Analysis of a hybrid heating system with alternative control strategies
Abstract: The potential of a hybrid heating system with the possibility to utilize both district heating and a ground source heat pump is of great interest due to the high prices for district heating in dense populated areas. By controlling a hybrid heating system in a more cost effective manner there might be a possibility to trim the lifetime cost of the entire system. By using the different heating sources to their full strength, the ground source heat pump for space heating needs and the district heating for peak coverage and domestic hot water a more efficient heating system could be achieved. The overall objective for this thesis is to construct and test alternative control strategies for a hybrid heating system in place at the multi-family housing cooperative BRF Artilleriberget 8 in Stockholm, Sweden. These control strategies were to be investigated from a lifetime cost and COP perspective over a time period of 18 years. Two alternative control strategies was constructed and tested by comparing them to the control strategy already in place. The simulation software TRNSYS was used to model and simulate the hybrid heating system. A model of the hybrid heating system with the same control which is used in the actual system was created and validated with measured data from the site. By applying a control strategy where the ground source heat pump is used to cover the full space heating demand instead of only being operational during a period between 1st September to 30th April it was shown in this study that the total cost of the 18 simulated years could be decreased by 4%. It was also shown that the the higher load on the boreholes did not affect the temperature inside the boreholes to any high extent, instead the temperature in the borehole decreased throught the simulated time with 5 ˚C.
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