Thermal Bridge Analysis

Transcription

1 Thermal Bridge Analysis

2 Basics of the Modeling The definition of the calculation model according to the Standards consists of 3 parts: Geometry Materials Boundary Conditions

3 Model: Geometry Using flixo: either by DXF-Import, by connecting predefined components or by drawing directly inside flixo To check The model must be large enough, cut-off planes should be positioned concerning the central element as follows (EN ISO 10211): In general at least 1 meter or if the thickness of the flanking element is greater than 33 centimeter, 3 times of the thickness of the flanking element At the line of symmetry, if one is present Omit the cladding and the air layer if the air layer is well ventilated (EN ISO 6946)

4 Model: Geometry Using flixo: either by DXF-Import, by connecting predefined components or by drawing directly inside flixo PHI recommendations: Length of components should be 4 5 x width, when measured using exterior dimensions Some components (with steel and concrete especially) may need even longer lengths. The goal is to achieve stable isotherms before they reach the cutoff plane. Inserting a cut off plane before isotherms have achieved a stable pattern introduces error.

5 Model: Materials Using flixo: either by Drag & Drop materials from the material database or the material list or using the «Assign Property»-Tool PHI recommendations: For unventilated air layers, use the still air U value calculator built into PHPP U values tab. Or use the database contained in Flixo (organized by direction of heat flow and offering large range of thicknesses)

6 Model: Materials Using flixo: either by Drag & Drop materials from the material database or the material list or using the «Assign Property»-Tool To check Proper «Air»-Material: Air cavities: equivalent conductivities according to EN ISO Air layers: equivalent conductivities according to EN ISO 6946 Well ventilated air layers: boundary conditions according to EN ISO 6946 Fillings of glazing: equivalent conductivities according to EN ISO 673 or by using the glazing wizard

7 Model: Boundary Conditions Using flixo: Defining the start points by using the «Boundary Condition»-Tool. The boundary conditions will be applied counter clockwise up to the next start point The boundary conditions depend on the type of analysis 1) Energy balance calculation (e.g. Uf-value, Psi-value) 2) condensation risk analysis

8 Model: B.C. for Energy Balance Calculation Surface resistances R si / R se [m 2 K/W]

9 Model: B.C. for Condensation Risk Analysis Surface resistances R si / R se [m 2 K/W] Note: These surface film resistances change if conducting a condensation risk analysis (f rsi )

10 Model: B.C. for Energy Balance Calculation Surface Temperatures for modeling constructions Exterior temperature: 10 Celsius (14F) Interior temperature: 20 Celsius (68F) Surface Temperatures for modeling windows Exterior temperature: 0 Celsius (32F) Interior temperature: 20 Celsius (68F) Note: The different BC temperatures can cause some headaches when calculating psi install values for windows. Must use surface temperatures for modeling constructions, but heat flux for the window may have been calculated with 0C exterior. If so, window heat flux needs to be recalculated at 10C.

11 U-Value: Periodic Thermal Bridges The influence of periodic thermal bridges are considered in a special U-value: equivalent U-value Φ Δ Φ Δ Recommendation: Calculate a U eq for any inhomogenous layer (that is, a layer interrupted by periodic thermal bridges studs, rafters) Using flixo: U eq -value object (U-value tool) Click 1 and click 2: start- and end point of the internal or external surface counter clockwise > Click 3: position of the dimension line

12 U-Value: Periodic Thermal Bridges PHI recommendations: For most of the inhomogenous layer, use a different material representing a combination of studs and insulation, with a lambda value calculated using U eq Only insert the actual periodic bridging elements at the intersection/junction

13 U-Value: Periodic Thermal Bridges Recommendations: U eq calculation for inhomogenous layer To create this model: 1) Use one bay width, with stud centered 2) End BCs are adiabatic 3) Assign one side interior conditions (20C), the other exterior ( 10C) 4) Make sure the surface film resistances are set to 0!

14 U-Value: Periodic Thermal Bridges Recommendations: Once U eq is known, calculate lambda value for the inhomogenous layer. U eq x thickness (m) = λ Go back to the TB model and create a new material with this lambda value.

15 -Psi value calculation: Above grade junction Note: Flixo needs homogenous layers to calculate the U values used in its psi value calculation.

16 -Psi value calculation: Ground Calculation according to EN ISO Often several 2dimensional calculations are needed Often the U-value of the base constructions are unknown or can t be applied 3 standard cases No Cellar Unheated cellar Heated cellar

17 -Psi value calculation: Ground Calculation according to EN ISO Often several 2dimensional calculations are needed Often the U-value of the base constructions are unknown or can t be applied 3 standard cases Not covered today: No Cellar Unheated cellar Heated cellar

18 -Psi value calculation: Ground Here s the problem: What is the U value of the ground?

19 -Psi value calculation: Ground 2 thermal bridge calculations are needed 1. Heat flow through the slab + ground alone (this allows determination of the ground effect) 2. Heat flow through the complete construction (slab + footing + wall + ground) (this allows determination of the thermal bridge effect)

20 -Value calculation: Ground, no cellar Model 1 Calculation The heat flow through the floor without thermal bridge effect has to be calculated in a separate 2dimensional calculation just the slab plus ground This model is built using slab and insulation thickness as designed, but placed on top of the ground block. The edges are given adiabatic BCs, so all heat flow is to the ground. All elements of the footing or thickened edge are removed.

21 -Value calculation: Ground, no cellar Model 2 Calculation 2nd model is built showing the complete junction. Rather than using a U value for the slab, Flixo uses the heat flux calculated from the first model. A-E-C, * = T - T - U 2 b 2 = = W/(m K)

22 Model: Ground - Geometry 4m 20m Recommendations: For most models, dimension b = 8m is acceptable 4m is then the exact distance from the edge of the slab insulation to cut off plane 20m x 20m is the size of the ground block 20m

23 Model: Ground - Geometry b: effective floor dimension if known, 8 meter if the floor dimension is unknown or greater than 8 m

24 Model: Ground - Material, B.C. Material -value of soil is 2.0 W/mK, if no other values are known (EN ISO 10211) Temperatures External Temperature Surface temperatures: -10 C Interior Temperature Surface temperatures: 20 C Surface Resistances Adiabatic condition applies to all cut-off planes and edges of ground block (except top) Top of ground block is standard Rse Interior and exterior surface resistances of the assemblies as normal

25 Model: Interior footing Linear footings away from perimeter For interior footings, ground block is not modeled. BC on bottom of insulation is 10 C, with no film resistance A-B = W/m B D U - = W/(m 2 K) U - = W/(m 2 K) E A C C-G-D = T - U 1 b 1 - U 2 b 2 = = W/(m K) Post footings away from perimeter Modeled same as the linear footing, but entered in PHPP with length of 1m

26 Model: Frame Geometry: Uf-Value Calculation, -Value Wall-Frame Replacing glazing by insulation panel (EN ISO ) d: effective thickness, if the frame is designed for a specific thickness, 24 mm for double glazing, 36 mm for triple glazing otherwise

27 Model: Frame Geometry: Uf-Value Calculation, -Value Wall-Frame Replacing glazing by insulation panel (EN ISO ) Notes: To calculate U f and install : Solid glazing panel always used instead of glass. Glazing panel λ = Length of panel has to be at least 190mm starting from the sightline Thickness of panel = actual thickness of glass. Or 36mm for triple glazing, if unknown.

28 Model: Frame Boundary Conditions: Uf-Value Calculation, -Value Wall-Frame Temperatures > T i =20 C, T e =0 C Resistances > Internal > Normal (R=0.13 m 2 K/W) (shown in red) > Reduced radiation/convection (R=0.20 m 2 K/W) (shown in yellow) > External (R=0.04 m 2 K/W) (shown in blue) Note: Exterior temperature for U f calculation = 0 C Exterior temperature for install calculation = 10 C

29 Model: Frame - Cavities Unventilated cavities > Completely closed > Slits 2 mm Slightly ventilated cavities > Slits between 2 mm and 10 mm Well ventilated cavities and grooves > Slits greater 10 mm Note: Flixo will automatically detect type of cavity and assign associated properties accordingly

30 Model: Frame - Cavities Determining factors > Geometry of the cavity > Temperature distribution in the cavity and on the cavity surfaces > Emissivity of the surfaces

31 U f -Value: Frame U f -value according to EN ISO Material [W/(m K)] Aluminium (Si Alloys) EPDM (ethylene propylene diene monomer) Elastomeric foam, flexible (1) Panel Silicone, pure (1) Slightly ventilated air cavity Softwood 500, typical construction timber Unventilated air cavity Boundary Condition q[w/m 2 ] [ o C] R[(m 2 K)/W] Epsilon Exterior, frame Interior, frame, normal Interior, frame, reduced Symmetry/Model section = W/m A U - = W/(m 2 K) U f x b f + U p x b p = φ/δt Using flixo: U f -value object (U-value tool) > Click 1: Select the result object > Define the width of the frame b f > Flixo calculates U p and φ, then solves for U f B U f A,B = T - U p b p b f = = 1.19 W/(m 2 K)

32 install value 2 thermal bridge calculations are needed 1. Heat flow through the frame + glazing panel alone (at -10C) 2. Heat flow through the complete construction (wall + frame + panel) with the same boundary conditions

33 install value B Material [W/(m K)] Aluminium (Si Alloys) EPDM (ethylene propylene diene monomer) Elastomeric foam, flexible (1) Panel Silicone, pure (1) Slightly ventilated air cavity Softwood 500, typical construction timber Unventilated air cavity Boundary Condition q[w/m 2 ] [ o C] R[(m 2 K)/W] Epsilon Exterior, normal Interior, frame, normal Interior, frame, reduced Symmetry/Model section A-B = 8.1 W/m Model 1 Calculation The heat flow through the frame + glazing panel Exterior BC is now -10C Flux value is higher A

34 install value Model 2 Calculation 2nd model is built showing the complete junction (wall + frame + panel). Rather than using a U value for the frame + panel, Flixo uses the heat flux calculated from the first model A B E Material [W/(m K)] Aluminium (Si Alloys) EPDM (ethylene propylene diene monomer) Elastomeric foam, flexible (1) Fiberglass batt Lambda Gypsum plasterboard (1) Panel Plywood Lambda Silicone, pure (1) Slightly ventilated air cavity Softwood 500, typical construction timber Boundary Timber 450 kg/m3 Condition (softwoods) q[w/m 2 ] [ o C] R[(m Unventilated air cavity Epsilon XPS Lambda Exterior, normal Exterior, ventilated, horizontal Interior, frame, normal Interior, frame, reduced Interior, heat flux, downwards Interior, normal, horizontal Symmetry/Model section A-C = W/m U - = W/(m 2 K) A-E-C, * = T - T - U 2 b 2 C D = = W/(m K)

35 -Psi value calculation: Reference Point Exterior Corner Exterior Reference Point > Choose the reference point based on exterior dimensions > Exterior dimensions should be taken from the outside face of thermal envelope > Flixo will automatically measure from the cut-off planes to the reference point Interior

36 -Psi value calculation: Reference Point Interior Corner Reference Point > Choose the reference point based on exterior dimensions > Exterior dimensions should be taken from the outside face of thermal envelope > Flixo will automatically measure from the cut-off planes to the reference point. Exterior Interior

37 -Psi value calculation: Reference Point Parapet Exterior Reference Point > For parapet TB, do not include any part of the parapet above the top surface of the roof s thermal boundary Interior 0 10

38 -Psi value calculation: Reference Point Perimeter Exterior Interior Reference Point > For perimeter TB, do not include any part of the footing below the lowest surface of the slab s thermal boundary

39 -Psi value calculation: Reference Point Rim joist Reference Point > For rim joist, position of the reference point doesn t matter much if the two wall assemblies are the same. Exterior Interior

40 -Psi value calculation: Reference Point Rim joist Reference Point > For rim joist with two different assemblies, the reference point needs to be aligned according to the assembly dimensions used in PHPP. Exterior Interior Notes: Does the above grade wall extend to here in PHPP?

41 -Psi value calculation: Reference Point Rim joist Reference Point > For rim joist with two different assemblies, the reference point needs to be aligned according to the assembly dimensions used in PHPP. Exterior Interior Notes: Or here?

42 -Psi value calculation: Reference Point Windows 012 Reference Point > For the window install psi value, the reference point is aligned with the bottom of the window frame, even if the frame is overinsulated. Exterior Interior

43 Model: Standards Thermal Bridge, Model EN ISO (geometry, mesh, accuracy, ground) EN ISO (frame U-value, edge -value) EN ISO (Ucw-value, 3D elements like screws) Materials EN ISO (general materials) EN ISO 6946 (air layers) EN ISO (frame) EN ISO 673 (filling of glazing) Boundary Conditions EN ISO 6946 (general) EN ISO (mold, condensation) EN ISO (ground) EN ISO (frame)

44

45 -value: Spacer 2 calculations are needed a) U f -value calculation with insulation panel instead of glazing b) Heat lost calculation with glazing and spacer T U f b f U g b g Using flixo: Psi-value Edge (context menu) > Click 1: selection of the result object > Select the file with the U f -value calculation