High Performing Buildings - Spring 2008 - (Page 48) P E R F O R M A N C E D ATA A N D C O M M I S S I O N I N G The building’s energy use was predicted to decrease by 56%, but actual energy use only decreased by 28%. This prompted the city to contract for a commissioning study. The commissioning agent helped reset the controls for lighting, mechanical equipment and systems. After commissioning, the electricity consumption of the building was drastically reduced by around 40% of the consumption when the building was initially occupied. The commissioning study identified and the city subsequently corrected a number of issues. Many of these issues could have been identified early on had the commissioning agent been on board in the design phases. Well pumps were run near full speed much of the time. In cold weather, AHU-1 was being run at low speed, in full recirculation mode, rather than being shut down completely, to safeguard against the building temperature dropping too low and freezing the coil. The heat pump had a COP of 2.88 at specified design conditions per the submittal, but the design drawings showed a heating COP of 3.5. Well pumps had 5 hp motors, where the design drawings showed 2 hp. Although 5 hp may be correct sizing, the energy model could have been based on 2 hp well pumps. AHU-1 had a 50 hp supply fan motor, although the design drawings showed 40 hp. Although 50 hp may be the correct sizing, the energy model could have been based on a 40 hp fan. The renovation benefited from skylights in the original design. © Dan Gair/Blind Dog Photo, Inc. street, no longer leads to a handicapinaccessible stairwell. The inviting two-story entry lobby sets a more appropriate civic tone and makes it easier for visitors to locate the services they need. In the redesign, we were able to capture space lost by the two-story atrium by using above-grade window openings in the previously uninhabitable cellar. Site-specific wall paintings by artist Michael Glier animate the main entry lobby and third floor public meeting areas with imagery conceptually tied to the function and mission of the building. The themes of transparency, flow, growth and pleasure are directly drawn from the mission statements of the city departments that occupy the building. The artwork depicts urban moments within a garden environment and reveals the complex relationships among civic goals, green design, historic preservation and public transparency. Air handlers were being operated at occupied mode at all times, rather than using the unoccupied mode controls provided. Controls for the fluorescent lights in the offices were set on “open office” rather than “private office.” This means that they were getting only two-thirds of the available savings from the occupancy sensors in private offices. The daylight dimming function on the office lighting was disabled. Dual temperature pump control was not working correctly. Exhaust fans were not scheduled to turn off at night. AHU-1 discharge temperature was higher than it should have been in the summer, resulting in more airflow for cooling and greater fan power. AHU-1 return fan was operating at the same speed as the supply fan when they should have a differential. The building was found to have high humidity during summer 2004. Factors that may have contributed to this include: Chilled water setpoint changed from 44°F to 47°F. AHU-1 discharge air temperature setpoint on a reset schedule was based on return air temperature rather than outside air temperature. Coils were balanced to heating flow rather than cooling flow. Benefits of Renovation The City of Cambridge understood that reusing an existing building, even one with serious remediation 48 HIGH PERFORMING issues requiring a complete interior renovation, acknowledges and values the role it has played in shaping the surrounding culture, society and history. Historic preservation merged with sustainable design offers a number of additional advantages. The renovation benefited from sustainable features inherent in the original design, in this case passive Spring 2008 ventilation and daylighting through large windows and skylights. There was embodied energy in the building materials, the energy required to duplicate a structure (Btu/ft2) multiplied by the building’s area. We saved on the cost of demolition, disposal of debris, and waste costs (85% of the debris from the interior demolition was recycled on this project). BUILDINGS
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