A Study in Solar Housing Technology: the Impact of Trombe Walls in Ladakh

EXAMENSARBETE INOM TEKNIK, GRUNDNIVÅ, 15 HP STOCKHOLM, SVERIGE 2020

A Study in Solar Housing Technology: The Impact of Trombe Walls in Ladakh

SEBASTIAN ARORA-JONSSON

KTH SKOLAN FÖR INDUSTRIELL TEKNIK OCH MANAGEMENT Abstract

The aim of this bachelor’s thesis is to examine the effect of installing a Trombe Wall in houses in Ladakh, India, and to evaluate its impacts for energy-saving, improvement in life quality, and its financial viability. Trombe Walls are a passive solar technology that use a dark wall with a glass covering to slowly heat living spaces by storing solar energy. Passive solar technology involves using the sun’s rays to heat or cool living areas without the aid of mechanical devices. In this thesis, two types of passive solar technologies are studied, Trombe Walls and direct gain technology. Direct gain technology is introduced in order to conduct a comparative study of Trombe Walls. Direct gain technology focuses on maximizing windows area to let in sunlight to warm the room. This was done through two-pronged approach. In a first quantitative step, data was collected from rooms heated by Trombe Walls and direct gain technology. In each room, data was recorded using temperature, humidity, pressure, and light sensors. This information was then used to analyze the indoor temperature of the rooms and calculate the solar radiation that hit the walls. This showed that Trombe Walls maintain a more stable indoor temperature as compared to direct gain technology, although often at the expense of the brightness of the room. Furthermore, a numerical model was developed to simulate the indoor temperature of a Trombe Wall. This quantitative analysis was complemented by a qualitative analysis where inhabitants from two villages in Ladakh were interviewed. All interviewees lived in houses heated by a Trombe Wall. The interviews show that Trombe Walls brings forth a myriad of positive effects, such as increasing indoor air temperature, improving air quality and generally raising the level of wellbeing in a family. Furthermore, a discussion of the economic feasibility of installing a Trombe Wall follows, to see if it is financially viable for villagers to adopt this technology. The Trombe Wall is analyzed as an investment using economic valuation tools such as the Internal Rate of Return method. Given current fiscal conditions in Ladakh, and that the lifespan of a Trombe Wall is at least 20 years, the Trombe Wall becomes a profitable investment for the individual if their required rate of return is less than 17 %. Lastly, this thesis concludes with a short discussion of how the quality of the data collected could be improved, as well as suggestions for future improvements to a Trombe Wall. Possible solutions are presented that might help make the Trombe Wall a more appealing heating solution and enable the technology to spread around the world.

Sammanfattning

Syftet med denna kandidatuppsats är att undersöka effekten av att installera en Trombe-vägg i hus i Ladakh, Indien och därigenom utvärdera dess bidrag till värmebesparing, förbättring av livskvaliteten och andra minskade kostnader. Trombeväggar använder en mörk vägg med en glasbeläggning för att långsamt värma upp hus genom att lagra solenergi. Trombe-väggar är en typ av passiv solteknik, en kategori som innefattar ett flertal olika teknologier som alla använder solens strålar för att värma eller kyla områden utan mekanisk hjälp. I denna uppsats studeras två typer av passiv solteknologi: Trombe-väggar och maximering av ljusinsläpp (Direct Gain Technology). Maximering av ljusinsläpp fokuserar på att tillföra så mycket solstrålning som möjligt in till rummet, och dessa studeras för att möjligöra en jämförande studie av Tromebväggens effekt. Studien utfördes i två steg. I ett första kvantitativt steg samlades data in från rum uppvärmda av Trombeväggar och maximering av ljusinsläpp. I varje rum registrerades data med hjälp av temperatur-, fuktighets-, tryck- och ljussensorer. Denna information användes sedan för att registrera rumstemperaturen inomhus och beräkna den mängd solstrålningen som träffade väggarna. Följande analys visade sedan att Trombe-väggar håller en mer stabil inomhustemperatur jämfört med maximering av ljusinsläpp, även om det ofta är på bekostnad av ljusstyrka. Dessutom gjordes ett försök att simulera inomhustemperaturen i ett Trombeväggs-rum med hjälp av en numerisk modell. Den kvantitativa analysen kompletterades i ett andra steg med en kvalitativ analys där invånare från två byar i Ladakh intervjuades. Alla intervjuade bodde i hus uppvärmda av Trombeväggar och hade begränsad tillgång till elektricitet. Intervjuerna visar att Trombe Walls ger upphov till en flertal positiva effekter, från att öka inomhuslufttemperaturen och förbättra luftkvaliteten till att höja välbefinnandet hos en familj. Därefter följer en ekonomisk analys av att installera en Trombevägg för att se om det är ekonomiskt lönsamt för bybor. Trombeväggar analyseras som en investering med hjälp av ekonomiska värderingsverktyg som IRR-metoden, Internal Return of Rate. Under antagandet att en Trombväggs livslängd är minst 20, är det en lönsam investering givet att en avkastningskravet på kapital är lägre än 17 %. Slutligen avslutas denna kandidatexamen med en kort diskussion om hur kvaliteten på de insamlade uppgifterna kan förbättras, samt förslag till framtida förbättringar av Trombeväggar. Möjliga lösningar presenteras som kan hjälpa till att göra Trombeväggar till en mer tilltalande värmelösning, och göra det möjligt för tekniken att spridas över hela världen.

2 Table of Contents 1. Introduction ...... 5 1.1 Background ...... 5 1.2 The Energy Situation in Ladakh ...... 6 1.3 Problem Discussion ...... 7 1.4 Purpose of Study ...... 8 1.5 Research Questions ...... 8 1.6 Design of Project ...... 8 1.7 Possible Contributions ...... 8 1.8 Scope ...... 8 1.9 Partner Organization, LEDeG ...... 9 2. Literature Review ...... 10 2.1 Sources of Information ...... 10 2.2 Overview of Passive Solar Technologies ...... 10 2.2.1 Direct gain Technology ...... 11 2.2.2 Trombe Walls and Indirect gain Technology ...... 12 2.3 Comparison of Direct gain and Trombe Walls ...... 14 3 Method ...... 15 3.1 Research Design ...... 15 3.2 Quantitative Method ...... 15 3.2.1 Designing and Building Measuring Equipment ...... 15 3.2.2 The Hostel ...... 17 3.2.3 Installing the sensors in the Hostel ...... 20 3.2.4 Advantages and Disadvantages of our Set-up ...... 21 3.3 Qualitative method ...... 21 3.3.2 Structuring the Interviews ...... 22 3.3.3 Reliability and Validity of Results ...... 22 3.4 Research bias ...... 23 4 Quantitative Results ...... 24 4.1 Outdoor Climate and Heat Degree Days ...... 24 4.2 Incident Solar Radiation ...... 25 4.3 Temperature Graphs ...... 26 5 Model of a Trombe Wall ...... 33 5.1 The Construction of the Model ...... 33 5.2 Comparing Calculated Results with Measured Results ...... 36 6 Qualitative Results ...... 38

3 6.1 Interview Responses to how People Perceive Changes in Indoor Climate ...... 38 6.2 Interview Responses to how People Perceive Changes in Indoor Climate ...... 39 6.3 Overall Responses ...... 40 7. Economic Feasibility ...... 41 7.1 Cost of Building a Trombe Wall ...... 41 7.2 The Trombe Wall as an Investment ...... 41 8 Analysis of LEDeG’s Trombe Walls ...... 45 8.1 Thickness of Trombe Walls ...... 45 8.2 Window Size in Trombe Walls ...... 47 8.3 Overall Conclusion of Trombe Walls ...... 48 9 Further Development of Trombe Wall ...... 49 10 Conclusion ...... 52 Acknowledgements ...... 53 Bibliography ...... 54

4 1. Introduction 1.1 Background Ladakh, a region nestled in the foothills of the Himalayas in the northern-most part of India, presents an interesting case for the adoption of passive solar technology. Ladakh is characterized by a harsh desert climate. Winters are severely cold and large amounts of energy are needed to survive. Additionally, Ladakh is situated at a very high altitude, with villages located at 3500m to 4500m above sea level, which makes it difficult for them to receive basic commodities such as food and electronics from other parts of the country. During the winter months, the only two roads leading to Ladakh are closed due to heavy snowfall, leaving air transport as the only way to access the region (1). With winter temperatures that plummet to -40 degrees centigrade (2), and roughly 320 sunny days a year, Ladakh presents an ideal environment for harnessing solar energy (3). Furthermore, Ladakh is not connected to the national power grid, and depends on a large hydropower station to power its capital city, Leh and nearby villages (4). Villages in more desolate parts of the region receive no access to central electricity, and often rely on stand-alone diesel generators or heating stoves as their energy source. Traditionally, the people of Ladakh have relied on a mixture of fuelwood, kerosene, cow dung and Liquefied Petroleum Gas (LPG) to heat their homes. However, each of these sources of fuel has their own drawbacks. They are expensive and some cause poor indoor air quality. With these disadvantages in mind, passive solar technology could prove to be a potential solution for people in Ladakh. There are advantages with passive solar technology. Previous research suggests that it has low variable costs, it is renewable and environmentally friendly (5). However, the main drawbacks of solar technology are its unreliability, high initial cost and the costs of storing solar energy (6). Furthermore, critics say that often solar technology has not developed enough to act as an independent heating source, and is therefore dependent on additional heating solutions to provide enough warmth throughout the year (7). Solar thermal technology is categorized into either active, or passive solar technology. Active solar energy technology creates energy by converting the sun’s rays into usable energy, often with the help of solar panels or other mechanical devices. In contrast to this, Passive solar technology uses the sun’s energy to heat or cool living spaces directly, without the aid of mechanical devices (8). This thesis focusses on a type of Passive Solar Technology, Trombe Walls. Their potential advantages and disadvantages will be explored through quantitative, as well as socio- economic, approaches.

Figure 1: Map of Ladakh and neighboring states (63)

1.2 The Energy Situation in Ladakh The energy situation in Ladakh has improved significantly in recent times. Thirty years ago, there was very little access to electricity, and the few people that had access relied on small, stand-alone diesel generators (9). In 2003, the government of India built a 45 megawatt (MW) hydro power plant, and expanded the local power grid, electrifying the capital city, Leh, and neighboring villages (10). This created enough electricity to power Leh through most of the day, although on most days, there are power outages for one or two hours during the early afternoon. However, this might change with the Indian government’s new project to connect the Himalayas to the national grid (11). Having allegedly pledged 11 000 crore rupees, (15.1 billion SEK), the government plans to connect the state of Ladakh, and the neighboring state Jammu and Kashmir, to the national power grid (12). Also, Ladakh was declared a union territory in October 2019, (13) that allowed external actors from outside the region to buy land in Ladakh. The new power grid, in combination with a potential influx of large energy companies, may drastically change the energy scene in Ladakh. This presents a scenario where Ladakh could become a powerhouse in renewable solar energy, as many companies look to set up large solar farms (14). At present, Ladakh has an estimated potential solar power generation of about 40 Gigawatt (GW), but with the inclusion of nearby regions Jammu and Kashmir, the energy capacity totals over 300 GW (15). This potential solar energy would be a huge boost for India’s energy mix, providing much needed renewable energy to the rest of the country.

6 However, not everyone in Ladakh is happy with the government’s plan to connect Ladakh to the power gird. Many people fear that big companies will invade Ladakh and drain the state of natural resources, polluting the land for the local inhabitants and destroying the fragile local eco-system, already endangered by commercial interests (16). Furthermore, most of the power generated is meant to be transported to the rest of India, providing further disincentives for local Ladakhis to support the new power grid plan. Although the new plan promises to improve access to electricity in Ladakh, many people are skeptical about the overall impact for Ladakh (17). Ultimately, the future of Ladakh is uncertain, and dependent on how well politicians can contain large companies from exploiting Ladakh’s natural resources. 1.3 Problem Discussion Traditionally, many households in Leh have heated their homes using a mixture of wood, kerosene, LPG, diesel generators and cow dung. This has stemmed from the poor energy situation in Ladakh, forcing inhabitants to resort to fuel options that cause negative externalities. Firstly, fuel is expensive and causes a significant economic burden for many villagers in Ladakh. Many villagers work as day laborers during the summer months, but struggle to find work during the cold winter months. Many people living in villages earn around 120 000 rupees per year (16 000 SEK) (9). According to local sources in the region, it is common to spend around 10 000-20 000 rupees per year on fuel, (1300-2600 SEK), which is a noticeable part of an inhabitant’s annual salary (9). Additionally, fuelwood in Ladakh is expensive, with vegetation being scant in the desert climate. Kerosene, LPG and diesel all have to be imported from outside Leh, and during the winter months when fuel is needed the most, only shipment by air is possible, which provides a significant additional cost for fuel sources. (18) Secondly, burning fuel indoors gives rise to dangerous particles in the air, which can cause several respiratory diseases. This is also a gendered question, since women are disproportionately affected by this problem, as they are most often responsible for the cooking and heating at home. (19) Therefore, finding a clean, reliable source of fuel becomes an important social issue, as well as a heating issue. Thirdly, heating solutions that involve burning fuel provide an unstable indoor climate. According to local villagers, when burning fuelwood, the stove needs to be stoked with wood every 15 or 20 minutes, forcing inhabitants to continuously fuel the fire or risk the temperature dropping dramatically.(9) This becomes impossible at night, which means that during most nights, temperatures can drop to zero degrees centigrade, or even freezing.(20) Hence, to improve the living conditions of the Ladakhi people, both in terms of indoor climate as well as socially, there is clearly a need for a new clean and sustainable heating technology. These negative heating factors, in combination with a local climate that is well adapted to embrace solar technology, make Ladakh a fruitful region to conduct this study in. This study focusses on one type of solar technology, passive solar technology. There are several types of passive solar technologies, and this thesis compares Trombe Walls to the direct gain approach. Trombe Walls are walls that trap solar energy using energy dense material and air pockets, and then slowly release the stored solar energy into the room during the day.(21) In comparison, the direct gain approach maximizes window area to let as much sunlight into the room as possible to heat and light up the room. (22) Another type of solar technology, active solar technology, is not discussed in this thesis, as it is often more expensive than passive

7 solar technology, and hence a less feasible option given limited fiscal resources of many Ladakhi citizens. 1.4 Purpose of Study The purpose of this thesis is to investigate the effectiveness of installing Trombe Walls in Ladakh. This will be investigated through a comparative study with direct gain technology, from the perspectives of their relative effectiveness in heating, social appreciation and financial viability. Hence, the aim is to draw well-rounded conclusions about Trombe Walls and how they can be used as heating sources. Hopefully, this thesis will serve as an guideline on Trombe Walls for prospective investors or house owners, in order to see if it is worth installing a Trombe Wall. 1.5 Research Questions RQ 1. What is the effectiveness of a Trombe Wall as a heating solution in Ladakh?

RQ 2. What is the social appreciation of installed Trombe Walls among users?

RQ 3. What is the financial viability of Trombe Walls as a heating solution for the inhabitants of Ladakh?

1.6 Design of Project This project was conducted with the help of two colleagues, Leo Björkman and Rita Nordström. Together, we collected data for both the quantitative and qualitative parts of the study. However, this thesis is written solely by undersigned, and hence the text will vary from using the personal pronoun “I” when I want to voice my own opinion, to “we”, when I am describing a part of the project that we conducted together. Furthermore, all graphs were created using the same data set, and hence they might also appear in their report, titled A Study on the Effectiveness of Passive Solar Housing in Ladakh. 1.7 Possible Contributions With our data collection and subsequent analysis, this thesis provide an insight into how effective Trombe Walls are as a heating solution for the inhabitants of Ladakh. Hopefully, this can be used in future decision-making when choosing what heating solution to implement. Furthermore, I show that there are sustainable ways to heat a home using solar energy, which may prove important in future housing projects that wish to reduce their environmental impact. We also build a simple model of the Trombe Wall, which can be used to experimentally gauge the effectiveness of a Trombe Wall in a certain climate. I also provide insights into how Trombe Walls can affect people living in Ladakh, in terms of improving their living conditions as well as fiscally. This is done to show how raising the indoor temperature can be correlated with improved quality of health, which can prove useful to anyone wishing to improve social welfare in Ladakh. Lastly, I also discuss the cost of building a Trombe Wall, and examine whether building a Trombe Wall can be a profitable investment. 1.8 Scope This thesis discussed Trombe Walls and their potential as heating solutions. It does not consider alternative solar technologies such as Photovoltaic cells or Concentrated Solar Power. (23) Furthermore, it does not focus on other heating solutions, such as

8 EEB, Energy Efficient Buildings, Attached Greenhouse Techniques or Advanced Window Control Systems. (23) Additionally, the regional area in which the Trombe Walls will be discussed is limited to Ladakh, India. Passive solar technology naturally varies in effectiveness depending on the local climactic conditions around the world, but that will not be taken into consideration in this thesis. 1.9 Partner Organization, LEDeG Ladakh Ecological Development Group is an environmental NGO in Leh, Ladakh. LEDeG works towards promoting “ecological and sustainable development which harmonizes with and builds on traditional culture”. (24) All the quantitative data was collected from rooms in LEDeG’s hostel, and the interviews were organized with the help of LEDeG staff. With over twenty years of knowledge and work with sustainable development and energy questions in Ladakh, LEDeG was an invaluable partner organization for this project.

9 2. Literature Review This section gives a brief overview of the existing research on passive solar technology. First, sources of information used in the thesis are discussed. This is followed by a brief introduction to different types of passive solar technologies, and an in-depth review of Indirect Passive solar technology and Direct Passive solar technology. Lastly, this section focusses on Trombe Walls and how they function. 2.1 Sources of Information In order to better under how Trombe Walls and passive solar technology work, we have considered earlier research on the topic. Much of our information stems from the article, Trombe Wall vs. Direct gain: A Comparative Analysis of Solar Heating Systems, written by Wray and Balcomb.(25) This article describes the fundamentals of both different solar technologies, and goes on to compare them in a further analysis. For more specific knowledge regarding Ladakh, we consulted a manual developed by several Ladakhi NGOs on low energy consumption design- written by Franck Clottes called L.E.C Integration Design Manual gives an in-depth account of building energy efficient houses in the state of Jammu & Kashmir and Ladakh.(26) The manual focuses specifically on Trombe Walls and other solar technologies that reduce energy demand. The book is set in the region of Ladakh and provides an excellent source of information for this study. This source, with general information about Ladakh, was complemented by key interviews. These three main sources served as the bulk of the literature but were complemented by additional sources such as articles on solar irradiance in Ladakh. 2.2 Overview of Passive Solar Technologies There are two main types of Passive Solar Technologies prevalent in Ladakh, direct gain technology and Trombe Walls. Direct gain involves south-facing windowpanes that can admit as much sunlight as possible to heat a room (27). In comparison, Trombe Walls are designed so that solar radiation heats pockets of air located between an inner and outer wall. This energy is then slowly transferred into the room, either by convective currents through openings in the wall or by conduction through the wall. There are several advantages of passive solar technologies according to established research. In their paper, Wray and Balcomb describe how passive solar technology is an affordable way to provide heating (25). They discuss how passive solar energy is environmentally friendly, causing no pollution or environmental degradation. Furthermore, passive solar technology does not require connectivity to a larger grid and is therefore perfectly suited for remote villages in Ladakh in need of heating. However, critics have often pointed out that passive solar technology is limited to the amount of incident sunlight, and therefore becomes volatile (7). It is difficult for a building to be completely reliant on Passive solar technology, as several days without sunlight will cause the temperature to drop significantly. This means that the technology needs to be integrated with other heating technology to maintain a stable temperature. Additionally, passive solar technology often has a high initial cost. Consequently, many people have opted out of passive solar technology in order to finance a single heating solution capable of providing enough heat around the year

10 2.2.1 Direct gain Technology Direct gain technology involves constructing rooms so that they absorb as much sunlight as needed. To successfully implement the direct gain technique, one must adhere to four important factors according to the LEC integration manual. (26) Firstly, the windows must be oriented towards the south, with a maximum deviation of ±20° from south. Depending on if the room is used mainly during the night, it is preferable to orient the windows 20° southwest from south, in order to maximize solar absorption during the afternoon. Conversely, if the building is mainly used during the day, the windows may be oriented 20° southeast from south, to maximize solar absorption during the morning. Secondly, it is important to avoid any obstructions that might prevent the incidence of sunlight. Near obstructions, such as buildings or trees, might be possible to move in order to construct direct gain housing. However, one must also be aware of distant obstructions, such as mountains or hills. These obstructions are impossible to move, and therefore require forethought and careful planning when constructing the house. Thirdly, the size of the direct gain windows must be optimized in order to ensure that the maximum amount of sunlight can be collected. One must strike a balance between allowing the maximum amount of sunlight to enter the room, whilst also minimizing heat loss through the windows during nighttime when temperatures cool outside. To gain a rough estimate of the optimal size of direct gain windows, an equation has been developed by local NGO’s in Ladakh.

�� = = (2.1) ��

Where • �� is the floor area • �� is the net area of windows which sunlight can enter through, usually defined as the area of glazed glass of a window.

A rough estimate of �� shows that it should be approximately 60 % of the total area of the window. Depending on where in Ladakh the house is being built, there is an optimal R-factor range, which depends on several factors such as the sun’s path and the average temperature. Lastly, the level of thermal mass in the room must be optimized for what time during the day the room is used. Thermal mass is the ability of material to absorb and store energy. (28) If a room has a high thermal mass, this will increase the capability of the room to store energy, but also increase the time it takes for the room to heat up. Thus, if the room is mainly used during the night, more thermal mass should be added in order to ensure that the room is warm during the night. On the other hand, if the room is mainly used during the day, less thermal mass should be added so that the room will quickly heat up during the first hours of the room’s occupation. Overall, direct gain technology is simple to implement and is relatively inexpensive. This makes direct gain technology accessible to a wide variety of people. However, the efficiency of direct gain greatly decreases during cloudy days. Furthermore, ensuring that a direct gain room has enough thermal mass can be expensive due to material costs. If the room does not have enough thermal mass, the indoor temperature may fluctuate greatly, causing temperatures to become too hot during the day and very cold at night.

11 2.2.2 Trombe Walls and Indirect gain Technology Indirect gain technology aims to store solar energy and slowly heat up a room through the redirection of energy. The most prominent example of indirect gain technology is the Trombe Wall. Trombe Walls are outer walls made by a dark, energy dense material, covered by a glazing that works much like greenhouse glass. As sunlight hits the Trombe wall, it heats up the dark, energy dense material and thus indirectly the air between the glazing. The air naturally rises as it becomes warmer and is then funneled back into the house through the use of an airshaft, heating the interior of the house and creating a flow of air through different rooms. The Trombe wall also transfers heat through the inner wall of the house, providing additional warmth. (29)

Figure 2: A Trombe Wall Source: Semiha Kartal (62)

To construct a house with a Trombe Wall, one still needs to consider most of the key factors of direct gain technology. Buildings need to be facing south, with a deviation up to ±20°, whilst additionally avoiding any obstructions that can impair the path of sunlight. However, the methods differ when it comes to thermal mass and the size of windows. When building a Trombe Wall, the layers of glazing presents an optimization problem. Additional layers provide better insulation, however at a greater cost with diminishing returns. Furthermore, the dark wall needs to be made of a material with very high specific heat capacity to store as much heat as possible. Additionally, the wall needs to be of a certain thickness, as it determines how fast energy may pass into the inside room. When the sun shines, we can imagine an energy wave that hits the outer side of the Trombe Wall. This energy wave will slowly pass through the outer wall to the inner wall to heat up the inside of the room. It is important to construct the wall thick enough so that the energy wave heats up the room during the night, when it is the coldest. However, if the wall is too thick, the energy wave will not reach the inner room during the night, resulting in cold night temperatures. Therefore, the thickness of the wall is a vital component of the Trombe Wall as it determines when the heat wave will reach the inner room. The time it takes for an energy wave to pass through a wall is modeled by the lag-time of the wall, and depends on the thickness, and materials, of the wall. This is modeled by the following equation. (26)

1 24 �� = ∗ � ∗ = � (2.2) � 2 3600 ∗ � ∗ � ∗ �

12 where, • � = �ℎ�� [�] • � = �ℎ�� ℎ� �� [ ] ∗ • � = �� ℎ� �� [] ! • � = �� ℎ�� [ ] (∗] • � = �� [ℎ��]

Usually, for walls made of mud or cement, the acceptable thickness of the wall is around 20 to 30 centimeters. Furthermore, apart from the time it takes for the heat wave to travel through the wall, the amplitude of the heat wave will also be reduced as it travels through the wall. This will reduce the amount of energy available in the room, and depends on the thickness and materials of the wall. The damping phenomenon is given by the following relationship.

⎛ � ⎞ � �� = �� −� ∗ = (2.3) ⎜ � ⎟ 24 ∗ 3600 ∗ � � ∗ � ⎝ ⎠ where, • � = �ℎ�� [�] • � = �ℎ�� ℎ� �� [ ] ∗ • � = �� ℎ� �� [] ! • � = �� ℎ�� [ ] (∗] • � �� = �� ℎ� ℎ�� [%]

Most of the Trombe Walls in Ladakh are built with a double-glazed window in the middle. This is to let sunlight into the room to illuminate the living space. However, as with most parameters in a Trombe Wall, one must find the optimal size of the window, balancing enough luminance with heat loss at night. This glazing area referred to here is of the window in the middle of the Trombe Wall that lets in light, and is not to be confused with the glazing area that covers the rest of the Trombe Wall. The equation for window size in Trombe Walls is given by the same relationship as for the window size in direct gain walls.

�� = = = 10 �� 12 % (2.4) ��

• �� is the floor area • �� is the net area of windows which sunlight can enter through, usually defined as the area of glazed glass of a window

The optimal value is within 10-12 % for the Ladakhi region, according to L.E.C Integration Design Manual. Ultimately, the building of a successful Trombe Wall involves several different factors. One must carefully adhere to orientation, avoid obstructions, thoughtfully

13 choose materials and make sure that the wall is of optimal thickness. If successful, the Trombe Wall reaps several advantages. Due to its storage of solar energy, a Trombe Wall can provide heat day and night, providing a stable temperature throughout the day, unlike direct gain technology. Additionally, it can also be effective during one or two cloudy days due to its ability to store thermal energy. However, Trombe Walls are more complicated and expensive to build compared to direct gain windows. Furthermore, the room may become too dark and people may not like the distinct aesthetic of the Trombe Wall. 2.3 Comparison of Direct gain and Trombe Walls Existing research on the subject suggests that Trombe Walls are usually better at sustaining a stable indoor temperature. This is due, in part, to the extra thermal mass, as well as the possibility to determine the thickness of the Trombe Wall, which enables control of when the energy wave hits the indoor room. Hence, Trombe Walls can sustain a stable temperature that direct gain technology usually cannot. However, Trombe Walls rooms are slow to heat up, unlike direct gain room that can reach much higher temperatures during the day and are significantly brighter. Trombe Wall rooms are dark unless a window is added. Trombe Wall are much more expensive than direct gain technology and are difficult to build. What is best for the citizens of Ladakh was not clear, and hence the need for further exploration was needed.

14 3 Method 3.1 Research Design When planning this study, the aim was to investigate how Trombe Walls compared to direct gain technology in terms of efficiency, social appreciation and financial viability. Thus, a mixed methods approach was adopted – with a quantitative and qualitative study. In the quantitative study we built and installed sensors in rooms heated by Trombe Walls, and then used the data we collected to study room temperature och brightness. In the qualitative study we asked villagers in Ladakh how Trombe Walls impacted them, in terms of indoor climate and fiscal savings, as well as if it contributed to saved time. To do this, we visited two villages in Ladakh, Palam village and Khardung village, where a LEDeG project had built Trombe Wall houses after a flash flood in 2010 and interviewed people living in houses heated by Trombe Walls. Together these two approaches combine to give a better understanding of Trombe Walls, in terms of how much energy is saved, as well as how it affects peoples’ lives. Mr. Chemet Rigzin was also interviewed, in order to gain a deeper understanding of the socio-technical landscape of Ladakh. Mr. Rigzin is the lead engineer at LEDeG, an established inventor who has worked in Ladakh for over fifteen years and has extensive knowledge within the field of solar technology, as well about the region of Ladakh. 3.2 Quantitative Method In the quantitative study, we compared the way Trombe Wall and direct gain technologies influenced indoor climate. The standard way of doing this is to collect data that gives an indication of how comfortable a room is for the individual. (30) We therefore measured temperature, pressure, humidity and luminance in rooms with DG or TW technologies over a period of time. We recorded the data using nine sensor kits that we constructed with a microcomputer unit, Arduino Nano, that were connected to compatible sensors. The sensor kits where then placed in nine different rooms in LEDeG’s hostel, and data was collected. 3.2.1 Designing and Building Measuring Equipment We decided to build our own sensor kits due to budgetary restraints. This had both advantages and disadvantages. By assembling the sensors ourselves, we were able to afford nine sensor kits, which otherwise would have been too expensive for this project. Additionally, we could design our sensor kits to the exact specifications of each room. However, there were also several drawbacks in constructing our own sensor kits. They broke easily. This led to a reduced amount of collected data since we had to spend several days fixing sensor kits or waiting for products to arrive so we could fix our sensors. All this required a lot of work and took a long time. We spent a lot of time soldering, connecting wires and writing code for our sensor kits to work. Additionally, the electronics purchased were not of the highest quality, which led to sensors suddenly breaking without an apparent reason.

15 Building the sensor kits started by choosing a microcontroller. A microcontroller is a programmable computer chip that can control other sensors or electronic equipment (31). The Arduino nano was chosen, which is a small microcontroller with an ATmega328P processor, because of its low energy consumption and ability to handle 3.3 volts logic and 5 volts logic. The ability to support both 3.3, and 5 volts logic means that the Arduino can function with sensors that run on both 3.3 volts and 5 volts. Additionally, low energy consumption is important because the sensor kits were powered by 2200 mAh LiPo batteries and needed to run as long as possible.

Figure 3: An Arduino nano

We used the following sensors described in table 1.

Table 1: Sensors

Name Measurements Accuracy Sensors used per kit DHT22 (32) Temperature and �� ± 0.5 ℃ 5 Humidity �� ± 5% TSL2561 (33) Luminous Intensity 0.01 �� 1 BMP280 (34) Pressure, �� 2 Humidity, ± 1 ℎ�� Altitude, �� ± 1 % Temperature �� ± 1� �� ±

Using a circuit board, we soldered together the Arduino with the sensors. We also used an SD card reader and an electronic clock module to save our data and record the time of each measurement.

16 The wiring diagrams in figure 3 depicts how to connect all the sensors and modules to the Arduino.

Figure 4: Wiring diagram 1. DHT 22 (Temperature and Humidity sensor) 2. BMP 280 (Temperature, Humidity, Altitude and Pressure sensor) 3. TSL 2561 (Lux sensor)2 4. DS3231 (clock module) 5. Micro SD Card reader 6. Arduino Nano 7. Pull-up resistors 3.2.2 The Hostel

Figure 5: LEDeG's Hostel

17 LEDeG hostel was built approximately ten years ago as a way for travelers to visit Leh whilst minimizing their carbon footprint. The hostel aims to have as low environmental impact as possible and relies on solar energy for indoor heating and warm water. The toilets are water free, eco-friendly compost pits and the food is vegetarian and locally sourced. The hostel is situated on a small hill, with Trombe Walls on the southern side to absorb as much sunlight as possible (seen in the picture). The hostel has six rooms on each floor, with three rooms in each wing. The two rooms at the end of each wing on the bottom floor has half Trombe Walls, and the two rooms above those have only glass windows, with no Trombe Walls. The last eight rooms are identical rooms with full Trombe Walls. There is no other source of heat than solar energy, and a 1.2 kW SPV plant nearby powers all electrical sockets. (35) The following image is a floor plan of LEDeG’s hostel, room 1 being Direct gain or half Trombe Wall rooms, 2 being storage rooms, 3 being Trombe Wall rooms, 4 being the common area and room 5 the entrance.

Figure 6: Schematic overview of hostel

From the outside, a Trombe Wall looks like this. Here we can see the dark wall behind the window glass, except for in the center of the wall, where a window was built to let in more light into the room.

Figure 7: A Trombe Wall from the outside

From the inside, the Trombe Wall rooms in LEDeG’s hostel looks like this.

Figure 8: A Trombe Wall from the inside

The Direct gain rooms are designed in the following way, slightly larger than the Trombe Wall rooms and filled with windows.

Figure 9: A direct gain room

19 Lastly, the half-Trombe Wall rooms are a mix of the Trombe Wall technology and Direct gain technology.

Figure 10: A Half Trombe Wall room

3.2.3 Installing the sensors in the Hostel We installed our sensors in LEDeG’s hostel, where we had access to eight rooms of which four had Trombe walls, two had half Trombe Wall and two were Direct gain rooms. In each Trombe Wall room, we placed five temperature sensors, two air pressure sensors and one light sensor. We wanted to collect enough data to get a sense of how the Trombe Wall functions, and therefore we placed the five temperature sensors in the Trombe Wall and the room. The two pressure sensors were placed in the air hole in the Trombe Wall in order to see if the heating and circulation of air caused a perceptible pressure difference. Lastly, the light sensor was placed on a small table near the center of the room to see how bright the room was. The red dots in the figure represent temperature sensors, whilst the blue dot symbolize pressure sensors.

Figure 11: Sensor placed in Trombe Wall room

20 In the two Direct gain rooms on the upper floor, sensor placement was similar to that of the Trombe Wall room, the difference being the two sensors placed inside the Trombe Wall. Hence, the direct gain room had three temperature sensors, two pressure sensors and one light sensor were placed. These rooms were used as control rooms as they only had glass windows without any Trombe Walls. The last two rooms had a half Trombe Wall, half glass wall set-up. We placed out four temperature sensors, two pressure sensors and one light sensor. These rooms were used as an extra source of information, in order to validate the results of the previous rooms. 3.2.4 Advantages and Disadvantages of our Set-up There were several advantages to our set-up, as well as some weaknesses. One considerable advantage was that all the rooms were located in the same building, which helps us control for some of the main confounding factors when interpreting the results, such as the thickness and material of the walls, the orientation of the building and the way that the local environment shades the building. A factor such as wind would normally be important to consider, but we can assume that on average, the wind will affect the temperature in each room by the same amount. Therefore, when we then compare the differences between the rooms, we assume that the effect of wind can be ignored. Another positive aspect of our set-up was that we had two or more of each type of room, so we could compare the results of similar rooms. This enabled us to improve the reliability of our measurements. We had four Trombe Wall rooms, and this would in general decrease the standard deviation of our measurements by one half. 1 1 1 = = (3.1) √� √4 2

Lastly, one major advantage with our set-up was that the hostel did not use any other source of heating other than solar energy. This means that we did not have to adjust for any other source of heating, and that we could equate all increase in indoor temperature with solar energy stored by the Trombe Wall. One disadvantage of our set-up was that the four rooms at the end of each wing, the half Trombe Wall rooms and the direct gain rooms were slightly bigger than the Trombe Wall rooms. This is an important factor to consider because a fixed amount of incident sunlight equates to a certain amount of energy. If this energy is spent heating a larger room, it is natural that this room will become cooler than a smaller room. Therefore, the room size is an important factor we take into consideration whilst performing a comparative analysis of the different types of rooms. The four rooms at the end of each wing had their outer wall in thermal contact with the outdoor temperature, whilst all the Trombe Walls only had Thermal contact with other rooms at each side. This is an additional factor to take into consideration, as it will create further heat loss for the four rooms, which we will have to take into consideration whilst conducting our analysis. 3.3 Qualitative method We conducted seventeen interviews in two Ladakhi villages, Pallam and Khardung. Pallam is a small village located 10 kilometers from Leh, nestled between a large mountain range and the Indus River. The village was severely affected by the flash floods in 2010, where most houses were washed away or destroyed. (36) As a part of

21 the restoration, LEDeG received money to rebuild the village and built solar passive houses, in a project that ran from 2012-2015. (36) In the same project, passive solar houses in Khardung village were also built. Khardung village is located 2 hours from Leh by car, in the Nubra district. This village is at an altitude of 4000m above sea level, and has harsh living conditions, due to the cold temperature as well as the lack of vegetation and trees. Fuelwood needs to be imported from nearby villages, forcing many villagers to resort to burning cow dung to heat their homes. 3.3.2 Structuring the Interviews When planning our interviews, we adopted the guidelines set out by the book, Den kvalitativa forskningsintervjun, translated as The qualitative research study. (37) We adopted a semi-structured interview process, where we encouraged the respondent to share their opinions and thereby gain further insights into how a Trombe Wall can affect people. Two research questions guided the interview process.

1. Does a Trombe Wall affect how people perceive their indoor climate? 2. Does a Trombe Wall affect how people allocate their time?

We then translated the two research questions into twenty-five interview questions, which we then proceeded to ask the interviewees. The full interview schedule with all questions can be found in the appendix. We recorded the interviews, and then transcribed all recordings. 3.3.3 Reliability and Validity of Results To gain as reliable results as possible, we asked all the interviewees the same question from our interview sheet. However, since we opted for a semi-structured interview method, we initiated more of a discussion, which caused many people to drift away into their own topics. Hence, all questions were not asked in the same order, nor were they worded in exactly the same way. We also tried our best to question a varied sample size, both in relation to gender and age. All interviewees lived and worked in small villages in Ladakh consisting of a few hundred people. Out of a total of seventeen respondents, ten were women and seven were men. The average age of all respondents was forty-four years. To maximize variety of age, we grouped people into four categories depending on how old they were and their gender. We defined four categories, young males, young females, all less than thirty years of age, and older males and older females, all above thirty years of age. Looking at our results, we had three young males, one young female, three older males and nine older females. The largest group is clearly older females, which we consider whilst conducting our analysis. However, managed to represent three out of four groups relatively well, with young females being the lone exception. We started our interviews by explaining who we were, what we were doing and the aim of our research project. We did this for two reasons. Firstly, to let the interviewees know who we were, and why we came to ask them questions. Our interview subjects mainly spoke Ladakhi, with some being able to speak English and, or, Hindi. Hence, our interviews were conducted in either Ladakhi or Hindi, and translated into English. In order to not loose semantics in translation, our interpreter translated answers into Hindi when she did not know how to answer in English. My knowledge of Hindi simplified and enabled this to work smoothly and gave us an opportunity to double-check what was being said.

22 3.4 Research bias The interviews were conducted with the help of an interpreter, and at risk of several potential biases. We tried our best to acknowledge these beforehand to mitigate their impact on the interviews.

Respondent • Acquiescence bias, also known as yes-saying, is a bias stating that people are more likely to agree or disagree, depending on how the question is formulated.(38) To minimize the impact of this bias, we made sure to word our interview questions as neutrally as possible. We also carefully went over the interview questions without interpreter beforehand to clarify and avoid any confusion. • Social desirability bias is a bias stating that respondents would like to answer in a way that will be viewed favorably by others. (39) This bias we saw as a potential threat, since we were strongly associated with LEDeG. LEDeG had built all the Trombe Wall houses years previously, and therefore we suspected that respondents would be hesitant to discuss any negative aspects about their housing, in case it would reflect negatively upon them in the eyes of LEDeG. To avoid this bias as much as possible, we tried to distance ourselves from LEDeG. We also made it clear that we specifically wanted to hear the good things and the bad things about living with Trombe Walls, so that we could get a better picture of how it impacted people.

Researcher • Confirmation bias, a will to analyze responses in a way to strengthen one’s own beliefs.(40) This was another realistic threat for us, since we employed an interpreter, and she might add her own interpretation of the responses in order to make the answers confirm what we wanted to hear. Furthermore, we also had to take into account that we could probably seek to confirm the answers the interpreter gave us. In order to avoid this, we were careful to strictly tell our interpreter to translate everything the respondent said word by word, without adding anything that can help us understand. This was not immediately adopted by our interpreter but was gradually improved throughout the course of the interviews and is one factor we took into consideration whilst analyzing results. Furthermore, we also employed reflexive practices in order to minimize our own confirmation bias. • Leading questions and wording bias, a bias caused by the wording of the questions or how the questions are formulated. (41) To avoid this bias, we were carefully thought through how we worded our questions. We also attempted to employ open-ended question that would encourage respondents to speak openly, and shy away from leading questions.

23 4 Quantitative Results In this section, we give an overview of the quantitative results we obtained in our study. We start of by discussing the outdoor climate of Ladakh to gain an understanding of the heating requirements that are needed. This is contextualized and compared with other countries with the help of Heat Degree Days, an established method of measuring heating need. (42) We then go on to discuss the incident sunlight on the building, and the potential energy that could be harnessed. With the heating requirements and potential energy source identified, we discuss the temperature graphs of the rooms with Trombe Walls, Direct gain technology and half Trombe Walls. 4.1 Outdoor Climate and Heat Degree Days To analyze the outdoor climate, we used an established method for gauging heating requirements, Heat Degree Days. HDD shows how many degrees multiplied by the amount of days a building needs to be heated, which gives an insight into how much energy is required to heat houses in similar climates around the world. This approach needed sufficient temperature data. Fortunately for us, LEDeG had set up a weather station on the hostel’s premises, giving us access to data from September of 2019 onwards, with one measurement every hour. Using this data, we can see that the average temperature near the hostel during February is -4.1 degrees centigrade. During the day, between 08:00 and 18:00, the average temperature is -2.6 degrees, whilst during nighttime, between 18:00 and 08:00; the average temperature falls to -5.6 degrees. To quantify the heating need for warming a room to an acceptable indoor temperature in this climate, we use the concept of Heat Degree Days, HDD. HDD uses a set base temperature, in our case 18 degrees Celsius, to see how many degrees, during how many days, a house needs external heating to achieve the base temperature of 18 degrees. Using hourly temperature measures, we can calculate HDD using the following sum,

�� = (� − �) (4.1) where � is the base temperature, and � is the temperature at each hour, and the sum of the difference of the two temperatures is evaluated for all 696 hours of February 2020. Given that we are looking at the month of February, this means that during the month, the total amount of degrees a building needs to be warmed up by is the value of HDD, divided by the days of the month. Using this calculation, we can see that HDD for our hostel becomes

�� = (� − �) = 644 ℎ�� (4.2)

The hostel needs a total of 644 heat degree-days in February. This equates to an average heating demand of 22.2 degrees Celsius, every day during the month of February. The advantages of using this measure is that it is standardized all over the world, so we can compare it to see how the energy demand in Ladakh relates to other parts of the world. Across the world, Anchorage, Alaska had 672 HDD in the same

24 period. (43) Using data that we received from Sweden’s metrological institute SMHI, we can see that the Stockholm region had a heating requirement of 430 HDD. Kiruna, situated in northernmost Sweden, required 794 degree-days whilst Lund, in southern Sweden, had 363 degree days during February 2020.(44) Hence, we can see that the heating demand for Leh could somewhat be likened to the heating demand of northern Sweden, and is also very similar to that of Alaska. In Alaska, with 677 HDD, the average energy consumption per capita spent heating one’s home for a month is 632 kWh. (45) 4.2 Incident Solar Radiation Ladakh is renowned for its abundance of sunny days, with an average of 320 sun days per year. (3) This allows for plentiful use of solar energy, which is the hostel’s only source of space heating. Hence, we can assume that the increase in temperature of the rooms is wholly accounted for by solar energy. Therefore, by getting a grasp of the incident solar radiation in Ladakh, we can see how much potential energy there is to harness. According to synenergy.com, the average solar irradiance per day in Leh, Ladakh, for the month is February is 3.77 kWh per square meter of vertical area. (46) Hence, in the month of February, the total solar irradiance would equal 109 kWh per square meter. According to the L.E.C Integration Manual, the average solar irradiance for the month of February is 125 kWh per square meter.(26) Comparing this to the energy consumption of Alaska 632 kWh, we can see that approximately six square meters of windows would be required to cover the monthly energy consumption of an average home in Alaska. This is of course impossible, as we assume a 100 % energy conversion ratio but it still serves as an indication of the possibilities of solar radiation. 109 kWh or 125 kWh per square meter, per month, is an average value of solar irradiance for the city of Leh. However, we wanted to obtain the amount of solar energy specifically available at the site of the hostel. Due to budgetary restraints, we were unable to purchase a pyranometer, which is used to measure incoming solar irradiance. We opted for a cheaper option and bought a lux sensor. Lux is a measure of brightness and is defined as the total amount of light that falls on a surface, as perceived by the human eye. (47) Luminous intensity is not a measure of energy and cannot directly be translated into watts. However, after doing some research on the subject, we discovered that there are ways to approximate the solar energy of the sun using Lux values. Based on the experimental research of Peter Michael, he describes in his paper, A Conversion Guide: Solar Irradiance and Lux Illuminance, a way to convert lux from sunlight to watt. From his research, we attempted to convert our total lux measurements to watt using the following equation derived by Peter Michael. 1 �� = ∗ �� (4.3) 119.97

Unfortunately, we were unable to record a full month’s data due to our sensors malfunctioning. However, we saw that on sunny days the lux values seemed to reach approximately the same values, and on cloudy days they were much less. Therefore, we scaled our data by the amount of sunny and cloudy days to receive a total amount of Lux for the month of February.

25 In the following graph, our measured Lux values are plotted out against time.

Figure 12: Recorded Lux values We lack data for the first days of February, the eleventh to the sixteenth and from the nineteenth to the twenty-second. Thus, we have data for nineteen out of twenty-nine days in February. Assuming that the missing days are equal to the average of the observed days, and converting Lux to Watts, we receive 77.3 kWh for the month of February. This is lower than the average value of 109 kWh proposed by synergy.com but serves to give an indication of the amount of solar energy that is available in the region. In India, the cost of purchasing 77.3 kWh of space heating in February of 2020 would be approximately 150 to 200 rupees. (48) This may be an overestimate, as we assume all the sunlight will be used to heat the room. On the other hand, we do not take into the account the addition insulation a Trombe Wall provides, which may balance out this factor However, it does give an indication that one square meter or Trombe Wall may be able to save upwards of 150 rupees per month (20 SEK/month) in heating costs. Given that a Trombe Wall for each room is about 6-7 square meters, this would imply that a whole Trombe Wall could save around 1000 rupees per month (130 SEK/month), and 12 000 rupees per year (1600 SEK/month). 4.3 Temperature Graphs We measured data from four Trombe Wall rooms, two rooms heated by Direct gain and two half Trombe Wall rooms. Starting off with the rooms in figure 11, we can see that the temperature rarely drops below fifteen degrees during nighttime, and seldom rises above twenty-five degrees during the hottest hours of the day. The one exception to this is room ten, but that room was inhabited during the first part of our measurements, naturally raising the average temperature of the room.

Figure 13: Temperature of Trombe Wall rooms If we take a closer look at rooms nine, four and three, we see that on average, the temperature seems to oscillate around a mean temperature of 17.4 degrees Celsius. This is slightly colder than the legally acceptable indoor temperature supplied by a third party in Sweden, which is twenty degrees Celsius. (49) With the addition of a small radiator, the average temperature could possibly reach twenty degrees. However, twenty degrees Celsius is the lowest temperature allowed, not the lowest average temperature. Hence, from these graphs it is clear that Trombe Walls contribute to a more comfortable indoor temperature, however, alone they are not enough to heat up a single room to the legal temperature a housing landlord must provide in Sweden. Comparing the Trombe Wall rooms to the rooms heated by Direct gain technology, we see that the temperature is much more volatile when a Trombe Wall is not present.

Figure 14: Temperature of Trombe Wall rooms

Figure 15: Temperature of Direct Gain rooms In these rooms, the extra windows allow more sunlight to directly pass into the room, heating the room to very high temperatures during the day. However, these windows also allow the warm air to escape during the nights, and the temperatures plunge below ten degrees. This creates a more hostile indoor environment, where the days become too hot and the nights too cold. From these graphs we can distill on of the most important factors of the Trombe Wall, the ability to store and slowly dissipate energy into the room. Both of these rooms have the same amount of window area, and are located very close to each other, implying that on average, they will receive the same amount of incident solar radiation. Additionally, the floor and the inner walls are made of the same material. However, since the Trombe Wall manages to store the heat unlike the Direct gain rooms, a much more comfortable indoor temperature is achieved.

28 Comparing these two types of rooms with half Trombe Wall rooms, we see that a half Trombe Wall resembles Direct gain rooms much more than Trombe Wall rooms. Unfortunately, our sensor kits malfunctioned so we were only able to collect data for

Figure 16: Temperature of Half Trombe Wall rooms parts of the month. Still, we can see that the temperature varies wildly, plunging below ten degrees at night and hitting thirty degrees during some warm days. Looking at the average temperatures of the three different types of rooms, we see that they differ substantially, with the Trombe Wall being the warmest and the half Trombe Wall the coldest.

Figure 17: Average room temperature

29 This may be because the Trombe Wall can retain the heat, which brings up the average temperature, unlike in the other rooms, where much heat escapes during the nights. What is most interesting to note is that the Direct gain Room has a higher average temperature than the half Trombe Wall Rooms. This seems counter intuitive, seeing as one would assume the half Trombe Walls would retain more heat than use windows. However, these results must suffer from the fact that we only had partial data from the half Trombe Walls. Therefore, a likely explanation for the Trombe Wall rooms is simply that we did not collect sufficient data, which thus skewed the results. One thing that also needs to be taken into consideration is that the half Trombe Wall rooms and the Direct gain rooms were on the side of each wing. Hence, they had two walls in contact with the cold air outside, whilst the Trombe Wall rooms only had one wall. This would naturally lead to less heat flow out of the room, thus raising the average temperature. Looking at the average temperature graphs for the three types of rooms, we see that yet again, the Trombe Wall rooms hold a more stable temperature compared to the other two rooms.

Figure 18: Average room temperature We can also note that the average temperatures for the half Trombe Wall and the direct gain room are very similar. This leads to the idea that it might be futile to build half Trombe Wall rooms, since they are significantly more expensive than the direct gain walls, but do not seem to make much difference when it comes to indoor temperature. Since these two types are so similar, we will continue our analysis by simply comparing Trombe Walls with direct gain rooms. Since we did not manage to obtain sufficient data from the Half Trombe Wall, and they correlate strongly with direct gain rooms, we decided to omit them in the rest of our analysis. Regarding the outdoor climate, we can see that both rooms are significantly warmer than the outdoor temperature. On average, the temperature difference between the Trombe Wall rooms (17.44 degrees) and the outside temperature (-4.2

30 degrees) is 21.64 degrees. Contrasting this to the average temperature difference for the direct gain rooms, we find that it is lower, at 19.00 degrees.

Figure 19: Indoor and outdoor temperature

Arguably the most important measurement is the amount of time a Trombe Wall manages to sustain a comfortable indoor temperature. In this case, we define a comfortable indoor temperature as between 15 and 25 degrees. This is low in comparison to other countries around the world, where indoor temperatures seldom drop below 20 degrees, but will suffice in this study. Below follows a graph of the average temperature of the Trombe Walls and direct gain rooms, plotted with the constraints of 15 and 25 degrees. We can see that the Trombe Wall rooms are mostly between 15 and 25 degrees, whilst the direct gain room varies much more. Computing the percentage of time each room spends in the zone of preferred temperature, we see that the Trombe Wall rooms spend 83.2 % of their time in that temperature range, whilst the direct gain room only spends 22.7 % in the temperature range.

Figure 20: Temperature span in comfortable temperatures

31 This is shown visually by the following graph, where a binary description of whether a room is in the desired temperature range is plotted against time. Note also that no data before the fourth of February was collected, and therefore that section is blank. This clearly shows the most effective aspect of the Trombe Wall, the ability to sustain a comfortable room temperature throughout the day. However, this does come at an extra cost compared to direct gain technology. Furthermore, Trombe Walls by themselves have a hard time fulfilling inhabitants’ energy needs, as they often need to be complemented by other sources of heating, thereby not reducing equipment costs, only fuel consumption costs.

Figure 21: Binary graph of pleasant temperature Overall, we can reinforce the conclusion that with the same amount of incoming solar energy, a Trombe Wall is more effective at distributing energy throughout the day. This means that the average temperature in the room will increase, as well as never dropping or rising to far above the range of comfort.

32 5 Model of a Trombe Wall Based on the qualitative and quantitative results Trombe Walls seem to viable heating solution in Ladakh, but how would a Trombe Wall fare in different climates? This section takes a brief look at this question by analyzing a simple model of a Trombe Wall that we constructed. First the model is discussed, how it has been constructed and the input variables. Then, results from the model are compared with our measured values in an attempt to gauge the accuracy of the simulation. Lastly, the model is rerun with different climactic data in an attempt to see how the Trombe Wall would fare in a different climate. 5.1 The Construction of the Model We constructed our model with the help of Microsoft Excel, setting up a large system of equations that linked together two input variables, outdoor temperature and solar irradiation, with the output value, indoor temperature of the Trombe Wall room. When constructing this model, it must be noted that we decided to make several simplifications of reality in order to ensure that we could finish the model in time. We studied the temperature of a single room, heated by sunlight passing through a Trombe Wall. We ignored bordering rooms and treated the Trombe Wall and the room as a closed system. We also adopted the adage, “All models are bad, but some are useful”, and went about constructing the model accordingly. The model consists of 2 input variables, that produce one output value. In addition, we have also input parameters that can model can be easily adjusted. In total, we have 47 input parameters that can be tweaked, ranging from the dimensions of the room to the material of the walls to the absorptivity of the window. Here is the list of all input parameters.

1. �� (�^2) 2. �� ℎ��, (�^2) 3. �� (�^3) 4. �� , �� (�^2) 5. ��ℎ (�) 6. �� , �� (�^2) 7. ��ℎ (�) 8. ��ℎ �� (�) 9. ��ℎ� (�) 10. �ℎ�� (�/ � ∗ �) 11. �� − 12. �� (�/ �� (�^2) �^2 ∗ �) 13. �� (�^2) 14. �� (�^2) 15. �� (�^2) 16. � �� (�/�^2 ∗ �) 17. �� (�^3) 18. �ℎ�� (�/ ��) 19. �� (��/�^3) 20. �ℎ�� (�) 21. �� (�/ 22. �ℎ�� (�^2/ �� ∗ �) �) 23. �ℎ�� (�) 24. �� (�^2/ �) 25. �ℎ�� (�^26.2/ �ℎ�� (�) �) 27. �� (28.�/ �� (�/��) �� ∗ �) 29. �� (��/ 30. �� 20 �� ^3)

33 31. �ℎ�� (�/ 32. �� (�/ ��) �� ∗ �) 33. �ℎ�� (�) 34. �� (��/�^3) 35. �� ℎ��ℎ �� (%) 36. �ℎ�� (�) 37. �ℎ�� 39. �� (�^3) 38. (�/�) 40. �ℎ�� (�/41. �� ) 42. �� ℎ��ℎ ��43. (� ) �� ℎ�� (�^3) 44. �� 1 45. �� (�/ (�� ∗ �) 46. �� 2 47. �� /�^3

48. �� ℎ�� 1

Given these input parameters, we can tweak the model, so it fits our needs, changing the size of the room, adjusting the material the room is made of and so forth. We start our calculations with the incident solar radiation on the windowpane. We assume a transmittivity of 0.9, which we use to calculate the energy in

� = 0.9 → � = �� (5.1)

This solar radiation then proceeds to enter the airgap and heat the Trombe Wall. We assume that all energy hits the outer layer of the wall. This outer layer of the wall is in thermal equilibrium with the air in the airgap, as well as the rest of the wall, acting as a storage of energy. The energy balance between the outer wall and the air is given by a simplification of Fourier’s Law,

� = ��(� − �) (5.2)

Additionally, we calculated the heat loss through the window based on the temperature of the air gap and the outdoor temperature. This is of course a simplification, as we first of all assume that all energy is absorbed into the wall, and then the wall heats the air. Additionally, we approximate a double paned window as a single pane by calculating its total U-value. However, these simplifications were deemed necessary to simplify calculations. The heat loss through conduction is modelled by the following equation

� = �� − � (5.3)

To simplify, we assumed that the heat loss from the window was in due from convection and conduction. In reality, convection currents affect conduction, thus creating greater heat loss. However, we decided to simplify this physical process into two parts. To calculate the heat loss from conduction, we determined the Raleigh Number, given by the following relationship:

��(� − �)� �� = (5.4) ��

34 To calculate the heat transfer coefficient, we also needed to Prantl number, the ratio of momentum diffusivity to thermal diffusivity. We looked up the Prantl number for air at 20 degrees given the air pressure of 650 hPa, as measured by our pressure sensors. (50) Using the relation proposed by Churman and Cho, we calculated the heat transfer coefficient for a vertical plane. (51)

⎛ ⎞ ℎ ⎜ 0.387�� ⎟ ℎ = ⎜0.825 + ⎟ (5.5) � ⎜ ⎟ 0.492 ⎜ ⎟ 1 + �� ) ⎝ . ⎠

With the heat transfer coefficient, we calculated the total heat loss through the windowpane � = ℎ�(� − �) (5.6)

Hence, we now achieved energy balance between energy into the Trombe Wall’s air gap and energy out. However, this was achieved with the following simplifications. We assume that no heat is lost to surrounding materials and nor do not take the wind into account The air in the airgap is warmed as it comes in thermal contact with the outer wall, causing a flow of air. The velocity of air flow is modelled with the help of Ruiz et al.’s equation, derived in A Calculation Model for Trombe Walls and its use as a Passive Cooling Technique. (52)

2∆� � = (5.7) � � � �(� + � + � � � �

The pressure difference can either be calculated from thermal specifications of air and temperature differences or measured. Since we had access to pressure measurements from our sensors, we decided to utilize our data to complement our model. The total air flow dictated how much air would flow into the room through the holes in the top, and how much air will be sucked in through the bottom hole. At each time step, the air had a certain temperature. Herein hides an important simplification, as we assume that all the air in the airgap is of constant temperature. Physically, this deviates from reality as on one hand we assume that the temperature difference causes the air to rise, and on the other hand we assume constant air temperature in the air hap. However, we assume that the energy from the outer layer of the Trombe Wall heats up the air in the air gap, as well as the air sucked in from the room, to a constant temperature. We calculate a pseudo air velocity, and then use that air flow to determine the amount and temperature of air entering the room.

35 Energy also passes from the outer layer of the Trombe Wall into the rest of the Trombe Wall and towards the room. The time it takes for the energy to pass through the Trombe Wall is given by the lag time, which is more thoroughly discussed in the literature section.

1 24 �� = ∗ � ∗ = � (5.8) � 2 3600 ∗ � ∗ � ∗ �

Additionally, from the perspective of the room, some heat is lost in the process of the energy wave traveling through the wall, and this is modelled by the dampening factor, which has also been touched upon in the literature section.

⎛ � ⎞ � �� = �� −� ∗ = (5.9) ⎜ � ⎟ � 24 ∗ 3600 ∗ � ∗ � ⎝ ⎠

Hence, we now have an inflow of air energy into the room, from both the Trombe Wall and the airflow, which we use to calculate an energy balance in the room. The temperature of the room is calculated by the total energy in the room, divided by the specific heat constants and mass of the air in the room and all the thermal mass. 5.2 Comparing Calculated Results with Measured Results Based on the results from our model, we obtain the following graph for the indoor temperature of the room, which we plot together with our measured results against the hours of February on the x-axis.

Figure 22: Measured temperature vs calculated temperature

As we can see, the two temperature graphs look similar during the middle of February but differ more towards the beginning and end of month. We lack data from our measurements in the beginning of February, but the model predicts significantly lower temperatures than measured. This may be in part due to the fact that outdoor temperature increases about this time. However, it is more likely that there is a flaw in the model, causing an increase in temperature throughout the month. Furthermore, we can see that our model has greater temperature volatility per day compared to our measured results, which may be due to a lack of thermal mass in the model. To improve the model, one would need to carefully examine the boundary conditions and create a more thorough model of the room the Trombe Wall is situated in. The thermal properties of the material of walls, floors and ceilings need to be found and successfully modelled. Additionally, several other parameters need to be more carefully calculated such as the global heat loss coefficient and heat loss through walls, ceilings and floors. Due to these challenges and our limited amount of time, we decided to leave the development of the model, and the calculation of yearly indoor temperature, to a future project where we have a longer time span.

6 Qualitative Results This section details the responses we received from conducting our interviews and is organized according to our two research questions. Interview responses to each research question are discussed, and the outcomes summarized in this section. 6.1 Interview Responses to how People Perceive Changes in Indoor Climate Starting with the fundamental question of temperature increase, all seventeen interviewees, reported an increase in indoor temperature after the installation of the Trombe Wall. They described how this increase in temperature led to a plethora of positive outcomes. First and foremost, five respondents reported that they now had the possibility to leave water overnight. Before, the temperatures would dip so much during the night that water would freeze, causing several problems for the inhabitants. However, due to the stable temperature due to the Trombe Wall, they could now leave water in jugs overnight, even during midwinter. One elderly woman reported that the best part of her Trombe Wall was that she could now leave water in her seven prayer bowls overnight. In the morning she could wake up and pray directly, without having to refill the bowls, which previously had been a big hassle. Secondly, the warmer temperature made it more pleasant to be indoors. Four interviewees responded that they were happier to be at home because of the warmer indoor temperature. Five people said that they were happy because they could now grow plants indoors, which had previously been impossible due to the cold. Also, the difference between nighttime temperature and daytime temperatures significantly decreased. Three respondents described how they now only needed one blanket to sleep at night, whilst before the Trombe Wall, they needed two or three blankets to escape the cold. Thirdly, two respondents correlated the warmer indoor temperatures with a decrease in illness. They described how in their previous house, family members were more prone to suffer from the common cold, headaches and other respiratory diseases. After the introduction of the Trombe Wall, they were much healthier they said. Lastly, one woman described how the increase in air temperature had brought a sense of security and relieved stress. Before, she had been hesitant to leave her older mother alone in the house with her small children. She was worried that her mother would be too cold without heating the stove, and additionally, she fretted about her small children burning themselves when they lit the stove. With the introduction of the Trombe Wall, she could light the stove before she left for work, and the room would still be warm when she came back from her work. This lifted a weight off her shoulders and allowed her to pursue a full-time job.

38 6.2 Interview Responses to how People Perceive Changes in Indoor Climate Another positive aspect was the increase in air quality. Before the Trombe wall, respondents had to fire their bhukari, a Ladakhi stove, several times during a day to achieve a passable indoor temperature. This caused indoor pollution, as the stove would let out smoke in the room. After hearing that this was a prevalent problem for several respondents, we decided to measure the indoor air quality before and after using the heating stove, the bhukari. Using a PMS5003 air quality sensor that we had purchased, we measured the particles in the air both before and after lighting the stove. Before lighting the stove, the ppm count, particles per million, was stable at around 40 ppm, which is classified as good, according to the Air Quality Index (AQI) of India. (53) After lighting the stove, the ppm spiked before decreasing steadily. Below is the graph of air quality, measured in ppm, during the process of lighting the stove.

Figure 23: Graph of temperature and PPM As we can see, the when the stove was lit, there was a sharp spike in air particles. The ppm value rose briefly to over 1800 ppm before dropping to around 1000 and steadily decreasing from there. According to AQI, anything above 500 ppm is classified as hazardous.(53) Prolonged exposure to such air particles has been linked to causing severe respiratory diseases, as well as cancer and other harmful diseases.(54) This increase in air particles caused by lighting the stove correlates well with the respondents’ answers, as thirteen interviewees reported that their quality of air had improved after the implementation of the Trombe Wall. One male interviewee connected the improvement of air quality with a general increase in respiratory health. He described how, earlier; his family members were more prone to nasty coughs that would linger on for a long time. Others described how black smoke would fill the room during winters, and when they used the bhukari repeatedly, a layer of sooth and grime would blacken the wall and prohibit sunlight from entering through the windows. All respondents said that they still had to rely on the bhukari to top up the indoor temperature with the Trombe Wall. Hence, we can see that Trombe Walls had

39 reduced the amount of times a bhukari needed to be used during a year but had not completely satisfied the heating demands to the extent that respondents felt warm enough with just the Trombe Wall. The introduction of the Trombe Wall also improved the brightness of the room as the Trombe Wall allowed for larger windows than inhabitants had before. When LEDeG built the houses, they put insulation in the walls, allowing the room to retain its heat better. The houses were also constructed facing south in order to absorb as much sunlight as possible. With the Trombe Wall raising the general temperature of the room, respondents could afford to have bigger windows without suffering too much heat loss. These factors resulted in brighter rooms that allowed plants to thrive. Overall, this was a positive factor noted by seven respondents. Thus, we can see that a combination of many factors led to significant improvement in the quality of life for the individuals. Another positive aspect resulting from firing the bhukari less was the saved fuel. In Pallam village, people either bought wood or cut it themselves in the forest. Most respondents said that they used about half as much fuel as before the Trombe Wall. One man said that his fuel costs decreased from 20 000 (2600 SEK) rupees per year to 8 000 (1050 SEK) rupees per year, slicing his fuel costs in more than half. Two young males who collected wood said that they saved one to two hours per day, that they now used to collect other sources of income. Aside from saving time and money, this also led to fewer injuries. One elder male reported that they would sometimes injure themselves whilst cutting wood in the forest for extended periods of time. But when they only had to collect half the amount of fuel wood, the risk of injury decreased significantly as they did now have to collect wood while they were exhausted. In Khardung village, the high altitude and barren vegetation makes it impossible to collect enough fuel wood. Instead, respondents said they had to resort to burning cow dung. To gather cow dung, two older women described how they had to walk behind the cows while they grazed, dry their dung and then bring it back to the village. By installing a Trombe Wall, they could usually save about half their consumption of cow dung. This made it much easier to transport the cow dung back to the village, and according to one woman, saved her a significant amount of personal energy. 6.3 Overall Responses Most respondents had no negative comments about the Trombe Wall technology. Everybody agreed upon the fact that it greatly helped them and their family, in different ways. However, most could think of improvements that could be made. Many wished that LEDeG had built the Trombe Wall room slightly bigger or built an additional Trombe Wall for their bathroom. Others wanted a bigger Trombe Wall room so that they could install their cooking stove there and use as a kitchen. In Trombe Wall houses in Pallam village, one male described how the walls would crack in the same places due to faulty construction. Overall, we were struck by how positive the respondents were about Trombe Walls. In part, this may have been due to respondents associating us with LEDeG, and being grateful for the help they received years ago. We tried our best to actively distance ourselves from LEDeG, but still people had only positive things to say about the Trombe Walls. This leads us to the conclusion that Trombe Walls in Ladakh seems to be a huge success, but also present us with an additional question. How economically feasible is it for a low-income villager to pay for a Trombe Wall by themselves?

40 7. Economic Feasibility The quantitative and qualitative results point to the fact that Trombe Walls seem to be more efficient than DG technology. However, the question of economic feasibility still remains. If the technology is too expensive for villagers, it will not be available to a large majority of Ladakhis, as installations would be dependent on external funding. To analyze this, a cost-benefit analysis was conducted. I start by discussing how Trombe Walls are built, and the cost required. I then continue by calculating the equivalence of the amount of money that can be saved by using less fuel, in order to conduct an Internal Rate of Return analysis. This analysis will then be used in a discussion to see if it is possible for villagers to invest in a Trombe Wall.

7.1 Cost of Building a Trombe Wall When talking to Chemet Rigzin, the lead engineer of LEDeG, or his assistant Tashi Noorbo, they estimated the cost of a Trombe Wall to be around 50 000-100 000 rupees (6500-13 000 SEK). (9) The main expense is born by the materials of the wall. The wall needs to be a certain thickness, between 20-30 centimeters, and should preferably be constructed from stone or wood. A newer building technology using rammed earth, has proven to be more efficient at restricting heat loss, but also proves to be significantly more expensive, and will therefore not be considered in this analysis. Aside from the cost of the materials, one also needs to pay laborers for their time. Another big factor to take into consideration is where the Trombe Wall is being built. In Khardung village, which is approximately a two-hour car ride away from Leh, getting hold of basic materials to build a Trombe Wall can be expensive, and difficult, due to transportation costs. 7.2 The Trombe Wall as an Investment Based on our interviews, many respondents said they had many friends who wanted to install a Trombe Wall but lacked the necessary funds. Therefore, we will consider if a Trombe Wall is a profitable investment. Our premise, based on our interviews, is that installing a Trombe can cut the fuel consumption in half. We will also make the assumption that the choice of fuel is wood, because that is easy to convert to monetary terms. One quintal, or 100 kilograms of wood, costs approximately 1500 rupees. Based on our interviews, an average Trombe Wall house uses about 500 kilograms of wood per year, as supposed to 1000 kilograms of wood annually to heat a house that does not have a Trombe Wall. Given that one saves 500 kilograms of wood per year, this would equate to 7 500 rupees of savings per year (1000 SEK/year). However, we are not accounting for the opportunity cost saved by spending less time traveling to the market to purchase fuel. Based upon our interviews, most people use the local stove, bhukari, for six months, from October to April. During this time, most people use around 500 kilograms of wood. Simplifying by assuming a constant wood consumption, this equates to around seventeen kilograms of used wood per week. Since most villagers did not have access to a car, they have to walk to the market, and thus carrying more than seventeen, or maybe twenty kilograms of wood per trip seems unrealistic. Therefore, let us assume that villagers have to travel to the market once a week to collect wood, instead of twice a week as before. This assumption implies that people will walk two times to the market instead of carrying double the weight, which might prove unrealistic. However, the more likely outcome

41 is probably that two people make the journey to the market, and then our reasoning would hold. Furthermore, we estimate that it takes thirty minutes reach the market. This would imply a one-hour round-trip every week, for 30 weeks, totaling 30 hours of unpaid labor time. From our interviews, we heard that hourly salary for an unskilled laborer is around 50 rupees per hour (13 SEK/hour). Computing the total cost of buying wood from the market then equals 1500 rupees per year (200 SEK/year), a substantial additional cost in this setting. Thus, the total savings would total to 9 000 rupees per year (1200 SEK/year). Additionally, air pollution has been linked to forcing people to take sick days due to various illnesses. According to Air Pollution and Sickness – Is there a correlation? by Hansen and Selte, an experimental study relating how sick leave is correlated to bad air quality, a one microgram increase in �� concentration raises the average sick-leave by 0.02 percentage points. (55) Hence, given that the average value of heating a bhukari over a long period of time is around 200 ppm, this would equate to an additional 4 % sick leave. In one year, there are on average 260 working days, which leads to an additional ten sick days per year. According to interviews, many respondents reported earning around 500 rupees per day, implying that ten extra days of sick leave means a fiscal loss of 5000 rupees per year. Totaling up the savings, we argue that a Trombe Wall saves approximately 14 000 rupees per year (1 900 SEK/year) in reduced fuel costs, timesaving and avoided health costs. This correlates well with one interviewee, who recalled his savings from just less purchase of fuel wood was approximately 10 000-12 000 rupees per year (1300- 1600 SEK/year). Therefore, let us continue with our assumptions and adopt our estimated value of 14 000 rupees per year (1900 SEK/year). If this is the amount of money saved per year, and the total cost to build a Trombe Wall is 75 000 rupees (10 000 SEK), the total payback time for the Trombe Wall would be 5 years and 4 months. Of course, this varies depending on the total cost of the Trombe Wall. If the Trombe Wall would cost 50 000 rupees instead, the payback time would drop to 3 years and seven months, and if the cost would rise to 100 000 rupees, the payback time would rise to 7 years and 2 months. The costs of the Trombe Wall are given by Chemet Rigzin as previously stated. Hence, we can estimate that the payback time for the Trombe Wall will be between 3 and 7 years. However, payback time is a rudimentary method to gauge investments, as it does not take into consideration the alternative cost of capital. Instead, the Internal Rate of Return (IRR) method presents a more developed way to consider the time value of money. To use the IRR method, we need to define a weighted average cost of capital, wacc. The wacc is given by the following equation

� � � = ∗ � + ∗ � ∗ (1 − �) (7.1) � + � � + � ∗ where, • � = �� • � = �� • � = �� • � = �� • 1 − � = �� ℎ��

42 However, given that we assume that the investment is completely financed by a loan, and the inhabitants do not benefit from a tax-shield of investment, wacc simplifies to just cost of Return on Debt, as everything else is simplified away.

� = � (7.2)

To find the Return on Debt, we researched interest rates in Leh. According to MyLoanCare.in, the cheapest available personal loan is with SBI bank, with an interest rate of 10. 55 %. Assuming the investment is borne fully by loans, the wacc would then equal the interest rate of 10.55 % (56). This is rather high, so we therefore contacted IREDA, India Renewable Energy Development Agency, a non-banking financial institution aimed at promoting renewable energy in India (57). Their lowest interest rate for energy efficient loans was at 9.8 % (58). If we assume that a Trombe Wall will be in use for twenty years, we can use an Internal Rate of Return analysis to find the breakeven rate of return. In this case, we assume steady cash inflows of 14 000 rupees per year (1900 SEK/year) for 20 years, and an initial cost of 75 000 rupees up front (10 000 SEK). Using this information in the annuity formula we set it equal to zero to find the Internal Rate of Return.

14000 1 0 = 75000 + 1 − (7.3) � (1 + �)

Solving for r gives the internal rate of return to be 17 %. Thus, we can see that the interest rates of around 10 % make this project a positive NPV project with a time horizon of twenty years. Comparing this with different lifetimes of the Trombe Wall, figure 24 depicts how a Trombe Wall with a lifetime of 10 years will have an IRR of 13 %, and with a lifespan of 40 years the Trombe Wall will have an IRR of 19 %.

Figure 24: Graph of Internal Rate of Return

43 Figure 24 show the NPV plotted against the IRR. The breakeven point occurs when the graph crosses the x-axis, thus implying that a higher rate of return will yield negative NPV. From our analysis, we see that if a Trombe Wall last for 20 years, it is a positive investment if the individuals required yield is less than 17 %. To put this into perspective, one would have to find out if villagers have a higher required yield than 17 %. Given the current fiscal conditions of Indian loan rates which are around 10 %, this seems improbable, which suggests that the Trombe Wall is a profitable investment given our conditions. However, there are also several difficulties when it comes to financing. First and foremost is the fact that the bulk of the payment needs to be paid at the start of the investment, whilst the savings will take several years to accumulate. Therefore, a person interested in investing in a Trombe Wall will need great solidity, or the ability to take a loan from the bank. Taking a loan may be hard for people living in rural areas, with banks usually located in the city. Whilst thinking of the Trombe Wall as an investment, it is also important not to forget that the Trombe Wall usually increases the quality of life for the inhabitants, and if that was to somehow be factored in the economic valuation, the results may differ enormously. From a societal perspective, there are several advantages to installing a Trombe Wall. If one correlates Trombe Walls with a general increase in health, then Trombe Walls may contribute to healthier individuals that take less sick leave and visit the hospital fewer times pear year, contributing to socio-economic returns. Furthermore, if individuals use less fuel wood to heat their house, this will reduce deforestation and reduce costs of caring for new forests. Therefore, one could argue that the government should provide subsidized loans for the villagers of Ladakh to build Trombe Walls. However, further discussion on the subject is beyond the scope of this thesis and will be left for further studies.

44 8 Analysis of LEDeG’s Trombe Walls Our quantitative results are based on measurements from LEDeG’s Trombe Walls, and to verify these results, we will discuss how well the Trombe Walls have been constructed. This is important because if the Trombe Walls LEDeG are faulty in some way, that would skew our results, thus preventing us to correctly gauge the Trombe Walls effectiveness. To verify if the Trombe Walls were constructed in the right way, we will follow the guidelines set out by the L.E.C Instruction Manual for building Trombe Walls. Firstly, we examined the thickness of the walls to discuss the lag time. We will then continue by analyzing the dampening of Trombe Walls, and compare this to the temperature graphs to see if we can see correlations. Lastly, we will analyze the total amount of window glass for each Trombe Wall and see if this is sufficient to heat the size of the rooms. 8.1 Thickness of Trombe Walls The reason the thickness of the Trombe Wall matters is because it affects the lag time. The lag time, which was discussed in the literature section, is the time it takes for solar energy to pass through the Trombe Wall. Depending on the thickness and material of the wall, heat will take a certain amount of time to pass through. We measured the thickness of the Trombe Walls to 18 centimeters. Based on recommendations from the L.E.C Instruction Manual, they advise that the average thickness should be around 20-30 centimeters In our case, the optimal solution would entail a lag time of around 9-12 hours. During February, on average the sun rose at 7:00 in the morning, and set at 18:00 at night. (59) This means that the first rays of sunlight will start hitting the wall at around 8:30- 9:00 in the morning. If the lag time is around twelve hours, the heat generate by the rays of sunlight will pass through the wall at 19:30-20:00, and continue to provide heating for an additional 8 or 9 hours. This would satisfy the heating demand during the night. The equation for the lag time of a Trombe Wall is thoroughly explained in the literature section and is given by 1 24 �� = ∗ � ∗ = � (8.1) � 2 3600 ∗ � ∗ � ∗ � where • � = �ℎ�� [�] • � = �ℎ�� ℎ� �� [ ] ∗ • � = �� ℎ� �� [] ! • � = �� [ ] (∗] • � = �� [ℎ��]

In our case, the thickness of the wall is 0.18 ��. The wall is made of mud, with a thin coating of paint. Based on values from the L.E.C Integration Manual, (26) as well as from research done by Fgaier et al. the thermal conductivity of a mud wall is around 0.2 . (60)The density of a mud wall is 1788 , and the specific heat ! capacity of the wall is 545 . Computing these values, we find that the lag time is ∗ approximately 9 hours and 10 minutes. Looking at our lux data, we see that the first

45 rays of sunlight hitting the Trombe Wall appear at around 9:00 in the morning. Given our lag time, the first heat wave will pass through the wall and into the room around 18:10. This is just after the sunset, and the temperature starts to dip. Hence, the Trombe Wall is able to maintain a stable temperature throughout the day, and into the night. However, given that sun sets at 18:00 in the evening, the heat wave will finish passing through the wall at 03:10 in the morning. Looking at our temperature data, we can see that this corresponds relatively well with the coldest period of the Trombe Wall, which is during 03:00-09:00 in the morning. In the following graph, we can see the average temperature for the Trombe Wall rooms and the direct gain room for each

Figure 25: Graph of temperature per hour hour of the month of February. Here we see the temperature decreasing from 01:00 at night until 09:00 in the morning when the first rays of sunlight hit the wall. This coincides rather well with the calculation of our lag time. However, we also see a strong correlation between the outdoor temperature and the drop in indoor temperature, making it hard to say if the decrease in indoor temperature is mainly due to the lag time, the outdoor temperature or a combination of both. However, dampening is another important factor to consider whilst analyzing the thickness of the wall. Damping is a phenomenon where the amplitude of the heat wave will decrease as it passes along through the wall. It is therefore important not to build the Trombe Wall to thick, as energy is dissipated in the process of heat transfer and is not available to heat up the room. The equation for the dampening process was further discussed in the literature section, and follows here.

⎛ � ⎞ � �� = �� −� ∗ = (8.2) ⎜ � ⎟ 24 ∗ 3600 ∗ � � ∗ � ⎝ ⎠ where,

46 • � = �ℎ�� [�] • � = �ℎ�� ℎ� �� [ ] ∗ • � = �� ℎ� �� [] ! • � = �� ℎ�� [ ] (∗] • � �� = �� ℎ� ℎ�� [%]

Using the same constants for the materials of the wall, � = 0.2 , ∗ " � = 1778 ! and � = 545 , we find that the dampening factor, = 9.1 % ∗ # We can see that the amplitude of the heat wave is reduced by 9.1 %. Given these two parameters, lag time and dampening, we are faced with an optimization problem. We see an acceptable lag time between 8 and 12 hours, given the path of the sun in Ladakh during the winter. Given this constraint, we can optimize our dependent variable, wall length, in order to minimize our dampening factor. Using Excel’s solver function, we find that if the Trombe Wall is 23.6 centimeters, the dampening factor drops to 4.3 %, and the lag time reaches 12 hours. Here we see that we reduced the energy loss at the expense of building a slightly thicker Trombe Wall and a significantly longer lag time. Hence, we are faced with a difficult optimization question. LEDeG could have built the Trombe Walls slightly thicker and reduced the heat loss, but they probably reasoned that they would rather value a shorter lag time so the rooms would become warmer during the evening, as compared to having three hours after the sun sets and before the heat wave reaches the room. 8.2 Window Size in Trombe Walls Another important aspect to consider when building Trombe Walls is the size of the window. Window size is yet another optimization problem between allowing adequate sunlight to light up the room, whilst minimizing heat loss through the glass. The equation for the optimal window size is presented in L.E.C Integration manual and is a question of window glazing and floor size. According to the manual, the optimal R-value should be between 10-12 % in Ladakh.

�� = = = 10 �� 12 % ��

Given that the Trombe Wall rooms are 3.12 � � 2.30 � = 7.2 �. The glazing area is defined as the area of glass in the windows, calculated as the total area of windowpanes subtracted from the total area of the window. For our Trombe Wall rooms, this value is 5.52 �.

�� 0.47 � = = = 6.6% (8.3) �� 7.2

This is below the recommended 10-12 % in the book, which means that the room might not receive enough sunlight to become bright enough. However, from a heating perspective, the wall should suffice.

47 8.3 Overall Conclusion of Trombe Walls To summarize this section, we can see that the Trombe Wall rooms LEDeG built seemed to be in accordance with the recommendations from the L.E.C Integration Manual. We can conclude that the thicknesses of Trombe Walls are well dimensioned. One could argue the walls should be slightly thicker in order to reduce energy loss, but on the other hand, it is probably more beneficial to have sufficient heating during the evening instead of when a family is sleeping. Furthermore, the window size might be slightly too small in terms of brightness, but from a heating perspective it should suffice. This means that we can improve the reliability of our results. Given that these Trombe Walls mostly follow along the guidelines of how Trombe Walls should be built in Ladakh, we can argue that building new Trombe Walls will most probably record similar results if the climate is comparable.

48 9 Further Development of Trombe Wall Based upon our research, Trombe Walls raise the indoor temperature, but not enough to bypass using an additional form of heating. However, if Trombe Walls could be developed, and thus raise the indoor temperature by three or four degrees more, they could push to achieve a minimum temperature of twenty degrees. This is the minimum legal indoor temperature in Sweden, and also other parts of the world. (61) Then Trombe Walls might become effective enough to use without any other source of heating. As we saw in our qualitative study, this will likely bring even more positive effects for the inhabitants, and also might make a Trombe Wall a more appealing solution for others. To develop this idea, we were in talks with Chemet Rigzin, lead engineer of LEDeG. Based upon his knowledge, and other sources of information, we have come across several promising ideas for the development of Trombe Wall technology. Given that a Trombe Wall looks like the following picture, there are several ways to improve the design.

Figure 26: Schematic view of Trombe Wall The holes in the bottom and top of the Trombe Wall are there to allow the possibility of air ventilation. When air in the Trombe Wall gap heats up, the density decreases, causing the air to rise and be pushed out to the room from the hole at the top of the Trombe Wall. This will create a pressure difference, causing the cold air to be sucked into the bottom of the Trombe Wall. This circulation of air is excellent to increase the temperature of the room but relies of the principle that the air in the Trombe Wall gap is warmer than the air in the room. During nighttime, the air in the Trombe Wall Gap may be colder than the air in the room, as it is in contact with the window and the cold outdoor air. According to the second Law of Thermodynamics, heat will travel from hot bodies to cold bodies, and hence warm air inside the room will attempt to heat up the colder air in the Trombe Wall gap. This is the reverse of what a Trombe Wall usually aims to achieve, as it will decrease the temperature in the room when it is colder outside. To combat this problem, the L.E.C manual suggested that one builds flaps to cover over these holes. During the daytime, the flaps remain open to allow the circulation of

49 air. When nighttime approaches and the outdoors temperature drops, the flaps close in order to prevent warm air from inside the room escaping. This would require a person to manually flip the flaps during morning and nighttime. However, together with Chemet Rigizin, we proposed a new idea to develop this. If one was to introduce electric flaps that open and close, one could program these to open and close automatically depending on the outdoor temperature. The circuitry would be quite simple. Connect an outdoor temperature sensor, and indoor temperature sensor and an electronic switch to control the flap, to an Arduino or another microcontroller unit. The programming code would be simple, based simply on a Boolean statement. It would read along the lines of, when the temperature difference between outdoor and indoor is greater than a certain value, say 10, the flaps would close. However, this might occur during the day, so we can chose to limit the flaps so they only open between six o’clock at night and eight o’clock in the morning.

If Temp_indoor-Temp_outdoor >10 and (08 > Time >18); Flaps = True; Else; Flaps = False;

When this Boolean statement is true, the flaps close. When it is false, the flaps open. Building and programing such a device would cost less than 1000 rupees. Unfortunately, the difficulty resides in developing and installing these flaps. It would require knowledge of basic programming and microelectronics, which may be hard to find. However, if this was to be implemented, it could have the potential to raise the average indoor temperature by a few degrees Celsius and could prove to be an affordable way to improve the Trombe Wall technology. Another development of this theory is to install small fans in the Trombe Wall holes in order to even further stimulate air circulation. The thinking behind installing small fans is if the circulation of air will increase, more warm air from the Trombe Wall gap will be pushed into the room, and more cold air from the room will be heated. Looking at temperature data, we can see that the warm air in the Trombe Wall gap can reach temperatures of over 40 degrees Celsius, which is much warmer than optimal. However, because of the relatively small change in air density due to heat, air needs to be heated to high temperatures in order to rise to the top and be able to enter the room. This problem could be avoided if the circulation of fans sped up the entire ventilation process. Of course, the speed of the fans will need to be experimentally optimized. If the fans circulate air too quickly, the air will not have a chance to heat up, thus partly defeating the point of a Trombe Wall. If the fan is too slow, it will not circulate enough air to make an impact. The fans could be implemented in the same code without too much hassle, with the flaps open.

If Temp_indoor-Temp_outdoor >10 and (08 > Time >18); Flaps = True; Fan = True; Else; Flaps = False; Fan = False;

With the introduction of fans, Chemet predicted that the average indoor temperature could increase with as much as three to four degrees. If this was to be the case,

50 Trombe Walls would suddenly go from providing enough heat with the addition of a radiator, to be fully able to heat up a room above twenty degrees using only solar energy. Furthermore, even if the fans require more technical expertise to be implemented, they could have a greater impact on heating, making it suitable for further studies. However, these ideas would require a small microcontroller unit that would have to be connected to power source. How this is managed adds another problem to the question. One last, more speculative idea, suitable for houses where firing a bhukari stove is still necessary, is to install air filters in the holes. This would probably decrease the ventilation, but if air filters were installed with the addition of fans, one could still achieve proper air circulation. The added bonus of this method would be that polluted air in the room could be cleaned with the help of the air filters, providing better indoor air quality for inhabitants whilst still keeping the rooms warm. However, this would pose several additional difficulties since one would have to clean and remove the air filters. Furthermore, without experimental testing, it is hard to say how the heat transfer would be affected by introducing an air filter. Presumably, the heat transfer coefficient would decrease, resulting in less efficient heating. We then arrive at a trade-off between air quality and room temperature, which would have to be optimized in some way. What is evident from this brief exploration of future improvements is that the technology is still ripe for development. Globally, Trombe Walls have never broken through, partly due to the fact that it is still a relatively new technology, but also probably due to the fact that other, cheaper heating sources can raise the indoor temperature by much more. However, with the climate crisis forming our socio- technical regime, Trombe Walls may come in vogue again. Hopefully, developments within the field will push the technology forward, and make it appealing to other regions around the world.

51 10 Conclusion To conclude this thesis, I have found that Trombe Walls are a more suitable heating solution than the direct gain approach for the people of Ladakh. My analysis suggests that Trombe Walls are more adept at sustaining a comfortable indoor temperature as compared to direct gain technology. Trombe Walls keep the air temperature at a passable temperature for most of the day, even if some additional source of heating is needed to push the average indoor temperature above twenty degrees. Furthermore, the qualitative research has shown that the Trombe Wall has many positive effects, which stem from three main improvements. Increased indoor temperature, better air quality and improved indoor brightness. These improvements improve the inhabitant’s quality of life by allowing them to live more comfortably, have plants indoors and not have to worry about water freezing at night. Moreover, a brief economic analysis was conducted where the Trombe Wall was discussed as an investment. There we saw that the average payback time for a Trombe Wall probably lies between seven and thirteen years. Additionally, using the NPV-method, the Trombe Wall becomes a positive investment if the time horizon is greater than thirteen years. However, such a large investment in cash may be difficult to procure, which leads to the question of how to finance Trombe Walls for the people of Ladakh, a question out of the scope of this essay. Lastly, future improvements in Trombe Wall technology were discussed, with electronic flaps and fans possibly being solutions to advance the technology further. Ultimately, what the future holds is unknown, but this thesis has help demonstrate how Trombe Walls may become a future sustainable housing technology not only in Ladakh, but in other regions around the world as well.

Acknowledgements There are several people that I owe credit to for making this project happen. First and foremost, I would like to thank LEDeG for their generous hospitality and their unwavering help. Specifically, I would like to acknowledge Tsewang Dolma, Chemet Rigzin, and Tashi Nordboo for their support, from helping us find an interpreter to attempting to build a homemade battery charger. Additionally, I would like to thank our driver Mr. Lobzng who was always willing to drive us to the hostel when the sensors broke, even if it was late at night. Furthermore, I would like to thank my supervisor at KTH, Nelson Sommerfeldt, for his comments on the thesis, as well as Per Lundqvist, for helping us with funding and making this project a reality. Lastly, I would like to thank my parents, Seema Arora-Jonsson and Stefan Arora-Jonsson, for their support and tireless editing.

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