Senior Form Physics – Sustainable Building
Sustainable Building
Student’s Version
Table of Contents
Activity 1: Introduction to sustainable building / P.1Activity 2: Don’t heat me up! / P.4
Activity 3: Investigating the energy efficiency of school & home / P.9
Activity 4: Why sustainable building? / P.12
Optional Activity: Design of sustainable buildings / P.13
Appendix 1: Reference information for different types of glasses / P.14
Appendix 2: Investigation Guide: Reference for Activity 2 / P.17
Appendix 3: More information for U-value of materials / P.19
© 2007 The University of Hong Kong – Faculty of Education. All rights reserved.
Senior Form Physics – Sustainable Building
/ Activity 1Introduction to sustainable building
The term “Sustainable Building” comes from “Sustainable Development”. In 1987, the Prime Minister of Norway, Dr. Gro Harlem Brundtland created the landmark definition of Sustainable Development in the Brundtland Report, “Our Common Future”
Q1.
Brainstorm some essential features of a sustainable building based on the landmark definition of “Sustainable Development” above, and what you may have learned through other aspects of environmental education.
Q.2
What are the different types of energy use in residential buildings and in commercial buildings in Hong Kong?
Among the uses of energy you mentioned, which consumes the largest amount of energy? You will look into it in Activity 2 – “Don’t heat me up!”
Q.3
The technology of air conditioning gives us a more comfortable environment during summer but it also brings us some negative impacts. Can you list some?
/ Activity 2Don’t heat me up!
Engineers have to make sure buildings are comfortable to live in – not too hot in summer and not too cold in winter. To achieve this aim they use different kinds of building materials to reduce the heat transfer through conduction and radiation.
Quick revision: How is heat transferred? By which three processes?
Investigation: To find out whether single glass or double-glazed glass can better slow down the heat gain of indoor space by sunlight. Draw your design in the space below:
First round of hot box test (Single glass VS Double-glazed glass)
B - Single glass [20 mm thick]
Temperature (oC) at 30-second intervals
Time (seconds) / 0 / 30 / 60 / 90 / 120 / 150 / 180 / 210 / 240 / 270 / 300Double-glazed glass
Single glass
Q. What is the result of the demonstration? How can you explain the result?
Second round of hot box test
(Glass with sun control film VS Low-e glass VS Clear glass)
A - Low-emission / Low-e glass [6 mm thick](coated with metallic oxide reflecting layer)
B - Glass coated with “3M” radiant energy blocking film (sun control film) [6 mm thick]
(solar films are used to reduce the heat gain of a building through radiation)
C - Clear glass [6 mm thick]
(ordinary glass with poor heat insulation properties)
Temperature (oC) at 30-second intervals
Time (seconds) / 0 / 30 / 60 / 90 / 120 / 150 / 180 / 210 / 240 / 270 / 300Low-emission glass
Glass with sun control film
Clear glass
Q. What properties of the sun control film and low-emission glass may account for the experimental results?
Third round of hot box test
A - Ceramic tile [6 mm thick](common on walls of kitchens, bathrooms and exterior surfaces)
B - High-density polystyrene board [6 mm thick]
(a kind of very high density foam, a common component of roof structure)
C - Wooden board [6 mm thick]
(used as building materials in countries overseas)
d
Temperature (oC) at 30-second intervals
Time (seconds) / 0 / 30 / 60 / 90 / 120 / 150 / 180 / 210 / 240 / 270 / 300Polystyrene board
Ceramic tile
Wooden board
Q. What is the result of the demonstration? How can you explain the result?
Further discussions
The hot box test (with a much more complex setup) is commonly used in buildings research. Discuss the importance of the hot box test to the design of sustainable buildings.
U-value and shading coefficient are two common measurements in comparing the thermal properties of materials in industry:
U-value is a measure of heat transmission due to thermal conductivity (conduction + radiation + convection) of a material. The lower the U-value, the less heat is transmitted through the material.
(Refer to appendix 3 for more detailed information for U-value of materials)
Shading coefficient is the ratio of solar heat gain through a piece of special glass to the solar heat gain through a single piece of 3mm thick clear glass under the same set of conditions. The smaller the number, the better the special glass at stopping the entry of solar heat radiation.
Rank the materials tested in second round by their shading coefficients.
Other special building materials: Fire-resistant glass
There are many types of specially made building materials and glasses serving for different needs of buildings. Fire-resistant glass: a kind of glass that is widely used in buildings for safety purpose. Can you think of some features of this type of glass that can enable it to have “fire-resistant” property?
/ Activity 3Investigating the energy efficiency of your school building and home building
The use of carefully selected building materials is only one of the many ways to improve the energy efficiency of buildings. We will explore some other ways in this activity.
Let’s first go back in time to learn about the most ancient sustainable “building“before investigating the modern buildings around you.
Before building technology began, people used to live in caves – the most ancient sustainable “building”. Cave dwelling (穴居), as shown in the pictures below, provided prehistoric people with a “comfortable” and “safe” home.
What are the advantages of cave-dwelling?
In China, cave dwellings are mostly found in the North and located on mountains. Why?
Now come back to the modern age. Can you think of:
1) Designs of buildings that can help to improve energy conservation?
2) Ways that the occupants can help to increase energy conservation in modern buildings?
Design changes of buildings / Ways that occupants can help:If you only have a few ideas, you are recommended to download and read the Energy Efficiency and Conservation for Buildings Guide from the website of Electrical and Mechanical Services Department (EMSD)
URL: http://www.emsd.gov.hk/emsd/eng/pee/em.shtml
(Last visited on 30 – 05 – 2007)
This contains many suggestions for the builders (designs of the buildings) and occupants (ways they can help) to reduce energy use in a building.
Action!
Part 1: Planning the investigation
Make a checklist based on the answers from the previous discussion with your groupmates. The checklist should consist of a list of energy efficiency features of buildings. Use it to investigate your school building and your home building. Evaluate the energy efficiency of these two buildings based on the results of your investigation and present the findings to your classmates.
Tips for investigation:
1. Take some photos of good or poor energy efficiency features of the building.
2. It is not easy to obtain first hand information about the designs of the buildings. You may need to talk with the people who are familiar with the designs and structures of the buildings. (E.g.: School staff, management committee or maintenance staff of your home building…etc)
3. You can investigate any other building if you are confident that you can get more information for the investigation, instead of your home building.
Part 2: Presenting your findings
You may organize your findings in a PowerPoint slide show and present it in front of class. You could show some photos from the investigation. Sometimes it is very difficult to compare the energy performance or energy saving features of different types of buildings, you may focus on describing the features you observed during the investigation instead of trying to do comparisons between different buildings. For your school building, you might write a class report for the Principal, suggesting ways the school could improve its energy sustainability.
Measurement is very important in science. For example the Air Pollution Index (API) is a tool created to compare the air pollution level of the air in different locations. (URL: http://www.epd-asg.gov.hk/english/api_you/whatapi.php ) When engineers perform an “energy audit” of a building, some measurements are needed to measure the energy performance of a building and compare different buildings’ energy performance. For example, the OTTV (Overall Thermal Transfer Value) is an index for comparing the thermal performance of buildings. It is a measure of the average heat gain into a building through the walls and other surfaces and consists of three major components: (a) conduction through opaque walls, (b) conduction through window glass, and (c) solar radiation through window glass. The usual practice is to have two sets of OTTV: one for the exterior walls and the other for the roof. You can read the website: http://www.bd.gov.hk/english/documents/code/e_ottv.htm for more information about OTTV.
/ Activity 4Why sustainable building?
(Further discussions on STSE)
Apart from the technical aspects (such as testing of building materials), the topic of sustainable building can lead to many useful discussions. Discuss the following questions with your classmates and teachers. This may be related to future careers if you want to be an architect, an engineer or a materials scientist for instance.
- Why do we need sustainable buildings?
- What are the benefits of sustainable buildings?
- Who are the beneficiaries?
- Can you illustrate the interactions between science, technology, society
and environment (STSE) with the context of sustainable building?
Discussion notes:/ Optional Activity
Appreciate the designs of some well known sustainable buildings in Hong Kong and globally
Dr. Sam Hui, a specialist in sustainable building, has found a data-base analysing some well known sustainable buildings in Hong Kong and all over the world. You are recommended to visit the following website for an interesting and deep exploration of sustainable buildings to develop your study of this topic.
“Case Studies on Sustainable Buildings”
URL: http://www.hku.hk/mech/sbe/case_study/index/top.htm
(Last visited on 30 – 05 – 2007)
Activity for your interest: Read the information about the following four sustainable Hong Kong buildings in the website and then have a close look at them when you have time to visit them!
Appendix 1:
Comparison of different types of glazing (Source: EMSD)
Criteria for good glazing: low thermal conductivity and high visibility
Characteristic特性 / Double glazing with coatings
有塗層的雙層玻璃 / Single glazing
with coatings
有塗層的單層玻璃 / Low emission double glazing
低放射性的
雙層玻璃 / Single glazing without coating
沒有塗層的
單層玻璃
Properties
特質 / Two layers of glass separated by a spacer
雙層，中間留有空間
Coating provides a reflective barrier with choice of colours such as silver, bronze and gold etc.
塗層具反射作用，備有銀色、銅色、金色等多種顏色可供選擇 / Only one layer of glass
單層玻璃
Coating provides a reflective barrier with choice of colours such as silver, bronze and gold etc.
塗層具反射作用，備有銀色、銅色、金色等多種顏色可供選擇 / Invisible metallic coating admits visible light but blocks radiant heat
表層為看不見的金屬塗層，可透光亦能阻隔輔射
Two layers of glass separated by a spacer
雙層玻璃，中間留有空間
Clear or laminated colours
透明或可塗上顏色 / Typical clear glass without any treatment or coating
一般的透明玻璃，沒有經過任何處理或加上塗層
Only one layer of glass with custom choice of colours or clear
單層玻璃，可以是透明，亦可自選顏色
Thermal transfer value (W/m2℃)
熱傳送值
(瓦特/平方米度攝氏) / 2.4 – 3.29 / 4.88 – 5.96 / 1.6 – 1.87 / 5.22 – 6.76
Shading coefficient
遮陽系數 / 0.4 – 0.89 / 0.23 – 0.47 / 0.12 – 0.45 / 0.73 – 0.89
Sound Reduction Index (dB)
隔音 (分貝) / Max. 33
最高值為33 / Max. 25
最高值為25 / Max. 32
最高值為32 / Max. 25
最高值為25
Solar load
日光負載 / Medium
中等 / Medium
中等 / Lowest
最低 / Highest
最高
Transmission load
透熱度 / Medium
中等 / Highest
最高 / Lowest
最低 / Highest
最高
Glare pollution
室外炫光效果 / Slightly High
稍高 / Highest
最高 / Slightly Low
稍低 / Lowest
最低
Reflectance
反射系數 / Slightly High
稍高 / Highest
最高 / Slightly Low
稍低 / Lowest
最低
Visibility
透光度 / Lowest
最低 / Lowest
最低 / Highest
最高 / Highest
最高
Fire-resistant glass
There is a transparent interlayer (called the intumescent layer) between two sheets of glass. It is the intumescents (materials in the interlayer) which give the fire-resistant properties to the glass.
An intumescent is a substance which swells as a result of heat exposure, thus increasing in volume, and decreasing in density. The chemical change is endothermic (absorbs heat) since the intumescent contains chemically bound water. Intumescents are very important in fire prevention and commonly used in fire protection products. A crucial factor in passing fire tests for fire protection products is to keep the item being protected below its critical temperature. For example, structural steel loses its strength above 550°C. Steel first expands with increasing heat, but once above its critical temperature, it weakens, like spaghetti in boiling water. (Remember the collapse of the Twin Towers in New York on 11 September 2001 (9/11) after they were set on fire by the plane crashes!)
Hydrates (chemically bound water) in the intumescent layer can keep their surroundings at around 100°C, the boiling point for water, until all the hydrates are boiled off. In fireproofing applications using intumescents with hydrates, the temperature increase in the item to be protected, tends to "flatline" at the 100°C mark, until all the water is gone. Then, the temperature begins to increase rapidly again.
Fire temperatures in a building can reach 1100°C depending on the fuel present and the availability of oxygen. The presence of hydrates in intumescents can keep the item exposed to the heat at or below 100 °C, until all the water boils away.