Presentation on theme: "Review of Energy Rating for Windows"— Presentation transcript:
1Review of Energy Rating for Windows Research Project SummaryBrittany Hanam MASc EITAl Jaugelis BSc ArchMarch 2013
2Agenda Background to the study Energy Rating Study methodology and energy findingsThermal comfort issuesConclusions
3Background Energy Rating (ER) originally developed in 1989 Some 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 CSA A440.2 Task Group recommended new research to validate ER parameters, but effort stalled due to lack of funding at NRCanIn 2011 RDH proposed a study to investigate ERBC Homeowner Protection Office (HPO) assembled coalition of funding partners from across Canadagiven the many changes in house archetypes and advances in glass coating and window framing technologyin the decades since 1989 when the ER was first developed.
4Funding partnersIncluded all parties with keen interest in the subjectAll points of view representedCooperative effort promoted mutual understanding, with possibilties for future collaborationQuebec fenestration association: Association des industries de produits de vitrerie et de fenestration
5Outcome of studyER 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 releasedBonus: resulted in follow-on study of Passive House windows, North American vs. European simulation methods, currently underway
7What is the Energy Rating? Canadian measure of window/glass door energy performance defined in CSA A440.2, Fenestration Energy PerformanceSingle 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
8The 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 sunIn 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.
9The ER calculation ER equation in CSA A440.2: Simplified Equation: Solar Heat GainConductionAir LeakageNote heating only ER – does not take into account cooling, thermal comfort(ERC and ERS exist but not widely used)
10ENERGY STAR qualification requirements Voluntary ProgramTwo Compliance Paths: ER or U-ValueWindowsZoneHeating Degree-Day RangeCompliance PathsEnergy Rating (ER)orU-ValueMinimum ER Max. U-Value0.35 Btu/h-ft²-F(2.00 W/m²•K)Max. U-Value Btu/h-ft²-F(W/m²-K )Minimum ERA<= 3500210.32 (1.80)13B> 3500 to <= 5500250.28 (1.60)17C> 5500 to <= 8000290.25 (1.40)D> 8000340.21 (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.
12Study 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 zonesVarious window types - investigate different combinations of U-values and SHGCsShow some important factors that impact window selection from energy standpoint
1323 different windows in the study, 5 representative Actual study looked at 23 different windowsWill show results for 5:Representative WindowU-Value[Btu/hr-ft2-F]SHGCERASHRAE 90.1 Compliant, Aluminum Frame0.500.6414High U-Value / High SHGC0.3526Low U-Value / High SHGC0.1649High U-Value / Low SHGC0.208Low U-Value / Low SHGC32
1423 different windows in the study, 5 representative Actual study looked at 23 different windowsWill show results for 5:Representative WindowU-Value[Btu/hr-ft2-F]SHGCERASHRAE 90.1 Compliant, Aluminum Frame0.500.6414High U-Value / High SHGC0.3526Low U-Value / High SHGC0.1649High U-Value / Low SHGC0.208Low U-Value / Low SHGC32
15Relation between heating, cooling, and total energy Cooling energy low relative to heating and total energyVancouverPlot shows Vancouver but trends for other locations were similarCooling energy much lower than heating energy – high SHGC provides overall lower energy savings
16Relation between heating, cooling, and total energy Lower U-value & higher SHGC generally result in lower energy useVancouverLowest energy use – from low U-value, high SHG window (triple pane)Second has same U-value, but lower SHG (also triple pane)ThirdLowestFourthSecond
17Energy simulation findings: ranking Generally higher ER results in lower heating energy consumption, with some exceptionsUsing 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
18Energy simulation findings: energy consumption Good correlation between energy consumption and ER
19Energy simulation findings: window orientation Orientation affects potential solar heat gainWhile primarily south facing windows used least energy, increasing ER correlates well with reducing heating energy use.
20Energy simulation findings: window shading Window shading affects solar heat gainHigher WINTER window shading from roof overhangs or operable window blinds results in lower solar heat gain, higher energy use.
21Summary of energy simulation findings In a typical house, low U-value & high SHGC result in lowest energy consumption in housesCooling energy use is low relative to heating and total energyHigh ER generally good indication of lower heating and total energy consumptionFactors affecting solar heat gainWindow to wall ratioOrientationExterior shadingBased on several house archetypes. Trends same for all.
22Thermal ComfortThermal 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.
23Windows and 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
24Windows and thermal comfort Main factors that affect thermal comfort:Air temperatureRadiant surface temperatureStudy explored:Operative temperatureWindow surface temperatureAir 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).
25Operative temperature Operative Temperature: Balance of surface temperature and air temperatureASHRAE acceptable range of operative temperature based on research studiesThe 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)
26Thermal comfort: methodology 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°CCount number of hours outside this range
27Thermal comfort: methodology Operative temperature example: Vancouver bedroomSimilar trend for other locationsMonthly Operative Temperature Distribution, Bedroom, Vancouver
285 representative windows from 23 in the study Actual study looked at 23 different windowsWill show results for 5:Representative WindowU-Value[Btu/hr-ft2-F]SHGCERASHRAE 90.1 Compliant, Aluminum Frame0.500.6414High U-Value / High SHGC0.3526Low U-Value / High SHGC0.1649High U-Value / Low SHGC0.208Low U-Value / Low SHGC32
29Thermal comfort: operative temperature “Warm” hours correlate with high solar gain products, across all climate zonesHigh SHGC WindowsOperative 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 hoursLow SHGC Windows
30Thermal comfort: operative temperature “Cold” hours more significant in colder climatesCold surface temperatures related to high U-valueOperative 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 hoursHigh U-value Windows
31Thermal comfort: surface temperature “Cold” hours correlate with high U-valueCompare with number of operative “warm” hoursU-0.5U-0.35U-0.16Window 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:
32Thermal comfort summary Overheating a function of high SHGC, not high EROverheating discomfort related to project-specific conditionsOrientationExterior shadingWindow to Wall RatioLow SHGC reduces overheating when no external summer shading presentLow U-value lowers surface temperature, leading to greater comfort year round, esp. winterNorth not likely to have overheating issues
34Study conclusionsHigher 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 shadingOverheating 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
35ER Study Recommendations 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“. . . 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 isappropriate and when it is not appropriate. Likewise, if the U‐value alone is used to select energy efficient windows, explanatorytext regarding the potential energy savings of a high or a moderate SHGC should also be provided.” from Exec summary.