Hi Every Energy Model Is Wrong—And Here Is Why They Are Indispensable.

Hi Every Energy Model Is Wrong—And Here Is Why They Are Indispensable.

Recently, LEED has come under fire for accounts of certified buildings not performing as well as their energy models predicted. Frequently mentioned amongst the antagonistic “gotcha” coverage is an out-of-context 2007 quote by the USGBC Research Committee acknowledging: “Buildings have a poor track record of performing as predicted during design.”

Within context, the research committee clarifies the reasons for the frequency of underperforming energy models, citing “inaccurate or improperly used analysis tools, lack of integration of complex interconnected systems, value engineering after design, poor construction practices, no building commissioning, and incomplete or improper understanding of operations and maintenance practices.” Not nearly an exhaustive list, but all legitimate considerations.

Energy models will continue to become more accurate as the market develops and methodologies and software become more robust and sophisticated. Models can be calibrated based on actual performance data to further increase their accuracy for measurement and verification purposes. But let’s be clear—to some degree, all energy models are wrong. They always will be. At first blush, one may reasonably presuppose energy models are based solely on physics and, as such, they should be extremely precise—perhaps 95 to 99 percent accurate. Yet all building energy models also require inputs based on assumptions and long-term trends. We cannot predict the future—e.g., abnormal weather patterns, mechanical malfunctions, changes in occupancy, occupant behavior—but all of these factors have a chaotic effect on performance outcomes.

Nevertheless, energy modeling is essential for any high-performance building project—no matter how big or small. Energy models facilitate sustainable design in three essential ways:

1. To Understand. Energy models allow us to understand more about how our buildings are likely to perform. They allow design teams to test hypotheses and simulate field conditions for both proposed designs and existing structures. I was once approached to advise on dripping water in the ceiling of a museum. Through energy modeling—specifically a hygrothermal (i.e., pertaining to both humidity and temperature) analysis—it was determined that an ill-advised vapor retarder was preventing vapor drive toward the exterior. Add seasonal temperature extremes and high interior relative humidity, and it was a recipe for condensation.

2. To Compare. It is easier (and much less expensive) to experiment in the computer than in real life. Energy models are most valuable during the earlier stages of the design process when their results can help guide decision-making. As a parametric design tool, energy models can be used to evaluate everything from conceptual massing options to different glass types. This is the very premise of the “simple box” energy modeling analysis within the LEED v4 integrative process credit—and there is an abundance of user-friendly software platforms currently available in the market, many of them free. This kind of early-stage design performance modeling allows design teams to go beyond rules of thumb to actually fine-tune environmental control systems and energy conservation measures.

3. To Forecast. Buildings are investments, and the separation between construction capital and operating expenses makes it difficult to finance long-term improvements in building performance. Energy models improve our insight of the connections between—and business-case benefits of—various building systems in relation to high-performance outcomes. Despite a certain degree of imprecision, energy models can be leveraged to forecast the return on investment in high-performance building upgrades, such as onsite renewable energy, automated exterior louver systems or even that extra inch of rigid insulation on the roof. More frequently, project teams are using energy models to anticipate the order of magnitude to which future climate change could impact the economics of building performance, operations and maintenance.

In a recent TED talk, climate modeler Gavin A. Schmidt, director of the NASA Goddard Institute for Space Studies, insisted, “Models are not right or wrong; they’re always wrong. They’re always approximations. The question you have to ask is whether a model tells you more information than you would have had otherwise.”

Energy models are not meant to predict the future. They are powerful tools that enable us to better understand the behavior of our structures, fine-tune building systems and strategies, and forecast future performance trends. 

Hi Researchers use HIVE to test latest building methods.

Hi Researchers use HIVE to test latest building methods.

A new research facility in Wiltshire is set to 

advance the development of sustainable 

construction materials and systems.

Funded by EPSRC, the £1m HIVE facility will allow construction companies and researchers to conduct realistic, full-scale testing of their facade designs in open-air conditions.

HIVE, located at Bath University’s Building Research Park in Swindon, consists of eight cells that are insulated from one another, each with a single face left exposed to the external environment.

The cells themselves will let researchers analyse the environmental impact of construction materials including their energy efficiency, flood resilience, structural capability and internal air quality.

‘People are interested in looking at the latest iteration of their products and trying to compare them with previous iterations or with competitive products to see whether or not the performance is something to shout about,’ said Dr Mike Lawrence, director of the Building Research Park.

He cautioned, however, that related projects are beset with issues surrounding finding a suitable location to build, gaining planning permission and installing the infrastructure to carry projects out.

Dr Lawrence said: ‘[HIVE is] plug-and-play…we’ve already got the data loggers, all the infrastructure, weather stations, communications [etc.].

‘They can, on day one, start their programme, which saves between six months to a year of time.

‘At the other end when you’ve finished your programme, you often have to deconstruct your building and put everything back to where it started. Again, we’ve got processes where the whole thing can happen much more quickly and effectively.’

Sixteen platforms will be available alongside HIVE for researchers to construct pods of up to 125m³ enabling flexible testing of construction systems and performance.

‘We can whack [buildings] up very quickly because the foundations are already there and when the experiment’s finished take it down and put something else up straight away – all of the infrastructure is there,’ said Dr Lawrence.

Carbon footprint:

The construction industry is widely acknowledged as having a considerable carbon footprint, a situation that Dr Lawrence is keen to redress.

‘The construction industry is responsible for half of global emissions, that’s an enormous amount and big target to hit,’ he said. ‘Let’s try and hit it, let’s both improve its on-going performance but also…make a building with a lower carbon footprint actually embedded into it.

‘So instead of putting in lots of steel and concrete, let’s put in materials which have much lower environmental impact, or indeed where the energy input into building [a structure] is less than the energy stored within the fabric of that building if you convert it into carbon dioxide.’

 Inside the HIVE:

• a hygrothermal cell to evaluate movement of heat and moisture through buildings, energy efficiency, air tightness and acoustic efficiency;
• a double-height and width cell that can be used for flexible construction design, testing façades, internal walls and floors, together with a strong roof, allowing for load testing;
• a flood cell that can be used for testing the resistance of construction materials to high water levels or for testing technologies that resolve the effects of flood damage;
• a bladder cell that enables the testing of construction panels against horizontal loading such as wind load and geotechnical forces.