Upgrading a District Heating System by Means of the Integration of Modular Heat Pumps, Geothermal Waters, and PVs for Resilient and Sustainable Urban Energy

Abstract

Krakow has an extensive district heating network, which is approximately 900 km long. It is the second largest city in terms of the number of inhabitants in Poland, resulting in a high demand for energy—for both heating and cooling. The district heating of the city is based on coal. The paper presents the conception of using the available renewable sources to integrate them into the city’s heating system, increasing the flexibility of the system and its decentralization. An innovative solution of the use of hybrid, modular heat pumps with power dependent on the needs of customers in a given location and combining them with geothermal waters and photovoltaics is presented. The potential of deep geothermal waters is based on two reservoirs built of carbonate rocks, namely Devonian and Upper Jurassic, which mainly consist of dolomite and limestone. The theoretical potential of water intake equal to the nominal heating capacity of a geothermal installation is estimated at 3.3 and 2.0 MW, respectively. Shallow geothermal energy potential varies within the city, reflecting the complex geological structure of the city. Apart from typical borehole heat exchangers (BHEs), the shallower water levels may represent a significant potential source for both heating and cooling by means of water heat pumps. For the heating network, it has been proposed to use modular heat pumps with hybrid sources, which will allow for the flexible development of the network in places previously unavailable or unprofitable. In the case of balancing production and demand, a photovoltaic installation can be an effective and sufficient source of electricity that will cover the annual electricity demand generated by the heat pump installation, when it is used for both heating and cooling. The alternating demand of facilities for heating and cooling energy, caused by changes in the seasons, suggests potential for using seasonal cold and heat storage.

Analysis of the Wider Potential for Heat Pump and Geothermal Energy Integration in Traditional Systems and Grids

“…Many cases related to DHC exist in the EU, with the incorporation of geothermal energy in the form of either shallow thermal or medium geothermal (direct use) applications. The available cases can be categorised into the 'retrofitting' or upgrading of the existing networks, new hybrid networks incorporating many sources [49], or geothermal only DHC networks. A specific European cost action project (Geothermal-DHC CA18219) addresses and promotes these cases where a web GIS tool has been developed to record as many cases as possible.…”

Fifth-Generation District Heating and Cooling Networks Based on Shallow Geothermal Energy: A review and Possible Solutions for Mediterranean Europe

“…Assuming a SPF of four (one unit of electricity to provide or remove four units of heat), just 50% of self-consumption by PV panels can increase the renewable fraction of the GSHP from 87% to 93%. Several authors also emphasize the benefits of hybridizing GSHPs with PV panels from the operational, economic, and environmental perspectives [71][72][73][169][170][171].…”

Optimal Planning of Future District Heating Systems—A Review

“…The benefit of this strategy is twofold. First, by enhancing the heat supply technology (such as switching from coal-fired plant to a CHP unit in [202]) or by replacing the fossil fuel with more sustainable resources [203,204], the overall energy conversion efficiency is increased, which leads to extra energy savings, lower heat generation cost and less GHG emissions. Furthermore, replacing fossil fuels with sustainable resources usually results in a lower operation temperature.…”