The Frustrating Realities of Cold Climate Design:

1
The Frustrating Realities of Cold Climate Design

• Piercing the Skin
• Ins-U-lation versus Ins-O-lation
• Terri Meyer Boake
• University of Waterloo

Richmond City Hall, Richmond, B.C.
2
From First Principles

• First Ins-U-late then Ins-O-late
• Walls are thick and have a very high (mandated)
  thermal resistance
• Windows are thin elements whose thermal
  resistance remains a fraction of the wall
• Energy efficient window (design) is costly
• If windows are improperly specified, designed and
  constructed, energy losses are significant

3
The Model National Energy Code of Canada for
Houses 1997

• MNECH is a stand-alone document
• Addresses environmental protection and resource
  conservation only
• Suggests but does not enforce its rules/ideas
• Relies heavily on CSA Standard A440.2 Energy
  Performance of Windows and Other Fenestration
  Systems

4
MNECH Minimum Insulating Values

• Minimum RSI and R values for up to 5000C Degree
  Days (9000F) for above ground opaque elements
  are
• Attic-type roofs 5.6 m2xoC/W or a U-value of
  0.178 W/m2xoC
• 31.8 hxft2xoF/Btu 0.031 Btu/hxft2xoF
• All other roofs 4.3 m2xoC/W or a U-value of
  0.233 W/m2xoC
• 24.4 hxft2xoF/Btu 0.041 Btu/hxft2xoF
• Walls 2.9 m2xoC/W or a U-value of 0.345
  W/m2xoC
• 16.5 hxft2xoF/Btu 0.061 Btu/hxft2xoF
• Floors 4.5 m2xoC/W or a U-value of 0.217
  W/m2xoC
• 25.5 hxft2xoF/Btu 0.039 Btu/hxft2xoF
• Windows must only have a maximum U value of 2.60
  W/m2xoC (0.457 Btu/hxft2xoF). This will permit
  7.5 times as much heat transmission per hour
  compared to wall elements!
• Skylights must only have a maximum U value of 3.4
  W/m2xoC (0.599 Btu/hxft2xoF). This will permit
  14.5 to 19 times as much heat loss as the roofs
  they displace!

5
The Energy Rating (ER) for Windows

• The MNECH uses a new Energy Rating system to
  compare the overall performance of windows
• Previous standards relied only on separate U, SC,
  SHGC and air leakage values
• The ER combines
• Solar heat gain coefficient (SHGC)
• Overall heat transmission coefficient (U-value)
• Air leakage

6
Solar Heat Gain Coefficient SHGC

• Fraction of solar radiation incident on a window
  that appears as solar heat gain in the building
• Dimensionless, expressed as a decimal, always
  less than 1.0
• Center of glass of a clear single glazed window
  has a SHGC of 0.87
• Shading Coefficient (SC) is no longer used
• SC is the SHGC of window relative to the SHGC a
  single glazed clear window under the same
  conditions
• The SC times 0.87 provides a good approximation
  of the SHGC for most glazing systems if that is
  the only data provided

7
ER total performance

• The ER gives a single number to indicate the
  combined response to solar heat gain, conductive
  heat loss and air leakage in typical Canadian
  (cold) climate conditions
• Based on total performance, including glazing,
  spacers, glass and frame (many other U-values do
  not include other than center of glass values)
• Developed in CSA Standard A440.2 Energy
  Performance of Windows and Other Fenestration

8
Understanding the ER

• Only applicable when comparing windows and
  sliding glass doors in houses under specified
  heating conditions
• Assumes vertical installation
• Based upon AVERAGE conditions for solar radiation
  on windows facing 4 cardinal directions (i.e.)
  north, south, east and west
• Minimum requirements are based on climate and
  fuel type

9
ER positive or negative

• The ER may be positive or negative
• A positive ER means that the window gains more
  heat than it loses in the heating season
• A negative ER means that the window has an
  overall loss of heat during the heating season
• Most windows have negative ER values

10
ER Requirements for Houses
CSA A440.2 sets out the following ER requirements
for energy efficient windows in houses in the
calculated Energy Level Regions across Canada.
To merely meet CSA 440.2 a window need only meet
the EL1 level.
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ER Limitations

• Good for builders who in a subdivision will have
  the same number of windows facing all directions
• Not good for passive solar buildings that do not
  have evenly oriented windows N,S,E,W (CSA A440.2
  does include a calculation method to
  differentiate based on solar orientation or on
  cooling rather than heating design)
• Not the correct number to be plugged into
  simulation programs (most want U and SHGC)
• Values are developed by window manufacturers
• Not presently many available for comparisons
  except through www.enermodal.com, CATALOGUE
  program

12
Ontario Building Code Requirements for Window
Design
The OBC seems to assume that most builders will
use a minimum amount of glazing and that the
thermal integrity of such buildings will not
likely be compromised by excessive amounts of
glazing.
13
Minimum OBC Energy Requirements

• For windows that meet the previous criteria, the
  only energy requirements are
• (a)Air infiltration shall not exceed 0.775 dm3/s
  for each meter (0.5 cfm for each foot) of sash
  crack when tested at a pressure differential of
  75 Pa (0.011 psi))
• (b)All glazing that separates heated space from
  unheated space shall have a thermal resistance of
  not less than RSI0.30 m2oC/W (1.70 ft2xhxoF/Btu)
• The OBC requirements are slightly more stringent
  for residences with electric heating and copy the
  MNECH in their requirement of an ER of not less
  than 13 for operable windows and sliding glass
  doors, and an ER of 0 for fixed glazing.
• Additionally, the Code requires that the maximum
  amount of glazing (including windows, skylights
  and doors) can not exceed 20 of the floor area
  of the story being served by the glazing nor
  exceed 40 of the total area of the walls of that
  story.

14
OBC and Passive Solar Design

• The Code does allow for passive, aka Thermal
  Design
• This design is considered alternative to normal
  thermal insulation requirements and allows for
  window areas that exceed the 20/40 rule
• Increases in window area allowed is proportional
  to the increase in its thermal resistance value

i.e. if the Code permitted the building of 10m2
of window with a resistance value of 0.30 m2oC/W
(1.70 ft2xhxoF/Btu), if you selected a window
with an insulation value of 0.40 m2oC/W (2.27
ft2xhxoF/Btu), your ratio would be 0.30/0.40
0.75. You could actually have 13.3 m2 of windows
as when 13.3 is multiplied by 0.75, it translates
to the value of 10m2. Therefore, the higher the
thermal value for the window, the proportionally
higher amount of glazing is permitted resulting
in theoretically identical heat losses.
15
OBC and South Facing Windows

• Glazing areas can also be increased where the
  design is using passive solar gain principles on
  south facing orientations. In such cases the
  glazing area may be calculated at 50 of what is
  actually being constructed, provided that
• (a) the area contains clear glass or has a
  shading coefficient of more than 0.70 (the MNECH
  uses a value of 0.61), and
• (b) faces a direction within 45o of due South,
  and
• (c) is unshaded in the Winter (calculating
  angles based on Dec. 21 at noon), and
• (d) the building is designed with a system that
  is capable of distributing the solar gain from
  such glazed areas throughout the building.
• Where houses are designed to be cooled, window
  areas cannot be increased, as outlined above,
  except where the glazing is shaded in the summer
  with exterior devices. The shading is to be
  calculated using noon sun angles for June 21.

16
CMHC Comparison of Typical Window Thermal
Efficiencies
17
Unrealistic Expectations?

• From the previous charts very few windows would
  meet the MNECH criteria of ER -13 for Ontario and
  Quebec
• No windows would meet ER criteria for Manitoba,
  Yukon and NWT (severe climates)
• Most call for low-e, argon fill and triple
  glazing, which is beyond most housing budgets
• All but one would exceed the minimum thermal
  rating of the OBC of 0.30 m2oC/W (1.70
  ft2xhxoF/Btu)
• If codes were to mandate the new ER requirements,
  we would save energy, but capital building costs
  would skyrocket -- what would window
  manufacturers do??

18
Finding the Right Information

• A very tough job!!
• Varies from Canada (SI) to US (Imperial)
• Must rely on window manufacturers for accurate
  information!
• Manufacturers info usually not there at all or
  inconsistently presented
• Use great terms like super energy efficient
  without data backup

19
Sample Manufacturers Test Data
Loewen Windows Test Data
In this instance the only windows which meet the
-13ER are triple glazed wood frame units. All
others fail. All pass the thermal minimum rating
of 0.30 RSI.
20
Understanding the Data

• The values achieved through Loewen testing are
  comparable to the CMHC ideals in some cases but
  not all
• Most of the windows exceed the 0.30 RSI OBC
  minimum so could be used to proportionately
  increase fenestration areas
• None have a SHGC that would permit increases
  based on passive solar south facing glazing
• Low-E coatings increase the RSI and decrease the
  SHGC indicating suitability in energy efficient
  thermal design but not passive solar design

21
Low-E wins over Solar Gain

• In the Loewen advertising, windows with low-e
  coatings are pushed for their insulating
  qualities and ability to reduce solar gain
• Anti-passive solar which would use differentiated
  glazing on the south side to promote solar gain
  and shading devices for cooling

22
Insulation is better than Insolation???

• Again the advertising clearly shows that
  insulating glass and protection from the suns
  free heat are the most important attributes of
  windows.

23
Balancing Ins-U-lation vs. Ins-O-lation

• The codes (and manufacturers) clearly favor
  insulation over insolation
• It is possible, however more complicated to
  design fenestration for passive solar design in
  order to achieve reasonable heating values
  through window design
• It requires separate design tactics for south
  facing windows, different windows than are used
  on the E,W,N elevations, and additional
  calculations
• Simpler to use computer simulation programs to be
  able to differentiate the elevations and design
  for solar passive

24
Balancing Insulation
Insolation Daylighting

• 1. INSULATION Calculate heat loss. Uses R/U
  values and infiltration
• 2. INSOLATION Calculate heat gain. Uses SHGC,
  precise orientation, shading, thermal mass.
• 3. DAYLIGHTING Calculate how windows reduce
  electrical/lighting energy requirements.

25
Selling Energy Efficient Window Design

• Most clients and builders regard Code
  requirements as maximum rather than minimum
  standards
• Up to Architects and educators to approach window
  design in more environmentally responsible manner
• Need to simulate performance to show long term
  energy savings over short term capital costs
• i.e. Frame Plus, Energy-10, Solar 5 or Hot2000
  can be used to run more accurate comprehensive
  simulations for different window solutions
• However, simulations are time consuming and can
  be expensive to run -- most clients not willing

26
In Conclusion

• Windows and skylights that simply meet the
  minimum energy standards as set by the Code
  account for 7.5 to 19 times the heat losses based
  on the same area as a wall or roof. These losses
  can be drastically reduced if energy efficient
  strategies are responsibly applied. To properly
  design energy efficient openings for cold climate
  applications is not an easy task. It is,
  however, essential. The Building Code provides
  us with minimum standards. The National Model
  Energy Code asks that we aim higher. Good
  conscience says that this is not enough. Tools
  exist which help to make this frustrating,
  complex task a little bit easier. It is up to us
  to use them.