| 1. |
- Arnroth, Lukas
(författare)
-
Some Investigations into the Class of Exponential Power Distributions
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, methods are developed relating to the exponential power class of distributions.Paper I considers Bayesian linear mixed models where the usual normality assumption is replaced by the multivariate exponential power distribution. Particular focus lies on Bayesian testing of the fixed effects.Paper II introduces a score test for the shape parameter of the exponential power distribution. A Pitman-type local analysis is used to establish asymptotic results.Paper III investigates quantile regression based on the skewed exponential power distribution. The bridge between standard and Lp quantiles is of particular interest.Paper IV investigates Bayesian composite Lp-quantile regression based on the skewed exponential power distribution.Paper V considers Bayesian composite quantile regression with a particular interest in es-tablishing theoretical justification from a non-parametric Bayesian perspective.
|
|
| 2. |
- Dahlberg, Anna-Karin, 1985-
(författare)
-
Environmentally relevant chemical disruptors of oxidative phosphorylation in Baltic Sea biota : Exposure and toxic potentials
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on toxicity and occurrence of hydroxylated polybrominated diphenyl ethers (OH-PBDEs) in Baltic Sea biota. The aims were to assess OH-PBDEs potency for disruption of oxidative phosphorylation (OXPHOS) and determine their and related compounds exposure in Baltic blue mussel, herring and long-tailed duck. A method for analysis of OH-PBDEs in herring and long-tailed duck plasma was also evaluated.Relevant OH-PBDEs were tested in vitro for OXPHOS disruption, using a classic rat mitochondrial respiration assay and a cell mitochondrial membrane potential assay. All compounds were found to disrupt OXPHOS either by protonophoric uncoupling and/or via inhibition of the electron transport chain. 6-OH-BDE47 and 6-OH-BDE85, were identified as particularly potent OXPHOS disruptors. Strong synergism was observed when OH-PBDEs were tested as a mixture corresponding to what is present in Baltic blue mussels.Baltic blue mussel is main feed for several species of mussel feeding sea ducks which have decreased dramatically in numbers. To assess long-tailed ducks exposure to brominated substances, liver tissue from long-tailed ducks wintering in the Baltic Sea and blue mussels were analysed. The result confirms that long-tailed duck are exposed to OH-PBDEs via their diet. However, low concentrations were found in the duck livers, which suggest low retention of these compounds despite daily intake. How the nutritional value of blue mussels as feed for sea ducks are affected by OH-PBDE exposure still needs further studies. Other species of sea ducks foraging on Baltic blue mussels during summer months can also be more exposed due to seasonal variation in primary production.Herring sampled in the Baltic Proper and Bothnian Sea, were found to contain OH-PBDEs and high levels of their methylated counterpart, MeO-PBDEs. As demethylation of MeO-PBDEs is known to occur in fish, MeO-PBDEs may pose as additional source for more toxic OH-PBDEs in herring and their roe.
|
|
| 3. |
- Milic, Vlatko, 1992-
(författare)
-
A techno-economic system approach for the energy renovation of residential districts built before 1945
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A key factor in the quest for sustainable development worldwide is reducing the energy use and greenhouse gas emissions from residential buildings. The residential and service sector represent 39% of the final energy use in Sweden. The housing stock in Sweden is fairly old with approximately 25% of the residential buildings built before 1945, many of which possess heritage values. Considering the generally poorer thermal performance in older buildings compared to newer ones, it is important to investigate the techno-economic energy efficiency potential in this part of the built environment. The aim of this thesis is to develop a bottom-up approach and to analyze energy renovation of residential districts built before 1945 from a system perspective with regard to targets of life cycle costs (LCC), energy use and preservation of building heritage values. The developed approach includes a combination of economic and environmental impacts from a building owner and energy utility point of view. The approach includes analysis on four different levels, i.e., building level, cluster level, district level and city level.The results show that the developed approach is successful in integrating targets of LCC and energy use, as well as preservation of heritage values, during techno-economic energy renovation. By a further development of the change-point model, data related to building thermal power characteristics, such as Qtotal and balance temperature, can be calculated and used for analysis of a residential district. Moreover, the cluster with the initial poorest thermal performance, i.e., the single-family houses in stone, account for the highest decrease in specific energy use (70–78%) and LCC (34–37%) during energy renovation at LCC optimum. The corresponding figures for the buildings with the best thermal performance initially, i.e., the cluster with multi-family buildings in wood, are 23–24% and 14%, respectively. Furthermore, it is concluded that the cost-effective energy efficiency potential is highly correlated with initial building properties and preservation requirements, which significantly affects the stone buildings. This is because insulation on the inside of the external walls is cost-effective in these buildings, but not in wooden buildings, which consequently decreases the energy savings potential from 46–69% in a balanced energy renovation scenario to 8–30% in a restricted energy renovation scenario.The findings also show that the environmental performance of the building district is closely linked with the selected energy system boundary. This can be exemplified by CO2 emissions of 0.7–1.1 kg CO2 eq./(m2·year) at LCC optimum for multi-family buildings when considering biomass an unlimited resource, compared to 28.9–40.0 kg CO2 eq./(m2·year) when considering biomass a limited resource with condensing coal power plants as the marginal user. Furthermore, on a city level it is concluded that the environmental performance of the district heating (DH) system is improved as a result of techno-economic energy renovation of a district, and that the net income is decreased (8%) despite a lower system cost (12–13%) due to less DH sold to end users. The global CO2 emissions are decreased by 3,545–3,737 tonnes/year and the primary energy use is decreased by 5.0–5.2 GWh/year. Apart from the developed bottom-up approach for analysis of the energy renovation of residential districts built before 1945, this thesis has provided valuable results to the research community, building sector and authorities in terms of (1) the further development of the change-point model, which enables time-effective analysis of the thermal performance of residential districts; (2) the environmental benefits with techno-economic energy renovation of residential districts from a DH producer perspective and (3) the need to develop packages of EEMs that are profitable for both DH producers and end users of DH.
|
|
| 4. |
|
|
| 5. |
- Nilsson, Emil, 1989-
(författare)
-
Borehole Thermal Energy Storage Systems for Storage of Industrial Excess Heat : Performance Evaluation and Modelling
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improving industrial energy efficiency is considered an important factor in reducing carbon dioxide emissions and counteract climate change. For many industrial companies in cold climates, heat generated at the site in summer will not be needed to fulfil the site heat demand during this time, and is thus removed to the outdoor air. Although a mismatch between heat generation and heat demand primarily being seasonal, a mismatch may also exist at times in the winter, e.g. during milder winter days or high production hours. If this excess heat instead of being sent to the outdoors was stored for later use when it is needed, purchased energy for the site could be decreased. One way to do this is by the use of a borehole thermal energy storage (BTES) system.A BTES system stores energy directly in the ground by using an array of closely drilled boreholes through which a heat carrier, often water, is circulated. So far, BTES systems used for heating purposes have mainly been used for storage of solar thermal energy. The BTES system has then been part of smaller district solar heating systems to reduce the seasonal mismatch between incoming solar radiation and heat demand, thus increasing system solar fraction. For this application of BTES systems, energy for storage can be controlled by the sizing of the solar collector area. At an industrial site, however, the energy that can be stored will be limited to the excess heat at the site, and the possible presence of several time-varying processes generating heat at different temperatures gives options as to which processes to include in the heat recovery process and how to design the BTES system. Moreover, to determine the available heat for storage at an industrial site, individual measurements of the heat streams to be included are required. Thus, this must be made more site-specific as compared to that of the traditional usage of BTES systems where solar thermal energy is stored, in which case long-time historic solar radiation data to do this is readily accessible for most locations. Furthermore, for performance predictions of industrial BTES systems to be used for both seasonal and short-term storage of energy, models that can treat the short-term effects are needed, as traditional models for predicting BTES performance do not consider this.Although large-scale BTES systems have been around since the 1970’s, little data is to be found in the literature on how design parameters such as borehole spacing and borehole depth affect storage performance, especially for industrial BTES applications. Most studies that can be found with regard to the designing of ground heat exchanger systems are for traditional ground source heat pumps, working at the natural temperature of the ground and being limited to only one or a few boreholes.In this work, the performance of the first and largest industrial BTES system in Sweden was first presented and evaluated with regard to the storage’s first seven years in operation. The BTES system, which has been used for both long- and short-term storage of energy, was then modelled in the IDA ICE 4.8 environment with the aim to model actual storage performance. Finally, the model was used to conduct a parametric study on the BTES system, where e.g. the impact on storage performance from borehole spacing and characteristics of the storage supply flow at heat injection were investigated. From the performance evaluation it could be concluded that lower than estimated quantities and/or quality of the excess heat at the site, resulting in lower storage supply flow temperatures at heat injection, has hindered the storage from reaching temperatures necessary for significant amounts of energy to be extracted. Based on the repeating annual storage behavior seen for the last years of the evaluation period, a long-term annual heat extraction and ratio of energy extracted to energy injected of approximately 400 MWh/year and 20% respectively are likely.For the comparison of predicted and measured storage performance, which considered a period of three years, predicted values for total injected and extracted energy deviated from measured values by less than 1 and 3% respectively, and predicted and measured values for injected and extracted energy followed the same pattern throughout the period. Furthermore, the mean relative difference for the storage temperatures was 4%. A time-step analysis confirmed that the intermittent heat injection and extraction, occurring at intervals down to half a day, had been captured in the three-year validation. This as predictions would become erroneous when the time step exceeded the time at which these changes in storage operation occur.Main findings from the parametric study include that 1) for investigated supply flows at heat injection, a high temperature was more important than a high flow rate in order to achieve high annual heat extractions and that 2) annual heat extraction would rapidly reduce as the borehole spacing was decreased from the one yielding the highest annual heat extraction, whereas the reduction in annual heat extraction was quite slow when the spacing was increased from this point. Another conclusion that came from the performance evaluation and the parametric study, as a consequence of the Emmaboda storage being designed as a high-temperature BTES system, intended working temperatures being 40–55 °C, was that the possibility of designing the BTES system for low working temperatures should be considered in the designing of a BTES system. Lower storage operation temperatures allow for more energy to be injected and in turn for more energy to be extracted and reduces storage heat losses to the surroundings.
|
|
