DOI: 10.25549/usctheses-c40-318623
title: Energy facade retrofit: energy performance and the impact of facade changes in non-residential buildings in the United States

description: The existing stock of buildings has become a major target of energy reduction for the 21st century (Architecture2030). Despite strong structures, a significant portion of these buildings were built with inefficient envelopes, on account of the relatively low-cost, abundant energy that was available to provide heating, ventilation, and air conditioning by mechanical means. With dwindling resources and an increase in energy prices, replacing inefficient equipment and lighting fixtures generally result in lower initial costs and more evident savings. These solutions typically constitute current retrofit practice. They are, however, inadequate, because the energy used still flows through an inefficient building skin.  Due to a paucity of information regarding proven cases of facade retrofit, other retrofit practices have yet to be fully explored. ❧ For this thesis, three main research objectives were set: to 1) identify, 2) quantify and 3) evaluate energy facade retrofits. A review was conducted of the existing literature, and online surveys, data collection and data processing were among the primary methods applied. The first-ever database of facade retrofit projects, comprising a number of existing cases was compiled, and the database was one of many resources used. Applying such as mixed methodology, exploratory and evidence-based research provided a better understanding of the potential benefits of including facade systems in building renovation strategies. ❧ The state of the art was described through a deep review of existing literature and online resources, following a search that identified a major gap in knowledge in the field: the need for quantification. Two online surveys provided an adequate sense of state-of-the-art practices used in facade retrofits. In the second survey in particular, energy data was specifically requested as the initial step in data collection, to identify ideal candidates among existing projects. ❧ The collected data covered a wide range, including anything from a general description of the building, to retrofit characteristics, and their results. Part of the information was made available to professionals and the general public on the FacadeRetrofit.org website, an online public resource with over 500 completed facade retrofit cases. During a follow up with the respective professionals, detailed data was collected for some of these retrofitted projects. ❧ A subset that allowed for quantifying energy variations was created from pre and post-retrofit energy data, obtained from actual building projects. Stepwise regression analysis and classification algorithms were used to analyze the data, which determined the most significant parameters such as location, building characteristics and retrofit actions, parameters that had the greatest impact/effect on energy consumption in the building. Where location was concerned, latitude and building orientation were identified as relevant factors. Where facades exclusively were concerned, sunshade and Window-to-Wall ratio (WWR) turned out to be the two main features impacting energy data. Controlling the use of artificial lighting with daylighting sensors was revealed to be an essential aid in achieving maximum energy reductions. ❧ The insights obtained from actual data were significant. In general, retrofit projects that included the facade along with equipment upgrades achieved larger energy savings than those focused only on internal systems. On average, the subset that included the facade achieved energy reductions of 27%, while systems-only retrofits achieved 17%. An average of 27% in energy reduction achieved by facade-inclusive retrofit buildings was statistically significant, when taking into account pre- and post-retrofit energy use intensities, and larger than the savings from systems-only retrofit buildings. However, these energy reductions were modest, considering the multiple building systems being include, and that deep-energy retrofits were conceptualized as interventions intended for an energy reduction of at least 50%. ❧ The energy use intensity (EUI) achieved in facade-inclusive retrofit buildings was 52 kBtu/sq.ft.-yr, which was lower, by a statistically significant margin, than the national 92.9 kBtu/sf-y EUI of US office buildings (One-sample T-test resulted on a t-value=-12.84 and p-value=0.000).  The overall achieved performance of facade inclusive retrofits, as refers to the post-retrofit EUI, was similar to the 57 kBtu/sq.ft.-yr of systems-only retrofit buildings, and the 58.6 kBtu/sq.ft.-yr best-practice (LEED) buildings (ANOVA Test p-value=0.801). ❧ However, these completed projects included facade changes, among several other energy improvement systems, representing compounded effects. To explore in greater detail the effects of facades in particular, the next phase of the research ran simulations which formed the basis of a parametric analysis. For this purpose, five groups of facade retrofit strategies were run based on a representative model office placed in three different US locations, which resulted in more than 4,000 iterations of energy simulations. The most significant facade strategies for larger energy reductions were identified and analyzed through stepwise regression analysis. The relevance of daylighting controls was ratified, which allowed internal loads to be affected by facade changes. Energy reductions of up to 13.4% were observed from single facade retrofit (FR) strategies, and up to 17.2% from pairs of different strategies. Facade retrofits in a cold climate offered the highest potential for energy reduction, though they represented a wider dispersion of results, as compared to results from warm and mixed climate conditions. The regression analysis of these iterations resulted in a defined set of significant parameters, separated by location, that are relevant in informing preliminary decisions regarding facade retrofits. ❧ A representative Mid-Century Modern building was chosen to investigate the maximum potential for energy reduction. Based on the set of variables previously identified by the stepwise regression analysis, the synergies and the trade-offs of combined strategies were explored. The greatest energy savings of up to 15.6% (37% facade-affected end uses) were observed in mild climate locations, while savings of 17.3% (30.6% facade-affected end uses) and 9.9% (17% facade affected end uses) were observed in cold and warm climate conditions respectively. ❧ Finally, the evaluation of facade retrofits required investigating means of comparison of the value of a facade retrofit, as compared to alternative retrofit strategies, or simply to the non-retrofitted condition. The facade retrofits’ energy impacts were comparatively analyzed with systems-retrofit buildings and non-retrofitted buildings (a control group) through regressions of actual data. Despite the energy reductions of non-retrofitted buildings, facade retrofit buildings still revealed higher energy reductions than the control group by 11.7% and systems-only retrofits by 2.9%. Systems-only retrofits resulted in an 8.8% higher energy reduction compared to the control group. ❧ As this dissertation moved from the evaluation phase to valuation, the study revealed frequently ignored parameters. Human and Real Estate aspects were estimated according to existing literature in these areas and incorporated into a decision tree. Using financial estimates as metrics, these previously unconsidered benefits could outweigh the limited, short-term benefits of single or system upgrades. The metrics were explored in a case study. The findings, along with the research, added valuable information to the design and investment decision process for many buildings awaiting renovation.