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Erstellung von Complex Glazing mit europäischen Daten für DesignBuilder und EnergyPlus


Steps for the input of complex glazing parameters in EnergyPlus / DesignBuilder using the specifications of German / EU manufacturer’s window datasheets

Background: EnergyPlus uses the inputs of “rated” values which have been established at “rated”[4] conditions to part-wise reverse construct a physical system which would yield the rated value at the rating conditions. This applies to many types of values generally, but here we specifically mean rated U-values, SHGC or g-values, Visible Light Transmittance, etc. EnergyPlus expects the input fields to be filled with rated values as documented in its documentation and are typically those specified by American norms and standards. These rated values may differ significantly from the rated values typically specified in the EU, not because the physical system is different, but because the rated values are established at different rating conditions. Consequently, Uw-values for the entire assembly may differ by as much as 0.1 W/m²K. This guide will try and show how to use EU rating values to enter the correct inputs in EnergyPlus / DesignBuilder.

You will need:

  • The LBNL program WINDOW 7.2 or better. (free download)
  • EU window manufacturer’s data sheet for a window specifying[1]:

o   That is it more recent than 31 December 2013

o   g-value, Ug, Uf, Uw, VT, GlazingSystemBuildup and frame dimensions (preverably referencing the norms CEN 673 & ISO 10077)

o   As much detail on the glazing system as possible

The steps by means of an example specification

Example EU specification:

Product Name: ThermoSolar-Geneo

Uf=0.99 W/m²K, Ug=0.6 W/m²K und Uw=0.8 W/m²K (the last value is for the window assembly)

SHGC=0.5 (g-Wert) …Our data sheet sadly only has the Glazing System SHGCg

VT=0.72 (Lichttransmission 72 %) …Our data sheet sadly only has the Glazing System VTg

GlazingSystemBuildup= 4/14/4/14/4 (Scheibenaufbau) …we’ll have to guess somewhat until we find the matching Ug using Window

 


Frame width (projected thickness) = 100 mm…estimated from pictures on datasheet or drawings…this is the area weighted equivalent thickness[2] and is used with the Uf-value

Frame = 86 mm (inside to outside)

Step 1 – strip off the air film resistance values from EU Uf

EU Uf=0.99 W/m²K

The EU Uf was created using rated interior and exterior air film resistances as per ISO 10077 of hi=7.69 W/m²K and he=25 W/m²K respectively.

EU Uf_nofilm = 1/(1/(EU Uf) - 1/he - 1/hi) = 1/(1/0.99-1/25-1/7.69) = 1.19 W/m²K

When generating the WINDOW output idf for energyplus, we expect to see this value (Step 6).

EnergyPlus expects an American rated Uf value WITHOUT the added air film resistances. The EU Uf was created using rated interior and exterior air film resistances as per ISO 10077 of hi=7.69 W/m²K and he=25 W/m²K respectively, together with the indoor to outdoor temperatures of 20ºC to 0ºC. The WINDOW program expects this temperature difference to be approximately[3] 21ºC (material dependant as per ISO 15099) to -18ºC (exactly as per NFRC 100-2010) for the EnergyPlus required NFRC 100-2010 calculation.

Step 2 – use WINDOW to find the EU glazing system results

We are going to find the glazing system results using EU inputs into WINDOW together with the EU settings in WINDOW.

Change the following settings in WINDOW:

  • File/Preferences/Thermal Calcs/Calculation Standard --> change ISO 15099 to EN 673
  • File/Preferences/Optical Data/Standards File --> change to prEN_410-WINDOW.std

Glazing Systems Library:

  • Click “New” to create a new list entry and rename it, e.g. ThermoSolar Glazing CEN
  • Environmental Conditions --> CEN
  • # Layers --> in our example from GlazingSystemBuildup= 4/14/4/14/4 --> 3
  • Glass 1 (outside)…double click on the name field and select the most likely glazing from the database (IGDB) --> in our example ID 14194 from the German firm Trösch. Hint: look for a Tvis higher better than what we require, but with emis 1 (the emissivity) as low as possible and a ca. 4 mm pane thickness as per our specification.
  • Flip the metal vapour coating to face to inside by ticking the flip tickbox.
  • Gap 1 …change the “Air” to “Air – EN673” and change the thickness as per our specification 14 mm
  • Press “Calc” at any time to see the calculated values and change the layers until the Ug, SHGC and Tvis match our specification
  • The following combination was a good fit:

Glass 1 : ID 11333

Gass 1: ID 107

Glass 2 : ID 14004

Gass 2: ID 107

Glass 3 : ID 11333

The gas fill Argon90% & Air10% is common. The middle layer being a float glass without miniral vapour treatment is common. The panes are from the same European manufacturer and meet the thickness specification. This is an iterative procedure and can take some time.

The results were:

Ufactor(Ug)=0.644 W/m²K --> rounded meets our specification 0.6

Tvis(VT) = 0.711 --> rounded meets our specification 0.72 within 0.01

SHGC(g) = 0.502 --> this is only for the glass. Our specification requires 0.5. Therefore we expect some solar energy gain addition through the frame.

Step 3 – Include a EU frame in WINDOW

Frame Library:

  • Click “New” to create a new list entry and rename it, e.g. ThermoSolar Frame CEN
  • Set frame U-value --> EU Uf = 0.99 as per our specification
  • Set the frame edge correlation as per the type of frame… in our case it is an insulated frame judging from the pictures in the datasheet --> 4

 

 

 

6.1.1 The Edge U-value

For ASHRAE/LBL frames the edge U-value is treated as a function of the spacer type and the cernter-of-glass U-value. The general polynomial representing this functionality is as follows:

UE = A1 + A2(UC)+A3(UC

6.1.1

The values of the coefficients are dependent on the spacer material, see Table 6.1. All coefficients are given in SI units. [NOTE: Some of these values are different than those used in WINDOW 3.1.]

Corr #

Spacer Type

A1

A2

A3

Source

1

Aluminium ASHRAE Metallic

2.33

-0.01

0.138

ASHRAE

2

Stainless Steel; dual steel

1.03

0.76

0.0085

Arasteh, 1989

3

Butyl/Metal (Fiberglass, Wood, Glass Edge)

0.82

0.8

0.0022

Arasteh, 1989

4

Insulated

0.35

0.83

0.018

Arasteh, 1989

5

Ug = UC

0

1

0

 

Table 6.1 Coefficients used to calculate edge-of-glass U-values

 

 

  • Set the frame projected dimension…as per specification -->100 mm
  • Set the frame emissivity if known, else 0.9 unless having a raw metal finish without coating 0.3 --> 0.9

 

Step 4 – create a CEN window assembly for testing in WINDOW

Window Library:

  • Click “New” to create a new list entry and rename it, e.g. ThermoSolar Window CEN
  • Set mode --> CEN
  • Type -->Fixed (picture)
  • Environmental Conditions --> CEN
  • Click on each frame in the graphic and select your own frame (ThermoSolar Frame CEN) for each from the frame field under the name dropdown menu.
  • Click on the glass in the graphic and select your own frame (ThermoSolar Glazing CEN) from the glazing system field under the name dropdown menu.
  • Calculate

Our example results are:

U-factor (Uw) = 0.786 W/m²K…rounded meets our specification 0.8

SHGC = 0.393…informatively lower for the entire assembly than the SHGCg 0.5 of just glass

VT=0.514…informatively lower for the entire assembly than the VTg 0.72 of just glass

Step 5 – Change over to American calculation mode in WINDOW

Now that we are satisfied that the physical description meet the specification as per its rating conditions, we switch over to the American rating conditions to find the American equivalent values for input in EnergyPlus / DesignBuilder.

Change the following settings in WINDOW:

  • File/Preferences/Thermal Calcs/Calculation Standard --> change EN 673 back to ISO 15099
  • File/Preferences/Optical Data/Standards File --> prEN_410-WINDOW.std

Frame Library:

  • Click “Copy” to create a new list entry as a copy of ThermoSolar Frame CEN and rename it, e.g. ThermoSolar Frame Eplus
  • Calculate the American equivalent Uf by taking the American Uf_nofilm value from step 1, and adding back the default air film resistances that WINDOW uses.

Uf = 1/(1/(Uf_nofilm) + 1/he + 1/hi) = 1/(1/1.190388331 + 1/30 + 1/8) = 1.001607247 W/m²K

  • Change frame U-value --> Uf = 1.001607247

Glazing Systems Library:

  • Click “Copy” to create a new list entry as a copy of ThermoSolar Glazing CEN and rename it, e.g. ThermoSolar Glazing Eplus
  • Environmental Conditions --> NFRC 100-2010
  • Change the gas layer values to the equivalent American values
  • For information, you can press “Calc” to appreciate the differences to the CEN values

Window Library:

  • Click “Copy” to create a new list entry as a copy of ThermoSolar Window CEN and rename it, e.g. ThermoSolar Window Eplus
  • Mode --> NFRC 100-2010
  • Environmental Conditions --> NFRC 100-2010
  • Click on each frame in the graphic and select your own frame (ThermoSolar Frame Eplus) for each from the frame field under the name dropdown menu.
  • Click on the glass in the graphic and select your own frame (ThermoSolar Glazing Eplus) from the glazing system field under the name dropdown menu.
  • Calculate

Our example results are:

U-factor (Uw) = 0.819 W/m²K…which is a minor deviation from the EU Uw 0.784 (difference is 0.035)

SHGC = 0.378…expect only small deviations. EU SHGC was 0.393

VT = 0.513…expect only small deviations. EU VT was 0.514

Step 6 – find the Ratio of Frame-Edge Glass Conductance to Center-of-glass Conductance AND the equivalent Frame Conductance for EnergyPlus / DesignBuilder inputs

 

  • Click on a frame and notice the Uedge value. This value contains the WINDOW default air film resistances and must be split off before calculating the Uedge/Ug ratio input required by eplus. For that ratio, the same default film resistances must also be spit of Ug, so in effect we need Uedge_nofilm/Ug_nofilm for the EnergyPlus input. You can calculate this by hand, but WINDOW can do this for us when we now click on “Report” and select EnergyPlus IDF or similar. In the text output file you should find the “Ratio of Frame-Edge Glass Conductance to Center-of-glass Co” = 1.491358 as well as the “Frame Conductance {w/m2-K}” = 1.190388
  • Using the Frame Conductance, you can back calculate the Frame Material Conductivity property required for DesignBuilder:

k = frame-inside-to-outside-distance*Frame Conductance = 0.086*1.190388331=0.102373396 W/(m∙K)

 

You now have all the information you need to input the data in both EnergyPlus / DesignBuilder:

Frame Material Conductivity k and total thickess (both inside and outside projections) for the "frame material" definition

Glazing ID and Gas IDs out of the IGDB

Ratio of Frame-Edge Glass Conductance to Center-of-glass Conductance (no films)

Frame Conductance (no films)

 

Summary

Inputting the correct values for a window to reflect the EU ratings in EnergyPlus and DesignBuilder can be achieved with this guide. If the reader finds any error with the guide, please contact the author Jean Marais under Diese E-Mail-Adresse ist vor Spambots geschützt! Zur Anzeige muss JavaScript eingeschaltet sein! so that we can make the corrections. Also note that currently, the window ratings for center-of- glass U-values reported in WINDOW will differ slightly from those reported by e+. WINDOW uses the NFRC-required ISO 15099 algorithms to calculate the internal film coeffients as does e+, however WINDOW 7.2 uses the latest ISO 15099 and e+ that of 2009. This applies to the reported rating conditions and does not influence the accurate physical description and modelling of the glazing during simulation. Experience seems to indicate that the typical deviation for the overall Uw difference between American and EU ratings is about 0.05 W/m²K which lies inside the allowable measuring errors in Europe.



[1] If this information deviates, then the user must reckon that the values will be better than they really should be. See the Bundesverband Flachglas e.V. home page for more details.

[2] EnergyPlus assumes a uniform frame thickness all round the window perimeter. However, if individual frames are defined, WINDOW can export the equivalent thickness.

[3] This temperature is material dependant and may change slightly as per ISO 15099. We assume “interior wood/vinyl (convection only)” as per the boundary condition database in THERM 7.2.

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