| Solar energy as a clean and renewable energy,using solar energy heating is an important measure to carry out the concept of sustainable development in China.However,solar energy has some problems such as low energy flow density and discontinuous fluctuations,and the cost of solar heat collection and storage system is much higher than of traditional heating system.As a result,continuous solar heating systems has problems such as high investment and high cost,and its promotion is severely restricted.Therefore,combined with the actual regularity of personnel activities and the intermittent use periods of different types of buildings,establishing an energy-saving operation mode of solar intermittent heating is an important means to solve the problem of large capacity and high cost of solar heating system.However,the intermittent heating demand fluctuates periodically and the load intensity and total amount have changed.It is difficult to apply the design methods of heat collection and storage systems in traditional continuous solar heating systems.Combined with the load fluctuation law of intermittent solar heating system,the design method of heat collection and storage system suitable for intermittent solar heating system should be established.Based on this,this study established three typical intermittent heating modes based on users’ energy habits and intermittent use of buildings.According to the influence of different intermittent thermal load fluctuation characteristics on the design of solar heat collection and storage systems,the design method of intermittent solar heating system heat collection and storage was established.The operating characteristics of the solar energy system under three types of typical intermittent heating modes are compared and analyzed.It provides design methods and operation optimization strategies for the efficient utilization of intermittent solar heating systems.The main research results of this paper are as follows:(1)According to the intermittent use of buildings,three typical intermittent modes are selected,namely:IHday is an intermittent mode with a period of days,IHday+period is an intermittent mode with a period of days and months,and IHday+week+period is an intermittent mode with a period of days,weeks and months.Through TRNSYS simulation,the heat load characteristics of the intermittent building are obtained,which provides the theoretical basis and design basis for the design method of the intermittent solar heating system.The results show that compared with traditional continuous heating,the annual cumulative heat load of intermittent heating has been reduced.Among them,IHday buildings are reduced by 24%,IHday+period buildings are reduced by 13.5%,and IHday+week+period buildings are reduced by 32.9.%;At the same time,the daily load of the building fluctuates greatly under the daytime heating/nightime stop heating mode,and the load is generally the highest during the heating start phase,while the building’s daily load fluctuation is smaller under the night heating/daytime stop heating mode.Taking a typical day as an example,the IHday building dynamic heat load fluctuation range is 33.67 W/m2-94.6 W/m2,and the IHday+period building dynamic heat load fluctuation range is 63.7 W/m2-67.2 W/m2.The dynamic thermal load fluctuation range of the building is 49.2 W/m2-93.5 W/m2.(2)Combining with the law of heat load of intermittent buildings,the calculation method of intermittent solar collector area is revised based on the matching of the cumulative heat collection of solar energy and the cumulative heat consumption of the building throughout the heating season.and according to the intermittent heating system at short/mid fluctuations in the cycle of heat and heat load change rule,proposed the intermittent heating system,heat storage water tank volume correction method.A design method of solar heat collection and storage system suitable for intermittent heating mode is formed,and three types of typical intermittent heating mode are combined to determine the required collector area per unit heating area Ac/m and the water tank volume required per unit collector area V/Ac has been calculated and analyzed.For IHday buildings Ac/m=0.119,V/Ac=0.12-0.32;for IHday+week+period buildings,Ac/m=0.136,V/Ac=0.07-0.22;for IHday+period buildings Ac/m=0.161,V/Ac=0.21-0.63.(3)Combined with the intermittent solar heat collection and storage design method,the TRNSYS model of the intermittent solar heating system is established to simulate and study the operating characteristics of the solar heating system under three typical intermittent modes.The simulation results show that:for the collector side,the temperature of the collector’s supply and return water fluctuates less in the daytime heating/night-off mode,while the temperature of the collector’s supply and return water fluctuates greatly under the night heating/daytime-off mode.And during the weekend period of IHday+week+period mode,due to the high temperature of the water tank,it is easy to cause the heat-collecting circulation pump to stop working,which may cause problems such as over-temperature gasification of the collector;for the heat storage side,the temperature of the hot water storage tank fluctuates slightly in the daytime heating/night-off mode,which is about 20℃;The temperature of the hot-storage tank fluctuates greatly in the daytime shutdown/night heating mode,which is about 30℃;For the heating side,when variable flow control is adopted,the daytime load of office buildings and classroom buildings fluctuates greatly,which leads to large flow fluctuations,which is difficult to control in actual operation;while dormitory buildings have a relatively stable night load,and the outdoor temperature is greatly affected during the heating season,so the method of phased variable flow can be adopted.Through theoretical analysis and simulation research,this paper has mastered the design method and operating characteristics of the intermittent solar heating system.The results can provide a reasonable basis for the design and operation control of the intermittent solar heating system. |
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