Life Cycle Energy, Costs, and Strategies for Improving a Single Family House
The life cycle energy, greenhouse gas emissions and costs of a contemporary 2,450 sq. ft. residential home (referred to as the standard home, or SH) were evaluated to study opportunities for conserving energy throughout pre-use (materials production and construction), use (including maintenance and improvement), and demolition phases. Home construction and maintenance materials and appliances were inventoried totaling 306 metric tons. The use phase accounted for 91% of the total life cycle energy consumption over a 50-year home life. A functionally equivalent energy efficient home (EEH) was modeled that incorporated eleven energy efficiency strategies including double 2x4 wall construction, efficient appliances, windows and lighting, and heat recovery. These strategies led to a dramatic reduction in the EEH total life cycle energy; 6,400 GJ for EEH compared to 16,000 GJ for the SH. For energy efficient homes embodied energy of materials becomes a more important design consideration; pre-use energy accounted for 26% of the total life cycle energy. The discounted (4%) life cycle cost, consisting of mortgage, energy, maintenance, and improvement payments varied between $426,700 and $454,300 for SH using four energy price forecast scenarios. In the case of EEH energy cost savings were offset by higher mortgage costs resulting in total life cycle cost between $434,100 and $443,200. Life cycle greenhouse gas emissions were 1013 metric tons for SH and 374 metric tons for EEH.