CASE STUDY | METLIFE BUILDING
The Building:
Most everyone is familiar with the MetLife building in New York City. Sitting atop Grand Central Station, it is the terminus for Park Avenue. Design by Walter Gropius in collaboration with Pietro Bulleschi and Emery Roth & Sons, it was completed in 1963 and stands as a testament to modernist architecture.
The facade utilized a precast concrete unit with alternating infill precast panels to create the signature punched windows, precast fins and spandrels which are hung on a steel structure. As with most buildings from that era, it is brilliant in it’s design but does not meet the energy code requirements of today.
The Intervention:
When looking at how to approach retrofitting the exterior envelope of such an iconic building, there a number of different approaches that facade retrofits can take which are:
Replacement
Recladding
Overcladding
Double Skin.
When it comes to the preservation of a landmark building, like The Metlife Building, the first two could be argued as the most appropriate, although probably not the most financially feasible.
In this case study, we looked at hybridizing the overcladding and double skin techniques to create a unitized frame which mounts directly over the existing precast panels. The Metlife facade is constructed of a primary precast panel with integrated fins on both sides that alternates every other bay. Between these primary panels, secondary infills are set at the spandrel conditions.
Because the Thermalswitch BEX™ unit is designed to fit over the existing single floor unit, once the units are unloaded on a floor above, the existing glazing is removed and they are set via a custom horizontal slide and floor crane through the opening of the precast unit. The animation below shows the fully removal of the existing window and installation of the Thermalswitch BEX™ panel along with the new punched window with integrated trickle vents
The crew on the reclad floor are tied off and can set temporary ledges off the precast unit to receive and anchor the Thermalswitch unit to the precast facade. Once this is set, the rough opening can be reglazed with a new fiberglass frame that features an integrated trickle vent at the head to complete the recladding.
This overcladding only requires two floors to be vacated at a time; the loaded floor and the recladding floor. As the crew moves up the building the loaded floor becomes the reclad floor while the remainder of the offices above and below can continue to occupy the space until the reclad has reached them.
Customizable Approach
In this case study application, the Thermalswitch BEX™ panel is a single ply stretched ETFE foil to create a volumetric geometry and works as a double skin over the entire precast unit.
This double skin zone becomes a slightly vented, preconditioned cavity that enables the use of trickle vents to be integrated into the new punched window unit.
Possible Kinetics:
The concept behind the Thermalswitch facade unit is to create a double skin. The cavity in the double skin is a slightly vented, preconditioned cavity. that tilts away or towards the sun depending on the temperature by utilizing Nitinol wire. Unlike most applications where a current is run through the wire, in the Thermalswitch unit, the Nitinol is activated by the ambient temperature within the cavity.
This tilting action, along with the various venting components at the top and bottom of the unit, creates a convection current which will pull outside fresh air into the cavity and warm it as it enters the office space, or vents hot air out by drawing cool air from the building core.
Thermal Performance
The thermal analysis shows that simply replacing the existing glazing with a new fiberglass frame and IGU with a Low-E coating does not increase the performance of the enclosure a great deal. However, by creating a preconditioned, slightly vented cavity between the existing precast and the exterior (17.3°F) the overall assembly mediates the temperature gradient better than only replacing the glazed portion of the facade.
Before
After
PLAN | ISOTHERM
PLAN | FALSE COLOR
Daylight Analysis
Traditional standards on the Daylight Factor, as defined by the UK and North American authorities, ranges from 2% minimum and higher. The LEED scoreboard also offers 1 credit for all buildings that can achieve a minimum of 2% in 75% of all spaces which require regular visual tasks.
In the Metlife building, the original facade allows 3.01% DF, which still requires additional lighting some of the time. With the addition of the Thermalswitch facade, the DF is only slightly reduced in both the summer and winter orientations. Winter seeing only a 0.45% reduction and the summer a 0.875% reduction, which is above the minimum requirements. Overall, the recladding does not significantly reduce the daylight factor from the original design.
Before
After
Conclusion:
We chose the MetLife building as a test case for the a fully customized Thermalswitch BEX™ system with the potential for integrated kinetics in order to showcase the variety in design and the opportunities that architects could explore not only in renovations and facade retrofits but also new builds. The utilizing of architectural foils like ETFE in building facades will only push designers to explore the edges of what is possible. We are here to help realize their dreams while increasing the performance of building envelopes across the world.