Carbon and Financial Payback Mismatched in Retrofits
Financial payback is a big deciding factor in choosing retrofit strategies, but the choices suggested by those calculations are not always the best in terms of reducing life-cycle carbon emissions, say researchers.
In a paper presented at avniR, a French conference focused on life-cycle assessment (LCA), researchers Seongwon Seo and Greg Foliente compare three different retrofit options for a conventional medium-sized office building in Australia. The authors point out that retrofits that reduce the most carbon while in use might have big embodied carbon impacts that are hard to compensate for.
According to the analysis, replacing single-glazed windows with double glazing reduces operational carbon emissions almost twice as much per year as upgrading the building’s chiller; however, manufacturing, maintaining, and disposing of those windows costs 2,539 lb. CO2 equivalent per ft2 of building area over a 50-year lifespan, compared to 71 lb. CO2 equivalent per ft2 for the chiller—less than 3% of the life-cycle emissions of the window replacements.
The chiller’s lowered embodied carbon means it would take less than a year for it to pay back its carbon debt, while the window replacement might take four to six years. A lighting retrofit had a similar four- to eight-year carbon payback in this analysis.
Despite carbon benefits, the chiller retrofit also got short shrift as measured by financial payback. It would take up to 17 years for energy cost savings to offset the cost of the chiller, but only eight for the windows and between nine and ten years for the lighting, the researchers found.
Although all three retrofits will have paid back their embodied carbon by the time an owner financially breaks even, an owner looking for the shortest financial return would likely bypass the retrofit that would reduce carbon emissions the most.
Published April 6, 2015