A Model Passive Solar Home Student Design Project

Paper ID #33159

Dr. Matt Aldeman, Illinois State University

Matthew Aldeman is an Assistant Professor of Technology at Illinois State University, where he teaches in the Renewable Energy and Engineering Technology programs. Matt joined the Technology department faculty after working at the Illinois State University Center for Renewable Energy for over ﬁve years. Previously, he worked at General Electric as a wind site manager at the Grand Ridge and Rail Splitter wind projects. Matt’s experience also includes service in the U.S. Navy as a nuclear propulsion ofﬁcer and leader of the Reactor Electrical division on the aircraft carrier USS John C. Stennis. Matt is an honors graduate of the U.S. Naval Nuclear Power School and holds a B.S. in Mechanical Engineering from Northwestern University, a Master of Engineering Management from Old Dominion University, and a Ph.D. in Mechanical and Aerospace Engineering from the Illinois Institute of Technology. Dr. Jin Ho Jo, Illinois State University

Dr. Jin Ho Jo is an Associate Professor of Technology at Illinois State University, teaching in the Renew- able Energy program. Dr. Jo is the program coordinator and also leads the Sustainable Energy Research Group at ISU. Dr. Jo is an honors graduate of Purdue University where he earned a B.S. in Building Construction Management. He earned his M.S. in Urban Planning from Columbia University where he investigated critical environmental justice issues in New York City. His 2010 Ph.D. from Arizona State University was the nation’s ﬁrst in sustainability. His research, which has been widely published, focuses on the use of renewable energy systems and sustainable building strategies to reduce negative impacts of urbanization.

c American Society for Engineering Education, 2021

A Model Passive Solar Home Student Design Project

Abstract

In a course focused on renewable energy technologies (especially focusing on solar energy and wind energy), a student project assignment has been developed wherein students design, build, and test a model passive solar home. Following an in-class lesson on passive solar design strategies, students choose a location on Earth where their model home will be “located.” Next, the students must design their passive solar home so that it incorporates good passive solar design principles and includes, at minimum: 1) roof overhangs that are long enough to shade more than 2/3 of the home’s south-facing windows at solar noon on the summer solstice, but short enough that they shade no more than 1/3 of the home’s south-facing windows at solar noon on the winter solstice, and 2) at least one other specific feature that maximizes the solar gain in the winter and/or minimizes the solar gain in the summer. Students build their model passive solar homes out of a material of their choosing. Foam board, poster board, cardboard, and plywood are common choices. The model home must be built to scale, and the scale of the model home must be specified. On the due date, students bring their model homes to the lab and test the shading performance of their roof overhangs. Students give a brief explanation of their home’s design and features, and then they adjust a heliodon – specifically built for this purpose – to the sun’s altitude angle for their home’s location at the summer solstice and then at the winter solstice. The instructor observes the shading performance of the home’s roof overhangs and determines whether the design criteria have been met. In addition to constructing the home, the students write a two page single-spaced paper explaining the design and features of the home. The assessment of the project is based on 1) whether the home meets the design criteria, 2) professionalism of the model home, and 3) clarity of the written description. The project ties together several important concepts in this course, and provides students with an opportunity to creatively apply what they have learned. Student feedback on the project has been overwhelmingly positive.

Introduction

A Bachelor of Science in Renewable Energy (RE) degree program was established by Illinois State University in 2007. The mission of the program is “to prepare technically-oriented managerial professionals and leaders for business, industry, government, and education by articulating and integrating competencies in Renewable Energy.” The program prepares graduates for jobs in the fields of energy and renewable energy systems as well as regulatory and governmental agencies. To meet the demand for well-rounded graduates who are knowledgeable in both technical and economic aspects of renewable energy systems, an interdisciplinary curriculum was developed, consisting of a multitude of selected courses from across the university. In 2018, the name of the program was revised to the “Sustainable and Renewable Energy” program to reflect the increasingly broad array of energy technologies that an energy industry professional should be familiar with.

The Sustainable and Renewable Energy (SRE) program has five overarching goals that align with the strategic goals of the college and university. The five goals of the Sustainable and Renewable Energy program are:

1. Provide students with high quality educational experiences by featuring a modern, up-to- date curriculum that will develop the technical and managerial knowledge, skills, and attitudes that are foundational to success as Renewable Energy professionals. 2. Recruit and graduate a diverse group of individuals to support companies and organizations that will employ Renewable Energy professionals in the state and throughout the United States. 3. Provide opportunities for students to interface with Renewable Energy professionals. 4. Provide service to companies and organizations that employ Renewable Energy graduates through applied research, consulting/workshops, and participation in professional organizations. 5. Develop industry and Renewable Energy alumni relationships in support of the program.

To meet Program Goal #1 and ensure that graduates acquire a fundamental understanding of renewable energy systems, a new required course was added for the fall semester of 2017 called TEC 258: Renewable Energy Technology Applications. The course has been offered every fall semester since that time, making Fall 2020 the fourth time that the course has been offered. The course is typically taken by students in their junior or senior year. The purpose of this course is to help students gain more in-depth and hands-on experiences by working with renewable energy technology, especially solar and wind energy technology.

After a brief review of electricity fundamentals, the first half of the course focuses on solar energy, beginning with a review of solar resources and the photovoltaic effect (both of which are covered in a previous course). Next the course includes the topics of solar siting considerations, passive solar design, types of solar systems, types of photovoltaic (PV) cells, inverters (including micro-inverters and DC optimizers), and battery storage applications. The first half of the semester includes 11 assignments, most of which are hands-on labs with solar resource assessment tools, PV cells, multi-meters, data loggers, charge controllers, and batteries. The second half of the semester takes a turn away from solar energy systems and moves into wind energy systems. During the second half of the semester the focus is on types of wind turbine generator systems and the factors that influence the energy generation of a wind turbine. The second half of the semester includes six assignments, most of which are hands-on labs with model wind turbines, a wind tunnel, and data logging equipment.

In addition to the aforementioned labs, both halves of the semester include a required student project relating to the course material. The project in the second half of the semester is to design, build, and test a model wind turbine that will produce as much energy as possible during a 20-second testing interval. The student project in the first half of the semester is to design, build, and test a model home that uses the principles that have been discussed in class. Because this includes passive solar design, the project has become known as the “Model Passive Solar Home Project.”

In the next section of this paper, a literature review describes current passive solar design strategies as well as methods of evaluating their effectiveness. Subsequent sections of this paper will further discuss how the “Model Passive Solar Home Project” is structured, how students’ projects are evaluated, and what students have gained from this assignment. Because the project ties together the concepts of passive solar home design, solar resources, thermal efficiency of buildings, and PV systems, the project fits neatly into the objectives of the course and the program as a whole.

Review of Literature

Passive solar design is utilized to collect, store, and distribute thermal energy by natural radiation, conduction and convection through appropriate building design and materials [1]. Passive solar design also involves blocking the direct solar radiation penetrating into buildings in order to provide cooling during the summer season [1]. By learning the concept of passive solar design, students will begin to understand the use of heat transfer processes, such as radiation, conduction, and convection, to distribute thermal energy provided by the sun. In addition, students will learn how incorporating passive solar concepts into the building design can save money by reducing heating and cooling energy demand.

Several previous research studies have shown the effectiveness of passive solar systems and how passive solar design strategies have been adopted. For example, Kruzner et al. [2] identified passive design strategies as the most cost-effective methods to reduce energy consumption in buildings, and evaluated a nationally representative sample of 1,000 existing homes. These buildings were evaluated for three passive design strategies including orientation, roof color, and level of shading using satellite images. Although the study found several statistically significant regional trends, at the national level, no statistically significant passive solar strategies were found among the sample houses evaluated in the study. Kruzner et al. claimed that policy measures and education are required to take advantage of the opportunity for cost-effective energy savings through more widespread passive solar design.

The next two examples show different analytical strategies to evaluate energy savings through passive solar design via simulation and empirical analyses. A study conducted in Sydney, Australia by Albayyaa et al. [3] analyzed two types of detached residential houses with two floors and four bedrooms using a building energy simulation software tool. Several scenarios were constructed based on passive solar parameters to determine the total energy required to achieve thermal comfort in the house. This study found that the total energy required for heating during winter is reduced 37% by using passive solar strategies. The method suggested in this study was insightful, and we will consider this type of simulation analysis to be adopted as part of the Model Passive Solar Home project to show the effectiveness of the passive solar design in the future. Another study was conducted in Tibet by Liu et al. [4] to evaluate the effectiveness of a passive solar house. The case study house was divided into two parts by a Trombe wall, and they measured the temperature of two different sections. The study found the passive solar design effectively maintained the indoor temperature higher than the outdoor temperature, although the temperature fluctuations were similar as the temperature changed outside.

Other studies have presented combined strategies with passive and active solar design aspects. Yu et al. [5] identified seven key decisions and 24 passive and active strategies that lead to an optimized Zero Energy Solar House with better architecture, comfort, and energy balance. They emphasize the importance of selecting passive strategies specific to the home’s shape, function, layout, and microclimate. Another study by Wu et al. [6] explored the role of Building Information Modeling (BIM) systems in facilitating sustainable living design and construction. They report that the emphasis of BIM education has been shifting from software training to problem-solving in the context of project execution and management

A review of projects submitted to the U.S. Department of Energy Solar Decathlon competition was helpful for the instructor of the Model Passive Solar Home project to develop grading rubrics for the Model Passive Solar Home project. This review of Solar Decathlon homes served as the inspiration for the requirement that the students’ Model Passive Solar Home projects include components of energy efficiency beyond passive solar.

Although several prior works have shown the effectiveness of passive solar strategies, these studies have not provided a clear demonstration of how passive solar design can be taught in a structured, hands-on way in the classroom. In this article we will describe a course project where students design and build model home projects and learn the critical concepts associated with passive solar design strategies through course activities.

Project Requirements and Evaluation

After a discussion of passive solar design principles early in the semester, students are assigned the Model Passive Solar Home Project. They are given approximately one month to complete the project. The assignment is to design and build a model home that utilizes efficient design principles, includes passive solar home design features, and also includes at least one other feature that improves the efficiency of the home. The home must be built to scale (the specific scale is selected by the students), and the home must be between 6 to 12 inches tall. Students choose the geographic location on Earth where their house would be located, because this has a significant impact on the geometry of the design. Students are given wide flexibility to build the home out of a material of their choosing. The most popular materials are poster board and cardboard, but plywood is also used occasionally. 3D printers are available for students to use, but most students choose not to use them to complete this project.

The most challenging design requirement is that the home must be designed such that the south-facing windows (or north-facing, if the home is located in the Southern Hemisphere) are at least two-thirds shaded at solar noon on the summer solstice, and no more than one-third shaded at solar noon on the winter solstice. This ensures that the home will receive solar gain through the south-facing windows during the winter months, while the solar gain will be mostly blocked during the summer months. On the due date of the project, the model passive solar homes are tested using a heliodon apparatus that is described in a subsequent section. Students are also required to write a brief paper describing their model home, its features, and the reasons that they built their home the way that they did. The requirements and rubric for the project are shown in Table 1.

Table 1. Model Passive Solar Home Project Requirements and Rubric Item Description Points Shading Performance  Overhangs/awnings shade more than two- thirds of the south-facing window area at summer solstice, and no more than one-third of south-facing window area at winter solstice.  Window geometry provides reduced solar gain /25 in summer and increased solar gain in the winter. Professionalism  Model includes an active or passive solar feature in addition to the appropriately-sized overhangs.  Model is well-constructed and visually appealing, built to scale, and between 6” and /25 12” in height. Written description  Clear explanation of the model home, its scale, its location, and its features.  Written in a professional manner with proper grammar, punctuation, and writing style. Paper is one to two pages in length, typed and single-spaced. /50  References cited in appropriate format (APA, MLA, IEEE, etc. References do not count towards page limit)

Students must perform trigonometric calculations and build their model homes accordingly to ensure that the design criteria are met. As an example, a prototypical home is shown in Figure 1. The altitude angle of the sun is 훼, the height of the window is 푤, the distance between the top of the window and the eave of the roof is 푥, and the length of the overhang is 표.

Figure 1. Diagram of a hypothetical passive solar home The trigonometric relationship between the altitude angle 훼 and the length of overhang 표 is given by 표 tan(90 − 훼)° = (1) 푥 + 푤 Solving for the overhang length gives

표 = (푥 + 푤) tan(90 − 훼)° (2) If the objective is to shade at least two-thirds of the window, then 2푤 표 ≥ (푥 + ) tan(90 − 훼)° (3) 3 If the objective is to shade no more than one-third of the window, then 푤 표 ≤ (푥 + ) tan(90 − 훼)° (4) 3 The altitude angles of the sun will need to be known in order to complete the design. Students are allowed to choose any location for their model home, and their choice of location affects multiple aspects of their home’s design. There are several different ways of finding the relevant solar altitude angles for their home’s location. As a set of convenient thumb rules, students are provided with the following equations: At solar noon on the equinox, the altitude angle of the sun is equal to:

퐴푙푡푖푡푢푑푒 푎푛푔푙푒 = 90° − (푙푎푡푖푡푢푑푒)° (5) At solar noon on the summer solstice, the altitude angle of the sun is equal to:

퐴푙푡푖푡푢푑푒 푎푛푔푙푒 = 90° − [(푙푎푡푖푡푢푑푒)° − 23.5°] (6) At solar noon on the winter solstice, the altitude angle of the sun is equal to:

퐴푙푡푖푡푢푑푒 푎푛푔푙푒 = 90° − [(푙푎푡푖푡푢푑푒)° + 23.5°] (7) Students use the trigonometric relationships in Equations (3) and (4) and the solar altitude angles given in Equations (6) and (7) to size the overhangs on their home appropriately. As an example, suppose the latitude of the model home is chosen to be 40° N, the height of the window is four feet, and the distance between the top of the window and the eave of the roof is three feet. From Equation (6), the altitude angle at solar noon on the summer solstice is, 퐴푙푡푖푡푢푑푒 푎푛푔푙푒 = 90° − [40° − 23.5°] = 73.5° (8) and from Equation (7), the altitude angle at solar noon on the winter solstice is,

퐴푙푡푖푡푢푑푒 푎푛푔푙푒 = 90° − [40° + 23.5°] = 26.5° (9) To meet the requirement that the window be at least two-thirds shaded at solar noon on the summer solstice, the result from Equation (8) is substituted into Equation (3). 2푤 표 ≥ (푥 + ) tan(90 − 훼)° (10) 3 2 ∗ 4 푓푡. 표 ≥ (3 푓푡. + ) tan(90 − 73.5)° (11) 3

표 ≥ 1.7 푓푡. (12) To meet the requirement that the window be no more than one-third shaded at solar noon on the winter solstice, the result from Equation (9) is substituted into Equation (4). 푤 표 ≤ (푥 + ) tan(90 − 훼)° (13) 3 4 푓푡. 표 ≤ (3 푓푡. + ) tan(90 − 26.5)° (14) 3

표 ≤ 8.7 푓푡. (15) Thus, the requirements can be met by designing the house to include an overhang that is more than 1.7 ft. but less than 8.7 ft. in the scale of the model home. These are fairly broad tolerances, and can be met even with imprecise cutting tools (e.g. scissors) and low-quality materials (e.g. cardboard or poster board) as long as the students take a moderate degree of care in the construction of their home.

Testing

A one-axis heliodon was constructed specifically for the purpose of testing the model homes built by the students. The heliodon consists of a standard LED light bulb installed at the top end of an eight foot long two-by-four. The bottom end of the two-by-four is attached with a hinge to a base made of a 36-inch long 2x12 board. The 2x12 base remains stationary on the floor, while the hinge allows the two-by-four to pivot at any angle between zero and ninety degrees relative to the horizontal base. This allows the heliodon to simulate any solar altitude angle between zero and ninety degrees. To accurately measure the altitude angle, a large protractor with increments of one degree is connected to the base. As the two-by-four pivots up and down, it is simple to read the altitude angle by comparing the lower side of the two-by-four against the protractor immediately behind it. To fix the two-by-four in position – so that the shading on the home can be inspected without having to hold the two-by-four by hand – several one-inch holes have been drilled in the two-by-four. A one-inch dowel rod passes through one of the holes in the two-by-four, and a clamp is attached to the dowel rod to prevent the dowel rod from sliding through the two-by-four. The clamp is mostly unnecessary, because there is sufficient friction between the two-by-four and the dowel rod to hold the two-by-four in position. This heliodon design is a simple and inexpensive yet effective way of simulating an infinite number of solar altitude angles between zero and ninety degrees. An image of the heliodon at a relatively high solar altitude angle, possibly around the summer solstice, is shown in Figure 2(a). Figure 2(b) shows the heliodon at a much lower solar altitude angle, possibly around the winter solstice.

(a) (b) Figure 2. One-axis heliodon used for testing of the model passive solar homes (a) at a large solar altitude angle and (b) at a small solar altitude angle

Because the heliodon has only one axis (it has only one hinge), it cannot easily be used to simulate the azimuth angle of the sun’s position. It is possible to simulate the azimuth of the sun, but the model home itself would have to be rotated to simulate the azimuth angle, rather than the two-by-four arm that holds the light. To simplify the evaluation of the model passive solar homes in this project, the heliodon is only used to simulate the conditions at solar noon. At solar noon, the azimuth angle is zero.

Of course, like most simulations, the heliodon is not perfectly accurate. One of the inaccuracies of the heliodon comes from the fact that the two-by-four arm holding the light bulb is much too short to be realistic. For practical purposes, the two-by-four arm is only eight feet long, but to match the scale of the real world it would need to be much longer. Because the arm is too short, the angular diameter of the light bulb is larger than the actual angular diameter of the Sun as seen from Earth. Specifically, the light bulb is approximately 2 ¼” in diameter, and the bulb is located approximately 93 inches from the pivot axis of the two-by-four (because the light bulb faces back toward the model home, it is not located exactly at the end of the eight-foot two- by-four). As seen from the perspective of the model home, this gives the light bulb an angular diameter of 1.4 degrees. By comparison, the angular diameter of the Sun is known to be approximately 0.5 degrees from the perspective of Earth. To accurately simulate the angular diameter of the Sun, the length of the heliodon’s arm would need to be approximately 257.8 inches (about 21.5 feet). Alternatively, the light bulb could be replaced with a light bulb that has a diameter of approximately 0.8 inches.

Besides the angular diameter, another inaccuracy is that the height of the model home is much too tall relative to the distance between the home and the light source. For example, because the distance between the Sun and Earth is so large, in reality the altitude angle of the Sun does not change appreciably even when it is measured at the top of a very tall skyscraper. The additional height of the skyscraper above the ground is miniscule compared to the distance from the Sun to the Earth, and so the geometry of the situation does not change noticeably. In contrast, the model passive solar homes are allowed to be up to 12 inches in height, and this height is not insignificant when compared to the distance between the light source and the model home. Therefore, the altitude angle at the top of the model home is not identical to the altitude angle at the bottom of the model home.

Despite its inherent limitations, the heliodon has proven to be a useful tool. As long as the limits of its accuracy are not pushed to the extreme, it provides a reasonably close approximation of the geometry between the Sun and buildings on Earth. Because the design requirements are not too tightly constrained – as demonstrated in Equations 12 and 15 - the heliodon provides a measurement tool that is more than adequate for the purpose of this project.

Results

Figure 3 shows ten examples of model passive solar homes built by students. Each home is shown from the southwest and southeast corners of the home. Due to the project requirements, all of the examples in Figure 3 use overhangs to minimize solar gain in the summer (when the altitude angle is large) and maximize solar gain in the winter (when the altitude angle is small). The homes in Figure 3(a) and (b) used solar daylighting techniques by using windows across the top of the home. These upper windows also had an overhang to shade the windows during the summer months. The home in Figure 3(e) is notable for using a strategically-located deciduous tree. The student had two model trees: one with foliage and one without (shown). In the summer months, the tree’s foliage provided additional shade to the home and further reduced the solar gain. The home in Figure 3(k) and (l) has an unusual octagonal shape, which is beneficial because it increases the home’s volume to surface area ratio, which reduces the total amount of heat transfer through the walls. The homes in Figures 3(m), (n), and especially (q) and (r) were built into the ground to make an Earthen home. This also increases the efficiency of the home by adding insulation to the home’s walls and reducing the rate of heat transfer through the walls. The home in Figure 3(m) and (n) also featured a large rainwater collection system. The homes in Figures 3(a), (b), (g), (h), (i), (j), (k), (l), (m), (n), (s), and (t) all incorporated a PV system. Considering that solar photovoltaics is a major portion of the course, and students gain significant lab experience working with PV system components, it is not surprising that most students incorporate PV systems into their model home designs. Many of the students also built interior walls and structures to demonstrate energy-efficient interiors in addition to the exteriors. For example, several students included Trombe walls in their interior design, and many students placed their high-usage rooms near the south side of the home while putting their low-usage rooms on the north side of the home.

(a) (b) (c) (d)

(e) (f) (g) (h)

(i) (j) (k) (l)

(m) (n) (o) (p)

(q) (r) (s) (t) Figure 3. Images of ten example Model Passive Solar Homes

On the project due date, the students bring their models to the laboratory and briefly describe their home’s features to the instructor and the other students. As part of their description, the students describe the real-world location where their model home was designed to be located. Then they place their home on the heliodon with the south side of their home facing the arm of the heliodon. Each home is tested at two altitude angles: solar noon on the winter solstice, and solar noon on the summer solstice. Based on the location and the resulting altitude angles, the student adjusts the heliodon to the altitude angle of one of the solstices. The student and instructor then inspect the model home to see if it meets the design requirements. After inspection, the student adjusts the heliodon to the altitude angle of the other solstice, and the student and instructor inspect the home again to see if it meets the design criteria at this solstice. Images two different model homes at two different altitude angles are shown in Figure 4.

In Figure 4(a) and (b), a model home is shown being tested with the heliodon at a relatively large altitude angle. Close inspection of the protractor in Figure 4(a) reveals an altitude angle of approximately 62˚. This is not necessarily the summer solstice altitude angle at the location for which this home was designed; it is merely an arbitrary large altitude angle shown for demonstration purposes. Figure 4(b) shows that the home’s overhang shades almost all of the south-facing windows. Figure 4(c) and (d) show an octagonal-shaped model home being tested at the same 62˚ altitude angle. Figure 4(d) shows that the overhangs completely shade all of the home’s south-facing windows. Figures 4(e) and (f) show the same home as in images (a) and (b), but the home is being tested at a much lower altitude angle. Inspection of the protractor in Figure 4(e) shows that the altitude angle is now approximately 30˚. Figure 4(f) shows little to no shading of the home’s south-facing windows at this low altitude angle, which would result in a large amount of solar gain during the winter months. Figure 4(g) and (h) show the octagonal home at the same 30˚ altitude angle. Inspection of Figure 4(h) shows that the south-facing windows are slightly less than half-shaded. This would not have been sufficient to meet the design requirements if the altitude angle at the winter solstice for this home’s selected location was actually 30˚. However, it is likely that this home was designed to be built in a location where the altitude angle at the winter solstice is less than 30˚. A smaller altitude angle would result in less of the south-facing windows being shaded.

On the day that the model passive solar homes are due, the students take turns testing their model homes. The testing takes only a short amount of time, approximately five minutes per student. Students have commented that it is interesting to see how their design calculations match up with the heliodon testing, and it is fun to see the designs that their classmates have created.

In the most recent offering of this course during the fall semester of 2020, there were 17 students enrolled in the class. Sixteen of the students completed the project. The average grade for the sixteen students that completed the project was 90.1%, and the median was 92.0%. These average scores were significantly higher than the average overall course scores, indicating that most students were successful in meeting the desired outcomes of the project. All but two of the students were able to successfully meet the shading requirement of having at least two-thirds of the south-facing windows shaded at the summer solstice and no more than one-third of the south- facing windows shaded at solar noon on the winter solstice. This appears to be evidence that after completing this assignment, the majority of students understand how to optimize the size of roof overhangs to allow for a specified amount of solar gain as described in Equations (1) – (15).

(a) (b)

(e) (f)

(g) (h) Figure 4. Examples of testing at high altitude angles (a), (b), (c), (d), and low altitude angles (e), (f), (g), (h) Student Feedback

Although the successful completion of learning objectives described above may be more important than the students’ impressions of the project, student feedback is important nonetheless. This project has been part of the course since the time that the course began in Fall 2017. Therefore, it is not possible to compare students who completed the course without doing this project with students who completed this project as part of the course. If such a comparison were possible, perhaps by comparing test scores before and after the introduction of this project, it is hoped that the students who completed the project as part of the course would show a higher level of mastery for the passive solar design concepts relevant to this project. Unfortunately, this direct comparison is not possible because there is no control group. In lieu of a direct comparison, however, students were given an anonymous survey where they were asked for their feedback about the project. The survey questions were:

1. On a scale of 1 (strongly disagree) to 5 (strongly agree), please rate the following statement: I learned more about passive solar design by building a Model Passive Solar Home than I would have learned by taking an exam on the same material. 2. On a scale of 1 (strongly disagree) to 5 (strongly agree), please rate the following statement: After completing the Model Passive Solar Home Project, I am better able to describe the characteristics that make for efficient home design. 3. On a scale of 1 (strongly disagree) to 5 (strongly agree), please rate the following statement: The Model Passive Solar Home Project was fun. 4. On a scale of 1 (strongly disagree) to 5 (strongly agree), please rate the following statement: I recommend keeping the Model Passive Solar Home Project as part of the curriculum in this class. 5. (Open response): Do you have any suggestions for how to improve the Model Passive Solar Home Project?

The results of this survey are shown in Table 2. As shown in the table, most of the students that responded to the survey had a very favorable view of the project. The survey was given in an online anonymous format in parallel with the end-of-semester course evaluations, and the response rate (31%) is not particularly high. However, based on the survey responses combined with the in-person conversations that the instructor had with the students, it seems apparent that the students enjoy the project, and that they believe that they learned a lot by completing the project. Furthermore, the students seem to have enjoyed the opportunity to apply relevant course topics in a hands-on design and construction project.

Table 2. Student responses to anonymous survey about Model Passive Solar Home project. Total number of student responses = 5. On a scale of 1 (strongly disagree) to 5 (strongly 1 2 3 4 5 Average agree), please rate the following statements: 1. I learned more about passive solar design by 5 building a Model Passive Solar Home than I would 0 0 0 0 5.0 (100%) have learned by taking an exam on the same material. 2. After completing the Model Passive Solar Home 1 4 Project, I am better able to describe the characteristics 0 0 0 4.8 (20%) (80%) that make for efficient home design. 3. The Model Passive Solar Home Project was fun. 1 4 0 0 0 4.8 (20%) (80%) 4. I recommend keeping the Model Passive Solar 5 Home Project as part of the curriculum in this class. 0 0 0 0 5.0 (100%) 5. (Open response) Do you have any suggestions for 1. None. I really enjoyed being able to build a home how to improve the Model Passive Solar Home based on my own calculations and watching it succeed. Project? 2. NO, I really like the project I had a ton of fun building my house and even learning about passive solar design and I think covid just hindered the class from getting the full experience.

3. Hopefully face-to-face class format will come back again so that both the instructors and students can do a couple of examples.

Conclusions

The two projects in this course – including the model passive solar home – have come to be popular aspects of the course. Overall, students have remarked that they appreciate the hands- on nature of this course, and the model passive solar home is one of the most hands-on and open- ended assignments in the course.

As demonstrated in the Project Requirements and Evaluation section, there is a considerable amount of thought that must necessarily go into the design of the model home in order for students to successfully meet the design requirements. The instructor reminds students repeatedly that they should begin working on their project well before the due date. Students are even allowed to test their home with the heliodon before the due date, so that they can verify the design of their home. Because this project requires a considerable amount of planning and effort, students are not likely to do well on the assignment if they wait until the day before the due date to begin the project. Fortunately, most students heed this warning and begin the project well in advance.

From an instructor’s perspective, it is rewarding to see students go above and beyond the expectations for the assignment. Because this project is open-ended, it leaves a lot of room for students to show their creativity. Many students have included components in their home that were never discussed in the class. For example, one student built part of his home from scale- model used tires, one built a high-rise apartment building, one used gravel to simulate permeable concrete, and some have built their homes with very complex geometry. One student modeled the effect of deciduous trees to achieve the desired solar gain, and another student designed and modeled a rainwater collection system. Many of the students have created detailed interior floor plans for their homes that increase the thermal efficiency of the home, and many students go well beyond the idea of a mere “passive solar home” to design a home that is truly sustainable in a variety of aspects. All of these students have used their creativity to significantly exceed the instructor’s expectations for the project.

Because the project ties together the concepts of passive solar home design, solar resources, thermal efficiency of buildings, and photovoltaic systems, the project fits neatly into the objectives of the course and the program as a whole. As described in the Introduction section of this paper, the first objective of the Sustainable and Renewable Program is to “provide students with high quality educational experiences by featuring a modern, up-to-date curriculum that will develop the technical and managerial knowledge, skills, and attitudes that are foundational to success as Renewable Energy professionals.” The model passive solar home project helps the program to achieve this goal by encouraging students to think creatively and independently about how to best construct homes and buildings in the future while taking energy efficiency, renewable energy, and sustainability into consideration.

Based on the students’ enthusiasm for the project, the gains in conceptual understanding that the students achieve (as evidenced by the high evaluation scores and the success in achieving the desired shading characteristics), and the fit of the project into the broader program curriculum, the instructor plans to continue assigning this project in the future. Despite the success so far, improvements could no doubt be made. Additional requirements could be added in the future, such as requiring the students to describe the home’s heating and cooling system. Based on knowledge of heat transfer principles that they learn in other courses, students should be able to perform heat loss calculations and describe the types of windows and the insulating values of the walls. The project could also be presented as an economic optimization problem, where students design their homes under given cost constraints. Finally, the students may learn more from their peers if they are required to give a brief but more formal presentation about their home’s design to the class.

References

[1] S. Barber and M. Behm, “History of Passive Solar Energy,” 2012. https://uncw.edu/csurf/explorations/documents/scottbarber.pdf.

[2] K. Kruzner, K. Cox, B. Machmer, and L. Klotz, “Trends in observable passive solar design strategies for existing homes in the U.S.,” Energy Policy, Vol 55, pp 82-94, 2013. https://doi.org/10.1016/j.enpol.2012.10.071.

[3] H. Albayyaa, D. Hagare, and S. Saha, “Energy conservation in residential buildings by incorporating Passive Solar and Energy Efficiency Design Strategies and higher thermal mass,” Energy and Buildings, Vol 182, pp 205-213, 2019. https://doi.org/10.1016/j.enbuild.2018.09.036.

[4] W. Liu, D. Liu, B. Li, and M. Zheng, “Effect Analysis of a Passive Solar House in Tibet,” Vol 608–609, pp. 1790–1794, 2012. https://doi.org/10.4028/www.scientific.net/amr.608- 609.1790

[5] Z. Yu, Z. Gou, F. Qian, J. Fu, and Y. Tao, “Towards an optimized zero energy solar house: A critical analysis of passive and active design strategies used in Solar Decathlon Europe in Madrid,” Journal of Cleaner Production, Vol 236, 2019. https://doi.org/10.1016/j.jclepro.2019.117646.

[6] P. Wu and B. Hyatt, “Experiential and Project-based Learning in BIM for Sustainable Living with Tiny Solar Houses,” Procedia Engineering, Vol 145, pp. 579-586, 2016. https://doi.org/10.1016/j.proeng.2016.04.047.