Design and experiment of root heating system for greenhouse potted crops
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摘要:目的
为解决长江三角洲地区冬季没有加温设备的温室或大棚中盆栽作物易受低温冷害的问题，设计一种适用于矮株作物的根区加热系统。
方法研制了一种嵌套式双层栽培盆，夹层采用绝缘脂发泡剂填充，栽培盆基质内分别放置2块80 W/m2、15 cm×12 cm的硅橡胶加热板，加热板由STM32单片机输出信号到固态继电器进行加热功率控制，使用模糊PID控制算法，实时控制作物根区温度到设定值。
结果根区温度控制相对误差不超过5%。在连续低温条件下(连续一周平均气温低于5 ℃)，当根区温度分别设定为15、20和25 ℃时，相比于对照组，高度为25~35 cm的作物地上部分日间平均温度分别提高1.4、2.6和3.7 ℃，夜间平均温度分别提高2.1、2.9和4.0 ℃；且与普通栽培盆相比，本文设计的保温栽培盆在3种不同根区温度下分别节省电能24.2%、25.3%和23.8%。
结论设计的作物根区加热系统，在连续低温条件下，不仅能有效提高作物根区温度，同时对作物地上部分也具有升温效果，一定条件下可缓解低温胁迫对冬季作物生长的影响。
Abstract:ObjectiveTo design a root heating system suitable for dwarf crops, so as to solve the problem that potted crops in greenhouse without heating equipment in the Yangtze river delta region are vulnerable to low temperature and cold damage in winter.
MethodA nested double-layer cultivation pot was designed. The interlayer was filled with insulating fat foaming agent. Two silicone rubber heating plates of 80 W/m2 and 15 cm ×12 cm were placed in the substrate of the cultivation pot. The heating plate was controlled by STM32 MCU, which output signals to the solid state relay for heating power control. Fuzzy PID control algorithm was used to control the temperature of the crop root area to the set value in real time.
ResultThe relative error of root zone temperature control did not exceed 5%. Under the condition of continuous low temperature (average temperature below 5 ℃ for a week), when the root zone set temperature was 15, 20 and 25 ℃, the average daytime temperature of the aboveground parts with 30-35 cm height of crops increased by 1.4, 2.6 and 3.7 ℃ respectively compared with the control group, while their average night temperature increased by 2.1, 2.9 and 4.0 ℃ respectively. Compared with the common pot, the pots with root zone temperature of 15, 20, 25 ℃ saved electric energy by 24.2%, 25.3% and 23.8% respectively.
ConclusionUnder the condition of continuous low temperature, our system can not only effectively increase the temperature of crop root zone, but also can heat up the aboveground part of crop. Under certain conditions, our system can alleviate the effects of cold stress on winter crop growth.
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Keywords:
- greenhouse /
- temperature control /
- crop root zone /
- cultivation pot /
- silicone rubber heating plate /
- STM32
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图 4 栽培盆导热示意图
λ1：栽培基质的导热系数；λ2：绝缘脂发泡剂的导热系数；θ1：栽培基质层的温度；θ2：绝缘脂发泡剂层的温度；θf：温室的温度；δ1：基质层的厚度；δ2：绝缘脂发泡剂的厚度
Figure 4. Schematic diagram of heat conduction in pot
λ1: Thermal conductivitiy of cultivated substrate; λ2: Thermal conductivitiy of insulating grease foaming agent; θ1: Temperature of cultivated substrate; θ2: Temperature of insulating grease foaming agent; θf: Greenhouse temperature; δ1: Substrate thickness; δ2: Thickness of insulating grease foaming agent
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图 6 模糊PID控制结构图
θs：温度信号的采样值；θc：温度信号的设定值；e(k)：温度信号误差；ec(k)：温度信号误差变化率；∆Kp(k)、∆Ki(k)和∆Kd(k)为PID控制器的参数调整量；θf、θh为温度控制量
Figure 6. Structural diagram of the PID control block
θs: The sampling value of temperature signal; θc: The set value of temperature signal; E(k): Error of temperature signal; EC(k): Change rate of E(k); ∆Kp(k), ∆Ki(k), ∆Kd(k) are parameter adjustment quantities of PID controller; θf, θh are control quantities of temperatare
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图 10 作物地上部测点分布示意图
Figure 10. Schematic diagram of measuring points on plant aboveground
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图 11 不同根区温度处理下作物温度日变化及温室气温变化
Figure 11. Changes in crop temperature and greenhouse temperature under different root zone temperatures
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图 12 不同根区温度处理下作物温度分布图
Figure 12. Crop temperature profiles under different root zone temperatures
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图 13 不同根区温度处理下2种栽培盆的耗电量
Figure 13. Power consumptions of two types of pots under different root zone temperatures
表 1 根区温度控制试验结果
Table 1 Experiment results of controlling root temperature
℃ 测量点
Test point15 ℃ 20 ℃ 25 ℃ CK 组1
Group 1组2
Group 2组3
Group 3组1
Group 1组2
Group 2组3
Group 3组1
Group 1组2
Group 2组3
Group 31 15.70 15.80 15.60 20.70 20.70 20.20 25.50 26.00 25.00 8.10 2 16.00 15.60 15.10 21.00 20.60 20.50 25.60 25.70 25.40 8.80 3 15.80 15.50 15.40 20.80 22.30 20.80 25.30 25.40 25.80 8.70 4 15.60 15.40 15.80 20.50 20.50 20.30 25.10 25.60 25.50 8.80 5 15.30 15.30 15.70 20.60 20.60 20.40 25.00 27.00 25.90 9.00 平均值 Average 15.68 15.52 15.52 20.72 20.90 20.44 25.30 25.54 25.52 8.68 相对误差/%
Relative error4.53 3.46 3.46 2.88 4.50 2.20 1.20 2.16 2.08 
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表 2 不同根区温度处理的作物地上部平均温度
Table 2 Average temperature of aboveground parts of crop under treatment with different root temperature
℃ θ/℃
Treatment temperature晴天 Sunny day 阴天 Cloudy day 日间 Daytime 夜间 Night 日间 Daytime 夜间 Night 15 11.0±2.08 9.4±1.46 10.2±1.60 8.8±1.58 20 12.1±1.97 10.5±1.04 11.5±1.46 9.7±0.72 25 13.2±1.66 12.0±1.20 12.5±1.93 11.4±0.77 CK 9.8±2.55 7.7±1.50 8.5±1.36 6.4±0.83
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