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Povzetek: This research study investigates the effect of different heating and cooling regimes on the effective cross-section of timber elements exposed to natural fires. An advanced calculation method based on a 1D finite-difference heat transfer model and effective thermo-physical properties is adopted to analyse the heat penetration and the consequent reduction in mechanical properties. In particular, the research focuses on the evolution and penetration speed of the char depth (300 ◦C isotherm) and zero-strength layer (determined through in-depth temperatures and reduced mechanical properties). Results reveal how the char depth mainly develops during the heating phase, with non-negligible contributions from the cooling phase. In contrast, the zero-strength layer increases throughout the whole fire exposure, particularly during cooling and, possibly, after the end of the cooling phase. In general, the heating phase contributes about 2/3 to the total effective char depth, while the cooling phase about 1/3. The most challenging conditions were found for the fires of the longest durations (heating and overall), corresponding to low ventilation and high fuel load density conditions. The study emphasises the necessity of incorporating the cooling phase in performance-based methodologies for fire-safe timber structures to avoid under-estimating heat penetration effects.
Ključne besede: timber structures, fire safety, charring, zero-strength layer, natural fire, heating, cooling, structural fire engineering, performance-based design
Objavljeno v DiRROS: 22.11.2024; Ogledov: 114; Prenosov: 425
Celotno besedilo (6,39 MB)
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Povzetek: Shallow geothermal energy (SGE) is a renewable energy that could contribute to the decarbonatization of the heating and cooling sector. SGE is predominantly harnessed through ground source heat pump (GSHP) systems. The choice of which type of GSHP system depends on various factors. Understanding these factors is crucial for optimizing the efficiency of GSHP systems and fostering their implementation. In this paper, we have analysed the spatial distribution of GSHPs in Slovenia. We identified 1073 groundwater and 1122 ground-coupled heat pump systems with a total heat pump capacity of almost 30 MW. We quantitatively assessed the influence of geological, hydrogeological, and climate conditions on their spatial distribution. Using the χ2 test and information value method, we identified hydrogeological conditions as the most influential factor for the GSHP systems’ spatial distribution. We also performed the spatial analysis of geological and hydrogeological data in 22 European countries, including Slovenia. We collected the reported numbers of installed GSHP units in 2020 and were able to distinguish the shares of groundwater and ground-coupled heat pump systems for 12 of these countries. The analysis showed that ground-coupled heat pumps predominate in most countries, even if the natural conditions are favourable for groundwater heat pumps.
Ključne besede: shallow geothermal energy, renewable heating and cooling, ground-source heat pump, spatial distribution, natural condition
Objavljeno v DiRROS: 19.03.2024; Ogledov: 511; Prenosov: 218
Celotno besedilo (15,39 MB)

Povzetek: In repressive protection of cultural/historical woodwork, microwaves have many advantages over conventional heating. The research%s objective was to examine conditions for eradication of house longhorn beetle larvae (Hylotrupes bajulus) in spruce wood (Picea abies) using microwaves. Larvae, inserted at different depths of spruce blocks containing 12% and 42% of moisture, were exposed to microwaves. Two apparatuses were used; a 750W commercial microwave chamber and a newly developed horn antenna microwave device with the power of 800W and a frequency of 2.45GHz, for targeted radiation. We discovered that the inner part of wood warmed up quicker than the surface heated to 65°C. For successful suppression larvae in the wood need to be heated to 54.5°C, for 10 seconds. The necessary exposure time increases with increasing thickness of wood. The surface of wood containing more moisture is heated quicker, but increased moisture slows down the penetration of microwaves into the wood specimen. Therefore, larvae in wood of lower moisture (12%) died faster, both those 20mm under surface (1.5min) and those at 130 mm of depth (10.5min).
Ključne besede: wooden objects, repressive wood protection, microwaves, heating, wood moisture content, house longhorn beetle, Hylotrupes bajulus
Objavljeno v DiRROS: 25.10.2017; Ogledov: 5483; Prenosov: 3147
Celotno besedilo (1,52 MB)
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Povzetek: Microwaves are very effective at wood pest eradication. However, elevated temperatures may pose a risk of damaging surface coatings used on cultural and historical artefacts. Therefore, we monitored changes in patterns of the original paint taken from such objects along with newly prepared coatings. We evaluated visual, mechanical, and chemical modifications of coatings when exposed to microwaves (750W, 2.4GHz), at 60°C or 80°C for 10 min. Whether old or new, only water-based coatings have proven to be resistant to elevated temperatures and no damage was observed at 80°C. Blisters have formed on layers of new oil paints and natural resins due to insufficiently cured film. Temperatures above 80°C may cause melting of coniferous wood resin and thus transport of resin to the surface; on the other hand, temperatures up to 60°C are completely harmless. Mechanical and chemical changes of coatings exposed to microwaves were not observed, but the studies showed that colour and gloss exhibited minor changes.
Ključne besede: wood, wood coatings, wood protection, microwaves, heating
Objavljeno v DiRROS: 03.07.2017; Ogledov: 6342; Prenosov: 3615
Celotno besedilo (2,63 MB)
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