# PH_Rev02.txt

 THERMAL BRIDGING ================= What is a Thermal Bridge? A Thermal Bridge, is where a penetration of the insulation layer by a highly conductive or noninsulating material takes place in the separation between the interior and exterior environments of a building. What is a Thermal Bridge also called? A Cold Bridge What types of Thermal Bridge exist? LINEAR Thermal Bridges POINT Thermal Bridges GEOMETRICAL Thermal Bridges - placed at the junction of two planes, such as at the corner of a wall What types of Point Thermal Bridge exist? Repeating POINT Thermal Bridges e.g. columns in a framed building Non-Repeating POINT Thermal Bridges e.g. single occurence Linear Thermal Bridges are measured in? Psi Value in W/mK What does the Psi symbol look like? 3 prong forkLike this: ψ Point Thermal Bridges are measured in? Chi Value in W/K What does the Chi symbol look like? 2 swords crossed (CostX symbol)Like this: χ What is the formula for Heat Loss through an area? Qt = A x U x ft x GtGt is based upon climate data for specific location What is the formula for Heat Loss through a Linear Thermal Bridge? Qt = L x Psi x ft x GtGt is based upon climate data for specific location Steps Psi calculated? U1 = U-Value of general insulation to areaU2 = Reduced U-Value of general insulation at Thermal Bridge Delta U = U1 - U2Psi = Delta U x width of Thermal Bridge exposed edgeorPsi = (U1 - U2) x w (width of Thermal Bridge exposed edge Calculate the Heat Loss thru' the Thermal Bridge illustrated below Insert image in QU1tot = 1/R1totR1tot = Rse + Rpe + RB1 + Rpi + Rsi= 0.04 + 0.04/0.07 + 0.425/0.08 + 0.015/0.35 + 0.13= 6.0968U1 = 1/R = 1/6.0968 = 0.16W/m2K U2tot = 1/R2tot R2tot = Rse + Rpe + RB1 +RC1 + Rsi= 0.04 + 0.04/0.07 + (0.425-0.175)/0.08 +0.19/2.3 + 0NB Rsi = 0 here as there is no internal surface= 3.819U2 = 1/R = 1/3.819 = 0.262W/m2 Delta U = U1 - U2 = 0.16 - 0.262 = 0.098Psi = Delta U x d (depth of Thermal Bridge )= 0.098 x 0.180= 0.018 W/K Calculate the annual Heat Loss thru' a 50m Thermal Bridge with a Psi Value of 0.018W/K and Gt of 82kKh/a Qt = L x Psi x ft x GtQt = 50m x 0.018W/K x 1 x 82kKh/a= 73.8kWh/a If Thermal Bridge Heat Loss = 73.8kWh/a and overall Heat Loss = 9.8W/m2 TFA, calculate Heat Demand (Pt) on worst day of year, when external temp is -10C Thermal Bridge Heat Loss /m2 TFA = 73.8kWh/a / 150m2 TFA= 0.49 kWh/m2/aHeat Demand = Pt = L x Psi x ft x Delta T= 50m x 0.018 x 1 x (20 - (-10))= 27WTFA = 150m2Heat Demand / TFA = 27W / 150m2 = 0.18W/m2Heat Demand for other heat losses = 9.8W/m2Add Thermal Bridge Heat Losses = 9.8 + 0.18 = 9.98W/m2Therefore it does comply with Passive House requirements as Heat Demand <10W/m2 Calculate the Payback Period for the addition of a reduced 50m Thermal Break given the following data; Psi without Thermal Break = 0.51W/mK; with Thermal Break = 0.02W/mK; Gt = 60kKh/a; Heat cost = 0.10 per kWh Qt = Delta Psi x L x ft x Gt= (0.51 - 0.02)W/mK x 50m x 1 x 60kKh/a= 1470kWhSavings per year = 1470 kWh x 0.10 = 147Cost of Thermal break = 50m @ 20/m = 1000Payback = 1000 / 147 = 6.8 years Calculate the additional wall insulation required for 100m2 of wall to compensate for a Thermal Bridge Heat Loss of 1470kWh/a when existing U-Value of wall is 0.15W/m2K and Gt is 60kKh/a and insulation conductivity is 0.04W/mK Qt(wall) = A x U x ft x Gt= 100 x 0.15 x 1 x 60= 900kWh/aAdditional Heat Loss from Thermal Bridge = 1470kWh/aTotal wall Heat Loss = 900 + 1470 = 2370kWh/aCalculate Equivalent U-Value U = Qt / (A x ft x Gt)= 2370 / (100 x 1 x 60)= 0.395W/m2KDelta R = 1/U(orig) + 1/U(inc T B)= 1/0.15 - 1/.3954.135Extra insulation thickness = Delta R x Sigma Insulation= 4.135 x 0.04= 0.165m Which as the greater Heat Loss, 2 columns with a Chi value of 0.47w/K or a 7m Thermal Bridge with a Psi of 0.15W/mK No need to use Qt as time is not involvedHeat Loss Columns = 2 x 0.47 = 0.94W/KHeat Loss Thermal Bridge = 7 x 0.15 = 1.05W/KTherefore the 2 columns have the lowest Heat Loss How is Treated Floor Area calculated? On the basis of external wall dims i.e. outside to outside How is Height of Treated Floor Area calculated? Height is measured from ceiling to underside of ground floor insulation What is the impact of negative Psi values? They do not generate negative heat losses, but ar used to cancel positive Psi values to reduce total Heat Loss Authormonqs ID249206 Card SetPH_Rev02.txt DescriptionPassive House Day 2 Updated2013-11-26T19:22:34Z Show Answers