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Potentialen av värmebesparing i ett avlopps luftningsledning

This thesis aims at determining the heat losses in a property vent stack and its roof valve. Upon request of a company, the vent stack is analysed for possible heat recovering solutions to be implemented, while relining of the drain system is executed and with a suitable payback time for the economic investments. The heat loss calculations are based on data for properties that are located in the Stockholm region, but also easy to change depending on the situation. The calculations are done on pipes made out of cast iron, which still is the most common type of drain pipe in Sweden, and these are the pipes that relining is usually made on. The calculations that needed to take several variables into account have been done in MatlabR2014a and the thermos dynamical properties that were used in those calculations have been extracted from EES.Three different types of heat losses in the vent stack have been taken into consideration in this thesis. The three types of heat losses are convection, radiation and one through airflow. These are calculated and subsequently compared with the losses present after possible heat recovering solutions have been implemented. Lastly the heat recovering solutions are evaluated with regards to their practicality and their respective payback time.The results show heat losses are fairly small in a vent stack implemented in a conventional way for a three story residential home in the Stockholm region. Furthermore, combined with the difficulties in the practical installation, excludes an investment in a heat pump or heat exchanger. The total heat losses for a 3-meter vent stack made out of cast iron varies from 6 and 30 W depending on the temperature surrounding the stack. The total heat loss for the valve on at the top of the vent stack, on the roof, varies from 3 to 13 W. If insulation is used around the vent stack, one is able to save around 4 to 15 W and between 2 and 6 W for the valve.In addition to this, there are losses due to heated air flowing out from the vent stack. This loss is estimated to be between 2 and 17 W if the flow of air is between 0,1 and 1 litre per second. It is however very likely that these flows are momentary and the heat losses therefore are practically non-existent. However, regulations regarding buildings prohibit the recirculation or any other usage of this air.With a price of 28 SEK/m2 for the insulation a payback time of approximately 5 months is achieved, if the price is increased to 50 SEK/m2 the payback time is increased to 9 months. These calculations only include the cost of materials and not the cost of executing the work. The company requesting this thesis will need to make this evaluation of work related cost in order to determine if the insulation is a potential investment. As a result, this thesis recommends that insulation of the vent stack with a roof valve may be a good solution for properties with a vent stack of at least 3 meters, if the property is in the area with low average temperatures or for properties with many sewage flows entering the drainage pipe.

Författare

Lovisa Bergman Amanda Enocksson

Lärosäte och institution

KTH/Energiteknik

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"Kandidatuppsats". Självständigt arbete (examensarbete ) om minst 15 högskolepoäng utfört för att erhålla kandidatexamen.

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