Techno-economic assessment of cascade air-to-water heat pump retrofitted into residential buildings using experimentally validated simulations

Abstract

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).

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

“…70%), there were cost benefits and carbon emissions savings if the CAWHP applied Strategy C was retrofitted into the houses using oil boilers. In the previous work [11], the CAWHP without TES could not defeat high efficiency oil boilers in terms of running costs. Therefore, the results in the present study indicates that Strategy C can help increase the retrofit rates of CAWHPs into the domestic buildings in offgas grid areas, where the heating systems highly rely on oil boilers [17], due to their better operating costs and carbon emissions compared to these fossil-fuel boilers.…”

“…The coupling models of the building and the CAWHP have been successfully validated against laboratory and in-situ results, as mentioned in the previous study [11]. Therefore, only experimental validation of the TES model is presented in this paper.…”

“…4. In this work, TRNSYS version 17 was obtained to develop the models as described clearly in our previous work [11]. The main components of the models are reported in Table 2.…”

“…Therefore, they can directly replace existing boilers without the requirement of considerable modifications to the heat distribution systems, thereby reducing installation costs and disruptions. The study by Le et al [11] also showed that cascade heat pumps could obtain running cost and carbon emissions savings in comparison with low efficiency oil boilers.…”

Heating Performance Analysis of an Air-to-Water Heat Pump Using Underground Air for Greenhouse Farming

“…These systems can maintain indoor thermal comfort as well as provide a potential for energy savings in buildings by extracting energy from the air, water, and soil [12][13][14][15]. Even though heat pumps often have excessive system complexity, they have increasingly been used to building applications [14,16]. Among the broad range of heat pump applications, heat pump technology can also be utilized in the area of agriculture.…”