Canadian Consulting Engineer

Mountain Equipment Co-op, Montreal

The typical retail "box" store today is far from what we think of as a sustainable building -- which is why the Mountain Equipment Co-op store stands out from its neighbours at the March Central Mtr...

December 1, 2004  Canadian Consulting Engineer

The typical retail “box” store today is far from what we think of as a sustainable building — which is why the Mountain Equipment Co-op store stands out from its neighbours at the March Central Mtropolitain of Montreal in the north of the city. Like other Mountain Equipment Stores, the Montreal building was designed according to an extraordinarily responsible environmental agenda.

The project was developed in an integrated design process involving the owner, all the design professionals and other parties, and using design “charrettes” to assess the implications of each building feature. The result was positive synergies between the architectural, structural and electromechanical features.

From the mechanical and electrical engineering point of view, Pageau Morel & Associates helped to ensure that the 4,200-m2 two-storey building uses 65% less energy than the Model National Energy Code for Buildings standard. It has also qualified as a Canada C-2000 project. The building systems do not use any fossil fuel, including natural gas, nor do they use ozone-depleting chlorofluorocarbon (CFC) or hydrochlorofluorocarbon (HCFC) refrigerants. The amount of potable water that the building uses has been reduced by one million litres a year.

Decoupled ventilation and heating/cooling

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First, the design team decided to decouple the heating/cooling system from the ventilation system and in that way avoid designing a “do-it-all” system that operates at less than optimum conditions. For heating and cooling they use a geoexchange system consisting of 12 wells, each 175-metres deep, and eight liquid-to-liquid R-407c energy efficient heat pumps. The system extracts heat from the ground in winter, and takes the stored cold energy from the ground in summer.

The main heating and cooling systems in the building are radiant slabs, since this type of system requires less power than the fan power to circulate the same amount of energy in an air system. Both the ground floor and second floor slabs have embedded PEX tubing.

The use of heat pumps is beneficial to this application, since the required water temperature for heating the radiant slabs at 30/35C matches well with the heat pumps’ temperature range. Moreover, cooling the radiant slabs requires water in the range of 18C. Since the ground temperature remains around 10-13C during the summer, a separate pumping system, parallel to the heat pumps, supplies cool water directly from the geoexchange system to the slabs. The system thus acts as a form of geothermal free cooling and reduces the use of the heat pumps since the compressors are off during that time.

Ventilation — hybrid and dedicated

Ventilation is supplied through two means: a hybrid system using underground tunnels, and a dedicated outdoor custom unit located on the roof.

The main system is the hybrid ventilation system. During free cooling hours (when the outdoor air temperature is above 13C dry bulb and below 18C dew point) up to four propeller fans draw fresh air from intakes located at ground level. This air is supplied to the building by underground tunnels along the perimeter. Inside, the air is distributed by vertical ventilation shafts to both the ground and second floors, then circulated along a horizontal displacement principle. It exits through dampers located in the roof monitor at the highest level of the building.

Using this near-natural ventilation system, the building has up to 23,600 litres per second of outside air. The stack effect is amplified by the curvature of the roof monitor, which draws inside air out. As well, the occupants are expected to tolerate a wider range of indoor temperatures (between 18C and 28C), making natural ventilation possible for longer periods over the year.

When the temperature is below 13C dry bulb, the outside air is too cold for natural cooling. On the other hand, condensation may occur on the cool slabs when the outdoor air dew point is above 18C. In these cases, the hybrid ventilation system closes its outside air dampers and fresh air is supplied by the 2,800 l/s custom roof unit, heated to 18C dry bulb or dehumidified to 11C dew point, according to the season. This air is injected directly into the “backstore” tunnel of the hybrid system. At that moment, the hybrid system acts as a 11,800 l/s recirculating distribution system, drawing air from the backstore of the building (including the fresh air supplied by the custom unit) and distributing it to the retail area. Lastly, if high temperatures occur while having a low dew point, the mechanical systems compensate by cooling the slabs using geothermal natural cooling without operating the heat pump compressors.

The custom unit is equipped with a 75% efficient enthalpy heat recovery wheel, reducing the fresh air energy loads.

The four propeller fans that are part of the hybrid system can supply up to 5.65 l/s per square metre of outside air.

Because the store is near a high-traffic boulevard and an urban highway, the fresh air supply had to be filtered. The situation would seem to pre-empt the use of natural ventilation, but by combining low horsepower fans with the natural ventilation system, outside air could be drawn through banks of 25-30% efficient flat pre-filters, and the air quality could be maintained even when massive amounts of outside air were supplied.

Automated operation from weather forecasts

Since the building is managed only by sales staff, the system is fully automated. Based on the outdoor conditions, it is able to automatically switch from heating mode to hybrid ventilation and geoxchange natural cooling mode, and to mechanical cooling mode.

Because the system is connected to the Internet, it can automatically retrieve weather forecasts for the next day and night. Using the forecasts and a simple predictive logic, the system pre-heats or pre-cools the slab, according to the need. The approach allows energy to be stored during the night, and limits the heat pump electrical demand during the day. Though the load calculations indicated 10 heat pump units were required, using this overnight storage/recovery method, the number of units could be reduced to eight.

There were no HCFC-free heat pumps on the market that matched the capacity requirements of this project. However, with help from a manufacturer, commercial heat pumps sold as HCFC-free units in Europe and made in the U.S. were converted for Canada and certified by the Canadian Standards Association on site. The units’ R-407c refrigerant has an ozone-depletion potential of 0.

Lighting, solar electrical systems, water conservation

Showers are available for the employees, many of whom cycle to work. For this need, a domestic hot water solar heating system was installed. Since it is assumed that the greatest need for showers is in the summer, the number of solar panels was reduced to four rather than the 16 that would otherwise have been required. Photovoltaic panels supply electricity to power the irrigation and solar panel circulating pumps.

A 10,000-gallon underground water cistern near the building recovers storm water from the building roof. When enough is available, this water is used to flush toilets or to water the landscaping. The cistern capacity was calculated to retain enough water after a large downpour to serve the building for two weeks. The toilets are fitted with low-flow plumbing fixtures and a waterless urinal.

The roof monitor and two sets of clerestorey windows were carefully sized to allow daylight to flood the second floor without inducing glare. Sensors shut down the general artificial lighting when the overall light exceeds a set minimum. It’s estimated that about half the yearly operating hours will use daylight, giving substantial energy savings. The installed artificial lighting capacity totals 58 kW, or about 13.8 W/m2, compared to the Model National Energy Code requirement of 27 W/m2.

Energy and emissions savin
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Energy simulations using NRCan’s EE4-CBIP software, with DOE-2 2.1e as the processing core, indicated that the building would use 67% of the Model National Energy Code for Building’s reference model. The most recent monitoring, for 12 months ending October 2004, showed a measured reduction of 65.5%; 672,557 kW-h consumption compared to 1,948,200 kW-h in the reference model. And the building is still being optimized in commissioning mode.

Based on the simulations, the yearly energy cost savings are more than $100,000. The annual estimated reduction of carbon dioxide emissions is 400 tonnes. The storm water recovery and conservation measures reduce the potable water and sewer flows by over 50% of a baseline case, equaling savings of more than 1 million litres per year.

In terms of its other sustainable characteristics, the building is located on a brownfield site close to public transportation, and as a two-storey building it leaves more space for landscaping than the typical single-storey box retail store. The client also stipulated that 80% of the building materials (by weight) be manufactured or assembled within 500 kilometres of the construction site in order to reduce emissions and costs associated with transportation. Recycled and recuperated materials and components were incorporated, including the wooden roof of the monitor. The wall insulation is made of recycled paper, and the concrete slab has integrated flyash. The roof and walls have a high insulation value of RSI 7.0 and RSI 6.2 respectively, compared to the Model National Energy Code requirement of RSI 3.5 for roofs and 3.0 for walls.

The project team achieved almost all the green goals initially set and the building was awarded the C-2000 certification. Designed on a fast track, it opened as planned in May 2003. Overall construction costs were $6.1 million, including $1.7 of electromechanical costs. Compared with a typical electro-mechanical installation for this type of building (direct expansion cooling with gas fired heating), the extra charge is about $430,000. However, based on the simulations, the yearly savings of $100,000 will give a payback period of 4.3 years.

Client: Mountain Equipment Co-op, Vancouver. Mechanical/electrical/energy: Pageau Morel and associates (Roland Charneux, ing., Frederic Genest, ing. Tuong Phong Huynh, ing.) Architecture: MTF/Studio MMA/Lyse M. Tremblay/Duschenes & Fish. Renewable energy: GPCO Structural: Saia, Deslauriers, Kadanoff, Leconte, Brisebois, Blais. Construction manager: Broccolini

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