A yearlong study of South Korea's first net-zero energy housing complex found that its mechanical ventilation system led to lower levels of air pollutants than in conventional apartments, which, in turn, was associated with a decreased risk of symptoms of minor health conditions for inhabitants.

The study's authors, who published their findings April 26 in Science of the Total Environment, said their work is important in understanding how energy-efficient housing affects human health, as South Korea and many other nations plan to lower the energy consumption of residential buildings to address climate change.

"Measuring the health status of the occupants is one of the most important aspects in assessing the impact of housing on their overall quality of life," said senior author Hae-Kwan Cheong, a professor of social and preventive medicine at Sungkyunkwan University. "Strategies for improving housing performance in response to reducing greenhouse gas emissions should also consider the health of occupants."

The paper is one of the first to continuously evaluate over long periods how indoor air quality and the health of inhabitants are affected by ventilation systems commonly found in energy-efficient homes. The small sample size and restriction to a single city district, however, could limit how the results could be more broadly interpreted, according to the authors.

A core feature of energy-efficient housing is an airtight construction that reduces the heat that leaks into or out of a building. Mechanical ventilation with heat recovery is often used to bring in fresh air and remove pollutants while also exchanging heat between indoor and outdoor air to maintain indoor temperatures.

Previous research has found that mechanical ventilation improves several dimensions of indoor air quality, the researchers behind the new study said, yet most of those studies used monitoring data that spanned less than two weeks. Additionally, nearly all of those studies were conducted in Europe, where energy-efficient housing was introduced relatively early, according to Ah-Young Lim, the paper's first author.

"Despite the growing interest in energy-efficient buildings worldwide, there is still a lack of evidence regarding the effects of mechanical ventilation on indoor air quality and occupants' health in a long term, particularly for residential buildings," said Lim, a Ph.D. student of environmental epidemiology at Sungkyunkwan University.

In addition to conventional apartments without mechanical ventilation, Lim and his co-authors studied units in the Nowon EZ House, the nation's first net-zero-energy multiunit residential complex. Spearheaded by the South Korean government, which also funded this study, the 121-household Seoul building has been a testing ground for dozens of technologies since its opening in 2017.

The Nowon EZ House is part of South Korea's larger effort to reduce greenhouse gas emissions from buildings, in adherence to the Paris Agreement and its goal to keep global warming within 2 degrees Celsius above preindustrial temperatures. The country plans by 2030 to require all buildings with a floor area larger than 500 square meters (5,400 square feet) to be zero-energy, accomplished by ensuring minimal energy use and employing renewable-energy generation.

In 25 Nowon EZ House units and 25 nearby apartment units, the researchers placed air-quality monitors that took measurements every five minutes. The team also surveyed the subjects every three months to track symptoms that may have been experienced and behavior that affected indoor air quality, such as opening windows.

Compared with the conventional apartments, the energy-efficient housing was found to have lower concentrations of carbon dioxide, volatile organic compounds and both coarse and fine particulate matter — all common indoor-air pollutants that can be produced by household products or activities as commonplace as cooking.

An increase in these pollutants, especially particulate matter, was also correlated with a higher risk of eye fatigue, dry skin and allergies. Earlier research found some evidence of mechanical ventilation being tied to increased health risks for conditions such as asthma and dry eyes, but this most recent study did not find that similar health risks were higher for Nowon EZ House inhabitants.

"Better indoor air quality in energy-efficient homes may have contributed to the lower risks of daily symptoms among people living in energy-efficient homes compared to conventional apartments," Lim said.

The Nowon EZ House participants also reported being more satisfied with their indoor air quality and humidity, as well as their quality of sleep.

The researchers recognize that their results contain some limitations, meaning it "may be difficult to generalize the results to other energy-efficient buildings in Korea or other countries," according to the paper. Despite the small sample size, they said, the frequent measurements strengthened the investigations' statistical power.

The two groups of participants were also not fully matched for age and medical history, and the Nowon EZ House units were somewhat smaller and newer than the other apartments, variables that may have affected the results.

The Nowon EZ House is still being monitored to test other energy-efficient technologies in residential housing, such as geothermal systems and automatic control of indoor conditions, according to study author Myoung Ju Lee, who led the development of the zero-energy housing complex and is a professor of architecture at Myongji University. 

"We are planning to improve the performance and disseminate these technologies to energy-efficient residential building complex[es] in Korea in the future," Lee said.

The study, "Effects of mechanical ventilation on indoor air quality and occupant health status in energy-efficient homes: a longitudinal field study," published April 26 in Science of the Total Environment, was authored by Ah-Young Lim, Miryoung Yoon, Eun-Hye Kim and Hae-Kwan Cheong, Sungkyunkwan University; and Hyun-Ah Kim and Myoung Ju Lee, Myongji University.