VO2-based films are thermochromic and exhibit high or low infrared transmittance when the temperature is below or above a critical temperature. The thermochromic switching is passive and reversible, and therefore VO2 based films are promising for energy-efficient window appli­cations. However the practicaluse of VO2 for energy-efficient windows has long been hampered by low luminous transmittance and low solar energy transmittance modulation. The main goal of this dissertation work is to address these issues. The first half of the work proposes the concept of nanothermochromics for simultaneous improvement of luminous transmittance and modulation of solar energy throughput. nanoth­ermochromics considers VO2 nanoparticle composite layers, whose optical properties were modeled by effective medium theories. Calculations on VO2 spheroids have shown that VO2 nanoparticles, especially nanospheres, can offer dramatically improved luminous transmittance and solar transmittance modulation that are not possible for films. Calculations done on coreshell nanoparticles showed comparable improvements and offer an opportunity to reduce the material costs. It was also found that the composite of In2O3:Sn (ITO) and VO2 can yield moderately high luminous transmittance, solar transmittance modulation and low-emittance properties. In the second half of the dissertation work, Mg-doped VO2 films were sputter deposited. Their band gaps and Mg-content were investigated by means of optical absorption measurement and Rutherford backscattering spectrometry, respectively. The band gaps of VO2 were found to increase by ∼3.9±0.5 eV per unit of atom ratio Mg/(Mg+V) for 0<Mg/(Mg+V)<0.21. Computations based on effective medium theory were done to estimate the performance of Mg­-doped VO2 films and nanoparticle composite layers. The results suggest that moderately doped VO2 films with 0<Mg/(Mg+V)<0.06 perform better than un-doped films and that the perfor­mance can be further enhanced with one layer of antireflection coating. The best results were achieved by un-doped VO2 nanospheres, closely followed by the VO2 nanospheres with low Mg-content. Furthermore, the an experimental study on sputter deposited VO2 nanorods has identified the geometry of the oxygen gas inlet, the type of substrate, the substrate temperature and the layer thickness as important factors that influence the growth morphology. Taken as a whole, nanothermochromics offered by VO2 nanoparticles was shown to be the best solution for VO2 based thermochromic energy-efficient window coatings.

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Purpose: This study aims to see how the total active heating demand and the indoor climate for a school in Vasteras can improve from two different energysaving-investments. The two measures that will be investigated are windows with an improved U-value and an exchange of the ventilation unit with a heat exchanger. The result of the investments will be connected to a value-added study which investigates its impact on social, economy and environmental aspects. Method: To accomplish this, a literature study has been made to gather information to support the calculations and compare our results with previous studies. A case study which consists of calculations, a study visits to the school and a documentation analysis to strengthen the accuracy of the results. Results: The yearly total active heating for the school was 426 MWh with a heat demand of 191 kWh/m2 which is bad compared to equal buildings which normally use between 120-180 kWh/m 2. The exchange of the ventilation unit and the implement of a heat exchanger decreased the yearly active heating demand with 105 MWh which is equal to 144 kWh/m2. This is a much better value and now in the category of equal buildings. By investing in windows with a U-value of 1.3 W/m2 K from 3.0 W/m2 saved the building 29 MWh every year to 178 kWh/m2 which is just under the maximum value of 180 kWh/m 2 . Conclusions: Investing in a new ventilation unit with a heat exchanger showed to be the best investment for the school at this moment in time. The new heat exchanger contributes to a large energy saving and the investment cost had a payback time between 9 - 18 years depending on the kWh price. The study got similar results in the value-added study where the ventilation unit showed a greater impact on almost all of FN: s global goals. Windows did not show as impressive results as the ventilation unit did and is why it contributed less to the global goals in the value-added study.