System and Actor Level Analysis of Potentially Disruptive
Wastewater Heat Recovery Technologies in Buildings
A Stockholm case study
WALTER DELTIN
Master of Science Thesis Department of Energy Technology
KTH 2020
System and Actor Level Analysis of Potentially Disruptive Wastewater Heat Recovery Technologies
in Buildings A Stockholm Case Study
TRITA: TRITA-ITM-EX 2020:487 Walter Deltin
Approved
2020-09-03
Examiner
Joachim Claesson
Supervisor
Timos Karpouzoglou Jörgen Wallin
Contact person
ings, 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 per- spectives. 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 multi- level perspective and the critical interface. Used for explaining how technological transi- tions 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 light- ning, while energy consumption for warm water has been relatively untouched. The identified actors frame wastewater heat recovery in a widely positive environment, hav- ing input on what to improve for its diffusion in the building sector. It is a technol- ogy 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 simultane- ously wanting to reduce energy costs. The motive used in the first case study, Töfsing- dalen, was to design an energy-efficient building, while the second case study, Pennfäk- taren 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 tech- nology being environmentally friendly. Wastewater energy recovered in the first and sec- ond 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 in- vestigate 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 inves- tigating where in the sewer system the greatest benefit for wastewater heat recovery is located. Finally, continuous innovative development of the technology is advantageous.
Keywords: wastewater heat recovery, green buildings, sustainable urban development, interface misalignment, critical interface, system analysis, niche, regime.
mvatten 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 fall- studien är från bostadsområdet Töfsingdalen och den andra är den kommersiella byg- gnaden 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 lit- teraturstudie, genom att analysera de installerade systemen ur ett tekniskt perspektiv. In- formation 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, venti- lation, och ljuskällor, medan värmeåtervinning av spillvatten har varit relativt orört som område. De identifierade aktörerna ser på värmeåtervinning av spillvatten ur en mes- tadels 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 min- ska 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 för- brukar årligen. Utifrån dessa resultat, dras ytterligare en slutsats att värmeåtervinning av spillvatten kan hjälpa vid hållbar urban utveckling men att den också har disruptiv poten- tial 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 avloppssys- temet som den största nyttan finns för att återvinna spillvärme samt fortsatt utveckling av tekniken är fördelaktigt.
Nyckelord: värmeåtervinning av spillvatten, byggnader, energieffektivisering, håll- bar stadsutveckling, systemanalys.
fore acquiring my Master of Science in Sustainable Energy Engineering. Throughout the process of writing, I have received great support and feedback. First and foremost, I would like to thank my supervisors Timos Karpouzolgou and Jörgen Wallin, for con- tinuous guidance, support, and interest. I also want to acknowledge the SEQWENS:
Ensuring sustainability and equality of water and energy systems during actor-driven disruptive innovation, financed by the Swedish research council FORMAS, Grant no.
2018-00239 research team, reference group, and students for providing with group feed- back and discussions on how to improve the overall research. Moreover, thank you to all of the respondents for your time and allowing to be interviewed and providing valuable data. A thank you to my friends Sebastian and Albin for proofreading.
Finally, to all of my friends, family, and classmates, thanks for all the good times and the support during my studies at KTH.
Much Appreciated, Walter Deltin
1 Introduction 1
1.1 Background . . . 1
1.2 Previous and Current Studies . . . 2
1.3 Aim and Limitations . . . 3
1.4 Research Questions . . . 4
2 Literature Review 6 2.1 Energy Consumption in Swedish Buildings . . . 6
2.2 Wastewater and Heat Recovery . . . 7
2.3 Locations for Wastewater Heat Recovery . . . 7
2.4 On-Property Wastewater Heat Recovery . . . 8
2.5 Regulations Affecting Wastewater Heat Recovery . . . 13
2.6 Theoretical Energy Available in Stockholm’s Wastewater . . . 14
3 Theoretical Background 16 3.1 Socio-Technical Studies . . . 16
3.2 Critical Interface . . . 18
4 Methodology 20 4.1 Data Collection . . . 20
4.2 Classification of Actors . . . 20
4.3 Classification of Socio-Technical System Challenges . . . 21
4.4 Case Selection . . . 21
5 Results 26 5.1 Actor Analysis . . . 26
5.2 Töfsingdalen . . . 27
5.3 Pennfäktaren 11 . . . 30
5.4 Case Study Comparison . . . 32
5.5 Opportunities for Wastewater Heat Recovery . . . 33
6 Discussion 36 6.1 Actors . . . 36
6.2 Socio-Technical System Challenges . . . 37
6.3 Theoretical Contributions . . . 38
6.4 Disruptive Potential . . . 39
6.5 Sustainable Urban Development and Energy Efficiency . . . 39
6.6 Self-Reflection and Lessons Learned . . . 40
7 Conclusion 41 7.1 Recommendations for Future Research . . . 42
Bibliography 43 A Appendices 51 A.1 Energy Estimation . . . 51
A.2 Derivation of Wastewater Heat Exchanger Efficiency . . . 51
A.3 Interview Compendium . . . 52
A.4 Case Study Locations . . . 53
A.5 Case Study Performance . . . 54
A.6 Full Actor Description . . . 55
1.1 Visualization of the research approach. . . 5
2.1 Trends for energy efficiency improvements. . . 7
2.2 Schematic figure over the three levels of WWHR. . . 8
2.3 Conceptualization of the wastewater heat exchanger. . . 9
2.4 A horizontally wall-mounted wastewater heat exchanger. . . 9
2.5 A standing multi-level heat exchanger. . . 10
2.6 Schematic view over a heat pump wastewater heat exchanger system. . 12
3.1 Adapted figure on the critical interface. . . 18
4.1 The wastewater heat exchanger installed at Töfsingdalen. . . 22
4.2 The wastewater heat exchanger at Pennfäktaren 11. . . 24
5.1 The actors’ interactions at Töfsingdalen. . . 28
5.2 The actors’ interactions in Pennfäktaren 11 case study. . . 31
A.1 Location of Töfsingdalen. . . 53
A.2 Location of Pennfäktaren 11. . . 54
A.3 The water temperatures at Töfsingdalen. . . 54
A.4 The wastewater flow at Töfsingdalen. . . 55
A.5 The efficiency of the wastewater heat exchanger at Töfsingdalen. . . . 55
A.6 Heat recovery performance for Pennfäktaren 11. . . 56
2.1 Energy compilation for multi-family buildings. . . 6
2.2 Calculated theoretical energy in Stockholm’s wastewater. . . 14
2.3 Estimation of recoverable energy in Södermalm. . . 15
4.1 The classification of actors. . . 21
4.2 Categories of socio-technical challenges. . . 21
4.3 Key average performance values at Töfsingdalen [38]. . . 23
4.4 Key average performance values at Pennfäktaren 11 [73]. . . 25
5.1 Classified and contacted actors. . . 27
5.2 Opportunities for wastewater heat recovery. . . 34
A.1 Explained symbols. . . 52
EIA Early Innovation Adopter.
MLP Multi-Level Perspective.
SDGs Sustainable Development Goals.
TSD Technology Supplier and Developer.
TT Technological Transition.
WWHR Wastewater Heat Recovery.
Introduction
1.1 Background
Increased awareness of global warming has encouraged Sweden to implement ambitious climate and energy targets to decrease its greenhouse gas emissions. The goals being that Sweden by 2030 should have 50 percent more efficient energy use compared to 2005 and to have a net-zero carbon footprint by 2045 [1]. Two studies, one by the Swedish Environmental Protection Agency [2] and one by Francart et al. [3], found that in a net- zero carbon footprint scenario, the building sector must decrease their greenhouse gas emissions by 90 percent. The study by Svenfeldt et al. concluded that reaching this target for buildings is feasible with the implementation of many energy efficiency measures, where wastewater heat recovery (WWHR) identifies as necessary [4].
Furthermore, in September 2015, the United Nations ratified a new agenda aimed at serving as a blueprint for a better and more sustainable future for everyone. Agenda 2030 consists of 17 Sustainable Development Goals (SDGs), of which SDG 7, 11, and 12 aligns to this study [5]. The applicable goals being:
“ SDG 7: Ensure access to affordable, reliable, sustainable and modern energy for all”
“ SDG 11: Make cities and human settlements inclusive, safe, resilient and sustainable”
“ SDG 12: Responsible consumption and production and climate action respectively”
This study aligns with these goals since investigating a technology aiming at mak- ing energy consumption more responsible and improving energy efficiency in buildings, results in creating more sustainable cities. Ultimately, connecting them all.
Today, in the average European household, about 15 percent of the total energy con- sumed in a residential building goes to water heating applications [6]. What is more, the heated water is often used during an instant and then wasted down the drain. That is also true for other buildings such as swimming halls, restaurants, hotels, and industries.
The temperature of the wastewater is 27◦C on average for households [7] and a com- pany involved in industry washing averaging 35◦C [8]. For multi-family residences in Sweden, the average energy consumption related to warm water is 25 kWh/m2Atemp
[9]. Yet with this knowledge, the implementation of wastewater heat recovery is still uncommon [10].
As of 2018 in Sweden, the building and service sector accounted for 147 TWh or 25 percent of the total energy consumed. Compared to 152 TWh in 2005, this makes for a decrease of a mere 3.3 percent [11]. One of the reasons why it can contribute to improving energy efficiency in buildings is the fact that 15 percent of the energy con- sumption goes to water heating applications. This is the second-largest purpose for en- ergy consumption [6] and will continue as such if WWHR remains unused. Despite the potential for WWHR in buildings [10], the utilization of the technology in Stockholm, Sweden, is limited to mostly a few specific case study installations where the actors have installed systems for testing, research, and development.
1.2 Previous and Current Studies
Numerous and diverse research is done on WWHR. Previous studies focus on answering questions about the technology, economics, solutions, modeling, experiments, analyses of wastewater temperature and flow, for instance, the performance of wastewater heat exchangers, and estimations on reduction in energy consumption and economic bene- fits. Literature shows promising results for passive systems, and specifically for wastewa- ter heat exchangers connected to heat pumps, called active systems. Nonetheless, there seems to be a general research gap in literature examining motives, strategies and chal- lenges for the adoption of WWHR.
1.2.1 System Analyses
There is an ongoing study called the HÅVA project (Sustainability Analysis for Wastew- ater Heat Recovery). A collaboration between the International Energy Agency, RISE (Research Institutes of Sweden), and Lund University, investigating how the wastewater temperature in the sewers could change with the large-scale implementation of WWHR and if it affects the processes at the wastewater treatment plants. The purpose of their study is to answer the question of whether it is possible for large-scale adoption with- out undesirable effects on the sewer system and the treatment plants [12] [13]. What is done so far is the evaluation where in Malmö’s sewer system WWHR is more opti- mal, suggested is that pumping stations are more suitable for heat recovery than at the wastewater treatment plant [14].
The other system analysis study is the SEQWENS: Ensuring sustainability and equal- ity of water and energy systems during actor-driven disruptive innovation. The project aims to evaluate the system effect of on-property WWHR installations, including the socio-technical aspects, to ensure a smoother transition to a sustainable society. Us- ing case studies in Stockholm, Göteborg, and Värmdö, assessing devices though the co- evaluation of actors, technology, and society, and how the new technology redistributes costs and benefits [15]. One study ordered by Energimyndigheten, have had the ap- proach to create material for how to perform tenders and to try to come up with ini- tial guidelines for the feasibility of WWHR [10], simultaneously evaluating the current technologies used for WWHR and juxtaposing several on-property WWHR case instal- lations for performance.
1.2.2 Passive Systems
Passive systems include WWHR as standalone systems not paired with any other device and often preheating the incoming cold water. Studies here focus on feasibility, per- formance, technology, and economics. Studies have evaluated the performance of such systems, partly from the feasibility study by Energimyndigheten mentioned earlier, or as a master’s thesis evaluating Töfsingdalen’s buildings by L. Ohlsén [16]. In Berlin, a study estimated financial and energy savings produced results promising 30 percent energy re- duction on hot water from passive systems [17]. There has been substantial research on shower drain heat recovery, studying feasibility [18], financial analysis [19], and experi- mental set-ups of such solutions [20]. Finding promising economic and financial results.
Researchers have also come up with models of variation in wastewater flow and temper- ature, producing daily trend coefficients for quicker estimations of energy savings [21], and supporting with decision-making and planning of WWHR [22].
1.2.3 Active Systems
Research concerning WWHR combined with heat pumps has been investigated thor- oughly, for example, modeling of WWHR systems going as far as proposing a cooling system [23], experimental set-ups [24] or using the wastewater heat for defrosting of heat pumps’s evaporators [25]. One study by F. Meggers and H. Leibundgut modeled the potential of a wastewater heat recovery system connected to a heat pump. The energy re- covered from wastewater managed to generate a heat pump coefficient of performance of 6, meaning that for every unit of work input, the heat pump produces 6 units of heat. Accordingly to the authors, the energy reduction this resulted in is a significant reduction even for a modern building [23]. The authors Zhang et al. field-tested a heat pump in Changchun, China, which recovers energy from wastewater to increase the heat pump’s performance. The results suggested that the coefficient of performance of the heat pump is 4.5. Compared to no installation, the system can save up to 53 percent of the consumed energy and decrease costs by 11 percent [26].
Master’s theses such as this study by P. Ngo and F. Bjurling, focused on the perfor- mance of a WWHR system using the wastewater heat for preheating of the heat source in a heat pump [7]. Another example of using active systems is in Stockholm’s district heating network. The recovered heat from wastewater and lakes amount to 20 percent of the total fuel mix [27].
1.3 Aim and Limitations
This study aims to provide knowledge about WWHR, performing a literature review, an actor, and WWHR analysis using case studies as a basis for the research method.
Technology-wise, the aim is to understand how the case study installations perform and behave, comparing them to each other but also how they perform compared to other energy efficiency measures. The purpose is then to investigate and categorize this tech- nology’s challenges split into four categories to understand its disruptive potential to the system and analyze synergies and incompatibilities.
The technology has evolved bottom-up without the current regime pushing for change via specific policy changes on WWHR. Instead, they have installed it on their behalf, and the aim is to understand why. To some extent, they are radical actors since they are not following the status quo and are experimenting with new approaches and technolo- gies. It is wanted to understand what is driving them to do that. Is it perhaps driven by new policies, ambitious energy efficiency targets, economic reasoning, or any other argument behind this change? The aim is to map and analyze the actors connected to WWHR. The actors classify with the assistance of using theoretical frameworks, and it is wanted to understand their motives, concerns, and strategies. Both those who push for these technologies, those more skeptical and those who oppose it. The idea is to provide knowledge where there is a gap, mainly motives, strategies, and current socio-technical system challenges for WWHR.
By using non-randomized case studies, the study cannot reach statistical significance even though patterns may appear . However, interviews like these can help with obtain- ing data valuable to analyze further and provide insights amongst the interviewed actors [28]. Another limitation is being able to reach all the actors have had a part in the instal- lation of the WWHR, meaning that the study primarily focuses on the innovation side actors. Therefore, initially reaching out to actors having had a direct or indirect influ- ence on the implementation of the WWHR system is prioritized. The case studies are covering commercial buildings and residential buildings such as apartment complexes, and there could be the possibility that other actors working with other buildings have additional motives and strategies.
1.4 Research Questions
In this thesis, to center the research and maintain focus, four research questions are to be answered. First, is the question of how the chosen installations technically perform, when understanding this, it will be easier to understand why actors may argue from a cer- tain viewpoint. The second question is who the actors in the case studies are and how they interacted during the WWHR installations, in other words understanding their communication with each other. Third, is the question of understanding how these actors frame WWHR. Investigating their motives, strategies, and what challenges and opportunities they see, including actors promoting the technology as well as actors that might be more skeptical or opposing it. Also, presenting a working business model if enough data is found and interviewing generates enough data, which is the fourth re- search question. Figure 1.1 visualizes the research approach and the list below is summa- rizing the goals.
1. How do the current systems perform technically?
2. Who are the involved actors in WWHR, and how do they interact?
3. How do the actors frame the implementation of WWHR?
4. How could a successful business model look like?
Figure 1.1: Visualization of the research approach.
Literature Review
2.1 Energy Consumption in Swedish Buildings
Sweden’s national energy target for buildings is to become 50 percent more energy effi- cient by 2030 compared to 2005 [1]. In 2005, the average multi-family residence con- sumed 170 kWh/m2per year , meaning that in 2030, the maximum consumption can- not exceed 85 kWh/m2as seen in Table 2.1. Today, the minimum requirement for en- ergy consumption of new multi-family residences is 85 kWh/m2. In 2018, the yearly consumption had improved to 138 kWh/m2, but being on-track would have required 128 kWh/m2.
Table 2.1: Energy compilation for multi-family buildings.
in [kWh/m2/year] [29] [30] [31].
Year 2005 2018 2030
Energy target - 128 85
Actual consumption 170 138 ?
Regarding energy consumption for warm water heating, an average building uses 25 kWh/m2/year [9] which remains constant over the year. Moreover, as seen in Figure 2.1, where most energy efficiency improvements have been done are in the heating and ventilation sector, the energy consumed to warm water has remained fairly stable [32].
Figure 2.1: Trends for energy efficiency improvements.
[32]
2.2 Wastewater and Heat Recovery
Wastewater, or sewage water, is water contaminated through human use [33]. It can come from households, restaurants, industries, hospitals, to mention a few examples.
Household wastewater can include contaminated water from showering, faucets, dish- washers, toilets, and washing machines. It is often used during an instant, then flushed down the drain of the building. The temperature of the wastewater is average 27◦C [7] and about 35◦C [8] for industry washing. Thus, there should be the possibility of recovering satisfactory amounts of energy from wastewater.
When the wastewater is flushed, it is transported through pipes to a wastewater treat- ment plant for purification. In Stockholm, the sewage system is over 3000 km long, and 200 pumping stations ensure that the transportation of wastewater functions correctly [34]. At the treatment plant, wastewater purifies in a multi-step process before being released back into the natural water. Recovering heat is implemented at some treatment plants.
2.3 Locations for Wastewater Heat Recovery
It is possible to recover heat at three different locations in the wastewater system. These are on-property, in the sewer system, and at the wastewater treatment plant [12]. On- property WWHR installs in the very same building as the common drain. Recovered heat at the property level guarantees that the wastewater has lost minimal energy. For instance, in the sewer system, wastewater and urban runoff water are mixed, lowering the temperature [35]. As mentioned, the wastewater temperature in a regular building is between 25-30◦C, and according to a study by Sveby, the temperature of the incoming cold water in Stockholm fluctuates between 5-16◦C [9]. Allowing for energy extraction under regulation as discussed in sections 2.5 and 2.6.
Next is the possibility to recover heat in the sewer system [12]. Sizing of this system can be that of a few houses, city districts, or an industrial park. When recovering heat at the sewer level, less heat recovery installations are needed compared to on-property WWHR. One location where heat recovery is possible is at pumping stations. Com- pared to recovering energy at the wastewater treatment plant, less energy is lost to the ground. For example, Stockholm has 200 pumping stations. A recent study concluded that pumping stations are a suitable location for WWHR because of its high wastewater flow without affecting processes at the wastewater treatment plant [14].
Last is to recover heat at the wastewater treatment plant [12] occurring at the final stage of the treatment process. Before releasing the purified water to its destination, the temperature further decreases from the usual 7-20◦C to 0.5-4◦C. At some treatment plants, this energy is recovered and used for district heating, a process implemented at the Hammarby and Solna thermal power station [34].
Carrying out heat recovery close to the property guarantees that minimal energy transfers to the ground, but responsibility ends up on the final consumers. Figure 2.2 shows a conceptual view of the three levels. The figure aims to illustrate wherein the system heat recovery is favorable and practiced. The levels are from left to right, on- property, district size, and at the wastewater treatment plant.
Figure 2.2: Schematic figure over the three levels of WWHR.
2.4 On-Property Wastewater Heat Recovery
The principle of on-property WWHR is to extract heat through the drain in a building, using the recovered heat for different services in a building [36]. On-property WWHR is estimated by Energimyndigheten to recover 10-20 percent of the theoretical energy or 1-5 kWh/m2/year for case study installations in Sweden [10]. The technology used to recover heat is through a heat exchanger connected to the desired mediums.
For WWHR, the warm medium is the wastewater, and the cold medium can be the inlet cold or hot water, the brine of the heat pump, or accumulated water stored in a tank.
Figure 2.3 is conceptual to understand the principle. To optimize the heat exchanger
efficiency design of the heat exchanger could be standing solutions situated on the floor such as horizontally, vertically, or wall-mounted. The wall-mounted device is hung on the wall leaving space for other activities below, such as a parking space for bicycles, cars, or general storage.
Figure 2.3: Conceptualization of the wastewater heat exchanger.
Translated into English [37].
The heat exchanger is often two pipes where the mediums are flowing in parallel or counterflow. Figure 2.4 shows such a solution where a horizontal and wall-mounted wastewater heat exchanger, is installed. Inside of the chromed isolation tubing is the heat exchange occurring, and the red tube is the drain tubing, while the grey pipe below is the inlet cold water. Inlet cold water flows in the grey pipe then into the heat exchanger.
Any time wastewater flushes down the drain, the cold water passing by at that very same moment is subject to heat transfer.
Figure 2.4: A horizontally wall-mounted wastewater heat exchanger.
Photo: Anders Nykvist [10].
Other installed heat exchangers can be standing solutions such as the WWHR in- stallation at KTH Live-in Lab. Figure 2.5 shows this. In this figure, the copper tubing swirled around the drain tubing is visible. Both of these heat exchangers are often re- ferred to as passive heat exchangers, because they do not consume energy during opera- tion and instead relies on gravity and titled pipes for creating flow.
For evaluating the performance of WWHR installations and the fraction of energy from the wastewater recovered, here, the wastewater heat recovery fraction (ηwwhrf) is used. It is defined as the fraction between the difference of the inlet and outlet tempera- ture of the wastewater divided by the temperature difference of the inlet wastewater and
Figure 2.5: A standing multi-level heat exchanger.
Photo: David Nilsson.
cold water [38] and is expressed as
ηwwhrf = Qww
Qmax = m˙ww∗ Cp,water∗ (T1− T2)
˙
mcw∗ Cp,water∗ (T1− T3) = m˙ww∗ (T1− T2)
˙
mcw(T1− T3)
In an optimal scenario, the two fluids’ mass flows are the same, leaving only the temper- ature difference to calculate. In other words, it is the energy recovered from the wastew- ater divided by the theoretical maximum energy that can be recovered from the wastew- ater. Common ηwwhrf are estimated to 10-20 percent [10]. Table A.1 in appendix ex- plains the introduced characters, while Figure 2.3 above aids as visualization.
2.4.1 Heat Exchangers
A heat exchanger is a device used for heat transfer between liquid or gases, they have in common that a warm medium is heating cold medium. Heat exchangers can be used for heating of a cold medium such as wastewater heat exchangers, or to cool a hot medium, for instance, combustion engines. It rests on the second law of thermodynamics that heat moves naturally from a warm to a cold body. There are various types of heat ex- changers, and the optimal type depends on the application for the heat exchanger. The heat transfer between the mediums classifies as either: [39] [40]
• Direct contact
• Indirect contact
If the mediums are in direct contact, they are often mixed, such as the case with emulsion fluids or gas-fluid systems. An example of such a system is cooling towers used at power plants for cooling. Naturally, for on-property wastewater heat exchangers, the mediums are not to mix. Hence the indirect contact concept is a must [39]. The principle is for the two mediums, wastewater, and incoming cold water, to be separated by a boundary, often in metal because of its conductive properties. The two mediums can flow in: [39]
[40]
• Parallel flow, same direction
• Counterflow, opposite direction
• Cross flow, perpendicular direction
The efficiency of the heat exchanger is dependent on several factors, heat exchanger area, flow direction, contact, conductive properties, and interaction time between the medi- ums [41] and describes the transferred amount of energy. For calculating the heat ex- changer efficiency, there are two frequently used methods, the Logarithmic Mean Tem- perature Difference (LMTD) method and the Number of Transfer Unit (NTU) method [39] [40]. Considering that both cold water and wastewater flow are heavily varying, the NTU method is best suited since it takes mass flow into account. The derivation of the wastewater heat exchanger efficiency is described more in detail in Appendix A.2.
These equations enable for quantification of the amount of energy saved by WWHR, and how the temperature of the wastewater and cold-water changes. One disadvantage of using a heat exchanger without the possibility of recirculation or storage is that heat exchange only occurs while flushing wastewater and consuming cold water.
2.4.2 Connecting Heat Exchangers to Heat Pumps
An alternative to using only a heat exchanger is to offer solutions where there is the ability to utilize stored energy or where low-grade energy can be used more effectively as with heat pumps. The concept of heat pumps is converting a low-grade energy heat source with work for generating high-grade useful energy for common heating appliances, such as warm water or floor heating. By taking advantage of a “free” low-grade energy source from example boreholes, air, or wastewater, the heat pump can produce more heat than the input work [41]. This ratio is called the Coefficient Of Performance, COP1, and is often in ranges between 3-6. In other words, a heat pump with a COP1of 5 means that 1 kW of electricity produces 5 kW of useful heat. A heat pump often uses electricity to generate work and the general size of a heat pump in a multi-family residence is in the range of 100 kW [41].
A heat pump consists of several parts [42] [41]:
• Heat source, Q2: the source of low-grade heat. It is used to heat the refrigerant at the evaporator.
• Heat sink, Q1: where to the high-grade energy is delivered.
• Refrigerant: the medium inside the heat pump working cycle.
• Evaporator: the low-temperature heat exchanger where the heat source heats the refrigerant through evaporation. It travels to the compressor as a low-temperature liquid.
• Compressor: here, the low pressure of the low-temperature refrigerant is raised to match that of the condensing temperature. Both the temperature and pressure increase when the pressure is raised, under the ideal gas law.
• Condenser: the high-temperature heat exchanger subjecting the now vaporized refrigerant to heat exchange with the heat sink, it leaves as high temperature and high-pressure liquid refrigerant.
• Expansion valve: its function is to decrease the pressure and the temperature of the high temperature and high-pressure refrigerant. The refrigerant starts to evap- orate, and heat is taken off, it leaves as low temperature and low-pressure liquid refrigerant pumped back to the evaporator.
Figure 2.6 shows how the heat pump’s components are connected [41] [42] and how it can connect to a wastewater heat exchanger, the figure is adopted from a study by P. ngo and F. Bjurling ”Energiåtervinning ur avloppsvatten.” In the figure, the wastew- ater heat exchanger abbreviates WWHE. Nevertheless, this is just one possible config- uration. The wastewater could be used only as preheating with or without storage or using wastewater as the main heat source as at the wastewater treatment plant. Further explorations could be to connect solar thermal for more “free” energy. Such a concept is explored at KTH but without wastewater heat recovery [43].
Figure 2.6: Schematic view over a heat pump wastewater heat exchanger system.
For the heat pump to work effectively, beneficial conditions for the heat pump are to have [41] [44]:
• Available and even high-temperature heat source.
• Producing only as high heat sink temperature necessary.
• Having the heat source close to the demand.
• Correctly sized systems.
It works by the following principle of using a low-temperature heat source (Q2), adding work (W ) to produce useful high-temperature energy (Q1). The following energy bal- ance is correct for a heat pump
Q1 = Q2+ W
this is visualized in Figure 2.6 [41]. Expanding Q2to include both a heat source (hs) and wastewater (ww) as a complementary heat source generates the following energy balance
Q1 = Qhs2 + Qww2 + W
if the other inputs are assumed constant, then the amount of work input can now de- crease. It is seen that increasing the amount of energy recovered from wastewater im- proves performance and decreases energy use by the heat pump. Nevertheless, the equa- tion represents an ideal world. In reality, there are losses in the system, such as defrosting, leakage of refrigerant, and electricity self-consumption for fans and pumps [41].
A way to express the COP1for the heat pump is through the maximum theoretical COP called the Carnot efficiency [7] defined
COP1carnot = T 1 T 1− T 2
Achieving a higher COP1carnot is through decreasing the temperature difference be- tween the heat source (T2) and the heat sink (T1). This relation explains the impor- tance of having a high-temperature heat source and only as a high heat sink temperature necessary. It is also the reason why wastewater as an energy source improves the over- all performance of a heat pump. Another advantage of utilizing wastewater is that the energy is close to the heat pump, decreasing self-consumption for the pumping of the mediums.
2.5 Regulations Affecting Wastewater Heat Recovery In the regulatory framework “ABVA Allmänna bestämmelser för vatten-och avloppsan- läggningen i Stockholm och Huddinge” (eng. General regulations for the water and wastewater systems in Stockholm and Huddinge) are three paragraphs likely affecting WWHR in the Stockholm and Huddinge area [45].
§18 regulates that water or wastewater that has been subject to heat recovery can only be led back into the sewer system after getting a written application approved.
§20 states that water or steam having a temperature above 45◦C is not allowed to enter to the connection points of the sewer.
§23 regulates that the temperature of the return wastewater cannot be lower than the temperature of the incoming cold water to the very same building.
In Sweden, regulations regarding warm water states it must exceed 50◦C for mitigat- ing the risk for Legionella bacteria being present [46]. It should not affect WWHR, since the heat exchange usually occurs before the inlet water is heated. In Sweden, only the cold water is quality regulated, having set criteria for external substances such as metals allowed. There are no such standards for warm water [47]. That means that the material quality of the wastewater heat exchanger is relevant to consider if wanting to preheat the cold water.
2.6 Theoretical Energy Available in Stockholm's Wastew- ater
As previously mentioned, §23 in ABVA limits the amount of energy allowed to extract from the wastewater. A study by Sveby measured the incoming cold water to vary be- tween 4.5-16◦C averaging 10.2◦C for Stockholm. Then using the average of 23◦C as the wastewater temperature, the average maximum theoretical recoverable energy is cal- culated to 14.9 kWh/m3ww. Showing the exact calculation in Appendix A.1. Table 2.2 displays monthly average. For reference, an average Swede consumes one m3of water in about a week. The calculation excludes losses, for example, heat exchanger efficiency or varying wastewater flow. Calculations provide that there is more energy to recover during the winter due to the inlet cold water having a lower temperature.
Table 2.2: Calculated theoretical energy in Stockholm’s wastewater.
Month Cold water WW temperature Theoretical energy [◦C] [9] [◦C] [7] [kWh/m3ww]
Jan 6.5 23 19.3
Feb 4.5 23 21.6
Mars 5 23 21.0
Apr 6.5 23 19.3
May 10 23 15.2
June 12.5 23 12.3
July 15.5 23 8.8
Aug 16 23 8.2
Sept 15.5 23 8.8
Oct 13.5 23 11.1
Nov 9.5 23 15.8
Dec 7 23 18.7
Avg 10.2 23 14.9
2.6.1 Potential Energy Recovery for Södermalm
Estimations of the potential of recoverable wastewater energy using Södermalm, with its 128,000 inhabitants [48]. Assuming an average person consumes 150 liters of water per day [49], a wastewater temperature of 23◦C, WWHR fraction of 15 percent from other studies and the case study, provides there is energy for about 1200 apartments flushed down the drain. Here the energy an apartment consumes is the total energy consump- tion including electricity, which is not replaceable for WWHR. Table 2.3 displays the calculation and inputs used.
Table 2.3: Estimation of recoverable energy in Södermalm.
Average energy in wastewater 14.9 kWh/m3 150 liters of water used per day 2.24 kWh/person WWHR fraction, 15 % 0.336 kWh/person Yearly energy recovered 122.7 kWh/person Recoverable energy at Södermalm 15,700 MWh/year One Swedish apartment consumes 12.6 MWh/year [50]
Energy recovery enough for 1246 apartments
Theoretical Background
3.1 Socio-Technical Studies
Socio-technical studies focus on the interactions between technological and social pa- rameters, often analyzing through theoretical approaches to make sense of technologies’
expansions and how they navigate through society’s sets of rules, regulations, and norms [51]. There exists the idea that connecting sociological and technical aspects yield better stability in applied technological transitions (TTs). Here, defining TT as a technological breakthrough or transformation of how a society functions at any given time and how it transforms from there, for instance: socialization, transportation, living and industrial production. TTs also involve societal changes in elements not only directly related to the TT itself but auxiliary parameters such as user practices, infrastructure, industrial networks, and job applications [52].
The research field of socio-technical studies has, over the last decades, gained promi- nence in the research field for being able to explore several dimensions for desirable path- ways for sustainable change [53]. That prompted some researchers having narrowed their TTs to include sustainable technological transitions in particular. These transitions are not only affecting the technology but could also encourage altercations in consumer practices, business models, and policies. Consequently, sustainable TTs are challenging to the already existing systems (the established technology) because they involve multi ac- tors, goals, long-term changes, and their non-linearity [54]. As a result, possible conflicts can arise between the established actors and niche actors. Another trait of sustainable TTs is that they often are solutions not providing distinct user advantages. Generally, they score worse on price per performance than established systems, and therefore are unlikely to penetrate existing markets without a push from economic subsidiaries such as tax cuts, regulations, or requirements [55].
An array of theories are available to explain such transitions. For example, methods investigating only single-level actors. Those aimed at analyzing the complete chain of actor level transitions, from the technology classifying as an innovation becoming the norm of society. An example of such a theory is the multi-level perspective (MLP), which recognizes three levels for analytical concepts [56]. Adopted from the approach are levels of actors altered from niche, regime, and landscape levels to micro, meso, and macro levels respective. According to the MLP, a TT takes place across all levels. However, the
scheme and the rate of diffusion are vastly varying. Depending on what level the TT is at [57].
In a given society, the macro-level is supposedly reflecting the norms and values of its people, for instance, views on religion and environmental issues. The macro-level is exhibiting the greatest amount of inertia to system changes, they take time, often decades, and are dependent on direct influence from the meso and micro-level. An example of a system change is the transition from fossil fuels to renewable energy. The macro-level is the broadest of the levels, often visualized as vertically on the top of the pyramid. It is often referred to as the “exogenous landscape” where typical parameters affecting it are: macro-economics, culture, and macro-politics. Examples of such parameters are oil prices, wars, emigration, norms, values, and environmental problems of society [56]
[52] [55] [54] [58].
The meso-level is where actors are following and upholding the current norms, sys- tems, and regulations of society. However, it is at the same time, the level that provides in- cremental adoption for innovations, if they are well-suited enough for meso-actors goals to approach. They are subject to change just as the macro-level, albeit much quicker.
This level is semi-structured and follows semi-coherent rules that steer and put together the innovations, to fit the meso-levels actors’ rules. Ultimately, altering them to some ex- tent. This level often follows a duality in structure, where actors can sometimes innovate upon existing regulations, while in some cases, strictly follow them [55].
The micro-level is where innovations are tested and evaluated. It occurs in the pe- riphery of the existing systems and often defined as a “sheltered zone.” Because of being shielding them from the existing market and its competition. Innovations financed as research projects aim at technological development and gaining experience, rather than creating competitive products for the market. Such actors are often entrepreneurs, start- ups, or activists exploring new concepts. Their degree of radicality is dependent on the deviation on the existing business models, products and social interactions [56] [52] [55]
[54] [58]. Evaluation of the innovation is dependent on what stage in the development the product is and classifies into four different phrases. These are experimentation, sta- bilization, diffusion, and institutionalization [59].
The MLP is often applied when evaluating TTs possible of innovating and replacing existing technological systems [58]. One example of such a transition is the shift from non-renewable energy production to renewable energy production.
In the example, before the penetration of renewable energy, the then-current meso- level produced energy on demand from fuels, such as oil or coal. Producing energy at centralized large power plants and then transports to the customer, a normative system adopted since the 20thcentury [60]. The shift came about when renewable energy re- sources (wind, solar, and hydro) became necessary as means to tackle climate change.
After the innovation of technology and policy adoptions from governments, renewable energy expanded and was slowly adopted onto the meso-level and finally developing into the norm to the macro-level, for some countries. They became competitive when tech- nology improved, partly with assistance from governmental financing. Due to their in- termittence, they challenged the existing systems of how and when to produce energy.
When the wind and solar energy production became cheaper than fossil energy, it fur-
ther forced the landscape to adopt. Another aspect of this transition is the possibility of consumers quickly becoming producers of energy as when installing solar photovoltaics.
As a result, individual small-scale producers now challenged former rigorous fossil sys- tems [60].
In contrast, the complication of directly translating the MLP into this study is that WWHR cannot single-handedly replace the current meso-level. Though, it can pene- trate and become an integral part of already existing systems in such ways as improving energy efficiency in buildings while becoming small-scale heat producers. This is where the critical interface, developed upon the MLP is better at explaining WWHR’s situa- tion.
3.2 Critical Interface
Given that MLP’s concepts are broad inter-level perspectives and that this study focuses primarily on the innovation side actors, the critical interface is better suited since its fo- cal point is solely on the micro and meso-level perspectives. The MLP broadly explains how the technological transition happens, and what stages it goes through. Contrary to the MLP, the critical interface zooms on the interaction between these two levels and explains how a successful technological transition occurs, emphasizing communication and vertical actor-level integration.
It is the boundary area between micro and meso-level actors, as visualized in Figure 3.1 below. It is where they can step outside of the current meso-level to initiate inno- vative solutions [61]. Here, the meso-level actors can adapt to the micro-level’s set of rules, stepping into the “sheltered zone” for innovations. By emphasizing the boundary area between the micro and meso-level. The argument made is that only the innova- tions aligned to the needs of the meso-level actors, e.g., assisting in reaching their targets or meeting requirements, are transitioned further in the process of becoming an estab-
Figure 3.1: Adapted figure on the critical interface.
lished technology [62]. Consequently, an essential part of the support of niche innova- tions is for meso actors to focus on the downstream section of the technological systems.
One idea of the critical interface is to highlight the need for vertical integration across the three levels [62] [61], by focusing studies on their relations and communication be- tween each other. From the standpoint of the current meso-level not recovering heat from wastewater on a satisfactory scale, the critical interface is used for discussing actors’
inter-level alignment and communication with each other.
Methodology
4.1 Data Collection
The approach to the data collection is through a literature study and semi-structured interviews, performing seven interviews. The construction of the interview compendia was inspired by W. Adams’ “Conducting Semi-Structured Interviews” [63], M. J. McIn- tosh’s and J. M. Morse’s “Situating and Constructing Diversity in Semi-Structured In- terviews” [64] and finally, P. C. Gugiu’s and L. Rodríguez-Campos’ “Semi-Structured interview protocol for constructing logic models” [65]. The interviewees were all sub- jected to the same framework of questions. Seeing that the interviewed actors all had varying degrees of involvement in the chosen case studies and are different actors, the exact questioning changed depending on the interviewee. The participants were briefed about the research topic and then subjected to an interview over telephone or video com- munication. In appendix A.3, is the overall interview compendium shown.
4.2 Classification of Actors
The classification of actors has taken inspiration from the multi-level perspective (MLP) and a study from Sabine Hoffmann et al. [66] with the coordination consisting of three levels: the micro, the meso, and the macro-level. The classifications and examples are from the perspective of wastewater heat recovery (WWHR).
The micro-level can be considered the innovation zone or safe space for WWHR.
Split into two subcategories, the technology suppliers and developers (TSD) and the early innovation adopters (EIAs) who have adopted WWHR, i.e., building owners. Mak- ing this differentiation even though they act on the same level because they could have different views on motives, strategies, and challenges since the TSDs develop and work with WWHR only, while the EIAs work with buildings and are not bound to using cer- tain technologies. They are categorized at the same level because they are developing or adopting innovation and are working on a building perspective.
The meso-level actors are those upholding and operating the current regime, e.g., city authorities, and they have soft power by having set environmental targets as they have in Stockholm. On the macro-level are actors navigating nationally. Here, classified as being financiers, meaning they can provide guidelines, financing, resources, and pro-
mote environmental targets. Both the meso and macro-level actors have broader knowl- edge about how the currently existing systems work, and how and where WWHR could fit in that frame. How the actors are classified is shown in Table 4.1.
Table 4.1: The classification of actors.
Micro-level Meso-level Macro-level
Technology supplier Early innovation City authority, Financier, and developer adopter District heating Regulator
4.3 Classification of Socio-Technical System Challenges One more section of the study is to highlight the current challenges as identified from the interviewing and the case study evaluation, categorized into four categories: tech- nological, financial, regulatory, and conflicts. Inspiration for the choice of categories came from the literature review about technological transitions, the MLP, and the criti- cal interface. Inspiration was also from other socio-technical studies such as “Advancing socio-technical systems thinking: A call for bravery” [67] and “System- and actor-level challenges for diffusion of renewable electricity technologies: an international compari- son” [68].
The choice of categories is to give a complete picture as possible over WWHR. Nat- urally, each actor will have varying amounts of input on each of the categories. In Table 4.2 is the categorization of challenges and examples given. Choosing technical and fi- nancial challenges because of WWHR being a new technology and innovations often face such challenges. Also, it is interesting to analyze for conflicts between the early in- novation adopters and the regimes. Rivalry often arises owing to innovations disrupting their business. Finally, because of finding regulations affecting WWHR, it is sought to understand if those have had any power in the decision making.
Table 4.2: Categories of socio-technical challenges.
Main Category Examples
Technical Retrofitting, performance, space, lack of knowledge Financial Return on investment, investment cost, payback time Conflicts Existing systems and regimes, other efficiency measures Regulatory WW return temperature, renovation permits
4.4 Case Selection
The study is utilizing case studies to effectively structuring the analysis of WWHR sys- tems and the actors. The choice of these case studies was to cover the installation of WWHR in a commercial and a residential building. Hoping to cover a broader range of motives, strategies, conflicts, technologies, and future perspectives since the build- ings are utilized for different reasons. Additionally, the choice of case studies were also
from the perspective of previous studies on WWHR. Firstly, choosing the residential buildings of Töfsingdalen as a case study since there are evaluations on the performance of Töfsingdalen’s buildings. Secondly, owing to research identifying prospect in active WWHR systems, choosing one such case study for advancing the understanding of ac- tive systems. That case study is on the commercial building Pennfäktaren 11. Both case studies are located in Stockholm.
The case studies act as a basis to analyze the actors involved in the development of their WWHR installations and categorize them for what part of the installment they conducted. The actors connected to these case studies are to some extent radical, because of bringing WWHR into a possible new market for energy recovery and heat generation.
4.4.1 Töfsingdalen
The residential district of Töfsingdalen is situated in Norra Djurgårdsstaden in Stock- holm, Sweden. It is a district appointed by Stockholm Stad as being one of Stockholm’s high-profile sustainable districts [48] [69]. The location is shown in appendix A.1. There are 141 apartments in each building spread over seven or eight floors [16].
Töfsingdalen’s buildings have had several technical solutions implemented to im- prove energy efficiency. One of the technologies installed is the wastewater heat ex- changer. Designed to passively preheat the incoming cold water by extracting heat from all of the outgoing wastewater. In Figure 4.1 is the installation shown. It is neatly fitted between two walls, hence making a picture of the total heat exchanger difficult. The heat exchange occurs inside of the chromed piping.
Figure 4.1: The wastewater heat exchanger installed at Töfsingdalen.
Photo: Jörgen Wallin.
Measurements at Töfsingdalen was taken during approximately four months be- tween 2019-07-03 to 2019-10-25 [38]. Table 4.3 summarizes the performance of the system and shows the values as the average value over the full measurement period. 2 kW is the average effect extracted from the wastewater, preheating the cold water by 3.7
◦C. During the testing period, the heat exchanger efficiency was 54 percent, and the wastewater heat recovery fraction is 15 percent.
Table 4.3: Key average performance values at Töfsingdalen [38].
Parameters Values
Preheating temperature difference 3.7◦C
Incoming Cold Water 14◦C
Outlet wastewater temperature 20◦C Wastewater heat recovery fraction 15 % Heat exchanger efficiency 54 % Warm water energy need 21.6 kW
Wastewater energy 12.5 kW
Available energy for extraction 3.5 kW Actual energy extraction 1.9 kW
The estimated yearly energy reduction is 16.6 MWh, using 1.9 kW as power savings.
Using an average price of 830 SEK/MWh for district heating [70], the savings accumu- late to 14,000 SEK/year. Given that an average Swedish apartment consumes 12.6 MWh per year [50], this WWHR installation is equivalent to the total energy that 1.3 Swedish apartments consume yearly or savings estimated to 1.15 kWh/m2, using 14 000 m2as Töfsingdalen’s total area [16].
Seeing that the outlet wastewater temperature never decreases below the incoming cold water means that the installation follow that regulation. Figures A.3, A.4 and A.5 in the appendices show how the system perform over the testing period. Key findings are that this system’s heat exchanger efficiency decreases over time, but not the overall energy extracted from the wastewater. Because at the same time, the wastewater flow increases over the testing period. Consequently, making preheating of the cold water fairly constant over the testing period.
4.4.2 Pennfäktaren 11
Pennfäktaren 11 is a commercial building situated in Vasagatan 7, Stockholm. The foun- dation of the building is that it has been designed accordingly to a green building concept where the focus has been on energy efficiency and sustainable material choices [71]. In- terestingly, Pennfäktaren 11 was the first building in Sweden to receive the gold standard of the LEED-certificate. As with Töfsingdalen, this building also has a lot of different smart energy solutions added during its renovation in 2009 [72]. In appendix A.2 is the location displayed.
The WWHR system connects to the building Pennfäktaren 11, which includes a hotel and a restaurant, adding to the total wastewater flow. The design of the system is to recover heat for preheating the brine of the heat pumps. What is more, the system is innovative in the sense that this system can emit energy back to the wastewater gener- ating better performance when the heat pumps produce cooling, e.g., during summer.
The implementation of the wastewater heat exchanger was a two-step process. The first test installation was 6 meters long. When the evaluation proved promising, during the second stage, they installed an additional heat exchanger, consequently having 12 meters of heat exchangers. It was during the second implementation that they also innovated the system into producing cooling by dissipating heat back into the wastewater. Figure 4.2 shows the wastewater heat exchanger. It is horizontally wall-mounted, leaving space for activities below. The heat exchange occurs within the chromed tubing.
Figure 4.2: The wastewater heat exchanger at Pennfäktaren 11.
Photo: Jörgen Wallin.
Performance was evaluated during approximately four months from 2016-11-17 to 2017-03-07. The system recovered 31.7 MWh with the average power of 12.2 kW, and the yearly energy reduction is estimated to 107 MWh [73]. Table 4.4 shows key data.
Conclusions drawn from the evaluation are that this investment is profitable and that
the heat exchanger efficiency did not decrease over the testing period, as shown in Figure A.6 [73]. Also, the average wastewater temperature after heat recovery is following reg- ulations. Cost reductions are estimated to 88,000 SEK when buying heat from district heating at 830 SEK/MWh. The yearly estimated energy recovered, is equivalent to the total energy consumption of 8.5 Swedish apartments. Economically, the investment is profitable with savings accumulating to 1.6 MSEK under its lifetime. The investment cost was 2.2 MSEK and saves 509.3 SEK/MWh. Interestingly, savings from cooling re- covery are larger and hence bigger benefits are from there. The analysis further proves that the investment is only profitable under the condition of recovering both heat and cooling [73].
Table 4.4: Key average performance values at Pennfäktaren 11 [73].
Parameters Values
Yearly estimated energy recovered 107 MWh Wastewater heat recovery fraction 30 %
Actual energy extraction 12.2 kW
Total energy recovered during evaluation 31.7 MWh
Avg WW temperature 22.3◦C
Avg WW temperature after HEX 16.5◦C
Results
This section presents results case study specific, with subsections explaining their mo- tives, strategies, and system challenges they faced when adopting wastewater heat recov- ery (WWHR), finalizing the chapter with a comparison and a section about the oppor- tunities.
5.1 Actor Analysis
All the interviewed actors have had a connection to either of the case studies. Energimyn- digheten, the financier, being interviewed because of their wide view navigating the na- tional level and ability to provide with financing. Therefore, deeming it valuable to un- derstand their current position and future perspective on WWHR.
Stockholms Stad, the meso-level actor, was interviewed for having probable knowl- edge about the existing meso-level actors’ view on WWHR, for having implemented ambitious climate targets, and if there are any strategies related to WWHR on a city or district scale. As can be seen in the Table 5.1, Energimyndigheten participated in the Pennfäktaren 11 case study by financing the evaluation report and were mentioned pro- viding resources enabling for Stockholmshem with their WWHR installations before Töfsingdalen [RES 4]. Table 5.1 shows what the name of the actors are, their reference number, and the main reason for interviewing. Below is a section focusing on analyzing the actor’s general strategy for reaching their goals and targets (for a full description of the actors see Appendix A.6).
Table 5.1: Classified and contacted actors.
Actor Classification ID Reason for interview
EFFAB Technology supplier RES 1 Developed and supplied
and developer the WWHR system
at Pennfäktaren 11 iNEX Technology supplier RES 2 Supplied the WWHR
and developer system at Töfsingdalen Vasakronan Early innovation RES 3 Developed and adopted
adopter the WWHR system
at Pennfäktaren 11 Stockholmshem Early innovation RES 4 Adopted the WWHR
adopter system at Töfsingdalen
Incoord Technology supplier RES 5 Developed the WWHR and developer system at Töfsingdalen Stockholms Stad City authority RES 6 Set environmental targets
for Norra Djurgårdsstaden Energimyndigheten Financier RES 7 Assisted with funding in the
renovation of Pennfäktaren 11
5.2 Töfsingdalen
Töfsingdalen, as a project, started in 2009, introducing the idea of WWHR first in 2013.
Incoord (TSD) was contacted by Stockholmshem (EIA) to develop and project Töfs- ingdalen, with Incoord employed as a consultant. Stockholmshem wanted to voluntar- ily reach their own ambitious energy consumption target of 55 kWh/m2/year [RES 4].
Incoord evaluated what technologies necessary to install to reach that target choosing WWHR amid other solutions.
During the installation of the wastewater heat exchanger, Incoord said there was a lack of information about the performance of the wastewater heat exchanger and how much savings to account for [RES 5]. Eventually, they retrieved information that the wastewater heat exchanger recovers 20 percent of the energy from the supplier [RES 5].
After finishing the feasibility study, they ordered material from iNEX (TSD) [RES 5].
Ultimately, they installed a passive floor-mounted wastewater heat exchanger preheat- ing the incoming cold water. The technology supplier and developer, iNEX, said they only functioned as a technology supplier during this project. Lacking communication between them and the other TSD, not performing any calculations [RES 2]. In Figure 5.1 is the proposed relationship between the actors at Töfsingdalen as identified from interviewing.
5.2.1 Motives and Strategies at Töfsingdalen
“Insane to waste 30 percent of the energy to the wastewater.” - Technology supplier and de- veloper
To encourage building owners to construct energy-efficient buildings, Stockholms Stad
Figure 5.1: The actors’ interactions at Töfsingdalen.
(city authority) has put ambitious energy targets for new production buildings. To en- sure that Stockholm reaches its targets to reduce the amount of energy bought and reach- ing the national environmental targets [RES 6].
Stockholmshem’s installed wastewater heat exchanger states to reduce their build- ings’ energy consumption with 5 kWh/m2/year [RES 4]. Stockholmshem says that such a reduction is first interesting for them when getting closer to the energy target for new production buildings, comparingly when wanting to improve existing buildings’ high energy consumption [RES 4]. Incoord said that the wastewater heat exchanger has close to 20 percent heat exchanger efficiency when cleaned then gradually decreases after that, stating to achieve an overall efficiency around 10 percent [RES 5]. Nevertheless, the attitude towards WWHR is positive when the system functions are guaranteed. They have feedback about how the system operates and that it does not fulfill self-cleaning and needing too much maintenance [RES 4] [RES 5].
Stockholmshem was motivated by both constructing an energy-efficient district, Töf- singdalen, and to reach their energy target of 55 kWh/m2/year for new production build- ings [RES 4]. That target is necessary to fulfill for buildings on Stockholm municipal- ity’s property, set by Stockholms Stad for Norra Djurgårdsstaden. Under normal cir- cumstances, the energy target is set to 85 kWh/m2/year by Boverket [RES 4] [RES 5], meaning that their targets are more ambitious than the national. That has led to the ex- ploration of new technologies not usually installed in buildings, to reach their ambitious energy targets [RES 4].
Incoord was contacted by Stockholmshem to design their buildings and ensure that they reach energy targets and to make an energy-efficient building [RES 5]. Similarly, to Stockholmshem, Incoord’s motives for installing WWHR at Töfsingdalen were to develop the residential buildings to reach the energy target. Regarding WWHR, it was more that it was suitable for that building rather than a particular interest in the technol- ogy [RES 5].
Incoord’s motive for adopting WWHR is the fact that they feel it is insane to waste
