thermal bridge analysis - passive house · 2017. 6. 6. · the influence of periodic thermal...
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Thermal Bridge Analysis
The definition of the calculation model according to the Standards consists of 3 parts:
Basics of the Modeling
Boundary Conditions
Geometry
Materials
Using flixo: either by DXF-Import, by connecting predefined components or by drawing directly inside flixo
Model: Geometry
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)
Using flixo: either by DXF-Import, by connecting predefined components or by drawing directly inside flixo
Model: Geometry
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.
Using flixo: either by Drag & Drop materials from the material database or the material list or using the «Assign Property»-Tool
Model: Materials
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)
Using flixo: either by Drag & Drop materials from the material database or the material list or using the «Assign Property»-Tool
Model: Materials
To check› Proper «Air»-Material:
› Air cavities: equivalent conductivities accordingto EN ISO 10077-2
› Air layers: equivalent conductivities accordingto EN ISO 6946
› Well ventilated air layers: boundary conditions accordingto EN ISO 6946
› Fillings of glazing: equivalent conductivities accordingto EN ISO 673 or by using the glazing wizard
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
Model: Boundary Conditions
The boundary conditions depend on the type of analysis 1) Energy balance calculation (e.g. Uf-value, Psi-value)2) condensation risk analysis
Model: B.C. for Energy Balance Calculation
Surface resistances Rsi / Rse [m2K/W]
Model: B.C. for Condensation Risk Analysis
Surface resistances Rsi / Rse [m2K/W] Note:• These surface film resistances change
if conducting a condensation risk analysis (frsi)
Model: B.C. for Energy Balance Calculation
Surface Temperatures for modeling constructions
Surface Temperatures for modeling windows
Exterior temperature: ‐10 Celsius (14F)Interior temperature: 20 Celsius (68F)
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.
The influence of periodic thermal bridges are considered in a special U-value:equivalent U-value
Using flixo: Ueq-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
U-Value: Periodic Thermal Bridges
Φ ⋅ Δ ⋅ ⟹ Φ
Δ ⋅
Recommendation:• Calculate a Ueq for any inhomogenous
layer (that is, a layer interrupted by periodic thermal bridges ‐ studs, rafters)
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 Ueq
• Only insert the actual periodic bridging elements at the intersection/junction
U-Value: Periodic Thermal Bridges
Recommendations:Ueq calculation for inhomogenous layer
To create this model:1) Use one bay width, with
stud centered2) End BCs are adiabatic3) Assign one side interior
conditions (20C), the other exterior (‐10C)
4) Make sure the surface film resistances are set to 0!
U-Value: Periodic Thermal Bridges
Recommendations:• Once Ueq is known, calculate
lambda value for the inhomogenous layer.
• Ueq x thickness (m) = λ• Go back to the TB model
and create a new material with this lambda value.
-Psi value calculation: Above grade junction
Note:• Flixo needs homogenous
layers to calculate the U‐values used in its psi value calculation.
› Calculation according to EN ISO 10211› Often several 2dimensional calculations are needed› Often the U-value of the base constructions are unknown or can’t
be applied› 3 standard cases
-Psi value calculation: Ground
No Cellar Unheated cellar Heated cellar
› Calculation according to EN ISO 10211› Often several 2dimensional calculations are needed› Often the U-value of the base constructions are unknown or can’t
be applied› 3 standard cases
-Psi value calculation: Ground
No Cellar Unheated cellar Heated cellar
Not covered today:
-Psi value calculation: Ground
Here’s the problem: What is the U‐value of the ground?
-Psi value calculation: Ground
2 thermal bridge calculations are needed1. 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)
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.
-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.
-Value calculation: Ground, no cellar
A-E-C, *
=
T-
T- U
2·b
2=
50.49830.000
-33.93530.000
- 0.278·1.410 = 0.160 W/(m·K)
Model: Ground - Geometry
20m
20m
4m
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
b: effective floor dimension if known, 8 meter if the floor dimension is unknown or greater than 8 m
Model: Ground - Geometry
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 - 0.04› Interior and exterior surface resistances of the assemblies
as normal
Model: Ground - Material, B.C.
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.
Post footings away from perimeter› Modeled same as the linear footing, but entered in PHPP
with length of 1m
AB
CD
E 15 15
11 11 13 13 17 17 19 19
C-G-D
=
T- U
1·b
1- U
2·b
2=
5.20110.000
- 0.117·2.250 - 0.117·2.250 = -0.005 W/(m·K)
A-B
= 5.201 W/m 88.58
U-= 0.117 W/(m
2
·K)
88.58
U-= 0.117 W/(m
2
·K)
Replacing glazing by insulation panel (EN ISO 10077-2)
d: effective thickness, if the frame is designed for a specific thickness,24 mm for double glazing, 36 mm for triple glazing otherwise
Model: FrameGeometry: Uf-Value Calculation, -Value Wall-Frame
Replacing glazing by insulation panel (EN ISO 10077-2)
Model: FrameGeometry: Uf-Value Calculation, -Value Wall-Frame
Notes:• To calculate Uf and install :• Solid “glazing panel” always
used instead of glass.• Glazing panel λ = 0.035• 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.
Model: Frame Boundary Conditions: Uf-Value Calculation, -Value Wall-Frame
Temperatures> Ti=20°C, Te=0°C
Resistances> Internal
> Normal (R=0.13 m2K/W) (shown in red)> Reduced radiation/convection (R=0.20 m2K/W) (shown in yellow)
> External (R=0.04 m2K/W) (shown in blue)
Note:• Exterior temperature for
Uf calculation = 0°C• Exterior temperature for
install calculation = ‐10°C
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
Model: Frame - Cavities
Determining factors> Geometry of the cavity> Temperature distribution in the cavity and on the cavity surfaces> Emissivity of the surfaces
Uf-value according to EN ISO 10077-2Uf-Value: Frame
Uf x bf + Up x bp = φ/ΔT
Using flixo: Uf-value object (U-value tool)
> Click 1: Select the result object
> Define the width of the frame bf
> Flixo calculates Upand φ, then solves for Uf
A
B
Uf A,B
=
T- U
p·b
p
bf
=
5.39220.000
- 0.649·0.192
0.123= 1.19 W/(m
2
·K)
-= -5.392 W/m
191.50 122.60
U-= 0.649 W/(m
2
·K)
Boundary Condition q[W/m2] [
oC] R[(m
2·K)/W]
Epsilon 0.9 0.900Exterior, frame 0.000 0.040 Interior, frame, normal 20.000 0.130 Interior, frame, reduced 20.000 0.200 Symmetry/Model section 0.000
Material [W/(m·K)]
Aluminium (Si Alloys) 160.000 0.900EPDM (ethylene propylene diene monomer) 0.250 0.900Elastomeric foam, flexible (1) 0.050 0.900Panel 0.035 0.900Silicone, pure (1) 0.350 0.900Slightly ventilated air cavity Softwood 500, typical construction timber 0.130 0.900Unventilated air cavity
2 thermal bridge calculations are needed1. 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
install value
install value
Model 1 Calculation› The heat flow through the
frame + glazing panel
› Exterior BC is now -10C› Flux value is higher
A
B
Boundary Condition q[W/m2] [
oC] R[(m
2·K)/W]
Epsilon 0.9 0.900Exterior, normal -10.000 0.040 Interior, frame, normal 20.000 0.130 Interior, frame, reduced 20.000 0.200 Symmetry/Model section 0.000
Material [W/(m·K)]
Aluminium (Si Alloys) 160.000 0.900EPDM (ethylene propylene diene monomer) 0.250 0.900Elastomeric foam, flexible (1) 0.050 0.900Panel 0.035 0.900Silicone, pure (1) 0.350 0.900Slightly ventilated air cavity Softwood 500, typical construction timber 0.130 0.900Unventilated air cavity
A-B
= 8.1 W/m
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
C D
E
0
0 10 -8 -4 4 8
12
14
16 18
18
18
Material [W/(m·K)] Aluminium (Si Alloys) 160.000 0.900EPDM (ethylene propylene diene monomer) 0.250 0.900Elastomeric foam, flexible (1) 0.050 0.900Fiberglass batt Lambda 0.044 0.044 0.900Gypsum plasterboard (1) 0.250 0.900Panel 0.035 0.900Plywood Lambda 0.12 0.120 Silicone, pure (1) 0.350 0.900Slightly ventilated air cavity Softwood 500, typical construction timber 0.130 0.900Timber 450 kg/m3 (softwoods) 0.120 0.900Unventilated air cavity XPS Lambda 0.029 0.029
Boundary Condition q[W/m2] [
oC] R[(m
2·K)/W]
Epsilon 0.9 0.900Exterior, normal -10.000 0.040 Exterior, ventilated, horizontal -10.000 0.130 Interior, frame, normal 20.000 0.130 Interior, frame, reduced 20.000 0.200 Interior, heat flux, downwards 20.000 0.170 Interior, normal, horizontal 20.000 0.130 Symmetry/Model section 0.000
A-E-C, *
=
T-
T- U
2·b
2=
14.16130.000
-8.060
30.000- 0.168·1.029 = 0.030 W/(m·K)
A-C
= -14.161 W/m 3
14.1
0 1
028.
70
U-= 0.168 W/(m
2
·K)
-Psi value calculation: Reference Point – Exterior Corner
0
0
15
15
-9
-9
-9
-9
-6
-6 6
6
18 18Reference 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
0
0 15
15
-9
-9 -9
3
6
6 9
12
18
18
-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
0
0 10
10
-8
6
16
-Psi value calculation: Reference Point – Parapet
Exterior
Interior
Reference Point> For parapet TB, do not
include any part of the parapet above the top surface of the roof’s thermal boundary
-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
0
0
15
15 -9
-9 6
6
9
9
-Psi value calculation: Reference Point – Rim joist
Exterior Interior
Reference Point> For rim joist, position of the
reference point doesn’t matter much if the two wall assemblies are the same.
0
0
15
15 -9
-9
6
-Psi value calculation: Reference Point – Rim joist
Exterior
Interior
Reference Point> For rim joist with two
different assemblies, the reference point needs to be aligned according to the assembly dimensions used in PHPP.
Notes:• Does the above grade wall
extend to here in PHPP?
0
0
15
15 -9
-9
6
-Psi value calculation: Reference Point – Rim joist
Exterior
Interior
Reference Point> For rim joist with two
different assemblies, the reference point needs to be aligned according to the assembly dimensions used in PHPP.
Notes:• Or here?
0
0 10 -8 -4 4 8
12
14
16 18
18
18
-Psi value calculation: Reference Point – Windows
Exterior
Interior
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.
Model: Standards
Thermal Bridge, Model› EN ISO 10211 (geometry, mesh, accuracy, ground)› EN ISO 10077-2 (frame U-value, edge -value)› EN ISO 12631 (Ucw-value, 3D elements like screws)
Materials› EN ISO 10456 (general materials)› EN ISO 6946 (air layers)› EN ISO 10077-2 (frame)› EN ISO 673 (filling of glazing)
Boundary Conditions› EN ISO 6946 (general)› EN ISO 13788 (mold, condensation)› EN ISO 10211 (ground)› EN ISO 10077-2 (frame)
ggff bUbUT
-value: Spacer
2 calculations are neededa) Uf-value calculation with insulation panel instead of glazingb) Heat lost calculation with glazing and spacer
Using flixo: Psi-value Edge (context menu)> Click 1: selection of the result object> Select the file with the Uf-value calculation
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