Life Cycle Optimization of Residential Clothes Washer Replacement
The energy efficiency of the average clothes washer in the United States improved by 88.4% from 1981 to 2003 (AHAM 2005). Replacement of old vertical-axis washers with new horizontal-axis washers results in decreased operating costs, both environmental and economic. But replacement also results in one-time financial and environmental impacts from purchasing, manufacturing and disposition. The purpose of this study is to quantify this trade-off and determine optimal replacement intervals for residential clothes washers.
The Life-Cycle Optimization (LCO) model employed to answer this fundamental research question uses as inputs separate Life-Cycle Inventory (LCI) and Life-Cycle Cost (LCC) profiles for each model year clothes washer from 1985-2020. These profiles represent four life-cycle phases of a washer: Material production, manufacturing and assembly, use, and end-of life management.
The results of the LCI and LCC studies showed that the use phase of the washer's life cycle accounts for 96-99% of energy, carbon dioxide emissions and water use, but just 61%-86% of total costs over an anticipated 20 year life. From an energy or carbon dioxide emissions perspective, any average washer, regardless of model year, should be replaced with a new horizontal-axis washer in 2006, 2011 and 2016. From a water use and cost minimization perspective an average washer should be immediately replaced with a horizontal-axis washer which should be held until the end of the study period.
In addition to a base case that seeks to model the typical American household, four alternative scenarios were examined. The first was a scenario where the consumer was assumed to have an electric water heater instead of gas. This did not substantially change the optimization routine. The second alternative assumed all clothes were washed with cold water, causing replacement only twice in 2013 and 2020 when minimizing energy and carbon dioxide emissions. The third scenario assumed that all clothes were washed with cold water and line-dried. This magnified the differences highlighted in the second scenario and changed the optimal interval for carbon dioxide emissions and energy, eliminating the need for a second replacement in 2013. The fourth alternative was a scenario where energy prices were assumed to remain constant in 2006 dollars as opposed DOE projections which forecast a decline in real dollar terms. This had little impact on replacement intervals.