energies Article Heat Pump Bridge Analysis Using the Modified Energy Transfer Diagram Florian Schlosser 1, *, Heinrich Wiebe 1 , Timothy G. Walmsley 2 , Martin J. Atkins 2 , Michael R. W. Walmsley 2 and Jens Hesselbach 1   Citation: Schlosser, F.; Wiebe, H.; Walmsley,T.G.; Atkins, M.J.; Walmsley,M.R.W.; Hesselbach, J. Heat Pump Bridge Analysis Using the Modified Energy Transfer Diagram. Energies 2021, 14, 137. https://doi.org/10.3390/en14010137 Received: 3 December 2020 Accepted: 24 December 2020 Published: 29 December 2020 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional clai- ms in published maps and institutio- nal affiliations. Copyright: © 2020 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department Sustainable Products and Processes, University of Kassel, Kurt-Wolters-Straße 3, 34125 Kassel, Germany; uk015044@student.uni-kassel.de (H.W.); hesselbach@upp-kassel.de (J.H.) 2 Energy Systems Integration Group, School of Engineering, University of Waikato, Hamilton 3216, New Zealand; tim.walmsley@waikato.ac.nz (T.G.W.); martin.atkins@waikato.ac.nz (M.J.A.); walmsley@waikato.ac.nz (M.R.W.W.) * Correspondence: schlosser@upp-kassel.de; Tel.: +49-561-804-3442 Abstract: Heat pumps are the key technology to decarbonise thermal processes by upgrading industrial surplus heat using renewable electricity. Existing insight-based integration methods refer to the idealised Grand Composite Curve requiring the full exploitation of heat recovery potential but leave the question of how to deal with technical or economic limitations unanswered. In this work, a novel Heat Pump Bridge Analysis (HPBA) is introduced for practically targeting technical and economic heat pump potential by applying Coefficient of Performance curves into the Modified Energy Transfer Diagram (METD). Removing cross-Pinch violations and operating heat exchangers at minimum approach temperatures by combined application of Bridge Analysis increases the heat recovery rate and reduce the temperature lift to be pumped at the same time. The insight-based METD allows the individual matching of heat surpluses and deficits of individual streams with the capabilities and performance of different market-available heat pump concepts. For an illustrative example, the presented modifications based on HPBA increase the economically viable share of the technical heat pump potential from 61% to 79%. Keywords: heat pump integration; Pinch Analysis; retrofit; Modified Energy Transfer Diagram 1. Introduction Pinch Analysis (PA) enables an engineer to target and develop heat integration solu- tions. The graphic tools of this method intuitively visualises the best paths to integrate a heat pump (HP) into an industrial process [1]. In PA, all thermal process streams are separated into heat surpluses and deficits and superimposed graphically according to temperature and heat capacity flow rate in the form of cold and hot Composite Curves (CC). As a step further, the Grand Composite Curve (GCC) is built by plotting the net heat deficits and surpluses for every temperature level. The resulting Pinch temperature is the characteristic temperature that divides the thermodynamic system into an area with cooling demand (below the Pinch) and an area with heating demand (above the Pinch). The correct integration of a HP is across the Pinch by recovering surplus heat from below the Pinch and upgrading heat for streams with heat deficits above the Pinch. Non-compliance with this principle leads to either an ineffective HP upgrading heat from above the Pinch (which can already fulfill a heating purpose), or additional waste heat being generated below the Pinch. The amount of additional waste heat is equal to the work provided to the HP. Figure 1 compares (a) the principle of the conventional separate supply of heating energy by a fossil-fired boiler and cooling energy by a chiller, and (b) a HP providing both for an exemplary GCC. The lighter green areas are excluded in the analysis of energy supply systems because they represent already exploited heat recovery pockets. Energies 2021, 14, 137. https://doi.org/10.3390/en14010137 https://www.mdpi.com/journal/energies