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Unformatted text preview: rizontal Mullion Profile at Spandrel Panel insulation Diagram from Spandrel insulation visible (prior to installation of outer panels). Thermal Bridging of Spandrel Insulation insulation metal pan Additional layers? Spandrel section with metal pan University of Waterloo “Environment 3” University of Waterloo “Pharmacy” University of Waterloo “Pharmacy” Concrete Slab Penetrations (Balcony Slabs) Photo from Photo from Concrete Slab Penetration of Insulated Envelope Exterior Interior Insulated wall Balcony Slab “Window Wall Construction” “Window Wall” Slab Similar to Curtainwall, but mounted on floor-slab (and fastened to slab above). Slab Exterior Interior Slab Example Window Wall Profile at Slab Combinations Window Wall with balcony slab penetration Exterior Interior An Alternative High-Rise Residential Style: “Insulated Concrete Forms” Building Energy Performance – Spring 2012 - Topic 9 - Energy Flow through Building Envelope (Part 4) Building Heat Loss • Thermal Transmission = ∙ − e.g. through walls, windows, roof, floor slab (to ground) • Air Leakage / Ventilation passive / active “Active Ventilation” (e.g. mechanical ventilation) - provision of fresh air and/or exhaust “Passive Ventilation” (e.g. uncontrolled paths) - “infiltration” and “exfiltration” air “leaks” in air “leaks” out Whole Building: the total rate of air leaving must be approximately equal to the total rate entering (subject to brief variations). , , , , , + , = , + , If , > , indoor pressure will rise until the air flows balance (exfiltration increases; fan volume decreases). If +ve pressure , < , indoor pressure will drop until the air flows balance (infiltration increases; fan volume decreases). -ve pressure These variations can occur locally too—air will always try to flow from an area of higher pressure to lower pressure. Commercial Buildings - estimating infiltration rate for a particular building can be very difficult - often have mechanical ventilation (fan-driven) Office building -airflow dominated by mechanical ventilation? Warehouse with roll-up doors -infiltration may be so great that mechanical ventilation is unneeded air changes per hour Houses - typical infiltration rates: 0.5 to 2.0 ACH - minimum 0.35 ACH often recommended for indoor air quality airflow in airflow out cools room “warms outside” Heating Incoming Air to Room Temperature 1 2 ℎ ℎ = ∙ ℎ − ℎ heat input rate heat input rate mass flow rate change in enthalpy Energy to heat/cool/humidify/dehumidify “moist-air” Humidity Ratio Psychrometric Chart Humidification (latent heating) Cooling Heating sensible cooling sensible heating Dehumidification (latent cooling) Drybulb Temperature Psychrometric Chart heat input, 1 2 ℎ ℎ 1 2 Humidity Ratio “SENSIBLE AIR HEATING” Drybulb Temperature Steady-State Energy Balance: energy in energy out ∙ ℎ + = ∙ ℎ = ∙ ℎ − ℎ = ∙ (ℎ − ℎ ) = heat input rate = mass flow rate ℎ , ℎ = enthalpy = volumetric flow rate = specific volume “Quick Approximation” – Sensible Air Heating IP Units: ≅ 1.08 × × ( − ) btu/hr Metric Units: cfm (ft3/min) °F ≅ 1.21 × × ( − ) W L/s °C Building Energy Performance – Spring 2012 - Topic 10 - Energy Flow through Building Envelope (Part 5) Windows Some important metrics of thermal/optical performance: • U-value “Overall Thermal Transmittance” • SHGC “Solar Heat Gain Coefficient” • VLT “Visible Light Transmittance” “Solar Heat Gain Coefficient” (SHGC) = fraction of solar heat gain through a window to the amount of solar energy striking the window includes visible and non-visible solar energy SHGC vs VLT ? “BEAM” vs “DIFFUSE & REFLECTED” SOLAR RADIATION Effect of Atmosphere on Solar Radiation Solar Radiation striking atmosphere (≈ 1367 W/m2) reflected to space At Receiving Surface (Ground Level) receiving surface diffuse + reflected radiation • Position of sun moves across sky—direction of beam radiation changes during the day (and over the course of a year) • Most windows receive diffuse and reflected radiation for much of the day Order of Magnitude of “Insolation” (Solar Radiation) overcast sky clear sky diffuse + reflected radiation receiving surface facing sun ≈ 1000 W/m2 night-time negligible i.e. approx 0 W/m2 diffuse + reflected radiation ≈ 100-200 W/m2 Solar Insolation level is highly variable. Solar Position June 11 Solar Noon Dec 10 Solar Noon ≅ 68° ≅ 21° HORIZON = " " = angle between horizontal and line to the sun observer at latitude = 45° N facing due south (Partial) Solar Position Diagram for Latitude 45° N (Based on Duffie & Beckman, “Solar Engineering of Thermal Processes”, 1991) 80° Solar Altitude Angle, 11 am Solar Noon 1 pm 10 am 60° 2 pm 9 am 3 pm 4 pm 8 am 40° 5 pm 7 am 20° 0° 6 pm 6 am -100...
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This note was uploaded on 10/04/2012 for the course ME 760 taught by Professor Davidmather during the Spring '12 term at Waterloo.

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