| Generally, many artificial heating systems which included hot-water heating system,hot-blast stove heating system, electric heating system, electricity heat pump heating systemand so on were adopted in order to maintenance production of the solar greenhouse under theextreme weather condition in winter. But application area of these heating systems waslimited due to the high cost of equipment and the operating.Fire-pit and underground heating exchange system in the greenhouse integrated fire pitheating system with underground heating exchange system, and this system can increase soiland air temperature, reduce humidity inside greenhouse during it operating. In the winterdaytime, soil temperature was increased with fire-pit releasing energy which was storedunderground through circulation of the blower and underground heating exchange pipes. Atnight, air temperature was increased and air humidity was reduced with the energy come fromthe fire-pit and part of stored underground through the blower, underground heating exchangepipes and over-ground pipes. In summer, air temperature inside greenhouse was reducedthrough circulation of the blower and underground heating exchange pipes.This paper main research includes: (1) Heat transfer mechanism of fire-pit and undergroundheating exchange system in the greenhouse was analyzed, and mathematics models of heatingtransfer were established according to the convection, the conduction and the radiation theory,and numerical value was analyzed. (2) Influence of structure parameters of fire-pit andunderground heating exchange system in the greenhouse on system thermal performance wasanalyzed according to analysis of the mathematics models. Moreover, technology andeconomy of structure parameters was optimized structure of fire-pit and underground heatingexchange system in the greenhouse on system was designed. (3) Influence of structureparameters of fire-pit and underground heating exchange system in the greenhouse on systemthermal performance was analyzed with experiment. And basic operating law of system wasresearched. (4) Temperature environment characteristic of fire-pit and underground heatingexchange system in the greenhouse was researched and heating transfer models were verified with experimental data. Furthermore temperature distribution characteristics of differentlay-form and influence on greenhouse temperature environment characteristic wereresearched with model (experiment). (5) Economy of fire-pit and underground heatingexchange system in the greenhouse was analyzed and synthesis evaluation was performed.Fire-pit and underground heating exchange system was applied in greenhouse still was forthe first time, which was an assistant heating equipment and was a supplement to heatingequipment of greenhouse. Innovation of this research main content includes: (1) Fire-pit andunderground heating exchange system was applied in greenhouse still was for the first time.And fire-pit and underground heating exchange system belongs to the floor-heating, this kindheating system heats crops-root area and has saving-energy advantage compares withhot-water heating system, hot-blast stove heating system and so on. Furthermore this kindheating system has benefiting influence on growth, output and photosynthesis of crop. (2)Heating mechanism of fire-pit and underground heating exchange system in the greenhousewas researched during winter operation. And heating mathematics model of this system wasestablished according to basic theory of thermodynamics and heat transfer. And coolingmathematics models were established according to cooling mechanism research underdifferent conditions (continuous ventilation and intermission ventilation during summercooling). And theory analysis and experiment research of this system was carried out. (3)Numerical value analysis and mathematics simulation about mathematics models of fire-pitand underground heating exchange system was carried out. And dynamic mathematics modelswas described with differential coefficient equation of two-dimensional unsteady conductionand boundary conditions, and underground heating exchange pipes were simulated to infinitycylinder, which can express actually dynamic process of air continuous movement along pipeslength and ventilation time. And calculating method of mathematics models was made out.Moreover differential coefficient equation was dispersed with finity difference method,calculating regional was meshed, and derivations were substituted with difference quetient,heat transfer differential coefficient equation was transformed into difference equation, whichwas foundation for settlement of model. And mathematics simulation analysis was carried outwith ANSYS heating analysis software and was verified with experimental data. (4) Synthesis economical benefit of fire-pit and underground heating exchange system in the greenhousewas analyzed, economy was evaluated with present value and annual value of expenditure,and returning time of primary investment was forecasted to fire-pit and underground heatingexchange system in the greenhouse through it operating condition.Main conclusion was made with systemic theory analysis and experiment research on fire-pit and underground heating exchange system in the greenhouse. (1) Heat transfer mechanismwas analyzed and mathematics models of heating transfer were established of fire- pit andunderground heating exchange system in the greenhouse. And cooling mathematics modelswere established, and underground heating exchange pipes were simulated to infinity cylinder,which can express actually dynamic process of air continuous movement along pipe lengthand ventilation time. And difference calculating method of mathematics models was made out,which was foundation for calculating of model. Moreover mathematics simulation analysiswas carried out with ANSYS/THERMAL and was verified with experimental data. (2) Soiland air temperature inside greenhouse was increased greatly with fire-pit and undergroundheating exchange system in the greenhouse. Testing results indicated that soil averagetemperature, day and night average air temperature, nighttime average air temperature of areawith fire-pit and underground heating exchange system was higher respectively 2.0℃, 2.6℃,4.2℃than contrast area. And soil temperature distributing was uniformity with this system.So temperature difference from maximal to minimum was respectively 0.3℃～0.9℃, 0.4℃～0.9℃along vertical section and cross section of underground heating exchange pipes.Furthermore both side humidity data which was analyzed indicated that saturation time ofrelative humidity was shortened greatly with adopted fire-pit and underground heatingexchange system in the greenhouse, which was shortened 2～3h. (3) Air temperature insidegreenhouse was reduced greatly with fire-pit and underground heating exchange system insummer. Testing results indicated that average air temperature was respectively 24.7℃, 25.4℃both heating exchanged area and contrast area, which temperature difference was small. Butaverage air temperature was respectively 30.3℃, 35.4℃both heating exchanged area andcontrast area during blower operating (operation time of blower was from 10:00 to 16:30during testing), and average air temperature was reduced 5.1℃. maximal air temperature ofheating exchanged area was 32.0℃, and maximal air temperature of contrast area was 38.0℃. But at night air temperature was higher in heating exchanged area than contrast area.Furthermore experiment results indicated that air average temperature was respectively 24.7℃, 19.8℃at import and exit of underground heating-exchanged pipes, and average airtemperature was reduced into 4.9℃. (4) Economy was evaluated with method of present valueand annual value of expenditure. Analysis indicated that present value and annual value ofexpenditure of fire-pit and underground heating exchange system in the greenhouse was lowerrespectively 30.8%,57.4% than hot-blast stove heating system, and lower respectively 27.4%,55.2% than hot-water heating system. And returning time of primary investment wasforecasted to 2.1 years according to operating condition of fire pit-underground heatingexchange system in the greenhouse. (5) Fire-pit and underground heating exchange system inthe greenhouse was able to utilize sufficiently solar energy and biomass energy, and savingenergy rate was 31.6%. So it has healthy economical, social and ecological benefit.Fire-pit and underground heating exchange system was used as assistant heatingequipment in the greenhouse. In this paper, primary research was carried with theory analysisand experimental data. And research results indicated that heating effect and capability offire-pit and underground heating exchange system has more improvement than fire pit heatingsystem and underground heating-exchanged system. But this heating system have manydisadvantage, such as heating capability was still limited, heating control was difficult,primary investment was large, fire-pit area possess part of space inside greenhouse and so on.If these problems were solved, application foreground of fire-pit and underground heatingexchange system was wide.
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