By Jon W. Douglas, Enermodal/MMM Group
Harnessing the Ocean Nova Scotia Power HeadquartersBuildings Building Mechanical & Electrical (HVAC) Systems Building Structure
Nova Scotia Power, a provincial utility, commissioned WZMH Architects, with Enermodal Engineering, a member of MMM Group, as the sustainability consultant, to take their defunct coal-fired generating plant on Lower Water Street in downtown...
Nova Scotia Power, a provincial utility, commissioned WZMH Architects, with Enermodal Engineering, a member of MMM Group, as the sustainability consultant, to take their defunct coal-fired generating plant on Lower Water Street in downtown Halifax and convert it into an office for 500 employees. Nova Scotia Power’s new head office opened in 2012 and recently became the first LEED Platinum certified building in Atlantic Canada.
With this project the provincial utility has revitalized what was once a derelict ecological hazard into an attractive downtown landmark for all citizens. The building sits at the starting point of Halifax’s boardwalk and provides access to the harbour, with a boardwalk café, patio and large open green space. By locating the project downtown instead of on the outskirts of the city, the utility is supporting urban development rather than sprawl.
The project is also a testament to how rehabilitating an unused building, taking advantage of inherent opportunities in the site location, and implementing energy saving design strategies with short incremental cost paybacks, can create a high performance building that transforms its community.
The focus for the building design was on achieving energy savings through strategic choices. Energy modelling was used to determine the best ways to achieve the highest energy savings at the lowest cost.
At the starting point, the former 1950s-era plant was merely a shell — a seven-storey windowless concrete clad steel structure enclosing several high-volume spaces that originally housed equipment for generating electricity. New openings were cut into the shell, resulting in 4.5 million pounds of concrete being removed. The process involved cutting through 10-12 inches of concrete up the entire height of the building.
Now transformed, the building comprises 13,000 square metres of floor space in three different sections, ranging from three to seven storeys. Breaking up these sections are two full height atriums. One is a galleria from north to south that features an old smoke stack opening as a new skylight to bring in natural light. The second runs east to west, allowing public access from Lower Water Street to the harbour.
One of the main new features of the NSP head office is an exterior curtain wall “skin” that consists of vision glazing units and spandrel units. These provide an improved thermal barrier with low-e film on the glazing units and argon gas between the two glass panes. The frames of the curtain wall system also have a 9-mm thick improved thermal break. The concrete walls have 3-in. (77-mm) thick semi-rigid mineral wool insulation board, with an effective thermal resistance of R-9. A new roofing system not only added insulation to the existing structure, but also has a high-albedo white roofing material to reduce heat gain.
Sea water for
heating and cooling
The design team looked for ways to take advantage of the adjacent harbour for heating and cooling the building. The principle of using a project’s context and existing resources to the best advantage is what the sustainability movement is all about.
However, finding a system that could handle below-zero temperature water and could be scalable to meet the 300-ton cooling requirements presented a challenge. Enermodal was able to locate a heat pump system from Winnipeg that is traditionally used in arenas. It allows the mechanical system to draw heating and cooling from the harbour water and is scalable to meet the cooling demands of the building.
The seawater runs through a heat exchanger made of titanium to prevent corrosion. Heat pumps pull the needed cooling and heating from the circulation loop, sending cooling to chilled beams and heating to the perimeter system.
The system has a bypass for free cooling when the water temperature from the harbour is adequate for cooling. This isn’t always the case as the harbour water temperature rises in the summer, so at those times the cooling system turns on. The system is able to move loads around during periods of simultaneous heating and cooling and only needs to draw from the harbour to make up the shortfall or to reject excess load.
The systems installed are proven technology, but the application and scale of installation are what make the project innovative.
Active chilled beams
The HVAC system includes active chilled beams to decrease its energy use and increase the occupants’ thermal comfort.
An active chilled beam is an induction unit mounted on the ceiling. They differ from radiant chilled ceilings as they transfer heat primarily via convection instead of radiation. The pre-treated (i.e. cooled and dehumidified fresh/outdoor air from the air handling unit) primary air supply from the forced ventilation system induces secondary (room) air across the chilled beam unit’s heat transfer coil (cooling coil). Here the secondary air is reconditioned prior to its mixing with the primary air stream. Thus the chilled beam discharges mixed air into the space by means of linear slots as well as delivering space cooling. The cooling coil in the chilled beam provides only sensible cooling. It is never intended to be used to condense or provide latent cooling in order to avoid having to add a drain pan and drain line to each beam.
Active chilled beam technology provides fan energy savings due to the reduced ventilation air flow from the air-handling unit, and chiller energy savings since a chilled beam requires a higher chilled water temperature than a conventional all-air VAV system. Since chilled beams require a higher chilled water temperature and entrain a large quantity of room air, they reduce the need for reheat. The technology also offers low maintenance due to the absence of any moving parts or filters. As well, occupants benefit from having individual zone control and a more uniform temperature without cold drafts.
Important design criteria include the sensible cooling load, chilled water temperature and room humidity. Co-ordinating installation with the lighting, sprinklers and other ceiling fixtures is important. For commissioning, accurate air-side and water-side balancing is critical.
Chilled beams are suitable for zones with medium-to-high sensible cooling requirements in buildings with a good airtight envelope. They can be used in spaces such as offices, meeting rooms, schools, libraries and laboratories, but are not suitable for spaces that generate high humidity, spaces with operable windows in a humid climate, or leaky buildings. They are also not suitable for spaces with ceilings higher than 12 ft. (3.6 m) high.
The disadvantages of active beams include their higher construction cost compared to a conventional VAV system, as well as poor ceiling aesthetics and their unfamiliarity to the North American construction industry.
Natural lighting, water savings and payback
By cutting large openings in the former plant’s walls, the renovation allowed for more glazed areas, giving the occupants access to views and daylight. Over 75% of the occupied spaces have access to daylight. The use of artificial lighting is reduced by occupancy and daylight sensors throughout.
High efficiency T5/T8 fixtures were used and the effective lighting power density (LPD) was designed to be 8.25 w/m², which is 40% lower than ASHRAE 90.1-1999. The lighting fixtures, ballasts, sensors and all controls are integrated.
A combination of water saving fixtures together with a rain harvesting system that uses an existing 43-m3 storage tank has reduced the building’s water demands by over 75% compared to a standard building.
The site landscaping uses native and adaptive vegetation species with reduced water demands. There is no irrigation system as the vegetation should be able to thrive on rainfall once it is established.
Investing in energy-efficiency tech
nologies and high-performance design features is not only important for reducing Nova Scotia Power’s environmental footprint, but also for creating an economically responsible head office that will achieve significant utility bill and operating cost reductions over the next 10 years and beyond. In terms of direct economic benefits, the retrofits made to Nova Scotia Power will save an estimated $650,000 in utility bills a year. cce
Jon W. Douglas is with the sustainability group of Enermodal/MMM Group in Kitchener, Ont. E-mail firstname.lastname@example.org
Nova Scotia Power. Architects: WZMH, with Fowler, Bauld & Mitchell. LEED consultant: Enermodal Engineering (Jon W. Douglas). Structural: BMR Structural Engineering. Mechanical & Electrical: M & R Engineering. Contractor: Aecon Atlantic Group.