Documentation of window energy performance

Assignment 2 – Report 2

Documentation of window energy performance

Kasper U. Nielsen

Kathrine N. Brejnrod

Theis H. Pedersen

Title page

Title: Assignment 2 – Report 2

Subtitle: Documentation of window energy performance

Written by: Kasper U. Nielsen [201300234]

Kathrine N. Brejnrod [20062459]

Theis H. Pedersen [201300223]

Report: Assignment 2

Study: Architectural Engineering

Course: Energy-efficient building envelope design

School: Aarhus School of Engineering

Project period: 19. Feb. – 27. Marts 2014

Mentor: Steffen Petersen

Pages: Main report: normal pages [2400 hits]

Basis for decision making: pages

Appendices: pages

Chapter 1 - Introduction

#Table of Contents

1 Introduction ...................................................................................................................... 1

2 Documentation ................................................................................................................. 3

2.1 Product development ................................................................................................ 3

2.1.1 Decreasing the complexity ............................................................................... 3

2.1.2 Engineering characteristic ................................................................................ 5

2.2 Frame profile ............................................................................................................ 7

2.2.1 EN ISO 10077-1 Annex D ............................................................................... 7

2.2.2 EN ISO 10077-2 Numerical method - Annex C + Therm................................ 7

2.2.3 Optimization ..................................................................................................... 8

2.3 Edge construction ................................................................................................... 11

2.3.1 Five different conductivities ........................................................................... 11

2.3.2 Final Spacer .................................................................................................... 12

2.4 Condensation risk ................................................................................................... 13

2.5 Window performance data ..................................................................................... 16

2.5.1 Case 1 ............................................................................................................. 16

2.5.2 Case 2.1 .......................................................................................................... 16

2.5.3 Case 2.2 .......................................................................................................... 16

2.6 Window energy performance in office room ......................................................... 16

3 Conclusion ...................................................................................................................... 19

4 Bibliography ................................................................................................................... 21

5 Appendix ........................................................................................................................ 23

Chapter 1 - Introduction


Kasper Ubbe Nielsen; Kathrine N. Brejnrod; Theis H. Pedersen Side 1

1 Introduction

This report is the technical report that supports the Basis for decision making.

In the following report, two suggestions for improvements of the Thema TA frame profile

are presented. The suggestions is based on a product development process, based on the

House of Quality method, and multiple analysis of the construction principle, spacer

material, risk of condensation and general performance data.

The main focus of this optimization is to reach a value of Eref ≥ 0, by maintaining the original

design of the frame. The program THERM 7 is used to perform the calculations combined

with the methods presented in EN ISO 10077 part 1 and part 2, which has been integrated

into a pre-developed spreadsheet. The program iDbuild is used to perform the energy

performance assessments, calculated for a reference office room, and thermal and daylight

conditions.

Regarding material use, the material database, “Termiske egenskaber for materialer brugt i

vinduessystemer”, developed by Teknologisk Institut is used. The listed material-

conductions in the database are in accordance with the EN ISO 10077-2.

Chapter 2 - Documentation



2 Documentation

2.1 Product development

2.1.1 Decreasing the complexity

To break down the complexity of the different aspect of the product development, a

clarifying of the different parameters, stakeholders and engineering characteristics is made

and their interdependence identified. The process helps to create an overview of the

individual factors influence on the rest of the product characteristics, and thereby creates a

basis for a simple an effective development of a product with the desired characteristic.

First the objectives of the product are clarified and the importance of the specific objective to

each of the stakeholders is estimated on a scale from 0-5 with 5 being very important. From

Figure 1 the importance of the objectives is illustrated, and in this case especially the

manufacturer’s point of view is important. Ideally the manufacture himself would evaluate

the importance of the different objectives to, but in this case the evaluation is done by the

general product development team.

Figure 1 – Clarifying objectives

Then the important engineering characteristics are identified, and the impact on the four

objectives are estimated on a scale varying from a positive to a negative impact, which is

illustrated on Figure 2. From the figure it is identified how none of the engineering

characteristic have a negative influence on the Eref and a high surface temperature. On the

contrary the manufacturing process is affected either slightly negative or directly negative


Side 4 Assignment 2 – Report 2

Kasper Ubbe Nielsen; Kathrine N. Brejnrod; Theis H. Pedersen

from all characteristics except the low spacer height. The stiffness of the construction is only

affected negative or slightly negative from a few of the characteristics. The overview in

Figure 2 is an important tool when starting to modify the window in order to improve the

current characteristics since it clarifies the negative and positive effects of each

characteristic.

Figure 2 – Engineering characteristics vs. Product attributes

As the last step in the clarifying process, the different engineering characteristics are help up

against each other to identify their inter-relational impact.

As Figure 3 illustrates there is remarkably few of the characteristics that has an actual effect

on each other, and on the negative side it clearly shows that the most effected characteristic

is the high stability which is affected negative by four other characteristics.




Figure 3 - Engineering characteristics vs. Engineering characteristics

With this last step completed, the complexity of the product development phase has now

been decreased by identifying and mapping the relations between the important factors in the

process. The overview is thus to be used when in the actual redesign process as a firm tool

for optimization.

2.1.2 Engineering characteristic

To create a firm goal of optimization for the frame construction, multiple combinations of

the engineering characteristics are to fulfill the objective goal of a neutral or positive energy

balance of the window is set up.

Since the product development is exclusively concerning the frame construction of the

window, the glazing is excluded as a variable factor and a standard glazing is defined to be

used consistently throughout the optimization process.

Table 1 – Glazing Properties

Ug

[W/m²K]

gg

[-]

LT

[-]

Glazing Properties 0.58 0.50 0.71




Table 2 – Window size

BW

[m]

LW

[m]

Window size 1.23 1.48

On the basis of the standard glazing given above the linear-loss through the spacer, Ψ, the

width of the frame, bf, and the U-value of the frame, Uf, are modified to create three

alternatives for a window with a positive energy balance. The alternatives are with

respectively three different U-values of the frame construction, two different linear heat loss

coefficients at the spacer and two different frame widths.

Table 3 - Prpoposals for engineerings characteristics

Uf

[W/m2K]

Ψ

[W/mK]

Bf

[m]

Uw

[W/m2K]

Eref

[kWh/m2]

Alternative 1 1,1 0,02 0,1 0,78 +1

Alternative 2 0,9 0,03 0,1 0,74 +4

Alternative 3 1,3 0,03 0,08 0,82 +2




2.2 Frame profile

It is chosen to work with and optimize the alu/wood frame profile from Thema. Figure 4

illustrates the frame build-up for a 2-layer glazing. In the following, the frame has been

alternated to fit a 3-layer glazing, by expanding the sash width.

Figure 4 - Frame section og ThemaTA

Figure 5 - Alternated profile for 3-layer glazing

2.2.1 EN ISO 10077-1 Annex D

The thermal properties of the frame are assessed according to the simplified method,

described in EN ISO 10077-1 Annex D. Table 4 below lists the measured and calculated

values from the altered profile. For description of method see Appendix A.

Table 4 - Frame specification according to EN ISO 10077-1 Annex D

d1

[mm]

d2

[mm]

df

[mm]

Uf

[W/m²K]

Thema TA 65.66 61.02 63.34 1.84

2.2.2 EN ISO 10077-2 Numerical method - Annex C + Therm

The numerical method described in EN ISO 10077-2 Annex C has been implemented in a

spreadsheet, see Appendix B. The result is seen in Table 5 below.




Table 5 - Frame specification according to EN ISO 10077-2 Annex C

Uf

[W/m²K]

Thema TA 1.84

It is seen that the result of the simplified method and the numerical method are equal. From

which it can be concluded that the chosen ThemaTA profile is a simple profile compared to

others. Hence the simplified method is assessed to applicable on simple profiles only.

2.2.3 Optimization

In Section 2.2.2 the U-value of the original construction is identified to Uf = 1.84 W/m2K,

which exceeds the proposed Uf-values in section 2.1.2 where the highest U-value proposed,

is 1.3 W/m2K. On basis of this, an optimization process of the frame construction is initiated

to decrease the U-value until it corresponds to the proposals set up in section 2.1.2.

On basis of the dependences clarified in section 2.1.1, different improvements are carried out

on the original frame and the effect on the U-value of the frame is identified through

calculations carried out in THERM 7.1.

Focus is mainly on improvements that do not change the appearance of the window frame

significantly, since it is assumed that the manufacture would like to keep the basis

appearance instead of developing an entirely new window.

From Table 6 a few of the improvements tested on the construction is shown together with

the effect on the U-value, se Appendix D and Appendix E for further information on the

improvements shown together with further improvements.

Table 6 - Uf for improvements

Improvement Uf

[W/m2K]

Compared to the

original Uf

Exterior sealing strip 1.78 -3 %

Cold bridges breaker 1.48 -20%

Replacement of sealing strips with foamed sealing’s. 1.8 -2%

PUR-foam in parts of the frame 1.61 -13

The improvements influence on the production of the construction is varied, and on the basis

of the identified effect of each of the improvements two alternative proposals are set up.




Both alternatives fulfill the proposed characteristics set up in section 2.1.2 but the one having

a lower U-value of the frame than the other and at the same time is expected to require

greater modifications on the production process than the one with the higher U-value.

2.2.3.1 Proposal 1

In the first proposal three improvements to the frame construction is applied. First a sealing

strip is added on the exterior side of the construction, to create still air in the frame cavities.

Then the continuous aluminum in the frame construction is partly replaced with

Polypropylene with 25% glass fiber to create a thermal brake. From Table 6 - Uf for

improvements it shows that this improvement with the thermal brake alone contributes to a

decrease in U-value of 20%. Further more the material of the sealing strips is changed from

EPDM to a foamed material with a lower conductivity.

The improvements in proposal 1 contribute to a decrease in the U-value of the frame of 30%

compared to the original construction.

Uf = 1.29 W/m2K

In section 2.1.2 it shows that with a U-

value of the frame of 1.3W/m2K a positive

energy balance of the window can be

achieved through a linear heat loss

coefficient of 0.03W/m*K and a frame

width below 0.08m. Since the current

frame height is 0.092m, the construction is

modified to fit the requirement.

2.2.3.2 Proposal 2

In the second proposal the continuous aluminum in the frame construction is also partly

replaced with Polypropylene with 25% glass fiber to create a thermal brake. On the exterior

side a sealing strip is added to create still air in the frame cavities, and then finally PUR-

foam is added to both frame and sash to lower the thermal conductance through the

sash/frame. The improvements in proposal 2 contribute to a decrease in the U-value of the

frame of 40% compared to the original construction.




Uf = 1.1 W/m2K

Compared to proposal 1 this proposal has a

lower U-value, but due to the PUR-foam in the

frame construction it is expected to require

further investigation of construction strength

and design and constructional possibilities.

In section 2.1.2 it shows that with a U-value of

the frame on 1.1 W/m2K a positive energy

balance can be achieved with a frame height

below 0,1m and a linear heat loss coefficient below 0.2 W/m*K. The frame width is

currently 0.92m which allows the linear heat loss coefficient to go as high as 0.035 W/m*K

and still keep a positive energy balance of the window.




2.3 Edge construction

In this section a suitable spacer is chosen on the basis of calculations performed in

accordance with the two-box approach. The value of the linear thermal transmittance is

calculated with different conductivities for the spacer profile and then compared for

assessments.

2.3.1 Five different conductivities

Table 7 lists the five different conductivities and their adjacent calculated overall thermal

conductance; L. L is calculated as a summation of each of the elements conductivities,

weighted with respect to the box height vs. spacer width. The thermal transmittance, Ψ, is

calculated using the supplied spreadsheet and Therm. It is done by subtracting the loss

through the frame and the pane part, from the 2D linear thermal transmittance, LΨ2D

.

Table 7 - Different conductivities effect on L and Ψ

λspacer,2.box

[W/m*K]

L

[W/m*K]

Ψ

[W/m*K]

0.1 0.1125 0.026

0.5 0.2625 0.049

1 0.45 0.067

2 0.825 0.086

5 1.95 0.108

The results of L and Ψ are plotted in Figure 6, below. Furthermore the derivative of the

function Ψ (L) is plotted, to clearly illustrate how the transmittance changes with respect to

the spacer conductivity. It is seen that for spacer conductivities below 1 W/m*K the effect on

Ψ is large compared to values above. And for values below 0.5 W/m*K the effects are more

obvious.




Figure 6 - Linear thermal coefficient as a function of L and the derivative of Ψ

From this, one could argue that it doesn’t make that much of a difference whether you chose

a “bad” or a “worse” spacer conductivity compared to the effect of whether you chose a

“good” or “better” spacer conductivity.

2.3.2 Final Spacer

From the former calculations and conclusion a spacer profile has been chosen. See Appendix

C for data sheet. The values for the two-box approach are list in

Box 1 Box 2

λ [W/m*K] 0.4 0.14

Ψ(L) = 0,0292ln(L) + 0,0897

R² = 0,998

0

0,05

0,1

0,15

0,2

0,25

0,3

0 0,5 1 1,5 2 2,5

Ψ

L

Ψ (L)

Ψ

Ψ'

Log. (Ψ)




2.4 Condensation risk

To determine if there is a risk of condensation on the inside of the window, a factor is

calculated as: oi

osi

TT

TT

Rsif The lower a value the greater the risk of condensation is.

Table 8 - Surface temperature and condensation risk factor

λspacer,2.box

[W / mK]

Tsi

[°C]

Fsi

[-]

0.1 15.2 0.76

0.5 13.7 0.685

1 12.6 0.63

2 11.4 0.57

5 10 0.5

The results listed in Table 8 clearly states, that the spacer material clearly affects the lowest

internal surface temperature. The lower conductance of the spacer material is the lower the

risk of condensation on the inside of the window.

The existing frame construction is shown at the sketch to the left and the optimized

construction to the right. Furthermore the surface temperature, at the two worst places is

shown. The improvement of the frame has resulted in a significant temperature

enhancement, which is of great importance to prevent condensation. Another consequence of

the improvements is that the node with the lowest temperature is moved.

Figure 7 - Existing and optimized construction

15.0 °C

15.9 °C

13.0 °C

12.6 °C

14.6 °C

15.1 °C




Table 9 - Comparison of spacers

λspacer,2.box

[W / mK]

Tsi

[°C]

Fsi

[-]

Existing construction (Chromatech Ultra F

spacer)

0.33 12.6 0.63

Optimized (Swiss Ultimate spacer) 0.14 15.0 0.75

As expected the risk of condensation is reduced due to the improvements.

A new feature in THERM 7 is that when you create the boundary conditions, it is possible to

set a relative humidity. Based on this RH and the internal temperature THERM marks if

there is any risk of condensation with a yellow line. The outside relative humidity is set to a

value of 50%.

Figure 8 - Surface condensation potential with inside RH of 65%

Figure 9 - Surface condensation potential with inside RH of 80%




The results above are taken directly from THERM. With an inside relative humidity at 65%,

there is not a risk of surface condensation at the optimized frame construction. When the

relative humidity is set at 80%, there are a potential of condensation at the surface. However

a relative humidity at 80% is very high, and would almost only appear in bathrooms and the

like. The results of the existing frame are also shown in order to compare.




2.5 Window performance data

2.5.1 Case 1

See Appendix F

2.5.2 Case 2.1

See Appendix G

2.5.3 Case 2.2

See Appendix H

2.6 Window energy performance in office room

To visualize the actual effect of the different window products the annual energy

performance is evaluated in the following section. The annual energy consumption is

evaluated on the basis of a standard office room with energy consumption below the current

requirements of the Danish building regulations.

Apart from the original frame construction and the two alternative solutions, the effect of

inserting a solar coated glazing or applying external solar shading is also evaluated to create

a basis for comparison. The specifications of the solar coated glazing and the external blinds

used are listed in Table 10.

Table 10

Description Ug [W/m2K] gg [-]

Solar coated Pilkington Suncool Brilliant

6B(66)-12Ar-4-12Ar-SN4

0.73 0.34

External blinds Hunter Douglas 0.150 light

blinds-20Ar-4SN-12Ar-4-12Ar-

SN4

0.76 0.49

From Figure 10 the annual energy consumption per square meter is illustrated. It clearly

shows how the annual effect of the optimized frame constructions is insignificant, and that

proposal 1 even effects the energy consumption slightly negative due to a higher ventilation

rate.




On the contrary the effect of the solar coated glazing and the external blinds contributes to a

decrease of the energy consumption of respectively 14% and 12% compared to the original

construction.

Figure 10 – Annual energy consumption

Apart from the energy consumption the different solutions also affects the daylight

conditions in the room. From Figure 11 it shows how the first proposal has a slightly positive

effect on the daylight factor due to the decreased frame width, but also how the solar coated

glazing contributes to a remarkable decrease in daylight factor.




Figure 11 - Daylight factor

Since both of the recommended solutions have a Eref = +2, a case with a window having

remarkable higher value on the positive energy balance is carried out. The window tested has

a linear heat loss coefficient of 0.01 W/m*K, a U-value of the frame of 0.8 W/m*K and a

frame width of 0.06, which contributes to Eref = +23.

Table 11

Original

construction

Proposal 1 Proposal 2 Window

Eref =

+23

Solar

coated

Uw [W/m2K] 1.02 0.79 0.82 0.64 1.13

Eref [kWh/m2] -19 +2 +2 +23 -52

Energy

consumption

[kWh/m2/year]

57 58 57 60 50

From the simulations it clearly shows, that the effect of optimizing the frame construction of

the window only affects the annual energy consumption minimal in the office room. It also

shows that the energy balance is not fit as a design objective when considering new office

buildings, since the one with the absolutely lowest Eref is the solar coated window but this is

at the same time the one with the lowest annual energy consumption.

Chapter 3 - Conclusion



3 Conclusion

In order to structure the optimization process, the development of a House of Quality mind

map, was carried out. From this the most important engineering characteristics was listed and

used in the optimization. This really made the process quicker and organized.

The final result was two optimized proposals, which both comply with a positive Eref. The

goal was to optimize the existing window frame, without making a totally new construction.

This is managed due to some few changes in the material use and by reducing the frame

height.

The consequence of the optimization is a lower Uframe and a higher internal surface

temperature, which leads to a lower risk of condensation on the inside.

Furthermore the performance of the optimized window has been tested in iDbuild by

evaluating the energy consumption, thermal and daylight conditions. The reference room is a

single office room, which has a very low heating demand. Therefore the altering of the

window frame does not affect the energy performance by much. The heating demand

reduces a little, but the ventilations rate increases, in order to satisfy the thermal

environment, and thereby the energy to the fans also increases. It is estimated that the effect

on the energy performance would be significantly large in a room with a higher heating

demand.

The daylight conditions do not change much, since only the frame has been optimized and

not the glass. However the glass/frame ratio is greater at proposal 2.1 since the frame height

is lowered. Therefore the daylight factor increases by 0.2.

Chapter 4 - Bibliography



4 Bibliography

European Standard, 2003. EN ISO 10077-2, s.l.: s.n.

Standard, European, 2000. EN ISO 1077-1, s.l.: s.n.

Teknologisk Institut, 2013. Teknologisk Institut. [Online]

Available at: http://matdb.teknologisk.dk/download.aspx

[Senest hentet eller vist den 03 2014].

Chapter 5 - Appendix



5 Appendix

Appendix A EN ISO 10077-1 – Annex D ............................................................................ 1

Appendix B EN ISO 10077-2 – Annex C ............................................................................ 3

Appendix C Spacer profile ................................................................................................... 5

Appendix D Single Improvements ....................................................................................... 7

Appendix E Combined improvements ............................................................................... 11

Appendix F Datasheet Result – Case 1 .............................................................................. 15

Appendix G Datasheet Result – Case 2.1 ........................................................................... 17

Appendix H Datasheet Result – Case 2.2 ........................................................................... 19




Appendix A EN ISO 10077-1 – Annex D

Figur 1 - Definition af d1 og d2

Figur 2 - Graf for aflæsning af Uf




Appendix B EN ISO 10077-2 – Annex C

Boundary conditions

hin W/m²K 7,69

hout W/m²K 25

Glazing 4-16-4-16-4

bg m 0,19

Ug W/m²K 0,54

Thickness Glass 1 m 0,004



Thickness cavity 1 m 0,016

Thickness cavity 2 m 0,016

glass W/mK 1

space W/mK 0,01916382

space, Therm W/mK 0,0162

Ug -Therm W/m²K 0,463532152

Insulation panel

bp m 0,19

Thickness (same as glazing) m 0,044

insulation material W/mK 0,035

Up W/m²K 0,700681547

Frame Profile

bf m 0,0900

Therm

bt m 0,2800

U-factor Out W/m²K 1,0684

U-factor In W/m²K 1,0684

U-factor average W/m²K 1,0696

Lf2D

W/mK 0,299488

Uframe W/m²K 1,84




Appendix C Spacer profile




Appendix D Single Improvements

Appendix D.1 Original Construction

Description

The original construction which

create the basis for the following

optimazations.

Characteristics

Uf = 1.84

File id: Thema TA2

Appendix D.2 1. Exterior sealing strip

Description

An exterior sealing strip is added

to create still air in the cavities in

the construction.

Characteristics

Uf = 1.78

Compared to the original

construction this constributes to a

decrease in Uf of 3%.

File id: Thema TA2_1_forbedring

Appendix D.3 2. Small thermal breake

Description

The aluminium in the frame is

broken with a small piece of

polypropylene with 25%

glassfibre. The polypropylene has

a thermal conductance of 0,25

W/mK.

Characteristics

Uf = 1.64


construction this constributes to a

decrease in Uf of 11%.

File id: Thema TA2_2_forbedring




Appendix D.4 3. Expanded thermal bridge brake

Description

The aluminium in the frame is

partly replaced with




W/mK.

Characteristics

Uf = 1.49


construction this contributes to

a decrease in Uf of 19 %.

File id:

Thema TA2_3_forbedring

Appendix D.5 4. Full thermal bridge breake

Description

A great part of the aluminium in

the frame is replaced with




W/mK.

Characteristics

Uf = 1.48



a decrease in Uf of 20 %.

File id: Thema

TA2_4_forbedring

Appendix D.6 5. Foamed sealing strips

Description

The sealing strips in the

construction is changed from

EPDM (λ = 0,25W/mK) to

foamed strips (λ = 0,08W/mK).

Characteristics

Uf = 1.8



a decrease in Uf of 2%.

File id: Thema

TA2_5_forbedring




Appendix D.7 6. PUR-foam in the frame

PUR-foam (λ = 0.030 W/mK) is

added in both frame and sash to

reduce the heat conductance.

Characteristics

Uf = 1.6




File id: Thema

TA2_6_forbedring




Appendix E Combined improvements

Appendix E.1 1_2

Description

Combination of the exterior

sealing strip and the small thermal

breake.

Characteristics

Uf = 1.54




File id: Thema

TA2_1_2_forbedring

Appendix E.2 1_3

Description


sealing strip and the larger

thermal breake.

Characteristics

Uf = 1.39




File id: Thema

TA2_1_3_forbedring

Appendix E.3 1_4

Description


sealing strip and the full thermal

breake.

Characteristics

Uf = 1.38




File id: Thema

TA2_1_4_forbedring




Appendix E.4 1_4_5

Description


sealing strip, the full thermal

breake and the replacement of the

existing sealing strips to foamed

strips.

Characteristics

Uf = 1.35




File id: Thema

TA2_1_4_5_forbedring

Appendix E.5 1_3_6

Description



breake and addition of PUR-foam

in both frame and sash.

Characteristics

Uf = 1.19




File id: Thema


Appendix E.6 1_3_6_7

Description



breake and addition of PUR-foam

in both frame and sash and

between the aluminium and the

wooden frame.

Characteristics

Uf = 1.17




File id: Thema

TA2_1_3_6_7_forbedring




Appendix E.7 1_11

Description


sealing strip and the full thermal

breake.

Characteristics

Uf = 1.32




File id: Thema

TA2_1_11_forbedring

Appendix E.8 1_11_9_12

Description



breake and two additional PUR-

foam boxes in respectivly frame

and sash.

Characteristics

Uf = 1.1




File id: Thema

TA2_1_11_9_12_forbedring

Appendix E.9 1_5_11

Description Combination of the exterior


breake and the foamed material

for all sealing strips.

Characteristics

Uf = 1.29




File id: Thema





Appendix F Datasheet Result – Case 1

See electronic file:




Appendix G Datasheet Result – Case 2.1





Appendix H Datasheet Result – Case 2.2


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