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This paper deals with the impact of the use of daylight on the overall energy demand for heating, cooling, and lighting in educational buildings. The energy performance of buildings is currently of the utmost importance as current European regulations, starting from 31st December 2020 impose that all new buildings must meet nearly zero-energy building requirements. This paper presents a study of the illuminance distribution in an educational room obtained from measurements and simulation results using two different models. One of the models, integrated with a thermal simulation software, was used to estimate the impact of daylight on the energy demand. The analysis included the use of various window types, lighting control system, reference point location, and daylight calculation model for a sample room in an educational building. Results of the analysis indicate that, due to the high share of lighting demand (reaching up to 78% of the primary energy balance), there is a need to take into account the efficiency of lighting systems during the design process to correctly determine the actual energy balance of a building, increase the quality of the design of lighting systems, as well as to select the optimal parameters of windows.

The paper analyses profitability of biogas production in livestock farms in Poland with a focus on micro-biogas plants. Due to the high value of investments a crucial issue, from the farmers' point of view, is the mechanism of financial support. The efficiency of investments has been measured assuming three variants of power of CHP plants. In addition, two scenarios of financial support have been taken into consideration: the "old" mechanism of green certificates and a forthcoming mechanism based on the new Act on Renewable Energy Resources. The new system introduces feed-in tariffs for small plants and auctions and guarantees of purchase for larger biogas plants. The results of the analyses indicate a strong dependence of the financial effects of micro-biogas plants on subsidies. It can be concluded that, under the current state of market development and financial support offered to micro-scale biogas production, investments in biogas plants are in general unprofitable.

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