Yes / This paper describes a new heat transfer parameterisation between wastewater and insewer air based on understanding the physical phenomena observed in free surface wastewater and in-sewer air. Long-term wastewater and in-sewer air temperature data were collected and studied to indicate the importance of considering the heat exchange with in-sewer air and the relevant seasonal changes. The new parameterisation was based on the physical flow condition variations. Accurate modelling of wastewater temperature in linked combined sewers is needed to assess the feasibility of in-sewer heat recovery. Historically, the heat transfer coefficient between wastewater and in-sewer air has been estimated using simple empirical relationships. The newly developed parameterisation was implemented and validated using independent long-term flow and temperature datasets. Predictive accuracy of wastewater temperatures was investigated using a Taylor diagram, where absolute errors and correlations between modelled and observed values were plotted for different site sizes and seasons. The newly developed coefficient improved wastewater temperature modelling accuracy, compared with the older empirical approaches, which resulted in predicting more potential for heat recovery from large sewer networks. For individual locations, the RMSE between observed and predicted temperatures ranged between 0.15 and 0.5 °C with an overall average of 0.27 °C. Previous studies showed higher RMSE ranges, e.g., between 0.12 and 7.8 °C, with overall averages of 0.35, 0.42 and 2 °C. The new coefficient has also provided stable values at various seasons and minimised the number of required model inputs.

As buildings have become more energy efficient, the energy demand for preparation of domestic hot water stands out as an increasing part of the operational cost and carbon footprint of a building. Most of the heat in the water is used for a short time and then discharged to the main sewer line. Clarion Hotel Stockholm is an example of such a building, with many showers, bathtubs and a spa. The hotel business is growing around the world and its customers demand comfortable stays. A parallel trend is a more environmentally aware tourism and business travel. Hotels show a great potential for energy savings, while still offering comfortable accommodation. In this master's thesis a case study evaluates the possibilities for heat recovery from the wastewater of Clarion Hotel Stockholm. Three types of heat exchangers were modelled in the system dynamic modelling environment STELLA: a horizontal, a vertical and a shower heat exchanger. Recovered heat was used for pre-heating of the incoming water for domestic hot water preparation. The flows of heat through the hotel's tap water and wastewater systems were schematically modelled using system dynamic modelling, which provides a foundation for the development of mathematical models and further research into the area. The first results point to possible reductions of the heating demand for domestic hot water preparation at Clarion Hotel Stockholm.

The energy used by building sector accounts for approximately 40% of the total energy usage. In residential buildings, 30-60% of this energy is used for space heating which is mainly wasted by transmission heat losses. A share of 20-30% is lost by the discarded residential wastewater and the rest is devoted to ventilation heat loss.   The main objective of this work was to evaluate the thermal potential of residential wastewater for improving the performance of mechanical ventilation with heat recovery (MVHR) systems during the coldest periods of year. The recovered heat from wastewater was used to preheat the incoming cold outdoor air to the MVHR in order to avoid frost formation on the heat exchanger surface.   Dynamic simulations using TRNSYS were used to evaluate the performance of the suggested air preheating systems as well as the impact of air preheating on the entire system. Temperature control systems were suggested based on the identified frost thresholds in order to optimally use the limited thermal capacity of wastewater and maintain high temperature efficiency of MVHR. Two configurations of air preheating systems with temperature stratified and unstratified tanks were designed and compared. A life cycle cost analysis further investigated the cost effectiveness of the studied systems.   The results obtained by this research work indicated that residential wastewater had the sufficient thermal potential to reduce the defrosting need of MVHR systems (equipped with a plate heat exchanger) in central Swedish cities to 25%. For colder regions in northern Sweden, the defrosting time was decreased by 50%. The temperature control systems could assure MVHR temperature efficiencies of more than 80% for most of the heating season while frosting period was minimized. LCC analysis revealed that wastewater air preheating systems equipped with temperature stratified and unstratified storage tanks could pay off their costs in 17 and 8 years, respectively. / <p>QC 20190830</p>

This thesis presents a system and actor level analysis of wastewater heat recovery in buildings, using two case studies in Stockholm, Sweden. The choice of these case studies was to cover the installation of WWHR in both commercial and residential buildings. The first case study is from the residential district of Töfsingdalen, and the second case study is the commercial building Pennfäktaren 11. The aim of the study is to understand why actors, as identified through these case studies, have adopted wastewater heat recovery. Taking into consideration, motives, strategies, conflicts, technologies, and future perspectives. The case study analysis is further supported by a literature review, analyzing the installed systems from a technical point of view. Using semi-structured interviews and literature review as the source of data collection. Theories utilized were the multilevel perspective and the critical interface. Used for explaining how technological transitions occurs and how they are best adopted by existing actors. Conclusions drawn from the study is that Swedish buildings over the last decades have improved in energy efficiency predominantly within heating, ventilation, and lightning, while energy consumption for warm water has been relatively untouched. The identified actors frame wastewater heat recovery in a widely positive environment, having input on what to improve for its diffusion in the building sector. It is a technology they regard as new and experimental but see potential with further improvements, mostly technical and economical. The actors having adopted wastewater heat recovery have incorporated ambitious climate policies in their business models while simultaneously wanting to reduce energy costs. The motive used in the first case study, Töfsingdalen, was to design an energy-efficient building, while the second case study, Pennfäktaren 11, the motives were different and centered around enthusiasm in the technology and economic benefits (energy savings). The shared motive is the liking towards the technology being environmentally friendly. Wastewater energy recovered in the first and second case study is equivalent to the total energy consumption of 1.3 and 8.5 Swedish apartments per year. For these reasons, energy recovery from wastewater can contribute towards urban sustainable development, but it can also have disruptive potential that is necessary to investigate and mitigate. Findings suggest a critical interface between the existing regime and the early innovation adopters which could lead to both conflict and cooperation. Future research to further confirm these findings are necessary analyses aimed at investigating where in the sewer system the greatest benefit for wastewater heat recovery is located. Finally, continuous innovative development of the technology is advantageous. / Detta examensarbete presenterar en system- och aktörsanalys på värmeåtervinning av varmvatten i byggnader via två fallstudier i Stockholm, Sverige. Valet av fallstudier gjordes för att nå installtioner i både en kommersiell och en bostadsbyggnad. Den första fallstudien är från bostadsområdet Töfsingdalen och den andra är den kommersiella byggnaden Pennfäktaren 11. Målet är att förstå varför aktörer som identifierats ur fallstudier har installerat värmeåtervinning av spillvatten. Där aktörers motiv, strategier, konflikter, teknologier, och framtida perspektiv beaktas. Fallstudierna är fortsatt förstärkta av en litteraturstudie, genom att analysera de installerade systemen ur ett tekniskt perspektiv. Information är inhämtad med semi-strukturerade intervjuer och litteratur. Teorierna som studien grundar sig i har varit multi-nivå perspektivet (MLP), det kritiska gränsskiktet. Dessa teorier används för att förklara hur teknologiska förändringar sker i ett samhälle och hur dessa ska ske optimalt. Slutsatser som har dragits från studien är att de svenska byggnaderna sedan ett par decennier tillbaka har förbättrat byggnaders energieffektivitet inom uppvärmning, ventilation, och ljuskällor, medan värmeåtervinning av spillvatten har varit relativt orört som område. De identifierade aktörerna ser på värmeåtervinning av spillvatten ur en mestadels positiv synvinkel, de har indata på hur tekniken kan utvecklas för framgång inom byggnadssektorn. De ser på tekniken som ny och experimentell, men ser potential vid framtida förbättringar, främst tekniska och ekonomiska. De aktörer som har adapterat tekniken har implementerat miljömål i deras företagsmodell, samtidigt som de vill minska energikostanderna. Motiven som användes i den första fallstudien, Töfsingdalen, var att designa en miljövänlig byggnad, och motiven i den andra var olika där entusiasm för tekniken samt ekonomiska besparingar var framträdande. Gemensamt är att de båda aktörerna tycker att det är miljövänlig lösning. Den återvunna energin i den första och andra fallstudien motsvarar den totala energin som 1.3 och 8.5 svenska lägenheter förbrukar årligen. Utifrån dessa resultat, dras ytterligare en slutsats att värmeåtervinning av spillvatten kan hjälpa vid hållbar urban utveckling men att den också har disruptiv potential som är viktigt att undersöka och mitigera. Resultaten visar på ett kritiskt gränsskick mellan den nuvarande regimen och de aktörer som har implementerat tekniken vilket kan leda både till konflikter och samarbete. Framtida studier behövs för att ytterligare konfirmera dessa fynd, även kvantitativa systemanalyser där det reds ut vart i avloppssystemet som den största nyttan finns för att återvinna spillvärme samt fortsatt utveckling av tekniken är fördelaktigt.

Buildings account for up to 32% of the total energy use in different countries. Directives from the European Union have pointed out the importance of increasing energy efficiency in buildings. New regulation in countries like Sweden establishes that new buildings should fulfill regulations of Nearly Zero Energy Buildings (NZEB), opening an opportunity for new technologies to achieve these goals. Almost 80-90% of the energy in domestic hot water use is wasted from different applications with almost no use and with a lot of potential energy to be recovered. The present work studied the characteristics of greywater heat exchanger as a solution to recuperate heat from greywater to increase efficiency in buildings. This study explored the fluid mechanics involved in the vertical greywater heat exchangers, analyzing the falling film effect present in drain pipes and the effects of the secondary flow generated in the external helical coil. A heat transfer model from a theoretical approach was proposed and validated. In addition, this study explored the different variables influencing the economic feasibility of the technology and an economic analysis was performed. A theoretical comparison between a greywater heat exchanger application and a reference case without it was evaluated highlighting the importance of all the variables involved in the potential of implementation of the technology. The technology shows big potential in households with high water consumptions, especially with electric boilers.