1/9/2013. Terminology Calculating Heat Transfer Code Requirements Design Examples and Sustainability

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1 1/9/13 By Brett T. Fagan, P.E. Presented by Marie Horan, P.E. Building Diagnostics, Inc. Building Diagnostics Terminology Calculating Heat Transfer Code Requirements Design Examples and Sustainability Evaluate the energy performance of a building enclosure. Allow designer to forecast thermal movements due to external temperature changes. Predict location of dew point within the wall assembly. Assess the suitability of the design. Roof/Ceiling Assembly Wall Assembly Vertical Fenestration ti and Skylights Floor Assembly Slab Edge Below Grade Wall Assembly Heat flows from hot to cold. 1

2 1/9/13 Water vapor moves from high vapor pressure to low pressure, from warm to cold. Cold air cannot hold as much water vapor as warm air at the same relative humidity. The dew point varies within the wall section based on the cross section materials. Heat is not an additive property, it is a form of energy constantly seeking equilibrium. Conduction Convection Radiation Heat transfer directly from molecules of hot building surfaces to the molecules of cooler solids in direct contact. This is the most effective method. Molecules of cool air absorb heat from a warm surface, rise, and carry it away. Heat flows in electromagnetic waves from hotter surfaces to detached distant cooler surfaces. The sun heats the earth by radiation. Energy described by British Thermal Unit Btu is the amount of heat required to raise 1 pound of water by 1 deg. F. Power is Btu / hour The total heat loss or gain of a building. Used to size heating and cooling equipment. 2

3 1/9/13 Architectural materials are either insulators or conductors. Conductors allow heat to pass quickly. Metals Based on the quick movement of electrons. Insulators are materials that do not quickly transmit heat. Wood Plastics Conductance (C) The rate of heat flow through a homogeneous solid for a stated thickness. Used for materials such as metal and glass that are not insulators. Thermal resistance to passage of heat. Measured in the number of hours needed for 1 Btu to flow through a given thickness when the temperature difference is 1 deg. F. Coefficient of heat transmission for assemblies. The rate of heat flow through a combination of materials air layers and spaces of materials, air layers, and spaces. U = 1 / Σ R or U = Σ C Value Btu s/hr Conductors Walls Windows Factors necessary to calculate heat flow. The rate of heat flow through various assemblies of materials that make up the envelope (value). The area of each assembly. The temperature difference between the inside and outside for the hour being calculated Insulators Value Hr s/btu 3

4 1/9/13 16 o.c. Weighted Average value is x at 16" o.c. 2x6 at 2" o.c. R value U value Area (SF) T Max Heat Exchange (BTU/H) Efficiency 71% Component R Studs R Cavity Outer Air Film Summer Brick Masonry inch Airspace 1 1 WRB 0 0 /8 inch osb inch Southern Pine in Batt Insulation 13 1/2 inch Gypsum Sheathing Interior Air Film R Value o.c. Weighted Average value is 21.3 Component R Studs R Cavity Outer Air Film Summer Brick Masonry inch Airspace 1 1 WRB 0 0 /8 inch osb inch Southern Pine in Batt Insulation 19 1/2 inch Gypsum Sheathing Interior Air Film R Value q = Σ ( U * A ) Δt q = Total heat exchange U = Rate of heat flow A = Area of each assembly Δt = Temperature difference Convert the value to the value then calculate the heat exchange. 2x at 16" o.c. 2x6 at 2" o.c. R value ( F*ft²*h/Btu) U value (Btu/ F*ft²*h) Area (SF) T ( F) Heat Exchange (BTU/H) Btu x6 at 2" o.c. 2x at 16" o.c ΔT Hour

5 1/9/13 IECC International Energy Conservation Code Residential Building Requirements Commercial Building Requirements Comply with ASHRAE 90.1 Or Comply with IECC C02 (Prescriptive) Or Comply with IECC C07 Total Building Performance And Marine Insulation entirely above deck ci ci ci ci ci ci 2ci 2ci 2ci 2ci 30ci 30ci 3ci 3ci 3ci 3ci Metal buildings (with thermal blocks) Attic and other Insulation considered continuous (CI) and must be entirely above deck Required in s 1-3 for low-sloped roofs (less than 2 units vertical in 12 horizontal), directly above cooled conditioned spaces Requirements: Minimum three-year aged solar reflectance of 0. and minimum threeyear aged thermal emittance of 0.7 OR Initial solar reflectance of 0.70 and initial thermal emittance of 0.7 OR Three-year aged solar reflectance index of 6 OR Initial solar reflectance index of 82

6 1/9/13 And Marine And Marine Mass.7ci.7ci.7ci 7.6ci 7.6ci 9.ci 9.ci 11.ci 11.ci 13.3ci 13.3ci 1.2ci 1.2ci 1.2ci 2ci 2ci Mass NR NR 10ci 10ci 6.3ci 8.3ci 10ci 10.ci 10ci 12.ci 12.ci 12.ci 1ci 16.7ci 1ci 16.7ci Metal building Metal Framed 6.ci 13= ci 6.ci 13= ci 6.ci 13= ci - i - 7.;ci 7.cfi 19. ci 1.6ci 19. ci 1 Joist/ Framing Steel/ (Wood) NR NR Wood Framed & Other or - or - 1.6ci or +R -10ci or or or or or or 3 or or + or + or + or + or + 1.6ci or + 10 ci And Marine Except Marine and Marine Vertical Fenestration Swinging factor Roll-Up Or Sliding.7 Fixed fenestrat ion Operabl e fenestrat ion Entrance Doors SHGC SHGC = Solar Heat Gain Coefficient 6

7 1/9/13 Minimize or eliminate gaps or joints that allow air movement Detail insulation requirements for penetrations. Avoid poorly fitting insulation or compressed insulation. Provide multiple layers of insulation. Minimize framing at non-load bearing walls. Provide drainage for walls with condensation risk. Terminology Calculating Heat Transfer Code Requirements Design Examples and Sustainability Thank You Building Diagnostics The Durability Experts 7