Sustainable design goes underground

Precast concrete earth tubes have an interior diameter of ±1950 mm (±77 in.) and carry fresh air underground to be pretreated by the earth’s latent heat before entering the building’s mechanical system. Photo © Nigel Tai
Precast concrete earth tubes have an interior diameter of ±1950 mm (±77 in.) and carry fresh air underground to be pretreated by the earth’s latent heat before entering the building’s mechanical system. Photo © Nigel Tai

By Nigel Tai, B.Arch, M.Arch, OAA, MRAIC, LEED AP
The Environmental Science and Chemistry building is the newest addition to the University of Toronto Scarborough (UTS) north campus, across from the original 1960s-era grounds. Joining the Instructional Centre, which opened in 2011, the two facilities will be connected by a green space, tentatively referred to as the Earth Tube Plaza.

The 15, 3290-m2 (165,000-sf) academic Instructional Centre building was the first building on the north campus. The Environmental Science and Chemistry building, designed by Diamond Schmitt Architects, is now being developed. The 10,219-m2 (110,000-sf) five-storey teaching and research lab also includes administrative offices and meeting rooms configured around a sky-lit atrium. Both buildings enhance the urban edge in the area, which is being developed as a pedestrian-friendly precinct.

Dotted across the shared green space are telltale signs of an unusual feature to improve the new facility’s energy performance. Tubular shafts will take in fresh air that will course 2 m (6.5 ft) below ground through precast concrete earth tubes before entering the basement mechanical system. The intent is to take advantage of the earth’s latent heat to precondition the air before it enters the building’s HVAC.

The installation of the earth tubes took place between May 30 and July 4. In all, six tubes with a combined length of 165 metres were laid to precondition intake air prior to entering the HVAC system. Photos courtesy Diamond Schmitt Architects
The installation of the earth tubes took place between May 30 and July 4. In all, six tubes with a combined length of 165 metres were laid to precondition intake air prior to entering the HVAC system. Photos courtesy Diamond Schmitt Architects

This energy-saving technique addresses the laboratory’s need for frequent air changes—typically six to 10 per hour—as chemical vapours that emanate from lab bench work require constant ventilation. This is just one of many sustainable design features, including geothermal boreholes and tapered vertical sunshade fins, unique fritted glazing, displacement ventilation, and a high-performance curtain wall.

Ideally, earth tubes require a long length to capture the heat transfer. However, the tight site did not allow for extended underground runs. Instead, six individual tubes varying in length from 20 to 35 m (65 to 114 ft) long—165 m (541 ft) of aggregate length—connect and feed fresh air to the mechanical system. To improve its heat transfer effectiveness and promote a more even distribution of airflow, hot-dip galvanized metal baffles were added to the earth tubes to lengthen the amount of time for heat exchange to occur with the soil, thereby increasing energy efficiency.

Each earth tube has an interior diameter of ±1950 mm (±77 in.) and is on a two per cent slope toward the building to drain any rain water or condensation into the drainage system. Within the earth tube air plenum, the wall and ceiling surface is coated with reflective material and a series of custom ultraviolet (UV) lights will sanitize the incoming air before entering the air-handling unit (AHU).

In all, six tubes with a combined length of 165 metres were laid to precondition intake air prior to entering the HVAC system.
In all, six tubes with a combined length of 165 metres were laid to precondition intake air prior to entering the HVAC system.

One of the tubes will have a translucent portion that passes under the entrance vestibule. A glass screen and floor opening floor section will allow occupants to see the earth tube in action. Wind deflector and colour light-emitting diodes (LEDs) will be integrated to illustrate the air movement within the tube and emphasize the free heating/cooling these tubes are extracting from the latent heat of the soil.

The air drawn from the tubes is supply air to the office space. Return air, depending on the season, heats or cools the open, five-storey atrium, and the return air in the atrium will be part of a heat exchange with fresh air coming from the outside to heat and cool the labs. Fume hoods and fans in the labs will then exhaust this air.

Back on the plaza, the six earth tube inlets are randomly scattered and are of varying height. The design intention is to present these intakes as a landscape sculpture element. The project is targeting Leadership in Energy and Environmental Design (LEED) Gold certification, which is a rarity for this building type. This fast-track design-build project is in collaboration with EllisDon and is slated to open in 2015, less than two years after its inception.

Nigel Tai Nigel Tai, B.Arch, M.Arch, OAA, MRAIC, LEED AP, is a staff architect at Diamond Schmitt Architects. The Environmental Science and Chemistry building is his second project at University of Toronto Scarborough (UTS), having also worked on the adjacent Instructional Centre. He has also been involved with CANMET Materials Technology Laboratory in Hamilton, the Osgoode Hall expansion at York University, and the Toronto Zoo Wildlife Health Centre. Tai can be contacted at 416-862-8800 ext. 509.

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