Thermal Properties of Aluminium Fenestration Products and Building Regulations - AD L1 & L2

Seffing the Standard No. 6

Thermal Properties of AluminiumFenestration Products and theBuilding Regulations - AD Li & L2

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CAJ$Council forAluminiumin BuildingPromoting Innovation.Quality and Service

The Council for Aluminium in Building (CAB) is committed to providing authodtalive. impartial advice on the use of oluminium throughoutthe construction industry CAB makes every effort to ensure the technical accuracy. correctness, appropriateness and completenessof its guidance publications and other Information. However CAB, Its members and Its employees can take no responsiblilly for anysubsequent use of information nor for any errors or omissions in the information supplied.

Setting the Standard No 6

Setting the Standard NoóThermal Properties of Aluminium Fenestration Products and theBuilding Regulations — AD Li & L2 (2002 Edition),

Table of contents

Section Page

Foreword and Scope 2

Introduction 3

Definitions 4

1. A guide to the Building Regulation requirements 5, 6 & 7

2 Routes to compliance 8

2 1 Indicative window U-values 8

2.2 Measuring thermal performance by test 8

2.2.1 BS EN ISO 12567-1 Hot Box Method Part 1 Windows and 8Doors

2.2 2 prEN 1241 2-2 Hot Box Method Part 2 Frames B

2.3 Simplified calculations to BS EN ISO 10077-1 8

2.4 Numerical calculation to prEN ISO 10077-2 and ISO DIS 15099 8 & 9

2 5. Comparison of whole window U-value calculation results by'linear' and 'edge' methods2 6 Presentation of results 9

2 7 Requirements for simulators for self-certification, etd 9

3. Curtain waIl 10

4 Rooflights and overhead glazing. 10 & 11

5 Structural Silicone Glazing 11

6. Shop fronts and entrances 11

7 Conservatories and Ama 11

8 Comparison of thermal assessments calculation methods 11

Annex A Example calculation BS EN ISO 10077-1 12 & 13

Annex B Example calculation prEN ISO 10077-2 and ISO DIS 15099 14. 15 &16

Annex C Related standards 17


Foreword

Thermal assessment of aluminium windows and curtain wall has beenconsidered by the aluminium window industry for many years Previous workdeveloped in the late i980s by the Aluminium Window Association (AWA)culminated with the publication of the informative document - "A Guide tothe Assessment of Thermal Performance of Aluminium Windows" updatedand published by the CAB and issued as "Setting the Standard No3" inconjunction with "No 4 A Guide to the Assessment of Thermal Performanceof Aluminium Curtain Wall Framing" The subsequent introduction of BuildingRegulations, Approved Documents Li and L2 Conservation of fuel andpower highlights the importance of those two publications. These revisedregulations have been introduced in an effort to reduce the Nation's carbondioxide emissions from buildings, the Regulations came into effect on1April 2002

Now the CAB has produced "Setting the standard No6, Thermal Properties ofAluminium Fenestration Products and the Building Regulations — AD Li & L2"The purpose of this booklet is to define the thermal critena relating toaluminium fenestration products and examines the methods of compliancewith, but should not overrule, Document L for product design U-values,example calculations, etc It is also intended to set out good practice and toclarify any obscure points that the Regulations may not have been able toaddress

NOTE. The designer / specifier must ensure conformity to the relevantStandards and Regulations in force at the time of their work.

Scope

The guide defines the basic requirements of the Building Regulation anddetails the methods of compliance For simplicity the guide demonstratescalculations for fenestration products by the Elemental methodRequirements for composite/coupled windows, curtain wall, overheadglazing and centre pane U-values, etc are considered in separate sectionsDisplay windows, shop front doors and similar glazing are exemptConservatones that are separated from the host building are also exemptNote that any Interconnecting doors and windows remaining unchangedfrom their original specification do not require alteration However, new doorsand windows must comply with the requirements of AD Li and L2 as if theywere external elements.

2


Introduction to the Requirements

England and Wales

The Building Regulations for England and Wales - Parts Li and L2Conservation of Fuel & Power 2002

New Build and Replacement

The document became effective from 1 Apnl 2002 and is in two parts; Part Lifor Dwellings or domestic applications includes both private and publichousing and Part L2 for non-dwellings or non-domestic applications. Therequired U-value for aluminium windows is 2 2 W/m2K There are differentU-value requirements in the Approved Documents for wood and PVC-Uwindows and doors (2 OW/m2K) than for metal-framed windows and doors(2.2W/m2K). This difference is to allow for the improved solar gain factorsrelated to slender metal frames provided by increased glass areas. This is astep towards considering Domestic Window Energy Ratings (DWER) whichmay be used in future Regulation revisions as more technical data becomesavailable.

Replacement Only

Replacement windows doors and rooflights may be assessed solely by thecentre pane U-value of the glazing, which shall be 1.2 W/m2K Also fordomestic replacement fenestration only, contracts signed before April 2002and completed before July 2002 were exempt.

Compliance is achieved by the normal application route to Local AuthorityBuilding Control Departments. Alternatively for domestic replacement work.by self-certification once an installation company has been accepted asmeeting the requirements of FENSA Ltd *

Scotland

For Scotland Part J is the requirement, implemented in March 2002 covenngdwellings and other buildings

The dwelling U-value will be 2 OW/m2K and it is linked to the efficiency of theboiler in the property There is no alternative centre pane U-value approachin the Scottish Regulation.

Note: The Scottish Executive has granted a 12-month Class Relaxation on thisrequirement such that until 1 March 2003 the requirement for replacementwindows and doors in dwellings will be a U value of 2 2W/m2K

Non-Dwellings must meet 2 2W/m2K

N Ireland and the Republic of Ireland

It is anticipated that N Ireland will follow Part L in a few years. The Republic ofIreland is due to introduce their new regulations for dwellings new build, inJanuaiy 2003 (replacement windows to have a U-value 2 2W/m2K from July2003) The regulations for buildings other than dwellings are expected in 2004.The window U-value for new build is to be considered as a percentage ofwindow and door openings being relative to the floor area

*FENSA Ltd is a Government approved pnvate company.

3


Definitions of terms used in this publication

Curtain Wall A form of vertical building enclosure, which supports no loads other than it's own weight andthe environmental forces, which act upon it The term embraces many different constructionmethods and matenals, generally comprising the following

1 A light carner framework of site assembled components, which support pre-assembledopaque, translucent or transparent infill panels

2 Sections of prefabncated wall which are transported to site as unitised frames, often pre-glazed, and hoisted into place on the building's facade

3 Prefabncated unitsed frames, often pre-glazed, hung onto site-assembled carnerframework

Edge method The ISO procedure for calculation of whole window U-values by area weighted values for thewindow frame, centre pane glazing and 63 5 mm glazing edge zone, the method uses arealistic frame U-value

External doorsets Single or double leaf with frame, completely or partially glazed or solid Complete withrelated hardware, with or without fanhights or lateral parts, and with or without incorporatedshutters and blinds

Emissivity Emissivity is a surface property of a matenal It is a measure of the extent to which a surfacewill absorb or emit radiation It has a value between 0 and 1 and, as it is a ratio, has no units

Normal emissivity is the value measured at near normal incidence and quoted in theindicative U value tables of Approved Document L Ordinary uncoated clear float glass has ahigh 'normal' emissivity of 089

For calculating the centre pane U value of any glass, the corrected emissivity is used Thistakes into account the radiation exchange where glass surfaces face each other (as ininsulating glass units) and where the glass surface faces the room

Fenestration Includes windows, doors, rooflights, and curtain walling

Glazing The clear, translucent, or opaque glass, plastic or other material secured in preparedopenings in, for example, windows, door leafs, screens and curtain walling

Isotherm A line connecting points at the same temperature

Linear method The CEN procedure for calculation of whole window U-values by area weighted values forthe window frame and linear thermal transmittance factor for the glazing edge effect

This method also allows frame values to be calculated using an insulated panel in place ofglazing to generate a Uf (frame) value, however when calculating whole window U-valuesusing the frame Uf value the glazing unit edge effect has to be taken into account byincluding an appropriate value for the linear transmittance, which has to be calculated foreach frame and glazing condition, a figure of 008 is used In the simplified calculations to BSEN ISO 10077-1, for coated glass in metal frames but may well be reviewed

Thermal Bairier A component of low thermal conductivity (up to 03 W/m2K) separating inner and outeraluminium elements of the framing profiles and also provide mechanical continuity ofsufficient strength to withstand design wind loads, etc,

Thermal ConductivityO,) A measure of the ability of a matenal to permit the conduction of heat, in W/mK

Thermal Resistance (r) A measure of the ability of a component to resist the conduction of heat, in m2K/W

Windows (including Fixed openable (hinged, projecting, pivoted, sliding), or partially fixed, with or withoutRoof Windows) fanlights and lateral parts Completely or partially glazed and including non-transparent infill

and complete with related hardware, and may incorporate shutters and blinds

4


1. A Guide to the Building Regulation Approved Document 1: 2002

Document L is in two parts, Li for dwellings and L2 for non-dwellings and therequirements prescribe the whole window U-value, which a window shallachieve

U-value requirements

The U-value is measured in Watts per square metre per degree oftemperature difference (W/m2K) It is a measurement of the rate at whichheat is lost through a matenal The lower the U-value the lower the heat lossA whole window U-value is determined from the area weighted averagevalues of three components, the frame, the centre pane and the insulatedglass unit edge effect.

The U-values may be determined from indicative values given in theApproved Document, 'hot box' testing, simplified calculations or detailedcalculations by computer simulations The basic procedures are defined laterin this publication

The U-value requirements for windows and doors are given in the table belowfor the Elemental Method -

Exposed element U-value W/m2K1 Windows doors and rooflights (area weighted average) 2 2glazing in metal frames2 Windows doors and rooflights (area weighted average) 20glazing in wood and PVC-U frames

For Dwellings the maximum areas for windows, doors and rooflights should notexceed 25% of the total floor area For non-dwellings see the figures below. -

Building type

Residential buildings (where peopletemporarily or permanently reside)

Windows & doors as% of the internal areaof exposed wall

30

Rooflights as % ofarea of roof

20

Places of assembly. offices and shops 40 20

Industrial and storage buildings 15 20

Vehicle access doors and displaywindows and similar glazing As required

Note: These figures are to be applied when using the Elemental method which isconsidered in this publication (see page 6, Methods of compliance)

U-value for lenesiration elements - extracted from AD Li & L2

Notes1 Rooflights include roof windows2 An alternative requirement for refurbishment and replacement of windows onexisting buildings is to provide weather-stnpped windows withi 2 W/m2K centre paneU-value3 Display windows for shop entrance doors and similar glazing are not required tomeet the standard given in this table4 The higher U-value for metal windows allows for additional solar gain due to thegreater glazed portion

Maximum area of openings unless compensating measures are taken


Methods of compliance

There are three methods to establish acceptable thermal performanceneeds for an installation. Failure to achieve the desired result by one methodof calculation does not imply that the glazing is unsuitable and byconsidering an alternative calculation method the same areas of glazingmay comply The methods differ for dwellings and non-dwellings, they are -

DwellIngs to Approved Document Li

1 Elemental Method in which the area weighted average U-value ofall the fenestration elements must not exceed the specified valuesThere are three methods of establishing the product U-values:

a) Use the Indicative value tables A2 and A3 in the Documentb) By calculation in accordance with the Standards specified in the

Approved Documents and the BRE Guide BR 443 'Conventionsfor U-value calculations'

c) By measurement (hotbox) on sample windows of size andconfiguration given in GGF Data Sheet 2 2Note: These tests are generally time consuming and expensive,particularly on non-standard sizes, compared with calculationmethods.

2 Target U-value Method, this is under the control of the buildingdesigner and takes into account insulation levels of individualelements of the building envelope and the efficiency of the heatingsystem.

3 Carbon Index Method, as with 2 this is under the control of thebuilding designer, developed from the SAP method of the previousRegulations L.

Non-dwellings to Approved Document 12

1. Elemental, this is similar to the Elemental Method procedure fordwellings

2 The Whole Building Method is under the control of the buildingdesigner and is based on achieving a maximum emission or energyconsumption. This permits flexibility with "trade off" between differentareas of the building (e g floors / walls / roofs I windows)

3. Carbon Emissions Calculation Method - as with 2 this is under thecontrol of the building designer The method allows designs thathave no greater carbon emissions than a notional building of thesame size and shape designed to comply with the ElementalMethod

Note' for simplicity only the Elemental method is considered in thispublication

Test and calculation assessment dimensions - Windows & Doors

To demonstrate conformity the standard window dimensions of 1 23 m wideby 1 48 m high are specified in the CEN Window and external pedestriandoor product standard prEN 14351, defined in BRE Guide BR 443'Conventions for U-value calculations', also the Glass and Glazing Federationdata sheet 2 2 as illustrated below Alternatively, the size and configuration ofthe test sample should be representative of those to be installed in thebuilding

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- 1 0 x 20 m - no side or top panels- 2 0 x 2 0 m - equal split, no side or top panels- 2.0 x 2.0 m - equal split one fixed one slider

for measurement methods a central transom may besubstituted for the mullion where the system designcannot meet the mullion configuration

_________ shding window samples shall be 2 panes Doors shall befitted with mid rails when or where applicable.

The Regulation provides guidance for compliance through indicative wholewindow U-values given in the tables A2 and A3 reconstructed belowCentre pane U-values have been added to the Regulation data to assistselection by glass type.

Table A2: Indicative U-values (W/m2K) For windows with metal frames (4 mm thermal barrier)

Note En tefers to normal emlssMty of the glass coating

Table A3: Adjustment to U-values in Table A2 for Frame with longer thermal barriers

Thermal bamer separation Adjustment to U-value W/m2K Adjustment to U-value W/m2Klength (mm) Windows or rooflights in buildings other

than dwellingsRooflights in dwellings

No bamer + 0.3 +0.14mm +0.0 +0.38mm -0.1 +0.212mm -0.2 +0.116mm -0.2 +0.1

Note Figures in these tables do not take into consideration the window type, profile dimensions or window sizebut are known to be based on a I m2 single pane window

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Door assessment dimensions for Li and 12 requirements are:-

Single leaf Doors

m Double leaf DoorsSliding leaf Doors

NotesADL1 Windows

AD L2 Windows

Li window for dwellings

— 1.23m —

1

NN

'—VV

18m Indicative window U-values

1.2 window for non-dwellings

6 mm Gap betweenpanes

12 mm Gap betweenpanes

16 mm Gap betweenpanesSingle glazing whole window

U=57

Double glazingDouble glazing (air filled)Double glazing (low-E En = 0 2)Double glazing (low-E En = 0 1)Double glazing (low-E En = 005)

Double glazing (argon gas filled)Double glazing (low-E En = 0 2)Double glazing (low-E En = 0 1)Double glazing (low-E En = 005)

Tnple glazingTnple glazing (air filled)Tnple glazing (low-E En = 0 2)Tnple glazing (low-E En = 0 1)Tnple glazing (low-E En = 0 05)

Tnple glazing (argon gas filled)Tnple glazing (low-E En = 0 2)Tnple glazing (low-E En = 0 1)Tnple glazing (low-E En 0 05)

Wholewindow U

3.32.62523

3.2252321

Wholewindow U

37333231

3.53.1

2.92.8

2.92.62.52.4

2.8242222

CentrePane U

27181615

26161412

Centrepane U

33272625

30232221

23181716

21151313

Wholewindow U

3.42.82.62.5

3.32.62.42.3

2.62.22.01.9

2.52.01.91.8

Centrepane U

29191817

27171513

19121110

18100908


2. Routes to compliance

2.1. Indicative U-values. The indicative whole window U-values given inTables A2 and A3 of the Regulation and reconstructed on page 7 of thispublication, provide conservative values for guidance on typical windowproducts. Compliance with the specified U-values should require no morethan a cross section detail of the window framing with dimension of thethermal barrier separation width, the gap between panes and a statementof glazing type, with its emissivity

Vanations in framing dimensions and more precise values make the detailedcalculation procedures a preferred alternative

2.2. Measuring thermal performance by test

2.2.1 BS EN ISO 12567-1 Thermal performance of windows, doors and shutters-Determination of thermal transmittance by hot box method: Part 1: Windowsand doors

This method tests a window assembly to the assessment dimensions as statedpreviously The limitation of this type of test is that the assessment sample maynot be representative of those to be installed onto the building

2.2.2 prEN 12412-2 Windows doors and shutters — Determination of thermaltransmittance by hot box method - Part 2: Frames

This method tests the window frame profile with an insulation panel withthermal conductance of 0.035 W/mK, Frame U-values determined by this testmethod should not be used in condensation prediction assessments

2.3 Simplified calculation frame and whole window U-values

BS EN ISO 10077-1 Thermal performance of windows doors and shutters -Calculation of thermal transmittance Part 1: Simplified method.

This Standard provides a simplified method of calculating frame and wholewindow U-values and requires only basic dimensions of the window framingand thermal barrier and data from tables to be entered into the equation

This simplified calculation procedure was used for the preparation of the tableof indicative window U-values (Tables Al and A2 of the Building Regulation)

A typical calculation to this standard is set out in Annex A of this publicationand the BRE U-value Calculator (http.//projects bre co uk/uvalues) includeswindow U-values to this standard

Note This simplified method is not suitable for curtain wall framing

2.4. Numerical calculation

prEN ISO 10077-2 Thermal performance of windows doors and shutters -Calculation of thermal transmittance Part 2: Numerical method for frames.

This standard provides a more detailed numerical approach for assessingframe and whole window U-value, by computer simulation software Theprocedure in the standard, known as the 'linear' method, assesses the frameU-value with an insulation panel replacing the glazing With the 'linear'method of the standard two conditions have to be simulated to obtain theresults, one to calculate the U-value of the frame, and a second simulation tocalculate the linear thermal transmittance V, of each glazing condition.

A typical calculation to this standard is set out in Annex B of this publication

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ISO DIS 15099 Thermal performance of windows, doors and shading devices -Detailed calculations.

The BRE Conventions includes the 'linear' method of prEN ISO 10077-2 andISO DIS 15099, which includes the 'linear' method but allows for thealternative 'edge' method It is also suitable for structural sealant glazingsystems (SSG) and condensation prediction assessments Both methodsproduce essentially the same whole window U-values

Atypical calculation to this standard is set out in Annex B of this publication.

Software

Software, such as Bisco, FRAME, WINDOW 5 and THERM 5 for the simulations isinexpensive, with WINDOW 5 and THERM 5 being free issue, includingcomprehensive instruction manuals, from the Lawrence Berkeley NationalLaboratory htt.//windows IbI ciov

2.5. Comparison of whole window U-value calculation results by 'linear' and'edge' methods

In calculations based on example D 4 of prEN ISO 10077-2 set out in Annex B,it will be seen that there is no variation in the calculated U-value, ie2 1 7W/m2K Any variations in calculated values will therefore be minimal andwell within experimental uncertainty

Further evaluation confirms this result An exercise assessing forty-four windowcombinations, with aluminium, aluminium wood clad, PVC-U, steel and woodframed windows with three to five glazing options, by both 'linear' and'edge' methods, the vanations between the methods are insignificantA comparison of calculation example results to the three standards is given inAnnex B of this publication

2.6. Presentation of results

The presentation of results for test or calculation is specified in theappropriate standard and include typical, cross section frame details withprinciple dimensions, material thermal conductances and boundaryconditions Results should be rounded to one decimal place When the valueis less than 1.0, it should be rounded to two decimal places. In accordancewith normal conventions 2 24 becomes 2 2 and 2 25 becomes 2 3 (see alsoBRE Conventions for U-value calculations, BR 443 Section 6)

2.7. Simulators and self-certification

In the future it may become necessary to consult an Independent Authoritywho may carry out the assessment or approval of simulators

In this assessment the simulator will be expected to carry out the ten examplecalculations, D 1 to D 10 given in Annex D of prEN ISO 10077-2 Thermalperformance of windows, doors and shutters - Calculation of thermaltransmittance - Part 2 Numerical method for frames, and submit results forapproval.

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3. Curtain wall/coupled windows

The Building Regulations Approved Document L2 does not make a positivestatement concerning composite/coupled windows and curtain wallingother than to refer to Trade documentation, produced by the CAB andthe CWCT. In view of this it is highly recommended that the buildingdesigner consults the curtain walling designers/suppliers at an eaily stageof a project in order that a proper and constructive assessment of thebuilding performance can be made.

Curtain Wall being a cladding fenestration system, larger than acomposite window, usually provides an enclosure to the building facade.These systems are generally constructed of vertical and honzontalmembers, assembled and connected together on site known as 'stick'systems or assembled and glazed off site, in panel form, known as'unitized' systems. Assemblies pass in front of and are attached to thesupporting structure of the building (floors etc) providing a gnd for the Figure 1. Typical 50 x 100 mm

glazing and infill panels to create a continuous facade to selected areas curtain wall mullion

of the building The basic requirement in AD L2 for such facades is 2 2W/m2K for glazed or vision areas, with 0.35 W/m2K for spandrel areasconsidered as walls. Any internal walls or structure behind the panel areawill improve this U-value.

Considering the Elemental Method of calculation, the weighted averageof the installation (large composite/coupled windows and curtain walling)can be considered as a "glazed area" with a U-value of 2 2 W/m2K.Calculations are to be carried out in similar manners to the CAB document'Setting the Standard No 4', or the detailed calculations descnbed in section2.

The percentage of the curtain wall façade glazed vision areas (AD L2,Table 2) should relate to the entire external wall not only to the areas ofcurtain wall facade Buildings with large areas of glazed curtain wallshould be designed by the 'Whole Building' method or the CarbonEmissions method, It is recommended that the performance of these largeareas be assessed at the design and planning stage so that any necessaryadjustments may be made to the overall building performance concept.

An alternative approach is proposed in a quartet of CWCT publications,on the subject but generally these relate specifically to the 40% maximumallowable glazed vision area related to the curtain wall façade area. i.e. amodule with 40% vision area and 60% spandrel area with a weightedaverage U-value of 1 2 W/m2K for the whole vision and spandrel area,allowing for benefits from other building works. This U-value is notapplicable where the 40/60% proportion area arrangement differs In suchcases the area weighted average U-value has to be calculated

prEN 13947 - Thermal performance of curtain wall - Calculation for thermaltransmittance - Simplified method This has been published for publiccomment but cannot yet be considered for assessment of standard sizecurtain wall assemblies

4. Rooflights and overhead glazing Figure 2 Typical 50 x 100mmcurtain wall mullion

In accordance with document L any part of a roof or inclined glazinghaving a pitch greater than or equal to 70 can be considered as a wall.

The procedures for measunng and calculating the U-values of roofwindows and overhead glazing installations are based on assessing theproduct in the vertical plane. For sloped glazing an allowance is made inAD Li for dwellings, tables Al and A3 However for non-domestic buildings,AD 12, no adjustment has to be made. Therefore the compliance ofglazed roof windows, patent glazing and other forms of sloped glazing to

I0


AD Li and AD L2, should be based on products assessed in the verticalplane

Rooflights and overhead glazing are in a similar situation to curtain wallfacades, insomuch as the CEN standard relating to rooflights. prEN 12567-2(Thermal performance of windows and doors -Determination of thermaltransmittance by hot box method - Part 2 Roof windows and other projectingwindows), has been published for public comment but is not yet approved

The test specimen size is slightly larger than the vertical window size of 1 23 x1.48 m as the roof or projected window has to fit over, rather than into thetest ng aperture The window is tested in the vertical plane

Calculation of U-values for roof and overhead glazing by the "edgemethod" of ISO DIS 15099 provides suitable results for the overhanging glazingconditions which are not fully framed Figure 3 illustrates this and shows atypical unframed condition in the vertical position as required for test

glazing eaves purposes.condition

5. Structural Silicone Glazing (SSG)

Structural Silicone Glazing is not referred to in Approved Document L, butwhere windows and curtain wall are constructed in this manner it is to beexpected that they should conform to the requirements

6. Shop fronts and entrances

Windows displaying goods on sale within the building are not required tomeet the standards given in AD L2, there are no limits on area In Scotland(part J) there is no requirement at access level. We advise that fenestrationmore than 3m above such access level should comply. Such provisions couldalso be acceptable in England and Wales

Doors requiring unusual strength, power operation and/or heavy usage, etc:These specifications take priority when assessing conformity with AD L2 Thismay mean poorer U-values, but where practical this should be offset bybetter performance elsewhere in the building

7. Conservatories and Atria

Figure 4. Typical

Structural Silicone Assemblies of vertical and overhead glazing do not need to comply ifa wallglazing condition and door(s) separate them from the host building Such a wall and door(s)

must be in accordance with the requirements of AD Li and AD L2 and anyheating should be separately controlled Otherwise the conservatones andatria should be in accordance with the regulations.

8. Comparison of thermal assessments calculation methods

All methods and standards referred to in this publication strive to produce anoverall window or façade area U-value but differ in their approach and forthis reason it is not possible to directly compare the separate elements of, forexample frame and glazing edge denved by different methods, see alsoAnnex B3. Whichever method is used it should be noted that obtaining bettervalues than those from physical test should not be possible.

In the case of condensation prediction U-frame values derived by BS ENlSO10077-1 or prEN ISO 10077-2 where the appropriate glazing is replaced byan insulating panel it will be found that much lower frame U-values resultthan are found in the as built construction The CAB publications - Setting theStandard No. 3 and 4 provide useful information on assessing the surfacecondensation nsk of aluminum fenestration framing

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Annex ABasic procedure of BS EN 1077-1 for simplified U - value calculation foraluminium thermal barrier windows.

Calculate the frame U-value

Determine framing dimensions, sight line and developed internaland external frame surface, the thermal barrier separation gapand the barrier width

Determine Uc, from Table 1

Select U for the appropriate thermal barrier gap and calculate

the thermal resistance of frame R, where - Rr =——O.I7

Calculate the frame U-value Uf, where - Uiie=RSIAfi/AdI+Rf +RA1,/A11

Select linear thermal transmittance W of glazing from Table 3

Determine centre pane U-value of glazing from Table 4

Calculate the whole window U-value Uk,, where -

— Agi,1g X Ugic,ng + Aframe x Ufiame +1g(

Xylwindow —

AJ1101

Example calculation (for window 1230 mm x 1480 mm)

Window dimensions and data see Fig A 2

Frame sight line 110mm

Internal developed frame surface 143 mm

External developed frame surface 138 mm

Thermal barrier gap 15 mm (from Table 1 U10 = 3 01and R1 = 0 162 (from calculation)

Total thermal barner width 8 mm (7.3% of sight line)

U-value centre pane glazing 1 30 W/m2K - from Table 4(or manufacturer's data)

Linear thermal transmittance of glazing 0 08 W/mK - from Table 3.

UframeU1 Th.13x110/143+0.162+0.04x110/138 =3403W/m2K

Figure A 1Dimenons required for simplifiedcalculations

Figure A2Dimensions of example frame

1.27 x 1.3 + 0.55 x 3.40 + 4.54 x 0.08UwindowU =

1.82=2.14W/m2K

NOTE: The calculations in Annex A and B use the aluminum frame example D 1 fromAnnex D of prEN ISO 10077-2 The Tables reproduced in this Annex are reconstructedfrom BSEN ISO 10077-1

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Thermal barrier gap width 1Jft

40 4080 3.55120 320150 30120.0 2 75240 262280 256320 2.52360 250

Table 1 Values of Ur0 taken fromFigure D 4 of BS EN ISO 10077-1


Ur U-value of frame

U U-value of whole window

A0 Area of glazing (vision area)

U0 U-value of glazing from Table 4

R30 l3m2KiW from Table Al of BS EN ISO 10077-2

A Internal frame dimension (sight line)

Ad Internal developed frame surface (vertical + honzontal)

Rf Thermal resistance of frame

R 004 m2KJWfromTabIeAl of prEN 1SO10077-2

A External frame dimension (sight line)

Ade External developed frame surface (vertical + honzontal)

Uro Value for developing frame U-value given in Table 1

L0 Length of glazing edge (penmeter of vision area)

X0 Linear thermattransmittance of glazing edge given in Table 3

Table 2 Formula definitions from BS EN ISO 10077-1(3 Definitions, symbols andunits)

Values of linear transmittance For glazing edge

Xg W/m2K Xg W/m2KFrame material DG clear glass DG low-E glassWood and PVC-U frames 004 006Thermal bamer metal 006 008Non thermal barner metal 000 0 02

Table 3 Values of linear thermal transmittance for glazing edgefrom 85 EN ISO 10077-1 (Table E 1)

Table of centre pane U-values related to Normal and corrected emissivity

GINormalemissivity

Corrected Glass and

emissivityAir fillcavity

Argon fillcavity

Onepanecoatedglass

En - 04 Ec —041=4-12-4 24 21

4 -16-4 2 2 204 -20-4 2 2 2 0

One panecoatedglass

En- 02 Ec—022-12-4 9 18

4-16-4 18 164 -20-4 1 1 8

One panecoatedglass

En-Ui Ec—Oli4 -12-4 8 1 —

14_1 4_

4-16-4 ———

164 -20-4 1 6

One panecoatedglass

En - 0 05 Ec — 0064-12-4 17 134 -16-4 1 5 1 24 -20-4 1 5 1 2

Table 4 Glazing U-values in W/rr?K extract from BS EN ISO 10077-1 (Table F 2)

Note (i) 6mm glass has a similar performance to 4mm Consuft yourglazingsupplier for detailed figuresGlazing U-values calculated to BS EN 673 and WINDOW 4 7 usecoirected emissivify, which is the value normal!y quoted by a glasscompany(ii) Hard coat with emissivity of O.i5 in a 4-16-4 unit with Argon fill.U—I 5W/m2K(iii) Use of warm edge spacei will improve the unit edgeperformance

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Annex B

Basic procedure of prEN ISO 10077-2 Numerical U-valuecalculation by the "linear" method and the alternative "edge"method of ISO DIS 15099,using [81 THERM and WINDOW software

prEN ISO 10077-2, 'linear' method

WINDOW 4.1, see Fig B 1, is used for calculating centre pane U-values of glazing. THERM may be used for calculating the frameU-value and thermal conductance L2D

In WINDOW 4 1 set up or select the appropnate insulating glazingunit.

___________ - -

Ik.s.iJr'l

-r . - -- -

In THERM draw the framing cross section from imported dxfdrawing, Fig. A 2, in a series of polygons, i.e. breaking up hollowextrusions, assigning each polygon with the appropriate materialsfor framing, gasket thermal barner and frame cavities, etc

FigureB 1. View of WINDOW 41insulation glazing library (Typical)

Draw CEN insulation panel with = 0.035 W/mK and/or import glazing toproject 190 mm from the glazing gasket.

Apply boundary conditions to external, internal and adiabatic surface, assignU-value tags to the frame for the U-value and the whole inside surface for L2D,and run simulations, see Fig. B 2 and B 3

Using spread sheet calculate whole window U-value from the formula: -

y,=Ly,2D -U1Xi Ug Xlg

u,,= Ag XUg +A1xU1

ISO DIS 15099, alternative 'edge' method.

The procedure requires only one sequence of frame drawings for simulationin THERM 5 but with a 63 5 mm glazing edge projecting from the gasketBoundary conditions are assigned as for the 'linear' method

Apply U-value tag to the interior frame and gasket surface, with a separatetag to the glazing edge

Run the simulation and export results to WINDOW to calculate the wholewindow U-value, which is based on the formula: -

u = XU5 +A xU- +AeXUe

B 1. Example calculation "linear" method (prEN ISO 10077 -2)

The example calculation reproduces Figure D lexample from the standard;see Fig A 1, for an aluminium thermal barner frame, illustrated by dxf drawingand THERM screen views

Figure B 2 View of THERMsimulation screen for'linear' frame U-valuecalculationCalculated thermalconductivityL20andthermal transmittanceL2D = 0.556 W/mK


Simulation 1, see Fig B 2, for frame U-value, draw the cross section for frameU-value with insulation panel with 7 = 0.035 W/mK

Assign surface resistance boundary conditions, CEN Exterior (250 W/m2K) tothe whole exterior surface, CEN Intenor (7 691 W/m2K) to vertical interiorsurfaces and CEN Reduced radiation/convection (5.0 W/m2K) to honzontaland immediately adjacent vertical surfaces.

Assign a U-value tag to the whole intenor surface of frame and insulation panel.

Run simulation to produce U-value of 1.855 W/m2K and multiply by 0.3 m, theprojected interior surface dimension to produce L = 0.556 W/mK

Calculate the panel U-value from the method explained in prEN ISO 10077-2In this example U, = 1 .03W/m2K

Take the panel U-value (U = 1 03 W/m2K) multiply by the projected width ofthe panel. 0 19m, to produce L = 0 196W/mK

Subtract L from L20 to produce 0 360W/mK.

Divide this value by 0 11 m, the projected width of the frame, to obtain theframe characteristic U-value

U = 3 27W/m2K

Simulation 2, see Fig B 3, for frame thermal conductance LZD of 4-20-4insulated glazing, with centre pane U-value 1.3 W/m2K

Modify previous simulation, erasing the insulation panel and importing theappropriate glazing from WINDOW 4 1 projecting 190 mm from gasket andspacer bar etc

Assign U-value tag to the whole interior surface of frame and glazing

Run simulation to produce U-value of 2 39 W/m2K and multiply by 0.3 m, theinterior surface dimension to produce L2D = 0 717 W/mK

Using a spreadsheet, calculate linear thermal transmittance of glazing edge:-

Y'g =0.717—3.27x0.11—1.3x0.19 = 0.110

Calculate the whole window U-value for an Li window 1 23 m high x 1 48 mwide with 1 3 W/m2K centre pane glazing' -

u = 1.27 xl.3+0.55 x3.27+4.54x0.110 = 2.17W/m2KW1.82

Whole window U-value = 2.2 W/m2K

Figure 83 View of THERM In practice the simulator would set up simulation 2 as the first step, thenmodify this by simply changing the conductivity of the glazing unit matenals

glazing to generate the first simulationL2D = 0.717'Pg =0 110

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B2. Example calculation "edge" method (ISO DIS 15099)

The example calculation reproduces Figure D 1 example from prEN ISO10077-2 for an aluminium thermal barner frame, illustrated in Figure B 4, togive a direct companson with the 'linear' method

Draw the frame cross section in THERM assigning frame matenal, otherconstruction materials and frame cavities to polygons and importappropriate glazing, with 63.5 mm edge projecting from gasket

Assign surface resistance boundary conditions, CEN Exterior (25 0 W/m2K) tothe whole exterior surface, CEN Intenor (7 691 W/m2K) to vertical interiorsurfaces and CEN Reduced radiation/convection (50 W/m2K) to horizontaland immediately adjacent vertical surfaces

Assign frame U-value tag to intenor frame and gasket surface and edgeU-value tag to intenor glazing surface and run simulation producing frameU-value of 3.91 7W/m2K and glazing edge U-value of 1 826 W/m2K, see Fig B 4.

Export THERM simulation result to WINDOW 4.1, to calculate whole windowU-value, Solar heat gain coefficient (SHGC) and Visible light transition (VT),which for a window 1230 wide x 1480 high produce -

Whole window U-value = 2,17 W/m2K and SHGC = 042 and VT = 0 53

B 3. Comparison of whole window U-value calculation results by 'linear' andedge' methods

From the three example calculations (based on example D 1 of prEN 10077-2) there is little variation in the calculated whole window U-values, see Table5 below

Further evaluation confirms this result from an evaluation exercise assessingforty-four window combinations, with aluminium, aluminium wood clad,PVC-U, steel and wood frame windows with three to five glazing options byboth 'linear' and 'edge' methods the vanations between the methods arerelatively insignificant.

Figure B 4 View of THERMsimulation screen for 'edge'method calculationU-frame = 3.917 W/m2KU-edge = 1.826 W/m2K

Standard BS EN 15010077-1 prEN iSO 10077-2 iso 015 15099

This document Page 12 Page 15 Para Bi Page 16 Para B2

Frame U-value 3 40 W/m2K 3 27 W/m2K 3 92 W/m2K

Whole windowU-value 2 14 W/m2K 2 17 W/m2K 2 17 W/m2K

Table 5 Example calculation results

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Annex C Associated standards and publications.

prEN 14351 Window and external pedestnan doors Product standard

prEN 13830 Product Standard for Curtain Walling

BS EN ISO 8990 Thermal Insulation — Determination of steady-state thermal transmissionproperties - Calibrated and guarded hotbox

BS EN 673 Glass in building — Determination of thermal transmittance (U-value) —Calculation method

BS EN 12567-1 Thermal performance of windows, doors and shutters - Determination ofthermal transmittance by hotbox method Part 1 Windows and doors

prEN 12412 - 2 Windows, doors and shutters- Determination of thermal transmittanceby hot box method Part 2, Frames

BS EN ISO 10077 - 1 Thermal performance of window, door and shutters - Calculationfor thermal transmittance Part I Simplified method

prEN ISO 10077 - 2 Thermal performance of windows, doors and shutters - Calculationfor thermal transmittance Part 2 Numencal method for frames

BS EN ISO 10211 - I Thermal bdges in building construction Heat flows and surfacetemperatures Part I. General calculation methods

BS EN ISO 6946 Building components and building elements Thermal resistance andthermal transmittance

ISO DIS 15099 Thermal performance of windows, doors and shading devices - Detailedcalculations

BS EN 12524 Building matenals and products - Hydrothermal properties - Tabulatedvalues

prEN 12567-2 Thermal performance of windows, doors and shutters - Determination ofthermal transmittance by hotbox method Part 2 Roof windows and other projectingwindows

prEN 13947 Thermal performance of curtain wall - Calculation for thermaltransmittance - Simplified method

BS EN ISO 13789 Thermal Performance of Buildings — Transmission Heat Loss Coefficient —Calculation Method

Council for Aluminium in Building 'Setting the Standard No 3 - Guide for assessment ofthe thermal performance of aluminium windows'

Council for Aluminium in Building 'Setting the Standard No 4 - Guide for assessment ofthe thermal performance of curtain wall'

CWCT Thermal Documents

Glass & Glazing Federation data sheet 2 2

BRE BR 443 Conventions for U-value calculations

DfEE, Guidelines for environmental design in schools, Building Bulletin 87, TSO, 1997

NHS Estates Achieving energy efficiency in new hospitals, TSO, 1994

Acknowledgements

The CAB would like to thank Dr Brian Anderson of the BRE and Dr Richard Hams ofSandberg for their valued contribution to this document The guidance on doors anddisplay windows has been developed in consultation with ODPM

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