Research On Improving The Thermal Environment Of Greenhouse With Built-in Phase Change Paraffin Structure

Greenhouse is widely used in intensive agriculture because of its advantages of simple structure,low cost and good light transmittance performance.However,the indoor temperature of greenhouse at night is too low in most areas.In order to ensure the normal growth of crops,manual heating is often required,which increases the energy consumption of greenhouse operation.Therefore,it is of great significance to study the regulation methods of indoor thermal environment in greenhouse for reducing energy consumption and improving energy utilization rate.Among the various methods,the increasingly mature phase change thermal storage technology has become the most widely used thermal environment regulation method because of its cost is cheaper and convenient operation.Therefore,this paper took the plastic experiment shed with built-in phase change board containing paraffin as the research object to carry out the research of the indoor thermal environment improvement and the effect of temperature rise.Firstly,the photo-thermal properties and thermal stability of paraffin were measured.Then,the measurement facility of the plastic experiment shed was built,and the experimental method and measurement content were explained.Based on the field monitoring data,the validity of the measured data was evaluated,and the improvement effect of phase change thermal storage and release performance of encapsulated paraffin on indoor thermal environment in the different seasons and typical weather conditions were compared and the influence of this thermal storage device on indoor light environment were discussed.Finally,the heat transfer and heating capacity performance of phase change board containing paraffin were analyzed,and the energy saving effect of phase change plastic experiment shed was discussed.The specific research contents are as follows:1.The thermal conductivity,viscosity and phase change performance parameters of paraffin were measured and detect its thermal stability,and then the transmittance of paraffin with different melting points were measured.The results showed that the thermal conductivity of paraffin varied irregularly with the increase of temperature,while the viscosity decreased regularly with the increase of temperature.The higher the melting point of paraffin,the higher the latent heat value and with the better heat storage performance.When the temperature was below 100 ℃,the paraffin had wonderful thermal stability performance.The optical distance and temperature had different effects on the transmittance of paraffin.The increase of optical distance can reduce the transmittance of paraffin,and the maximum difference was about35.63%,while the temperature had a weak influence.The transmittance of paraffin to visible light were better,and the lowest value was more than 61%.Addition,under the same measurement conditions,the transmittance of 18# paraffin was the lowest.2.Summarized the production of phase change board containing paraffin,the materials and specifications of phase change plastic experiment shed and measuring instruments.Then introduced the experimental method and measurement content,and evaluated the feasibility of the experimental method and the degree of data dispersion through the parallel experiments by variance calculation.The results showed that the average of variance of the parallel experimental data was less than 0.36,and the ratio of variance ≥ 1 were less than 13.47%.It was showed that the degree of data dispersion was very small,which indicated that it was feasible to use the current experimental method to study the indoor thermal environment.3.Investigated the effect of heat storage and release performance of three kinds of builtin phase change board containing paraffin with different melting points on indoor thermal environment improvement and room temperature regulation in the different seasons and typical weather conditions,and explored the influence of this heat storage device on indoor light environment.And according to the minimum and maximum temperature,the indoor thermal environment conditions were discussed and the planting suggestions were given.The results showed that the built-in phase change board containing paraffin can effectively improve the indoor thermal environment of the experiment shed,and the highest temperature increased by 5.80～10.20 ℃ in different seasons.And the average indoor sunlight intensity of each experiment shed was more than 8000 lux,which could meet the requirement of the lower limit of suitable sunlight intensity for most crops.4.The energy composition and equilibrium equation of the experiment shed system were summarized,and the estimation method of heat load and heat consumption were introduced.Then analyzed the heat transfer performance of the phase change board containing paraffin,calculated the accumulated heat supply of each month to evaluate its heating capacity.And finally,discussed the energy saving potential of phase change plastic experiment shed.The results showed that the built-in phase change board containing paraffin can reduce the energy consumption of the experiment shed.The energy saving rate were more than 46.30% in late autumn and the lowest was 12.79% in early winter.