Development of a seasonally adaptive indoor environmental quality evaluation model and grading standard for libraries based on Weber/Fechner's law

Traditional evaluation of indoor environmental quality (IEQ) relies on static models that overlook user comfort and lack unified grading standards. Based on on-site measurements and subjective surveys conducted in a university library in Guangzhou across summer, transitional, and winter seasons, this study develops and validates a seasonally adaptive evaluation framework. A key innovation is the establishment of a five-level comfort grading system (from excellent to very poor) built upon a novel index, the predicted mean vote index (PMVi). The PMVi applies Weber/Fechner's law to normalize thermal, air quality, acoustic, and lighting indicators into a single variable, and its validity is confirmed through user evaluations. Importantly, the analytic hierarchy process revealed seasonal shifts in occupants’ environmental preferences: thermal conditions dominate in summer (weight = 0.45), while acoustic factors become most influential during transitional (0.37) and winter (0.40) periods. Ultimately, this study establishes an integrated evaluation model; the proposed integrated evaluation model, combining objective PMVi with dynamic seasonal weightings, aligns closely with occupants’ perceived comfort. This framework provides a practical and unified approach for dynamic IEQ evaluation and regulation in library environments.