T101 Thermal performance

Window energy rating

T101-2006

Energy rating schemes

NFRC

National Fenestration Rating Scheme, USA

BFRC

British Fenestration Rating Scheme

EWERS

European Window Energy Rating Scheme

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FENSA

FENestration Self Assessment

Approved by ODPM as complying with Part L1

Self certification by dealer/installer

Administered by the GGF

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FENSA

Self certification

Frame type

Thermal break

Low e-coatings

Gas filling

Part L1 U-values

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Part L2 2002

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Part L2 2002

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Part L2 2002

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NFRC

Operating for 15 years in the USA

Rating scheme showing;

U-value

Solar Heat Gain Coefficient

Air leakage

Factors combined differently for different climates

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NFRC

6 climatic regions cover USA

Heating climates

Cooling climates

Sunny climates

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NFRC

U-valueSHGC Light

transmittance

Airleakage

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BFRC

Independent UK body

Spun out of UK Government funded research

Partners were Trade Associations, Laboratories, Analysts and Universities

Establishing links in Europe

May feature in the next version of the Building Regulations

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BFRC rating

Takes account of;

U-value

Conduction, convection, radiation

SHGC

Solar Heat Gain Coefficient

Air leakage

Air leakage at 50Pa, L50

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Original BFRC label

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BFRC rating

DWERS

Domestic Window Energy Rating Scheme

Ratings in the range G - A

A is most energy efficient, DWER > 0

Today’s good windows normally fall in band C, -20 < DWER < -10

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DWER

DWER = 218.6 x Window Solar factor – - 68.5 x (Window U-value + Air infiltration factor)

Factors of 218.6 and 68.5 recognise the influence of Window Solar factor, U-value, and air leakage in the UK

Windows will perform differently in different UK climates but will always be ranked consistently

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BFRC rating

Separate values given for:

Window U-value, Uw

Window solar factor, gwindow

Window air infiltration factor, 0.0165L50

To allow for fuller consideration

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Light transmittance

A good DWER can be achieved by selecting right SHGC

This can be achieved by using a tinted glass

Heavily tinted glass will affect light levels in a building and may lead to an increased energy use for artificial lighting

The light transmittance value is given to allow specifiers to avoid this problem

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EWERS

European Window Energy Rating Scheme

Adopted in Denmark

Uses scale of A,B,C,D,E

Similar to rating schemes for domestic appliances

May be taken up in UK with BFRC as the operating agent

Will use a common label but each state will set its own classification on the basis of climate and window styles!

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EWERS labelling

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Linking rating to regions

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BFRC rating label