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Is Heritage Protection a Limiting Factor for Passive Deep Energy Retrofitting? A Cold-Climate Case Study of University Buildings
Full text linkReducing the energy consumption of the existing building stock is of paramount importance in the race to reach national and international climate goals. While multiple initiatives are in place and provide guidance, heritage-protected buildings are often not part of the equation. Protected buildings make up a large share of the existing building stock and therefore offer large savings potential. In Trondheim, Norway, alone, that share is close to 10%, which demands the establishment of representative retrofitting cases. A case study of the central buildings on the NTNU campus was established to specifically test passive retrofitting measures, which are greatly affected by heritage protection. The application of measures selected in collaboration with heritage authorities led to overall energy savings of 16% to 18%, while the energy for heating alone was reduced by 34% to 40%. The reductions were especially prominent during cold winter months, where overall consumption peaks were reduced by up to 37%, greatly decreasing the dependence on cold outdoor temperatures. The results make a case for the application of passive retrofitting measures to heritage-protected buildings despite them not reaching deep energy retrofitting goals, especially in cold climates and alongside other energy-saving or -producing measures.publishedVersio
Building Envelope Modelling. The development of simulation and optimization models for energy-flexible operation in the built environment
Full text linkThis memo describes the development process of simulation and optimization models for energy-flexible operation of building envelopes. These models consist of linear time invariant state space models designed to consider space heating qsh as the input and the following inputs as disturbances: outdoor temperature Tout, global horizontal solar radiation solGlob, internal gains Qint and ventilation heat qvent. A set of nine archetypes has been developed, consisting of three types of building – House, Apartment, and Commercial – at three energy efficiency levels – Regular, Efficient, Very Efficient. The House archetype represents detached and semi-detached houses containing 1.25 dwellings; Apartment represents an apartment building with 16 dwellings; and Commercial represents a building used for commercial purposes. The efficiency levels represent three categories of heat demand required by the buildings: Regular represents a building with energy demand representative of an average of the building stock, Efficient represents buildings from 2010 and later adhering to current energy efficiency guidelines, and Very Efficient represents buildings with energy demand similar to buildings adhering to a Passive house standard. FLEXor is a simulation and optimization tool for energy generation, demand, and use in the built environment. It is implemented in Python. All the sub-models in FLEXor, including the one described in this memo, are designed to be self-standing. Thus, they are self-contained, and do not include the control and/or optimization of other components. However, these models are to become part of a larger high-level model, FLEXor, that may include DHW tanks, electric vehicles, and other different components. Therefore, the models are designed to be i) linear, ii) in state space form (when applicable), and iii) transparent. This will allow the high-level model to be fast, lean, relatively simple, and able to leave a component out of the optimization process if necessary. The main intention of FLEXor is the quantification of energy flexibility in buildings. In particular, the envelope model is used to quantify SH flexibility: this is a demand-side management strategy that relies on shifting the supply of heat for space heating away from hours with high energy prices, and/or by reducing its peak power to lower costs related to power-driven grid tariffs.publishedVersio
Energy system modelling for studying flexibility on industrial sites
Full text linkWith an increasing share of non-dispatchable renewable energy sources in the European grid, energy flexibility will be key for the industrial sector to support the green transition. The EU-project Flex4Fact aims at finding solutions for energy and process flexibility for industry, using SINTEF s open-source energy system model EnergyModelsX to quantify the potential benefits. This work presents some extensions done in EnergyModelsX, denoted as EnergyModelsFlex, to accommodate energy and industrial flexibility, adding new functionalities to assist with industrial flexibility potential. The extended EnergyModelsX model is described and demonstrated through two case studies in the plastic and polymeric products manufacturing sector to evaluate their potential for increasing renewable generation and flexibility. The first use case, being energy intensive, consumes both natural gas and electricity. This site enables the use of heat recovery and utilization, hydrogen blending, on-site hydrogen production, which can reduce CO2 emissions. The second use case relies solely on electricity consumption, and the considered flexibility is energy shifting by electric batteries and production flexibility. The focus of this case study is on the interplay between energy storage, on-site energy production and process flexibility to increase the degree of self-produced renewable energy in the energy mix. Together, the two case studies demonstrate how the extended EnergyModelsX framework can be used to explore process and energy flexibility in the industry to aid the transition from a fossil-based society to a renewable based society.Energy system modelling for studying flexibility on industrial sitespublishedVersio
Spørreundersøkelse om astma/allergi og inneklima/ventilasjon norske barnehager
Full text linkProsjektet "Barnas luftkvalitet: En studie om innendørs luftkvalitet i barnehager og astma og allergi", finansiert av Forskningsfondet for astma og allergi, gjennomførte en spørreundersøkelse blant norske barnehager sommeren 2024. Målet var å undersøke forhold ved barnehagene som kan påvirke inneklimaet. Undersøkelsen ble sendt til 4 400 barnehager og hadde lav svarprosent, men resultatene vurderes som tilnærmet representative.
Det ble identifisert et behov for mer kunnskap om ventilasjon og helse, både i barnehager og hjem. Få barnehager tilbyr opplæring, men mange ønsker å kunne tilby dette. Erfaringer fra studien viser også behov for bedre utforming og testing av spørreskjema, samt å begrense omfanget for å øke svarprosenten.publishedVersio
A Case Study of System Reliability and Availability of Blue Hydrogen Production
Full text linkThe transition toward a low-carbon future has positioned hydrogen as a critical energy carrier, with blue hydrogen emerging as a bridge between conventional fossil fuels and cleaner alternatives. Blue hydrogen is produced by reforming natural gas with carbon capture and storage (CCS) to reduce CO2 emissions, representing an intermediary solution between grey and green hydrogen. However, ensuring the reliability of the complex systems (e.g. the hydrogen production systems) is critical for economic feasibility, operational safety, and environmental sustain-ability. This paper analyses the system reliability of blue hydrogen production technologies, evaluating the challenges in reliability modelling and assessment specific to these systems. It addresses key issues such as the integration of multiple technologies, data limitations, operational risks, and the performance of critical equipment. Through this analysis, the study highlights the importance of robust reliability engineering frameworks towards the challenges of blue hydrogen systems.A Case Study of System Reliability and Availability of Blue Hydrogen ProductionpublishedVersio
Quantification of NO in the post-flame region of laminar premixed ammonia/hydrogen/nitrogen-air flames using laser induced fluorescence
Full text linkAmmonia-based fuels have been identified as a promising alternative as zero-carbon energy carriers due to their high energy density and simpler logistics compared to hydrogen. As a disadvantage, the presence of fuel-bound nitrogen can lead to order of magnitude higher emissions of undesired nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O) compared to more conventional fuels. Presently, chemical kinetics schemes for the combustion of ammonia and ammonia blends show large variations in the prediction of NO and there is a lack of quantitative experimental data to validate and optimize these reaction mechanisms. This paper presents measurements of NO in the product gases of laminar premixed NH3/H2/N2 air flames on a flat-flame burner for 4 different ammonia decomposition ratios and over a range of equivalence ratios using laser-induced fluorescence in the NO A-X (0,1) system. A linear calibration approach based on the addition of NO to a lean premixed CH4 flame is presented. Initial signal treatment includes the correction of laser absorption, fluorescence absorption (signal trapping) and fluctuations in laser energy. The LIF signals are corrected for changes in the Boltzmann fraction, line overlap, number density, and quenching between calibration and measurement, which requires knowledge of the local temperature and mole fractions of the main species. Temperature measurements using N2 thermometry, where a theoretical N2 Raman spectrum is fitted to an experimental N2 Raman signal, excited by a 532 nm cw laser, allow characterization of the local near-adiabatic flame conditions as a function of operating conditions and adjustment of the signal corrections to the local temperature. Major species are extracted from 1-D simulations. The measured NO mole fractions are compared with five recent chemical kinetic schemes, which show good agreement for rich mixtures, however, a systematic underprediction of NO is found for stoichiometric and lean mixtures. Novelty and significance Emissions of NO are a major challenge for advancement of ammonia as a carbon-free fuel, yet very few measurements of NO levels in ammonia flames exist in the literature. In this paper, we present much needed quantitative experimental data on NO emissions from premixed NH3/H2/N2-air flames using laser-induced fluorescence (LIF). Our diagnostic approach employs a linear calibration method based on the addition of NO to a lean CH4 flame. Post-flame temperatures are measured by Raman spectroscopy to ensure accuracy of the local thermochemical states used in converting LIF signals to quantitative NO concentrations, accounting for variations in number density, electronic quenching, Boltzmann fraction, and the line overlap integral. Additionally, laser absorption and signal trapping are corrected using the spatial shape of the LIF signal. The presented data set can be used by modelers to refine chemical kinetic models with respect to NO emissions. © 2025 The AuthorsQuantification of NO in the post-flame region of laminar premixed ammonia/hydrogen/nitrogen-air flames using laser induced fluorescencepublishedVersio
The prospects of massively scalable nuclear-powered direct air capture as a climate solution
Full text linkDirect air capture (DAC) has recently emerged as a promising and scalable solution for removing accumulated CO2 in the atmosphere to mitigate global warming. Because DAC needs to capture CO2 from highly diluted levels in the air, it has considerably higher energy demands than conventional CO2 capture from concentrated industrial sources, making cheap input energy essential. The present study proposes that DAC facilities be powered by dedicated large-scale nuclear power plants designed to deliver the optimal heat/electricity ratio to a DAC unit serving as the condenser in the Rankine power cycle. Such plants are unbound by proximity requirements to CO2 point sources or electricity demand centres and can be built where nuclear reactors are cheapest to construct, strongly improving the business case. A bottom-up techno-economic assessment and uncertainty quantification study for the year 2050 showed median and 90 % confidence intervals of the levelized cost of removed CO2 to be 101.6 (71.3–153.9) ¤/ton when conventional nuclear reactor technology is used. An advanced configuration employing emerging high-temperature nuclear reactor technology to generate excess electricity for co production of green methanol was slightly more expensive with a larger uncertainty range: 108.0 (68.8–176.1) ¤/ton. Despite the uncertainty in the assessment, the calculated CO2 removal costs are attractive compared to projected CO2 prices in climate change mitigation scenarios targeting substantial emissions re ductions by mid-century. However, several non-economic challenges were identified and further work on these topics is recommended to clarify the long-term potential of nuclear-DAC technology as a leading climate change solution.publishedVersio
Local Field Factors in Dielectric Liquids: Cyclohexane and Ethyl Laurate
Full text linkLocal electric field factors have been calculated for cyclohexane and ethyl laurate liquids by using a force-field model for the local field response to an external field based on liquid configurations generated from molecular dynamics simulations. For cyclohexane, we found field factors up to around 1.5 and 2.0 at the carbon and hydrogen atoms, respectively. Ethyl laurate has larger local field factors, up to 3.5 at the carbon atoms and 2.4 at the oxygen atoms, respectively. The local field factors at the hydrogen atoms in ethyl laurate are similar to those of cyclohexane. The electric fields in liquids arising from the electronic polarization of the molecules by the external field can thus be considerably larger, here with up to a factor 3.5, than the applied electric field.Local Field Factors in Dielectric Liquids: Cyclohexane and Ethyl LaurateacceptedVersio
Large-scale LH2 pipeline infrastructure concept for airports
Full text linkInfrastructure and processes for handling liquid hydrogen (LH2) is needed to decarbonize aviation with hydrogen aircraft. Large airports benefit from pipeline refuelling systems, which must be operated to keep the fuel subcooled due to LH2 vaporization challenges. In this paper, we estimate LH2 demand for aircraft and the gaseous H2 demand for ground support equipment (GSE) at Schipol in 2050. Modelling and simulation of aircraft refuelling via pipelines show that continuous LH2 recycling is required to maintain subcooling. Vaporization of LH2 during refuelling is heavily influenced by pipeline temperatures. Refuelling aircraft in the morning causes the highest vaporization (2.2 %) due to a long period with low LH2 flow (no refuelling at night). The vaporization decreases to 0 % throughout the day. Furthermore, increasing the recycle rate during night lowers the pipeline temperatures, reducing the vaporization to 1.7 %. The amount of vaporized hydrogen corresponds well with the GSE demand for gaseous H2.Large-scale LH2 pipeline infrastructure concept for airportspublishedVersio