Ψ VALUE ... PROBLEM WITH U VALUE
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Robin Mitchell
Nov 20, 2020, 2:46:19 PM11/20/20
to Kostas Hatzopoulos, THERM
To generate a U-value, you need to add U-factor tags to the boundary conditions.
Robin
On Fri, Nov 20, 2020 at 1:02 AM Kostas Hatzopoulos <xatzop...@gmail.com> wrote:
I WONT TO FINED THE Ψ VALUE .. BUT I HAVE THE PROBLEM WITH U VALUE. PLZ HELP ME
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Robin Mitchell
Building Technology and Urban Systems Division
Energy Technologies Area
Lawrence Berkeley National Laboratory
Energy Technologies Area
Lawrence Berkeley National Laboratory
yal...@gmail.com
Mar 5, 2025, 5:35:59 PM3/5/25
to THERM
See section 6.5.2 of the latest NFRC simulation manual.
archi...@gmail.com
Mar 18, 2025, 12:04:50 PM3/18/25
to THERM
Hi.
From what you write I suppose you write from Europe (Greece perhaps?) so European standards should apply to your case, in particular EN ISO 10211
Yours is the typical corner Thermal Bridge to which 2 psi values are associated depending on which dimension system is used: gross external or net internal.
Boundary conditions
Example 1. The corner refers to two walls than BCs to be adopted are: external side Rse=0.04 m2K/W, every BC segment's U-factor name could be "External", internal side Rsi=0.13 m2K/W and every BC segment's U-factor name could be "Internal" (see file "Example 1 corner 2 walls Psi.THM").
Example 2. The corner refers to a vertical wall and a horizontal roof than BCs to be adopted are: external side Rse=0.04 m2K/W, every BC segment's U-factor name could be "External", internal side for the vertical wall Rsi=0.13 m2K/W for the horizontal roof Rsi=0.10 m2K/W and every BC segment's U-factor name could be "Internal" (see file "Example 2 corner wall-roof Psi.THM")
Thermal Resistance and thermal Transmittance
According to EN ISO 6946 structures thermal resistance is Rtot = Rsi + sum s/L + Rse and U = 1/Rtot
Example 1. According to the material's thermal conductivity and thickness adopted in the Therm files the brick wall's thermal transmittance is U1=0.141 W/m2K and the concrete wall's thermal transmittance is U2=0.153 W/m2K
Example 2. According to the material's thermal conductivity and thickness adopted in the Therm files the brick wall's thermal transmittance is U1=0.141 W/m2K and the concrete roof's thermal transmittance is U2=0.154 W/m2K
Dimension system
According to EN ISO 13789 buildings' thermal performance may be calculated using externale gross dimensions or external net dimensions. Thermal bridges' Psi-values calculation must be consistent with the dimension system used in thermal calculations.
From the illustration you posted I suppose that you mean to calculate Psi-value consistent to net internal dimension.
In both examples the structures' internal net dimensions are 1,50 m and the gross external dimensions are 1,90 m
L2D Calculation
According to EN ISO 10211 L2D = Phi/deltaT. The thermal bridge's Phi value is found in Therm's calculation results.
Example 1. Phi = 10.3027 W/m, deltaT = 20 K, L2D = 10.3027/20 = 0.515135 W/mK
Example 2. Phi = 10.3415 W/m, deltaT = 20 K, l2D = 10.3415/20 = 0.517075 W/mK
Psi-value calculation
According to EN ISO 10211 Psi-value of a 2D Thermal Bridge must be calulated using the following equation: Psi = L2D - sum(UxL)
Example 1. Psi(i) = 0.515135 - (0.141x1.5 + 0.153x1.5) = 0.074 W/mK, Psi(e) = 0.515135 - (0.141x1.9 + 0.153x1.9) = -0.044 W/mK
Example 2. Psi(i) = 0.517075 - (0.141x1.5 + 0.154x1.5) = 0.075 W/mK, Psi(e) = 0.517075 - (0.141x1.9 + 0.154x1.9) = -0.043 W/mK
From what you write I suppose you write from Europe (Greece perhaps?) so European standards should apply to your case, in particular EN ISO 10211
Yours is the typical corner Thermal Bridge to which 2 psi values are associated depending on which dimension system is used: gross external or net internal.
Boundary conditions
Example 1. The corner refers to two walls than BCs to be adopted are: external side Rse=0.04 m2K/W, every BC segment's U-factor name could be "External", internal side Rsi=0.13 m2K/W and every BC segment's U-factor name could be "Internal" (see file "Example 1 corner 2 walls Psi.THM").
Example 2. The corner refers to a vertical wall and a horizontal roof than BCs to be adopted are: external side Rse=0.04 m2K/W, every BC segment's U-factor name could be "External", internal side for the vertical wall Rsi=0.13 m2K/W for the horizontal roof Rsi=0.10 m2K/W and every BC segment's U-factor name could be "Internal" (see file "Example 2 corner wall-roof Psi.THM")
Thermal Resistance and thermal Transmittance
According to EN ISO 6946 structures thermal resistance is Rtot = Rsi + sum s/L + Rse and U = 1/Rtot
Example 1. According to the material's thermal conductivity and thickness adopted in the Therm files the brick wall's thermal transmittance is U1=0.141 W/m2K and the concrete wall's thermal transmittance is U2=0.153 W/m2K
Example 2. According to the material's thermal conductivity and thickness adopted in the Therm files the brick wall's thermal transmittance is U1=0.141 W/m2K and the concrete roof's thermal transmittance is U2=0.154 W/m2K
Dimension system
According to EN ISO 13789 buildings' thermal performance may be calculated using externale gross dimensions or external net dimensions. Thermal bridges' Psi-values calculation must be consistent with the dimension system used in thermal calculations.
From the illustration you posted I suppose that you mean to calculate Psi-value consistent to net internal dimension.
In both examples the structures' internal net dimensions are 1,50 m and the gross external dimensions are 1,90 m
L2D Calculation
According to EN ISO 10211 L2D = Phi/deltaT. The thermal bridge's Phi value is found in Therm's calculation results.
Example 1. Phi = 10.3027 W/m, deltaT = 20 K, L2D = 10.3027/20 = 0.515135 W/mK
Example 2. Phi = 10.3415 W/m, deltaT = 20 K, l2D = 10.3415/20 = 0.517075 W/mK
Psi-value calculation
According to EN ISO 10211 Psi-value of a 2D Thermal Bridge must be calulated using the following equation: Psi = L2D - sum(UxL)
Example 1. Psi(i) = 0.515135 - (0.141x1.5 + 0.153x1.5) = 0.074 W/mK, Psi(e) = 0.515135 - (0.141x1.9 + 0.153x1.9) = -0.044 W/mK
Example 2. Psi(i) = 0.517075 - (0.141x1.5 + 0.154x1.5) = 0.075 W/mK, Psi(e) = 0.517075 - (0.141x1.9 + 0.154x1.9) = -0.043 W/mK
Ciao
Fabrizio
Hamid BADI
Mar 20, 2025, 4:13:37 AM3/20/25
to THERM
Juergen
Jun 20, 2025, 3:07:07 AM6/20/25
to THERM
This looks really nice. How do you create this graphical output in Therm? And how do you get the Psi values?
Fabrizio Prato
Jun 21, 2025, 4:54:50 PM6/21/25
to Juergen, THERM
Hi Juergen.
These images are not made with Therm, but with some sw used in France, I think. Perhaps the author may confirm.
They're certainly a good representation of a thermal bridge calculation, since everything needed to reproduce it is clearly shown: internal and external dimensions (and relative psi values), materials conductivities and BCs.
Very nice ... But it is not Therm.
Ciao
Fabrizio
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