High Performing Buildings - Winter 2008 - (Page 54)

Canadian dollars for a simple payback of about 4.75 years. Greenhouse Gas (GHG) Reductions Combining geoexchange, radiant slabs, natural ventilation and daylighting results in substantial energy demand and consumption savings. When compared to a regular all-electrical building, the reduced energy consumption avoids the emission of more than 400 tons of CO 2 per year, based on a generic thermal plant producing electricity using coal or natural gas at 66% efﬁciency. As the emission factor for the electrical energy distributed in Quebec is 1.22 g of CO2 per kWh (±100% hydroelectricity), the GHG emissions are in fact reduced by 1.7 tons. The avoided peak demand and energy consumption can then be used to supply Ontario or New England, avoiding GHG emissions in those areas using Quebec’s hydropower. Indoor Air Quality The four propeller fans that are part of the hybrid ventilation system are able to supply up to 50,000 cfm of fresh air into the building, equal to 1.11 cfm/ft². Therefore, the building beneﬁts from up to six times more outdoor air than if designed according to ANSI/ASHRAE Standard 62.1-2004, Ventilation for Acceptable Indoor Air Quality. During DOAS operation, up to 6,000 cfm of preheated or dehumidiﬁed outside air is supplied to the building via the tunnels. Since the maximum building occupation is anticipated to be 300 members, this allows for 20 cfm/person. A CO2 sensor located in the building exhaust controls the actual amount of outside air supplied by the DOAS (down to the minimum required for sanitary exhaust). Monitoring of the CO2 levels in the building during its ﬁrst winter showed concentrations well below the recommended limit. Also, in this mode, the hybrid system continuously recirculates 25,000 cfm in the building, ensuring a good mixing of fresh air and the dilution of pollutants. Additionally, because the building was constructed using low or no VOC emitting materials, emission of indoor pollutants is low. The ﬂooring is bare concrete with a protective ﬁnish, and other indoor ﬁnishes do not use VOC or urea-formaldehyde. Finally, due to the close proximity of ENERGY AND COSTS SAVINGS Load Calculations The building’s heating load was calculated at 600 MBh, while the cooling load was in the range of 25 tons for mechanical cooling. To reduce installed capacity compared to peak loads, the building’s automated system uses predictive logic coupled with weather forecasts retrieved from the Internet to benefit from the thermal mass of the radiant slabs and counter the associated thermal inertia. The slabs are precharged (heated or cooled) at night according to the forecasts. Because the indoor temperature is allowed to swing, the building is able to pass through the extreme weather periods without difficulties while reducing peak electrical demand. Based on this, only eight of the 10 required heat pumps were installed. The two-stage heat pumps give 16 stages of operation and minimize energy waste, often associated with low part-load operation, through two dedicated circulating pumps (load and source). Energy Simulations and Predicted Cost Savings With the combination of systems and attributes described earlier, simulations were done using Natural Resources Canada’s EE4 CBIP software and C-2000/CBIP simulation rules. The results showed a reduction of 68% in energy consumption compared to a MNECB reference building, while yearly energy costs were reduced by $105,000 in 2003 Canadian dollars which is 69% lower than reference. Actual Energy Consumption The building has been in operation for more than three years and the actual energy billed is shown in Figure 5. After the first year was above predicted values for a few months, the commissioning of the HVAC systems brought the consumption close to target values. Since then, values vary from year to year according to changes in building operation (e.g., sales hours) and weather conditions, yet they always remain close to predicted levels. Figure 5 Actual energy billed during the first four years of operation. 54 HIGH PERFORMING BUILDINGS Winter 2008

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High Performance Buildings - Winter 2008 Passing On the Gift: Heifer International Headquarters Head of the Class: University of Florida’s Rinker Hall How Far Can You Go? Pearl River Tower The Proof Is Performance: How Does 4 Times Square Measure Up? Lighting the Way: Two Guilford County Schools Montreal’s Retail Example: Mountain Equipment Co-op® (MEC)

High Performing Buildings - Winter 2008

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