[Paper Reading] A review of factors affecting occupant comfort in multi-unit residential buildings

Publication year: 2019
Authors: Maedot S. Andargie, Marianne Touchie, William O’Brien

Introduction

• With the improvement of living standards, growing awareness of the impact of indoor environmental conditions on wellbeing as well as increased value for healthier residences, greater importance is being given to improving the indoor environment in residences. Consequently, there has been an increase in studies which evaluate factors that affect occupant comfort and health in residential buildings in the last few years.
• However, most of these studies are performed only on one building type. Transferring results to multi-unit residential buildings (MURBs) can be more challenging due to their compartmentalized interior zones, building height and control options for occupants, such as operable windows and the level of control over the HVAC system
• Similarly, design and control features can vary between MURBs and office/commercial buildings and thus, directly applying research findings about comfort in offices to MURBs can be challenging. The amount of space available per occupant is much lower in commercial buildings compared to MURBs which impacts occupants’ visual and acoustic privacy
• Office occupants might also have limited control over the source of pollutants and odor, and ways to mitigate air quality issues (e.g., no operable windows, the possibility of affecting colleagues if using portable air filters or opening windows) whereas residents in MURBs can have partial control over sources of pollutants and more mitigation options.
• Occupants in office/commercial buildings have limited control over the sources of noise and have more acoustic privacy issues especially in open-plan offices. Visual comfort is also a challenge in office buildings where there are restrictions on adjusting artificial lighting, natural lighting (adjusting blinds/curtains), furnishing and layout which result in visual discomfort and privacy issues
• This paper presents a critical review of studies which investigated occupant comfort in MURBs in relation to indoor environmental quality (IEQ) and non-IEQ variables. The main objectives of this paper are to compare the various methodologies used in assessing occupant comfort, identify which IEQ and non-IEQ factors are important determinants of occupant comfort, and identify gaps in the literature.

Variables affecting occupant comfort in MURBs

IEQ

Indoor thermal conditions

• Thermal comfort is the most widely studied comfort aspect. As such, most studies have assessed the relationship between thermal comfort and indoor thermal conditions such as temperature, relative humidity and air speed.
• Results of the literature survey show that outdoor climate might play a more significant role. Neutral temperatures reported in the surveyed studies are higher during the summer compared to winter. Neutral temperatures also vary based on the availability of control over thermal conditions
• Several studies indicate a deviation of occupants’ reported temperature ranges for comfort from that predicted by standard models, such as ASHRAE’s thermal comfort model. This indicates that thermal comfort is dependent on factors other than temperature. Clothing level is a key factor that affects thermal comfort and thermal acceptability, and one that is particularly important in a residential environment where people have control of both temperature and clothing level
• Occupants adjusted their clothing based on their metabolic activities, which varies throughout the day. Such clothing variation based on time of the day is, however, rarely observed in office buildings.
• Air speed is also an important determinant of thermal comfort [51,77,78,106] while studies reported contradictory results regarding the importance of humidity to thermal comfort.
• Occupants’ behavioral and physical adaptations or expectations, as well as other personal factors, and indoor and outdoor conditions can also impact comfort levels

IAQ

• A review of the literature, however, shows that there is a lack of in-depth analysis regarding IAQ and its impact on comfort in MURBs. Many studies simply evaluate the level of occupant satisfaction with air quality without attempting to understand reasons for the varying levels of satisfaction. Thus, only a few studies assess how IAQ satisfaction varies with environmental parameters.
• In addition to the aforementioned IAQ indicators, several other factors impacted occupants’ satisfaction with IAQ. Studies that relied on subjective reporting for causes of dissatisfaction with IAQ found that odor, stuffy air, and dust affect IAQ satisfaction levels

Indoor visual conditions

• Research shows that there are six main parameters that impact indoor visual comfort: glare, outside view, daylight, lighting level, uniformity of lighting, and privacy
• The decreased importance of glare for visual comfort reported in these studies shows that occupants’ ability to relocate or control blind positions easily in residential environments results in lower dissatisfaction levels than commercial settings where occupants’ ability to adjust environmental conditions are limited

Indoor acoustic conditions

• Unlike visual conditions, occupants in MURBs have minimum control over indoor noise levels and sources. The literature survey shows noise sources originating from the occupants’ buildings, referred to in this paper as indoor noise sources, are the main sources of acoustic discomfort for occupants in MURBs.
• This might be due to poor acoustic insulation, construction type (e.g., single panel walls) and high-density development where neighboring units might have windows within close proximity resulting in noise propagation through windows as well as shared walls and floors
• Studies that included acoustic monitoring used sound pressure levels to evaluate acoustic comfort. This is a significant limitation because acoustic comfort is also affected by the frequency of noise. The sensitivity of the human ear to noise varies with frequency
• While the Aweighted sound pressure level used in the surveyed studies is a good way to measure such loudness as perceived by the human ear, it has been proven to reduce the effects of low-frequency sounds, especially those below 100 Hz

Impact of outdoor environment

• Outdoor climate is one of the key factors that affect occupants’ perception of thermal comfort. Studies show that long exposures to a certain outdoor climate lead to physiological adaptations affecting occupants’ preferences and responses to their indoor thermal conditions.

Outdoor climate

• For naturally ventilated MURBs, outdoor climate can directly impact indoor thermal conditions. Thus, occupants’ comfort levels can vary with season and time of day
• Similarly, occupants feel warmer and prefer cooler conditions during months with high outdoor temperatures compared to colder months
• Occupants’ socioeconomic status can also impact indoor temperature levels where occupants use less heating/ cooling to save on energy bills which results in different adaptations and neutral temperatures to similar outdoor conditions

Surrounding infrastructure

• Traffic and construction noise are the two main external sources of acoustic discomfort reported in the literature. Traffic noise is reported as less important, especially for high-rise MURBs, as the noise level decreases with height.
• Construction noise, such as renovation of neighboring buildings, can have a higher importance as the noise source can be relatively closer to occupants.
• Surrounding infrastructure can also affect occupants’ visual comfort and overall satisfaction in MURBs. Although highly subjective, outside view is identified as one of the important parameters for visual comfort

Impact of occupant characteristics

• Several studies assessed the impacts of occupant related characteristics on comfort levels. The studied characteristics include age, gender, socioeconomic background, marital status, ownership, lifestyle and health, relationship with neighbors, job, energy saving awareness, pride in residence, years occupying residence and years lived in the countries the studies were conducted.

Age

• The literature presents conflicting results regarding the impact of age on occupant comfort.
• Older occupants are more comfortable with indoor conditions in their residences and exhibit a higher acceptance rate compared to younger residents. This might be due to older occupants using adaptive behaviors, such as changing clothing level, more frequently than younger occupants to adapt to uncomfortable indoor conditions, or their reluctance to report discomfort compared to younger occupants

Gender

• Variations in comfort levels due to gender differences are mainly observed for thermal comfort levels. Female occupants have higher neutral temperatures than men and tend to wear more clothing due to their preference for warmer temperatures. In addition to clothing adaptation, physiological and psychological adaptations can explain the observed differences
• Women are more tolerant and satisfied with the indoor environment in their residences which might be because surveyed female occupants spent more time in their residences compared to their male counterparts resulting in a higher level of adaptation. The difference in comfort levels can also be due to psychological and cultural factors that affect the levels of thermal control between the genders

Relationship with neighbors

• Comfort studies in commercial settings have shown that occupants’ personal relationships, for example, with their coworkers and supervisors, are important determinants of their comfort with their indoor environment. Studies, however, give very little consideration to the importance of such personal relations when evaluating comfort in residential buildings.
• The present literature survey revealed that only two studies assessed the impact that occupants’ relationship and attitude towards their neighbors have on their comfort levels.

Ownership and economic status

• The literature suggests that ownership and economic status can influence occupants’ comfort with indoor environmental conditions.
• Occupants from low economic groups tend to use natural ventilation to mitigate IAQ issues and thermal discomfort due to their financial inability to afford space conditioning which can lead to lower satisfaction levels with acoustic conditions as opening doors and windows can increase external noise levels. Their inability to make improvements to their indoor conditions can, thus, impact their comfort levels.
• Similarly, ownership status also influences occupant comfort. Studies report that owners are more satisfied with their indoor environment and exhibit a higher acceptance level

Other characteristics

• The surveyed studies also reported significant relationships between comfort and other occupant characteristics. These include marital status, lifestyle and health, energy saving awareness and pride in residence.

Impact of building characteristics

Type of buildings

• The literature indicates that occupant comfort with thermal and IAQ conditions are different for mechanically conditioned and non-conditioned buildings. Occupants in mechanically conditioned buildings show a higher level of comfort and satisfaction with thermal conditions than those living in non-conditioned MURBs.
• Occupants in mechanically ventilated buildings tend to report higher satisfaction with IAQ than those living in naturally ventilated buildings which is likely because of a higher level of pollutants due to lack of proper ventilation. Mechanical ventilation systems equipped with filtration units also perform better than natural ventilation in areas where the outdoor air is highly polluted
• Most other studies, however, report that occupants in low-energy MURBs are more satisfied with thermal conditions, IAQ, artificial lighting and acoustic conditions than those in conventional MURBs. This might, however, be due to the availability of control in the studied buildings.

Window area

• Windows are one of the most important architectural features for occupant comfort in buildings. The type and area of windows in a building can significantly affect thermal, visual and acoustic comfort as well as IAQ satisfaction.
• The reported direction of the relationship between comfort and window size is different for different comfort metrics. Occupants in MURBs with small windows reported decreased levels of visual comfort due to insufficient daylight
• Even though the comfort level provided by different sized windows depends on other factors, such as the climate, orientation and performance of the glazing, these findings indicate that various comfort aspects should be considered when optimizing window area

Other building characteristics

• Floor level is reported to have a significant impact on occupant comfort where occupants on higher floors report higher comfort and acceptability of indoor conditions compared to lower floors.
• Available shading, such as roof overhangs, reduce glare and overheating resulting in higher comfort levels.
• In addition, occupants in units with balconies are generally more satisfied with thermal and acoustic conditions than those in units without balconies. Balconies can, however, result in lower satisfaction with natural lighting as occupants with balconies might regularly use internal shading for privacy reasons

Ranking importance of IEQ factors

• Most studies report thermal conditions and air quality as the two most important factors for occupants’ overall comfort. While this is in line with most other comfort studies performed in buildings other than MURBs, our findings suggest that identifying the most important environmental condition is not always direct as it depends on several factors.

Health and productivity

• Sick building syndrome, nose and head discomfort specifically, are the most significant determinants of occupants’ overall satisfaction with environmental conditions in their residences. Studies identify age, gender, time spent in the residence, poor air quality, acoustic and thermal conditions as the most important predictors of these sick building symptoms
• building-related symptoms affected occupants’ missed work and school days which indicates that IEQ issues in residences indirectly affect occupants’ productivity in their workplaces.

Conclusion and recommendations

• The review of the literature showed occupant comfort is affected by various indoor environmental conditions as well as outdoor conditions, building characteristics and occupant-related characteristics. Among the indoor conditions, thermal conditions and IAQ are identified as the most important factors for overall comfort in MURBs. The review also shows that indoor environmental conditions can affect occupant health as well as their productivity in their homes or their workplaces. Findings, however, indicate that the exact relationship between occupant comfort and the determining factors is complex and requires more research. Understanding this relationship is an important step in providing indoor conditions for optimal comfort.
• Many of the single-aspect studies are focused on thermal comfort while visual comfort, acoustic comfort and satisfaction with indoor air quality are underexplored. There is also a lack of studies that do a comprehensive exploratory study on what impacts comfort in MURBs (including all IEQ and non-IEQ factors).
• The lack of such comprehensive analysis is also manifested in the limited exploration of the interrelationships between various environmental conditions and how they affect different comfort metrics.
• There are very few studies that evaluated how environmental conditions in MURBs can affect occupants’ long-term health as well as their productivity in their workspaces, or at their residence if they work from home.
• Guidelines for survey design and data collection methods can provide specific strategies to minimize response biases. Laboratory studies with residential setups can also significantly contribute to our understanding of comfort in MURBs.