Cascade Air-to-water Heat Pump With and Without Thermal Energy Storage
: A Study for UK Domestic Retrofit

  • Khoa Le

Student thesis: Doctoral Thesis


Cascade air-to-water heat pumps have better overall efficiency than single-stage air-to-water heat pumps when operating at low ambient temperatures for high temperature water supply. Cascade heat pumps therefore have good potential for retrofitting UK domestic buildings because they can directly replace existing conventional boilers without significant modifications to the heat distribution systems, compared to single-stage heat pumps. However, little information about retrofit applications of cascade heat pumps in residential buildings is available in the literature, especially for the UK’s context.
In this research, the techno-economic assessment of a variable capacity cascade air-to-water heat pump retrofitted into UK residential buildings was conducted by means of experimentally validated TRNSYS simulations. The cascade heat
pump coupled with thermal energy storage operating in different scenarios was further studied. Laboratory and field trial results were obtained to develop and calibrate/validate the developed models. Additionally, different load shifting
strategies for the integrated system of the cascade heat pump and thermal energy storage were simulated. These simulations were investigated to find the best load shifting algorithm which could help to achieve enhanced system energy
efficiency with minimised running costs and reduced wind energy curtailment, while avoiding peak demand periods and guaranteeing thermal comforts for end-users.
Date of AwardMay 2020
Original languageEnglish
SupervisorMing Jun Huang (Supervisor) & Neil Hewitt (Supervisor)


  • Demand-side management
  • Carbon savings
  • Cost savings
  • Energy performance
  • Model validation
  • Field experiments
  • Load shifting

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