Balancing Energy Consumption and Thermal Comfort Energy Ratings for Windows

!   Brittany Hanam M.A.Sc., P.Eng.

!   Graham Finch M.A.Sc., P.Eng.

!   Susan Hayes P.Eng.

March 2013

Agenda

!   Background on Energy Ratings for Windows !   Energy Efficiency

!   Thermal Comfort

!   Conclusions

!  Windows account for significant portion of energy consumption in buildings – “weakest link”

!  Windows impact heating and cooling energy

!   Can have conflicting priorities !  Cooling vs. Heating energy consumption

!   Lower energy consumption versus preventing overheating

The Issues

Window to Wall Ratio Impacts

Value of High Performance Windows

ASHRAE 90.1-2007 Maximum 40% Glazing Area

Non-Compliant

Compliant

1. Allows for Higher Window-Wall Ratios

Improve Enclosure R-value

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

!  Single number rating

!  Evaluates both solar gains (SHGC) and losses due to thermal transmittance (U-value) and air leakage

!  For low-rise residential applications, vertical applications only (no skylights)

What is the Energy Rating?

!   Canadian Energy Rating (ER) originally developed in 1989 !   Concerns raised about validity of ER, given changes to

house archetypes, technology advances, and original assumptions !  Also concerns regarding overheating in some markets

!   Research study was undertaken (2011 – 2012) to investigate the ER !  Should it continue to be used as-is?

!  Should it be modified?

!  Should it be abandoned?

Background

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

!   Highest ER products have a low U-value and a high SHGC

The ER Concept: Include the Sun

!   ER equation in CSA A440.2:

!   Simplified Equation:

The Canadian ER Calculation

Solar Heat Gain Conduction Air Leakage

!   Voluntary Program !   Two Compliance Paths: ER or U-Value

ENERGY STAR Canada Qualification Requirements

Windows  

Zone  Hea-ng  

Degree-­‐Day  Range  

Compliance  Paths  Energy  Ra-ng  (ER)   or   U-­‐Value  

Minimum  ER  Max.  U-­‐Value    0.35  Btu/h-­‐F²-­‐F  (2.00  W/m²•K)  

Max.  U-­‐Value  Btu/h-­‐F²-­‐F  (W/m²-­‐K  )  

Minimum  ER  

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

!   Includes U-Value OR ER path

2012 National Building Code of Canada

Zone 4 Zone 5 Zone 6 Zone 7a Zone 7b Zone 8

HDD <3000 3000 to 3999

4000 to 4999

5000 to 5999

6000 to 6999

≥7000

Max U-Value, Btu/h-ft2-F (W/m2-K)

0.32 (1.8)

0.32 (1.8)

0.28 (1.6)

0.28 (1.6)

0.25 (1.4)

0.25 (1.4)

Minimum ER 21 21 25 25 29 29

Zone A <3500 Zone B <5500 Zone C <8000

Additional Zone D >8000

!   Similar to ENERGY STAR Canada:

!   None, but new ENERGY STAR qualification criteria include Solar Heat Gain Coefficients

Energy Ratings in the US

!   ISO 18292: Energy performance of fenestration systems for residential buildings

!   United Kingdom has an Energy Rating similar to the Canadian ER !   Translated into letter ratings, A to G

!   Germany has an Energy Rating following ISO 18292

!   Australia and New Zealand have energy rating systems called the Window Energy Rating Scheme (WERS, and in New Zealand NZ-WERS) !  Determined differently from the Canadian ER, using energy

simulations

Energy Ratings Around the World

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 zones

!   Various window types - investigate different combinations of U-values and SHGCs

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

!   Study looked at 23 different windows !   For example,

Typical Windows

 -­‐

 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  Ene

rgy  Co

nsum

ption,  kWh e

Window

Heating  Energy Cooling  Energy Total  Energy

!   Lower U-value & higher SHGC generally result in lower energy use !  Cooling energy low relative to heating and total energy

Energy Simulation Results – Total Energy

Lowest Third Second

Vanc

ouve

r

Fourth

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

Heating Energy versus ER

Increasing ER

!   Good correlation between energy consumption and ER !  Dashed lines indicate typical range of ENRGY STAR windows

Heating Energy versus ER

R²  =  0.9721R²  =  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  Heatin

g  En

ergy  

Consum

ption,  kWh e/year

Energy  Rating  (ER)  for  Simualted  Windows

Yellowknife Winnipeg MontrealToronto Vancouver Linear  (Yellowknife)

!   Correlation between U-Value and ER not as good !   Impact of SHGC on energy consumption is visible

Heating Energy versus U-Value

R²  =  0.73

R²  =  0.56

R²  =  0.47R²  =  0.55R²  =  0.47

0

5000

10000

15000

20000

25000

30000

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Annu

al  Heatin

g  En

ergy  

Consum

ption,  kWh e/year

U-­‐Value  of  Simulated  Windows,  Btu/hr-­‐ft2-­‐F

Yellowknife Winnipeg MontrealToronto Vancouver Linear  (Yellowknife)

Total Energy Consumption vs. ER

R²  =  0.89R²  =  0.95

R²  =  0.97R²  =  0.93

R²  =  0.932000022000240002600028000300003200034000360003800040000

0 10 20 30 40 50 60 70

Total  A

nnua

lEne

rgy  Co

nsum

ption,  

kWh e/year

Energy  Rating  (ER)  for  Simualted  Windows

Yellowknife Winnipeg MontrealToronto Vancouver Linear  (Yellowknife)

!   Cooling energy is very low compared to heating in Canadian climates, even in locations with warmest summers

Total Annual Energy Consumption

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Vancouver Kelowna Toronto Montreal Winnipeg Yellowknife

Annu

al  Ene

rgy  

Consum

ption,  kWh e/year Lighting,  Plug  Loads,  DHW Cooling Heating

!   Correlation for north- and south-facing windows not as good as for windows distributed equally

Limitations: Window Orientation

R²  =  0.98R²  =  0.95

R²  =  0.92

 -­‐

 2,000

 4,000

 6,000

 8,000

 10,000

 12,000

 14,000

 16,000

0 10 20 30 40 50 60 70Annu

al  Heatin

g  En

ergy  Con

sumption,  

kWh e/year

Energy  Rating  (ER)  for  Simulated  Windows

Toronto  -­‐  Equal Toronto  -­‐  North Toronto  -­‐  South

!   Correlation better with minimal or no shading than with significant winter shading

Limitations: Window Shading

R²  =  0.99R²  =  0.94

 -­‐

 2,000

 4,000

 6,000

 8,000

 10,000

 12,000

 14,000

 16,000

0 10 20 30 40 50 60 70

Annu

al  Heatin

g  En

ergy  

Consum

ption,  kWh e/year

Energy  Rating  (ER)  for  Simulated  Windows

Typical  Roof  Overhang All  Windows  have  1.5m  (4.9ft)  Overhang

!   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

!   Location (far north)

Summary of energy simulation findings

Thermal Comfort

!   How to “measure” thermal comfort? !   ASHRAE Standard 55: Thermal Comfort Conditions for

Human Occupancy !   6 Primary factors that affect thermal comfort:

!  Air temperature

!  Radiant Surface Temperature

!  Humidity

!  Air Speed

!  Metabolic Rate

!  Clothing Insulation

Window Selection for Thermal Comfort

!   Operative Temperature: Balance of surface temperature and air temperature

!   ASHRAE acceptable range of operative temperature based on research studies

Window Selection for Thermal Comfort

!   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

Window Selection for Thermal Comfort

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 windows !  Will show results for 5:

0500100015002000250030003500400045005000

Vancou

ver

Kelowna

Toronto

Mon

treal

Winnipe

g

Yellowknife

Total  H

ours

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

!   “Warm” hours more significant !   SHGC important for overheating

Operative Temperature: Too Cold and Too Warm

High SHGC Windows

Low SHGC Windows

0

5,000

10,000

15,000

20,000

25,000

Van

couv

er

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 more significant !   U-value important for surface temperature

Surface Temperature: Too Cold and Too Warm

U-0.16

U-0.5 U-0.35

!   Percentage of hours in a year where the operative temperatures are higher than 25°C

Percentage of Overheating Hours

0%

2%

4%

6%

8%

10%

12%

14%

0 10 20 30 40 50 60

Percen

t  of  Y

ear  O

utside

 of  C

omfort  

Range

ER

Operative  Temperature  >25°C

Vancouver

Kelowna

Toronto

Montreal

Winnipeg

Yellowknife

!   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, particularly in winter

Thermal comfort summary

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 may 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 to 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

Study conclusions

!   Keep both U-value and ER paths in codes and ENERGY STAR program

!   Need to educate consumers, designers and builders on how to select the best windows for their project-specific conditions

!   Atypical homes and site-optimized energy performance design should use both U-value and SHGC characteristics for selecting windows

ER Study Recommendations

!   Final report is available online: http://www.hpo.bc.ca/whats-new

!   Bonus: Research resulted in a follow-up study of Passive House windows and North American vs. European rating systems, currently underway !  NFRC and European window simulation rating systems result

in different U-values and SHGCs

!  Report coming soon

Final Report and Next Steps

Questions?

bhanam@rdhbe.com