| The winter season in Yangtze River Delta is from December to February,with extremely low temperature and high humidity.Due to its geographical location and meteorological conditions,the area is subject to winter months of a harsh continuous low temperature.During these extreme cold climatic conditions,plants have to survive severe cold stress conditions,even if they are being kept in greenhouses.These winter months affect the farmers directly by putting extra financial means of investment in the form of heating the greenhouses.Most of the greenhouses of these areas have rarely heating systems because of high costs of heating systems and high operational costs of these systems.It is very difficult for farmer to afford such kind of greenhouse heating systems.Ultimately the greenhouse production reduced in these months.Therefore,studies focused on improving greenhouse production in winter in this region should be a priority on the basis of plant physiology and morphology combined with agricultural engineering technology theory.The details were described as blow.(1)The feasibility of heating method on plants root zone in winter was studied by referring to literatures.During the winter,greenhouse heating is an essential aspect of specialty-crop production and sustaining plants growth.In greenhouses,maintaining a constant and uniform temperature is essential because it has a direct impact on the feasibility of growing crops when temperatures found very low then heating greenhouse becomes vital practice to get optimum plants development results.Many types of greenhouse heating systems and methods are applied worldwide.In a greenhouse,ambient temperature can be regulated by many means.However,altering root zone temperature is more difficult.Several root zone temperature control systems have been developed.Root zone heating systems allow operators to adjust the root zone temperature accurately.The benefits of the root zone heating method have been well documented.The major advantage of zone heating is energy conservation,while achieving optimum plant growth at the same time.This renders a large cost to the greenhouse operation and,hence,many growers have begun implementing various measures to reduce these heating costs.If heating costs can be reduced,profit margins can increase.Some growers have therefore begun growing annual bedding plant crops at lower greenhouse air temperature set points,in high tunnels,or even growing outside.The main reason why root zone temperature is important to plants is that RZT has an ability of adjusting the rate of physiological processes,such as water and minerals uptake,leaf growth and metabolite concentrations.The objective of this study was to design,develop and investigate a heating system that can provide heat directly to the root zone instead of heating the entire greenhouse,which is a viable option to reduce energy consumption.Root zone heating could be an effective alternative for the maintainable development of plants during the winter.(2)A kind of heat preserving pots and its heating system were developed and its performance was studied.The current research was conducted to design,develop and evaluate performance of root zone heating system developed with supportable materials for application in low temperatures,a specialized root zone heating plant-growing container was developed.First,two pots were installed properly.In between these two pots,a polyurethane foam insulation layer was installed to reduce heat loss.The coco peat Growing medium was used during this study which provides multiple crop cycles by eliminating the need to replace growing media after every crop with better water holding capacity.Two silicon rubber heating pads were used as the root zone heating source;these were installed within the growing medium vertically.These pads were waterproof and can give temperature 0? to 250?.The resistance to high temperature,makes this component ideal for high temperature applications.Two plastic polypropylene pots were used,the interior pot containing the growing medium and the exterior pot to act as an exterior boundary and to reduce heat losses.To monitor and control the temperature variations of the growing media inside the growing container,a control system was also designed to monitor and control the heating system.A Pt100 sensor probe was installed inside the soil near the root zone.The other side of the probe is completed by an insulated lead containing 3 wire tails,which are connected to the temperature measuring and controlling equipment.The temperature measurement device was also connected to the leads of the probe that automatically converted the measured resistance into a temperature reading.The temperature controller's model number REX-C100FK02 with Range 0-400? and Supply of 220V were used supported with relay switch.The hourly data collection was conducted in the middle of the container which corresponded with the root zone.the total heating time applied to the designed pots was 6 h/day and the total observation time was 12 hours.The maximum set temperature at the root zone was 35?.When the root zone temperature exceeded the set temperature on the controller,the controllers cut the power to the heating source automatically.The Comsol Multiphysics 5.1a package were used in the current study to simulate the heat transfer in porous media.Then a comparative analysis between simulated and experimental results was performed.For Plant response experimental setup five different temperature conditions with three replicates were tested to check the morphological effects of root zone heating on winter-grown pepper plants.Treatment T-15 used a 15? root zone temperature,T-20 was 20? RZT,T-25 was 25? RZT,T-30 was 30? RZT,and TC was used as the control treatment without root zone heating.For this study,15 insulated growing pots were used for root zone heating and investigating the heat transfer rates to different canopy parts of the pepper plant.The plant canopy temperature was obtained by using Infrared laser thermometer.The root zone heating process lasted for more than four weeks.After that all plants were removed from heating pots for further investigation.Roots and leaves with branches were separated from plants.The height of the stem,root height,number of leaves,and fresh weight were recorded.All the separated segments were oven-dried for 72 h at 70? to obtain the dry mass.During this experimental investigation,mean daily energy consumption and specific energy consumption for root dry mass was also calculated.(3)The performance of the heating system was simulated.The root zone heating system was heated for six hours and then the hourly heat transfer rates were measured for twelve hours.Additionally,a simulation model of the heating system was developed using the COMSOL Multiphysics 5.3a package.The heat transfer in a porous media model was used in this study.Finally,the simulation results obtained from the model were analysed and compared to the experimental results.The simulation results illustrated the continuous increasing temperature trend of the temperature profile with the heat flux expands in all directions through the pot over time during first six hours of heating on power switch on mode while after six hour the root zone temperature showed a decreasing trend because of switched off mode of heating system.The maximum RZT for the heated pots was 36.2?,with an RZT range of 2? to 36.2?,while for the simulation the range was 2? to 31.02?.The results also showed that with the decrease in ambient temperature of the greenhouse,the root zone temperature of the non-heated pots also decreased.The temperature dropping trend was observed for both ambient temperature and non-heated pot temperature during the experimental investigation,showing the non-heated pot temperature to be directly proportional to the greenhouse ambient temperature.(4)A novel type of root zone heating system was applied to evaluate the energy consumption during different greenhouse ambient temperature conditions,the effects of root zone heating systems on pepper plant morphology,and heat transfer rates to plant canopy in the greenhouse.The temperature analysis of the root zone of different heated treatments,unheated control treatment,and the ambient temperature illustrated that the ambient temperature had shown a continuously decreasing trend with extreme values of 3.6? and 0.3? with similar decreasing trend of controlled treatment without a root zone heating system.Heat transfer analysis for plant canopy indicated that the temperature of the lower canopy was higher as compared to the middle and upper canopy of the plant as heat transfer was from the root zone to the top canopy of the plant.In the current system,the heat transfer to the plant canopy proved more viable as the heating source was within the growing medium,while other root zone heating systems like a benchtop root zone heating system have lower heat transfer rates to the plant canopy as the heating source is not fixed within growing medium.The results of plant canopy heat distribution also illustrated that,as the ambient temperature indicated a continuous drop,the canopy temperature of control treatment also showed a continuous decline.The results revealed that if the ambient temperature increases the energy consumption will be decreased while specific energy consumption for root dry mass production was found feasible in T-20.The maximum root dry mass production with minimum energy consumption was found in T-20.The results for the dry mass of different segments of plants,such as roots,stem,and leaves,also showed differences among treatments.T-20 had the highest leaf dry weight,stem diameter,and number of leaves,while T-25 had the highest root dry weight and stem dry weight.T-30 and T-15 had the minimum dry weight of plant segments in all heated treatments.TC has the minimum dry mass production as compared to all root zone heated treatments.The T-20 and T-25 root zone temperatures were found to be optimal. |
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