| Solar-thermal-driven cooling technology can realize a reasonable energy conversion from theexcess solar radiation on building envelope to the cooling supply in summer. However, lowenergy flux and unstable supply of solar radiation limitation technology application. Forexample, chilled water from solar-driven absorption chiller is commonly in a highertemperature range than that produced by common electricity driven chiller. Thus, it isunavailable for a direct application for indoor terminal unit due to disability indehumidification. On the other hand, solar-assisted heat pump is a high-efficiency technologywhich has already been applied in demonstration projects. However, this kind of systemcannot meet cooling demand of building in a reasonable technology solution, like what itoperates in heating mode. Meanwhile, overheat problems in the solar collector loop andstorage devices increase potential risks during the summer operation. So developing anintegration device which combines solar-assisted and heat pump technologies for acomprehensive demand of building, such as cooling, heating and domestic hot water, becomean important research direction. For this purpose, a solar-assisted sub-cooling carbon dioxideheat pump was studied in this research. The cooling supplied by solar-thermal-drivenabsorption chiller was employed to sub-cooling carbon dioxide heat pump in cooling mode. Inthis way, cooling efficiency of heat pump can be increased and meanwhile match performancebetween device and building comes into a better state.The numerical module was firstly built for CO2transcritical baseline cycle as a primarypreparing for thermodynamic analysis. The subcooling process was analyzed and the difference of subcooling concept between subcritiacal cycle of synthetic refrigerants and CO2transcritical cycle was compared. With an assistance of steady state simulation, theperformance improvement of updated cycle process was proved in terms of energy-saving.Furthermore, the feasibility of solar energy integration was discussed for enhanced subcoolingin air-conditioning application. The simulated results show that cooling COP of proposedcycle process can achieve4.0when ambient temperature is28oC which is45.5higher thanthat of baseline cycle. Moreover, when solar-driven temperature is90oC, the percentage ofassisted cooling from renewable energy to the total cooling capacity is22%, and it can reach33%when solar driven temperature is94oC.Based on the thermodynamic analysis, a prototype with the proposed cycle process wasdeveloped and on-site test systems for cooling and heating performance was built respectively.The cooling test contains two stages for hybrid mode and independent mode. The differencebetween these two modes is assisted subcooling. The test shows that cooling COP ofprototype in hybrid mode is2.32when ambient temperature is28.0oC. The heating test wascarried out as well and result shows that heating COP is2.60when ambient temperature is10.4oC.Because of integration with solar energy utilization device, amount of parameter whichinfluences the prototype performance is more than that of a conventional CO2HP. Hence,research object is transfer from the prototype to the entire system due to more externalconditions. One system module, which contains solar collector, tank, developed HP andbuilding, was estiblished for the whole year dynamic simulation. The influences from weatherconditions, indoor load and DHW load was analyzed and quantified. The comparison betweenproposed cooling system and conventional synthetic refrigerant HP was carried out as well.The integration solution for solar utilization and CO2HP in heating supply is different to thatin cooling supply. The latter solution applied the in-shell integration while the former schemechooses solar collector array and CO2HP as two thermal sources in parallel connection for heating supply. In this case, the system module was updated and performance influence fromsingle parameter, such as: solar collector area, tank volume, indoor load and controlconditions, was obtained through simulation. Based on the single parameter analysis,influence weight can be got for sensitivity analysis in order to conduct multi-parametersoptimization. The optimized system was evaluated in terms of solar fraction, deviceperformance, etc.Finally, the developed CO2HP was applied in an energy system as the core device for a netzero energy building (NZEB). The entire energy system can meet the year round demands ofcooling, heating and DHW of90m2demonstration apartment and meanwhile the net energyconsumption per year is zero. An overview about all components in NZEB, such as: passivedesign, HVAC&DHW system, indoor terminal units and renewable power system was present.The annual performance for the entire system was analyzed. Not only the consumption ofevery section in building, but also the comparison between renewable power generation andmaintenance consumption were obtained based on simulation. Besides energy balances for netzero energy aim, indoor comfort performance was also discussed in evaluation. |
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