thermal bridge analysis for the phpp
TRANSCRIPT
-
8/10/2019 Thermal Bridge Analysis for the PHPP
1/33
Thermal Bridge Analysis for the PHPPPassive House Conference 2009
PH Consultant Session
Urbana, October 15
Revised Nov 29 2009
David White, Right Environments
-
8/10/2019 Thermal Bridge Analysis for the PHPP
2/33
Overview: Overall Method for Envelope Analysis
1. Analyze the envelope component areas & U-values using outside dimensions.
Areas go in the Areas tab and U-values go in the U-Values tab. This is
called the simplified method.
2. Examine the thermal bridges at the intersections between component areas.
Based on best judgment, decide whether or not the bridge is a significantextra heat loss (or may win back significant heat relative to the simplified
method in step 1).
3. If the bridge is not significant (less than 0.01 W/mK), dont bother to calculateit. If it is significant, you can account for it by taking a value from a catalog of
thermal bridges or doing your own 2D calculation. Input the thermal bridges in
the areas tab of the PHPP.
4. PHPP calculates total envelope loss as the sum of component area lossesand bridge linear losses.
-
8/10/2019 Thermal Bridge Analysis for the PHPP
3/33
This workshop includes:
Key Concepts
Calculation Guidelines
Tutorial with THERM and Excel
It does not include:
Dynamic analysis methods
-
8/10/2019 Thermal Bridge Analysis for the PHPP
4/33
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
5/33
Component Areas and Intersections
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
6/33Components
roof
wall
slab center
slab perimeter
slab edge
wall
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
7/33Intersections
roof
wall
slab center
slab perimeter
slab edge
wall
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
8/33
Intersections Note: taking windows from NFRC to PHPP has two problems: 1) physics
of ISO vs. NFRC and 2) NFRC has one combined value for glass, frame, and spacer.
Check my website for window inputs calculation method coming in time.
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
9/33Thermal bridging typically means that the heat gets a short cut across the envelope.
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
10/33
In PHPP, whether or not the heat gets a short cut, a thermal bridge coefficient can beapplied any place where heat flow cant be accurately calculated using the simplified
method, i.e. an intersection!
Thermal Bridges
wall to slab (can be a big one!)
wall to roof
wall to wall
glass to frame (spacer in WinType) frame to wall (installation in WinType)
etc
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
11/33
= -(W/K per meterinto the page) (W/K per meterinto the page)(W/K per meterinto the page)
Key Concepts
Key understanding: the thermal bridge is the extra heat loss associated with the
intersection. This means that the thermal bridge loss is the total loss from 2D analysis
minus the loss calculated for that same section using the simplified method.
-
8/10/2019 Thermal Bridge Analysis for the PHPP
12/33
For component heat loss, use simpleparallel heat transfer calculation in PHPP.
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
13/33For thermal bridge heat loss, either reference a calculation done by others...
Details for Passive Houses
Key Concepts
-
8/10/2019 Thermal Bridge Analysis for the PHPP
14/33...or do it yourself, for instance using THERM.
Key Concepts of Thermal Bridges
K C t
-
8/10/2019 Thermal Bridge Analysis for the PHPP
15/33
Thermal bridges must be specific to
ambient, ground, or perimeter.
Key Concepts
K C t
-
8/10/2019 Thermal Bridge Analysis for the PHPP
16/33
Ambient no ground
interactions
Ground bridge is in
contact with ground, far
from grade. Do not
include ground orexterior air film in model.
Perimeter partly
above, partly below
grade. Special!
Key Concepts
C l l ti G id li
-
8/10/2019 Thermal Bridge Analysis for the PHPP
17/33
Calculation Guidelines
C l l ti G id li
-
8/10/2019 Thermal Bridge Analysis for the PHPP
18/33
Schneiders, Protocol 16: Thermal Bridge Free Construction, PHI, January 2008
R-0.45 R-0.74
R-0.22
R-1.14
R-0.97
Calculation Guidelines
Surface Film Coefficients
C l l ti G id li
-
8/10/2019 Thermal Bridge Analysis for the PHPP
19/33
Calculation Guidelines
Surface Film Coefficients from ASHRAE Fundamentals
PS: I used some incorrect surface coefficients during the tutorial!!!!! sorry!
IP units METRIC units
C l l ti G id li
-
8/10/2019 Thermal Bridge Analysis for the PHPP
20/33
EN 10211-1 recommends straight sections extend 1m clear (consistent construction)
Rule of thumb: 4x wall thickness (although for PH this can be 6 feet!)
Beware: adiabatic boundary will force isotherms to be parallel! Red herring!
Above example is for a simple detail higher fluxes may need longer straight sections Too long can cause inaccuracy through rounding errors (?)
When in doubt, test it at various lengths (as above)
Calculation Guidelines
Schneiders
Calculation Guidelines
-
8/10/2019 Thermal Bridge Analysis for the PHPP
21/33
Useful hint: when applicable, put adiabatic boundary at a line of symmetry!
Calculation Guidelines
Calculation Guidelines
-
8/10/2019 Thermal Bridge Analysis for the PHPP
22/33
Perimeter Insulation is included in ground sheet calculations and in thermal bridge
calculations (I think).
Calculation Guidelines
Calculation Guidelines
-
8/10/2019 Thermal Bridge Analysis for the PHPP
23/33
This is how to model a perimeter thermal bridge! (from Schnieders 2008). Theindoor/outdoor temps are arbitrary in terms of of calculating psi. The specific temps
used here are useful because they also tell us something about condensation risk.
Outdoor temp,
e.g. 13F for NYCIndoor temp, e.g. 68F
Average of Indoor and Outdoor
temp, e.g. 40.5F
2.5m 1.0m
2.5m?
Adiabatic
Calculation Guidelines
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
24/33
Tutorial with THERM and Excel
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
25/33
Thermal bridge analysis: not just for masochists anymore!
Tutorial with THERM and Excel
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
26/33
Wall
Slab
Tutorial with THERM and Excel
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
27/33
Draw detail in THERM (to save time, it is pre-drawn for the tutorial).
Assign boundary conditions and U-factor tags.
Tutorial with THERM and Excel
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
28/33
Note: U-factor tags are drawn in red along interior surface. The U-factor tags can go anywhere as
long as they mark one gate through which all heat flow passes so THERM can measure the flow.
Note: German and US air film values differ slightly, so there are a few discrepancies w/ slide #18
Tutorial with THERM and Excel
adiabatic
outdoor temp with
exterior resistance
(R-0.17)
indoor temp, vertical
surface film (R-0.68)
indoor temp, downward
flow film (R-0.92)
outdoor temp withrain screen
(R-0.45)
half way between
indoor and outdoor
temp, no air film
ad
iabatic
adiabatic
indoor temp, inside corner film(R-1.14) for 8 inches or so
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
29/33
Set error tolerances and max iterations Then run it. Manual (7.3.2) warns of accumulated
rounding errors below 5% Maximum Error Energy Norm. Software author says 5% is ok.
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
30/33
Set up calculation sheet on PHPP
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
31/33
Calculate heat loss of straight sections by one of the following methods:
simulate straight section on THERM (more accurate, but how much more?)
use PHPP calculation (faster)
Tutorial with THERM and Excel
-
8/10/2019 Thermal Bridge Analysis for the PHPP
32/33
Subtract 1D losses from 2D losses. Be careful to assign the correct temperature difference to each
component. Divide the net loss by the deltaT to ambient (not ground) because PHPP asks for
perimeter thermal bridges with respect to outdoor temperature. The result is the -value.
-
8/10/2019 Thermal Bridge Analysis for the PHPP
33/33