Repair or Rebuild: Part II

Office Building Environmental AnalysisIn a previous article I dug into the first half of the Midcentury (un)Modern study conducted by Terrapin Bright Green that raised the question of what we should do with a group of over 100 energy deficient New York office towers built between 1958 and 1973. Once it became clear that a series of unique conditions were making this particular group of poorly performing buildings unadaptable the question became if there was a positive scenario for demolition and reconstruction. There could be a number of ways to stimulate or incentivize the replacement of these buildings to coax building owners into action–essentially paying them to make a change. However, even though it’s possible, is it positive? Is there a process that creates a new building while providing a net gain? Not only a monetary gain for the city, but a net gain in things like energy use, water consumption and air quality.

Terrapin’s design team held an “ecocharrette” for possible parameters of a suitable replacement building for these troubled towers, gathering seasoned professionals from across the building industry to put their heads together for a highly efficient building. In order to make monetary sense, the building also had to reach the level of “Class A” office space, defining the zenith of market demand. For those hoping for a zippy rendering for what this new age building may look like, there isn’t one. This research exercise was more about trying to establish construction criteria that could be modeled rather than doing a theoretical architecture project for a specific site.

I’ll Take a Green One, Please

Energy Model HVAC SystemStarting from the exterior, the team needed to balance goals of sustainability with attributes of market demand–a common dilemma of the design profession, especially in places like New York City. Realtors will consistently push for floor to ceiling glass, marking the view as preferable to potential tenants, but the thermal value of a solid wall is much higher (this is yet another example of sustainability not yet commanding economic value). More glass may be good for sales, but less good for energy efficiency.  The team chose a triple-glazed envelope with configurations of an 18″ or 30″ solid sill beneath. The southern side of the building would incorporate external sun shades to mitigate solar heat gain.

As the organs of a building, the mechanical systems have an important role to play on the overall efficiency of a building. After testing four different system configurations for the distribution of heating and cooling throughout the building the design team settled on the underfloor air system with an 18″ sill as the most cost-effective solution for a high efficiency system. The test case also incorporated biophilic elements like sky gardens in order to distribute access to green space vertically throughout the building. Terrapin employed a relatively young metric for their greenspace known as a Green Area Ratio, which measures the total amount of horizontal green surfaces as a ratio to the footprint of the site. In countries like Indonesia where forests are scarce, projects can be required to achieve Green Area Ratios of over 2.0–effectively doubling the amount of natural surface from a virgin site. In this case, through the use of green roofs and sky gardens the design team reached a ratio of 1.05 (or 105%).

When all was specified and modeled, the final tally had the new building using 48% less per person than the existing case, but its still a building that is holding 44% more people. As we covered in Part I, the big question isn’t just efficiency but whether or not we are using less energy over all. The answer turned out to be an astounding “yes” with the whole tower still using 5% less energy than the one before it. On top of that it would also collect every drop of rainwater that fell on the site (an estimated 549,000 gallons) and use it for flushing toilets, irrigation and cooling tower make-up. Overall the design case used half of the water of the building it was replacing.

What About the Embodied Energy?

Another piece of criteria that had to be tested was the energy that had already been used to make the building that is currently there. In many cases, this bolsters the argument for building reuse. In this case, however, it wasn’t enough. Terrapin notes that “over it’s 46-year operating life, the amount of energy consumed is already equivalent to having rebuilt it 5.8 times.”  Put another way, the inefficiency of the building left it paying for it’s own embodied energy every 8 years. As a result the new structure would repay the debt of demolition and former construction in approximately 16 – 28 years (well below the life of the building).

It is important to remember that despite the fact that the design standard of the building was termed as “LEED Platinum, then a little bit more” it did not empty the entire arsenal of existing, let alone conceptual, tactics for a more efficient building. Things like on-site power generation or ice storage tanks found at One Bryant Park would be icing on the cake, pushing the efficiency of the building even higher.

The Future of Existing Cities

Data like that found in this study can help us assess our existing city stock with more than just sweeping generalities, especially in mature cities where increasing amounts of capital and energy are at stake. The testing and modeling of our existing buildings to the levels utilized in Midcentury (un)Modern is still in its infancy, but as more buildings (and infrastructure) get older we need to become better at weighing the options for improving them. When the topic of an increasing population (sometimes even eclipsing the problems normally associated with the environment) the proposal becomes even more alluring. With forecasts pointing towards an increasing population, studies like this can help reveal what sites are best suited to make way for more space required by more citizens.

At the same time, there are some things that the study admittedly does not look at. Increasing the capacity of any site by 44% brings ramifications to the neighborhood at the city at large in the form of infrastructural demand. Further study would be required to determine whether or not the grid could handle increases in pedestrian traffic, street congestion and subway ridership. The study also did not look at the redevelopment of residential buildings instead of new office space given that the two are much more difficult to compare. Variables like the depth of apartments, types of occupancy, operable windows, egress and ceiling height all make living and working unique animals in the eyes of the building and zoning codes, but in an increasingly digital age one has to wonder whether or not square footage devoted to living will be in greater demand than the corporate workplace.

Image Credits: Courtesy of Terrapin Bright Green