High Performing Buildings - Spring 2008 - (Page 50) Energy Use Intensity A building that meets code without any additional efficiency measures has an Energy Use Intensity (EUI) of 79. The design EUI for the renovated Cambridge City Hall Annex was 29. The building was expected to perform at or below the design EUI. However, the actual EUI as measured in kBtu/ft2 per year, including renewable energy, was 59 in 2005 and 63 in 2006. The annex houses many of the city’s public offices and the Arts Council’s art gallery. P O S T- O C C U PA N C Y SURVEY FINDINGS After the building opened, commissioning reduced electricity consumption by 40%. Around 20% of the survey respondents perceived that their productivity increased after the building’s renovation. Seventy-three percent of the respondents were aware of at least seven out of 12 green features of the building. Occupants perceived the building’s important green features as occupancy light sensors, skylights, photovoltaic-based electricity generation and wood from sustainable forests. The survey also identified that the building’s indoor temperature was too high or too low on some days, and there were issues with the relative humidity levels in the building. 50 The building was not performing as expected because of discrepancies between initial assumptions and actual conditions for building systems, occupants, use, and operations and maintenance practices. A commissioning study in 2005 identified operations and maintenance practices and system design flaws contributing to the lower than anticipated building performance. The city corrected many of these issues and hired a consultant to review building energy use to determine why there is a difference between the design and actual EUI. Spring 2008 Photovoltaic System The 26.5 kW photovoltaic system has been partially offsetting the electricity consumption of the building through on-site electricity generation. A simple financial payback analysis indicates that the system payback due to the avoided energy costs (taking into account a $236,250 photovoltaic system design and construction grant from the Massachusetts Technology Collaborative) is around 46 years. However, the payback period is reduced to 33 years when considering the demand charge avoided because HIGH PERFORMING BUILDINGS Photos © Dan Gair/Blind Dog Photo, Inc.
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