Updating building codes in response to climate change

by Katie Daniel | March 1, 2017 10:17 am

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By Chris Van Dongen, B.Arch.Sc., LEED AP, and Paul Carter, B.Arch.Sc., CET
Canada’s climate is changing. Projections for the next 30 years all point to warmer minimum, maximum, and average yearly temperatures. However, the construction industry is still working to energy efficiency requirements referencing historic climate data, which do not take this change into account. A building constructed using these code criteria will become less efficient as the climate changes over its life cycle, and will have higher operating costs as temperatures continue to rise.

Of particular interest in this area is the future energy efficiency of buildings with glass cladding, which is becoming increasingly common in many commercial and residential towers. Such glass-clad buildings have relatively lower thermal performance and are likely less resilient to local temperature increases than buildings with predominantly opaque cladding. To identify the potential impacts of this on similar contemporary building types, a study was undertaken in Toronto to review the implications of projected climate change for their compliance with current building codes.

Current code compliance
Ontario Building Code (OBC) requirements for energy-efficient design can be met using one of two compliance paths:

• the prescriptive path, which requires designers to follow specific parameters for mechanical, electrical, and building envelope systems; and
• the performance path, which requires the designer to create one computer model simulating the designed building’s energy use, and another simulating energy use of a ‘reference’ building constructed using the prescriptive path.

To meet code requirements with the performance path, the simulated energy use of the designed building must not exceed that of the reference building. The performance path allows greater design flexibility, since building systems can be customized to offset other systems’ inefficiencies, then verified through energy use simulation.

The prescriptive path allows for a maximum of 40 per cent of a wall area to be glass (i.e. fenestrated), while the performance path allows up to 100 per cent, provided the walls’ resultant lower energy efficiency is offset by efficiencies in the mechanical and electrical systems.

While glass-clad tall buildings may meet the OBC energy efficiency requirements under the performance path, this may no longer be the case when the climate has changed in 30 years.

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Historic and projected climate data
Historic weather data gathered at Toronto’s Pearson International Airport shows maximum, minimum, and average temperatures have steadily increased from 1979 to 2009 (Figure 1).

A comparison between 2040 to 2049 projected data and 2000 to 2009 historic data from “Toronto’s Future Weather and Climate Driver Study” (“Toronto’s Future Weather”) indicates minimum, maximum, and average temperatures will continue to rise (Figure 2). The study suggests projected temperatures may be overestimated by up to 2.6 C (37 F). However, the temperatures in Figure 2 nonetheless illustrate a significant warming trend. (The study, undertaken by SENES Consultants for the City of Toronto, can be downloaded online here[3].)

“Toronto’s Future Weather” is a detailed climate study providing regional projected weather data. It is based on the Intergovernmental Panel on Climate Change (IPCC) A1B climate change scenario, a mid-point of greenhouse gas (GHG) emissions severity among the various IPCC emissions scenarios.

Case study of a high-rise office tower
In an effort to evaluate the impact of increasing local temperatures, a case study on an archetypal high-rise commercial office tower was completed. Created using a building energy simulation program meeting code software requirements, the tower possesses the following parameters:

• a gross floor area of 44,593 m² (480,000 sf);
• a total of 36 floors, comprising six podium floors along with 30 tower floors;
• a window-to-wall ratio of 30 per cent for the podium floors and 80 per cent for the tower floors;
• a glazing system thermal conductivity rating (U-value) of 1.987 W/m²/K (0.35 Btu/h/sf/F);
• a glazing solar heat gain co-efficient (SHGC) of 0.37;
• a chiller co-efficient of performance (COP) of 5.5;
• a boiler efficiency of 91.5 per cent (condensing type)’;
• pump control with variable speed drives; and
• light power density of 1.1 W/sf.

The mechanical systems were auto-sized by the software to meet heating and cooling loads. While mechanical system efficiencies remained consistent across all models, equipment capacities fluctuated to meet the loads of current and projected climates.

Current and projected weather data from “Toronto’s Future Weather” are not yet available in a useable format, so the data used for modelling was exported from software containing worldwide weather data. The projected weather data from the 2050 to 2059 period was selected as representative of a 30-year projection, and was based on the IPCC A2 emission scenario, which is the worst-case future GHG emission scenario. Current weather data was based on observed values during the 2000 to 2009 period at a weather station in Toronto. Changes in various monthly temperature measurements between the 2050 to 2059 and 2000 to 2009 periods are shown in Figure 3.

The temperature values in Figure 3 are noticeably lower than those in Figure 2, likely because IPCC global climate models are based on average future climate conditions, while data from higher-resolution modelling in “Toronto’s Future Weather” includes weather extremes. The temperature increases shown in the case study are expected to be smaller than actual future weather projections—as such, the case study is an illustration of the relative impacts of climate change.

Results
The case study models showed energy usage from cooling increased by five per cent, increasing building operating costs. Energy usage from heating was reduced by about nine per cent in the 2050s model, which completely offsets the total cooling energy usage increases.

Using current costs for electricity and natural gas, total energy costs were calculated for both modelling scenarios. A five per cent increase was observed in yearly costs for heating and cooling (Figure 4).

Using outputs from the future energy model, improvements in window-to wall-ratio, glazing SHGC, and U-value were also compared. The goal was to determine which of the parameters included in the code’s prescriptive path have the greatest impact on building energy use and building energy costs.

Window-to-wall ratio was found to have the most significant effect, followed by SHGC. U-value improvements had the smallest impact on energy use and resulted in increased energy costs, since these improvements reduce heat rejection through the exterior walls, increasing the requirement for mechanical cooling during spring and fall. Figures 5 and 6 illustrate the relative impacts of improving the three exterior wall parameters.

Analysis
The case study suggests high-rise buildings with primarily glass cladding require improvements if they are to counteract climate change-induced increases in cooling requirements and energy use costs.

Improvements in window-to-wall ratio, SHGC, and U-value have different impacts on energy use, so larger-scale, more-detailed studies should be done to find which among these most effectively counteract climate change’s effects on building energy use. The findings of this type of sensitivity analysis could inform changes to prescriptive requirements in upcoming versions of OBC, to address effects of climate change on building energy use.

The trend in recent energy code versions, including American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, which the OBC references, has been to emphasize reducing thermal transmittance through the envelope (Figure 7). While there are various documented advantages to improving envelope U-values, it is apparent reducing heat loss through exterior walls—particularly in winter and shoulder seasons—yields diminishing returns in reducing overall energy usage.

Reducing SHGC has significantly greater impact, yet prescriptive requirements for this value have remained largely unchanged over the last several code versions. Additionally, where efficiencies in other building systems have historically been used to allow buildings to exceed prescriptive fenestration ratios, re-evaluation may be required under future climate conditions, as these may not result in equivalent energy savings.

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Future climate data and the code
Organizations such as Engineers Canada, the Office of the Auditor General of Canada (OAG), and the Institute for Catastrophic Loss Reduction (ICLR) have recommended projected future climate data be addressed in the National Building Code of Canada (NBC)—the basis of OBC. The National Research Council (NRC), which publishes NBC, has agreed, and is addressing climate change adaptations for the 2015 to 2020 code cycle, with completion anticipated in 2020.

These organizations have focused their attention on how projected changes in severe weather events, flooding, and wind patterns will impact the built environment—with good reason, as these changes can have major life safety and cost implications. However, little information is available to designers with respect to energy performance in the face of changing climatic conditions.

In typical commercial buildings in Toronto, projected temperature increases will significantly affect energy use. Creating building envelopes using design solutions proven to be effective in both current and projected climates can limit energy usage and the resulting GHG emissions contributing to accelerating climate change. To provide designers with the information necessary to inform their decisions, and to regulate industry practices, it is critical for codes to include climate data and envelope performance requirements more accurately accounting for projected climate conditions.

[4]Paul Carter, B.Arch.Sc., CET, is a building envelope specialist at Entuitive with 12 years of experience. Carter has worked on numerous new and existing healthcare projects as a building envelope consultant, and is experienced in restoring historic building enclosures. He can be reached at paul.carter@entuitive.com[5].

 

 

[6]Chris Van Dongen, B.Arch.Sc., LEED AP, is an Entuitive building envelope specialist. He has worked extensively on restoring existing building envelopes and as a building envelope consultant on new construction projects. With 10 years of experience, Van Dongen has considerable knowledge of thermal and hygrothermal modelling, and of restoration of brick masonry façades. He can be reached at chris.vandongen@entuitive.com[7].

Source URL: https://www.constructioncanada.net/updating-building-codes-in-response-to-climate-change/

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