## 4 Conclusions  
This paper presented an attempt to evaluate the perception of summer internal conditions by middle-aged and elderly people whose health conditions allowed them to live independently in their apartments. This target group (to the knowledge of the authors) is much more self-sufficient than occupants of nursing homes but may demand better thermal conditions than adults or younger adults. The monitored dwellings were located in prefabricated buildings constructed in Lublin, Poland, in the 1970s and 1980s. Originally constructed from large-plate concrete prefabricates, they may represent wider reserves of the residential buildings erected in that time in Eastern and Central Europe. The research allowed us to present the following conclusions:  
* The thermal environment in the observed dwellings differed noticeably, with the highest temperature ranging from 26.4 to 30.3 \({}^{\circ}\)C and the number of hours exceeding the comfort level recommended for vulnerable occupants ranging from 0 to 163 (10.5% of the observation time). * As the construction of buildings was practically the same and the thermal transmittance coefficients of the similar dwellings' outer shells did not differ much, the differences may be attributed to the occupants' behaviour and methods of dealing with excessive temperatures. * In five of ten apartments (A2, A3, A6, A8, A9), the internal temperature was below level I of the internal comfort, or the overheating time did not exceed 0.8% of the monitoring period. All dwellings were located in the central parts of the buildings and, except for A2, had external walls at the opposite sides, which enabled cross-ventilation. Common measures of lowering the internal temperature were keeping the windows partly open during the day and night and enhancing airflow by opening the balcony doors daily. * In two apartments (A4 and A10), the thermal conditions went above level I of internal comfort but did not go above level II for longer than 3 h. Strategies for lowering the internal temperature were similar here to the group described above, but the worst results could have been caused by the higher internal gains coming from additional equipment (A2) or the presence of two occupants (A10). * In three apartments (A1, A5, and A7), the conditions were the worst, instead, the internal temperature did not go above level III of internal comfort. The reasons for these were clearly connected with the specific construction and location within buildings as follows: top floor placement (A1 and A5), lacking the possibility of cross-ventilation (A5, A7), additional equipment in a dwelling, and a neighbouring room with high solar gains (A5). * Apartments A1 and A7, with the highest internal temperature and the longest overheating periods, were occupied by the eldest participants of the survey. This could contribute to the worse ability to handle overheating problems and was an important observation, suggesting the possibility of deteriorating internal conditions in the future. * In some parts of the experiment, a good correlation between monitoring and personal perception of comfort was noticed (highest internal temperature vs. TSV scale), instead, the overheating time was overestimated by the occupants compared with the share of overheating hours in the time of the monitoring. To summarise the presented problems, in most cases, prefabricated large-plate dwellings could be maintained in the comfort zone, even by ageing, self-sufficient occupants. Nevertheless, when specific unfavourable factors related to the building's construction appeared, overheating was remarkably longer and more disturbing, surpassing the potential of the elderly handling it. A significant rise in solar radiation intensity in Poland during the warm half of the year over the period 1971-2020 was reported by publication [59].