Identification of waste heat sources in Uppsala - with potential use in Bergsbrunna as a case study

Sammanfattning: Reducing energy losses within the energy system is essential for a sustainable future. Waste heat usage could be a part of an increased energy efficiency and a sustainable use of resources. Uppsala Municipality aims to become a climate positive municipality in 2050, with negative net emissions of CO2. Increasing waste heat usage represent one possible measure in order to achieve this goal. Vattenfall AB is the local supplier of heat, cooling, steam and electricity in Uppsala and has a strong ambition for a sustainable future. The main objective of this work is to identify, quantify and classify low and high temperature waste heat sources within Uppsala Municipality. Also, the objective is to assess the potential contribution from low temperature waste heat sources for a low temperature district heating network in Bergsbrunna, a planned urban area in Uppsala. The contribution was evaluated based the technical and economic feasibility.  To reach the objectives, a survey on the waste heat and waste heat generating processes within different businesses in Uppsala Municipality was created and sent to 374 businesses of different type within the Municipality. The selection of targeted businesses types was based on the findings of potential waste heat within these businesses in the literature and limited to available contact information.  This work contributes with profiles of the waste heat transfer rate from a number of businesses on an hourly basis, which can be applied to any area to estimate the waste heat potential. Waste heat profiles were developed for grocery stores of different sizes, a restaurant, a hotel, an ice rink, and an indoor swimming pool. In addition to this, a decision-making matrix was created to facilitate comparison of the waste heat sources. The considered waste heat parameters are quantity, temperature, daily and seasonal variations and distance to the present district heating network.   Calculations of the theoretical amount of low temperature waste heat sources in Uppsala Municipality have been made based on the developed waste heat profiles and the number of identified businesses. The results show that the quantified amount of low temperature waste heat within Uppsala Municipality amount to approximately 62 GWh annually, which is available at temperatures between 22°C to 55°C.  From the developed waste heat profiles, it was found that a grocery store has a potential or delivering between 1,200 MWh and 3,500 MWh waste heat annually depending on its size. A restaurant could potentially deliver 90 MWh waste heat annually, whereas a hotel has the potential of 80 MWh. Additionally, an ice rink and an indoor swimming pool could potentially deliver 1,400 MWh and 600 MWh of waste heat, respectively.  By means of the decision-making matrix, grocery stores and ice rinks were presented as the most prominent low temperature waste heat sources in Uppsala Municipality. Mostly due to the continuity of waste heat delivery, but also thanks to favorable geographic positions. When evaluating the contribution of waste heat sources to a low temperature district heating network in Bergsbrunna, it was seen that the waste heat contributed to almost 14% of the heat demand if the waste heat temperature was raised to 65°C with heat pumps. However, the economic assessment shows that the lowest cost is approximately 0.34 SEK/kWh for raising the temperature to 65°C. Additionally, it was seen that the temperature of the waste heat could be raised to 85°C to be utilized in the conventional district heating network. However, the associated production cost where higher in comparison with the cost of utilizing the waste heat in a network with a lower design temperature, where the lowest cost is approximately 0.39 SEK/kWh. It should be mentioned that a number of assumptions have been made to calculate the waste heat potential. The most important assumption is addressed to the fact that the potential is based on secondary data of an average energy use in different buildings on a national level, which was not intentionally collected for calculating waste heat potential. The urban planning used in the case-study of Bergsbrunna is based on several assumptions. Thereby, it is not certain that this represents Bergsbrunna in the future or another area of the same size. Also, the heat production cost only includes approximated investment and installation costs of the heat pump and the electricity costs, which are based on historical data.