Tariff-based load shifting for domestic cascade heat pump with enhanced system energy efficiency and reduced wind power curtailment

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Cascade air-to-water heat pumps may have good potential for retrofitting UK domestic buildings because they can directly replace existing fossil-fuel boilers without the requirement of considerable modifications to heat distribution systems. A widespread uptake of these heat pumps, however, would pose challenges to the grid. Furthermore, wind power generation has increased in the UK to achieve the target of decreasing CO2 emissions by 2050, but there are high levels of wind curtailment due to the mismatch between electricity supply and demand. In this paper, a load shifting study for cascade heat pumps coupled with thermal energy storage addressing these issues is presented. The main objective is to find the best tariff-based schedule load shifting for cascade heat pumps, which can help to avoid peak demand periods while obtaining enhanced system energy efficiency with minimised running costs and reduced wind energy curtailment. How the retrofit performance of the cascade heat pumps with load shifting is further investigated. TRNSYS was used to simulate the system performance validated against experimental results. Northern Ireland (UK) was selected as the evaluated scenario. Simulation results showed that the tank temperature set point of 75 °C and the storage size of 1.2 m3 could wholly shift the cascade heat pumps’ operation to off-peak periods. The best times to start the cascade heat pumps to charge the storage were at 3 am and 2 pm for the morning and afternoon heating demands, respectively. Compared to oil boilers, the cascade heat pumps with load shifting could obtain lower running costs (16–34%) and carbon emissions (20–37%).

Original languageEnglish
Article number113976
Number of pages16
JournalApplied Energy
Early online date21 Oct 2019
Publication statusPublished (in print/issue) - 1 Jan 2020

Bibliographical note

Funding Information:
The authors would like to acknowledge the support funding from the European Commission via H2020, IDEAS [Grant No.: 815271 ]. The authors also thank for the financial contribution from the European Commission via H2020, CHESS-SETUP project [Grant No.: 680556 ] and CHESTER project [Grant No.: 764042 ]. Finally, the authors are grateful to the European Union for the funding through Interreg VA SPIRE 2 project [Grant No.: IVA5038 ].

Publisher Copyright:
© 2019 Elsevier Ltd

Copyright 2020 Elsevier B.V., All rights reserved.


  • Cascade air-to-water heat pump
  • Enhanced system energy efficiency
  • Reduced wind energy curtailment
  • Tariff-based load shifting
  • Thermal energy storage
  • TRNSYS simulation


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