Breaking through the Glass Curtain Wall to Net Zero Energy

Building Efficiency

Breaking through the Glass Curtain Wall to Net Zero Energy

Mike Rovito for Zondits, August 15, 2013

Paul Torcellini of the National Renewable Energy Labs (NREL) gave a presentation last year on net zero energy (NZE) buildings to folks from NYSERDA, the NY Department of Public Service, consultants, and others who buzz about in New York’s efficiency circles. Towards the end, he drew a graph. Along the x-axis were energy savings, and along the y-axis were costs. A rendering of his hand-drawn graph is reproduced below.

glass-curtain-wall-graph

We have, in the upper right quadrant, higher costs and higher energy savings: better stuff, to borrow the language of the presentation. Energy engineers like me are most familiar with this quadrant and its LEDs, super-efficient chillers, and VFDs.

In the upper left quadrant are higher costs and worse energy performance. In Paul’s telling, this is the realm of architects and glass curtain walls. It is aesthetics and the like, the things that undercut efficiency and add to the bottom line.

Below that, in the lower left quadrant are owners, who sacrifice long-term energy performance for first cost. Value engineering leads here, the graveyard of efficiency.

And then there is the lower right quadrant. This is the mystical land of lower costs and greater energy savings. Measures do exist in this quadrant. For instance: don’t construct a building with floor to ceiling windows! Glass is expensive. It also increases energy use. If you size your windows thoughtfully, you can save costs relative to the average building and save energy.

It may be old hat to some, this idea that you don’t have to pay more to save more, but it’s a powerful one – and one that is fundamental to NZE. The NREL went about systematically plotting the cost/energy-use frontier – the lowest-cost building possible at each point along the energy-use spectrum. They did this by using an optimization model that played around with the various elements of a building. That parabolic dotted line shows, roughly, that frontier. And research my team and I have done on behalf of NYSERDA suggests that you have to follow this line or something similar to achieve energy consumption levels consistent with NZE.

If we know the recipe for a NZE building – and if it’s no more expensive than a normal building – why, then, aren’t all buildings NZE? The simple observation that nonresidential NZE buildings number fewer than a hundred in this country indicates that something is missing from the instructive, but incomplete two-dimensional framework. In fact, what’s implicit and not shown is a whole dimension: aesthetics – or, more broadly, non-energy building performance. Non-energy performance characteristics such as aesthetics, comfort, and functionality aren’t confined to the upper left quadrant as in the above graph. Rather, they permeate all quadrants and every decision an owner/architect team makes. After all, buildings aren’t made simply to consume energy.

So it may be more useful to think of buildings in three dimensions, not two. And when you do this it becomes obvious why people don’t ride that parabolic curve, with its negative incremental costs. In the NREL model, non-energy performance was a floating variable, one that was given no weight. But in reality, non-energy performance almost always trumps energy performance. This hierarchy is baked into the design process; the owner and architect settle on a design, and then the engineers are called in to design the energy systems. To put it into the terminology of the three-dimensional framework: the owner and architect pick a spot on the dimension of non-energy performance and leave the engineers to squeak out as much energy savings as possible with the money that’s left. The engineers are stuck in a two-dimensional world, a single plane in which to move, the plane selected by an architect who gave near zero consideration to energy. And without the freedoms of the third dimension, the engineers lose the ability to tap into most negative incremental cost measures, which often involve fundamental aspects of design. Thus, energy engineers – and the entire efficiency community – are banished persistently to the upper right quadrant in the two-dimensional framework.

Understanding this reality is somewhat depressing, but also deeply instructive. NZE buildings must exist at least partially in the lower right quadrant; the evidence – most notably, inventories of design features in existing NZE and high performance buildings – suggests that they cannot be achieved by “better stuff” alone. The building must be thoughtfully oriented and laid out. It must have appropriately sized and shaped windows. There must be fewer enclosed offices and more open floor space. These sort of design choices (and those are just a few) lead to lower heating, cooling, ventilation, and lighting loads and, consequently, smaller and less (read: cheaper) energy-consuming equipment than one would purchase otherwise. Owners still need to buy the best lights tied to daylight dimmers and occupancy sensors. Their heating and cooling must be top notch, with fans and pumps driven by efficient motors with VFDs. But on balance, this whole package doesn’t cost all that much more than a typical building. In some cases, research has shown, NZE buildings can even cost less.

This is a powerful observation. It says that we don’t lack the money. It says that we don’t lack the technology. What we lack are owners who both understand this reality and who are interested in pursuing it. Glass half full: we can make people understand. We can show them that it is not hard and that it is not expensive – and understanding alone would undoubtedly increase the volume of high performance buildings being built. Glass half empty: NZE takes real tradeoffs. People like floor to ceiling windows; owners install them because they sell. So what is really needed to make NZE mainstream is for owners to stop marketing comfortable, practical, attractive buildings and to start marketing comfortable, practical, efficient buildings. How do we do that?

I’ll leave that to the marketing folks. It’s going to be a challenge, but not to worry. In the meantime, we in the efficiency community can keep chugging along: the vast majority of energy use is and will be rooted in the existing building stock, which is stuck, primarily, in two dimensions. There is still plenty of “better stuff” out there that needs to be engineered.


Michael Rovito is a senior consultant with ERS where he works with utilities and state government agencies across the country to promote energy efficiency. He has experience in program design, implementation, and evaluation as well as market, technical, and policy research. His previous experience is with the NYC Mayor’s Office of Long-Term Planning & Sustainability.