While the world still contends with the largest global pandemic since the Spanish influenza 100 years ago, New York City (NYC) is starting to emerge from lockdown, with restrictions that began in mid-March slowly being lifted over the summer.
Many in the architecture, engineering and construction (AEC) industry are wondering how our work will resume, what construction might look like post coronavirus and what is its relevancy. It will take some time before these questions can be fully answered, but we can say that construction is indeed essential. As this virus has demonstrated, people will continue to need hospitals, research laboratories and healthcare facilities. Maintaining utilities including power, water, telecommunications and data centers as well as logistics and transport networks is vital. And as from the dawn of time, human survival relies on consistent access to food, clothing and housing.
While the reopening, occupancy, use and development of museums, universities and retail establishments currently deemed nonessential remains to be seen, construction ofnew essential facilities and refurbishment of existing ones will continue.
However, the manner in which we move forward with design post coronavirus remains for us to determine.
As our remote working from home on design projects has pushed forward, a portion of the world’s manufacturing has reduced. Global carbon emissions have dropped 5.5% compared to 2019, air pollution has improved, and oil prices have briefly plummeted into negative values.
Has the Covid-19 health crisis indirectly jumpstarted the AEC industry into a designing with climate change in mind? And what changes to our design will be provoked by this pandemic?
Dovetailing with coronavirus, recent code changes have begun to force the design and construction industry to consider how our work can positively impact climate change; specifically, regarding carbon neutrality, energy efficiency and bird safety in our built environment.
Several initiatives passed in NYC over the last year look particularly at buildings to help achieve sustainable design goals, namely, Local Law (LL)97 passed in May 2019, Local Law (LL)32 / New York City Energy Conservation Code (NYCECC) 2020 in effect from May 2020 and the Bird Friendly Materials Bill enacted in January 2020.
Globally, buildings generate nearly 40% of annual greenhouse gas emissions due to the use of large amounts of energy for heating, cooling and lighting. This is also due to the use of energy compensating for inefficient, leaky existing buildings that lose heat in the winter and cool air in the summer through old windows or inadequate insulation. In New York City, nearly 1 million buildings generate about 73% of the city’s emissions.
NYC’s zoning code sets limits on building heights, density and retail space, aiming to preserve daylight, allow for communal spaces, plazas and parks and promote a healthier city. It dictates where and how new buildings can be constructed within the existing building fabric. As available greenfield construction spaces decline, and code changes focus on sustainability, more emphasis will be placed on the question of how to upgrade, refurbish, reuse and reimagine the existing building stock.
It is estimated that 2/3 of the building area that exists today will still exist in 30 years. Currently, building renovations affect less than 1% of the building stock annually; therefore, a significant increase in the rate of existing building energy efficiency renovations (and the generation and procurement of renewable energy) will be required if NYC is going to reduce emissions.
To address this, last year New York City passed the Climate Mobilization Act known as Local Law 97. Currently, the most ambitious law in the world to tackle emissions from existing buildings, it will impact over 57,000 buildings across the city with the goal of reducing building-based emissions 40% by 2030 and 80% by 2050 (compared to a 2005 baseline) through retrofitting.
Carbon emissions, or the “carbon footprint” of a building, is measured by totaling the carbon dioxide emitted into the atmosphere during the production of the energy that is consumed by a building to heat, cool, light and power the activities of its occupants.
Buildings over 25,000 ft2 must meet annual whole-building carbon intensity limits based on occupancy group and space use. Building owners must submit yearly emissions intensity reports demonstrating compliance or pay substantial fines ($268 per metric ton if emissions exceed the stated limits).
Building upon LL97 and emissions reduction is the enactment of LL32 and the adoption of the 2020 NYC Energy Conservation Code. The new ECC requires construction to be built to more stringent energy efficiency standards targeting 20% energy reduction over the previous ECC. With it, NYC is striving towards net-zero energy for all newly constructed buildings by 2030.
In the new 2020 NYCECC, building envelopes are limited to perform 15% above the code minimums when energy trade off modeling is used to meet the energy code. U values (measure of thermal transmittance) are more stringent for all fenestration, solar heat gain coefficient (SHGC) values for center of glass are limited to 0.36 and detailing will be scrutinized to reduce thermal bridging and eliminate losses.
The quantity and assembly of the façade systems will impact the efficiency of the heating, cooling and daylighting systems. From an energy point of view and the fact that NYC is in a heating dominated climate, the U value typically becomes the strongest driver for the design. Adequate light as measured by visible light transmittance (VLT), reducing solar gains and limiting air infiltration are also important.
Glazing assembly and material selection is closely coordinated with our mechanical engineering and whole building energy modeling colleagues to look at building energy performance in a holistic way for all systems. All energy savings measures are included, namely: HVAC, lighting, occupancy density and schedules, in addition to façade performance.
The ECC allows for tradeoffs between systems when the façade is not meeting prescriptive window-to-wall-ratios, U values, or SHGC values. By creating a whole building energy model, the building performance can be considered allowing for all systems and positive effects for the façade (e.g. free cooling or heating in the shoulder seasons, positive solar heat gain in the winter, etc.) To obtain a building permit, models must demonstrate that the building performs equal or better than the baseline building.
One project example which demonstrated improved energy performance in an existing building is the iconic Time Life Building at 1271 Avenue of the Americas in Rockefeller Center. Completed in 1958 by Harrison, Abramovitz, and Harris, the building is 48 stories tall (587 ft) with a cladding area of 456,000 ft2. Working in collaboration with Pei Cobb Freed & Partners, Arup provided engineering services in Façade, Structures, MEP, Sustainability, Acoustics and Energy Modelling.
The vision glass areas of the existing façade limited ingress of daylight and provided narrow views to the exterior. The single glazed façade system and induction units along the perimeter, combined with the un-insulated air supply risers on the building exterior lead to very high operational costs. The retrofit adopted a performance-based design approach to develop a new double-glazed façade that improved the VLT, U value, SHGC and reduced the air infiltration rate, thus minimizing the whole building energy consumption.
The existing façade was removed and replaced with a curtain wall, allowing for a continuous, insulated building envelope line. Vision areas were increased for better views and connection with the outside such that daylighting levels increased by 28%. The existing single glazing was replaced with high performing double glazing with a Guardian SNX 62/27 low e coating on surface 2 and stainless steel warm edge spacers to achieve a 42% improvement in the overall U value and a 31% improvement in SHGC. A thermally broken, structurally glazed unitized curtain wall achieved 73% improvement in airtightness. Additionally, the opaque portions of the reclad were insulated to improve the overall U value by 64%. Looking at the façade in conjunction with MEP systems in the whole building energy model, the reclad yielded an energy savings of 30% and energy cost savings of 21% over the existing building.
In April 2019, NYC Mayor Bill de Blasio made global headlines when he warned that upcoming legislative will “ban the glass and steel skyscrapers that have contributed so much to global warming”. The legislation he was referring to led to the enactment of the 2020 NYCECC. In that speech, the mayor does not “ban” any materials but does mention several buildings as examples of how glass-wrapped structures could be made energy efficient.
One such example is The Emma and Georgina Bloomberg Center, the first academic building on Cornell Tech’s new 12-acre campus on Roosevelt Island in New York City.
For that project, Cornell University, Morphosis and Arup worked together to push the boundaries of what could be achieved for a large-scale net-zero energy building acting as an innovation hub on an academic campus. The Bloomberg Center incorporates sustainability and smart building goals that meet the functional requirements of an advanced academic facility, while creating a building that is low carbon, energy-efficient, healthy and comfortable. Designed in accordance with the LEED NC 2009 rating system, the Center is LEED Platinum certified.
Arup provided multidisciplinary services including structural, mechanical, electrical and plumbing/fire protection engineering, acoustic and audiovisual consulting, IT and communications consulting, façade engineering, lighting design, security consulting and sustainability consulting for this 160,000 ft2 facility.
Energy-efficient design elements include a 40,000 ft2 roof-mounted photovoltaic system that is part of a campus-wide array of dedicated solar panels and ground source heat pumps that harness the constant temperature of the earth to both warm and cool the building. The building is also designed to be resilient against potential flood conditions and utilizes a rainwater harvesting system to reduce combined water discharge as well as potable water usage. Building loads were analyzed thoroughly and allowances for lighting and computers carefully planned to ensure MEP design and energy modelling assumptions were not overly conservative.
The building facades over the second, third and fourth floors are typically opaque, clad in bronze-colored stainless steel rainscreen panels and topped by a swooping lily pad-shaped roof. The system traps air between the exterior of the building and the elements to help regulate the internal building temperature. The panels feature three-dimensional disks cut into the metal panels with each disk rotated in different directions. The overall eye-catching and unique design is meant to mimic a waterfall that evokes the Cornell campus in Ithaca, with the tilt of the disks catching sunlight in interesting ways.
The façade design contributed towards the net zero energy goal by maintaining a very low window to wall ratio, achieving overall U values of 0.06 BTU/hr-ft2-°F with the use of large, unitized, insulated opaque façade panels and incorporating double glazing with a Guardian SNX 62/27 low e coating on surface 2, argon filled cavities and warm edge spacers.
The most recent façade related legislation enacted in NYC is the Bird Friendly Materials Bill which aims to reduce the number of birds colliding into buildings. In addition to all-glass buildings requiring large amounts of energy to provide heat, cool, light and power, highly transparent and reflective glass facades are also known to be dangerous to birds.
Over the last 40 years, North America has lost 3 billion birds (29% of the avian population) due to climate change, habitat loss, loss of insect prey and other threats. Window collisions are another major threat, with 600 million birds dying each year after crashing into glass surfaces. In NYC alone, collisions with glass affects up to 230,000 birds each year as they pass through the city along the Atlantic Flyway migration route.
Besides designing with less glass, birds can be protected by using screens, shutters, and shading devices that obscure the glass while still providing a view, or by using twodimensional patterns that birds perceive as actual barriers.
The Bird Friendly Materials Bill defines materials with a maximum threat factor of 25 or below as being “bird friendly” and mandate that these must be used on 90% of a façade up to 75ft above grade. Non-bird friendly materials are limited to 10 ft2 within any 100 ft2 area within this region. This provision applies to both new buildings and renovations of existing buildings when the façade is being replaced and is due to take effect in January 2021.
• Differentiating between texture, color and opacity to fragment reflections and reduce transparency
• Utilizing surface treatments, etching, fretting, UV patterning or opaque patterned glass to reduce transparency
• Using glass with external reflectivity below 10%
• Angling glass from 20° to 40° from vertical to avoid reflections from the sky
Connecting the goals of limiting emissions, increasing energy efficiency and keeping birds safe is the Solar Carve project at 40 Tenth Avenue. The 145,500 ft2 ten story office building is located on the Hudson River between the West Side Highway and the High Line at West 14th Street, Arup provided structural and façade engineering services along with acoustic and daylight consulting to the architects, Studio Gang.
The building takes it unique form by the allowable zoning line for the envelope and the incident angles of the sun path to carve out surfaces across it’s Southeast and Northwest corners. This allows the High Line access to sunlight, fresh air and river views and results in canted, diamond shaped glazing surrounded by vertical triangulated glass to create three dimensional facets articulating the carved tower corners. The angled facades also avoid casting glare onto the drivers on the West Side Highway and help to avoid bird strikes.
The low e coating for this all-glass building was carefully selected with both a very low SHGC and extremely low external reflectivity. The SHGC serves to both reduce solar gain from the exposed facades and reduce cooling loads. The low external reflectivity helps reduce collisions for birds along the Hudson River migratory route.
Early design studies looked at utilizing a more neutral low e coating in conjunction with an exterior frit that would assist in mitigating bird strikes. However, the client decided against exposing frit to the elements and selected a darker, highly efficient triple silver low e coating (appearing grey) to meet a SHGC of 0.23, a VLT of 38% and exterior reflectivity of 8%. The double glazing is comprised of Ipawhite low iron substrates with Interpane Ipasol 38/23 on surface 2, argon filled cavities and Chromatech Ultra warm edge spacers.
Solar Carve brings into question how to balance VLT, natural daylighting and electric lighting requirements with exterior views and sustainability. Do neutral low e coatings with high visible light transmittances continue to be aesthetically necessary? Can occupants accept darker all-glass facades with lower VLT that allow a building to be more energy efficient and help protect birds? Can the use of frits be eliminated and substituted with a move to printed interlayers to enable the glass to be recyclable?
In keeping with United Nations Sustainable Design Guidelines (UN SDGs) for a more sustainable planet and new NYC legislation to reduce carbon emissions, make buildings more energy efficient and keep birds safe, lies a huge opportunity to improve the performance of both our new constructions and existing building stock.
If the building facades of the future are to address these issues, the trend would be taking us to select glazing with lower SHGC, lower VLT, lower U values and lower exterior reflectivity. Alternatively, trade-offs with higher values could occur with lower window to wall ratios. In these ways, façades can contribute in a more robust way within the whole building energy modelling and offset the energy required of the mechanical and electrical systems. This strategy will apply both to new buildings and to recladding and improving existing buildings stock.
In tandem with smart material selection, we can also expect the integration of renewable energy sources into more of the façade area. Transparent building integrated photovoltaics (BIPV) can now generate 8% power conversation efficiency. For example, a 10,000 ft2 south facing vertical façade in NYC could generate up to 98,000 kWhr/year. Perovskite cells could potentially reach even higher efficiencies of 17%. If darker glazing generally becomes more accepted, energy generation could increase, thereby contributing to reaching net zero energy targets and helping to keep our avian neighbors flying.
With the move towards designing net zero energy buildings becoming codified, transforming buildings to ensure sustainable, energy efficient and safer futures in urban landscapes will become the reality.
This article was originally published in IGS Magazines Summer 2020 USA Special Edition: Read the full Magazine here for more thought-leadership from those spearheading the industry
Author: Tali Mejicovsky
Tali Mejicovsky is an Associate Principal at Arup and Façade Skills Leader across four façade groups in the Americas (Los Angeles, New York, San Francisco and Toronto). She has more than 20 years of façade experience around the globe, having worked on projects in Australia, Asia, the Middle East, Europe and America. With a background in design and structural engineering, Tali has expertise through all stages of design and construction and has presented and published widely on the discipline of façade engineering. Her project typologies have been wide ranging in scale and performance, including humidity sensitive art museums, laboratories and hospitals, retrofits, renovations and expansions of existing historic buildings and large transit hubs to standalone art pieces, handrails and canopies, one-off glazed jewels and temporary structures. With each project, Tali seeks to optimize the façade to dovetail with the architectural design intent, multidisciplinary performance requirements and client objectives.