ma nouvelle famille pour être si compréhensive avec la diminution du nombre de vi- sites. Merci Carlos et Diana d’avoir partagé les nouvelles avec moi et de m’avoir gardé dans la boucle, cela a vraiment soulagé ma frustration de ne pas pouvoir vous rejoindre toute de suite, dans ce moment si spécial. Je voudrais aussi remercier mes parents, Margarida Sousa et Carlos Fraga pour avoir toujours cru en moi. Malgré mon éloignement depuis de (trop) nombreuses années, leur intelligence, leur confiance, leur tendresse, leur amour me portent et me guident tous les jours. Merci pour avoir fait de moi ce que je suis aujourd’hui.
Acknowledgements
Acknowledgements
This thesis would not have been possible without the support, help and encouragement of many different people and organizations.
First and foremost I would like to express my sincere gratitude to my co-supervisor Pierre Hollmuller for believing in me from the start. His guidance helped me in all the time of research and writing of this thesis. His immense knowledge, patience, methodical ways, expertise and time were indispensable. This leads me to a big fat thank you to Urânia Sampaio for being so understanding and conceding some of her time with Pierre so we could progress with this work.
A very special thank you is due to my doctoral supervisor Prof. Bernard Lachal, who so wisely advised me throughout this work. His right on the spot remarks, based on his long term knowledge and experience, were a must have for the quality of this work. I would also like to emphasize how his incredible ability to manage the Energy Systems Group and all his members with such sincerity, respect and openness made this PhD so much easier.
My sincere thanks also goes to Floriane Mermoud, for being a huge participant in this work. For hiring me, for manag- ing the project COP5 and for sharing her knowledge on monitoring and heat pumps.
I thank Eric Pampaloni, his support was crucial in the monitoring phase of this work. Moreover, his patience while teaching me French… was stoic. I thank him for making me feel at home away from home.
The members of the Energy Systems Group have contributed immensely to my personal and professional time at Ge- neva. The group has been a source of friendships as well as good advice and collaboration. Loïc Quiquerez for being my partner in PhD, with his clear ideas and our fruitful intellectual exchanges. Jad Khoury for his wise advice on how to successfully finish a PhD, and all his knowledge on the Geneva building stock. Pierre Ineichen for the unlimited source of coffee, his precious solar data of excellent quality and his sharp remarks that made learning French that much challenging and that much fun. Jérôme Faessler for his activeness, reactiveness and knowledge which are a source of inspiration. Fleury de Oliveira, for his practical and technical knowledge, and for bringing a southern vibe to the group. Zeinab Alameddine for her encouragement and reassurance. Elliot Romano for his expertise in electricity tariffs, good laughs and Belgian chocolate. Daniel Cabrera for his technical knowledge on electricity measuring and electricity savings, and also for being so understanding. Jean-Luc Bertholet for his knowledge in statistics and for being such a sweet tooth. Stefan Schneider for his knowledge with data bases, his work in the SCCER FEEB&D and for being so helpful whenever I needed some data. Theodora Seal for her English knowledge. Pauline Calame for taking care of me and teaching me French. Ivana Quatrini for all the joyfulness she spread whenever she was around. Pascale Pavesi
Acknowledgements
I would also like to express my appreciation to:
the various members of the IEA Solar, Heating and Cooling Task 44. Their input and expertise along with our meetings were an excellent source of knowledge;
all members of the project COP5 biannual meetings, for their remarks and observations;
ERTE and Suntechnics, the designers and energy managers of the solar and heat pump system that was moni- tored in the first part of this study. Our frequent meetings and data exchange was crucial to this work;
the reviewers of the published articles. Their pertinent remarks were an added improvement to this work;
Laurent Parisse for sharing is knowledge on heat pumps.
I gratefully acknowledge the financial support given by the Swiss Federal Office of Energy (SFOE), the “Services Indus- triels de Genève” (SIG), the “Office cantonal de l’énergie de l’Etat de Genève” (OCEN) and the CTI within the SCCER FEEB&D project (KTI.2014.0119).
My time at Geneva was made enjoyable in large part due to the many friends that became a part of my life. I am also grateful for Monique Bornand’s hospitality as I finished up my Masters and started the PhD.
Finally, and not at all the least, a giant thank you to Gustavo Sousa for his everlasting patience, calm and soothing support, pertinent remarks and help, especially in the final phase of this work. I am grateful to my new family for be- ing so understanding with the decreasing number of visits. Thank you Carlos and Diana for sharing your news with me and keeping me in the loop, this has really eased my frustration of nothing being able to join you in this so special moment. I would also like to thank my parents, Margarida Sousa and Carlos Fraga for always believing in me. For cheering me all the way, and for all their support.
Résumé
Ce travail vise à analyser, d’un point de vue énergétique, le potentiel et les contraintes de l’utilisation des systèmes de chauffage avec pompe à chaleur (PAC) dans les bâtiments résidentiels collectifs. Il se base sur un retour d’expérience d'un système innovant de PAC avec source froide solaire, implémenté dans un nouveau complexe résidentiel. Par simulation numérique, le potentiel de ce système pour 6 bâtiments résidentiels collectifs différents est analysé, suivi par une analyse comparative des potentiels et contraintes de 6 sources froides différentes, mises en œuvre dans les 6 bâtiments en question. Le travail se termine par une discussion concernant l’impact potentiel, en termes de consom- mation électrique annuelle et de puissance de pointe (en valeurs journalières), d’un développement généralisé de ce type de systèmes sur le parc résidentiel collectif genevois.
La première partie de cette étude présente les résultats du retour d’expérience d'un système existant qui combine des PAC avec des capteurs solaires thermiques non vitrés (utilisés pour la production de chaleur ou comme source froide des PAC). Le système fournit le chauffage et l'eau chaude sanitaire à un complexe d'habitation (~ 10'000 m2 chauffés) construits récemment à Genève. Le suivi énergétique détaillé d'une des allées (~ 1'000 m2 chauffés, 32 habitants) a permis de caractériser le comportement du système (demande de chaleur du bâtiment, stratégie de contrôle, niveaux de température) et de déterminer les flux d'énergie ainsi que la performance énergétique du système. Les résultats montrent une demande de chauffage très faible pour la Suisse (~ 20 kWh/m2/an) et une consommation d'eau chaude sanitaire inhabituellement élevée (~ 50 kWh/m2/an). Le coefficient de performance annuelle du système (SPF), y com- pris le chauffage électrique de secours et la pompe de circulation du solaire, est de 2,9 pour 2012 (moyenne de 2,5 en hiver et de 4,4 en été). Ce résultat s'explique en partie par la forte consommation d'eau chaude sanitaire, ce qui im- plique une production de chaleur à haute température.
La deuxième partie de cette étude analyse le potentiel du système mentionné précédemment sur différents bâtiments résidentiels collectifs (nouveaux et existants). L'étude utilise la simulation numérique comme complément au suivi énergétique. Après une description de l'étude de cas et un résumé des résultats du suivi, le modèle numérique élabo- ré pour cette étude est présenté. Les résultats de simulation sont validés avec les valeurs mesurées in situ, au niveau des composants et du système, en termes de profils mensuels et d'intégrales annuelles. Sur cette base, une analyse de sensibilité approfondie concernant les principaux paramètres de dimensionnement du système est réalisée. Enfin, on étudie la sensibilité du système aux demandes de chauffage et d'eau chaude sanitaire (ECS), en particulier en ce qui concerne l'applicabilité du système analysé dans des bâtiments rénovés. Pour les conditions météorologiques de Ge- nève, un facteur de dimensionnement de 3 m2 de capteur solaire par kW de puissance PAC est un bon compromis entre la taille et la performance du système, ce qui donne un SPF compris entre 3,1 et 4,1 (dépendant de la demande de chauffage). La consommation d'électricité associée (allant de 12 kWh/m2 pour un nouveau bâtiment à faible con- sommation énergétique, jusqu'à 45 kWh/m2 pour un bâtiment non rénové) dépend fortement de la demande de cha- leur. C'est également le cas pour la surface des capteurs solaires (de 0,08 m2 par m2 de surface chauffée pour un nou- veau bâtiment à basse énergie, jusqu'à 0,20 pour un bâtiment non rénové). Enfin, un SPF de 5 pourrait être atteint, mais seulement dans les nouveaux bâtiments avec une très bonne enveloppe thermique, une faible température de distribution de chauffage et une aire de captage d'au moins 0,20 à 0,25 m2 par m2 de surface chauffée. Cependant, l'investissement connexe peut ne pas être intéressant, compte tenu de la faible économie d'électricité associée, sans oublier qu'une telle aire de collecte ne serait pas adaptée aux bâtiments de plus de 4 étages.
La dernière partie fournit une analyse comparative des potentiels et contraintes de différentes sources froides (air, géothermie, eau profonde de lac, rivière, nappe phréatique et solaire), valorisées par des PAC mises en œuvre dans les différents types de bâtiments résidentiels collectifs analyses. Après caractérisation des différentes sources froides
Résumé
consommation finale d'électricité inférieure à 15 kWh/m2 pour la majorité des cas (facteur 2 entre les extrêmes des ressources), et une puissance de pointe allant jusqu'à 150 Wh/m2/jour. Pour ces bâtiments, la décision de choisir la ressource dépendra probablement d'autres facteurs que la performance énergétique (disponibilité des ressources, restrictions légales, coût d'investissement, acceptabilité sociale, intégration des systèmes dans les bâtiments existants, ...). Pour les bâtiments à plus forte demande (90% du parc résidentiel collectif du Canton de Genève), l'électricité an- nuelle finale peut atteindre 35 kWh/m2 et la puissance de pointe peut arriver à 500 Wh/m2/jour.
En complément à l'électricité finale consommée, l'électricité annuelle injectée dans le réseau est de l'ordre de 15 à 20 kWh/m2 pour les bâtiments de faible hauteur, et la moitié pour les immeubles de grande hauteur. À titre exception- nel, dans les systèmes PAC solaires, la surface de toiture disponible pour le PV est tellement réduite que l’électricité annuelle injectée sur le réseau est significativement plus faible.
Si l'ensemble des bâtiments résidentiels collectifs du canton de Genève (19,3 millions de m2 en 2010) possédaient une très bonne enveloppe thermique et si la totalité était équipée de systèmes PAC, le total de l'électricité finale consom- mée resterait inférieur à 300 GWh, ce qui représente 10% de la demande totale d’électricité du canton. Cependant, la demande maximale au cours de l’année (en valeurs journalières) pourrait augmenter jusqu'à 3 GWh/jour, correspon- dant à 30% de la demande maximal du canton au cours de l’année (en valeurs journalières).
Bâtiments à faible hauteur (0.2 m2 /m2 ) Bâtiments à grande hauteur (0.1 m2 /m2 )
Performance énergétique des systèmes PAC et PV combinés (Efinal en valeurs annuels et puissance de pointe ainsi que le SPFfinal) pour des bâtiments à faible (en haut) et grande (en bas) hauteur.
Enfin, l’indicateur de performance énergétique du système (SPF) n'est pas suffisant car il ne reflète pas la valeur abso- lue de la demande d'électricité, qui dépend principalement de la demande de chaleur du bâtiment. Par ailleurs, tant le SPF que la demande annuelle d'électricité sont limitées aux bilans annuels. Une indication de la puissance de pointe de l'électricité consommée par les systèmes donne des indications précieuses sur l’impact potentiel de ces systèmes sur le réseau électrique.
Mots-clés
Pompe à chaleur avec source froide solaire; bâtiments résidentiels collectifs; retour d’expérience; opération en condi- tions réelles d’utilisation; analyse du système; simulation numérique; indicateurs de performance; clé de dimension- nement; pompe à chaleur à air, géothermie, lac, rivière, nappe phréatique; systèmes combinés PAC et PV.
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Air Géothermie Lac Rivière Nappe phréatique Solaire
Abstract
This work analyses, from an energy performance point of view, the potential and constraints of heat pump (HP) heat- ing systems in new and existing multifamily (MF) buildings. It starts by a monitored case study of an innovative solar and HP system implemented in a new MF building. Then, and via numerical simulation, the potential of this particular system is analysed for 6 different MF building heat demands, followed by a comparative analysis of the potentials and constraints of 6 different heat sources for those building demands. Finally, the potential impact of a generalised de- velopment of these types of systems in Geneva’s MF building stock is discussed in terms of annual electricity con- sumption and daily peak loads.
The first part of this study presents the monitoring results of an existing large scale system that combines HPs with unglazed solar collectors (used for heat production or as heat source for the HPs). The system provides space heating and domestic hot water to a new housing complex (~10’000 heated m2) in Geneva, Switzerland. Detailed monitoring of one of the blocks (~1’000 heated m2, 32 inhabitants) enables to characterize the behaviour of the system (building demand, control strategy, temperature levels) and to determine the energy flows as well as the performance of the system. The results show a very low space heating demand for Switzerland (~20 kWh/m2/yr), and an unusually high domestic hot water consumption (~50 kWh/m2/yr). The measured Seasonal Performance Factor of the system, in- cluding backup electric heating and heat source circulation pump, is 2.9 for 2012 (average of 2.5 in winter and 4.4 in summer). This result can partly be explained by the high domestic hot water consumption, which implies a heat pro- duction at high temperature.
The second part of this study analyses the potential of the previously mentioned combined solar thermal and HP sys- tem for 6 different MF building heat demands (2 new, 3 retrofitted, 1 non retrofitted, all based on monitored case studies situated in Geneva). The study uses numerical simulation as a complement to the monitored case study. After a description of the case study and a summary of the monitoring results, the numerical model developed for this study is presented. Simulation results are validated with the monitored values, at component and system level, in terms of monthly profiles and yearly integrals. On this basis, an extensive sensitivity analysis concerning the principal sizing parameters of the system is carried out. Finally, the sensitivity of the system to space heating (SH) and domestic hot water (DHW) demands is investigated, in particular concerning the applicability of the analysed system in the case of building retrofit. For Geneva’s weather conditions, a sizing factor of 3 m2 solar collector per kW of HP capacity is a good compromise between system size and system performance, resulting in a system seasonal performance factor (SPFsys) between 3.1 and 4.1, depending on the SH distribution temperature. The associated electricity consumption (ranging from 12 kWh/m2 for a new low-energy building, up to 45 kWh/m2 for a non-retrofitted building) strongly depends on the heat demand. Such is also the case for the collector area (from 0.08 m2 per m2 heated area for a new low-energy building, up to 0.20 for a non-retrofitted building). Finally, a SPFsys of 5 could potentially be achieved, but only in newly constructed buildings with a high efficient envelope, a low SH distribution temperature, and with a col- lector area of at least 0.20 - 0.25 m2 per m2 heated area. However, the related investment may not be worthwhile, given the rather small associated electricity saving, not to mention that such a collector area would not fit on buildings with more than 4 storeys.
The third and final part of this study concerns a comparative analysis of the potentials and constraints of different heat sources (air, geothermal, deep lake, river, groundwater and solar), valorised by HPs implemented in the 6 previ- ously mentioned MF buildings. After characterizing the various heat sources and building demands and presenting the numerical model, we study two distinct situations: i) combination of the HP systems and the MF building demands, disregarding possible constraints on available roof area (Solar HP) or ground area (geothermal HP); ii) combination of
Abstract
buildings, …). For buildings with a higher demand (90 % of the Canton of Geneva multifamily building stock), the final purchased electricity can rise up to 35 kWh/m2 and the daily peak load to 500 Wh/m2/day.
Aside from the final purchased electricity, the annual electricity injected into the grid is in the order of 15 – 20 kWh/m2 for low-rise buildings, and half that much for high-rise buildings. As an exception, in solar HP systems, the reduced available roof area for PV leads to significantly lower values.
If the entire MF building stock of the Canton of Geneva (19.3 million m2 in 2010) was transformed to current best case buildings and would all use such HP systems, the total final purchased electricity would remain below 300 GWh which represents 10% of the total Cantonal electricity demand. However, the associated daily peak load could rise up to 3 GWh/day, corresponding to 30% of the cantonal daily peak load.
Low-rise building (0.2 m2 /m2 ) High-rise building (0.1 m2 /m2 )
System performance (Efinal in annual energy and daily peak load, and SPFfinal) of the combined HP & PV systems, for a low-rise (top) and high-rise (bottom) buildings.
Lastly, SPF alone is not a sufficient indicator of the HP system performance, since it doesn’t reflect the absolute value of the electricity demand, which primarily depends on the building heat demand. Furthermore, both SPF and annual electricity demand are limited to annual balance considerations. As a complement, an indication of the peak electricity load of the system would give valuable information on the potential stress caused to the grid.
Keywords
solar heat pump; multifamily buildings; in situ monitoring; real operation performance; system analysis; numerical simulation; performance indicators; sizing factor; air, geothermal, lake, river, groundwater heat pump systems; com- bined heat pump and photovoltaic systems (HP and PV).
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0 5 10 15 20 25
0 20 40 60 80 100 120 140
SPFfinal(-)
Qdem[kWh/m2/year]
Air Geothermal Lake River Groundwater Solar
Table of Contents
Remerciements ... i
Acknowledgements ... iii
Résumé ... v
Abstract ... vii
Table of Contents ... ix
Introduction ... 1
Chapter 1 In-situ monitoring of a solar assisted heat pump system in a multifamily building ... 5
Chapter 2 Abstract ... 5
Nomenclature ... 6
2.1 Introduction ... 8
2.2 Description ... 10
2.2.1 Research project ... 10
2.2.2 Building complex and monitored block ... 10
2.2.3 Energy concept ... 10
2.3 Monitoring methodology ... 12
2.4 Climatic conditions ... 12
2.5 Characterization of the systems elements ... 13
2.5.1 Building demand ... 13
2.5.2 Solar collector array ... 14
2.5.3 Heat pump ... 16
2.5.4 Heat storage ... 17
2.6 System behaviour ... 18
2.6.1 Temperature levels during HP production ... 18
2.6.2 Typical days ... 18
2.6.3 Heat storage dynamics... 20
2.7 System performance ... 21
2.8 Comparison with other blocks ... 23
2.9 Conclusions and perspectives ... 24
Table of Contents
3.2.1 System description ... 30
3.2.2 Monitoring results ... 31
3.3 Numerical Model ... 32
3.3.1 System layout and operating modes ... 32
3.3.2 Algorithm and System Components ... 36
3.3.3 Heat demand ... 38
3.3.4 System operation ... 38
3.3.5 System performance ... 39
3.4 Validation ... 40
3.5 Normalization ... 42
3.5.1 Normalization to standard weather ... 42
3.5.2 Normalization to standard heat storage/distribution ... 44
3.6 Sensitivity analysis ... 45
3.6.1 Sensitivity to system sizing ... 45
3.6.2 Sensitivity to evaporator temperature limit ... 47
3.6.3 Sensitivity to heat demand ... 48
3.7 Conclusions ... 52
Potential and constraints of available heat sources in relation to various building Chapter 4 demands. ... 53
Abstract ... 53
Nomenclature ... 54
4.1 Introduction ... 56
4.2 Heat sources / Local Resources ... 58
4.2.1 Resource typologies ... 58
4.2.2 Reference year ... 59
4.3 Heat demands / Buildings ... 62
4.3.1 Building sample ... 62
4.3.2 Benchmarking with the multifamily building stock of Geneva ... 62
4.3.3 Rescaling of annual and hourly heat demand ... 64
4.4 Heat production system ... 66
4.4.1 System layout ... 66
4.4.2 System sizing ... 68
4.5 Numerical model ... 70
4.5.1 Solar, Air and Hydrothermal systems ... 70
4.5.2 Geothermal borehole system ... 70
Table of Contents
4.6 Simulation results ... 71
4.6.1 Intrinsic potential of heat pump heat sources, disregarding available area constraints ... 71
4.6.2 Effect of limited roof and ground area ... 74
4.6.3 Complementary PV production ... 78
4.6.4 Potential effect on regional load curve ... 84
4.6.5 Discussion ... 86
4.7 Conclusions ... 90
Conclusions ... 93
Chapter 5 5.1 Main results ... 93
5.2 Future development... 97
List of Figures... 99
List of Tables ... 103
List of Annexes ... 104
References ... 105
Annexes ... 111
Chapter 1
Introduction
According to the IPCC, 2014, “Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems”. It also states that “Substantial [greenhouse gas] emissions reductions over the next few decades can reduce climate risks in the 21st century and beyond, increase prospects for effective adaptation, reduce the costs and challenges of mitigation in the longer term and contribute to climate-resilient pathways for sustainable development”.
In this context, countries all over the world are making efforts to mitigate climate change (e.g. United-Nations, 2015, Paris Agreement). To tackle this subject, Switzerland (one of the parties that signed the Paris agreement) has come up with an energy strategy that is based in the 2000 W society concept (2000watt, 2017) and aims at 1 ton of CO2 per capita by the end of the 21st century (FOEN, 2012).
In Geneva, the present CO2 emissions related to the energy sector represents 4.2 tonnes of emitted CO2 per capita, of which 2.2 emitted by the heating sector, 1.1 by the transport sector (not including the airport) and 0.8 by the electrici- ty sector (Quiquerez et al., 2016). Consequently the main CO2 emissions reduction potential lies in the heating sector, which represents about half of the final energy consumption in the Canton. In 2014, the energy consumed by the heating sector in Geneva amounts to 5’444 GWh or 40.6 GJ/capita, mainly based on fossil fuels (Figure 1:1).
Introduction
Figure 1:2 Geneva building stock, in 2010. Left: Number of buildings; Right: Heated surface (SRE). (source: Khoury, 2014)
In parallel to building retrofit, replacing fossil fuels by renewable energies will also reduce CO2 emissions. In Geneva, the potential of renewable resources for the heating sector has been estimated to about 5’500 GWh/year (Faessler, 2011), not including the heat potential of the outdoor air, which is difficult to quantify. Although the potential of re- newable energy resources covers the heating demand of the Canton, their integration in the energy system can be limited by: (i) their spatial availability, temporal dynamics and quality (e.g. temperature); (ii) their costs; (iii) their so- cial acceptance.
One of the possible options to valorise locally available renewable heat sources, independently of their quality (e.g.
temperature), is by using heat pumps (HPs). HPs can be centralized (connected to district heating, i.e. at a regional scale) or decentralised (at building level, i.e. at a local scale/ individual). Nowadays, neither of these solutions occupy an important place in Geneva’s heating sector (1% of supplied heat demand, see Figure 1:1). Nevertheless, prospec- tive scenarios show that the development of HPs (to supply 15 to 25% of the heat demand of the Canton) in combina- tion with other heat supply solutions and reduction of the heat demand, would reduce the Canton’s CO2 emissions to the goals aimed for the year 2035 (Quiquerez et al., 2016).
HPs are a known technology, commercialised since the second half of the 20th century (IEA-ETSAP et al., 2013). Its performance depends on the quality of the machine itself, the heat source temperature and the heat demand tem- perature. Moreover, a successful replacement of fossil fuels by HP systems will also depend on:
The availability of heat sources that are at good technical, economic and environmental conditions (this im- plies the development of standard and easily reproducible system solutions for the different types of heat sources)
The origin of the electricity (from fossil fuels, combined heat and power plants or renewables) and the dura- bility of its production;
Nowadays, the most common, standard and easily reproducible system solutions in the market are HP systems that use air or ground as their heat source (EHPA, 2015, Observ'ER, 2015). Erb et al., 2004, monitored 199 of such systems (small systems, for single-family buildings only) in Switzerland, both in new and renovated buildings. They observed an annual system performance factor of 2.7 for the 105 air source HP, and of 3.5 for the 94 ground source HP. In another study, Miara et al., 2010, monitored 74 HP systems. The observed annual system performance factors were of 2.9 for the 18 air source HP systems and of 3.9 for the 56 ground source HP systems.
Introduction
Geothermal HP systems are, therefore, the systems with better performance and they have the added value of being able to cover cooling demands in summer (geocooling). However, the use of this type of system will depend on availa- ble ground area to place the geothermal boreholes; geological constrains (protected geological layers); lack of re- charge heat in summer (when an important borehole field is implemented and there is no important cooling demand);
and low performance of the system for domestic hot water production.
In this regard, the use of solar collectors combined with HP systems seems a good combination to increase the system performance (Hadorn, 2012). An idea that arose is that the use of cheap unglazed solar collectors as a heat source of a HP would answer some of the problems mentioned above:
Easily reproducible and applicable to most buildings, with a well-known and mature technology;
Possible high performance due to the good quality of the heat source (absorption of solar irradiance at lower temperatures);
Domestic hot production solely by solar collectors in summer.
This type of systems is regularly proposed by solar and/or HP promoters. Nevertheless, its implementation in a multi- family building, with a traditional construction, seems difficult and quite risky given the fact that there are not many feedbacks of similar systems in similar conditions.
This study emerged from the will to closely monitor an innovative solar assisted HP system, implemented in a multi- family building in Geneva. Furthermore, to analyse its sensitivity to different heat demands, assessing the possibility of its standardisation and reproducibility in different types of multifamily buildings. Lastly, to compare the combined effect of different heat sources and different heat demands in the HP system performance, with and without added PV production, while hinting to constraints that might arise from the electricity consumption and load of the system.
This work is structured in the following order:
The first part (Chapter 2) presents the monitoring results of the existing large scale system that combines HPs with unglazed solar collectors (used for heat production or as heat source for the HPs). The system provides space heating and domestic hot water to a new housing complex (~10’000 heated m2) in Geneva, Switzerland. Detailed monitoring of one of the blocks (~1’000 heated m2, 32 inhabitants) enables to characterize the behaviour of the system (building demand, control strategy, temperature levels) and to determine the energy flows as well as the performance of the system.
The second part (Chapter 3) analyses the potential of the previously mentioned combined solar thermal and HP sys- tem on new and existing multifamily buildings. The study uses numerical simulation as a complement to the moni- tored case study. After a description of the case study and a summary of the monitoring results, the numerical model developed for this study is presented. Simulation results are validated with the monitored values, at component and system level, in terms of monthly profiles and yearly integrals. On this basis, an extensive sensitivity analysis concern- ing the principal sizing parameters of the system is carried out. Finally, the sensitivity of the system to space heating (SH) and domestic hot water (DHW) demands is investigated, in particular concerning the applicability of the analysed system in the case of building retrofit.
Chapter 2
In-situ monitoring of a solar assisted heat pump system in a multifamily building
The content of this chapter is published in:
Fraga C., Mermoud F., Hollmuller P., Pampaloni E., Lachal B., 2015, Large solar driven heat pump system for a multi- family building: Long term in-situ monitoring, Solar Energy, 114, 427-439.
Abstract
This chapter presents the monitoring results of an existing large scale system that combines heat pumps with un- glazed solar collectors (used for heat production or as heat source for the heat pumps). The system provides space heating and domestic hot water to a new housing complex (~10’000 heated m2) in Geneva, Switzerland. Detailed monitoring of one of the blocks (~1’000 heated m2, 32 inhabitants) enables to characterize the behaviour of the sys- tem (building demand, control strategy, temperature levels) and to determine the energy flows as well as the perfor- mance of the system. The results show a very low space heating demand for Switzerland (~20 kWh/m2/yr), and an unusually high domestic hot water consumption (~50 kWh/m2/yr). The measured Seasonal Performance Factor of the system, including backup electric heating and heat source circulation pump, is 2.9 for 2012 (average of 2.5 in winter and 4.4 in summer). This result can partly be explained by the high domestic hot water consumption, which implies a heat production at high temperature. This project is part of IEA SHC Task 44 “Solar and Heat Pump Systems”.
Keywords
Solar driven heat pump; system analysis; in-situ monitoring; real operation performance
In-situ monitoring of a solar assisted heat pump system in a multifamily building
Nomenclature
Abbreviations
DHW domestic hot water
HP heat pump
SH space heating
Latin letters
COP coefficient of performance of the heat pump [-]
Csol heat capacity of the solar collectors [Wh/m2/K]
Cst effective heat capacity of the storage [kWh/K]
dt time step [h]
EHP electricity consumption of the heat pump [kWh]
EBackup electricity consumption of the backup [kWh]
EHsc aux electricity consumption of the heat source circulation pumps [kWh]
EHsk aux electricity consumption of the heat sink circulation pumps [kWh]
EDist aux electricity consumption of the building distribution circulation pumps [kWh]
Gh global solar irradiation in the horizontal plane [W/m2]
Gi global solar irradiation in the collector plane, taking into account shed shadow effects [W/m2] h0 convective heat transfer coefficient [W/m2/K]
hv wind-dependent convective heat transfer coefficient [W/m2/K/(m/s)]
Hst storage effective heat loss coefficient [kW/K]
Qbuilding heat demand of building, SH and DHW [kWh]
QHP heat production of heat pump [kWh]
QIR infrared irradiation balance [W/m2] Qsol solar heat production [W/m2] ΔQst net daily heat storage [kWh]
SPF seasonal performance factor
SPF1 seasonal performance factor of the heat pump [-]
SPF2 seasonal performance factor of the heat pump, including heat source circulation pumps [-]
SPF3 seasonal performance factor of the system, including backup and heat source circulation pumps [-]
SPF4 seasonal performance factor of the system, including backup and heat source + sink + distribution circu- lation pumps [-]
T0 temperature of the technical room [°C]
Text outdoor temperature [°C]
THP evap temperature at evaporator input [°C]
THP cond temperature at condenser output [°C]
Tsol temperature of the solar collector array [°C]
Tst temperature of the heat storage [°C]
ΔTHP heat pump temperature difference (condenser output – evaporator input) [K]
ΔTsol temperature increase of the solar collector array during time step dt [K]
ΔTst temperature increase of the storage during time step dt [K]
v wind speed [m/s]
In-situ monitoring of a solar assisted heat pump system in a multifamily building
Greek symbols
η0 optical efficiency of the solar collectors [-]
ηHP thermodynamic efficiency of the heat pump [-]
In-situ monitoring of a solar assisted heat pump system in a multifamily building
2.1 Introduction
Over the past decades, the global warming and the depletion of fossil resources induced a growing interest in heat pumps systems, especially using air or boreholes as a heat source. Erb et al., 2004 monitored 236 Swiss installations in both new and renovated buildings, in order to estimate their performance. The average seasonal performance factor of the system for the 105 air source heat pumps was 2.7, whereas it was 3.5 for the 94 ground source heat pumps.
A recurring question is to look for heat sources that lead to better performances than air or boreholes. The use of solar collectors seems interesting, as the collectors enable to benefit even from a low solar irradiation.
Different authors worked on this topic, both numerically and experimentally. A wide range of experimental setups concern small size prototype systems (typically less than 10 m2 solar collectors, a few kW heating capacity) that are installed in lab facilities. They mainly concern serial linking of the solar collectors to the evaporator of the heat pump, with an intermediate thermal storage (usually water, sometimes phase change material or ground storage), frequently without possibility of direct solar heat production (bypass of the heat pump) at high radiation level.
In a few cases, these systems are actually connected to the lab, with a potential contribution to space heating (Kaygusuz et al., 1999, Kuang et al., 2003), which is not reported or analysed. In some other cases, the systems are connected to building test cells/rooms, however without clear definition of the demand or operation procedure (Caglar et al., 2012, Dikici et al., 2008). In some setups the systems are connected to a climatic chamber and tested in controlled steady state conditions (Fernandez-Seara et al., 2012, Liang et al., 2011). A specific configuration concerns separate testing of the solar collectors, which are then emulated on the heat pump testing facility, along with a simu- lated domestic hot water demand (Eicher et al., 2012). In all other cases the systems are used in specific short-term experiments that are not connected to an actual thermal demand. Although they are usually intended to facilitate the characterisation of the system for a specific utilisation (DHW: Anderson et al., 2007 and Li et al., 2010; SH: Bakirci et al., 2011 and Xi et al., 2011); drying of agricultural products: Hawlader et al., 2008), a few of them do not clearly men- tion the expected utilisation (Georgiev, 2008, Hawlader et al., 2001, Huang et al., 2005, Ito et al., 1999). For all of these systems, the reported experimental tests only cover a short period from a few hours to a few days. They are mainly designed for rapid validation or calibration of models, which are used for sensitivity analysis to diverse sizing parameters. Since they are not operated over long term periods nor connected to a real scale building, they do not provide any information on the overall energy balance in real scale operation. Besides these bench tests, only a few authors report experimental results concerning in-situ measurements (Energie Solaire SA, 2012, Hahne, 2000, Loose et al., 2011, Miara et al., 2010, Trillat-Berdal et al., 2007, Trillat-Berdal et al., 2006, Wang et al., 2010), of which some did not yet result in journal articles (Energie Solaire SA, 2012, Loose et al., 2011, Miara et al., 2010). Most of these studies concern small scale systems for individual housing.
Generally, the performance of HP systems is analysed in terms of the seasonal performance factor. In this chapter the definitions used for SPFs will be the same as the ones defined by the SEPEMO-build project (Zottl et al., 2012) where COP is used for instant performances (ratio between heat power production and electric power consumption) at de- fined temperature conditions and SPF for performances over a long period of time (month/year). Depending on the system boundary, following SPF values are defined.
When considering the heat pump only:
𝑆𝑃𝐹1 =𝑄𝐸𝐻𝑃
𝐻𝑃 (1)
When considering the heat pump, including related ancillary electricity:
𝑆𝑃𝐹2 =𝐸 𝑄𝐻𝑃
𝐻𝑃+𝐸𝐻𝑠𝑐 𝑎𝑢𝑥 (2)
In-situ monitoring of a solar assisted heat pump system in a multifamily building
When considering the entire system:
𝑆𝑃𝐹3 =𝐸 𝑄𝑏𝑢𝑖𝑙𝑑𝑖𝑛𝑔
𝐻𝑃+𝐸𝐻𝑠𝑐 𝑎𝑢𝑥+𝐸𝐵𝑎𝑐𝑘𝑢𝑝 (3)
When considering the entire system, including ancillary electricity:
𝑆𝑃𝐹4 =𝐸 𝑄𝑏𝑢𝑖𝑙𝑑𝑖𝑛𝑔
𝐻𝑃+𝐸𝐻𝑠𝑐 𝑎𝑢𝑥+𝐸𝐵𝑎𝑐𝑘𝑢𝑝+𝐸𝐻𝑠𝑘 𝑎𝑢𝑥+𝐸𝐷𝑖𝑠𝑡 𝑎𝑢𝑥 (4)
It should be noticed that the system performance indicators SPF3 and SPF4, which are based on the net heat demand of the building, include both HP and direct solar heat, as well as storage losses. For this reason, SPF3 and SPF4 can have higher values than SPF1 and SPF2, as can be seen in the literature review below, as well as in the results of our study.
The SPF values in the literature review below refer to the boundaries defined above. Whenever there was a lack of information or the boundary conditions did not exactly correspond to one of these SPFs, the closest definition was used.
A specific IEA Task, namely SHC Task 44 (Hadorn, 2012), is in charge of studying the coupling between heat pumps and solar collectors. Different authors (Energie Solaire SA, 2012, Loose et al., 2011, Miara et al., 2010, Trillat-Berdal et al., 2007, Trillat-Berdal et al., 2006, Wang et al., 2010) monitored such systems in individual housing. The system SPF varies strongly from one case to another. Wang et al., 2010 studied a solar-assisted HP with geothermal boreholes for seasonal storage resulting in a SPF4 of 6.1, but only for SH application. Trillat-Berdal et al., 2006, monitored a similar system described in Trillat-Berdal et al., 2007. Even though they did not mention any annual SPF, the monthly values of SPF1 were between 3.5 and 4 and SPF4 between 3.5 and 4. The average solar fraction of the DHW storage was 68%.
For an installation including a water storage and borehole heat exchangers, Loose et al., 2011, reached a SPF1 of 3.7 and a SPF4 between 5 and 5.3 (excluding EDist aux), with an annual renewable heat fraction (solar + borehole) of 81%.
Miara et al., 2010, monitored 2 solar thermal/geothermal heat pump systems with SPF4 of 4.9 and 6, as well as 4 solar thermal/aerothermal heat pump systems with SPF4 between 2.8 and 3.4 (in all cases excluding EDist aux) . Energie Solaire SA, 2012, studied a system with an ice storage (allowing to cut the cold peaks) with a SPF4 of 4. Finally, Bertram et al., 2012 analysed a coupled PVT – borehole – heat pump system, with a SPF4 of 4.2 (which, according to simulation, would drop to 3.8 without the solar recharge).
The potential of developing solar heat pumps systems at larger scale is important, but has not been widely investigat- ed. The only study found in literature is the one of Hahne, 2000, dealing with a solar-assisted heat pump in operation since 1985 for the heating of their Institute building. They measured a SPF4 between 2.9 and 3.2 for combined heating and cooling.
In-situ monitoring of a solar assisted heat pump system in a multifamily building
2.2 Description
2.2.1 Research project
The results presented here are part of a research project (Mermoud et al., 2014) which aims to assess the concept of coupling solar thermal collectors and heat pumps for domestic hot water (DHW) and space heating (SH) production in collective housing. The two main parts of the project are: (i) to assess the actual operation and efficiency of an existing system implemented in a housing complex; (ii) to extrapolate the experimental results in different conditions (such as different sizing, different building – in particular retrofit – or different control strategy) by numerical simulation. The goals of the project are:
Evaluate the relevance of this concept in a technical, energy and economical point of view, in order to identi- fy its potential of standardisation;
Identify the opportunities and obstacles that may appear when applying these systems in existing buildings with low quality envelope or in retrofit;
Compare these systems with other market possibilities, such as heat pumps coupled with geothermal bore- holes.
This chapter presents the first part of the work, i.e. system analysis and energy balance of an existing plant, based on detailed monitoring over an entire year.
2.2.2 Building complex and monitored block
A system coupling solar collectors and heat pumps was implemented in a new housing complex located in Geneva (Switzerland) which was commissioned in autumn 2010 (cf. Figure 2:1). The complex is composed of 4 buildings, each divided into 2 or 3 blocks of 8 flats (total of 10 blocks). The buildings present a high thermal performance envelope (Minergie standard1) and a total heated surface of 9’552 m2. The full monitored block (in red, Figure 2:1) has 927 heated m2 and a total of 32 inhabitants.
Figure 2:1 Left: studied housing complex and monitored block (source: Google maps). Right: solar collector array.
2.2.3 Energy concept
The energy concept was designed and is being managed by an engineering bureau, the University of Geneva was not involved in its conception nor in its operation. It consists of a heat pump directly coupled to unglazed solar collectors as its heat source. Each of the 10 blocks is equipped with its own system, totally independent from the other ones.
The components of each system (Figure 2:2) are: a 30 kWth heat pump; 116 m2 of unglazed solar collectors; 2 x 3’000 L
1 http://www.minergie.ch/ see “The MINERGIE-Standard for Buildings”
In-situ monitoring of a solar assisted heat pump system in a multifamily building
of water for centralized heat storage with an electric rod in the storage tank in case of heat pump failure. A specificity of the system consists in a single distribution circuit to the flats, so that SH (floor heating) and DHW cannot be sup- plied simultaneously and therefore are supplied alternatively. Each flat is therefore equipped with a 300 L DHW tank.
DHW distribution has priority over SH distribution, which means that when one of the 300 L tanks is at a temperature below 40°C (sensor placed at 2/3 of the tank height, from the bottom), the system switches automatically to DHW mode and rises the temperature of all the 300 L tanks up to 60°C. Note that this configuration does not allow for solar preheating of the DHW tanks, at least in this particular case. As a matter of fact: i) since the heat exchangers cover the entire height of the DHW tanks, “preheating” at temperatures below 55-60° would cool down the hot upper third volume of the tanks; ii) even if such was not the case, preheating of the lower part of the tanks would imply an indi- vidual recharge regulation and flow control, so as to avoid destratification of the tanks that are already full.
The solar collectors can be used for direct solar heat production, via a heat exchanger, but are also the heat source of the heat pump (they are directly connected to the evaporator, without storage or geothermal boreholes). Hence, when there is no solar radiation, the solar collectors work as a heat absorber on ambient air. In the following, the energy flow provided by the collectors will therefore be called “Solar + Ambient”. Whether by direct solar heat pro- duction or via the HP, the produced heat is used for SH (floor heating) or DHW (heat distribution to charge the indi- vidual 300 L tanks), and the surplus is stored in the centralized heat storage for future use. Note that, due to the sys- tem design, throughout this paper the term “DHW demand” refers to the energy delivered to the individual tanks and not the DHW directly consumed by the users in the flats.
Figure 2:2 Hydraulic diagram of the system.
The system has 4 main operating modes, with the following priorities:
1. Direct solar heat production for SH or DHW (bypassing the heat pump), the surplus being used to charge the heat storage;
2. Storage discharge, which is activated when the solar production does not reach the required distribution temperature;
