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 given the many changes in house archetypes and advances in glass coating and window framing technology in the decades since 1989 when the ER was first developed.

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 Quebec fenestration association: Association des industries de produits de vitrerie et de fenestration

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 In this presentation keep in mind that products can achieve a high ER with or without high solar heat gain, though the highest ERs are achieved with both low U-value and high solar heat gain.

The ER calculation ER equation in CSA A440.2: Simplified Equation: Solar Heat Gain Conduction Air Leakage Note heating only ER – does not take into account cooling, thermal comfort (ERC and ERS exist but not widely used)

ENERGY STAR qualification requirements Voluntary Program Two Compliance Paths: ER or U-Value Windows Zone Heating Degree-Day Range Compliance Paths Energy Rating (ER) or U-Value Minimum ER Max. U-Value 0.35 Btu/h-ft²-F (2.00 W/m²•K) Max. U-Value Btu/h-ft²-F (W/m²-K ) Minimum ER A <= 3500 21 0.32 (1.80) 13 B > 3500 to <= 5500 25 0.28 (1.60) 17 C > 5500 to <= 8000 29 0.25 (1.40) D > 8000 34 0.21 (1.20) NECB and NBCC Part 9.36 energy requirements also have separate qualification paths, one based on U-value, the other on ER. Both paths are considered to be equivalent from a an overall energy efficiency point of view. Why do we need two paths? Will become clearer.

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 Show some important factors that impact window selection from energy standpoint

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 26 Low U-Value / High SHGC 0.16 49 High U-Value / Low SHGC 0.20 8 Low U-Value / Low SHGC 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 26 Low U-Value / High SHGC 0.16 49 High U-Value / Low SHGC 0.20 8 Low U-Value / Low SHGC 32

Relation between heating, cooling, and total energy Cooling energy low relative to heating and total energy Vancouver Plot shows Vancouver but trends for other locations were similar Cooling energy much lower than heating energy – high SHGC provides overall lower energy savings

Relation between heating, cooling, and total energy Lower U-value & higher SHGC generally result in lower energy use Vancouver Lowest energy use – from low U-value, high SHG window (triple pane) Second has same U-value, but lower SHG (also triple pane) Third Lowest Fourth Second

Energy simulation findings: ranking Generally higher ER results in lower heating energy consumption, with some exceptions Using all 23 windows in this series of graphs. Exceptions related to lower SHG in Northern locations . . . And low solar gain high ER products. Increasing ER

Energy simulation findings: energy consumption Good correlation between energy consumption and ER

Energy simulation findings: window orientation Orientation affects potential solar heat gain While primarily south facing windows used least energy, increasing ER correlates well with reducing heating energy use.

Energy simulation findings: window shading Window shading affects solar heat gain Higher WINTER window shading from roof overhangs or operable window blinds results in lower solar heat gain, higher energy use.

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 Based on several house archetypes. Trends same for all.

Thermal Comfort Thermal comfort was studied as comfort concerns were important to those who questioned the utility of the ER. Overheating discomfort is associated with high solar gain products in some parts of the country, especially in homes with high window-to-wall ratios, windows facing primarily south or west, and in high solar gain climate zones.

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 Air temperature and radiant surface temperature the comfort factors we sense the most. Study focused on operative temperature (combines mean radiant temperature MRT and air temperature), and window surface temperature (related to MRT).

Operative temperature Operative Temperature: Balance of surface temperature and air temperature ASHRAE acceptable range of operative temperature based on research studies The uniform temperature of an imaginary black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment. Simplified example: If you are standing in a box, and the surfaces of the box (walls) are all 10C, and the air temperature is 20C, you might feel a temperature of about 15C. (not that simple)

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 Monthly Operative Temperature Distribution, Bedroom, Vancouver

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 26 Low U-Value / High SHGC 0.16 49 High U-Value / Low SHGC 0.20 8 Low U-Value / Low SHGC 32

Thermal comfort: operative temperature “Warm” hours correlate with high solar gain products, across all climate zones High SHGC Windows Operative temperature: mean of [mean air temperature] and [mean surface temperature]. [verify] General comfort, measured in the center of the room. Most operative discomfort is associated with overheating, and overheating potential is greatest with high solar gain windows. Cold operative temperature discomfort becomes an issue with higher U-value products in Montreal, Winnipeg, Yellowknife. But it is absent when you use low U-value products. Winter – ‘too cold’ hours doesn’t make much difference esp. in Vancouver. Summer – high SHGC windows result in much higher discomfort hours Low SHGC Windows

Thermal comfort: operative temperature “Cold” hours more significant in colder climates Cold surface temperatures related to high U-value Operative temperature: mean of [mean air temperature] and [mean surface temperature]. [verify] General comfort, measured in the center of the room. Most operative discomfort is associated with overheating, and overheating potential is greatest with high solar gain windows. Cold operative temperature discomfort becomes an issue with higher U-value products in Montreal, Winnipeg, Yellowknife. But it is absent when you use low U-value products. Winter – ‘too cold’ hours doesn’t make much difference esp. in Vancouver. Summer – high SHGC windows result in much higher discomfort hours High U-value Windows

Thermal comfort: surface temperature “Cold” hours correlate with high U-value Compare with number of operative “warm” hours U-0.5 U-0.35 U-0.16 Window surface temperature is a surrogate for discomfort arising from radiant asymmetry: windows feeling colder than adjacent walls. The sensation will be strongest when you are near a window, less so in the center of a room. Window surface temperature doesn’t cause significant overheating discomfort. It is noticed more in the winter, and results in far more discomfort hours than Operative temperature overheating discomfort. Looking at cold temperature hours, the high U-value products are least comfortable. Lower U-values always lead to more winter comfort. Compare the relative scales of operative vs. surface temperature comfort:

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 North not likely to have overheating issues

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 “. . . for houses that are non‐typical, have more site‐specific design or energy efficient design, it would be best to select windows based on its U‐value and SHGC rather than only the ER. If the ER is incorporated into standards then it should be accompanied by explanatory text regarding when it is appropriate and when it is not appropriate. Likewise, if the U‐value alone is used to select energy efficient windows, explanatory text regarding the potential energy savings of a high or a moderate SHGC should also be provided.” from Exec summary.

Questions? bhanam@rdhbe.com