research project summary review of energy rating for windows brittany hanam masc eit al jaugelis bsc...
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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
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