Elemental is proud to announce that it’s award-winning historic reconstruction of Shepard Hall at The City College of New York is included in the current exhibition on view at the Center for Architecture in New York City as part of the month-long celebration Archtober. The exhibition explores how critical choices and consumption patterns of professionals and building occupants can make positive energy changes in our cities. Shepard Hall was selected as an exemplar of sustainability in historic reconstruction. his is particularly evident in considering the use of Glass Fiber Reinforced Concrete (GFRC) as the primary reconstruction material, in lieu of other materials.
The project’s 72,000 units of replicated terra cotta – the largest terra cotta replacement project in the world – yields an embodied energy savings by using GFRC of approximately 29,880,000,000 Btu or the equivalent of about 207,000 gallons or about 4,900 barrels of #6 oil when compared with cast stone and approximately 57,600,000,000 Btu – the equivalent of about 400,000 gallons or about 9,500 barrels of #6 oil – when compared with terra cotta.
In addition, in considering just the energy savings in transportation of the much lighter GFRC, the 72,000 units of replicated terra cotta, the savings in the weight of material that must be fabricated, transported to the building, lifted and installed is 14,400,000 pounds – or 7,200 tons.
Here is how we arrived at the findings in savings. Information on the embodied energy of various materials is from the Handbook of Energy Use For Building Construction prepared for the US Department of Energy by Elemental’s Carl Stein and the late Richard G. Stein:
EMBODIED ENERGY and WEIGHT OF MATERIAL COMPARISON
The analysis examines two alternative systems for replacing decorative, cast masonry units – thin shell glass fiber reinforced concrete and cast stone. Cast stone is used for the solid alternative because there is limited embodied energy data available glazed terra cotta, the original material and, at other buildings on the CCNY campus, cast stone has been used to replace deteriorated terra cotta. Note, however, that structural facing tile – a clay-bodied vitreous-glazed unit masonry product that is similar in composition to glazed terra cotta – has an embodied energy of about 860,000 Btu/ft3 as compared with that for precast concrete which is approximately 318,000 Btu/ ft3
The exterior reconstruction of Shepard Hall was the first large-scale use glass fiber reinforced concrete (GFRC) – thin shell units for historic preservation. This greatly reduced the quantity and weight of the replacement cladding as well as achieving a number of technical goals such as accommodation of thermal movement
Currently, more than 65,000 damaged terra cotta units have been replaced. When complete, the total will be approximately 72,000 units. As a frame of reference, GFRC (Glass Fiber Reinforced Concrete), with an average wall thickness of ¾” is compared with cast stone (precast concrete) having and average thickness on 6” including the complex molding and sculpture.
Embodied energy in precast concrete is 318,000 Btu/ ft3.
Average face area per unit is approximately 3 ft2
Volume of GFRC is 0.19 ft3
Embodied energy for GFRC is approximately 60,400 Btu/unit
Volume of cast stone is 1.50 ft3
Embodied energy for cast stone is approximately 477,000 Btu/unit
GFRC saves approximately 415,000 Btu/unit (average) when compared with cast stone.
Note: this does not include the embodied energy in the polymers and matakaolin that would be added to both materials, increasing the embodied energy savings for GFRC; however, it also does not include the Alkali Resistant glass fiber reinforcing (approximately 4½% of the total weight) which would apply only to the GFRC. If the embodied energy in the glass reinforcing is similar to that in conventional glass fiber, it would be about 6,500 Btu/pound or about 9,000 Btu per unit. In other words, even discounting the fact that there would be significantly more polymer and metakaolin in the cast stone, the addition of about 9,000 Btu of reinforcing results in the saving of about 415,000 Btu of concrete
The 72,000 units of replicated terra cotta for the entire project yield an embodied energy saving for GFRC of approximately 29,880,000,000 Btu (the equivalent of about 207,000 gallons or about 4,900 barrels of #6 oil) when compared with cast stone.
Using the embodied energy for structural facing tile to represent that of glazed terra cotta gives the following analysis:
Difference in volume of concrete between GFRC and terra cotta is approximately 1.0 ft3/unit. (The cellular construction of the terra cotta body allows it to made with somewhat less volume of material than with cast stone
Volume of GFRC is 0.19 ft3/unit
Embodied energy for GFRC is approximately 60,400 Btu/unit
Volume of terra cotta is 1.00 ft ft3/unit
Embodied energy for terra cotta is approximately 860,000 Btu/unit
GFRC saves approximately 800,000 Btu/unit (average) when compared with terra cotta
The 72,000 units of replicated terra cotta for the entire project yield an embodied energy saving for GFRC of approximately 57,600,000,000 Btu (the equivalent of about 400,000 gallons or about 9,500 barrels of
#6 oil) when compared with terra cotta
Weight of Materials:
Although not directly convertible to energy quantities, it is also instructive to consider the weight of materials that must be handled in the reconstruction process. At 1.5 ft3/unit, the average cast stone unit weighs 225 pounds. At 0.19 ft3/unit, the average GFRC unit weighs 28 pounds. The weight saving for GFRC when compared with cast stone is +/- 200 lbs/unit.
For the 72,000 units of replicated terra cotta, the savings in the weight of material that must be fabricated, transported to the building, lifted and installed is 14,400,000 pounds – or 7,200 tons.