Manitoba Hydro Head Office
March 1, 2007
By Canadian Consulting Engineer
A new $258-million headquarters for Manitoba Hydro is under construction in the centre of Winnipeg. Covering an entire city block on the south side of Portage Avenue between Edmonton and Carlton Stree...
A new $258-million headquarters for Manitoba Hydro is under construction in the centre of Winnipeg. Covering an entire city block on the south side of Portage Avenue between Edmonton and Carlton Streets, the 22-storey building is scheduled to be completed later this year. The building’s 64,600 square metres of space will be home to 1,800 Manitoba Hydro employees, now located in various offices around the city.
Architects Kuwabara Payne McKenna Blumberg designed the form as two glass towers that splay open to the south and are set upon a podium.
Not surprisingly, given that the owner is a power utility, the building is designed to be a model of energy efficiency. The design uses passive techniques and integrates many environmental systems to be 60% more energy efficient than the Model National Energy Code for Buildings. Energy consulting and energy modelling was performed by Transsolar Energietechnik of Stuttgart, Germany. Natural Resources Canada (NRCan) assisted and provided further verification of the energy saving using DOE-2 software.
The mechanical-electrical consulting engineer for the project is Earth Tech (Canada), with Alan Aftanas, P.Eng. in Winnipeg as project manager, John Munroe, P.Eng. in Calgary as chief mechanical engineer, and Mike Shewchuk, P.Eng. in Edmonton as lead electrical engineer.
MECHANICAL & ELECTRICAL DESIGN
Earth Tech (Canada)
An integrated design process modeled on the successful C-2000 program by Natural Resources Canada was adopted for the Manitoba Hydro Head Office project. The full design team met regularly from day one, with all issues — architectural, structural, mechanical and electrical — on the table for discussion. Passive techniques are maximized in the building and all members of the design team approached their designs with this philosophy in mind.
The extreme Winnipeg climate presented challenges. The building has a winter design temperature of –35C and 10,620 heating degree-days per year.1
Double facade and opening windows
The building has a double facade which provides a superior buffer between the outdoors and the indoors. The interior glass is located approximately 1 metre inside the outer facade. Natural ventilation is permitted under the correct weather conditions. Vents in the exterior facade automatically open with actuators, while the building mechanical ventilation systems are shut down. The occupants will be signalled by the internal computer network that the building is in natural ventilation mode, and are free to open windows located on the interior facade at their own discretion. If they want more fresh air they simply open their windows. In addition, under the right solar conditions, some preheating will take place in the double facade buffer zone, which will extend the season for natural ventilation.
Concrete mass helps to stabilize temperatures
Low intensity thermo-active concrete ceilings heat and cool the building by circulating heated or cooled water in plastic tubes embedded in the concrete. The system allows the thermal mass of the concrete to stabilize the building temperature. By having only minor temperature swings from day to night, the building uses less energy and the size of the heating/cooling plant could be reduced.
Since the human body not only feels air temperature, but also the temperature of surrounding surfaces, the radiant heating will provide superior comfort. The radiant slab system is also more energy efficient than a traditional air system due to the better thermal properties of water compared to air.
When it is -35C outdoors on frosty Winnipeg winter days, the space between the outer facade and the inner facade will be heated and the occupants will never be exposed to the cold exterior glass surfaces.
Atria as lungs
The building has north and south atria called “winter gardens.” Each of the south atria is six storeys high and each of the north atria is three storeys high. They are stacked in modules, one on top of the other, reaching 18 storeys of the building. The south atria are the “lungs” of the building and absorb solar radiation for preheating the air in the winter.
In winter, 100% fresh air is filtered and preheated to 10C before entering the atria. Waterfalls in the atria provide humidification; for humidifying the water is warmed, and for dehumidifying the water is chilled. The atria in turn provide pre-warmed, pre-filtered, humidified/dehumidified air into the individual floors. In summer, exterior windows at the bottom and the top of the atria are opened to remove heat from the space.
100% fresh air through raised flooring
By de-coupling the heating/cooling function from the ventilation systems, we were able to provide 100% fresh air in a once-through ventilation system located in a raised floor. Typical North American buildings recirculate about 80% of their air.
The raised flooring serves as a plenum for the pressurized fresh air, which is distributed by displacement ventilation. It is introduced at a low velocity at the floor level and rises into the breathing zone through convection currents created by heated objects e.g. occupants, computers, etc. Contaminants expelled by the occupants (carbon dioxide, germs, etc.) are exhausted at ceiling level directly to the outdoors via the solar chimney.
The raised flooring system also allows for plug-in electrical and communication system networks that are easy to access and modify.
Solar chimney exhausts air
The building has a large solar chimney, 12 metres long by 1.8 metres wide, at the north end of the building. Extending 26 metres above the top of the office tower, the concrete is replaced by glass construction above the roof line to assist in creating a negative pressure in the building. The solar chimney will power air movement in the building without the use of fans. A solar absorber (a heat retaining thermal mass constructed using phase change materials) will assist the solar chimney operation later in the day, after the sun has set.
In winter, the solar chimney serves as a large duct to collect exhaust air from the occupied zones and uses it to heat the parking garage below the building.
Geothermal field extends a city block
The building uses a geothermal heating and cooling system. Heat extracted from the building during the summer months is stored in the earth for use in the winter.
The geothermal earth heat exchanger extends for the entire city block and deep into the bedrock below the building and the parking structure. The exchanger is possibly the first of its kind of this size completely located under a structure. It consists of 280 boreholes on a 4.5-m grid throughout the 7,500 sq.m site. The boreholes are drilled to a depth of 116 metres. A plastic tube filled with a thermally enhanced grout to enable an effective heat exchange is looped in each borehole to exchange energy with the earth.
Installing the geothermal field below the building presented challenges to ensure that the boreholes would not affect the foundation system. The installation took six months over the winter months when conditions are difficult and drilling is a wet, messy process.
Supplementing the geothermal plant are high efficiency natural gas condensing boilers, chillers and cooling towers.
Responding to the weather
A central building management system will coordinate all the building functions. In addition to controlling the HVAC system, it will monitor and control various stand-alone systems such as the blinds, lighting, security system, fire and windows on the exterior facade.
The slab temperatures are controlled with sensors embedded in the concrete.
Unique features of the building controls are:
* A weather station mounted on a mast on the top of the building will monitor outdoor climatic conditions including day
light intensity, wind speed and direction, as well as temperature and humidity.
* Vents on the exterior facades will automatically open and close with actuators when outdoor temperatures and conditions are suitable for natural ventilation.
* The vents will close when the winds are too strong, when it is raining, or when temperature or solar gains are not suitable for natural ventilation.
* The temperature in between the outer facade and the inner facade is monitored. If excessive heat builds up in this space it will be relieved to the outdoors by opening the vents.
* The blinds between the inner facade and the outer facade are automated, and open or close based on factors like the intensity of the sunlight and the desire to shed solar gain. Each blind has a motor to raise it, lower it, or adjust the angle of the blades. The upper blades are maintained horizontal to bounce daylight onto the ceiling. The occupants will also be able to override the automated controls.
Daylighting and artificial light
The lighting systems have their own integral lighting level and motion sensors. Daylighting is a big part of the building design. For example, the floor plates are much slimmer, and the floor to ceiling heights are higher than typical to optimize daylight penetration into the spaces. The users should be able to rely on natural light about 80% of the time.
For the general office lighting, luminaires are suspended from the exposed concrete ceilings with approximately 70% up-lighting to reflect the light off the ceiling. Light fixtures will be T5 high output fixtures with integral sensors.
LED sources have been adopted throughout to both enhance energy efficiency as well as to promote the client’s commitment to sustainability.
Owner: Manitoba Hydro
Electrical & mechanical: Earth Tech (Canada) (John Munroe, P.Eng., Mike Shewchuk, P.Eng., Alan Aftanas, P.Eng.)
Energy engineering: Transsolar Energietecknik GMBH
IDP Advisor: Natural Resouces Canada
Architects: Kuwabara Payne McKenna Blumberg, Smith Carter Architects, Prairie Architects
Structural: Crosier Kilgour & Partners
Geotechnical: UMA Engineering, Dyregrov
Building envelope: Brook Van Dalen & Associates
Civil: Wardrop Engineering
Construction manager: PCL Constructors