Cascade air-to-water heat pumps have better overall efficiency than single-stage airto-water heat pumps when operating at low ambient temperatures for high temperature water supply. While many studies in the literature investigated the specific features of equipment performance of cascade heat pumps, there is little information about retrofit applications of these heat pumps in residential buildings using experimentally validated dynamic building simulations. In this study, the techno-economic assessment of a variable capacity cascade air-to-water heat pump retrofitted into residential buildings is conducted by means of experimentally validated TRNSYS simulations. The cascade heat pump coupled with thermal energy storage operating in different scenarios is further studied. Laboratory and field trial results were obtained to develop and validate a cascade heat pump model integrated with a dynamic building simulation model. Regarding the heat pump system without storage, the predicted annual COPs were almost below 2.5 at ambient temperatures of from-11.2°C to 29.5°C, even the heat pump adopted weather compensation control. Simulation results also indicated that the cascade heat pump could not defeat gas boilers and high-efficiency oil boilers (90%) in terms of operating costs, but there were CO 2 reductions (from 14% to 57%). As for the heat pump coupled with storage, simulation results showed that at ambient temperatures of between-5.6°C and 23.8°C, the continuous coupling between the heat pump and the storage revealed the lowest annual performance (actual COP of 1.41), while the direct heating obtained the highest efficiency (actual COP of 2.12) followed by the load-shifting (actual COP of 1.88).
Tank size and temperature set point of 1.2 m 3 and 75°C are optimal system design. • Should charge storage at 3am and 2pm for morning and afternoon demands, respectively. • The best load shifting positively affects the grid. • Achieve running costs and CO 2 savings with the best load shifting, compared to oil boilers.
It has become a major point of interest and possible bone of contention that in a future neardecarbonised electricity network i.e. approaching 100% reduction in emissions by 2050, a low carbon space heating market will be enabled through the deployment of electricallydriven heat pumps. It is recognised that such a vision will place a significant extra burden on the existing electricity network. This will be especially true of the low voltage network at Distribution System Operator level e.g. 11kV or below but as such systems do not operate in isolation, challenges will also be seen at the Transmission Operator level as well. This may be further complicated by the perceived rapid deployment of Electric Vehicles well before 2050. Domestic and local Photovoltaic (PV) system deployment would provide electricity network relief when accompanied by energy storage. Thermal storage will satisfy thermal comfort needs when operating with heat pumps while battery deployment may operate with electric vehicles and/or electric heat pumps at times of local grid congestion. Such batteries and electric vehicles will also become demand side response units in their own right, the latter whether you are at home or not, with Vehicle-to-Grid technology. This paper will link these aspects and others into viable pathways to the decarbonisation of domestic space heating in the UK. It will highlight current progress and research gaps and offers some recent comparisons with Ireland where biogas may offer an alternative scenario.
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