| As an important part of the facilities production in Northern China,it relies on solar energy to maintain indoor temperature and realize the four seasons production.Research on the solar energy utilization rate in solar greenhouse,the typical brick structure greenhouse in Jinzhong,Shanxi was selected as the research object in this experiment,which a total length of 43.0 m,a total span of 9.75 m,4.5 m high ridge,the north wall height of 3.0 m,0.05 m thick.A real-time measurement of the north wall,ground,front and black roof,and air temperature and the solar radiation intensity in solar greenhouse be aim to building the solar energy distribution model.It is determined the thermal coefficient of the front roof covering according to the energy balance principle of the solar greenhouse,then is analyzed the distribution rule of solar energy and is built the solar energy distribution model in solar greenhouse.Finally,it set up low temperature layer(8?,12?,16?)and high temperature layer(26 ?,30 ?,34?),a total of 9 temperature range according to different temperature requirements of the different crops in different growth periods.The model can be used to calculate the relationship between the energy and indoor temperature,and then obtain the energy surplus or shortage in different temperature range in solar greenhouse,and analysis the solar energy utilization in a hypothesis,which the black bags are placed in the ridge.The following conclusions are obtained:1.In this experiment,the thermal flow coefficient of composite insulation covering is estimated based on the principle of energy balance,and the sensitivity of air temperature to the energy change.The thermal flow coefficient of a composite thermal insulation covering "plastic film + thermal insulation quilt(3 layers of composite cotton + reinforced reinforcement)" of a solar greenhouse in the spring varies from 8?12KJ·m-2·K-1·h-1,and the average value is about 11.01 KJ·m-2·K-1·h-1.A similar calculation method is used to verify the thermal flow coefficient of the transparent plastic film,which is close to the value given in the literature.It is proved that this method is feasible to estimate the thermal flow coefficient in the front roof of the solar greenhouse.This method can be used to determine and compare the thermal flow coefficient of different external thermal insulation.2.The energy changes of north wall,ground,front and black roof and indoor air with the solar radiation were "not closed loop curve" in the solar greenhouse,which is divided into two part(morning and afternoon)with maximum indoor solar radiation,the linear regression of each part varies linearly in the afternoon.The energy change of the ground(-20 to 160 MJ)is higher than that of the north wall(-20 to 60 MJ)in daytime,which is the water content of ground is high,and it starts to release heat when indoor energy is lower than 235 MJ and 135 MJ,respectively.The front and black roofs are in the state of heat dissipation all day,but the front roof is the main heat dissipating body,which is related to the large area and the heat flow coefficient of the front roof.The air energy change did not have a certain rule in the morning and it showed a linear decline in the afternoon,because of poor sealing and unstable meteorological factors in outdoor.3.It were compared and analyzed the difference between the total solar energy and the accumulation energy measured in different parts of the solar greenhouse from February 24th to March 25th(30 d),and the solar energy utilization rate are averaged 82.1%.Through the statistical analysis of SAS,a simple mathematical model of solar energy distribution in solar greenhouse is obtained:Y=546.175 + 0.990X1 +1.197X2-1.031X3-3.784X4-0.919X5(R2=0.97)Y represents solar energy received in solar greenhouse during the daytime,X1 represents the energy change of the north wall,X2 represents the energy change of the ground,X3 represents the energy change of the black roof,X4 represents the energy change of the front roof,and X5 represents the indoor air energy change,all the units are MJ.It showed that the north wall and the ground are in the heat absorbing state during the day and the heat absorption of the ground is slightly higher than that of the wall,because of the coefficient of the north wall and the ground is about +1,and the difference is small.The heat amount in the black roof is much higher than that of front roof during the day,because of the coefficient of the front roof(-3.8)is significantly lower than that of the black roof(-1.0).The coefficient of the air is negative,it is believed that it may be related to the sealing and thermal insulation effect of the solar greenhouse,considering the actual production situation of the solar greenhouse.With the error rate,standard deviation,relative error and absolute error method to evaluate the accuracy and reliability of the model and found that the standard deviation,relative error and absolute error were 188.07 MJ,1.11%and 0.39 MJ,and the error rate in the range of-11.26%?17.57%,-5%?5%,within the range of the number of the data up to 56.7%.4.The relationship between the energy of each part of solar greenhouse and indoor air temperature can be obtained by using this model,and the energy surplus and shortage of solar greenhouse can be calculated.Under the combination of 9 different temperature ranges,the greenhouse energy surplus shows at 11:30?16:30,and the energy shortage occurred in the range of 16? and 12?,and there was no energy shortage in the range above 8?,and the total energy were short of-157.3 MJ/d and-59.7 MJ/d in the range of 16??34? and 16?30?.The total surplus energy of were between 211.8 MJ/d and 570 MJ/d.We can make corresponding measurement to maintain the temperature stability according to the profit and loss of energy,such as heating,natural ventilation,forced ventilation and so on.It can also be planned and calculated the heat storage method and quantity based on the profit and loss of energy,which black bag for accumulation of greenhouse excess energy and released in short,calculated to meet the basic requirements of the temperature changes.According to the above analysis,the energy of all parts of the greenhouse were in a "ring curve" state with the change of indoor air temperature.When the indoor air temperature is around 10?20?,the energy of each part is relatively stable,indicating that the energy change is not affected by indoor air temperature at night.5.It shows that the model can be used in environmental control,design,calculation of heat storage of the solar greenhouse and so on. |
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