Case Studies

  • Library Buildings – Comparison of Actual Energy Performance


    Thanks to the recent building energy reporting ordinances passed by the City of Boston and City of Cambridge, we were able to compile the above chart, comparing the actual energy performance of Athol Public Library in Athol, Massachusetts, for which we were the MEP/FP engineer and energy modeling consultant, to the other libraries in Boston area.

    Some observations and notes about the chart above:

    1. The total building energy use intensity (EUI) are all based on actual energy usage. Based on this chart, the differences in actual energy performance of the recently renovated libraries are staggering. Here are some close-up comparisons for a few that have similar basis such as square footage, time of renovation and/or LEED certification:

    a. Athol Public Library, 20,065 SF, 2013 renovation & new addition, LEED Platinum, EUI = 44 kBTU/SF;
    b. BPL Brighton Branch, 17,208 SF, 2011 renovation, LEED Silver, EUI = 100 kBTU/SF, Athol is 2.3 times better (100/44=2.3);
    c. BPL Mattapan Branch, 21,000 SF, 2009 renovation, no LEED certification, EUI = 152 kBTU/SF, Athol is 3.5 times better;
    d. Cambridge Public Library, 120,186 SF, 2010 renovation & new addition, LEED Silver, EUI = 136 kBTU/SF, Athol is 3.2 times better.

    2. A LEED certified library does not necessarily perform better in terms of energy than a non-certified library:

    Brighton branch (LEED Silver), Honan-Allston branch (non-certified) and Hyde Park Branch (non-certified) have the same performance (EUI=100).

    3. Two libraries with the same level LEED certifications could have considerably different energy performance:

    Brighton Branch EUI = 100, Cambridge PL EUI = 136, they are both LEED Silver.

    4. The old libraries are showing impressive EUI numbers. That, however, could be misleading. As we know, a typical old library may not have air-conditioning in the summer time; it may not even have proper ventilation to meet the code; their energy use numbers are therefore lower than a renovated contemporary library.

    5. As MEP engineers, we strongly believe that the actual energy performance of a LEED-certified building has a lot to do with how the building systems are engineered and built. Athol Public Library is a great example demonstrating a highly energy efficient LEED building.

  • Private Driveway Snow-melting, Rye, NH

    AWE engineered the geothermal snow-melting system for a 7,500 sq-ft existing private driveway. Project was completed in 2010. A vertical borehole close-loop ground source heat pump system was designed to retrofit the existing propane-fired hot water snow-melting system. The geothermal heating system successfully passed the test of the unusually big and frequent snow storms in the winter of 2010 – 2011. Significant energy cost savings were achieved by the geothermal system based on metered data and previous utility bills: 66% savings compared with 2009, 88% savings compared with 2008.

    A ground loop system that consists of 62 vertical boreholes was built. Water-to-water ground source heat pumps were installed, with a total heating capacity of over 140 tons.

  • Private Community Development, Cape Cod, MA

    AWE was the geothermal HVAC engineer for the project. We designed a centralized geothermal heating and cooling system for the small community consisting of 9 houses. The community will share the central geothermal ground loop with individual houses being responsible for their own heat pumps to maximize geothermal efficiency and energy savings. Due to the location being all sand, sonic drilling was used for the project. 26 boreholes were drilled. Most boreholes were drilled in groups of 3, 1 at 90, 1 at 70 and 1 at 50 degrees. Sonic drilling not only prevented boreholes from collapsing, but also shortened the drilling time and saved cost.

  • Private Residence, Rye, NH

    AWE engineered the geothermal heating and cooling system for the 15,000 sq-ft existing house retrofit project. Project was competed in 2009. Energy cost savings achieved 60% for heating & 40% for cooling, per metered electricity data & propane bills for previous propane-fired hot water boiler heating system (based on 2009 propane price $2.11/gal. Savings would be even more compared with current fossil fuel prices).

    The 6 existing outdoor condensing units were no longer needed and were removed. Compressed air rotary DTH hammer drill rig was used to drill the vertical boreholes. 13 boreholes were drilled. Boreholes were ganged together to form a ground loop system. Header pipes of the ground loop run to the pump room inside the house. Variable speed ground loop pumps were used to conserve pump energy. Ground source heat pumps were installed in mechanical space inside the house.

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