Life Cycle Inventory Data for Life Cycle Assessment (LCA) of Highly Energy Efficient Case Study House in Dillingham, Alaska

Published: 25 January 2018| Version 1 | DOI: 10.17632/sg59vbryx2.1
Contributors:
Yasmeen Hossain,
Tom Marsik

Description

This life cycle inventory data is used to conduct a life cycle assessment of a case study house. While energy efficiency features can significantly reduce the greenhouse gas emissions during a building’s operational stage, extra materials and processes associated with these features typically involve higher greenhouse gas emissions during the construction phase. In order to study this relationship, a case study of a highly energy-efficient house in rural Alaska was performed. For the purposes of this case study, a theoretical counterpart home was designed that has the same interior space, but insulation values close to the code minimum requirements. Using computer simulations, LCA was performed for the case study home as well as its conventional counterpart. The extra greenhouse gas emissions associated with the construction of the case study home were compared to the annual savings in greenhouse gas emissions achieved thanks to the energy efficiency features, and carbon payback was calculated to be just over 3 years. The house is located in Dillingham, Alaska. Net living area of the house is about 54.8 square meters, outside dimensions are 7.3 m by 7.3 m with 71 cm thick walls. The house falls into the category of a net-zero energy ready building, consuming roughly 3,000 kWh annually for all energy needs. Air tightness was measured at 0.05 air changes per hour (ACH) at 50 pascals. The case study home was built utilizing a “box-in-a-box” technique with a continuous polyethylene vapor barrier surrounding the interior “box”. This construction method allowed for a continuous vapor barrier with minimal thermal bridging. The vapor barrier is on the outside of the interior framing so that the wiring for the interior of the house does not puncture the vapor barrier. The 60 cm cavity between the interior and exterior wall was filled with blow-in cellulose insulation. There is fiberglass insulation within the interior framing. The walls have an RSI value of about 16 K·m2/W. The ceiling of the house has an RSI of about 25 K m2/W. The theoretical conventional counterpart home model has the same interior dimensions of 5.9 m by 5.9 m. The wall structure is a frame with 38 mm x 140 mm studs (referred to as 2x6 frame in the U.S.) with RSI of 3.7 K·m2/W fiberglass insulation and 25 mm polystyrene foam board on the inside, giving the walls an RSI 4 K·m2/W value. The ceiling is a frame with 38 mm x 286 mm ceiling joists (referred to as 2x12 frame in the U.S.) with RSI 6.7 K·m2/W fiberglass insulation and 25 mm foam on the inside giving it an RSI 7.2 K· m2/W value. The air tightness of the house was modeled at 1.0 ACH at 50 Pascals. The conventional model has a 45.7 cm crawl space to create room for the plumbing structures.

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The software used for the LCA was SimaPro 8. For this case study, we calculated the climate-change impacts using the Intergovernmental Panel on Climate Change (IPCC) global warming potential 100-year time horizon impact assessment method. Because this study looked at one impact category, the climate-change impacts, it is classified as a single attribute LCA. The libraries used are the European ecoinvent 3 and the Industry data 2.0. We used secondary data. The LCA includes the impact of the building materials, from cradle to warehouse, and the disposal of the materials at the end of the life cycle of the houses. It does not include transportation of the building materials from the warehouse to the building site, nor from the building site to the town landfill or incinerator. It does not include maintenance of the house or the heating system. Differences in on-site energy use during the construction of homes were also not included. In the material list for both houses, items of very small quantities such as sill sealer were not included, assuming the difference in the amount of sill sealer between the houses to be negligible. When calculating the operational greenhouse gas emissions, only the heating energy was considered. The waste scenario used for this analysis was based on present day disposal options, rather than making a prediction as to what waste disposal might look like 100 years into the future. In 2014, the city of Dillingham had a permit to incinerate all lumber and buried all other construction materials in the landfill

Categories

Energy Efficiency, Rural Area, Life Cycle Assessment, Alaska

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