As part of an investigation aimed at gaining a better understanding of indoor thermal environments, energy consumption levels, and occupant behavior, the householders of 587 detached houses in six cities of the Tohoku City region were surveyed in the winter of 2018 via a questionnaire and recorded liquid crystal thermometer measurements. Houses in the cities of Sapporo and Fuchu were used as references. Similar investigations have been performed at 10-year intervals since 1982. The obtained data were then applied to create an overview covering the past 36 years, which resulted in additional information that will be useful for future indoor environmental design. This paper begins by describing wintertime occupant behavior changes and indoor temperature in each city over a 20-year period and then discusses changes to space-heating energy consumption during the cold winter periods. The influence of various factors on indoor morning temperatures and space heating energy consumption are then analyzed using a multivariate analysis method.
1. The results of this investigation show that the thermal performance levels of houses the Tohoku City region are becoming increasingly similar to those of Sapporo City and that differences among all cities examined have lessened in the last 16 years. In particular, it was confirmed that the thermal performance levels of cities in the northern Tohoku City region had become closer to those of Sapporo City. From the viewpoint of thermal performance levels, these cities can be classified into the following groups: i) the cities of Aomori, Morioka, Akita and Yamagata (which have similar performance levels to Sapporo City); ii) Sendai City (including households with high energy consumption levels); and iii) the cities of Fukushima (which show performance levels similar to Fuchu).
2. The average floor area of Tohoku City detached houses was almost the same as recorded in 2002. Additionally, we found that the use of double windows or double-paned windows has increased among Tohoku region cities since 2002, while heating times have shown overall increasing trends over the last 36 years. Previously, kerosene heaters, including both vented and portable types, were popular among Tohoku region residents, but this investigation found that kerosene heater usage rates have been decreasing since 2002 while the use of electric heaters has increased.
3. Early morning room temperatures have been trending upward for the last 36 years. In fact, the average temperature recorded during this investigation was 17.1 ℃, which is a 1.0 ℃ increase from 2002. It is believed that this increase in the early morning temperature level was not only due to improvements resulting from insulation and airtight building envelope conditions, but also due to increased heating times.
4. To clarify the factors influencing morning living room temperatures and energy consumption levels for space heating, a multi-level analysis method was applied. The factors that were considered to influence temperature were sunshine levels, thermal insulation, heating equipment type, heater usage times, morning thermal environment, and indoor humidity level perceptions. As for the dispersion of energy consumption for space heating, the factors considered were sunshine levels, completion, floor area, primary heating equipment, and heater usage times. It was also shown that the average energy consumption for space heating in northern cities was the highest among the cities surveyed, and that room temperatures were less susceptible to outdoor temperature declines due to increased thermal insulation performance levels.
