Värmeåtervinning i ventilationsluft : En studie om FX- och FTX-ventilation vid energieffektivisering av flerbostadshus
Sammanfattning: To reduce the heating demand and do savings in energy cost of buildings there are several possible actions while renovating. Thru using heat recovering systems in buildings or constructions that are well-insulated the heat demand in buildings gets reduces. Air and supply air systems with heat recovery (FTX) and exhaust air heat pump (FX) are two different ventilation types that can recycle heat in a building. Heat recovery in FTX systems is done with a heat exchanger, while in FX systems it is done by a heat pump. In this degree project, a comparison has been made between the two ventilation systems, FTX and FX, by calculating the energy consumption of a building and their recycling opportunities. Possible energy savings have been calculated and how the profitability of the systems looks. Further, the actual performance of the FTX system is investigated and if it complies with the currently reported temperature efficiency specified by the ventilation manufacturers. Indoor air is used as a heat source when it is taken out of the building and is called exhaust air, energy is then recycled from the hot exhaust air. Exhaust air is hot because it contains indoor temperature. If heat recovery does not occur, the heat in the extract air is vented out of the housing, which means that the heat energy is lost. The energy calculations that gave an answer to how much energy is saved for each system compared to an F system has been performed in Excel and the recovered heat of the systems is calculated for each hour for a whole year and in different parts of the country, such as Kiruna, Stockholm, Örebro and Ystad . Moisture and temperature variation can affect the efficiency and recovery rates of the investigated units, therefore, cities with such geographical depiction have been chosen to be analyzed. The residual heating requirement in the house is supplied by district heating. The result of this study shows that the FTX system brings the greatest cost savings, while the FX system offers the highest energy savings. However, FTX ventilation has a relatively large energy saving in colder climate, which makes the system more competitive with FX with respect to energy savings. Installation costs are slightly lower for FX ventilation compared to FTX ventilation, but the life span of FTX systems is 40 years while it is only 15 years for the FX system. In a short period of time, FX systems can be cheaper, but in the long run, FTX systems become more profitable. Due to the fact that the electricity price is higher in relation to the price paid for district heat, energy savings in FX systems can not lead to cost savings. This means that the heat pump already has no economic competitiveness at many locations in the country today. According to the building rules of the building, real estate is to be calculated by 85% after the introduction of primary energy factor, which is 1.85 for electricity in a few years, which means that FX systems will not become more competitive even in energy use against the FTX system. This means that FTX systems should stand as an obvious choice of ventilation in the future. The current temperature efficiency of FTX systems can be replaced by an energy efficiency rate, which might be more accurate measure of recycled amount of energy. The energy efficiency could therefore be introduced to avoid that more energy than expected is actually needed in the energy use of the house.
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