Indoor environmental quality benefits of apartment energy retrofits
Introduction
Approximately 20 percent of all U.S. households live in multifamily buildings [1]. Older apartments serving low-income populations are often poorly maintained, with deficiencies in indoor environmental quality (IEQ) such as poorly controlled thermal comfort conditions and high levels of pollutants [2], [3]. The U.S. is implementing many energy retrofits in homes with the goal of reducing building energy consumption and carbon dioxide emissions, as well as improving national energy security. Several protocols and tools exist to help with the selection and implementation of housing energy retrofit measures [4]. These protocols are typically based on energy models, engineering judgment and cost-benefit analysis, rarely considering potential effects on IEQ. Features of IEQ that may be affected by retrofits include thermal comfort conditions, indoor air pollutant concentrations, and acoustic and lighting conditions [5], [6], [7]. Although retrofit efforts provide an opportunity to simultaneously save energy and improve occupant's health and comfort, potential IEQ improvement opportunities are often not considered during selection of retrofits measures. If IEQ is neglected when retrofits are selected and implemented, the retrofits have the potential to degrade IEQ. In particular, sealing leaks in building envelopes, a very common practice, will reduce outdoor air ventilation and lead to increases in indoor air concentrations of indoor-generated air pollutants.
Improvements of IEQ have been demonstrated in a few home retrofit studies. Studies from New Zealand reported improved comfort, indoor air quality (IAQ), and health symptoms resulting from upgrading insulation and replacing ineffective heating systems or heating systems that vent combustion gases to indoors [8], [9]. Because pre-retrofit indoor air temperatures were lower than typical temperatures in U.S. homes and because many of the New Zealand homes had heating systems that vented combustion gases indoors, the results of this study are not generally applicable to U.S. homes. Some retrofit studies have focused on a specific IAQ challenge in multifamily buildings – the inter-apartment transport of pollutants. Bohac et al. [10] reported reduced transfer of secondhand tobacco smoke between apartments resulting from apartment air sealing and increased ventilation. However, to the best of our knowledge, no study has empirically investigated the potential for simultaneous energy and IEQ benefits when broad packages of retrofits are implemented in apartments.
The current paper describes the changes in IEQ conditions (air quality and thermal comfort conditions) from the implementation of energy and IEQ retrofits in a total of 16 apartments serving low-income populations within three buildings in different California climates and seasons. Energy savings data are still being collected and will be described in a future paper. The retrofits were selected using a protocol [4] that estimates the value of energy, comfort, and IEQ benefits of retrofit measures for the purpose of optimizing retrofit packages to achieve these three goals.
Section snippets
Apartments and retrofits
Buildings and apartments were selected and retrofit specifically for this project. Selection criteria included low-income residents (subsidized housing), heating and cooling systems that serve individual apartments (not shared among apartments), and locations in multiple California climate zones. Also, building owners, management companies, and individual residents had to agree to participate. For more information on the buildings and the selection process see Ref. [4]. Buildings 1, 2, and 3
Results
Tables S2–S4 in the supplemental information provide the main IEQ measurement results from periods before and after the retrofits for apartments in buildings B1–B3, respectively. These tables provide for each apartment, for both pre-retrofit and post-retrofit periods, values of the IEQ parameters described in Section 2. When applicable, outdoor air values of parameters are also provided. Carbon monoxide concentrations were consistently below guidelines and near to the level of measurement
Discussion
This study was based on the hypothesis that a set of practical retrofits could simultaneously save energy and improve IEQ conditions in apartments. Because energy data are still being collected, the validity of this hypothesis cannot yet be assessed. The findings presented in this paper do indicate an overall improvement in IEQ conditions. In general, the measurements indicate improvements in comfort conditions, bathroom humidity, and concentrations of carbon dioxide, acetaldehyde, VOCs, and
Conclusions
The results of this study indicate the potential for overall improvements in IEQ when a package of retrofit measures is implemented in apartments to both save energy and improve IEQ. There was a general improvement in comfort conditions, bathroom humidity, and concentrations of carbon dioxide, acetaldehyde, VOCs, and PM2.5. However, not all findings were positive. Formaldehyde levels decreased in B1, which had the highest concentrations, were unchanged in B2 and increased in B3. Also, NO2
Acknowledgments
Funding was provided by the California Energy Commission, Public Interest Energy Research Program, Energy Related Environmental Research Program, through contract 500-09-022 and by the Assistant Secretary for Energy Efficiency and Renewable Energy, Building Technologies Program of the U.S. Department of Energy under contract DE-AC02-05CH11231. The authors thank Marla Mueller and Chris Early for Program Management; the Technical Advisory Committee for input and assistance in apartment
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Present address: EURAC Research, Institute for Renewable Energy, Bolzano, Italy.