This document discusses laboratory tests performed to quantify the effectiveness of various options for improving the thermal performance of traditional windows. Options tested included heavy curtains, traditional and insulated shutters, modern and Victorian blinds, and secondary glazing. The tests measured the reduction in heat loss through the window glazing with each option compared to single glazing alone. Results showed that secondary glazing was the most effective at reducing heat loss, followed by insulated shutters and modern roller blinds with low-emissivity film.

1. The thermal performance ofThe thermal performance of
traditional windows andtraditional windows and
practical measures to reducepractical measures to reduce
heat loss and air leakageheat loss and air leakage
Paul BakerPaul Baker
Glasgow Caledonian UniversityGlasgow Caledonian University
Centre for Research on Indoor Climate & HealthCentre for Research on Indoor Climate & Health
Paul.Baker@gcal.ac.ukPaul.Baker@gcal.ac.uk
11

2. 22
IntroductionIntroduction
27% of the UK27% of the UK’’s carbon dioxide emissions can be attributed to thes carbon dioxide emissions can be attributed to the
energy used in peopleenergy used in people’’s homes.s homes.
A third of the COA third of the CO22 emissions from the average home could be savedemissions from the average home could be saved
by adopting simple energy saving measures.by adopting simple energy saving measures.
Achieving further reductions in carbon emissions from UKAchieving further reductions in carbon emissions from UK
households to meet the UK Governmenthouseholds to meet the UK Government’’s 60% target is a majors 60% target is a major
challengechallenge

3. Scottish distribution of dwellingsScottish distribution of dwellings
33
Figure 1: Age of Dwelling (Scottish House Condition Survey
Key Findings for 2005/6)
17%
13%
25% 25%
20%
0%
5%
10%
15%
20%
25%
30%
Pre-1919 1919-1944 1945-1964 1965-1982 Post 1982

4. National Home Energy Ratings of Scottish housing stockNational Home Energy Ratings of Scottish housing stock
by age as a percentage of the total housing stock (SHCS 2005/06)by age as a percentage of the total housing stock (SHCS 2005/06)
Poor % Moderate % Good%
Pre-1919 2.4% 10.6% 3.9%
1919-1944 0.5% 7.5% 4.9%
1945-1964 0.7% 13.0% 11.2%
1965-1982 0.5% 12.6% 12.1%
Post 1982 0.0% 5.1% 15.2%
TOTAL 4.1% 48.6% 47.2%
44
53% of dwellings in Scotland may be considered to have only53% of dwellings in Scotland may be considered to have only
moderate or poor energy efficiencymoderate or poor energy efficiency
PrePre--1919 are the largest proportion with poor rating1919 are the largest proportion with poor rating

5. 55
Traditional Buildings:Traditional Buildings:
Refurbish or Replace?Refurbish or Replace?
Traditional buildings are viewed as energy inefficient.Traditional buildings are viewed as energy inefficient.
TheThe operationaloperational carbon emissions of new buildings are lower thancarbon emissions of new buildings are lower than
traditional buildings.traditional buildings.
However, traditional buildings already embody carbon.However, traditional buildings already embody carbon.
Energy is required for demolition and disposal of waste, and toEnergy is required for demolition and disposal of waste, and to
produce and transport new building materials.produce and transport new building materials.
Existing building also have cultural and societal value.Existing building also have cultural and societal value.

6. The challengesThe challenges
Improve the housing stock in response to climate change andImprove the housing stock in response to climate change and
reduce COreduce CO22 emissionsemissions
Improve comfort and lower energy bills for occupantsImprove comfort and lower energy bills for occupants
Maintain our architectural heritageMaintain our architectural heritage
The options for upgrading the thermal performance are particularThe options for upgrading the thermal performance are particularlyly
limited for prelimited for pre--1919 dwellings with solid wall constructions.1919 dwellings with solid wall constructions.
66

7. Traditional WindowsTraditional Windows
Traditional single glazed windowsTraditional single glazed windows -- easiest option for replacementeasiest option for replacement
with modern double glazing?with modern double glazing?
Traditional windows are often considered to be draughty, prone tTraditional windows are often considered to be draughty, prone too
condensation and hard to maintain.condensation and hard to maintain.
But, with good care and maintenance traditional windows will outBut, with good care and maintenance traditional windows will outlastlast
modern replacements and should be considered as a sustainablemodern replacements and should be considered as a sustainable
resource.resource.
However, the heat lost through a single glazed window is aboutHowever, the heat lost through a single glazed window is about
twice that through a double glazed window meeting the currenttwice that through a double glazed window meeting the current
Building Standards targets.Building Standards targets.
77

8. OptionsOptions
Secondary glazingSecondary glazing –– most effective option to preserve existingmost effective option to preserve existing
traditional windowstraditional windows
Little information on the performance of more traditional (andLittle information on the performance of more traditional (and
cheaper) methods of reducing heat loss, such as, draught proofincheaper) methods of reducing heat loss, such as, draught proofing,g,
shutters, blinds and curtains.shutters, blinds and curtains.
This paper quantifies the effectiveness of relatively simple meaThis paper quantifies the effectiveness of relatively simple measuressures
to improve the thermal performance of traditional windows byto improve the thermal performance of traditional windows by
DraughtDraught--proofingproofing
Blinds, curtains, & shuttersBlinds, curtains, & shutters
Secondary glazingSecondary glazing
Replacing single glazed panes with double glazingReplacing single glazed panes with double glazing
88

9. 99
Laboratory StudiesLaboratory Studies -- ObjectivesObjectives
Determine the benefits of various options on reduction of heat lDetermine the benefits of various options on reduction of heat lossoss
through glazing of a sash & case windows provided by Historicthrough glazing of a sash & case windows provided by Historic
Scotland (HS).Scotland (HS).
Measure the benefits of draughtMeasure the benefits of draught--proofing.proofing.

10. 1010
Historic Scotland Window 1.89m (h) x 1.06m (w)

11. 1111
Laboratory StudiesLaboratory Studies –– ThermalThermal
PerformancePerformance
Tests performed in environmental chamber usingTests performed in environmental chamber using in situin situ heat fluxheat flux
measurements on glazing.measurements on glazing.
Approach justified since NPL guarded hot box measurements on HSApproach justified since NPL guarded hot box measurements on HS
window indicate that 72% heat lost through glazing.window indicate that 72% heat lost through glazing.
The reduction in heat using the various option compared withThe reduction in heat using the various option compared with ‘‘basebase’’
measurement on single glazing only.measurement on single glazing only.
Surface temperature measurements also made to determine USurface temperature measurements also made to determine U--
values and assess impact on thermal comfort.values and assess impact on thermal comfort.

12. 1212
GCU Environmental ChamberGCU Environmental Chamber

13. 1313
Cold Room
2C
Warm Room
22C
Windows
mounted in
300mm thick
insulated panel
Environmental ChamberEnvironmental Chamber
window #1 window #2
insulated frame

14. 1414
Heat Flux MetersHeat Flux Meters
Sensor area
Guard area
Sensor area
Guard area

15. 1515
Test SequenceTest Sequence
0
5
10
15
20
25
21-May 22-May 23-May 24-May 25-May 26-May 27-May
Temperature[C]
0
10
20
30
40
50
60
70
80
HeatFlux[W/m2
]
Warm
Cold
Heat Flux
Set up test, e.g.
change option to
curtain
Allow conditions to stabilise Use data for analysis

16. 1616
Options testedOptions tested
Heavy curtains.Heavy curtains.
Timber shutters (salvaged traditional panelled shutters)Timber shutters (salvaged traditional panelled shutters)
Modified traditional shutters, with insulation inserted into panModified traditional shutters, with insulation inserted into panels andels and
covered with 6mm plywood. The insulated area of the shutters iscovered with 6mm plywood. The insulated area of the shutters is
55%.55%.
Modern roller blind.Modern roller blind.
Modern roller blind, covered with a low emissivity film.Modern roller blind, covered with a low emissivity film.
Victorian blind fitted to the top of the recess formed by the wiVictorian blind fitted to the top of the recess formed by the windowndow
case pulley stiles at the side of the upper sash.case pulley stiles at the side of the upper sash.
AA ““thermalthermal”” Duette honeycomb blind manufactured by HunterDuette honeycomb blind manufactured by Hunter
Douglas Europe b.v.Douglas Europe b.v.
Secondary glazing system with lowSecondary glazing system with low--e glazing.e glazing.
Window reWindow re--glazed with Slimlite lowglazed with Slimlite low--e double glazed panes,e double glazed panes,
manufactured and installed by Fountainbridge Windows Ltd.,manufactured and installed by Fountainbridge Windows Ltd.,
Edinburgh.Edinburgh.

17. 1717
Heavy Curtains Traditional ShuttersHeavy Curtains Traditional Shutters

18. 1818
Insulated Shutters with SpacethermInsulated Shutters with Spacetherm

19. 1919
Modern Roller BlindModern Roller Blind Blind with lowBlind with low--e foile foil
appliedapplied

20. 2020
Victorian Blind Honeycomb BlindVictorian Blind Honeycomb Blind
Metallised interior of
honeycomb

21. 2121
LowLow--e Secondary Glazinge Secondary Glazing

22. 2222
ResultsResults
The effect of the various options on the heat loss through the gThe effect of the various options on the heat loss through the glazinglazing
was estimated as follows:was estimated as follows:
The reduction in heat lossThe reduction in heat loss compared directly with the test oncompared directly with the test on
glazing only.glazing only.
A centre of pane UA centre of pane U--valuevalue, calculated from the average heat flux, calculated from the average heat flux
meter reading and surface temperature difference between the outmeter reading and surface temperature difference between the outerer
glazing surface and the inside (roomglazing surface and the inside (room--facing) surface of the curtain,facing) surface of the curtain,
shutter or blind with a correction for the standardised internalshutter or blind with a correction for the standardised internal andand
external surface resistances.external surface resistances.
A correction was also applied for the thermal resistance of heatA correction was also applied for the thermal resistance of heat fluxflux
meter.meter.
Uncertainty of UUncertainty of U--values is 0.3 W/mvalues is 0.3 W/m22
K.K.

23. 2323
TCold
TWarm
Surface glazing temperatures

24. 2424
TCold TWarm
Surface glazing temperatures
3
1025.617.0
1
−
×−+⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −
=
Q
TT
U
sesi

25. 2525
Reduction in heat lossReduction in heat loss
14%
28%
22%
36%
45%
51%
58%
62%
60%
63%
66%
75%
77%
55%
0% 20% 40% 60% 80%
Curtains
Victorian Blind
Modern RollerBlind
Duette honeycombblind
Modern RollerBlind + Foil
Shutters
Blind & Shutters
Blind,Shutters & Curtains
Insulated Shutters
SecondaryGlazing
SecondaryGlazing & Curtains
SecondaryGlazing & Shutters
SecondaryGlazing & Insulated Shutters
Double glazing

26. 2626
Effect of Closing Shutters
0
10
20
30
40
50
60
70
80
90
100
21-Apr 22-Apr 23-Apr 24-Apr 25-Apr 26-Apr 27-Apr 28-Apr
HeatFlux[W/m2
]
Glazing only
+ Shutters
Fitting Shutters

27. 2727
UU--ValuesValues
5.4
3.2
3.2
3.0
2.4
2.3
2.2
1.8
1.6
1.6
1.7
1.3
1.1
1.0
1.9
0.0 1.0 2.0 3.0 4.0 5.0 6.0
Glazing only
Curtains
Victorian Blind
Modern RollerBlind
Duette honeycombblind
Modern RollerBlind + Foil
Shutters
Blind & Shutters
Blind,Shutters & Curtains
Insulated Shutters
SecondaryGlazing
SecondaryGlazing & Curtains
SecondaryGlazing & Shutters
SecondaryGlazing & Insulated Shutters
Double glazing
U-value of Glazing + Option [W/m2K]

28. 2828
Airtightness MeasurementsAirtightness Measurements
The airThe air--tightness of the window was measured bytightness of the window was measured by
depressurisation with both test rooms at 22depressurisation with both test rooms at 22ooC.C.
Measurements were made:Measurements were made:
Before and after draughtBefore and after draught--proofing by Ventrollaproofing by Ventrolla
After installation of secondary glazing.After installation of secondary glazing.

29. Airtightness MeasurementsAirtightness Measurements
2929
WindowWindow
Pressure
Difference - ΔP
Flowmeter
Differential
Pressure
Gauge
Variable fan/fow control
Air Flow - Q

30. 3030
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35 40 45 50
PRESSURE DIFFERENCE DP [Pa]
AIRFLOW[cu.m/h]
HS WINDOW AS RECEIVED
HS WINDOW AFTER DRAUGHT-PROOFING
HS WINDOW DRAUGHT-PROOFED + 2ndry GLAZING

31. 3131
ResultsResults
Professional draught proofing reduces air leakage by 86%Professional draught proofing reduces air leakage by 86%
compared with the ascompared with the as--received conditionreceived condition
The addition of the secondary glazing system provides a furtherThe addition of the secondary glazing system provides a further
reduction in air leakagereduction in air leakage
A trickle vent with an area of 4000mmA trickle vent with an area of 4000mm22
(Section 3.14 SBS 2007) has(Section 3.14 SBS 2007) has
an air leakage about 5 x that of the draught proofed window.an air leakage about 5 x that of the draught proofed window.
Whole window UWhole window U--value measurements by NPL show no significantvalue measurements by NPL show no significant
difference before & after draught proofingdifference before & after draught proofing

32. 3232
In situIn situ measurements at Lauristonmeasurements at Lauriston
Place, EdinburghPlace, Edinburgh
Shutters & SecondaryShutters & Secondary
Glazing TestedGlazing Tested
Shutters similar performance toShutters similar performance to
laboratory testslaboratory tests
Secondary glazing resultSecondary glazing result
(2.3W/m(2.3W/m22
K) higher than theK) higher than the
environmental chamber result.environmental chamber result.

33. 3333
Effect of closing shuttersEffect of closing shutters
3RD FEBRUARY
0
10
20
30
40
50
60
70
00:00
01:00
02:00
03:00
04:00
05:00
06:00
07:00
08:00
09:00
10:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
19:00
20:00
21:00
22:00
23:00
HEATFLUX[W/m2
]
0
2
4
6
8
10
12
14
16
18
20
TEMPERATURE[C]
HEAT FLUX
ROOM TEMPERATURE
EXTERNAL TEMPERATURE
Shutters CLOSED
Shutters OPEN
Shutters CLOSED

34. 3434
ConclusionsConclusions
All measures have significant benefits.All measures have significant benefits.
Shutters are most effective of traditional methods particularlyShutters are most effective of traditional methods particularly withwith
addition of insulation.addition of insulation.
Improved blind designs also have potential to reduce heat lossImproved blind designs also have potential to reduce heat loss --
roller blind with lowroller blind with low--e foil facing glazing very effective (but note foil facing glazing very effective (but not
attractive?)attractive?)
High performance secondary glazing and replacement doubleHigh performance secondary glazing and replacement double
glazed panes offer improved thermal performance throughout theglazed panes offer improved thermal performance throughout the
day.day.
Careful installation of the secondary glazing also results in imCareful installation of the secondary glazing also results in improvedproved
airair--tightness.tightness.
All measures offer improved thermal comfort due to higher surfacAll measures offer improved thermal comfort due to higher surfacee
temperatures compared to single glazing alone.temperatures compared to single glazing alone.