Review of Energy Rating for Windows
Research Project Summary
Brittany Hanam MASc EIT
Al Jaugelis BSc Arch
March 2013
Agenda
Background to the study
Energy Rating
Study methodology and energy findings
Thermal comfort issues
Conclusions
Background
Energy Rating (ER) originally developed in 1989
Some early ER-qualified products were associated with
discomfort and dissatisfaction in some markets
Concerns about validity of ER, given changes to house
archetypes, technology advances, and original
assumptions
Oct. 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 ER
BC Homeowner Protection Office (HPO) assembled
coalition of funding partners from across Canada
Funding partners
Included all parties with keen interest in the subject
All points of view represented
Cooperative effort promoted mutual understanding, with
possibilties for future collaboration
Outcome of study
ER is generally valid for ranking the relative energy
efficiency of windows and sliding glass doors, with some
exceptions
ER is better at ranking energy performance of windows
than U-value alone
Comfort issues related to unwanted solar heat gain and
high U-values are better understood
Clarified limitations of ER and recommended guidelines
for its use
Final 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
What is the Energy Rating?
What is the Energy Rating?
Canadian measure of window/glass
door energy performance defined in
CSA A440.2, Fenestration Energy
Performance
Single number rating
Evaluates both solar gains
(SHGC) and losses due to
transmittance
(U-value) and air leakage
For low-rise residential
applications vertical
applications only,
no skylights
The ER concept: include the sun
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 calculation
ER equation in CSA A440.2:
Simplified Equation:
Solar Heat Gain Conduction Air Leakage
ENERGY STAR qualification requirements
Voluntary Program
Two Compliance Paths: ER or U-Value
Windows
Zone
A
B
C
D
Heating
Degree-Day
Range
<= 3500
> 3500 to <= 5500
> 5500 to <= 8000
> 8000
Compliance Paths
Energy Rating (ER)
Minimum ER
Max. U-Value
0.35 Btu/h-ft²-F
(2.00 W/m²•K)
21
25
29
34
or
or
or
or
or
U-Value
Max. U-Value
Btu/h-ft²-F
(W/m²-K )
Minimum
ER
0.32 (1.80)
0.28 (1.60)
0.25 (1.40)
0.21 (1.20)
13
17
21
25
Study methodology and energy findings
Study used whole building energy simulations
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 zones
Various window types - investigate different
combinations of U-values and SHGCs
23 different windows in the study, 5 representative
Actual study looked at 23 different windows
Will 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
23 different windows in the study, 5 representative
Actual study looked at 23 different windows
Will 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
Annual Energy Consumption, kWhe Vancouver
Relation between heating, cooling, and total energy
Cooling energy low relative to heating and total energy
Heating Energy
Cooling Energy
Total Energy
25,000
20,000
15,000
10,000
5,000
U-0.50
SHGC-0.64
U-0.35
SHGC-0.5
U-0.16
SHGC-0.5
Window
U-0.35
SHGC-0.2
U-0.16
SHGC-0.2
Annual Energy Consumption, kWhe Vancouver
Relation between heating, cooling, and total energy
Lower U-value & higher SHGC generally result in lower energy
use
Heating Energy
Cooling Energy
Total Energy
25,000
20,000
15,000
10,000
5,000
U-0.50
SHGC-0.64
U-0.35
SHGC-0.5
Third
U-0.16
SHGC-0.5
Window
Lowest
U-0.35
SHGC-0.2
U-0.16
SHGC-0.2
Fourth
Second
Energy simulation findings: ranking
Generally higher ER results in lower heating energy
consumption, with some exceptions
Increasing ER
Energy simulation findings: energy consumption
Good correlation between energy consumption and ER
Annual Heating Energy
Consumption, kWhe/year
30000
Yellowknife
Toronto
Winnipeg
Vancouver
Montreal
Linear (Yellowknife)
25000
20000
R² = 0.9721
15000
R² = 0.9864
10000
R² = 0.9694
R² = 0.9854
R² = 0.9714
5000
0
0
10
50
40
30
20
Energy Rating (ER) for Simualted Windows
60
70
Energy simulation findings: window orientation
Orientation affects potential solar heat gain
Energy simulation findings: window shading
Window shading affects solar heat gain
Summary of energy simulation findings
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 consumption
Factors affecting solar heat gain
Window to wall ratio
Orientation
Exterior shading
Thermal Comfort
Windows and thermal comfort
How to “measure” thermal comfort?
ASHRAE Standard 55: Thermal Comfort Conditions for
Human Occupancy
6 primary factors affect thermal comfort:
Air temperature
Radiant surface temperature
Humidity
Air speed
Metabolic rate
Clothing insulation
Windows and thermal comfort
Main factors that
affect thermal
comfort:
Air temperature
Radiant surface
temperature
Study explored:
Operative
temperature
Window surface
temperature
Operative temperature
Operative Temperature: Balance of surface temperature
and air temperature
ASHRAE acceptable range of operative temperature based
on research studies
Thermal comfort: methodology
Hourly energy simulations – extract window surface
temperature, air temperature, operative temperature
Defined comfort parameters:
Operative temperature 19°C to 25°C
Surface temperature 15°C to 30°C
Count number of hours outside this range
Thermal comfort: methodology
Operative temperature example: Vancouver bedroom
Similar trend for other locations
5 representative windows from 23 in the study
Actual study looked at 23 different windows
Will 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
Thermal comfort: operative temperature
Operative Temperature Hours < 19°C
Operative Temperature Hours > 25°C
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Low SHGC Windows
Yellowknife
Winnipeg
Montreal
Toronto
Kelowna
High SHGC Windows
Vancouver
Total Hours
“Warm” hours correlate with high solar gain products,
across all climate zones
Thermal comfort: operative temperature
High U-value Windows
Yellowknife
Winnipeg
Montreal
Toronto
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Kelowna
Operative Temperature Hours < 19°C
Operative Temperature Hours > 25°C
Vancouver
Total Hours
“Cold” hours more significant in colder climates
Cold surface temperatures related to high U-value
Thermal comfort: surface temperature
“Cold” hours correlate with high U-value
Compare with number of operative “warm” hours
Window Surface Temperature Hours <15°C
Window Surface Temperature Hours >30°C
25,000
U-0.5
U-0.35
U-0.16
15,000
10,000
5,000
Yellowknife
Winnipeg
Montreal
Toronto
Kelowna
0
Vancouver
Total Hours
20,000
Thermal comfort summary
Overheating a function of high
SHGC, not high ER
Overheating discomfort related
to project-specific conditions
Orientation
Exterior shading
Window to Wall Ratio
Low SHGC reduces overheating
when no external summer
shading present
Low U-value lowers surface
temperature, leading to greater
comfort year round, esp. winter
Study conclusions
Study conclusions
Higher ER generally results in lower heating energy
consumption in typical Canadian houses
ER is generally better at ranking energy performance of
windows than U-value alone
ER does not correctly rank windows:
In the far north due to lower solar gain in the winter months
Primarily oriented in one direction
With high window-wall ratios
With exterior winter shading
Overheating is a function of solar heat gain, not ER, and
comfort can be managed with summer shading or A/C
ER is not suitable for MURBs with high window to wall
ratios (>40%) due to overheating and cooling energy use
ER Study Recommendations
Keep both U-value and ER paths in codes and ENERGY
STAR program
Need to educate consumers on how to select the best
windows for their particular situation, considering all
factors that are important to them
Atypical homes and site-optimized energy performance
design should use both U-value and SHGC characteristics
for selecting windows
Questions?
bhanam@rdhbe.com