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).

Although energy for heating and cooling represents the largest proportion of demand, little progress towards meeting environmental targets has been achieved in these sectors. The recent rapid progress in integrating renewable energy into the electricity sector however, can help in decarbonising heat by electrification. This paper investigates the impacts and benefits of heat electrification in a wind dominated market by considering two options; with heat pumps, and with direct electric heating, both operated with energy storage. The Irish all-island electricity market is used as a case study. Modelling results reveal the significant potential of heat pump electrification, delivering at least two and three times less carbon emissions respectively, when compared with conventional options such as gas or oil for 20% of domestic sector of the All Ireland market. Heat electrification using direct, resistive heating systems is found to be the most carbon intensive method. Energy storage systems combined with heat pumps could deliver potentially significant benefits in terms of emissions reductions, efficient market operation and mitigating the impacts of variable renewable energy on baseload generation. The main barrier to heat electrification in the all island market is the absence of appropriate policy measures to support relevant technologies.

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.

Heat pump and thermal energy storage are important technologies to decarbonise heat and electricity sector. Heat pump integrated with thermal energy storage can provide flexibility to electrical system operator to shift demand to accommodate non-synchronous generators. However, ageing housing stock and high temperature wet radiator central heating system possess some challenges for heat pump installation in the UK. To understand the challenges of retrofit technologies in the domestic sector, a field trial was carried out with a cascade heat pump integrated with a thermal storage tank. The heat pump replaced an existing gas boiler to provide flow temperature of 75°C as a retrofit measure without any modification/replacement to existing controller or radiators in the house. The heat pump was integrated with a 600l thermal store to meet heating demand and system performance was measured in different operation mode such as direct mode, storage mode and combined mode during one-year. The paper provides performance analysis of the system in different mode with operational experience, limitation and issues with the heat pump, house heat loss/insulation and sizing of thermal store in retrofit installation. Additionally, heat pump performance was compared with gas boiler to establish emission and cost saving benefits.

This paper presents experimental study of diesel engine heat pump (DEHP) system to find potential as retrofit technology in off-gas or weak electricity network area to replace existing gas/oil/electric heating system in domestic sector. Test setup of diesel engine driven waterto-water heat pump system was built which included heat recovery arrangement from the engine coolant & exhaust gas. The system was designed to meet typical house heating demand in Northern Ireland. Performance of DEHP was evaluated to meet house-heating demand at different flow temperature (35, 45, 55 & 65°C), a typical requirement of underfloor space heating, medium/high temperature radiators and domestic hot water. The performance was evaluated against four-evaporator water inlet temperature (0, 5, 10 & 15°C) and at three different engine speed 1600, 2000 & 2400 rpm. Experiment results were analysed in terms of heating/cooling capacity, heat recovery, total heat output, primary energy ratio (PER), isentropic efficiency etc. Test results showed that DEHP is able to meet house-heating demand with help of heat recovery with reduced system size. Heat recovery contributed in a range of 22 to 39% in total heat output. It is possible to achieve high flow temperature in a range of 74°C with help of heat recovery. Overall system PER varied in a range of 0.93 to 1.33. Speed increment and flow temperature has significant impact on heat recovery, total heat output and PER. A case scenario with different flow temperature to match house-heating demand has been presented to show working potential with different heat distribution system. In addition, DEHP shows good potential to save primary energy consumption and CO 2 emissions, a helpful technology to achieve national emission reduction target.

An engine driven heat pump (ENHP) can provide better efficiency compared to electric heat pump (EHP) considering primary energy consumption. The present work aimed to find suitability of diesel engine heat pump as a domestic retrofit application for off or weak gas/electricity network area. For this project work, water-to-water heat pump test facility was developed which consisted heat pump, diesel engine and heat recovery arrangements. The system performance was evaluated for 65°C flow temperature from condenser at three different engine speeds (1600, 2000 & 24000 rpm) and four evaporator water inlet temperature (0, 5, 10 & 15°C). The system performance was evaluated by heating capacity, isentropic efficiency, coolant heat recovery, exhaust gas heat recovery and PER. Performance analyses showed that heat recovery contributed 33% in total heat output where heat recovery was in a range of 1.7 to 3.7 kW. PER varied in the range of 0.9 to 1.4 showing good potential in terms of 35-65% primary energy saving and 23-42% CO 2 emissions reduction compared to conventional system. DEHP optimisation showed ability to meet water flow temperature requirement of 65-73°C by speed variations and heat recovery providing good potential to meet heating demand during winter and summer periods in retrofit settings.

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The evolution of nanofluids over the years have opened new research opportunities in the field of renewable energy. Research on the optical properties of nanofluids for application in direct absorption solar collectors (DASCs) is progressing at a burgeoning speed. In a direct absorption solar collector system, nanofluid with high optical absorptivity will convert the incident solar energy to the thermal energy of the fluid. The dispersed nanoparticles in the fluid acts in the process by the phenomenon of absorption and scattering. Studies conducted on the optical property characterization of monocomponent nanofluids have become saturated. Moreover, the photothermal efficiency of the nanofluid could be enhanced by using multicomponent nanofluids. Nanofluid prepared by varying materials, shapes, and size of nanoparticles could tune the absorption spectra of the bulk fluid to improve the photothermal efficiency. A hybrid nanocomposite can similarly enhance the absorptivity due to the synergy of materials present in the nanocomposite particle. In this review, a comprehensive survey on the synthesis and optical characterization of different blended and hybrid nanocomposite nanofluids have been performed. Besides, works on different mono nanofluids that have been studied over the years have been reviewed.