A residential cogeneration system (CGS) is highlighted because of its efficient energy usage on both the supplier and consumer sides. It generates electricity and heat simultaneously; however, there is insufficient information on the efficiency according to the condition of usage. In this study, we analysed the performance data measured by the home energy management system (HEMS) and the lifestyle data of residents in a condominium of 356 flats where fuel cell CGS was installed in each flat. The electricity generated by CGS contributed to an approximately 12% reduction in primary energy consumption and CO₂ emission, and the rate of generation by the CGS in the electric power demand (i.e., contribution rate) was approximately 38%. The electricity generation was mainly affected by the use of electricity up to 4 MWh/household/year. Gas or water use also impacted electric power generation, with water use as the primary factor affecting the contribution rate. Electric power generation changes monthly, mainly based on the water temperature. From these results, we confirmed that a CGS has substantial potential to reduce energy consumption and CO₂ emission in condominiums. Thus, it is recommended for installation of fuel cell CGS in existing and new buildings to contribute to the energy-saving target of the Japanese Government in the residential sector.

In the international movement to combat the threat of climate change, the timely implementation of residential energy-saving practises is becoming an urgent issue. Because the number of apartments is increasing, we analysed data from home energy management systems (HEMSs) and data from questionnaire surveys of 309 households in a condominium. We focused on the seasonal variation in air-conditioning (AC) use in living-dining rooms to determine the tendency of energy use for heating/cooling related to the characteristics of flats, the profiles of residents, and energy-saving behaviours. In winter, 80% of residents mainly used gas floor heating rather than AC and 24% did not use AC in winter. In households where someone stays home for long hours, they prefer gas floor heating rather than AC in winter. These households also tend to engage in energy-saving behaviours to adjust the indoor thermal environment. There are several types of energy-saving lifestyles; therefore, effective energy-saving measures should be considered for both energy efficiency and the thermal comfort of residents.

Thermal comfort and sensation for each person might be different and varies despite being exposed to the same indoor environment due to the differences of their physiological factors such as gender and age. Thus, it is more challenging to provide suitable thermal environment that can satisfy each individual in the building or in the same dwelling. However, only a few studies pursue and focus on investigating the effect of physiological factors on individual thermal comfort perception. A field measurement was conducted in a condominium from September 2015 until October 2016. The measured indoor air environment in each 46 selected dwellings and 17,026 votes from thermal comfort survey for each individual person involved were collected. Therefore, this study aims to examine the variation of indoor thermal environment and determine the factors for the differences in individual thermal comfort. Hence, we categorized the individual from all selected dwellings into several groups depending on the gender and age. The results showed that there is a variation of comfort indoor air temperatures. Thus, these results can be important in designing guideline for each type of building as different user groups most likely to have different expectation regarding indoor thermal environment.