The fundamental goal of modern high-performance buildings is to achieve low environmental carbon footprint while securing indoor conditions that promote human health and well-being. Current procedures for indoor environmental quality (IEQ) assessment are often sporadic, expensive, intrusive and often limited to few parameters and experts-use only. This research examines an overall IEQ assessment model in three field studies. The assessment of IEQ is achieved with the methodology for the integration of relevant IEQ parameters into an overall index through derivation of their individual weighting coefficients. A low-cost open-source platform "ENVIRA" was developed and deployed for continuous measurement of relevant IEQ parameters. A total of 125 occupants participated in the field studies-69 in two open offices and 56 in the educational building. The results from occupant survey regression analysis for offices showed that indoor air quality is the most critical IEQ parameter with the weight of 0.35 followed by thermal comfort (0.285), acoustic comfort (0.195) and illumination (0.17). The occupant preference differed in the educational building where thermal comfort was the most dominant component (0.31) followed by indoor air quality and acoustics (0.25), and lighting (0.19). Results show that individual weighting coefficients are not equivalent and could differ across building types. Finally, the mean absolute error between the average survey results and the overall IEQ index for the three field studies was <3% suggesting that the platform can be used for generating large IEQ datasets for researchers and practitioners.