Data-driven Modelling and Optimized Management of the District Cooling System and Thermal Energy Storage in Gothenburg
Publicerad
Författare
Typ
Examensarbete för masterexamen
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
District cooling system (DCS) is a sustainable and cost-effective way to provide
cooling energy in urban areas[1]. DCS is growing in Sweden due to the increase
in cooling energy demand. In Gothenburg, an expansion of DCS will be done by
installing more cooling units and a cold-water thermal energy storage unit (TES).
This paper first models the potential operation of the TES of low loading temperature
below 4 °C by using computational fluid dynamics model Ansys Fluent. Then,
it formulates an investment model by using linear programming (LP) to investigate
the optimal size of the units, potential benefits and drawbacks to the system, in 2040.
The research results in this study demonstrate that the operation of discharging
temperature of water of 1 °C is unlikely in the operational point of view due to
the intensive mixing in the low-temperature zone. The thermocline layer is only
established between the warm return water zone and the cold zone. The thickness
of the thermocline layer grows with time with the conduction and diffusion due to
temperature difference within the medium.
The balance between the investment and the operational cost decides the optimum
size for the TES and the new production plant. TES has an investment priority
advantage as it has a cheaper investment cost compared with the use of mechanical
chillers, and a lower operational cost because it can be charged during the off-peak
hours with low electricity prices. However, one of the limiting factors for the size of
TES is the available chiller’s capacity for charging the TES, and another factor is
the peak cooling demand. TES is optimized with the lowest total cost by running
on a daily cycle. It saves operational costs by charging during off-peak hours and
discharging during peak hours.
In addition, the absorption chiller is a cost-effective choice to invest in to charge
the TES over the compressor chillers. This is due to the availability of free waste
heat, which has given an operational cost advantage for the absorption chillers, even
though they have higher investment costs.
The optimal size of the investment of cooling units has some uncertainties due to
the unavailability of assured data on the electricity price and cooling demand, which
greatly affect the operation of the overall DCS in the future.
Beskrivning
Ämne/nyckelord
Cooling Thermal Energy Storage, District Cooling Network, CFD, cost optimization v