For background details regarding this teleconference, and access to other segments, click here.
Presenters: Stephen Selkowitz and Dale Sartor, Lawrence Berkeley National Laboratory
Selkowitz: I will talk about NZE enclosures and daylighting, and Dale Sartor is going to talk about NZE HVAC solutions. Unlike some of the other presentations, this will focus more on examples of new technologies and systems that contribute to NZE laboratories rather than particular buildings. Within the building envelope world, I am going to focus on fenestration: glazing, framing, and daylighting. There's plenty more to talk about, with many interesting developments in cool surfaces, new insulation, better use of mass, etcetera, but that's for another discussion.
In terms of lab buildings, when looking at fenestration, it's critical to think about the space in the building rather than the actual whole building. There may be a tension between designing for the needs of occupants and/or for the needs of the experiments so that what you do in a lab where you are doing experiments that are light-sensitive or require tight temperature control might be completely different than in a lab that can accept variation in those conditions. But within a lab building in addition to the lab space you have office environments, support spaces like cafeterias and libraries, and circulation. The solutions you come up with here need to be tailored to those types of spaces.
From an energy point of view, we would like to talk about a performance goal for the envelope as a subset of a performance scope of the whole building, and that goal might be a net zero energy envelope. We can do that today with the fenestration part, although it's not so easy to do with the opaque part.
Classically, what you are going to do is minimize thermal loads, with the usual load-avoidance strategy such as minimizing heat losses, and minimizing solar gains. But there is both a plus and minus on the facade side. With glazing we have the ability to supply solar heat to the building in winter or other times when you need it due to high air exchange loads, and the ability to supply daylight which will offset electric lighting.
Although this is posed as an energy challenge, the real issues here are not only reducing energy use, but also dealing with thermal and visual comfort. We all have far too many examples of systems that may work right from an energy point of view but are clearly disastrous from a thermal comfort and visual comfort point of view. And I am going to argue that these are not exclusive direction: If you are doing the right things from an energy perspective and you are thinking about visual and thermal comfort, you can find solutions that meet both of these goals.
In designing a lab building we may too often be picking up our design cues from the world of class A office buildings with highly glazed facades. You really want to break the façade down into functional components; there probably should be opaque elements, and there should be vision components where the key issue is seeing out or maybe looking in, and then there's the daylight component. To try to use the same glazing and shading for all three of those makes little sense. So there's a great opportunity to distinguish these design and functional features architecturally.
Orientation is obviously critical. In almost every climate, orientation makes an enormous difference. And the other aspect of orientation is going from vertical to horizontal. When we are talking about zero net energy, we may be talking about using photovoltaics to supply electric power. But before we jump to PV as an energy source, for example for lighting, its instructive to do a comparison of the role of the window and skylight as a source of lighting, vs. the pathway of PV to electric power to light in a room. If you do that analysis you will find that windows and skylights are anywhere from four to 10 times as efficient in converting a unit of external sunlight to interior illumination. If you are putting PV on the roof to generate power for lighting during the day, and you are not doing daylighting, you are missing a big piece of the puzzle.
Glass types
Heating and cooling impacts of fenestration represents a large, complex topic, and I would like to just highlight the technology options. We do a lot of work here at the lab in modeling and measuring performance, and partnering with companies with emerging technologies.
So what's new? On the heat-loss side, it's technically straightforward these days to come up with the glazing that's essentially a net zero performer in the winter (although it may not be "cost effective").
A U value in the range of 0.2 and below (an R5 to R10 window) would generally be needed to reach this performance level. There are a variety of ways of achieving that performance level (coatings, gases, etcetera), but I won't get into the details here.
A designer needs to be careful about specs based on center of glass values vs. total window properties that include framing. You can get led astray with a glass-only value. A state-of-the-art, triple-pane, low-E, gas-filled glazing that has a good center of glass value but then is matched with thermally unbroken framing results in an overall window with mediocre properties. NFRC [the National Fenestration Rating Council] has software and rating numbers to help get consistent numbers for this. With DOE support we have developed software tools for this, the WINDOW and THERM software, which I know many of you know already use. These tools calculate the required properties for any fenestration system, including shading. (Download at http://windows.lbl.gov).
On the cooling side, the challenge is letting daylight in but keeping solar gain out in most cases. There are some excellent "spectrally selective" glazings out there with that separate the visible and near-infrared portions of sunlight. This can be characterized by a "light-to-solar gain ratio" term, LSG, that has some popularity. Typical tinted glazings are down around 0.5, and clear glazing is around 1. But good spectrally selective glass can admit twice as much light as heat and will have a light-to-solar gain ratio as high as 2.3.
In addition to LSG you can of course tune the absolute visible transmittance of the window anywhere from 3% up to about 75%. So there are a couple of parameters to choose from here. There are thousands of glass types to play with (LBNL maintains a library of data on 3,800 glazings) and assemble into a fenestration product that will meet almost any requirement.
Sometimes it's not good to have so many choices. We are often asked for guidance on the optimum glass area and the optimum properties. There's clearly no single answer here. Since we should consider day vs. night, winter vs. summer, clear vs, cloudy, etcetera, a single, static solution is not going to work ideally all the time. So, the solution we are promoting is to look more in the direction of "dynamic glazing" whose properties can change over time. And here we have got a couple of interesting new options.
Dynamic products
On the glass side itself, there's some emerging technology referred to as "smart glass." Electrochromic glazings have coatings whose solar-optical properties vary widely with a small applied voltage. Several manufacturers are in the market now, with more coming, and while the costs are pretty high now they are coming down. These will go from roughly 3% light transmission to 60%, with a solar heat gain coefficient that changes from about 0.09 to about 0.45. This provides interesting dynamic control that we have never had before.
Several manufacturers are now also offering thermochromic coatings whose properties change with temperature. You can also provide this dynamic control capability with various types of automated shading—for instance, interior and exterior automated and motorized blinds and shades. These options are not well-understood and used in the U.S. but they are widely used in Europe.
We have tested all these dynamic products at LBNL in outdoor test rooms and think they have great potential. We are working with owners and suppliers on building-scale demonstration projects as well. Most of these dynamic systems can be manually controlled or controlled automatically via sensors and the building BMS. We design controls not just for sunlight control but to optimize daylight levels and control glare from the sun and sky.
Sensors and controls
I should comment on sensors and controls for these smart systems. I am a believer that we should move in the direction of better sensors and controls, but acknowledge that they aren't consistently reliable today, but they ought to be. I would be nervous about specifying a sophisticated control system in small spec office building. But if you are working in a lab environment in a high-tech building environment, you are in the ideal building where you should have smart capable people who understand and think about and worry about controls issues, and can calibrate and commission systems and make them work.
You also have to look at development over time. The technology suppliers are doing a better job, the construction and commissioning community is becoming more adept at addressing "smart building" systems, and I'm optimistic that these systems will someday be as reliable and robust as the sensors and controls in our cars.
Today we are already seeing more examples that seem to be working pretty well. We worked five years ago with the New York Times on their headquarters in New York, a 52-story, 1.6 million-ft2 building, which implemented automated dimmable, addressable lighting throughout the building and automated shading, which seems to be working pretty well. We are going back to the building to measure energy performance, system operation and occupant response and should be able to report results in the next 18 months.
So there's a huge set of issues around system integration in design, construction, and commissioning. They are difficult but solvable challenges. We are very interested in working with any of you that have good examples or good challenges in this area. We have continued support from DOE and others to help manufacturers and early adopters push the technology forward.
Software tools
My last comments focus on tools for decision support. Again, courtesy of the DOE, three or four simulation tools are available at no cost. WINDOW, THERM, and Optics tell you what the properties of a fenestration system will be. They now include a wide variety of shading systems and within the next year, we will have hundreds of shading products fully characterized in the database.
Radiance is a daylighting software tool that will work off the same materials database to help designers understand the daylighting impacts of optical technologies and innovative design solutions. It not only calculates light levels from which energy use can be analyzed but it also provides detailed information about the spaces from which glare and comfort can be analyzed, and realistic imagery of the appearance of the space which may be useful in fine-tuning design elements.
For early design, we built a tool called COMFEN, that does a room-based analysis of building facades include energy, peak cooling, daylight, comfort, carbon, cost, and so on. It uses EnergyPlus as its underlying calculation engine, but it features a user-friendly interface that allows architects to quickly do trade-offs and optimization on all of the key fenestration design variables at the level of the space.
And then there are further developments with EnergyPlus, DOE's whole-building design tool. By the end of 2011 there will be a new publicly available version with a good interface that will fully implement all the HVAC capabilities and can import an architect's design via a BIM file, using an IFC/Buildingsmart file from any CAD vendor that exports those files.
Finally, one of the questions with all tools is, are they any good? Do they appropriately represent what goes on in the real world, and thus provide useful design guidance? Increasingly there's good data coming out of measurement and verification programs and other building measurement projects that is helping to answer this question.
In the case of thermal and daylighting performance of façade systems, we have a test facility at LBNL that has been used in several projects to field test high-performance façade systems in fully instrumented side-by-side rooms. And we have some new funding from DOE to build eight new "integrated systems" testbeds. These are being designed now by a team led by Stantec. They will be operational in about a year, and will feature completely changeable façades, with flexible HVAC and lighting systems to test all the integration issues we talked about. They can also include occupant effects in the spaces if desired. We think these will be very useful in learning more about the kinds of challenges we are facing in state-of-the-art buildings.
Five HVAC strategies
Sartor: My role here is to tie together some of the key concepts in terms of efficiency in wet labs that are typically three to eight times more energy-intensive than other commercial buildings, and HVAC dominates these loads. I am going to cover five keys to success. But I want to preface this by mentioning the importance of benchmarking and not just calling a laboratory green, but quantifying and setting targets, then providing feedback through the design, construction, and operations phase. The Laboratories for the 21st Century program (Labs21) provides tools to help set targets and report actual benchmarks during operations. The more owners that use these tools, the more robust the database and tools, and the better information the design community will have in the future.
- Scrutinize the air changes. The first key concept is to scrutinize the air changes. We shouldn't assume that the thermal loads are the drivers for air changes; it is rarely actually true. And we should question when 12 air changes per hr is safe and six or lower is not. It's actually much more important to design for safety in terms of how the air flows rather than the number of air changes. Most of the Labs21 community has dropped to no more than 6 air changes, and the most aggressive have dropped to 2 to 4 ACH with sophisticated monitoring and controls.
- Taming the hoods. The second key concept is taming the hoods. Each hood accounts for the approximate energy consumption of three houses. We want to reduce the size and number of hoods to that actually required, and make them very easy to add and remove. In that way users are not motivated to over-provision and hoard resources. Typically the number of hoods in a lab just keeps increasing until we run out of air, where in fact a lot of those hoods are underutilized or are being used for inappropriate storage. We want to consider high-performance hoods and then use VAV as well to minimize the airflow through those hoods. Hoods should almost always be closed for safety and efficiency. Where users can't be counted on to close the hoods, we can use automatic closure systems. The overall objective is to improve safety and remove fume hoods from being the driver for air flow.
- Drop the pressure drop. The third concept is to drop the pressure drop. Up to half of laboratory HVAC energy use is for fans. The question is how low a pressure drop can we go to? We should move from designs of about 1.8 W per CFM to more like 0.6 W per CFM though techniques such as good duct design and low face velocity filter and coil selections.
- Get real with plug loads. The fourth concept is to get real with plug loads. Here we want to measure actual energy use in similar labs. We did this exercise for the design of LBNL's Molecular Foundry Lab, and we were able to save energy and first cost. "Right sizing" reduced the first cost by 4% or $2.5 million. This allowed us to implement additional sustainability measures that garnered us a LEED Gold rating.
- Just say no to reheat. The last key concept I want to mention is just saying no to re-heat. Lab loads have a huge level of diversity, and it's quite frequent that there will be one or two zones that have a high internal load, maybe even exceeding the designer's expectations, while the rest of the zones have internal gains less than that found in an occupied office. Often the equipment is present, but it is not on. The one or two "hot" zones drive the supply air temperature down, in which case all the other zones have to be re-heated. It is not uncommon to find the boiler to be the largest cooling load during typical cooling operation. The best tools we have to just say no to re-heat is to separate the cooling systems from the ventilation systems.
Hopefully these five key concepts will help to understand some of the great design features that were discussed in the projects that have been presented. For further information on these and other design techniques see the tools and resources available in the Labs21 Tool Kit.
