Research Project Summary

Review of Energy Rating for Windows

Brittany Hanam MASc EIT

Al Jaugelis BSc Arch

March 2013

Agenda

Background to the studyEnergy RatingStudy methodology and energy findingsThermal comfort issuesConclusions

Energy Rating (ER) originally developed in 1989Some early ER-qualified products were associated with discomfort and dissatisfaction in some marketsConcerns about validity of ER, given changes to house archetypes, technology advances, and original assumptionsOct. 2009 CSA A440.2 Task Group recommended new research to validate ER parameters, but effort stalled due to lack of funding at NRCan In 2011 RDH proposed a study to investigate ERBC Homeowner Protection Office (HPO) assembled coalition of funding partners from across Canada

Background

Included all parties with keen interest in the subjectAll points of view representedCooperative effort promoted mutual understanding, with possibilties for future collaboration

Funding partners

ER is generally valid for ranking the relative energy efficiency of windows and sliding glass doors, with some exceptionsER is better at ranking energy performance of windows than U-value aloneComfort issues related to unwanted solar heat gain and high U-values are better understoodClarified limitations of ER and recommended guidelines for its useFinal Report released http://www.hpo.bc.ca/whats-new

Bonus: resulted in follow-on study of Passive House windows, North American vs. European simulation methods, currently underway

Outcome of study

What is the Energy Rating?

Canadian measure of window/glass door energy performance defined in CSA A440.2, Fenestration Energy Performance

Single number ratingEvaluates both solar gains (SHGC) and losses due to transmittance (U-value) and air leakageFor low-rise residential applications vertical applications only, no skylights

What is the Energy Rating?

To rate winter window performance don’t just measure heat loss through windows . . .

Conduction through glass and frame (U-value)Air leakage

. . . ADD heat gained from the sun

The ER concept: include the sun

ER equation in CSA A440.2:

Simplified Equation:

The ER calculation

Solar Heat Gain

ConductionAir Leakage

Voluntary ProgramTwo Compliance Paths: ER or U-Value

ENERGY STAR qualification requirements

Windows

ZoneHeating

Degree-DayRange

Compliance PathsEnergy Rating (ER) or U-Value

Minimum ERMax. U-Value

0.35 Btu/h-ft²-F(2.00 W/m²•K)

Max. U-ValueBtu/h-ft²-F(W/m²-K )

MinimumER

A <= 3500 21 or 0.32 (1.80) 13B > 3500 to <= 5500 25 or 0.28 (1.60) 17C > 5500 to <= 8000 29 or 0.25 (1.40) 21D > 8000 34 or 0.21 (1.20) 25

Study methodology and energy findings

Hourly energy simulations performed using the program DesignBuilder (EnergyPlus engine)Several archetype houses – sizes, enclosures, etc.Cities from across Canada selected to represent various climate zonesVarious window types - investigate different combinations of U-values and SHGCs

Study used whole building energy simulations

Representative Window

U-Value[Btu/hr-ft2-

F]

SHGC ER

ASHRAE 90.1 Compliant, Aluminum Frame

0.50 0.64 14

High U-Value / High SHGC

0.35 0.50 26

Low U-Value / High SHGC

0.16 0.50 49

High U-Value / Low SHGC 0.35 0.20 8

Low U-Value / Low SHGC 0.16 0.20 32

23 different windows in the study, 5 representative

Actual study looked at 23 different windowsWill show results for 5:

Representative Window

U-Value[Btu/hr-ft2-

F]

SHGC ER

ASHRAE 90.1 Compliant, Aluminum Frame

0.50 0.64 14

High U-Value / High SHGC

0.35 0.50 26

Low U-Value / High SHGC

0.16 0.50 49

High U-Value / Low SHGC 0.35 0.20 8

Low U-Value / Low SHGC 0.16 0.20 32

Actual study looked at 23 different windowsWill show results for 5:

23 different windows in the study, 5 representative

Cooling energy low relative to heating and total energy

Relation between heating, cooling, and total energy

-

5,000

10,000

15,000

20,000

25,000

U-0.50SHGC-0.64

U-0.35SHGC-0.5

U-0.16SHGC-0.5

U-0.35SHGC-0.2

U-0.16SHGC-0.2

Annu

al E

nerg

y Co

nsum

ption

, kW

h e

Window

Heating Energy Cooling Energy Total EnergyVancouver

-

5,000

10,000

15,000

20,000

25,000

U-0.50SHGC-0.64

U-0.35SHGC-0.5

U-0.16SHGC-0.5

U-0.35SHGC-0.2

U-0.16SHGC-0.2

Annu

al E

nerg

y Co

nsum

ption

, kW

h e

Window

Heating Energy Cooling Energy Total Energy

Lower U-value & higher SHGC generally result in lower energy use

Relation between heating, cooling, and total energy

LowestThird Second

Vancouver

Fourth

Generally higher ER results in lower heating energy consumption, with some exceptions

Energy simulation findings: ranking

Increasing ER

Good correlation between energy consumption and ER

Energy simulation findings: energy consumption

R² = 0.9721

R² = 0.9864

R² = 0.9694R² = 0.9854R² = 0.9714

0

5000

10000

15000

20000

25000

30000

0 10 20 30 40 50 60 70

Annu

al H

eatin

g En

ergy

Co

nsum

ption

, kW

h e/y

ear

Energy Rating (ER) for Simualted Windows

Yellowknife Winnipeg MontrealToronto Vancouver Linear (Yellowknife)

Orientation affects potential solar heat gain

Energy simulation findings: window orientation

Window shading affects solar heat gain

Energy simulation findings: window shading

In a typical house, low U-value & high SHGC result in lowest energy consumption in houses

Cooling energy use is low relative to heating and total energy

High ER generally good indication of lower heating and total energy consumptionFactors affecting solar heat gain

Window to wall ratioOrientationExterior shading

Summary of energy simulation findings

Thermal Comfort

How to “measure” thermal comfort?ASHRAE Standard 55: Thermal Comfort Conditions for Human Occupancy6 primary factors affect thermal comfort:

Air temperatureRadiant surface temperatureHumidityAir speedMetabolic rateClothing insulation

Windows and thermal comfort

Main factors that affect thermal comfort:

Air temperatureRadiant surface temperature

Study explored:Operative temperatureWindow surface temperature

Windows and thermal comfort

Operative Temperature: Balance of surface temperature and air temperatureASHRAE acceptable range of operative temperature based on research studies

Operative temperature

Hourly energy simulations – extract window surface temperature, air temperature, operative temperatureDefined comfort parameters:

Operative temperature 19°C to 25°CSurface temperature 15°C to 30°C

Count number of hours outside this range

Thermal comfort: methodology

Operative temperature example: Vancouver bedroomSimilar trend for other locations

Thermal comfort: methodology

Representative Window

U-Value[Btu/hr-ft2-

F]

SHGC ER

ASHRAE 90.1 Compliant, Aluminum Frame

0.50 0.64 14

High U-Value / High SHGC

0.35 0.50 26

Low U-Value / High SHGC

0.16 0.50 49

High U-Value / Low SHGC 0.35 0.20 8

Low U-Value / Low SHGC 0.16 0.20 32

5 representative windows from 23 in the study

Actual study looked at 23 different windowsWill show results for 5:

0500

100015002000250030003500400045005000

Vanc

ouve

r

Kelo

wna

Toro

nto

Mon

trea

l

Win

nipe

g

Yello

wkn

ife

Tota

l Hou

rs

Operative Temperature Hours < 19°COperative Temperature Hours > 25°C

“Warm” hours correlate with high solar gain products, across all climate zones

Thermal comfort: operative temperature

High SHGC Windows

Low SHGC Windows

0500

100015002000250030003500400045005000

Vanc

ouve

r

Kelo

wna

Toro

nto

Mon

trea

l

Win

nipe

g

Yello

wkn

ife

Tota

l Hou

rs

Operative Temperature Hours < 19°COperative Temperature Hours > 25°C

“Cold” hours more significant in colder climatesCold surface temperatures related to high U-value

Thermal comfort: operative temperature

High U-value Windows

0

5,000

10,000

15,000

20,000

25,000

Vanc

ouve

r

Kelo

wna

Toro

nto

Mon

trea

l

Win

nipe

g

Yello

wkn

ife

Tota

l Hou

rs

Window Surface Temperature Hours < 15°CWindow Surface Temperature Hours > 30°C

“Cold” hours correlate with high U-valueCompare with number of operative “warm” hours

Thermal comfort: surface temperature

U-0.16

U-0.5 U-0.35

Overheating a function of high SHGC, not high EROverheating discomfort related to project-specific conditions

OrientationExterior shadingWindow to Wall Ratio

Low SHGC reduces overheating when no external summer shading presentLow U-value lowers surface temperature, leading to greater comfort year round, esp. winter

Thermal comfort summary

Study conclusions

Higher ER generally results in lower heating energy consumption in typical Canadian housesER is generally better at ranking energy performance of windows than U-value aloneER does not correctly rank windows:

In the far north due to lower solar gain in the winter monthsPrimarily oriented in one directionWith high window-wall ratiosWith exterior winter shading

Overheating is a function of solar heat gain, not ER, and comfort can be managed with summer shading or A/CER is not suitable for MURBs with high window to wall ratios (>40%) due to overheating and cooling energy use

Study conclusions

Keep both U-value and ER paths in codes and ENERGY STAR programNeed to educate consumers on how to select the best windows for their particular situation, considering all factors that are important to themAtypical homes and site-optimized energy performance design should use both U-value and SHGC characteristics for selecting windows

ER Study Recommendations

Questions?

bhanam@rdhbe.com