5. Passive Designs

Students will be able to:

1. Recognize and explain the four basic principles of passive design.
2. Explain the different types of energy and the application of basic thermodynamic principles as applied to the design of buildings.
3. Distinguish between active and passive design at different building scales.
4. Identify the site-specific roles of orientation, insulation, ventilation, roofing, roof pitch, overhangs, and window placement in optimizing passive design.

The module should be useful in a variety of courses, from introductory to more advanced settings. It can be used as part of a green energy course, or as unit in an environmental science class. This activity is designed for lecture/lab and can involve outdoor components to demonstrate heating/cooling of different building materials. Educational level is undergraduate, with class size up to 20 (limited by the number of participants in demonstration activities). The write-up suggests using thermometers, ball jars, and different building materials to have students experiment with heating/cooling of these materials, but other components could be used to demonstrate the same principle. The activity takes a single lecture/lab period, anywhere from 1.5 to 3 hours. In the course, aspects of energy and power are presented in the first module; this passive design module can occur any time after the first module.

The full text and figures for the module are provided in the Student Section.

Structuring your classroom time

1. Quiz & Discussion. This module typically will be delivered after the initial module on Electricity, Work, and Power, but can function as a stand-alone module. Begin the class with a quiz from the prior week's module. Have students come to class with quiz questions and select five students to read their questions aloud. After each student recites her/his question, pause for the appropriate time for their classmates to write answers. After all five questions have been completed, ask five different students how they answered. This format allows focused discussion on the topic. Students have an opportunity to work through what is right and what is wrong with their understanding. The teacher gets feedback on the effectiveness of teaching materials and teacher delivery—what is clear and what is still muddy. Use the instructor regulated discussion pedagogy as explained in the course overview for developing discussion of the current module.

Scaffolding Learning

It is important to help the students use what they learned in the first module to build deeper understanding of this module. As the professor, you can help them make the connections between energy and Passive Designs. Passive Designs is mostly about solar energy and how the orientation and structure of buildings can work to exploit/avoid solar energy accumulation, storage, and transfer. The opening quiz reinforces the scaffolding of learning and forces students to revisit the previous module twice, once during their studies when they review for the quiz and formulate the quiz questions, and again when they participate in class discussions.

Metacognition

The flipped-classroom structure advocated for this course facilitates the development of metacognition by the students, directly involving them in the learning process. The use of student-generated questions for quiz and discussion helps students become aware of how they learn and understand the material. This is a big departure from the simple memorizing of terms and concepts that characterized much of their earlier education. Having students think of questions for quiz and discussion will inform their approach to learning in general. Another metacognitive strategy used in the course is requiring the students to apply basic science concepts to understand a technology, and then to require them to think about the application of that technology in the real world. The exercise having students examine the possible heating/cooling issues associated with buildings on their own campus brings the lesson close to home. Because students have probably not had occasion to be responsible for paying for heating, examination of an annual heating bill for the college or the professor allows students to appreciate the seasonality of heating requirements and the cost. The provision of heat energy via burning of fuels is costly to the pocketbook and potentially to the environment as well. That opportunities are available to reduce these individual and environmental costs via passive building design should be an emergent take-home message for the students.

Systems -Thinking

A major theme of this course is that students see the various technologies in the context of the global system, and this requires systems-thinking. This module on Passive Designs provides excellent opportunities for students to exercise systems-thinking. The simple exercise of examining the distribution of solar energy delivered to Earth's surface allows students to consider spatial and seasonal variation in heating derived from solar energy. At the Earth systems scale, discussion of thermal energy can move into consideration of, e.g., convective air and water flows, the distribution of wind and water currents across the planet, and global climate change. The examination of the relationship between heating degree days and the costs of heating brings home the point that human systems are intimately related to the climate system.

At the local level, passive designs can be examined with respect to microtopographic variation in the availability of solar energy and possible construction materials. Geographic features such as aspect and slope can be discussed in the context of costs and benefits: for example, placing a building on a steep, south-facing slope might provide access to heating from trapped thermal energy, but building on a slope might be difficult. Bricks might be great for heat storage and re-radiation, but local geology might not provide the sand and clay required for brick formation. From a systems perspective, the concept of "energy flows" can be exploited in the passive design of buildings (solar chimneys, Trombe walls, etc).

2. Student Presentation. Each class should have one or two PowerPoint presentations by students, given either during the current module or at the beginning of the next module. This activity involves peer instruction. For the Passive Designs module, students could consider a case study examining the costs and benefits of two different buildings that exploit passive design, comparing the approaches used in each building and evaluating the usefulness for each.

The passive designs activity begins by having students examine the relationship between heating degree days and eCO2 emissions from heating fuels on a college campus. From there, the global variation in heating and cooling is considered (and can be examined in greater or lesser detail as desired). Have students explore heating costs in some way, either for the professor's home or for the college. You can use GoogleMaps to have students examine an aerial view of their campus and consider which buildings they think have the greatest heating and cooling costs, based on things like aspect and insolation and surrounding vegetation. Then have them consider the number and placement of windows and potential for heating interiors of buildings.

For the plot comparing heating degree days and energy use, do the following Think-Pair-Share exercise (learn more about Think-Pair-Share (TPS)): Describe the relationship. In 2007 and 2008, the college was proud of its reduction in GHG emissions, relative to 2004–2006. Was this difference due to energy efficiency?

TPS exercise: Have students go to GoogleMaps and find their college campus. With respect to orientation, which buildings are situated to take advantage of a southern exposure? What other local environmental features come into play when considering exposure to solar radiation (topography, climate, vegetation, etc.)?

TPS exercise: BTUs are often used in conversions as ways to represent energy use. For example, a coal-fired power plant generates electrical energy; the amount of coal needed to heat the water to generate the steam to turn the turbine to generate the electricity often is expressed in BTUs. Thus, if a power plant burns coal to release 10,000 BTUs, that is sufficient to generate 1 KWh of electrical energy. Calculate the conversion efficiency of the power plant.

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Picture of a canning jar with a thermometer and construction material for measuring relative thermal mass and heat capacity.

Provenance: Randolph Chambers, College of William and Mary
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

If you fill another canning jar completely with water (one pint) and determine its initial temperature, then track its temperature after placement in the sun, you can calculate the energy input to heat the water. The British Thermal Unit (BTU) is the amount of energy required to heat 1 pound of water by 1 degree Fahrenheit. A pint of water weighs about a pound, so every degree increase in temperature in the water represents the input of 1 BTU. From the perspective of energy gain or loss over time, you can calculate the power needed to increase temperature (i.e., the amount of energy expended per time, or BTU/h). Energetically, one BTU is equivalent to about 0.3 watt-hour, and in terms of power, 1000 BTU/h is equivalent to about 300 W.

Discussions of other passive designs (solar chimneys, Trombe walls, etc.) and how they can take advantage of differential heating and cooling can finish the activity.

The assessment methods for this module can be found on the course assessment page. It is essentially what was provided on the course overview page. Below are selected Pre/Post Test questions. One approach is to have the students take the pretest for all the modules at the beginning of the class, and then to administer it again at the end of the class to document advancement in learning.

Pre-Post Questions:

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• Passive Solar Design Primer from the New Mexico Solar Energy Association (p. 71)
• Passive Solar Home Design article from the US DOE
• DeKay, M. and G.Z. Brown. 2013. Sun, Wind and Light: Architectural Design Strategies. John Wiley and Sons.
• Givoni, B. 1992. "Comfort, climate analysis and building design guidelines." Energy and Buildings, 18:11-23.