Simulation Research Of Absorption Heat Pump System Driven By Solar Energy With Phase Change Materials

With the rapid development of the national economy,China has become one of the largest energy consumers in the world.Energy and environmental issues have become increasingly prominent.The proportion of HVAC energy consumption in building is increasing.Clean and renewable energy instead of traditional fossil energy was used,which can reduce environmental pollution during mining and combustion.Solar energy is an inexhaustible clean energy.Applying it to the HVAC field has become a meaningful task.This thesis was based on the sensible heat storage method of the traditional solar absorption system,and associated it with the latent heat storage method of PCMs.The PCMs were filled into the hot water storage tank,an improved solar absorption system with PCMs was proposed.It could compensate for the intermittentness and instability of solar energy to a certain extent.Absorption air conditioning and heating system driven by solar were built.The application was simulated and analyzed in an office building.The structure and operation principle of solar absorption refrigeration and heating system with and without PCMs were introduced.According to the thermophysical properties of fatty acids,myristic acid（MA）and expanded graphite（EG）were selected as composite phase change materials.The meteorological file TMY2 of Tai ’an area was derived with Meteonorm7.3,and TRNSYS software was used to build the system with and without PCMs in an office building in Tai’an respectively.Simulation was carried out on typical days in winter,summer,whole cooling and heating period.The useful energy absorbed,collector efficiency,electric heating power consumption,performance of absorption refrigeration unit and energy consumption of the system were compared between the two systems with and without PCMs.The economic and environmental benefits of direct combustion,solar absorption system with and without PCMs were analyzed.The main results of the thesis:（1）According to the characteristics of various phase change materials,fatty acid phase change materials were selected in the thesis.Various ratios of myristic acid（MA）and expanded graphite（EG）binary composite phase change materials were prepared,and the optimal ratio was determined to be 16:1 through DSC test and leakage test.The phase transition temperature and latent heat of the prepared composite phase change material are56 ℃ and 184.85 J/g.The leakage percentage is 2%,and the performance is stable to meet the demand of direct heating in winter.（2）The performance of the flat-plate collector was improved after adding PCMs,which increased the useful energy absorbed by the flat-plate collector and the efficiency.In a typical year,compared with the traditional solar absorption system,the useful energy absorbed by the collector in the improved system was increased by 55962.14 MJ and the efficiency was increased by 8.98%.The existence of PCM device greatly reduced the power consumption of electric heater,reducing 4616.75 k Wh in the whole cooling period and 271.46 k Wh in the whole heating period,reducing 4888.21 k Wh in total,or 17597.56 MJ.On typical days in winter and summer,the temperature of the water tank of the improved system decreased slowly in the evening and early morning（low radiation intensity）.During the whole cooling period,the COP of the absorption chiller of the traditional system fluctuated around 0.73,and the COP of the absorption chiller with PCMs fluctuated around 0.68.The chiller capacity of traditional systems was higher than the office building needs,and excess cooling capacity will be generated,resulting in waste.In the systems with PCMs,the PCMs will absorb the excess cooling capacity of this part of the heat,so as to achieve the effect of energy saving.（3）In terms of economic analysis,the initial investment of the solar absorption system with PCMs was the highest,followed by the traditional solar absorption system,and the direct-fired type was the lowest.The system with PCMs had the lowest operation and maintenance cost,followed by the traditional system,and the direct-fired type was the highest.From an environmental benefit point of view,the system with PCMs saved 2 tons of coal than the traditional system,and 12 tons of coal than the direct-fired system,which had the best energy-saving effect.In terms of carbon emissions,the system with PCMs had 5080 kg less than the traditional system,and had 6660 kg less than the direct-fired system.It has great environmental benefits.In the thesis,the cooling and heating of an office building was taken as the research object,and an absorption air conditioning system driven by solar was constructed.According to the heating demand,we reasonably selected the PCMs,and applied it to the solar absorption refrigeration system and the solar heating system.It provides a basis for the development and popularization of solar absorption system with PCMs.