Optimizing Industrial Energy Systems: Synergies Between Cooling Demand and Waste Heat Recovery for Heating Demand

Kurzfassung

Achieving net-zero goals requires decarbonizing all sectors, which can be facilitated by electrifying heat supply systems. In the UK, industrial waste heat accounts for 17% and in the USA it is 20%. Europe’s energy consumption could be reduced by 15% if waste heat is utilized. However, in cooling systems such as refrigeration, this heat is often discarded, highlighting the need and potential for heat recover. This research investigates electrifying heat supply and coupling waste heat from cold demand to hot demand in industrial energy systems. Using MTRESS, an open-source optimization tool, a model of the DLR Weilheim energy system is developed. The energy system of DLR Weilheim uses an oil-fuel boiler for heating and chillers for cooling a 24/7 server room, with waste heat expelled to the environment. Three core scenarios (Scenario 1, 2, and 3) are examined with two extra scenarios, noted with a star annotation (Scenario 4* and Scenario 5*). The core scenarios do not have any annotation: Scenario 1 replaces the oil-fuel boiler with a heat pump, and couples the hot and cold demands with PV panels. Scenario 2 reduces the heat pump size and adds thermal storage to lower investment costs. Scenario 3 uses only chillers with hot and cold storage, eliminating the heat pump to further reduce investment costs. Lastly, based on Scenario 3, the extra Scenario 4* replicates the technologies of Scenario 3 but reduces the storage sizes of the hot and cold storages, attempting to reduce the investment cost of the storage units. Scenario 5* does the same, but reduces the storage sizes even more. Both Scenario 4* and Scenario 5* provide valuable information on how much MTRESS is able to optimize the energy system with these smaller sizes and how the results differ from core Scenario 3. All three core scenarios successfully operate the industrial energy system at DLR Weilheim. The operational costs, determined by electricity purchases from the grid and revenues from excess PV electricity sold back to the grid, vary by scenario. Negative operational costs indicate that the scenario generates a profit through the feed-in tariff. Scenario 1 has an operational cost of approximately €-75K per year, Scenario 2 is slightly lower at €-74K, and Scenario 3 is the least expensive, with €-71K. All three core scenarios are able to generate profit. The available investment budgets are calculated based on the savings of each scenario compared to the current energy system over a 10-year period. The investment budgets are €235.740 for Scenario 1, €230.084 for Scenario 2, and €203.334 for Scenario 3, each with a 10-year payback period. The main reason why Scenario 3 has a lower budget is due to the higher operational costs compared to Scenario 1 and Scenario 2. Both Scenario 4* and Scenario 5* have operational costs of around €-71K per year, which is similar to Scenario 3. Scenario 4* has an investment budget of €206.325 and Scenario 5* has an investment budget of €207.208. Both Scenario 4* and Scenario 5* have a higher operational cost compared to Scenario 3. A key finding of this study is that the industrial energy system at DLR Weilheim is able to operate effectively with only the chiller, hot storage, and cold storage. The absence of a heat pump, as demonstrated in Scenario 3, does not seem to be an issue when the chiller is able to provide the heat needed for the heat demand. This is achieved by coupling the heat and cold demands and incorporating both hot and cold storage. This highlights the potential of coupling and the benefits it offers for decarbonizing the industrial sector with a hot and cold demand.