GRUNDNIVÅ, 15 HP
STOCKHOLM SVERIGE 2020,
A Study on the Effectiveness of Passive Solar Housing in Ladakh
LEO BJÖRKMAN RITA NORDSTRÖM
KTH
SKOLAN FÖR INDUSTRIELL TEKNIK OCH MANAGEMENT
0
This study has been carried out within the framework of the Minor Field Studies Scholarship Program, MFS, which is funded by the Swedish International Development Cooperation Agency, Sida.
The MFS Scholarship Program offers Swedish university students an opportunity to carry out two months' field work, usually the student's final degree project, in a country in Africa, Asia or Latin America. The results of the work are presented in an MFS rep ort which is also the student's Bachelor or Master of Science Thesis.
Minor Field Studies are primarily conducted within subject areas of importance from a development perspective and in a country where Swedish international cooperation is ongoing.
The main purpose of the MFS Program is to enhance Swedish university students' knowledge and understanding of these countries and their problems and opportunities. MFS should provide the student with initial experience of conditions in such a country. The overall goals are to widen the Swedish human resources cadre for engagement in international development cooperation as well as to promote scientific exchange between universities, research institutes and similar authorities as well as NGOs in developing countries and in Sweden.
The International Relations Office at KTH the Royal Institute of Technology, Stockholm, Sweden, administers the MFS Program within engineering and applied natural sciences.
Katie Zmijewski Program Officer
MFS Program, KTH International Relations Office
KTH , SE-100 44 Stockholm. Phone: +46 8 790 7659. Fax: +46 8 790 8192. E- mail: katiez@kth.se www.kth.se/student/utlandsstudier/examensarbete/mfs
Abstract — Energy use in buildings account for 32% of total global final energy consumption, and consequently, a large portion of energy-related greenhouse gas emissions. Passive Solar Designs are sustainable building techniques that use solar energy to heat or cool living spaces without the aid of mechanical or electrical devices. This paper aims to evaluate the effectiveness of Passive Solar Housing as a possible solution to the heating challenges currently faced in Ladakh, India, from the environmental, social, and economic sustainability perspectives. Two types of Passive Solar Techniques are studied:
Trombe Walls and Direct Gain. This is to be achieved by a dualistic approach, combining quantitative and qualitative data to gain a holistic view of the situation. Quantitative data were collected from rooms built with the two different approaches.
This information was used to determine the energy efficiency of each Passive Solar Design, and as a basis for building a numerical model that simulates the behaviour of Trombe Walls in conditions not observed during the data collection.
Qualitative data were obtained through interviews with the residents of Passive Solar Houses in the villages of Palam and Khardong. The results show that Trombe Walls are significantly more effective at keeping a stable temperature than the Direct Gain technology. The interview responses verify and validate these findings whilst describing many positive effects of living in houses with Trombe Walls. Using the numerical model, it becomes apparent that increasing room size reduces the effectiveness of the Trombe Wall room. In conclusion, Passive Solar Housing can be, both from a social and economic perspective, a very effective method to maintain comfortable living conditions while reducing the environmental impact compared to traditional construction methods.
Sammanfattning — 32% av den globala energikonsumtionen kommer från energianvändning i byggnader. Det innebär att en betydande andel utsläpp av växthusgaser kommer från dem.
Passivhus är en samling hållbara byggtekniker som använder solens energi för att värma upp eller kyla ner en levnadsyta utan att förlita sig på mekaniska eller elektriska medel. Denna studie ämnar utvärdera lämpligheten av Passivhus som en lösning på de uppvärmningsutmaningar som Ladakh, Indien ställs inför, vilket görs ur de miljömässiga, sociala, och ekonomiska hållbarhetsperspektiven. Två typer av Passivhus undersöks:
Trombeväggar och Direct Gain. Metoden innefattar en kvantitativ och en kvalitativ datainsamling för att ge en heltäckande bild av situationen. Kvantitativa data insamlades i
This work was supported by the Swedish International Development Cooperation Agency (SIDA) under the Minor Field Study scholarship.
A. R. Nordström is with the School of Industrial Engineering and Management, Royal Institute of Technology, Stockholm, Sweden (e-mail:
ritan@kth.se). L. N. N. Björkman is with the School of Industrial Engineering and Management, Royal Institute of Technology, Stockholm, Sweden (email: leobj@kth.se).
1 Edenhofer, O., R. et. al PCC (2014). Climate Change 2014:
Mitigation of Climate Change. Contribution of Working Group III to the
rum byggda med de två olika teknikerna – denna data användes sedan i en numerisk modell som simulerar hur en Trombevägg beter sig under omständigheter som inte direkt observerats inom ramen för denna studie. Kvalitativa data erhölls från intervjuer med invånarna av Passivhus i de två byarna Palam och Khardong. Resultaten påvisar att Trombeväggar är märkbart mer effektiva på att hålla en stabil inomhustemperatur jämfört med Direct Gain. Intervjusvaren verifierar och validerar resultaten samtidigt som de beskriver flertalet positiva följder av att bo i ett Passivhus. Genom att använda den numeriska modellen blir det tydligt att en ökning av storleken på rummen minskar Trombevägg-rummens förmåga att bibehålla en adekvat inomhustemperatur.
Sammanfattningsvis kan Passivhus, från sociala och ekonomiska perspektiven, vara en mycket effektiv metod för att säkerställa tillfredställande levnadsvillkor, samtidigt som de har en mindre negativ påverkan på miljön än traditionella byggnadsmetoder.
Index Terms— Energy, Ladakh, Passive Solar Technology, Trombe Wall, Numerical Modelling
I. INTRODUCTION
HE energy sector is considered to be the biggest single contributor to energy consumption and greenhouse gas emissions. Energy use in buildings form a large part of this consumption: buildings account for 32% of total global final energy use, and consequently, a large portion of CO2
emissions 1. With energy consumption already growing more rapidly than in any other time in history, and with an expected population growth of 2 billion people by 2050 2, providing sustainable housing will only become more crucial in the fight against climate change.
Facing this situation, amplified efforts should be put to find realistic and permanent solutions. One of these solutions is improving energy efficiency by implementing adequate strategies and measures. Passive Solar Designs are sustainable building techniques that collect solar energy in form of heat without the involvement of mechanical and electrical devices. Under the right circumstances, such as in the cold desert environment of Ladakh, India, these techniques may be a powerful method to reduce energy consumption in buildings and cutting the resulting emissions.
Fifth Assessment Report of the Intergovernmental Panel on Climate Change Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2014 [Online]. Available at:
https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_full.pdf
2 United Nations, “Growing at a slower pace, world population is expected to reach 9.7 billion in 2050 and could peak at nearly 11 billion around 2100” New York, USA, 2019, June 17, accessed on 2020, 11 May Available at:
https://www.un.org/development/desa/en/news/population/world- population-prospects-2019.html
A Study on the Effectiveness of Passive Solar Housing in Ladakh
L. N. N. Björkman, A. R. Nordström
T
This is in line with the goals of United Nation Development Program’s Agenda 2030, in particular 7. “Affordable and Clean Energy”, and 11. “Climate Action”. By using more energy efficient sources of heating, such as Passive Solar Housing, less greenhouse gases are expelled into the atmosphere, limiting the rise in average global temperature as stipulated in the Paris Agreement.
This study was funded by the Swedish International Development Cooperation Agency (Sida), the Swedish government agency for development cooperation. Ladakh Ecological Development Group (LEDeG), an Indian non- governmental organization dedicated to promoting ecological and sustainable development in Ladakh, supported the project by providing access to their premises and allowing measurements to be done there. In addition, LEDeG offered regional expertise and support. “A Study in Solar Housing Technology: The Impact of Trombe Walls in Ladakh” by Sebastian Arora-Jonsson is a related thesis written by a team member of this project. Certain figures are shared between this and the aforementioned paper.
A. Background
The cold, mountainous region of Ladakh, India, is characterized by a rugged topography and severe climatic conditions: the temperature variations are extreme as temperatures often plummet to -30 degrees Celsius in winter.
This frigid climate requires extensive heating for the houses in the area to become liveable, especially considering that the houses, often without any wall and roof insulation, are currently not energy efficient. Traditionally, heating has been accomplished by a reliance on conventional biomass energy resources (cow dung, bush, wood), which is burned in a local stove called bukhari. The high demand on the limited biomass results in huge pressure on local resources, a situation exacerbated by the fact that challenging weather conditions restrict all travel through the Great Himalayan Range for six months each year – resulting in a complete geographic isolation of the region from the Indian subcontinent during this time. Furthermore, using electricity for heating has proven difficult due to the volatility of the local power grid, which is not connected to the rest of the country. The result is an energy vulnerability for much of the population: tens of thousands presently endure very harsh living conditions, where indoor temperatures frequently reach below zero degrees Celsius. Traditional space heaters produce a considerable amount of noxious smokes.
Developing alternative heating solutions is of utmost importance.
These factors, together with the fact that, despite the cold climate, Ladakh benefits from having 320 sunny days a year3, served as two fundamental reasons for the decision to initiate a Passive Solar Housing project in the area. From 2008 to 2012, a large amount of buildings was constructed in Ladakh, through two main projects led by the sustainable energy development focused NGO Geres and implemented on the field by Ladakhi partner organisation Ladakh Ecological Development Group (LEDeG) 4. These projects allowed the construction of around 1000 buildings that integrated Passive Solar and Low Energy Consumption techniques, with the aspiration of making these structures less dependent on
3 Parvaiz, A. P. Here comes the sun: Ladakh embraces solar energy. 2013.
[Online] Available at: https://www.thethirdpole.net/2013/11/26/here- comes-the-sun-ladakh-embraces-solar-energy/
traditional heating practices. Some of the houses were built in the villages of Palam and Khardong outside of the region’s capital Leh.
B. Purpose
This paper aims to evaluate the effectiveness of Passive Solar Housing as a possible solution to the heating challenges currently faced in Ladakh, India, from the environmental, social, and economic sustainability perspectives. The research questions to be answered are:
1. How do different Passive Solar Techniques, and variations of them, affect indoor climate of a room?
2. Is Passive Solar Housing a feasible heating solution for the inhabitants of Ladakh?
C. Scope
The efficiency of Trombe Walls in general has been studied multiple times before and will not be the subject of this paper.
Instead the study will focus on how it performs in Ladakh, India. The quantitative study will be delimited to the Ecology Hostel in Leh and compare nine rooms in the same building.
Most of the quantitative data were collected during the month of February 2020, any time series analysis of other periods will not be done. We will examine how Trombe Walls in Ladakh perform in comparison to Direct Gain techniques during this period. Since the numerical model is based on this limited data, there will be inherent validity issues if used to predict temperature data far into the future. Therefore, this part of the analysis will be constrained to simulations mainly based on the spatial dimension. The findings from those parts will then be compared to the interview answers received from the qualitative research.
D. Previous Studies
Passive Solar building designs are not new inventions – the designs were popularised in the middle of the 20th century, but a thermal mass wall was patented as early in the 1880’s.
This naturally results in there being numerous studies on the subject. Renewable energy technologies for sustainable development of energy efficient building by Arvind Chel and Geetanjali Kaushik, published in the 2nd issue of the 57th volume of Alexandria Engineering Journal in 2018, is only one out of many studies that recognize the reduction in energy consumption, and therefore reliance on fossil fuels, of Passive Solar houses.
There is also a sizeable body of work on the mathematical modelling of Passive Solar techniques, namely Trombe Walls, which have served as guidance for the authors of this paper when constructing their numerical model. Two such papers are Experimental and numerical model of wall like solar heat discharge passive system (2006) by V. Hernández et al [10]; and Mathematical modelling of the steady state heat transfer processes in the convectional elements of passive solar heating systems (2013) by J.Z. Piotrowski, A.
Stroy, M. Olenets [11]. Both studies based their analytical models on thermal balance and steady state heat transfer processes, which are then used to simulate the Trombe Wall’s behaviour.
4 LEDeG. Promoting Passive Solar Houses in the Trans-Himalayan Cold Desert Region of Ladakh. 2019. [Online] Available at:
http://www.ledeg.org/2019/09/17/promoting-passive-solar-houses-in-the- trans-himalayan-cold-desert-region-of-ladakh/
II. THEORY
Passive Solar Buildings are a type of low energy consumption buildings that integrate thermal insulation coupled with passive solar architecture. The purpose is to significantly reduce fuel consumption compared to standard buildings, as well as provide a comfortable living environment. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices for neither transportation nor transformation of the solar energy. Instead, sunlight is converted into usable heat (in air and thermal mass) and cause air movement for ventilating, with little to no need for other energy sources: In average, fuel consumption is cut down to 50%; in some cases, no fuel consumption is necessary for heating purposes [1]. The goal of all passive solar heating systems is to capture the energy radiated by the sun within the building’s materials and to conserve during periods when the sun is not shining, be that during the night or cloudy days.
While the building’s materials are absorbing heat for later use, solar heat is available for keeping the space at a comfortable temperature.
Passive heating techniques incorporate the building’s site, building design, and materials to minimize energy loss and assure that the solar energy collected is sufficient for an adequate indoor temperature throughout the day. The building needs to be sited to maximize solar gain during the colder months of the year. The rays of the sun should hit the building’s facade directly, unhindered by any obstructions that could prevent proper collection of solar energy. In addition to this, passive buildings should be south facing, with a maximum variation of 20 degrees either west or east 5. By choosing the correct site and orienting the building southwards, the prerequisites for satisfactory performance of passive solar techniques have been fulfilled; now, the passive solar building must be designed efficiently.
Building design can be divided into two parts: floor plan and shape. Areas with the greatest heating requirement should be located on the southern side, where rooms that primarily are to be used in the first half of the day should be located in the south east corner, while rooms mainly used later in the day should be located in the south west corner. Areas that need not be warmed to the same extent (storage, corridors, toilets, etc.) should be located on the north side of the building to create efficient buffer zones for the warmed southern rooms. Heat loss is reduced when a room is in contact with a buffer zone, since the buffer zone has an almost constant, higher temperature than outside (albeit a lower than the warmed room) 6.
The more volume the building has, the more air must be heated and thus the larger the energy requirements. Two things to keep in mind when designing a passive solar building is to limit the height of the room, which results in a decrease of volume needed to be heated, as well as the width (the eastern or western wall), to not decrease the ratio between the south face (whence the solar energy is collected and used to heat the room) and the area of the room.
Furthermore, to diminish heat loss towards the exterior, the shape of the building should minimize its envelope surface
5 Clottes, Franck. L.E.C Integration Design Manual – Techniques for domestic and public buildings in cold regions of Jammu & Kashmir and Himachal Pradesh states, India. 2012. Geres. Page 14.
6 Ibid. Page 16.
7 Ibid. Page 16.
8 Ibid. Page 22-24.
(the part of the structure in direct contact with the exterior) while still meeting the requirements on volume and size. The smaller the surface to volume ratio is, the lower the heat loss of the building is 7.
Passive solar buildings must collect energy from the sun, but also retain as much heat as possible when solar energy collection is not possible, ensuring a consistently satisfactory indoor temperature. Choosing the correct materials for these two aspects is essential. The thermal mass absorbing the energy from the sun must be made of a material with high heat absorbance: suitable materials include cement bricks, burnt mud bricks, rammed earth, and cement hollow blocks filled with cement or mud. In turn, insulation must be made from material with low thermal conductivity, i.e., the material should have a low capacity to transfer heat by conduction.
Generally, materials with low density (straw, wood shaving, polystyrene, etc.) also have a lower thermal conductivity than materials with high density (stone, mud, cement, etc.), making them more suitable as insulation 8.
Passive housing techniques exploit the energy transmitted from the sun by utilizing three basic natural processes: the thermal energy flows associated with radiation, the transferring of heat by electromagnetic waves without material support like fluid or solid; conduction, the transferring of heat throughout a solid or a fluid; and natural convection, the transferring of heat due to the bulk movement of molecules between a surface of a solid and a fluid. When sunlight strikes the structure, the building absorbs the solar radiation and retains it in materials with high thermal mass, which are thus suitable for storing heat. Under the laws of thermodynamics, the flow of thermal energy will always go from the hotter body to the colder one. The rate at which energy is conducted as heat between two bodies depends on the properties of the conductive interface through which the heat is transferred and the temperature difference (and hence thermal gradient) between the two bodies. The higher the difference between the temperature is, the higher the amount of thermal energy transferred. Since the thermal mass has been heated by the sun it will have a higher temperature than the indoor air, thermal energy will be transferred through convection from the wall to the air inside the room [2].
Lag time is the time delay between when a temperature rise occurs outside and the onset of the temperature to the air in the room, that is, the time it takes for heat to flow through the thermal mass 9. The length of the lag time depends on the chosen material’s property to store energy, and can be calculated with the following formula:
𝐿𝑎𝑔 𝑡𝑖𝑚𝑒 = 1
2∙ 𝑥 ∙ √ 24 3600 ∙ 𝜋 ∙ 𝜆
𝜌 ∙ 𝐶
where 𝑥 is the thickness of the wall, 𝜆 is the thermal conductivity of the material, 𝜌 is the density of the wall, and 𝐶 is the specific heat capacity10.
Thermal mass is essential in any Passive Solar technique.
However, where in the structure the thermal mass is located
9Institut Catalá d’Energia. Sustainable Building Design Manual, Volume 2. 2014. New Delhi: Energy and Resources Institute.
10 Clottes, Franck. L.E.C Integration Design Manual – Techniques for domestic and public buildings in cold regions of Jammu & Kashmir and Himachal Pradesh states, India. 2012. Geres. Page 20-21.
can vary, affecting the effectiveness of the passive system and its suitability in different situations. The two most prominent approaches to passive solar heating are the direct gain and Indirect Gain techniques.
A. Direct Gain
The basic principle of Direct Gain design is that sunlight is admitted into the living space, directly through openings or glazed windows, to heat the walls, floors, and thereby the air inside; in this system, the actual living space becomes the solar collector, heat absorber, and distribution system. These processes can be observed in Figure 1. The requirements of a Direct Gain system are glazed windows and thermal storage.
To maximize the collection of sun radiation during winter daytime (in the northern hemisphere), large glazed windows are generally located facing south. Additionally, by having double glazed windows equipped with thick, insulating inner curtains, heat loss during evening and night-time can be reduced. With Direct Gain techniques, thermal storage is made up by functional parts of the house: floor, walls, and even furniture all absorb and store heat for later reradiation back into the room, warming the space.
The key to success with Direct Gain passive solar heating is to provide an adequate amount of south facing glass area and thermal mass. The area of glazing is determined in response to the duration and severity of winter temperatures, the building size, the amount of interior thermal mass, and the degree of insulation. A correct balance between these factors must be established to avoid large daily temperature fluctuations that could result in overheating – a common problem of Direct Gain techniques, even in winter. The substantial temperature swings are due to large variations in the input of energy, in the form of solar radiation, into the room. There are several techniques that, when applied, can reduce the overheating problems associated with the mentioned temperature fluctuations. These techniques
11 Clottes, Franck. L.E.C Integration Design Manual – Techniques for domestic and public buildings in cold regions of Jammu & Kashmir and Himachal Pradesh states, India. 2012. Geres. Page 17.
include the installation of horizontal overhang above Direct Gain windows, installation of external vertical blinds, plantation of deciduous vegetation in front of the windows, and more11.
B. Indirect Gain
A Trombe wall consists of a thermally massive, south-facing masonry wall with a dark, heat-absorbing material on the exterior surface covered by a double glass frame. Heat from sunlight passing through the glass layer is absorbed and stored in the wall, and then conducted slowly inward through the masonry. To further increase the absorption of solar energy, the wall is painted black (since black has the highest absorption coefficient of all colours). Moreover, the greenhouse effect helps this system by trapping the solar radiation between the double-glazed frame and the thermal wall during the day. Short wavelength radiation from the sun passes through the glazing largely unimpeded. This energy is absorbed by the wall when striking its thermal mass, whereupon it is re-emitted in the form of longer wavelength radiation that cannot pass through the glazing as easily.12 Hence, the heat becomes trapped in the air space between the glass and the thermal wall. Figure 2 shows these processes.
Trombe walls can be outfitted with or without a venting system. In the former case, the wall has one or several vents at the bottom and the top of the wall, and although the main heating is accomplished by radiation and convection from the inner face of the wall, the vents in the wall also allow daytime heating by the natural convection loop. Cool air from the living space enters the air channel between the wall and the glass through the lower vent, whereupon it is heated by the energy stored in the thermal wall. As this occurs, the warming air rises and is fed back into the building through the upper vent – and thus the circulation pattern is established.
12 Chris Reardon, Max Mosher, Dick Clarke. Your Home Technical Manual – Section 4.5 Passive Solar Heating. 2010. Australian government.
[Online] Available at:
https://web.archive.org/web/20130502231120/http://www.yourhome.gov.a u/technical/pubs/fs45.pdf
Figure 1: The figure shows the inter-related components that work together to make the building, constructed with direct gain technique, energy efficient. 1. Energy, in form of radiation emitted from the sun reach the building facade. 2. The sun’s rays pass through the double-glazed frame unobstructed. 3. The solar radiation is absorbed and stored in the thermal mass. 4. The heat is released to the interior of the building. 5. Proper insulation to minimize heat loss.
Figure 2: The figure shows the inter-related components that work together to make the building, constructed with the Indirect Gain technique of Trombe wall, energy efficient. 1. Energy, in form of radiation emitted from the sun reach the building facade. 2. The sun’s rays pass through the double-glazed frame unobstructed. 3. The solar radiation heats the air in the gap between the glazing and the thermal wall. 4. The solar radiation is absorbed and stored as heat in the thermal wall for later release into the living space. 5. Warmed air rises and enters the living space through the upper vent, while cool air from the room enters the air gap through the lower vent, establishing a natural circulation pattern. 6. Proper insulation to minimize heat loss.
However, the effect is different during night-time: the upper vent on the thermal wall sucks the heated air from the warmer indoor spaces to the cooler air space between the wall and the glazing, a completely counterproductive consequence that effectively cools the room. To avoid this from happening, it is necessary to close the vents at the top and bottom of the wall, ensuring that the now cool air in the channel between the glazing and the wall does not re-enter the home. Heat absorbed by the concrete wall is still able to maintain a comfortable indoor temperature overnight, and the window, often made out of double glass and located at the centre of the wall, can be opened for ventilation as required. A disadvantage with this vented system is its user-dependence and that it can be a liability to operate movable insulations or shutters in a daily basis. In the cases where adequate opening and closing of the vents is hindered, by the inhabitants’
routine or for another reason, a non-vented system can be more suitable since it maintains a more stable temperature overnight. A non-vented system is also referred to as a “solar wall.” The functionality of a non-vented system is equal to the vented one, except for a decrease in natural ventilation.
III. MATERIAL
To conduct the necessary measurements for the quantitative data collection, kits consisting of a central micro processing unit (MCU) and several connected sensors were built. In this segment, the material used when constructing the kits is presented; the construction method itself will be discussed in the coming section of Method.
The MCU used in this project was an Arduino Nano, belonging to the Arduino family. Arduino is an open-source electronics platform that consists of both a physical programmable circuit board (the microcontroller) and a piece of software (Integrated Development Environment or IDE), in which the user writes code in Arduino programming language or C and C++ languages.13 The boards are equipped with a set of digital and analogue input/output (I/O) pins that may be interfaced to various breadboards and other circuits.
The Arduinos can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators.
The Arduino Nano is a small but complete board, based on the microchip Atmega328p. The board has 22 I/O pins, of which 14 are digital and 8 are analogue, that act as input pins when they are interfaced with sensors. This model has a relative low energy consumption and the ability to handle both 3.3- and 5-volt logic, a crucial capability since the different sensors used required different logics. It also has a reset pin and a reference voltage for analogue input pin – the complete pinout can be found in Appendix A. The Arduino Nano can be powered in multiple ways, but in this study a 11.1-volt Li-Po battery was used. 14
13 What is Arduino, Arduino Inc, accessed on 2020, May 11 Available:
https://www.arduino.cc/en/Guide/Introduction.
14 Arduino nano specification page, accessed on 2020, May 11 [Online]
Available: https://store.arduino.cc/arduino-nano
15 DHT22 Datasheet, Aosong Electronics Co.,Ltd, accessed on 2020, May 11, [Online] Available:
https://www.sparkfun.com/datasheets/Sensors/Temperature/DHT22.pdf
16 BMP280 datasheet, Bosch Sensortec, accessed on 2020. May 11, [Online] Available at: https://cdn-shop.adafruit.com/datasheets/BST- BMP280-DS001-11.pdf
A. Sensor Specification151617181920 Name Measuremen
t
Operatin g Range
Accurac y
Numbe r per kit DHT22 Temperature,
humidity
-40 to +80 ºC, 0-100%
±0.5 ºC,
± 2%
3-5
BMP280 Temperature, pressure
-40 to +85 ºC, 300 to 1100 hPa
±0.5 ºC,
±0.12 hPa
2
TSL2561 Illuminance 0.1 to 40,000 lux
- 1
TSL2591 Illuminance 0.000118 to 88,000 lux
- 1
(separat e kit) DS18B2
0
Outside temperature
-55 to 125
ºC ±0.5 ºC 2
(separat e kit) PMS5003 Particle
concentration
>1000 µ
g/m3 - 1
(separat e kit) Table 1: Shows all of the sensors used in this project and their respective specifications. “–” denotes unavailable information.
Table 1 summarizes the features of each sensor used for the quantitative research part of this study. The sensors were assembled in several measuring kits; the process is described later in the Quantitative Method section. In addition to the aforementioned sensors, a real-time clock (model DS3232) and a micro SD-card reader were used to keep a precise account of the current time of each measurement and to store the collected data locally, respectively. A plastic container of adequate size was used as a protective casing for the microcontroller and other central components.
IV. METHOD
The first step of any study is to formulate the main objective or question that will guide the research process. The purpose of the project was to evaluate the effectiveness of Trombe Walls as a heating solution in cold desert environments such as Ladakh, which was to be done by comparing this passive solar technique with Direct Gain. It soon became apparent that both quantitative and qualitative tools were necessary to gain a holistic view of the situation: quantitative tools would point to the magnitude of the problem and allow for objective data collection on the efficiency of different Passive Solar techniques while applying qualitative methods would provide contextual information, a deeper understanding of relational dynamics, as well as make possible to make visible any unexpected aspect we did not have enough knowledge to foresee. Subsequently, by utilising the collected quantitative data to build a numerical model that through its simulations could quantify the effects of varying conditions on the indoor
17 TSL2561 datasheet, Adafruit Industries, accessed on 2020, May 11, [Online] Available at: https://cdn-
learn.adafruit.com/downloads/pdf/tsl2561.pdf
18 TSL2591 datasheet, Adafruit Industries, accessed on 2020, May 11, [Online] Available at: https://cdn-
shop.adafruit.com/datasheets/TSL25911_Datasheet_EN_v1.pdf
19 DS18B20 Datasheet, Dallas Semiconductor, accessed on 2020 May 11 [Online] Available at:
https://cdn.sparkfun.com/datasheets/Sensors/Temp/DS18B20.pdf
20 PMS5003 technical details page, Adafruit Industries, accessed on 2020, May 11 [Online] Available at:
https://www.adafruit.com/product/3686
temperature, and, as such, help evaluate the efficiency of Trombe Wall as a heating solution, would be advantageous in answering the research questions and help broaden the use of the research findings. Because of the use of multiple methods, the practical steps outlined by Maria Cecília de Souza Minayo in Limits and Possibilities to Combine Quantitative and Qualitative Approaches (2016) [3] were deemed as suitable guidelines for the planning and executing of this study’s methodical process.
The application and combination of both quantitative and qualitative methods is referred to as a Methodological Triangulation. Methodological Triangulation involves using more than one kind of method to study a phenomenon – in our case, both quantitative and qualitative research and a subsequent numerical modelling– with the aim to increase validity of findings and enhance the understanding of the subject. The intention of integrating multiple observers and methods is to overcome the intrinsic biases and problems that come from a single method study. In the quantitative part we were interested to know temperature, humidity, and luminosity, to determine how indoor environmental conditions changed over time and depending on building choice. The qualitative study was to achieve information about the resident’s subjective opinion about the changes observed in the quantitative study – even if we can see in the quantitative data that certain indoor conditions either improved or declined, any conclusion about how this has affected the lives of the inhabitants, without asking for their personal input, would only become a detached speculation.
The computer simulation was aimed to helping expand the analysis by evaluating the Trombe Wall in different settings than the specific ones in which the data were collected, such as larger rooms and a different amount of people inhabiting the space, as well as giving a prediction for indoor temperature in the near future.
After a thorough studying of appropriate theoretical frameworks, the following steps, in accordance to de Souza Minayo, consisted of coordinating the qualitative and quantitative and organizing the fieldwork. It is required to have adequate training both for the application of quantitative and qualitative tools. However, a gap in our team’s knowledge was identified: our lack of knowledge of local language and customs. To compensate for this, LEDeG helped with identifying relevant interview subjects and provided us with a translator, fluent in both Ladakhi, Hindi, and English, that had close ties to the community and were to serve as our link with the people surveyed. The final steps, analysing the information obtained, using this information in our simulations, and preparing the final research report, will be explained more thoroughly in the coming sections of this paper.
A. Quantitative Method
To quantify the effect of the different passive solar techniques on indoor climate conditions, and compare the Indirect and Direct Gain techniques, we decided to collect data that could indicate how comfortable a room is for the individual. Three important factors on the comfort of a room’s climate are temperature, humidity, and luminosity; therefore, these were measured in each room. An adequate temperature is not only important for comfort and health, but also for several practical reasons. As an example, if the water freezes during the night it is not possible to drink it or wash the face in the morning. Humidity affects the apparent temperature: in
humid conditions, the air feels hotter because less perspiration evaporates from the skin, and vice versa. Since the degree of humidity influences the perception of the indoor climate, it is relevant to measure. Sufficient light is necessary for reading, working, and completing other tasks at home – the enabling of productivity is a meaningful aspect to consider. Indoor temperature, humidity, and luminosity thus have a direct, tangible effect on the well-being of the inhabitants, and, as such, are essential to measure to be able to answer this paper’s research questions. Pressure data were also collected, not as a measurement of indoor climate but to calculate the airflow that emerges from the natural convection loop of air through the vents of a Trombe Wall.
To be able to correlate the data from the rooms with outside climatic conditions a complete weather station was used to measure outside temperature in the shade, relative humidity, wind speed and direction, rainfall, and dew point. The weather station was set up before the start of this project by LEDeG and had recorded weather data from September 2019 onwards, with one measurement every hour. From a separate unit, data from the outside temperature in the sunlight and illuminance from the direct sunlight hitting the Ecology Hostel’s southern wall was collected. Out of these measurements, outside temperature and sunlight will be the most relevant since they have the most considerable impact on the data from the inside of the rooms.
Location of Quantitative Data Collection
The quantitative data were collected at the Ecology Hostel, built by LEDeG as an eco-friendly lodging for travellers visiting Leh, Ladakh. The hostel aims to have as small environmental impact as possible, and therefore relies solely on passive solar techniques for heating the building and the water used by the guests. No additional heating method is used, even during the cold winter months. Ecology Hostel has eight small, identical rooms equipped with Trombe Walls, and two bigger rooms built with Direct Gain techniques. For a detailed view of the different types of rooms, see Appendices C-F and G respectively. The building is south- oriented and without any obstructive objects in front of the building that could block sunlight, the rooms receive the same amount of it.
The fact that all rooms implementing the same passive heating technique are identical, and that the two types of rooms are in the same building, was essential for the study. It enabled the disregard of multiple factors and therefore the isolation of the effect of the different techniques. However, one disadvantage with the hostel is that the two Direct Gain rooms were larger than the Trombe rooms, and also located on the wings – meaning they all had one additional wall in direct contact with the outside compared to the Trombe wall rooms. Room size is an important factor to consider because a fixed amount of incident sunlight equates to a certain amount of energy, and if this energy is spent heating a larger room, naturally, this room will become cooler than a smaller one. Furthermore, having another wall towards the outside will result in further heat loss for these four rooms. These circumstances will have to be taken into consideration when conducting our analysis.
Measuring and Collecting Quantitative Data
It was necessary to collect different types of data from many rooms, which meant that we required a specific set of sensors that could meet these requirements. Imposed on these
requirements was a budget restraint that made it impossible to opt for ready-made measuring instruments. Consequently, we decided to build our own sensor kits consisting of one central microcontroller unit (MCU) with multiple attached sensors. For a summary of the sensors used, see Table 1. All electrical components were connected to the microcontroller through a circuit board, into which the wires from every sensor had been soldered. For more information on the construction and configuration of the sensor kits, the reader is referred to Appendix H. A schematic of the sensor kits’
wiring can be found in Appendix B. To get a visual on the exact sensor placement in the rooms, please see Appendix E.
Data Refinement and Aggregation
Issues with the MCU’s real-time clock resulted in only approximate time measurements for a large portion of the early data points. The watchdog timer, an inbuilt low-power physical timer with the ability to reset the Arduino, measures on standardized intervals and thus the number of readings after a set time could be used to determine an approximate time of measurement. The device made one measurement every 598.0 seconds, with a standard deviation of 1.5 seconds. After adding the average number of seconds to the point before, the last timestamp was validated by comparing the difference of the latest approximated time to the next measured one. If the difference is near the expected value of 598 seconds there had been no issues other than a faulty clock, otherwise, the data had to be disregarded. The fact that data points from different units were not measured at the exact same time introduced the need to aggregate to be able to compare different units.
Five types of units with different output and timings were normalized to compare and analyse them objectively. After connecting the data points to the closest 10-minute mark and appending it to the same comma-separated file, the data had been sufficiently cleaned and could now be used for the exploratory data analysis and modelling.
Long term weather data from a station installed by LEDeG was collected every hour instead of every 10 minutes.
To solve that the first inside measurement of every hour was used when comparing to the outside weather station. Another method of comparing the inside and outside data could be to take the average of the entire hour. In one perspective it would be more accurate since it captures changes during the time interval, but since the outside data came from one specific datapoint finding the closest point would give the most accurate representation in the sense that the comparison is done the same time.
B. Qualitative Method
The goal of the qualitative study was to gain an understanding of the impact on people’s lives after the change from living in a traditionally built house to a Passive Solar building. To answer this, we formulated two research questions linked to the qualitative part of the research:
How does a Trombe Wall affect people’s perception of their indoor climate?
Does a Trombe Wall affect how people allocate their time?
The interview questions asked to the subjects were constructed based on the research questions, an arrangement recommended by D. Cohen and B. Crabtree in Qualitative Research Guidelines Project (2006) [4]. To encourage a more
open discussion that would allow the informants the opportunity to express their views in their own terms, giving us as researchers a deeper contextual knowledge, we opted for a Semi-structured interview. Semi-structured interviews are often preceded by observation, informal and unstructured, to allow the researchers to develop a keen understanding of the topic of interest necessary for developing relevant and meaningful semi-structured questions [4]. Since our relative unfamiliarity with Ladakhi culture limited our understanding of the cultural nuances and particularities of the people we were about to interview, we enlisted help from LEDeG. With their adept input, a set of twenty-five interview questions was decided upon. While there was a clear interview form, it was not followed strictly, and we remained flexible. The complete Semi-structured interview form can be found in Appendix I.
Location of Qualitative Data Collection
The interviews were spread out over two Ladakhi villages, Khardong and Palam, both with less than 500 inhabitants.
Palam is located ten kilometres away from Leh between a mountain range and the Indus River, with access to a sparsely forested area near the body of water. The village was severely affected by flash floods in 2010 when most houses were destroyed, and the inhabitants were forced to live in small huts. An aid project was launched by LEDeG, who rebuilt parts of the village with passive solar houses between 2012 and 2015. In the same period, LEDeG also built passive solar houses in Khardong, located in Nubra district, two hours away from Leh by car. This village is at an altitude of 4000 meters above sea level and has harsh living conditions, due to the cold temperature as well as the lack of vegetation. In contrast to Palam, residents of Khardong does not have the opportunity to collect fuel from any nearby vegetative sources. This means that it must be purchased and imported from other locations, forcing many villagers to burn cow dung for heating purposes.
Measuring and Collecting Qualitative Data
We conducted a total of seventeen interviews in the two Ladakhi villages, in a mixture of the Ladakhi language, Hindi, and English, depending on the fluency of the interview subject. Most of the interviews were performed in Ladakhi, translated to English by our local translator. Some interviewees were sufficiently proficient in Hindi, which was an advantage since both our translator and one team member speak the language, reducing the amount of information lost in translation. We explained to the interviewees who we were and tried to make clear that we were, in fact, not a part of LEDeG, while describing the aim of our research project. We did this for two reasons. Firstly, it let the interviewee know who we were, and why we were asking them questions.
Secondly, we wanted to make sure the subject felt as comfortable in expressing their honest view as possible, reducing the feeling of obligation to the organisation that had built the houses in which they now resided, which hopefully would increase the validity of the study.
Each interview took between 45 minutes and 1 hour 15 minutes. To gain as reliable results as possible, all interviewees were asked the same questions from the interview sheet. However, due to the choice of semi- structured interview form, all questions were not asked in the same order or explicitly worded in the same way. The flow of each interview depended on the interview subject, which also explains the variation in length. The ambition was to choose
a sample with the highest representability of the overall population; however, our choice of interview subjects was somewhat limited to the availability and responsiveness of the individuals in the villages (and, probably, a variety of cultural factors whose subtleties and intricacies were not grasped by the authors of this paper). In the end, the sample was relatively varied with ten women and seven men. The average age of all respondents was forty-four years, however, there was an overrepresentation of older females and a lack of women under the age of thirty.
C. Modelling for Different Conditions
To draw comprehensive conclusions on the effectiveness of certain Passive Solar techniques, it was relevant to simulate the results on indoor temperature with conditions other than the ones measured, such as room size and amount of people residing in it. Furthermore, a prediction of how the Trombe Wall would behave in the near future would give deeper insight into its effectiveness. Hence, a numerical model of a room with a Trombe Wall was constructed to predict the behaviour of this thermodynamic system and estimate its performance in new situations, giving additional insights into the effectiveness of the Trombe Wall technique.
Using data collected on outside temperature and incoming solar radiation the total energy, i.e. the temperature, of the room was modelled. The energy flow was calculated in three major phases. Firstly, the energy passed through the glass of the Trombe Wall and was absorbed by the dark surface. Secondly, the transfer of heat from the surface of the wall, into the actual wall and into the air gap which depends on the difference in temperature between the units. Thirdly, heat transfer into and out of the room is calculated and the energy inside is used to approximate the room temperature.
In each step, some energy is lost, in the first one due to reflection and absorption of the window, since absorption heats the window, which is quickly cooled down by the outside air. In the second step, some of the energy that transfers into the air gap is lost through the glass, and in the third step heat loss is through the isolation, based on the outside temperature. The model splits up the room into seven different units which are the glass of the Trombe Wall, the glass of the window, the air gap, the surface of the Trombe Wall, the rest of the Trombe Wall, the thermal mass of the room, and the air in the room. These all have different mass and specific heat capacity which can be used to calculate their temperature. The model saves the amount of energy in every unit of the building, then, based on the difference in temperature, thermal conductivity, and convection, calculates the energy transferred during one minute of static conditions.
After the minute the state changes and the process is repeated.
To get accurate results a number of constants had to be used, both simple ones that we could measure such as the dimensions of the room and Trombe Wall, but also complex ones such as the Prandtl Number and Kinematic Viscosity of Air. Most of these constants were precise numbers, either calculated, measured, or accredited to a reliable source, but for a few inputs, it was not possible to get exact values.
Examples include the global heat loss coefficient of the building or the width of the area absorbing direct sunlight, a value that should be zero. But since our approximation only assumes one transfer of heat every minute it must have a
thermal mass to stabilize the model. To get as accurate a model as possible, these input constants had to be optimized.
Parameter Optimization
The error of the model is defined as the sum of squares error:
𝐸𝑟𝑟𝑜𝑟 = 1
𝑛 ∑(𝑥𝑖− 𝑥𝑖∗)2
𝑛
𝑖=1
where 𝑥∗ is the modelled value of indoor temperature and 𝑥 is the real value at the same point in time, as measured by our sensors in the Trombe Wall rooms. To minimize this error, and thus increase the accuracy of our model, model coefficients are chosen such that the sum of the squares is minimal. These coefficients’ optimal values were calculated by an optimization algorithm. The basic process of most optimization algorithms is to first assign a reasonable starting value for each of the parameters, and then improving upon this value through several iterations, whereupon the final value results in the least possible error.
Since there is no direct relationship between an independent variable and a dependent variable, and the parameters to be optimized had to be constricted within a reasonable span from a physics perspective, the issue was identified as a constrained nonlinear optimization problem. Constrained minimization of this type is a problem of finding a vector that is a local minimum to a multivariable scalar function (the error function) 𝐹(𝑥1, … , 𝑥𝑛) subject to constraints on the variables (𝑥1, … , 𝑥𝑛).
Sequential Least Squares Programming (SLSQP), an algorithm for nonlinearly constrained, gradient-based optimization based on quasi-Newton methods, was chosen for its quick convergence and high precision [5]. The optimization algorithm was written in the programming language Python and utilised several of its libraries for scientific computing, including NumPy and SciPy.
V. RESULTS A. Quantitative Measurements
Data were measured from four Trombe Wall rooms and two Direct Gain rooms for almost the complete month of February 2020. Ladakh is subject to an average of 320 sun days per year, which allows the Ecology Hostel to rely solely on solar energy as its form of heating. All rooms were south-facing, had the same amount of window area, and received the same amount of incident sunlight throughout the whole period of measurement. It is assumed that all solar energy from the sunlight reaching the outer wall of each room is used to heat that room. The illuminance from the sun can be observed in Figure 3.
Figure 3: The incoming illuminance from the sun hitting the southern wall of the Ecology Hostel during the month of February 2020. The y-axis shows illuminance measured in Lux while the x-axis shows the date in which the datapoint was measured. Data is missing between the 11th to the 16th, and the 19th to the 22nd of February.
The average temperature of the Trombe Wall for the month of February 2020 is 17.44 degrees Celsius, 2.63 °C higher than the Direct Gain rooms’ average temperature of 14.81 degrees Celsius. Both types of rooms receive the same amount of solar energy, meaning the Trombe Wall is more effective in maintaining the energy received. In Figure 3, we can see how the temperature in the two types of rooms varies during one normal day. The temperature in the Trombe Wall room peaks two hours after the Direct Gain room, which indicates that it takes longer time for the heat from the sunlight to be conducted through the Trombe Wall’s masonry into the room than through thermal mass of the Direct Gain (floor, walls, furniture, etc.).
The lag time, i.e. the time it takes for solar energy to pass through the thermal mass to the surrounding air of the room, is longer for the Trombe Wall than Direct Gain. Illuminance data shows that first rays of sun hit the outer wall of the Ecology Hostel at around 8:30 in the morning, which corresponds well with when the rooms start heating up after the night’s cooling. Considering that the specific heat capacity, thermal conductivity, and the density of mud, of which this Trombe Wall is made of, is 860 J/kg°C, 0.9 W/m°C, and 1800 kg/m3 respectively, the lag time for the Trombe Wall is calculated to nine hours and ten minutes. The first wave of heat each day will, therefore, reach the interior of the room at 17:40, which is around the time the sun starts to set in Ladakh in February. Given that sun sets at 18:00, the final solar energy will pass through the wall at 03:10 in the morning. Until the sun rises again the next morning, there will be no additional heating of the room. Looking at Figure 4 below, we can see that the room is coldest during this period when there is no heat being released from the Trombe Wall, that is, between 03:00 and 09:00. In Direct Gain rooms, a larger percentage of the solar energy is used to directly heat the air, which, together with the lower heat-storing capacity of the materials in the furniture that partially make up the thermal mass composition, results in a lower lag time. Hence, the Trombe Wall can maintain a stable temperature throughout the day, and into the night, much more so than the Direct Gain technology.
Figure 4: The average temperature of the rooms with Trombe Walls respectively the Direct Gain rooms, compared to the average outside air temperature. The y-axis shows temperature measured in degrees Celsius while the x-axis shows the date in which the datapoint was measured. Only the points in time when data from both types of rooms existed were used in the plot.
Looking at the temperatures for the different Passive Solar techniques over the month of February 2020, as shown in Figure 5, it becomes apparent that the temperature in Trombe Wall rooms is held to a more stable level compared to the Direct Gain rooms: the Direct Gain rooms reach both much higher and much lower temperatures than their Trombe Wall counterparts. This becomes apparent when looking at the standard deviation as a measure for the spread of the two datasets. The data from the Direct Gain rooms have a standard deviation of 6.97 – over two times higher than the standard deviation of 2.97 of the data from the Trombe Wall rooms.
This indicates that the data points for the Direct Gain sample are spread out over a large range of values, compared to the Trombe Wall sample that are closer to the mean. The Direct Gain technique relies on having large windows that allow more sunlight to directly pass into the room, which, considering that the sun often shines the whole day in Ladakh, results in the room becoming overheated during the day.
However, these windows also allow the warm air to escape during night-time, and there is no sun to keep heating the room, explaining why the temperature plunges to below ten degrees during this time.
Figure 5: The fluctuations in temperature over the month of February 2020. The y-axis shows temperature measured in degrees Celsius while the x-axis shows the date in which the
datapoint was measured. The temperature spikes during the day and dips during the night. One day of data is missing in the beginning of the month due to sensor malfunctions.
One of the most effective aspects of the Trombe Wall is the ability to sustain a comfortable room temperature throughout the whole day, its success becoming more apparent when compared to the Direct Gain rooms. In this study, we defined comfortable living temperature as between 15 and 25 degrees Celsius – a quite wide range containing temperatures that many countries would consider uncomfortable but will suffice here considering the cultural context in which the study was conducted. The lower end of the spectra is supported by measuring the temperature in homes and asking the owners if they deemed it comfortable at the time of the measurement. The temperature in the Trombe Wall rooms are kept in this acceptable comfort range of 15 and 25 degrees Celsius 83.2% of the time. In comparison, the corresponding number for the Direct Gain rooms is 22.7% – the indoor climate being either too hot or too cold a large majority of the time. This is visualized in the next graph, Figure 6.
Figure 6: The amount of time where the indoor temperature is between 15 and 25 degrees Celsius in the different rooms.
The description is binary, meaning that the line is filled when the temperature is in this range and left blank when it is not.
The x-axis shows the dates in February 2020.
Isolating the data from Direct Gain rooms in Figure 7, large temperature swings can be observed more closely.
Temperatures could drop to close to freezing levels during the night, at least in the beginning of February, only to drastically increase to upwards thirty degrees Celsius during the day.
Figure 7: The temperatures in the two Direct Gain rooms in the Ecology Hostel during the month of February 2020. The y-axis shows temperature measured in degrees Celsius while
the x-axis shows the date in which the datapoint was measured. Gaps in the graph are missing data due to sensor failure.
The temperature in the Trombe Wall rooms seldom drops below fifteen degrees Celsius or rise above twenty-five degrees Celsius during the day, as is shown in Figure 8. The deviant results from Room 10 and 4 can be explained by it being inhabited by guests, while all other rooms remained empty during the time of the measurements. Room 10 had two guests during most of the month while room 4 only had one guest living there between the 18th and 27th.
Figure 8: The temperatures in the Trombe Wall rooms in Ecology Hostel during the month of February 2020. On the x- axis we have the date and on the y-axis the temperature measured in degrees Celsius. Room 10 was mostly inhabited by 2 persons.
There was no statistically significant difference in humidity between the Direct Gain and Trombe Wall rooms. However, there was a substantial difference in amount of natural light entering the two types of rooms. The illuminance in Direct Gain rooms was substantially higher than the Trombe Wall rooms, with an average (during daytime) of 2606 lux. In contrast, the brightest level of illuminance measured in a Trombe Wall room was 322 lux. A comparison over a five- day period can be observed in Figure 9.
Figure 9: The light intensity in Trombe Wall rooms (blue) compared to Direct Gain rooms (orange) during a five-day period. The y-axis shows illuminance measured in Lux while
