Background
Literature Review
Our research into the efficiency of building envelopes began with a study of the double-skin facade typology. Although our research topic is not specifically tied to this typology, our interrogation of cavity depth and heat transfer through convection are partially influenced by the double-skin and its features. A double-skin facade is a building envelope system consisting of two exterior building skins which create an intermediate cavity between two layers of glass. The main layer of glass is typically insulated, with the air cavity between the two layers acting as insulation against temperature extremes, winds and sound. The construction of these layers can influence what occurs within the buffer zone of the cavity, especially when air is brought into the cavity from the outside. It determines whether or not the introduced air is trapped, heated from solar radiation and used for passive heating to an interior space, or if that heated air is pushed directly into the space in order to heat it. The geometry and type of double-skin building envelopes are crucial for the conditions of air within the cavity.
Our research into the efficiency of building envelopes began with a study of the double-skin facade typology. Although our research topic is not specifically tied to this typology, our interrogation of cavity depth and heat transfer through convection are partially influenced by the double-skin and its features. A double-skin facade is a building envelope system consisting of two exterior building skins which create an intermediate cavity between two layers of glass. The main layer of glass is typically insulated, with the air cavity between the two layers acting as insulation against temperature extremes, winds and sound. The construction of these layers can influence what occurs within the buffer zone of the cavity, especially when air is brought into the cavity from the outside. It determines whether or not the introduced air is trapped, heated from solar radiation and used for passive heating to an interior space, or if that heated air is pushed directly into the space in order to heat it. The geometry and type of double-skin building envelopes are crucial for the conditions of air within the cavity.
Thermal Comfort:
Thermal comfort is the outcome of a well-balanced combination of building systems adapted to the building’s location and program. One of the first steps to consider when achieving thermal comfort is the design of an efficient building envelope. The building envelope can greatly affect the indoor thermal environment of the building. In the physical environment, thermal energy is transferred through conduction, radiation and convection. A balanced thermal environment is essential to feeling comfortable within a building. A person’s concentration, level of fatigue and manual and mental dexterity are all influenced by excessively high or low temperatures.
Key considerations for designing for thermal comfort include:
Thermal comfort is the outcome of a well-balanced combination of building systems adapted to the building’s location and program. One of the first steps to consider when achieving thermal comfort is the design of an efficient building envelope. The building envelope can greatly affect the indoor thermal environment of the building. In the physical environment, thermal energy is transferred through conduction, radiation and convection. A balanced thermal environment is essential to feeling comfortable within a building. A person’s concentration, level of fatigue and manual and mental dexterity are all influenced by excessively high or low temperatures.
Key considerations for designing for thermal comfort include:
- Air tightness and ventilation - An airtight envelope, along with natural or mechanical ventilation, can control the indoor thermal environment by managing the air exchanges with the outside
- Thermal inertia - The material choices of a building have an impact on how quickly changes in weather conditions are felt
- Solar gain - The building envelope can control how much heat from the sun is allowed to enter the building
- Insulation - Insulation of the building envelope and the use of thermally efficient windows reduces heat loss in the winter and conduction heat gains in the summer
Radiant temperature (measured as mean radiant surface temperature MRT) from heat sources like the sun, heaters or other machinery has a greater impact than air temperature on how we lose or gain heat. The rate of air movement or air velocity also influences the loss or gain of heat -- the faster the air movement, the greater the exchange of heat between the occupant and the air. Relative humidity is the ratio between the actual amount of water vapor in the air and the maximum amount of water vapor the air can hold in that temperature.
Thermal Behavior of Building Envelopes:
Cavity and roof insulation are common issues needed to be addressed in assessing the thermal behavior of building envelopes. Thermal insulation is used to resist the flow of heat and so raises the thermal impedance of the element to which it is attached. Thermal resistance (R-value) is a measure of the insulating ability of a material layer. A higher R-value represents a more effective insulator which can improve the thermal comfort of an internal environment.
Site influencing factors like temperature and moisture impact the practical thermal resistance and behavior of the wall unit. The movement of air and heat flow in cavity walls becomes quite complex with the combination of conduction, convection and radiation. Air tightness and cavity depth affect the wall unit’s thermal performance. For uninsulated walls, materials can continually transfer heat from its warmer side to its cooler side. If a wall is insulated, a large proportion of stored heat within the wall can return to the internal environment.
Cavity and roof insulation are common issues needed to be addressed in assessing the thermal behavior of building envelopes. Thermal insulation is used to resist the flow of heat and so raises the thermal impedance of the element to which it is attached. Thermal resistance (R-value) is a measure of the insulating ability of a material layer. A higher R-value represents a more effective insulator which can improve the thermal comfort of an internal environment.
Site influencing factors like temperature and moisture impact the practical thermal resistance and behavior of the wall unit. The movement of air and heat flow in cavity walls becomes quite complex with the combination of conduction, convection and radiation. Air tightness and cavity depth affect the wall unit’s thermal performance. For uninsulated walls, materials can continually transfer heat from its warmer side to its cooler side. If a wall is insulated, a large proportion of stored heat within the wall can return to the internal environment.
Water Bath Examples:
Example Experiment 1: Water bath demonstration of the fluid mechanics of natural displacement and natural mixing ventilation (two forms of buoyancy ventilation)
Source: Fortin, Remy; Osborne, Peter; Craig, Salmaan; Moe, Kiel; Jemtrud, Michael, 2020, "Water bath demonstrations of two buoyancy ventilation modes: displacement vs. mixing", https://doi.org/10.5683/SP2/G5ALEH, Scholars Portal Dataverse, V1. McGill University
Example Experiment 1: Water bath demonstration of the fluid mechanics of natural displacement and natural mixing ventilation (two forms of buoyancy ventilation)
Source: Fortin, Remy; Osborne, Peter; Craig, Salmaan; Moe, Kiel; Jemtrud, Michael, 2020, "Water bath demonstrations of two buoyancy ventilation modes: displacement vs. mixing", https://doi.org/10.5683/SP2/G5ALEH, Scholars Portal Dataverse, V1. McGill University
Example Experiment 2: Testing water density using ink
Source: The Canada Science and Technology Museum
Source: The Canada Science and Technology Museum
Sources
Aziiz, Akhlish Diinal, S. Wonorahardjo, and M.D. Koerniawan. “Effectiveness of Double Skin Facade in Controlling Indoor Air Temperature of Tropical Buildings.” Institut Teknolgi Bandung, 2018. https://iopscience.iop.org/article/10.1088/1755-1315/152/1/012016/pdf.
Boake, Terri Meyer. “The Tectonics of the Double Skin: Green Building or Just More Hi-Tech Hi-Jinz?” Montreal, Quebec, 2002. http://www.tboake.com/pdf/tectonic.pdf.
Faggal, Ahmed Atef. “Double Skin Facade Effect on Thermal Comfort and Energy Consumption in Office Buildings.” Ain Shams University, 2014. https://www.researchgate.net/publication/312040800_Double_Skin_Facade_Effect_on_Thermal_Comfort_and_Energy_Consumption_in_Office_Buildings.
Poirazis, Harris. Double Skin Facades for Office Buildings: Literature Review. Vol. 4. 2004. Division of Energy and Building Design, Lund Institute of Technology, Lund University, n.d. http://www.ebd.lth.se/fileadmin/energi_byggnadsdesign/images/Publikationer/Bok-EBD-R3-G5_alt_2_Harris.pdf.
Boake, Terri Meyer. “The Tectonics of the Double Skin: Green Building or Just More Hi-Tech Hi-Jinz?” Montreal, Quebec, 2002. http://www.tboake.com/pdf/tectonic.pdf.
Faggal, Ahmed Atef. “Double Skin Facade Effect on Thermal Comfort and Energy Consumption in Office Buildings.” Ain Shams University, 2014. https://www.researchgate.net/publication/312040800_Double_Skin_Facade_Effect_on_Thermal_Comfort_and_Energy_Consumption_in_Office_Buildings.
Poirazis, Harris. Double Skin Facades for Office Buildings: Literature Review. Vol. 4. 2004. Division of Energy and Building Design, Lund Institute of Technology, Lund University, n.d. http://www.ebd.lth.se/fileadmin/energi_byggnadsdesign/images/Publikationer/Bok-EBD-R3-G5_alt_2_Harris.pdf.