Engineering a LEED platinum office tower

RBC Waterpark Place could potentially be a record-setting new project in Ontario
Monday, July 29, 2013
By Michael Pires

Oxford Properties Group recently announced its 930,000-square-foot RBC Waterpark Place office tower will aim to be the first new speculative office tower in Ontario to achieve Leadership in Energy and Environmental Design (LEED) platinum – the highest green building rating attainable. At this point in time, no new office tower in the province has achieved this status.

Being built in downtown Toronto, the 50-storey office tower is set to be complete in 2014. The cost of construction is $400 million, with Oxford expecting about a one per cent incremental cost to go from LEED gold – the developer’s initial goal – to LEED platinum. Oxford is also expecting a four-year payback period given the expected operating cost savings are $150,000 annually. A comprehensive engineering study was conducted and energy model created to examine the cost benefit of a wide range of technologies and determine which strategies would yield the highest energy savings at the lowest cost.

Optimizing vision glazing for an improved envelope
Instead of using triple glazing, the tower will get a high-performance building envelope by ensuring that vision glazing is only used where it provides the most benefit. By insulating wall areas near the floor, above the ceiling and in front of obstructions such as pillars, the vision glazing only accounts for slightly more than half the exterior walls. This provides energy efficiency and occupant comfort improvement over most new office buildings, which typically have 70 to 80 per cent vision glazing.

Dedicated outdoor air system
RBC Waterpark Place will feature a dedicated outdoor air system (DOAS) and high-performance mechanical system combination.

A DOAS is a well-tested and relatively simple system to design and operate. It is often paired with innovative, high-performance heating and cooling systems such as variable refrigerant flow, chilled beams or radiant slabs. A DOAS-based strategy can deliver a superior indoor environment with low operating costs and excellent long-term performance.

Design teams need not venture too far from their technical comfort zone to implement a DOAS strategy. A DOAS, running in parallel with a standard variable air volume (VAV) system that delivers thermal control, will provide significant savings relative to a traditional office mechanical system. In this configuration, ventilation air from the DOAS, which is provided to match occupancy needs, is delivered to the space independently of heating and cooling and is controlled by carbon dioxide sensors. The VAV system has a more or less traditional design and is controlled by thermostats in each zone.

While there is a little more ductwork in the ceiling space with a DOAS and VAV system, the control strategy is simple and allows each zone to receive what it actually needs – fresh air, heating or cooling without one compromising the other. Plus, because most building operators are already well-versed in traditional VAV systems, the learning curve to manage a DOAS and VAV system is fairly gentle.

RBC Waterpark Place will use a DOAS for ventilation and an independent VAV for delivering the heating and cooling. Deep lake water cooling and dedicated natural gas high-efficiency boilers will supply the energy required by these systems.

This project will demonstrate that designers can achieve the same level of savings simply with added ductwork and VAV boxes with added controls. This very reliable, well-understood and easy to maintain design is less expensive and more reliable than the underfloor systems that are often considered a default for high-performance office towers.

Ongoing measurement and improvement
A sub-metering system will be installed to monitor energy and water use for the first year of operation, to determine the actual energy efficiency levels of the office tower.

Michael Pires, P.Eng, is manager of sustainability for Enermodal Engineering, a member of MMM Group. Enermodal Engineering provided sustainable design facilitation, LEED consulting and energy efficiency modelling on the RBC Waterpark Place project.

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