Constructing thermal comfort: Investigating the effect of vegetation on indoor thermal comfort through a four season thermal comfort quasi-experiment

Several short term studies have found evidence that plants may improve occupant thermal comfort, yet this phenomena has not yet been rigorously evaluated. The aim of this paper is to present the results of a quasi-experiment that evaluated the effect of indoor plants on the thermal comfort of 67 office workers within an office building in De Lier, The Netherlands, for four months, one month each season, in 2013. The participants' thermal comfort was recorded twice a day, while the globe temperature, relative humidity, and light levels of the workspaces were monitored. The indoor operative temperature of the test rooms were varied between typical and more extreme indoor operative temperature ranges throughout the quasi-experiment in a controlled manner. The presence of a substantial quantity of plants in the work environment was found to have a significant effect on the thermal comfort of the participants. For example, the occupants of the two rooms in which the presence of plants was alternated, were both, on average, approximately 12.0% more thermally comfortable when plants were present in the room. In addition, they were approximately 1.79 and 1.95 times more likely to be thermally comfortable when plants were present in the room, respectively. These results indicate that the incorporation of a substantial quantity of plants in office buildings can lead to reduced building energy consumption and carbon emission rates, by allowing the temperature setpoint to be raised in the summer and lowered in the winter. •Plants had a positive, statistically significant effect on thermal comfort.•This positive effect was found for a range of indoor temperatures and seasons.•This positive effect of plants was psychological in origin.•Interior plants can reduce buildings' operating energy consumption rates.•The quality of workspaces can reduce buildings' operating energy consumption rates.