Värmeöverföring till kallvatten i flerbostadshus

Sammanfattning: This Bachelor thesis is based on a request from Säker Vatten AB, a company that develops industry regulations within the HVAC line of business regarding safe installation of water systems. In addition, they hold responsibility to approve of and authorize HVAC-corporations that follow these regulations. Säker Vatten AB also provide education and training of HVAC-workers, all this to ensure that water installations shall be performed as risk free as possible. This project aims to validate a method of calculation developed by Säker Vatten AB, that claims to be able to determine the temperature of the water in the cold water pipes in apartment buildings. This calculation model is based on the lumped capacity method, which is a simplified heat transfer method to calculate how the temperature of a body changes over time. The water supply in apartment buildings is provided by so called tap water shafts installed in the bathrooms. In this project the calculation model is tested in practice through a self constructed tap water shaft prototype to determine whether the calcuation model is accurate enough to be applied to the real world. Boverket is an authority responsible for building regulations, which include one regulation regarding bacterial growth of legionella in water. The temperature of the cold water pipes cannot exceed 24 ◦C in 8 hours. The results from this project indicates that Säker Vatten’s calculation model is relatively adequate to use for calculation of the average cold water temperature. It generally showed a higher value than what was measured out in practice, where the model itself possesses an incertitude of approximately ± 0,5 ◦C. Although, if the highest emerged temperature at any point in the pipe is the most important factor to consider to avoid bacterial growth, the model cannot be used for that purpose since it assumes that the cold water temperature is homogeneous everywhere in the pipe. This assumption turned out to not quite apply to the tests performed in this project. The test results also pointed to insulation thickness being a crucial factor for the prevention of heating up the cold water. To conclude, when used to calculate the average temperature of the cold water in tap water shafts, Säker Vatten’s calculation model overall generates a higher value than what the practical measurements showed. As long as it generates a value below 24 ◦C the shaft installation should be approved.