IBS 1-Envelope_3.pdf

Module 1 Envelope 3 Integrated Building Systems 1 Module1: Rawad El Kontar Previously on IBS 1 1. 3 different properties of Windows: U-value, SHGC, VLT 2. Calculating U-value of Windows vs SHGC 3. Shading devices are main contributors to reduce SHGC 4. Calculating Projection Factor PF for vertica...

Module 1 Envelope 3 Integrated Building Systems 1 Module1: Rawad El Kontar Previously on IBS 1 1. 3 different properties of Windows: U-value, SHGC, VLT 2. Calculating U-value of Windows vs SHGC 3. Shading devices are main contributors to reduce SHGC 4. Calculating Projection Factor PF for vertical fins and overhangs 5. Calculating adjusted SHGC after calculating the shading equivalent factor (SEF) 6. WWR the ratio of total area on window to the total gross area exterior walls 7. Visual Light transmission is an optical property of a light transmitting material 8. Thermal bridge is a section where heat flow is different/facilitated. Windows SHGC 100 % Energy Reflection (ER) Directly Energy Transmitted (ET) Solar Heat Gain Coefficient (SHGC) Re-radiated Outside Re-radiated Inside Energy Absorption (EA) ER + EA + ET = 100 % SHGC vs U-value Solar Radiation Energy = 800 W Temperature difference = 20 ℃ Glass Area = 1 𝑚! SHGC = 0.3 U-value = 3.0 3 x 20 0.3 x 800 240 Watts SHGC contribution = 80 % + 60 Watts Total Heat Gain = 300 Watts U_value contribution = 20 % Shading devices can be characterized by Projection Factor Projection Factor Calculation Horizontal shading - Overhangs Vertical shading – vertical fins Learning Objective 1 In what states (phases) does water exist around us? In what states (phases) does water exist around us? Solid: Ice Liquid: Water Gas: Vapor Water is Mass unlike heat which is energy, and thus transfer of water is considered a form of mass transfer and not energy transfer Learning Objective 2 What are the processes that occur when the water phase is changing? What are the processes that occur when the water phase is changing? Gas Liquid Freeze Solid Thaw Water can change states through several processes depending on the conditions around it, mainly Temperature, and Pressure Learning Objective 3 When does phase change occur? When does phase change occur? Solid: Ice Liquid: Water 0 C⁰ 32 F ⁰ Gas: Vapor 100 C⁰ 212 F ⁰ When does phase change occur? Solid: Ice Liquid: Water 0 ⁰C 32 ⁰F Gas: Vapor 100 ⁰C 212 ⁰F Water is no different than any other object and the same rules of thermodynamics apply. Hotter objects will heat it up by giving it their energy and cooler objects will cool it down as the water gives off its energy to heat them up When does phase change occur? As energy received increases, the temperature should increase When does phase change occur? Boiling Point Assuming Pressure at 1 atm When does phase change occur? What is the phase at this point? When does phase change occur? At 100 C (212 F) and 1 atm pressure the Temperature- Energy Curve would exhibit a flat region When does phase change occur? What is the phase of water in this region? When does phase change occur? At this region water is undergoing phase change and is in a state between both When does phase change occur? • Sensible Energy is the energy received that raises the temperature of the substance • Latent Energy is the energy received that the substance uses to change phase. It does not change the temperature of the object. When does phase change occur? KEY TAKEAWAY: Phase Change will occur when a substance gains or losses enough sensible energy to reach the phase change point (ex. Boiling, Freezing etc) and then gains or losses enough latent energy to change its phase. The sum of Sensible and Latent Energy is called Enthalpy. Learning Objective 4 How does moisture transport occur? How does moisture transport occur? Moisture transport can occur through: • Diffusion: Movement from region of higher humidity concentration to lower concentration of humidity • Capillary Action: Liquid flowing in narrow spaces • Osmosis: Movement from a region of higher water potential to lower water potential through a semipermeable membrane • Gravity: Being a form of mass transfer gravity can move moisture when possible How does moisture transport occur? Diffusion Area of Higher Humidity Area of Lower Humidity • Just like the example with Heat, moisture moves from regions of higher humidity (moisture) to regions of lower humidity following the same laws of equilibrium • While Heat and Temperature have an influence on which direction the flow of moisture occurs moisture always moves from regions of higher absolute humidity to lower absolute humidity How does moisture transport occur? Capillary Action Water when found in a narrow space has the capability to “climb”. In concrete it has the theoretical ability to climb 6.2 miles. How does moisture transport occur? Capillary Action Moisture Transport by Capillary Action is more common than designers think How does moisture transport occur? Osmosis Osmosis is a problem prevalent in areas where groundwater has a high concentration of salt in it How does moisture transport occur? Osmosis Efflorescence and Spalling in bricks can occur due to the process of osmosis Learning Objective 5 How to measure moisture in the air? How to measure moisture in the air? • Air has a capacity to hold a finite amount of moisture particles. This amount changes with temperature • The higher the temperature of the air the more moisture it can hold • The amount of water vapor that is present in the air, relative to the amount it could hold at that given temperature is called Relative Humidity • The ratio of the mass of moisture in the air over mass of dry air is called Absolute Humidity How to measure moisture in the air? 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 𝑉𝑎𝑝𝑜𝑟 𝑖𝑛 𝑡ℎ𝑒 𝐴𝑖𝑟 𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝐻𝑢𝑚𝑖𝑑𝑖𝑡𝑦(%) = 𝐻𝑜𝑤 𝑀𝑢𝑐ℎ 𝑉𝑎𝑝𝑜𝑟 𝑡ℎ𝑒 𝐴𝑖𝑟 𝑐𝑎𝑛 𝐻𝑜𝑙𝑑 𝑖𝑛 𝑇𝑜𝑡𝑎𝑙 VS. 𝐴𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝐻𝑢𝑚𝑖𝑑𝑖𝑡𝑦( 𝑔 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑊𝑎𝑡𝑒𝑟 𝑉𝑎𝑝𝑜𝑟 𝑖𝑛 𝑡ℎ𝑒 𝐴𝑖𝑟 )= 𝑘𝑔 𝑀𝑎𝑠𝑠 𝑜𝑓 𝐷𝑟𝑦 𝐴𝑖𝑟 Since how much total vapor the air can hold changes with temperature Relative Humidity will change with temperature, but absolute humidity will not Learning Objective 6 How to read a Psychrometric Chart? How to read a Psychrometric Chart? Outside (92 F) RH: 60% Inside (68 F) RH: 30% We need to determine at which conditions will this assembly fail How to read a Psychrometric Chart? The Psychrometric Chart is the single most handy tool for the designer How to read a Psychrometric Chart? Use this link to access the interactive Psychrometric Chart https://drajmarsh.bitbucket.io/psychro-chart2d.html How to read a Psychrometric Chart? Outside (92 F) RH: 60% Inside (68 F) RH: 30% We need to determine at which conditions will this assembly fail How to read a Psychrometric Chart? Intersection with 100% RH line is the Dew Point for this Air Dew Point is 77 F Outside (92 F) RH: 60% How to read a Psychrometric Chart? Dew Point (77 F) Outside (92 F) RH: 60% Inside (68 F) RH: 30% At 77 F the water vapor will being to condense How to read a Psychrometric Chart? Dew Point (77 F) Outside (92 F) RH: 60% Inside (68 F) RH: 30% The now liquid vapor will continue to move from regions of more to less humidity How to read a Psychrometric Chart? Dew Point (77 F) Outside (92 F) RH: 60% Inside (68 F) RH: 30% If the water meets a water/vapor impermeable surface it cannot move further and will accumulate on it which could cause numerous problems How to read a Psychrometric Chart? Dew Point (77 F) Outside (92 F) RH: 60% Inside (68 F) RH: 30% If the water passes through vapor permeable surfaces, then it will dry out at the final surface with the interior/exterior environment How to read a Psychrometric Chart? Dew Point (77 F) Outside (92 F) RH: 60% Inside (68 F) RH: 30% In this case the vapor barrier can be set towards the warmer side where there is (theoretically) no risk of condensation Learning Objective 7 How do materials and moisture interact? How do materials and moisture interact? Adsorb Absorb • Moisture can be absorbed into the material. • The materials capacity to store moisture is called the moisture buffer capacity (g/m2) • Adsorption is effectively when moisture sticks on the surface of the material Learning Objective 8 How to select a Vapor Barrier/Retarder? How to select a Vapor Barrier? • The unit of measurement used in characterizing the water vapor permeance of materials is the “Perm” • 1 Perm is one grain of water vapor per hour per square foot per inch of mercury • In simpler terms how much water vapor does a material allow through over a period of time How to select a Vapor Barrier? Key Takeaway A Good Vapor Barrier will: 1. Keep the Water Out 2. Let it Out if it gets in How does evaporation/drying occur? KEY TAKEAWAY: The difference in Absolute Humidity is what drives diffusive moisture transport. The ratio of Relative Humidity is what drives evaporation. Learning Objective 10 What happens when moisture doesn’t dry out? What happens when moisture doesn’t dry out?