53 Climate change In Trondheim the average temperature has not had a sharp increase in the 30 years from 1961 to 1990: only temperature-value dispersion has increased. This datum, confirmed also for the 30 years from 1991 to 2020, means an increase in extreme phenomena (hotter summers VS shorter and colder winters), with the consequent variation in the length of the different seasons. The increase in temperature fluctuations in the first and last months of the year causes freeze and thaw cycles, which usually occur precisely in winter. The cycles are harmful to the materials, e.g., the hygroscopic wood (damage functions). Object comfort versus human comfort - challenges and approaches Built heritage and heritage collections require conservation approaches, which can cause conflict with the demands of human comfort. Passive environmental control strategies historically focused on the wellbeing of the people who inhabited the buildings. This was at a time, where no electricity and advanced heating methods were available. As a side effect, many of these building constructions were also very conducive to the preservation of the building fabric. Unfortunately, not all of these approaches can be applied to the conservation of cultural heritage. In addition, the official regulations for the use and air conditioning of buildings in terms of health regulations and well-being have become more stringent, which limits the possibilities for using the buildings. According to ISO 7730:200515the level of comfort for a sedentary activity should be inside the margin between 19°C and 29°C on the floor surface, with the most ideal temperature being around 26°C. One of the main issues in developing suitable conservation concepts is balancing the essential conservation requirements of the objects with the needs of the people who live or work in these buildings. In terms of the challenging Norwegian climate, this makes things even more complicated. KING and PEARSON discussed this problem in relation to buildings in Australia, but important key messages are applicable to this topic [Pearson et al., 200016]. ➔ Objects and buildings are static and cannot move away from an adverse environment. In contrast,humans can adapt to unfavourable climate conditions by changing their location, seeking shelter, or dressing appropriately. ➔ Sensory compensations and comfort preferences by humans can be contrary to the conservation requirements of the historic materials, for example: O Lowering of relative humidity increases human comfort but hastens the desiccation of wood and leads to mechanical stress in the form of shrinkage and cracking.
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