A critical part of designing for exceptional energy efficiency is selecting the most cost effective combination of energy systems, building materials, and design features. To reduce some of the guesswork on the design of two new houses on the coast of Maine, we employed Ekotrope Optimizer, software developed by MIT scientists to determine energy investment ":sweet spots." It enabled us to reduce construction costs and improve performance of the houses simultaneously.

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These models represent two variations on thermal boundary locations. The first is a minimal configuration in which the attic is insulated at the flat ceiling and walls to the unfinished attic, and the crawlspace is unconditioned. Thermal losses from ducts and equipment in these spaces are significant. Conversely, the second model is an optimal configuration in which the crawlspace is conditioned and the attic rafters are insulated. Thus the thermal losses from ducts and equipment are eliminated

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While the capital costs to achieve the optimal thermal boundary ranged around $10,000, this chart displays the payback period from energy savings to be 10;.5 years with a cumulative cost savings of over $30,000. 


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The mechanical equipment was another avenue of analysis. A conventional mechanical system was compared to a system with a higher initial cost, but yielded a huge return on the investment over the lifetime of the system."

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The payback period for the optimal mechanical specs is only 1.9 years, with a total savings over a 30 year period of around $198,000