| Earth air heat exchanger(EAHE)has great energy-saving effect and environmental protection benefit.The pipeline layout with good performance in the limited soil volume plays an important role in reducing the construction cost of the system and avoiding the waste of land.However,it needs to be equipped with reheating equipment because of the outlet temperature of EAHE in winter is fairly low.At present,flat-plate solar air heater(SAH)of reheating equipment is simple to operate and low in cost,but it has the weaknesses of low efficiency and large fluctuation of supply air temperature.Therefore,the heat transfer performance of EAHE with different pipeline geometries was studied and the PCM-corrugated SHA for reheating equipment combined with EAHE was proposed,which can improve the efficiency and solve the problem of large fluctuation of supply air temperature caused by the instability of solar radiation in a day,and then further optimized the design of its structure.In addition,the energy-saving effect and economic benefit of the coupled system in the application of earthen site museum were analyzed.This will be of great significance to the application and promotion of EAHE and SAH,so as to reduce the energy consumption of traditional air conditioning and alleviate the energy crisis.The main research contents are as follows:(1)In order to obtain a better pipeline layout in the limited soil volume,seven kinds of pipeline geometric structures were set by changing the number of serial pipelines,and the performance of the EAHE with different pipeline layouts was simulated.The results show that the heating and cooling capacity of EAHE in Zhengzhou area is equivalent.For single-layer pipes,the thermal influence range between the two pipes is 3m.Considering the system performance,pipeline and operation cost,it is advisable to use four rectangular series pipelines when the horizontal spacing(Sh)is 1m and 2m.At this time,when the vertical spacing(Sv)is1.5m,the outdoor air can be increased by 8.1℃ and 9.1℃ in winter and reduced by7.4℃ and 8.4 ℃ in summer.While the Sh is 3m and 4m,it is more suitable to use five series pipelines.Meanwhile,when the Sv is 1.5m,the outdoor air can be heated by10.3℃ and 10.9℃ in winter and cooled by 9.5℃ and 10℃ in summer.(2)In order to study the influence of the type of collector surface and phase change material on the performance of SAH,the traditional SAH and SAH with PCM models were established,and the heat transfer performance of the three kinds of SAH was compared.The results show that the outlet temperature of the traditional SHA fluctuates greatly with time,and the air will not be heated after the solar radiation disappears.Whereas the PCM solar air heater can keep the outlet air temperature within a certain range for nearly 6 hours.And the use time of system is prolonged because of the PCM releases heat when the solar radiation disappears.Meanwhile,no matter whether there is phase change material layer or not,the corrugated SHA has good heat transfer performance.For the traditional SHA,the outlet temperature of the corrugated SHA is 3.3℃ and 5.6℃ higher than that of the V-type SHA and flat-plate SHA.However,the air retention in the trough of the corrugated SHA is more serious.For the SAH with PCM,the outlet temperature of the corrugated SHA is 2℃ and 4℃higher than that of the V-type SHA and the flat-plate SHA,and the temperature distribution on the heat-absorbing surface is uniform.(3)In order to further improve the performance of the corrugated SHA with PCM,the flow and heat transfer characteristics of traditional corrugated SHA with different characteristic height ratio A and geometrical ratio L were simulated firstly.Based on this,the structure of corrugated SHA with PCM was optimized.The results show that for the traditional corrugated SHA,the increase of A not only makes the contact area between air and the heat-absorbing surface large but also increases the velocity of center and wave crest,so the temperature drop of heat-absorbing surface is large.When A increases from 0.4 to 0.5,the increase of outlet temperature is small.As the L decreases,the contact area between the air and heat-absorbing surface increases,and the temperature drop of the heat-absorbing surface is small,so the outlet temperature increases gradually.For the corrugated SHA with PCM,in the stage of energy storage,with the increase of A,the outlet temperature increases continuously.But in the stage of energy release,when A is too large,the outlet temperature drops faster and fluctuates greatly.In the range of simulation,when A is0.4,the performance of the system is better.For different L,the smaller the L,the higher the outlet temperature and the better the performance.Therefore,the L value should be reduced as much as possible in the design of collector.(4)In order to study the energy-saving effect and economic benefit of the coupled system in the application of earthen site museum,the economy of the coupled fresh air system and the common fresh air unit was compared by using the method of static payback period.The results show that compared with the common fresh air unit,the coupled system has good energy-saving effect,and the static recovery period of the coupled system is 6.88 years,which can recover the investment funds of the project during its lifetime. |
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