Building Envelopes: A Take on Three Technologies
As frequent readers of HEALTHCARE DESIGN can attest, the “look” of hospitals has changed radically over the past 10 years—perhaps no more so than in their exterior appearance. The gray monoliths of yesteryear are no longer with us (or at least not as prevalently). Hospitals today shimmer, gleam, swoop, display colors, and even change color throughout the day. What's behind building envelope technology, and where might it go from here? Addressing these questions is T. Brett Roberts, Anshen+Allen's director of technical design, reviewing developments in glass façades, cladding technology, and air handling in a recent interview with HEALTHCARE DESIGN Editor-in-Chief Richard L. Peck.
Richard L. Peck: One of the most striking recent developments in the field has been the extensive use of glass on the hospital façade, on par with commercial buildings over the past few years. Your comments on that?
Roberts: We've seen a lot of evidence-based design studies indicating that not only views but also availability of natural light aid in the healing process, particularly in terms of reducing length-of-stay. Unfortunately, more vision glass results in increased solar heat gain which, in turn, results in greater energy consumption. Luckily, we have high-performance glazing that is both insulating and uses low-emissive coatings, screening out UV radiation. In fact, many state energy codes mandate the use of insulated glass. The problem is that this is a big cost concern for project sponsors—insulating vision glass is much more expensive than monolithic glass. This is where you have to go to life-cycle cost analysis, showing that in five to eight years, the higher-cost glass pays for itself. And in the healthcare field, where many project sponsors own their buildings and see them more as long-term investments, they understand the value of a decision such as this.
Peck: Aren't there design elements that can modify solar heat gain, such as sunscreens?
Roberts: Yes, façade consultants model our designs, do a close analysis based on the orientation of the building, the size of openings, and so forth, and come up with data for solar heat gain. In this way we can best orient and position the sunscreens to shade the glass and reduce solar heat gain. Sunscreens are also used as design elements to add visual depth and complexity. Like insulated glass, sunscreens cost money. By proactively working with our mechanical engineering consultants and armed with our solar heat gain studies we can, early in the design process, establish a more economical energy budget which, in turn, allows us to downsize mechanical systems. For example, we are currently designing a large hospital in San Francisco that has vision areas of 88 square feet per patient room, while using a mechanical system that is 50% smaller than one in an average U.S. hospital. From a sustainability perspective, that is especially significant, when you consider that a hospital is a 24/7 facility.
Peck: Would you discuss some technological modifications of structural glass, such as fritted glass and dichroic glass that change color throughout the day?
Roberts: Ceramic frits have been used for the past 15 to 20 years and can be used for opacifying, coloring, and even patterning glass. Using silk-screen technology, frit designs can be customized to reduce solar heat gain while permitting views to the outside and blocking views from the outside in, a situation that is reversed at night when interiors are illuminated. As for dichroic, we are using it to give life and sparkle to an exterior, allowing a façade to change its appearance throughout the day and bring prisms of light into the interior spaces. Owners love it. Interestingly we're using it in one of our hospital designs and, even though we're in the process of substantial value engineering, the dichroic glass is off the table. The owners see it as the signature for that building.
Peck: What about developments in cladding materials? Anything to note along those lines?
Roberts: We're seeing a lot more acceptance of unitized façades right now. With curtainwall technology, you're hanging façade elements of all kinds off building slabs and structure. Rather than building them stick by stick, we unitize the cladding into prefabricated modules one floor high and 5 to 10 feet wide. And these can incorporate all kinds of materials—glass, stone, aluminum, anything you can hang off a mullion. You can weave different materials and effects such as sunscreens and lighting into a façade, adding to complexity and visual interest, without changing the underlying structure. These units, being shop-fabricated, have better quality control than site-built components and are thoroughly tested to withstand the worst expected weather conditions without leakage or catastrophic failure. Moreover, during the construction phase, unitized construction can take two or three months off the schedule, often saving as much money as you would from years of value engineering. Interestingly, the Empire State Building in New York was constructed in this way, obviously using much heavier materials, but completing the project in an unbelievably short period of time—one year and 45 days, to be exact, including Sundays and holidays.
Peck: How has building envelope technology contributed to air handling in these large facilities?
Roberts: In addition to what I already mentioned about designing a façade for solar heat gain, I think architects these days are better at understanding the interplay between fenestration—views and light—and energy input. It sounds obvious, but it's actually a really complicated design problem and, unless an architect was very motivated to design an energy-efficient building and try equally as hard to sell it to an owner, it was just easier to utilize conventional HVAC systems. Nowadays, energy is more and more expensive; owners see the prudence of spending money on a design to save money on building operations. In addition, anyone who has built a new hospital lately knows all too well how much space HVAC systems require and how difficult they are to coordinate. It's not hard to understand that a smaller, more efficient mechanical system can often be easier to install and require less building area.
There is a technology that is very common in Europe that makes a lot of sense: the double-skinned envelope. The structure has two façades separated by as little as six to eight inches, with air rising between them naturally by convection, and vented out the top. Solar convection drives ventilation in the warmer months and acts as a thermal blanket in the winter months. Admittedly, this works best for rooms of particular size and predictable utilization—a large board room with groups of people coming and going make temperature control more difficult. But it still can be an option in many cases. In one such project completed by our London office for the University of Manchester, a 30% savings in energy has been achieved by using a double-skin façade.
The problem in healthcare is twofold: First, the medical profession is concerned about infection control, which has meant, from a regulatory standpoint, that all ventilation air in a healthcare facility must be 100% outside air and HEPA-filtered, period. Second, these code restraints discourage change. We could benefit from a look at many government standards and allowing design professionals to meet performance standards, rather than just complying with prescriptive standards. The problem is compounded by the fact that, as projects go, we just don't have the time or the fees to propose too many innovations, absent political leadership, and owner endorsement. For many years, America has gotten away with ridiculously cheap energy and has accommodated inefficient and expensive-to-operate mechanical systems. The energy cost situation has been changing of late, and this may eventually lead to code revisions and newer approaches to building; a lot depends on political leadership. As things stand now, though, Europe is far, far advanced compared to the United States when it comes to building envelope technology. HD