| In north China,the heating area is large and the total energy consumption for building heating is amazing,which leads to serious environmental pollution during the heating period.Seeking to use renewable clean energy for heating is one of the main ways to solve this problem.Solar energy,as an easily available clean energy,is widely used in China and is often used as the heat source for building heating.In northwest China has sufficient solar energy resources,most of area’s solar energy resources can above Ⅲ level,qinghai and Tibet’s solar energy resources can achieve Ⅰ level.However,most cities of northwest China is mostly in cold regions,and the thermal environment adjustment of buildings is mainly in winter heating,supplemented by air conditioning in summer.As a result,the heat required for heating in winter is much higher than that in other seasons.At present,the heat collecting capacity design of solar heating system is usually based on the heating demand in winter,which makes the heat collecting capacity of the system in other seasons,especially in summer,being too large,so that the heat collecting system is easy to overheat.This paper will carry out a study on the factors,affecting the overheating characteristics of the solar collector system.In this paper,by analyzing the dynamic heat balance of solar heating system,the main factors affecting the overheating of solar collector system are obtained.The influence of outdoor temperature,radiation as well as design conditions such as collector slope,heat flux and tank volume on the overheating characteristics of solar collecting system was analyzed.The overheating degree of each design factor on the solar collector system was obtained.Finally,under certain environmental conditions,combined with the design factors,the system is optimized to prevent overheat with the overheating degree and solar fraction as the optimization objectives,and the optimal design factor value is obtained.The main conclusions are as follows:(1)The influence factors of solar collector system overheat are mainly divided into two parts: environmental factors and design factors.Environmental factors include outdoor environmental temperature and solar irradiance,design factors include heat flux,collector inclination,tank volume,etc;(2)The overheating degree of the solar collector system will decrease with the increase of collector inclination,heat flux and tank volume,and will increase with the collector area’s rising :1)for ordinary buildings,the influence of four factors on the system overheat is from high to low,which are as follows: collector inclination Angle > area of collector > water tank volume > heat flux;2)for energy-saving buildings,the influence degree of four factors on the system overheat is from high to low,which are as follows: collector inclination Angle > collector area > heat flux > water tank volume;(3)Based on the calculation of the average daily heat load ratio and overheat degree in various regions,the following conclusions can be drawn: the annual temperature and irradiation in most regions of xinjiang are greatly different,and the solar energy resources are abundant.As a result,xinjiang is a region which is easy to overheating compared with other regions.Tibet and western sichuan have less possibility to be overheating.(4)Through the above research,we had took the key factors which influencing the system overheat,therefore,to prevent the system from overheat in summer,solar collector system in Lhasa,and hami were optimized.The results showed that: hami’s overheating degree is larger,even after the system design and parameter optimization,were still need to use an additional means of preventing overheat in summer.Energy-saving building’s heating system in Lhasa has lesser overheating degree,by optimizing the design parameters,it can make the system without extra technology to prevent the overheat in the summer. |
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