Research On The Performance Of Solar Assisted Heat Pump With Latent Thermal Energy Storage Heating System

In the recent two decades, various researches have been done on solar assisted heat pump to serve as an alternative for renewable energy, and achieved impressive progress for promoting and utilizing the device. In China, approximately 70% of its region needs heating in winter. And coal is usually burnt for the heating devices, which consequently causes energy and environment problems in China. Hence, the Solar Assisted Heat Pump with Latent Thermal Energy Storage (SAHPLTES) is proposed to address the above-mentioned problems. This novel heating system uses solar radiation as a heat source, thus it is energy efficient and environment friendly.Based on the researches done on the solar assisted heat pump and latent thermal energy storage technology, a novel system combined the above-mentioned two systems was proposed and named as SAHPLTES heating system. It consists of a solar energy collecting system, a latent thermal energy storage tank (LTEST), a heat pump unit, heating terminal devices and auxiliary heat source. CaCl₂·6H₂O was used as a latent heat storage material, and a ground-source heat pump as auxiliary heat source. This study is based on the following aspects:Firstly, the operation modes and principles of SAHPLTES under different heating stage are introduced, and modelled by finite time thermodynamics theory for thermal economic analysis, through which the major parameters, i.e. area of solar collector, outlet temperature for solar collector, etc., for the system can be determined on an optimum yearly operation basis if the heat loads and weather conditions are given. Besides, the impact of the major system parameters on the optimum system characteristics is tested. Based on this, the corresponding heat storage capacity of LTEST can be determined. This part gives a theoretical support for the system design and assessment.Secondly, the numerical models are built for the different components of the system with a detailed description of the internal heat transfer numerical model for the LTEST component. The LTEST component model consists of a numerical model of the heat exchanger, water, and a PCM numerical model. The PCM uses an isothermal-phase-change model, in which dividing partitions or chasing the phase-change surface is not necessary. Base on the above models, the on/off conditions for the SAHPLTES can be determined, so that the operation of the system and switching of the system among different operation modes can be simulated.Thirdly, based on the system numerical model and mode-switching control conditions, the system operation throughout the whole heating period in Harbin was simulated with a heat load of 10 kW. The different operation modes, heating characteristics and heating performance of the system during the different stages of the heating period was tested. The use of the system in some other typical regions in China was also predicated and tested with different weather conditions. Thus, the suitable areas to use the system were recommended based on the system performance simulation results in different regions.Fourthly, the major design parameters of the system, including the area of solar collector, the package size of the PCM capsule, the weight percentage of PCM in LTEST as well as the operation characteristics of the whole system throughout the heating period were studied. It was found that the optimum area of solar collector in the SAHPLTES in Harbin with a heat load of 10 kW is 60 m2, and the weight percentage for PCM in LTEST is 70%.Lastly, a SAHPLTES system was set up to validate the simulation results during the period between 15 November 2007 and 31 March 2008 in Harbin. The results between the objective measurements and simulations under the same conditions are similar, so that the numerical model was validated within an acceptable accuracy.Because of some certain financial constrain, the novel SAHPLTES heating system cannot be quite popular at this moment. However, with the increasing energy prices and decreasing energy sources, together with an increasing awareness of the sustainable development, SAHPLTES promises a bright future as an alternative means for heating. It is believed that the system could be popular with the development of the solar energy heating and air conditioning technologies. The study done in this thesis provides a fundamental and theoretical support for the further application of this system.