Conference paper

"Dynamic analysis of the low-temperature district network ""Suurstoffi"" through monitoring"

The Lucerne University of Applied Sciences has been analysing and monitoring the low- temperature district heating and cooling network (LTN) “Suurstoffi” since 2012. The analysis showed that heating demand was twice as high as expected. On the other hand, waste heat from free cooling was much lower than expected. The higher heating demand and the lower heat recovery combined resulted in a negative energy balance and hence in an average temperature decrease of the ground storage over the last two years. First of all, a pellet oven was installed as an interim solution in order to supply additional heat to the LTN. Secondly, direct electric heating was used to support the domestic hot water production in order to reduce the energy demand out of the LTN. These temporary measures were only set up until the first part of the planned hybrid solar panels (PVT) were taken into operation in summer 2014. The upcoming data of the monitored summer 2015 will help taking the decision if the temporary measures have to be extended and if additional PVT panels need to be installed. So far, the measured electricity demand to operate the LTN and the connected heat pumps was more than twice as high as expected. This is mainly due to the high electricity demand for temporary electrical heating for domestic hot water, circulation pumps and heat pumps. Thanks to the monitoring, hydraulic shortcoming, which caused the high electrical consumption of the circulation pumps, could be identified. The heat pumps consumed more electricity than planned due to the excess space heating demand and domestic hot water of the consumers. If, in addition to the electricity demand for the heat pumps, the electricity demand of the circulation pumps is taken into account, the overall network efficiency (yearly COP measured = 4.6) is lower than expected (yearly COP planned = 6.8). As a result of the monitoring analysis over the last two years, the following outputs and outcomes could be provided: - The real efficiency of the thermal network has been calculated and benchmarked - Design mistakes have been identified and guidelines for planning have been developed - The energy efficiency has been improved by optimizing the system operation - The accuracy of the monitoring has been improved - The influence of the user on the energy efficiency has been quantified.

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