THE IMPLICATION OF ENERGY EFFICIENT BUILDING ENVELOPE DETAILS FOR ICE AND SNOW FORMATION PATTERNS ON BUILDINGS

Transcription

1 THE IMPLICATION OF ENERGY EFFICIENT BUILDING ENVELOPE DETAILS FOR ICE AND SNOW FORMATION PATTERNS ON BUILDINGS Neil Norris, Dave André and Peter Adams, Morrison Hershfield Limited, and Mike Carter and Roman Stangl, Northern Microclimate Inc.

2 Presenters Peter Adams, P.Eng Principal Senior Building Envelope Engineer Morrison Hershfield Michael Carter, C.E.T. President Microclimate Consultant Northern Microclimate Inc. Graduate Mechanical Engineer Senior Technical Advisor for MH Over 22 years of Building Science Experience Architectural Technologist Senior Technical Advisor for NMI Over 20 years of Microclimate & Building Science Experience 2

3 Disclaimer We are going to talk about some problems associated with constructing more energy efficient buildings This should in no way be used as an argument against building energy efficient buildings Energy efficient buildings are good Please don t stop building energy efficient buildings Ever.. 3

4 Basics of Ice and Snow Formation and Hazard Prediction 4

5 Winter Weather Impacts Precipitation: Wind driven wet snow, snowfall, sleet, freezing mist, freezing rain, rain, and in-cloud icing Other weather factors: Wind speed and direction, solar exposure, air temperature, etc. Building: elevation, size, form, shape, slope, texture, colour, orientation, etc. Predicting this phenomenon is challenging!!! Climate: Climate experts and recent historical records agree that storm severity and peak volumes of winter precipitation are on the increase. 5

6 Facades: Falling Ice and Snow Photograph Published 2011 charlotteobserver.com Northern Microclimate Inc. Northern Microclimate Inc. Northern Microclimate Inc. Published in The New York Times Paper Multiple events of falling ice from the New York Times Building occurs annually. Northern Microclimate Inc. Published 2011 in The New York Times Paper A large sheet of ice, at least a foot across, fell.. 6

7 Roofs: Falling and Sliding Ice and Snow Northern Microclimate Inc. Northern Microclimate Inc. Northern Microclimate Inc. Northern Microclimate Inc. 7

8 Tall Buildings: In-cloud Icing Pole Ice Mass on a Single Pole: Photograph Courtesy of Mt. Washington Observatory Example of In-cloud Icing: Photograph Courtesy of Mt. Washington Observatory Which way is the wind blowing? 8

9 Criteria Building Codes and Standards: Codes acknowledge the issue and prescribe action. However, only address roofs and do not offer criteria, standards or procedures. Common Approach: Trial & Error Incidents are Not discussed publically Consider: Cannot be completely eliminated Once an incident has occurred, an extremely stringent solution is required Client education is far less onerous! What is Acceptable? 9

10 Thermal Performance 10

11 Buildings for Tomorrow Conference Toronto Canada - October 28-30, 2014 Reducing Energy Use Ontario Building Code: Supplementary Standard SB-10 5% more energy efficient ASHRAE or 25% more energy efficient than MNECB 1997 Ontario has some of the strictest building energy use regulations in North America. 14th Canadian Conference on Building Science and Technology 11

12 Reducing Energy Use Then and Now 12

13 Curtain Wall Systems ~25% RH at o C 9.1 o C ~45% RH at 22 13

14 Vision IGU s Double glazed with aluminum Spacer Double Glazed with silicone warm edge spacer Triple Glazed with silicone warm edge spacer 14

15 The Building Envelope 15

16 The Building Envelope 16

17 The Building Envelope How does this affect high-rise building assemblies? 17

18 The Building Envelope Air Temperature 0 o C 18

19 The Building Envelope Northern Microclimate Inc. 19

20 Case Study: Danger Falling Ice! 20

21 Case Study High-rise Tower Coastal climate Over 700 feet tall Snow, freezing rain, sleet, and rain with morning fog or mist. Snow and ice formed on various façade and roof surfaces. Notably - Ice sheets formed in the middle of vertical glazing, released and fell as air temperatures rose. Unitized curtain wall system was deemed high performance 21

22 Case Study High-rise Tower Double glazed IG s at vision area Mid-range performing low-e coating on surface 2 Fritting pattern installed using a window film Outer glass lite was low iron 4-sided structural silicone Raised floor heating 22

23 Case Study Theory Wet snow and freezing rain more likely to adhere to sub-freezing surface This is where ice is expected to form Surfaces that dip below freezing and then back are particularly more sensitive to ice formation Melt water from one area can accumulate in another Larger ice sheets then release as surface temp warms 23

24 Case Study Results Surface Temperatures Below Freezing Exterior surface temperatures for an exterior air temperature of -4.4 C Exterior surface temperatures for an exterior air temperature of -1.9 C 24

25 Case Study Timeline of Surface Temperatures Outdoor and Modeled Surface Temperatures - Observations Freezing Rain/Sleet Ice Falling Reported 1. Below freezing vision glass temperatures aligned with wet winter precipitation occurrence. 2. Falling ice sheet reports (Tuesday) coincided with predicted rise in glass temperatures. 3. Further falling ice was witnessed when spandrel segments were predicted to rise above freezing. 25

26 Concluding Arguments 26

27 Influencing Design Variables Exterior surface temperature can be influenced by: glazing type glass thickness number of glass lites finish coating type coating placement quality of frame components others type and placement of HVAC sources placement of solar shading internal and external obstructions 27

28 Sensitivity Analysis Completed sensitivity analysis on several parameters 1. Raised interior set point to 24 C 2. Varied low-e coating from 0.05 to none 3. Varied the gas fill for the vision glass from Argon to Air fill 4. Varied conductivity of thermal breaks for curtain wall system 28

29 Future Work Analyze additional buildings with reported issues Study and model interior influences Analyze additional variables 29

30 Closing Remarks Buildings in cold climates need to deal with snow and ice We have been overestimating the thermal performance of many traditional envelope systems. Improvements in thermal performance is resulting in colder surfaces and potentially increasing snow and ice formation. Duplication of icing events with model was accomplished; however, due to significant variables further investigation is required. Lots of glazing being installed. Further study is warranted. Problems likely under reported. Don t stop building energy efficient buildings, ever. 30

31 Buildings for Tomorrow Conference Toronto Canada - October 28-30, 2014 Thank You from 14th Canadian Conference on Building Science and Technology 31