Effects of Indoor Plants on the Physical Environment with Respect to Distance and Green Coverage Ratio

Effects of indoor plants on CO2 concentration, indoor air temperature and relative humidity in office buildings

This experimental study investigates the influence of indoor plants on three aspects of air quality in office spaces: relative humidity, indoor air temperature, and carbon dioxide concentration. Employing a Latin square design, we rotated three different treatments across three offices over six time periods. These treatments included a control (no plants), a low-volume treatment (five plants), and a high-volume treatment (eighteen plants) of Nephrolepis exaltata (Boston fern). Air quality parameters were continuously monitored at five-minute intervals using Trace Gas Analyzers. Generalised linear mixed modelling (GLMM) was employed to examine the effect of each treatment on relative humidity, indoor air temperature and CO2 concentration. We observed a significant positive correlation between the number of indoor plants and relative humidity levels. In offices without any plants, the median relative humidity was 29.1%. This increased to 38.9% in offices with 5 plants and further to 49.2% in offices with 18 plants. However, we did not find significant associations between the number of indoor plants and indoor air temperature or corrected CO2 concentration. Our research provides support for the use of indoor plants to increase relative humidity, which can have health benefits in dry climates, but does not provide support for using indoor plants to regulate indoor air temperatures or CO2 concentration in office environments.

Effects of Indoor Plants on Human Functions: A Systematic Review with Meta-Analyses

The influences of indoor plants on people have been examined by only three systematic reviews and no meta-analyses. The objective of this study was therefore to investigate the effects of indoor plants on individuals' physiological, cognitive, health-related, and behavioral functions by conducting a systematic review with meta-analyses to fill the research gap. The eligibility criteria of this study were (1) any type of participants, (2) any type of indoor plants, (3) comparators without any plants or with other elements, (4) any type of objective human function outcomes, (5) any type of study design, and (6) publications in either English or Chinese. Records were extracted from the Web of Science (1990-), Scopus (1970-), WANFANG DATA (1980-), and Taiwan Periodical Literature (1970-). Therefore, at least two databases were searched in English and in Chinese-two of the most common languages in the world. The last search date of all four databases was on 18 February 2021. We used a quality appraisal system to evaluate the included records. A total of 42 records was included for the systematic review, which concluded that indoor plants affect participants' functions positively, particularly those of relaxed physiology and enhanced cognition. Separate meta-analyses were then conducted for the effects of the absence or presence of indoor plants on human functions. The meta-analyses comprised only 16 records. The evidence synthesis showed that indoor plants can significantly benefit participants' diastolic blood pressure (-2.526, 95% CI -4.142, -0.909) and academic achievement (0.534, 95% CI 0.167, 0.901), whereas indoor plants also affected participants' electroencephalography (EEG) α and β waves, attention, and response time, though not significantly. The major limitations of this study were that we did not include the grey literature and used only two or three records for the meta-analysis of each function. In brief, to achieve the healthy city for people's health and effective functioning, not only are green spaces needed in cities, but also plants are needed in buildings.

Greenness Index and Preferences for Interior Landscapes in Residential Spaces

Modern people have limited opportunities to experience the natural environment due to reduced outdoor activity time and are not provided with enough opportunities to encounter landscape, even in indoor spaces. Due to the current COVID-19 pandemic, the time spent indoors is getting longer. As the number of health-conscious people increases, interest in the introduction of indoor plants, which help purify the air and improve emotional stability, has increased. This study aimed to identify the direction of creating interior landscapes in residential spaces by examining the Greenness Index (GI) and resident preferences. This study targeted 65 households in residential spaces with over two rooms and growing plants. Pictures and descriptions of interior spaces were collected and analyzed. Case studies were conducted to analyze interior landscape planning preferences. The results indicated that public spaces (72.3%) contained foliage plants (98.5%) and containers using soil (93.8%). Residents perceived all components, from plants to containers, considering the GI. Residents’ subjective perceived GI (15% on average) was higher than the objective GI (10% on average) calculated from photos. Psychological stability and visual beauty were high for all items. Preferred locations for interior landscapes were living rooms (55.4%), which are public spaces, and living room verandas (38.5%), which are functional spaces, with foliage plants (52.3%) being predominant. These findings indicated that interior landscape could link the indoor environment in residential spaces and external spaces using nature, creating aesthetic and environmental effects indoors. Furthermore, this study is meaningful, as it identified residents’ preferences for interior landscape planning in residential spaces.

Rapidly Quantifying Interior Greenery Using 360° Panoramic Images

Many people spend the majority of their time indoors and there is emerging evidence that interior greenery contributes to human wellbeing. Accurately capturing the amount of interior greenery is an important first step in studying its contribution to human well-being. In this study, we evaluated the accuracy of interior greenery captured using 360° panoramic images taken within a range of different interior spaces. We developed an Interior Green View Index (iGVI) based on a K-means clustering algorithm to estimate interior greenery from 360° panoramic images taken within 66 interior spaces and compared these estimates with interior greenery measured manually from the same panoramic images. Interior greenery estimated using the automated method ranged from 0% to 34.19% of image pixels within the sampled interior spaces. Interior greenery estimated using the automated method was highly correlated (r = 0.99) with interior greenery measured manually, although we found the accuracy of the automated method compared with the manual method declined with the volume and illuminance of interior spaces. The results suggested that our automated method for extracting interior greenery from 360° panoramic images is a useful tool for rapidly estimating interior greenery in all but very large and highly illuminated interior spaces.

Effects of Indoor Plants on Self-Reported Perceptions: A Systemic Review

Bringslimark, Hartig, and Pati conducted a literature review of empirical studies investigating the psychological benefits of indoor plants, all of which adopted an experimental design and were written in English. However, the researchers did not follow the rigorous Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol. Additionally, the reviewed data were obtained at least a decade ago, and thus require an update. Therefore, the present article reports a systemic review of the quantitative empirical research (in English and Chinese) exploring the effects of indoor plants on subjective psychological perceptions. The information sources were mainly Web of Science (1900–) and WANFANG DATA (1980–), in which only empirical studies using quantitative methods were selected. The eligibility criteria were studies (1) involving any participants, (2) regarding indoor plants (real or surrogates) as an intervention, excluding those equipped with a power-driven biofilter, (3) involving comparators to facilitate within-subject and between-subject comparisons, (4) presenting psychological perceptions as outcome measures, and (5) of all study designs. The two authors collected 45 journal papers (with 50 studies in total). The (1) authors and publication years, (2) participants’ nationalities, sex, and age, (3) number of interventions, (4) duration of plant exposure, (5) participant–plant distance, (6) experiment room size, (7) room climate (i.e., lighting, temperature, and humidity), (8) study designs (i.e., experimental, field experimental, quasi-experimental, field quasi-experimental, or survey designs), and (9) self-reported perceptions (i.e., emotion, cognition, health, restoration, thermal comfort, productivity, and satisfaction) were identified and reviewed. These 50 studies were also analyzed for their quality. Most had moderate research quality. The synthesized results of the reviewed studies showed that the most noticeable effects of indoor plants on participants were increasing positive emotions and reducing negative feelings, followed by reducing physical discomfort. Because members of the general public today spend most of their time indoors and are faced with increasingly severe problems associated with physical–mental health and wellbeing, the application of indoor plants to improving people’s physical–mental health is worth exploring.