High Performing Buildings - Spring 2009 - (Page 63) the effect of adding a photovoltaic system using renewable energy to reduce the net energy use. A 4.9 kWp system would produce roughly 6,000 kWh/year in a Concord, Mass., climate at the orientation used. This would more than cover the meter electrical use of the past year (3,865 kWh), and start to partially offset the energy use of site fuel combustion (gas use). Note that in the graph “Energy Use Before, After Renovation,” the electricity produced by the PV system is graphed in terms of the amount of source energy it offsets (i.e., roughly three times multiplier). The overall result would be an 83% reduction from the benchmark house. renovation Costs The total renovation to date has cost $300,000 or $83 per ft2. This amount includes upgrades that were not done purely for energy efficiency, including total electrical and plumbing replacement, the finishing of the attic and basement space, the addition of two new full baths and the renovation of the existing baths and kitchen. It also included the cost of a new roof and new exterior siding. Separating the cost of the windows, the insulation, and the heating system, the additional cost to provide energy improvements alone came to $75,000. A natural gas price of $1.50 per therm financed over a 30-year mortgage with an interest rate of 7%, results in a negative cash flow per year of $827. However, reduce the interest rate to 4% and it is cash flow neutral. Furthermore, imagine the cost of gas increasing over the $1.50 per therm rate, and the improvements are easily justified. The experience allowed my company to understand what parts of this renovation were the most costly and how savings might be achieved while still achieving the same impact on the energy performance. • about the author Betsy Pettit, FAIA, is a founding principal of Building Science Corporation, a Somerville, Mass., architecture and building science firm. spring 2009 HigH Performing Buildings 63 HPB.hotims.com/25005-11 http://www.friterm.com http://www.friterm.com http://HPB.hotims.com/25005-11
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