Research on the feature of thermal environment and auxiliary behavior of air-conditioning in buildings with substandard central heating

The occurrence of extreme cold weather poses significant challenges to the operation of urban heating systems and indoor thermal comfort in buildings. This situation not only increases the demand for heating energy, but also puts forward new requirements for building thermal management. This study investigated the use of auxiliary heating devices (such as air-conditioning, abbreviated as AC) to maintain indoor thermal comfort in extreme cold conditions with insufficient central heating. Field surveys and equipment monitoring were conducted in 13 residential buildings and 13 office spaces in Beijing in winter from 2020 to 2022. The research results indicated that almost all auxiliary heating equipment used by users were ACs. Based on investigation and on-site measurement, the usage modes of AC for auxiliary heating were constructed and the energy usage under different modes had also been evaluated. Users were categorized into six groups, 4 types in residential buildings and 2 types in office buildings, working households (A1), mixed households (workers and students) (A2), retiree households (A3), and households with infant (A4), high-occupancy offices (B1), and low-occupancy offices (B2). Analysis showed that outdoor and indoor temperatures significantly influenced AC usage in household A1, A3 and A4, while household A2, office B1 and B2 were only affected by indoor temperature. Binary logistic regression models are developed to correlate temperature with AC usage probability, revealing critical indoor temperature thresholds for 80% AC usage. Results indicated that pre-adjustment conditions in residences were largely outside the comfort zone than offices, improving marginally after adjustment. This study highlights the critical role of auxiliary devices in enhancing indoor comfort and provides valuable insights for optimizing heating strategies.