October 2013

Volume 22, Number 10

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Article Contents

Designing for the Next Century's Weather

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How do you create a climate-responsive building in a changing climate? Brand new modeling techniques are helping us figure it out.

By Paula Melton


The San Francisco Federal Building, initially considered a marvel of climate-responsive design due to natural ventilation and daylighting, received an occupant satisfaction rating of just 13% during a post-occupancy evaluation. Getting predictable results from passive design strategies will get even harder as the climate changes.

Natural ventilation, daylighting, rainwater harvesting: these and many other “climate-responsive” strategies are hallmarks of sustainable design because they take advantage of freely available, inexhaustible resources. Working with nature is all very well as long as nature is fairly predictable, but in a changing climate, that’s no longer the case. As temperatures and humidity levels rise, and as wind and precipitation patterns fluctuate, climate-responsive buildings may no longer respond as they were designed to do.

What if, 20 years from now, night flushing is no longer possible? What if “right-sized” mechanical equipment (and operational budgets) become overwhelmed by heat waves happening throughout the year? What happens to those rainwater cisterns when nary a drop falls for two years?

Whether buildings rely on natural or mechanical ventilation, maintaining acceptable levels of efficiency, comfort, and durability will likely become more difficult and expensive as the planet heats up. Buildings not designed with this future in mind could become impractical to operate. Even architects trying to design for the future face a great deal of uncertainty.

Fortunately, experts are developing new ways of modeling future weather and more flexible methods of predicting building performance. Not so fortunately, huge unknowns remain, which is why this nascent field of research is focused not on producing definitive weather forecasts years into the future but rather on helping project teams make reasonable, affordable accommodations for a range of equally probable future climate conditions.

What to Expect When You’re Expecting Climate Change

We’ve all heard about the projected impacts of global warming: higher average temperatures, even at night; stronger and possibly more frequent storms; heat waves and drought; rising sea levels. But global climate scenarios vary, and modeling how the effects might play out by region—let alone on a particular building site—is a developing science whose outputs we cannot fully verify until it’s too late.

What we know

Region by region, “the best information we can give is the direction of change and a variable,” says Joel Smith, principal at Stratus Consulting, an environmental research company. For example, the northeastern U.S. “was projected to get wetter, and it actually is getting wetter,” but translating that into precise monthly or even seasonal rainfall projections may not be possible. “Extreme precipitation is going to go up, but exactly how much is hard to know,” he adds.

There are many reasons for this, explains Smith, who has also co-authored assessment reports for the Intergovernmental Panel on Climate Change (IPCC—see sidebar):

• The general circulation models (GCMs) of Earth’s atmosphere, which are used to produce global climate scenarios, have low resolution—“about 60 miles across at mid-latitudes,” according to Smith.

• GCMs don’t account for topography or other local variations that can create significant microclimates.

• GCMs rely on projections regarding greenhouse gas emissions, and different assumptions about emissions can lead to dramatically different results. “If the climate model gets the basic climate wrong, the regional model isn’t going to fix it,” quips Smith.

Uncertainty doesn’t mean we should give up on designing buildings to weather climate change: it merely means learning to rely on ranges of possible answers rather than on a single definitive answer—and many in the field of energy modeling believe this is needed in any case (see “Remodeling Performance Predictions,” below).

Planning for unknowns

“There is fundamental uncertainty about climate change,” Smith emphasizes. “People can get hung up on that.” Focusing on what we don’t know doesn’t aid decision-making, so Smith says he tries to reframe the deadlock as a kind of cost-benefit analysis, asking clients, “What are the costs in terms of bumping up to higher protection?” He suggests considering what decisions you would make if you knew certain changes would occur and then weighing the costs against what you would do if you weren’t sure they were going to happen.

Having recently worked on a green infrastructure plan for the City of Philadelphia, Smith offers the example of culverts. “They come in discrete sizes,” he points out. How much does it cost to upgrade to the next size, or the next? Is that insurance worth investing in? Some upgrades “aren’t very expensive,” he notes. If you would typically plan for a two-inch rainstorm as a 25-year event, “maybe in the future, that will be 2.5 or 3 inches. What does that mean in terms of what you do when you design a building? Can you tolerate occasional exceeding of the standard?”

“There’s an interesting question of climate-responsive design,” notes Christoph Reinhart, Dr.-Ing., associate professor of architecture at the Massachusetts Institute of Technology. “Everybody likes to use this buzzword right now,” but the term “climate-responsive” is too vague, he contends, and designers should really be asking themselves, “What am I optimizing for? Cost? Greenhouse gas emissions? How long a time period am I considering? When you change these numbers, your building morphs.” Reinhart argues that claiming climate-responsiveness in a changing climate is questionable and advocates instead for “climate-resistant buildings” that are designed to be less sensitive to temperature and humidity.

Comparing Emissions Scenarios


These charts show differences in emissions assumed by the full range of IPCC emissions scenarios (see sidebar). The U.S. Government references B1 as is lower range and A2 as its higher range.

Matthew Eames, Ph.D., a research fellow at the University of Exeter, working with a team of fellow physicists, has converted regional climate models into “morphed” weather files for various locations in the UK; these can be used in EnergyPlus and other tools to compare future heating and cooling loads in different years under different conditions (see “The making of a weather file”). There’s no point in adding a cooling system now that won’t be needed for decades, he told EBN. “But if you think you’re going to need a cooling system in 2080 and you don’t leave space for the pipework now, it will be much more expensive to retrofit it. You’re not going to adapt for 2080 now, but if you have the ability to adapt, that’s a very good place to be.”

Heating and Cooling in a Warming World

Although resilient design must focus on flood prevention, hurricane and wildfire resistance, and passive survivability after natural disasters, designers are also beginning to appreciate a more mundane level of resilience: if a school, home, or office cannot be kept comfortable and safe—affordably—from day to day, it may be torn down prematurely. The significant resources used to create these buildings will go to waste just as surely as if they had washed downstream or blown away. More resources will have to be mined or harvested, and more materials manufactured and transported and installed, to replace these structures.

“It would really raise the bar if buildings were designed with conceptual energy modeling at very the outset,” argues Drake Wauters, AIA, of the American Institute of Architects’ Technical Design for Building Performance Advisory Group. With smarter massing and orientation strategies, Wauters argues, add-ons such as screens, barriers, window coverings, and automation shouldn’t be needed as much. “I believe there’s going to be a lot of work to do repositioning existing buildings to deal with changes in climate, including less predictable weather. I’d rather people with those skills be able to focus on those projects than trying to fix new projects that could have been designed with better energy modeling tools.” (See “Energy Modeling: Early and Often.”)

Adjusting for higher highs

At least in terms of peak loads, which are used primarily for mechanical system sizing, “the climate’s not changing that fast and isn’t predicted to do so for quite a while,” contends Dru Crawley, Ph.D., director of building performance at software developer Bentley Systems and one of the original creators of both EnergyPlus and OpenStudio. Crawley says the ASHRAE handbook used to calculate those loads is tracking the new peaks. “We are seeing change already, but we’re talking about a degree centigrade right now”—though he adds that because of the urban heat island effect, areas with more-urban airports (where weather stations are typically located) are hitting higher peak temperatures more rapidly. London and Phoenix weather stations, for example, “used to be in the middle of nowhere” and are now much closer to their respective cities due to sprawl. “Places like that have increased a little bit more over the last 40 years than other locations,” he said. Peak loads will continue to creep upward, but HVAC equipment has a shorter service life than the envelope, so many building owners will simply adjust for new peak loads when equipment needs to be replaced.

Projected Changes in Heating and Cooling Degree Days


Source: U.S. Global Change Research Program

Peak loads don’t only affect system sizing, however. “Certain mechanical systems can’t even be used if you get too much of a peak load,” notes Kjell Anderson, AIA, sustainability specialist at LMN Architects and author of the forthcoming book Design Energy Simulation for Architects. Anderson has seen projects that could not use radiant cooling or natural ventilation until designers had reduced glazing ratios to lower the overall peak load. Will buildings that crossed that threshold in a 2013 energy model still function during a 2030 or 2050 heat wave?

That remains an open question, especially in low-energy buildings with unconventional design elements, Anderson notes. “In the ’80s, they oversized everything, and it led to a lot of problems and energy waste. So now we’re trying to right-size them—and in low-energy buildings, you try to ‘tight-size’ them” (meaning they’re even smaller than a “right-sized” system). Project teams taking this approach may use annual energy files, which are developed from past weather data, instead of peak-load calculations. “If we get a year that is 100ºF in Seattle for five days, it’s going to be impossible for this building to cope,” Anderson argued. “You have to factor in safety, and at some point, it’s not good design.”

Adjusting for higher averages

Once you’ve sized your mechanical system, it needs to operate day after day, year after year, and that’s where average temperatures come into play in energy models. Engineers use typical month-to-month ranges from 30-year time periods (TMY or EPW files, for example—see “The making of a weather file”) to predict overall energy performance. “For looking at building performance, we use a typical year,” Crawley explains. “That’s where my concern is,” he adds, because using these ranges “could be masking some of that response to warmer, colder, or sunnier conditions,” making models highly inaccurate for predicting future performance, especially as heat waves get hotter and longer. Crawley is working with the consulting company Weather Analytics to develop new types of weather files for use in energy modeling that reflect fewer (but more recent) years and that can be updated more often than TMY files are.

In the meantime, we have mostly trends to work with. In cold climates, the news is mostly good, notes Crawley: “Energy use is going down, changing from massively heating-dominated building types to more cooling in those locations.”

Reinhart puts a different spin on the same information. For a paper co-authored with Seth Holmes, Reinhart created morphed weather data (using a “weather generator” tool developed by researchers at the University of Southampton) for Boston and modeled an existing 1980s office building to produce a payback analysis for an HVAC retrofit. “It was pretty dramatic,” he said. The building “used one-third more energy for cooling and 25% less for heating through 2080. Overall, the energy use will be a little lower, but it has a big effect. That switches the whole energy market.” And now for the bad news: “If you’re going further south, in Washington, D.C., or Phoenix, their energy use is just going up. If we make energy more expensive, climate change will hopefully happen slower”—but whether it’s energy prices or energy conumption that rises, “the cost of maintaining buildings in the South will go up a lot.”

Boston...or Baltimore?


The top psychrometric chart, created in Climate Consultant, shows that during summer days, using current TMY3 weather data, a Boston building needs heating about 43% of the time and cooling about 38% of the time. According to U.S. government projections (based on the A2 emissions scenario), a building in Boston today will likely need to manage a Baltimore climate by 2040. The lower chart shows, in that scenario, a future need for heating just 18% of the time during summer days—but the need for cooling spikes to 68%.

Screen Capture: Climate Consultant 5

Although Reinhart and Holmes did a great deal of technical background work to model a variety of future performance scenarios and calculate paybacks, his advice is simple: “The main thing this paper shows is that when you build the most energy-efficient solution, you see the uncertainty drop.” In other words, the higher-performing your building envelope—regardless of climate—the less your energy use will fluctuate and the less expensive your building will be to operate in extreme conditions.

The future of natural ventilation

“It’s not necessarily just a heat wave,” cautions John Kennedy, senior product line manager at Autodesk and a member of ASHRAE Technical Committee 4.2, which develops climatic data for ASHRAE Fundamentals. “It the past ten years, it has really come to our attention that the climate zones [in North America] are migrating north.” In areas where summers used to be mild, “the stack effect is no longer functioning as well as it was.”

In the U.K., natural ventilation will become more difficult within two decades. Project teams there have been working with morphed weather files for a few years now to help them adapt. “Schools and residential buildings do not put in mechanical cooling systems because of the temperate nature of the climate,” explains Varun Singh, senior vice president of engineering and development at Sefaira, developer of the Concepts energy modeling tool. Based on energy models that U.K. project teams have developed using Concepts with morphed weather files, he claims, even a small rise in summer temperatures can make natural ventilation ineffective for up to 200 hours of the year. “Peak [cooling] conditions in residential buildings happen in June, July, and August,” he said, but “with climate change, they are starting in April all the way through October in year 2030,” according to the models. One project team dealt with this problem by adding shading devices, Singh says, “to ensure that 30 years from now, when the climate gets worse, the buildings are resilient enough in terms of comfort.”

Fortunately, though, “people have wider comfort ranges in naturally ventilated buildings,” says Anderson. “In mechanically cooled buildings, they tend to complain if it gets to be 76ºF, but in a building with natural ventilation, they would be comfortable at 76, 77—even possibly 83. It gets into a little bit of psychology at that point.” He emphasizes the importance of trying to predict how many days per year the building is likely to be uncomfortable and having frank conversations with clients about their expectations. If they are committed to natural ventilation, how do they intend to deal with these periods of overheating?—by shutting down the building, relaxing dress codes, or having a backup mechanical cooling system that may only be used a few times a year? Although sometimes awkward, “that kind of conversation has to happen once you start designing at the edge of what is possible,” he said.

Overheating becomes a public health threat in large cities with existing multifamily housing that relies exclusively on natural ventilation. Reinhart frames this looming problem, which will be worst in poor neighborhoods where most residents cannot afford to buy or operate individual cooling units, as an environmental justice issue. “Natural ventilation tends to rely on nighttime flushing,” he points out, and nights are warmer in cities not only because of climate change but also due to independent increases in the urban heat island effect (caused by sprawl). A ceiling with radiant cooling may be a relatively inexpensive retrofit that could mitigate the effects, he says, but the problem is far from being solved for residents of these buildings.

It’s the Humidity

With higher temperatures, higher humidity is expected in many regions; wetter air can produce more extreme storms, and it also has more subtle effects that some designers may not have considered.

First, the higher humidty could increase the risk of moisture problems in exterior walls, as humid outdoor air gets into the wall and condenses on a cool surface. Hygrothermal analysis (studying the relationship between heat and moisture in buildings) along with a greater focus on barrier continuity and drying potential (rather than on which “side” the vapor retarder goes on) could become even more central to building longevity with climate change. The increased risk that comes with even a small rise in temperature should be taken into account during design, construction, building enclosure commissioning, and operations.

“Vapor pressure is becoming greater,” cautions Wauters. “There are large areas of the U.S. where architects and engineers and building owners have had a hard time figuring out what to do about vapor barriers, air barriers,” and other ways of managing moisture. This uncertainty has already led to many problems, but these are only likely to get worse as buildings in mixed and cold climates gradually come to have vapor retarders on the “wrong side” of the wall. “Buildings with such barriers should be inspected and reanalyzed regularly to address current and future environmental shifts,” Wauters continues. (And it’s not just vapor retarders, either: many common materials, like vinyl siding and multiple layers of latex paint, prevent drying even though they aren’t installed for vapor control.)


The Queensbridge housing project in New York was designed without central cooling; such buildings could pose a public health threat for residents who cannot afford to purchase or operate window air conditioning units, a few of which are visible in the photo.

Photo is in the public domain.

Ideally, Wauters adds, these problems will be avoided altogether in new construction. “Design professionals should in most cases eliminate non-breathable barriers from exterior enclosures,” he argues. “Where hygrothermal analysis indicates barriers are required, they should be designed in a manner that allows condensation to dry harmlessly.” Wauters emphasizes that the building industry should not “just simply wait for the codes to change” because these changes could take far too long. (For more on managing moisture in building envelopes, read “The Hidden Science of High-Performance Building Assemblies.”)

Higher humidity in interior air can also affect thermal comfort, compromising the effectiveness of natural ventilation and potentially straining mechanical systems. If you don’t have access to morphed weather files, consider researching what climate zone your project’s climate is likely resemble in 2030, 2050, and beyond; you can use tools like Climate Consultant to get a quick, if rough, idea of your building’s performance throughout its service life under low and high emissions scenarios (see psychrometric charts for an example).

Although many buildings that did not need mechanical cooling or dedicated dehumidification may eventually require it, LMN’s Anderson sees a silver lining: condensate is an excellent source of graywater, “purer than rainwater,” he says. (See “Alternative Water Sources: Supply-Side Solutions for Green Buildings.”)

There Goes the Sun?

“It would take an asteroid to blow us off our path” for major changes to occur in solar radiation, jokes Eames at the University of Exeter. But cloud cover and haze do affect building performance.

In general, cloudier skies are a positive for daylighting design (less glare and less unwanted heat gain—see “Doing Daylighting Right”) but a negative for both passive solar heating and photovoltaic energy generation. Although skies are likely to be hazier due to higher humidity, we know very little about how climate change will affect light quality. “Cloud cover that’s within the [climate] models is consistent with the underlying weather,” explains Eames. In other words, it’s not considered as its own variable but tends to ride on the coattails of the temperatures and relative humidity being forecast; so if an 80ºF summer day with 80% RH in your climate is typically sunny, a modeled 80ºF spring day with 80% RH in a future climate model will show up as sunny as well. “There’s probably modeling uncertainty and error in there,” he adds, so morphed weather files aren’t really applicable to daylighting design at this stage.

MIT’s Reinhart, who helped pioneer more sophisticated metrics for daylight modeling in the early 2000s, told EBN that daylighting is the least of his worries with global warming. “Daylighting might change a bit, but that’s a part where I’m least concerned,” he said.

Questions Are Blowin’ in the Wind

Like cloud cover, wind speed and direction are “not actually one of the outputs of our climate change projections,” says Eames.

“Some of those variables are hard to know,” concurs Smith. “Wind speed is very difficult; we just have to shrug and say we don’t know. With higher temperatures, will there be increased winds? We just don’t know.” Accounting for day-to-day changes in wind pressure—which can affect air infiltration significantly—is not possible right now.

Luke Leung, P.E., sustainable design leader at SOM, notes that average global wind speed has been decreasing since 1974. The impact of this can be positive for building performance due to decreased air infiltration. However, he says, other impacts include more buildup of contaminants in outdoor air as well as lower output from wind turbines—which could be compounded by the lower air density associated with higher temperatures.

We do know that many regions of the world are already experiencing stronger storms than has previously been normal, and many of these storm types (hurricanes, tornados, blizzards) come with extreme winds. Consequently, BuildingGreen’s Alex Wilson, who is also founder of the Resilient Design Institute, argues, “We should be designing everywhere for the Miami-Dade County code as a default minimum for wind resistance.” He notes, “There are some environmental penalties to such a strategy, with increased use of materials, and stronger materials, inevitable,” but, Wilson says, “The durability benefits will counter those increased environmental costs, in my opinion.”

It Never Rains But It Pours 

Projected Increase in Precipitation in North America


Source: U.S. Global Change Research Progr

Although designing buildings for efficient future energy performance is important, says Anderson, he sees the issue of water as much more urgent. “Energy is this abstract thing out there, but water is a physical, tangible thing that you can’t go for two days without, or else you die.” Doing without adequate energy may be possible, if inconvenient, but “drought leads to refugees and war,” he continues. “I think future-proofing for water conservation is a huge deal.” (See maps in this section for U.S. government precipitation projections throughout North America.)

Indeed, one of the most important reasons to curb energy consumption in the built environment is to save water, points out Smith at Stratus Consulting. “The availability of water is needed for the cooling of power plants,” he said. “Energy is one of the major users of water. In the West, supplies could get tighter, so anything that reduces demand for water reduces vulnerability to drought.” (See “The Water-Energy Connection.”)

Predicting future precipitation patterns is “one of the most important things one could do right now,” argues Anderson.

Anyone who has ever been disappointed by a faulty weather forecast knows how difficult it can be to predict rainfall amounts even for the next day; predicting a range of annual precipitation by region is easier, and certain trends are expected. It makes a lot of sense in many regions to plan for more intense and more frequent flooding—and, where possible, to try to manage rainwater in a way that could prevent such floods—while in other areas, it makes more sense to plan for extreme drought. But for certain modeling purposes, general trends may not be enough.

Historical Change in Very Heavy Precipitation in the U.S.


Source: U.S. Global Change Research Program

Using general data to size a rainwater harvesting system, for example, is difficult. “In the U.K., the [annual] rainfall amount is not meant to change at all,” says Eames, “but the seasonality is. We are supposed to get much wetter winters and much drier summers.” This shift affects a number of design decisions, including “foundations, drain sizing, rainwater harvesting, underground pipework, and weatherproofing.” When consulted by a project team about rainwater catchment, Eames related, researchers recommended “a slightly bigger hole for the same tank” to accommodate less frequent but more intense rainfall. He adds, “Anywhere where it’s important to be risk-averse, even though we’re quite uncertain about the variable itself, it’s probably best to sort it out now—if it’s affordable. You could probably adapt it later,” but such retrofits are unlikely to happen, he believes, unless buildings are designed today to make these adaptations inexpensive.

In response to demand from the insurance industry, meteorological experts are working to produce more accurate precipitation models. According to Charles Khuen, co-founder and executive vice president of Weather Analytics, accurate precipitation predictions are “going to be a bigger driver than the energy-efficiency side, but the energy-efficiency side of things will benefit from this work.”

Remodeling Performance Predictions

Uncertainty about how to plan for climate change has led to scrutiny of how we design our buildings in the first place—and this is much-needed scrutiny, some practitioners contend. When we run only one energy model using only one weather file, argues Dru Crawley, “we do a disservice to our users. Presenting a single number is just not right. The accuracy implied is just not there.”

If nothing else, learning to design for future weather could help change the way we use—and the way we present—performance modeling for buildings. Experts are making headway in this arena—both on developing new datasets they hope will more accurately reflect possible future weather and on making our modeling tools more agile so that multiple scenarios can be explored in parallel. “We should be doing multiple simulations—change the weather files, change the windows, or whatever you want to do to look at the change in results,” continues Crawley. Unfortunately, he says, “Most users are struggling to get enough resources, either money or people, to do analysis on just a single file.”

The making of a weather file

We rely on weather data for designing mechanical systems, planning for natural ventilation, modeling energy consumption, engineering PV arrays, sizing rainwater harvesting systems, and many other things. However, the available data offer only a very rough outline of weather expectations—and many people think it’s far too rough.


Weather stations like this one have been tracking rainfall, temperature, humidity, and other data for decades. Historical weather files rely on actual observations from these spread-out stations. New types of files integrate data from the upper atmosphere and satellite observations and use fluid dynamics to provide localized historical weather modeling.

Photo: NOAA

“We set out with the recognition many years ago that the world of weather data hadn’t changed in 30 to 40 years,” says Khuen of Weather Analytics, explaining the origins of his company. “It is a segregated, gappy, messy world with lots of inconsistency being used in modeling, analytics, and control systems that require things to be precise and available at digital speeds.” He wants to help move weather data “into a digital, rational world so we have a globally consistent, statistically stable database from 30 years back through the current time and into the future.”

Right now, most building modeling tools incorporate a Typical Meteorological Year (TMY) dataset. TMY data (often integrated into modeling tools in an EPW file format, for EnergyPlus weather file) is simulated hourly data produced by choosing typical month-to-month ranges for 15 to 30 years based on observations at weather stations. “If you’re doing analysis using this weather data, you’re effectively siting your building at the airport,” remarks Autodesk’s Kennedy. Autodesk has its own approach to this problem: the company worked with a consultant to produce more localized TMY data using “mesoscale meteorological modeling” to integrate ground-level observations with satellite data and upper-atmosphere observations along with elevation and land use, he explains; these models were “validated with real data showing they can at least get temperature and humidity levels very close.” Current Autodesk tools reflect TMYs produced using mesoscale modeling in 2006.

Weather Analytics is trying to push similar technology even further. When the U.S. National Oceanic and Atmospheric Administration (NOAA) released “re-analyzed” TMY files in 2011—which were already integrated with satellite observations to “squeeze the air out of the data,” says Khuen—“we pulled in that whole dataset and have been bringing it in every six hours since. We’ve taken that data, which is in a very esoteric format, and we’ve processed it” into EPW formats and other types of files, which can be purchased from the company for use in modeling tools.

Parallel Comparison of Morphed Weather Data in Concepts


Sefaira’s Concepts modeling tool allows users to import multiple weather files and compare key performance attributes under different scenarios. According to the company, the total energy use in this U.K. building is decreasing over time because it is naturally ventilated (space heating needs are reduced with warming). Since this is a conceptual model, the company warns, building performance should be revisited regularly to develop up-to-date strategies for continued comfort in the building.

Source: Sefaira

These refinements may increase resolution and accuracy, but TMY files still can’t predict the frequency or intensity of heat waves, droughts, or strong storms.

“It’s a synthetic year, not a real year,” says Anderson. “If you look at it for wind direction, for example, you may well be right—but you might also be wrong, and you wouldn’t know it.” Better, he says, “would be to have all 30 years of data available and run all 30 years: then you could see the variability. That’s something I’ve talked with engineers about many times about. Why do we only run an energy model under a single scenario?” Anderson says this one-track modeling can produce absurd results at times. “If you model for 15 people in the office, you’ve completely failed if there are 30 people in there. Not only that, but buildings often get repurposed 10, 20, or 30 years later. If you design to one scenario, when it gets repurposed, it may fail completely. That doesn’t seem like a very future-proofed building.”

Tool developers have recognized this problem and are trying to solve it.

Making new kinds of weather data

Eames and others in the U.K. have worked to produce future weather files—EPWs based on a morphed TMY or on a morphed Design Summer Year (DSY) to account for higher cooling loads in extreme heat.

Future Weather Impact on a Naturally Ventilated Building


Using data produced in Concepts (see screen capture, above), the design team for this naturally ventilated U.K. building produced this bar graph showing rising temperatures alongside strategies for managing the hotter weather. Electrochromic glazing and shading may compromise daylighting plans—a potential tradeoff of continuing natural ventilation rather than introducing mechanical cooling.

Source: Sefaira

Khuen and Crawley are developing a number of new datasets they think will fill in many gaps, starting with what may be more relevant TMY files. “We could create a TMY that reflects the last seven years, very quickly,” notes Crawley. “There is less data to deal with, so it could be processed much quicker, and we could be more responsive in updating these.” Crawley adds, “ I also think there may be some advantage in using just the last three years of data. With 2012 being the hottest year on record worldwide, maybe that would be a good one to start with.”

Khuen also mentioned the possibility of an Extreme Meterological Year, which will look at “the coldest typical year, then the warmest,” he explains. “At least you can make a design and bound it and test it against different boundary conditions.” The pair also plan to develop Future Meteorological Year sets for locations beyond the U.K., and they may combine the two concepts as well. “Does it make sense to have a hot/dry year, a cool/wet year, and a still year?” asks Crawley. They are still exploring how “we can bracket what really affects energy and give better guidance to users.”

Moving modeling tools forward

Once multiple weather files are available to designers, they still need the capability to compare different weather impacts.

Sefaira’s Concepts tool is designed specifically to allow architects to run multiple energy models side-by-side to inform early design choices (no promises about predictive accuracy, but design teams that have piloted the software have found comparative analysis can be fruitful). Once multiple types of weather files are available, architects can plug several at a time into Concepts and compare outputs for key performance attributes. Sefaira doesn’t provide these files, but morphed weather data can be imported.

Potential Energy Savings in Revit


A new Revit tool allows project teams to investigate the effects of key energy reduction strategies (this capability is also available in the conceptual modeling tool Vasari). Autodesk is working to enable parallel runs using different weather files as well.

Source: Autodesk

Autodesk tools are moving in a similar direction, says Kennedy. “One thing I’m predicting that building design teams will have to do to address [climate change] is a lot more energy simulations as well as comfort simulations for different scenarios,” he told EBN. Teams will then “provide a probability result to owners; rather than giving them an exact number, it’s how this building is going to perform under these scenarios.” Revit and Vasari can both now produce “potential energy savings” outputs that compare different design variables in parallel. “We do envision adding climate-specific runs,” explains Kennedy. “We want to get it out as quickly as possible,” he adds, while also making the methodology robust enough to be accepted by ASHRAE technical committees.

“What the World Needs Today”

Although it’s easy to get wrapped in what-ifs related to climate change, Eames reminds us that “there is still uncertainty in the climate scenarios,” and we shouldn’t use morphed weather files or other data as though they were a weather forecast. The U.K. files available through the University of Exeter take a variety of scenarios into account, which he says gives a sense of the range of possibilities. Even then, he adds, “It’s important that your building operates today—and then worry about the future.”

And when worrying about the future, sensible decision-making may include not only adaptations that take place now but also an adaptation plan that can be referenced and implemented over the next decades in response to actual weather trends. For a 2012 competition sponsored by the U.K. Department for Environment, Food, and Rural Affairs (Defra), project teams submitted adaptation plans to receive funding for climate change preparation. These plans (fact sheets are available on the Design for Future Climate website) based energy modeling on morphed weather data, using the results to develop a variety of strategies, from inexpensive (or free) upgrades to major renovations—raising cooling set-points and changing dress codes; reducing internal loads with more efficient lighting and lower occupancy density; and retrofitting glazing to reduce solar heat gain. Adaptation plans look at a range of risks, include a cost-benefit analysis of each potential strategy, and provide a time-line for implementation.

Developing an Adaptation Plan


In a report prepared for the London School of Hygiene and Tropical Medicine, AECOM developed a methodology for performing cost-benefit analysis for a variety of energy- and water-saving strategies. Many were not considered viable because the hospital is a historic building, but they would be easier to implement on a new building or even a more modern existing one.

Source: AECOM

Meanwhile, as important as energy and water performance are in individual buildings, experts in the field agree that effective climate change mitigation and adaptation will require widespread action. “The modeling industry was born out of code compliance,” says Kennedy. Design teams are trained to ask, “How do I compare to that fictional building?” he adds, arguing that “rather than a reference building, you should be measuring to zero. What the world needs today is tens of millions of net-zero-energy buildings.”

That won’t happen quickly—but the closer we get to zero-impact buildings as a design standard, the less harm we’ll wreak on our planet and its atmosphere, and the more prepared we will be for the consequences of the harm already done.

Comments (5)

1 design for flexibility posted by Karin Miller on 10/22/2014 at 01:59 pm

I appreciate the point that Matthew Eames makes "You’re not going to adapt for 2080 now, but if you have the ability to adapt, that’s a very good place to be.” Anticipate that the use may change, systems may change, and design a building that’s adaptable to future conditions. Think through passive systems, floor heights, orientation; a net-zero building today isn’t necessarily a net-zero building in the future, give future occupants the space for creative solutions. 

2 Volatility against Actual Future Weather posted by Jacob Parz on 08/14/2014 at 04:18 pm

The problem with right- or tight-sizing a low-energy building that's designed using annual energy files is that energy files that take their data from past weather data cannot be seen as totally reliable. There will be some variability between past years and current conditions; what that variability is a reflection of the climatic changes of adjacent regions of the entire planet and cannot be just thought of as just region specific. The problem with designing for based on peak load calculations is the accuracy of the prediction of what that peak load will be exactly, and, going back to the idea of a volatile and unstable course of the current climate, I would assume that would be just as difficult with forecasting based on past weather data.

3 Net-zero posted by Nora Rizzo on 05/05/2014 at 12:24 pm

This article provides a nice overview of the programs and technology being used to analyze future weather.  I think the most profound statement comes at the very end of the article.  Why are we modeling buildings against fictitious structures?  We absolutely should be designing, modeling, and building net-zero buildings.  We shouldn't wait for state and federal code requirements to kick in at 2020, 2030 or 2050.  We need to start mandating net zero energy now.

4 I agree with Nora comment on posted by Vandita Mudgal on 09/15/2015 at 12:33 am

I agree with Nora comment on madating net zero energy for all project now. But as a green building consultant, I often come across project with tight budgets and very little overall knowledge and acceptance of green building design in general. The question is how do you make a case in front og such clients to purue net zero energy buildings.

Also, I have repeatedly seen that net zero energy might not be the most suitable strategy for all project, some projects can really work on net positive water, some of 100% Red list free materials etc etc. So, the strategy to go deep green should be customized per project and client type

5 Natural Ventilation Disadvant posted by Ibrahim El-Shair on 03/12/2014 at 08:57 am

1- Depend on outdoor climatic conditions (temperature, humidity). 2- Natural driving forces can for longer periods be quite small, which limits possibilities for application of filtration and heat recovery, that might result in poor indoor air quality and/or increased energy use for heating. 3- Results in limitation in the choice of building layout. 4- Outdoor dust and traffic noise requires special solutions. 5- It is difficult to fulfill requirements to thermal comfort in winter if preheating of incomming air is not applied. 6- The air flow rate will always be dependent of the natural driving forces as well as the occupant’s control. This might result in an increased energy consumption. 7- The indoor temperature will variate more than for mechanical systems.

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Continuing Education

Receive continuing education credit for reading this article. The American Institute of Architects (AIA) has approved this course for 1 HSW Learning Unit. The Green Building Certification Institute (GBCI) has approved this course for 1 CE hour towards the LEED Credential Maintenance Program. The International Living Future Institute (ILFI) has approved this course for 1 LFA hour.
Learning Objectives
Upon completing this course, participants will be able to:
  1. Understand how to adjust building designs to rising temperatures and humidity.
  2. Recognize how climate-responsive buildings may not respond as expected in fluctuating winds and precipitation.
  3. Explain climate-change implications for natural ventilation, daylighting, and rainwater harvesting.
  4. Stay abreast of changing energy and precipitation models and future weather files.
To earn continuing education credit, make sure you are logged into your personal BuildingGreen account, then read this article and pass this quiz.
Discussion Questions
Use the following questions to inform class discussions or homework assignments.
  1. What's the problem with right- or tight-sizing a low-energy building that's designed using annual energy files?
  2. Choose a favorite existing building. How would you "reposition (it) to deal with changes in climate"?
  3. Your client wants you to design a climate-responsive building but you think designing a climate-resistant building would be wiser. How do you argue your case? Can you think of (or imagine) a project that accomplishes both goals?
  4. What's the difference between "mesoscale meteorological modeling," "reanalyzed TMY files," and "morphed TMY (or DSY) files"? Compare them to the possibility of "Extreme- and Future-Meteorological Year" sets. How might you implement these tools for comparative analysis of weather files to develop adaptation plans such as those by "Design for Future Climate" project teams?
  5. How do you think the "more mundane level of resilience" mentioned in the article relates to the future of natural ventilation? Consider both the general tendency to tolerate wider comfort ranges in naturally ventilated areas as well as ways to avoid overheating in large cities with existing multifamily housing. Pull from the reading and ponder additional measures in both practice and policy.
  6. Familiarize yourself with the Working Group 1 contribution to the IPCC Fifth Assessment Report: Summary for Policymakers. As the ASHRAE [4.2–Climatic Information] Committee takes direction from that report on how we should be projecting into the future climate, can you translate the B1 scenario into some key action tasks for your colleagues in the green building industry?

September 30, 2013