Abstract: Vår moderne verden har et enormt behov for tilgang på energi i form av elektrisitet, varme og drivstoff. Fossile energikilder, som har dominert til nå, er ikke bare skadelige for miljø og klima, de tar også slutt en gang. Derfor er fornybar energi veien fremover, men er det helt uten ulemper og utfordringer?
I denne læreboka får du en grunnleggende innføring i energisystemets oppbygning, og en forståelse av de fysiske størrelsene og prinsippene som ligger til grunn for utvinning av energi fra ulike kilder. Hva innebærer det i praksis når vi skal gå fra fossilsamfunnet til fornybarsamfunnet?
Egne kapitler er viet innføring i de fornybare energikildene vannkraft, vindkraft, bioenergi, solenergi, geotermisk energi og havenergi. Her går forfatterne inn på alt fra produksjon, bruk og potensiale nasjonalt og globalt, til hvordan du regner på effekt og energiproduksjon. Alle kapitlene har (regne)oppgaver med fasit.
Læreboka er skrevet for ingeniørstudenter og andre studenter som har valgt en utdanning der fornybar energi inngår.

Abstract: The integrated energy system is widely acknowledged as an effective method for advancing the adoption of renewable energy sources and reducing carbon emissions. To address economic issues caused by the inconsistency between traditional single-stage planning capacities of the park-level integrated energy system (PIES), the long-term planning model is proposed, which consists of multi-stage divisions and incorporates the ladder-type carbon trading mechanism. The model utilizes the long-term, multi-stage planning approach to determine the optimal installed capacity of equipment. Meanwhile, the ladder-type carbon trading mechanism is conducted considering the relationship between actual carbon emissions, carbon emission quotas, and carbon trading cost. The study assesses the impact of carbon trading mechanisms and various planning stage divisions on the economic feasibility of the PIES and its ability to reduce carbon emissions. The results indicate that compared to fixed carbon price trading strategies, the implementation of ladder-type carbon trading increases costs by 0.15 %–0.18 %, but reduces carbon emissions by 0.36 %–0.6 %; as the number of planning stages increases, carbon emissions significantly decrease, and lifecycle costs also significantly decrease. Compared to traditional single-stage planning, carbon emissions decrease by 14.6 % and lifecycle costs decrease by 15.17 % at number of planning stage K = 15; when the baseline price is set at 0.5 yuan/kg and the price growth rate is 0.5, the optimal values of carbon emissions and carbon trading cost are achieved. In conclusion, this study serves as references for the strategic implementations of PIES, emphasizing the importance of economic efficiency and low-carbon practices in line with the system’s long-term development and sustainability objectives.
Permalink: https://doi.org/10.1016/j.rineng.2024.102107

Abstract: This research investigated the energy efficiency of decentralized ventilation (DV) systems in cold weather conditions in comparison to centralized ventilation (CV) systems, focusing on three locations in Norway. The study found that DV systems with higher heat recovery unit (HRU) efficiency consumed less thermal and fan energy due to shorter air distribution pathways, utilizing a hybrid natural ventilation strategy in mild climates, and simpler space zoning for ventilation. This study proposes to determine a suitable ventilation system for adapting to cold climate. These methodologies are presented in three major parts: 1) ventilation energy demands of DV and CV systems in Norway, 2) performance of the heat recovery unit in the DV system, and 3) numerical analysis of the total ventilation energy demand of the DV system in cold climates using occupant ratio and existing measured data.The results showed specific time periods when it is ideal to use a fan-assisted NV system in cold climates, and in local conditions, 4–20% per year could benefit from a fan-assisted NV system using DV technology. A DV system with 0.7 HRU efficiency can save up to 14.5% of total HVAC energy compared to a CV system. The HRU heating efficiency played a crucial role in thermal ventilation energy demands in cold weather, while the cooling efficiency had no significant effect on energy demands. However, if a hydronic heating and cooling coil is added to the DV system, it consumes more than 9.08% of energy than using a pump. The energy-saving performance of the DV system decreases significantly if its HRU efficiency is below 50%, and there is no real advantage of using the DV system over the CV system in such cases. Nonetheless, the DV system can be utilized in various working conditions to conserve energy, such as different occupancy ratios, individual room space zoning, and indoor air pollution rates.
Permalink: https://doi.org/10.1016/j.egyr.2023.11.050

Abstract: Highlights:
• Transition to sustainable multi-building energy systems can reduce greenhouse gas emissions by synergising the multiple renewable energy sources with specific structural characteristics and occupancy constraints of buildings.
• To ensuring energy flexibility and resilience, optimization strategies for multi-building energy systems vary significantly with the climatic context and potentials for integrating energy storage technologies, highlighting the necessity for adaptable designs considering future energy demands and the expansion of district-level systems.
• There is a pressing need for more user-friendly multi-building energy system simulation tools to facilitate effective long-term planning and to optimize the design and management of energy flows among multiple buildings, ensuring maximum efficiency and sustainability.
Permalink: https://doi.org/10.1016/j.enconman.2024.118210

Abstract: The gray model simplifies calculations by ignoring phonon polarization, but sacrifices a certain level of computational accuracy. In effect, the frequency and wavevector of phonons form complex polarization patterns, which means their propagation modes and vibrational directions have different influences. Therefore, based on the phonon dispersion relations in silicon, the lattice Boltzmann method is used to analyze the phonon transport characteristics in nano-silicon films under ultrafast laser excitation. The results show that the total energy density distribution obtained by superimposing acoustic and optical branches exhibits multiple wave-like behaviors. Among them, the acoustic branch has excellent transfer capability, dominating the rate at which the total energy density reaches a steady state distribution, while the optical branch has stronger heat capacity characteristics, with a greater impact on the peak value of the total energy density. When the heat transfer approaches a steady state, the longitudinal optical branch surprisingly contributes up to 52.73%. This indicates that the often-neglected optical phonons should also receive sufficient attention. Additionally, compared to the results of the gray model, it is found that the dispersion model is preferred when more attention is paid to the propagation characteristics during phonon transport.
Permalink: https://doi.org/10.3390/buildings14010210

Abstract: This study aimed to evaluate the reliability of using airborne particles to estimate the real-time Air Exchange Rate (AER) of buildings, considering particle size and outdoor conditions’ impact on the AER estimation accuracy. The study utilized on-site data collection and numerical simulations to analyze the factors affecting the AER prediction accuracy. Results showed that the PM1.0- and PM2.5-based empirical correlation could predict the AER of buildings with a Normalized Mean Error (NME) of less than 10% and a correlation coefficient (r) of over 0.97, outperforming the pressurization method. Fine particles with a diameter under 2.5 μm were found to be a reliable tracer for AER prediction, with a negative correlation between particle size and AER prediction accuracy due to their higher penetration rate. The study also found that outdoor particle levels and pressure differentials positively impacted the accuracy of PM-based AER estimation. These findings have practical applications for maintaining Indoor Air Quality (IAQ) and accurately predicting a building’s heat losses.
Permalink: https://doi.org/10.1016/j.apr.2023.101955