Keywords

1 Introduction

The Internet of Things (IoT) is the fourth information revolution after computers, the Internet, and mobile communication technologies. Since 1999, the Massachusetts Institute of Technology introduced the concept to major countries in the world such as the United States. Planet) “, the European Union proposed the” Internet of Things Action Plan “in 2009, China proposed,” Perceive China “and made the Internet of Things one of the strategic emerging industries [1,2,3,4].

In agriculture, various sensing terminals have been used to comprehensively sense collection facilities, Environmental information of production processes such as field planting, breeding, etc. to gradually achieve the optimal control and intelligent management of agricultural production processes [5].

For example, the Orchard Internet of Things is mainly used to collect the related data such as soil or air temperature, humidity, light and the weather condition in the orchard environment, and can carry out independent irrigation, integrated water and fertilizer management, and insect forecasting, which improves the orchard Information level, management efficiency and fruit yield [6,7,8,9,10,11,12].

However, China as the biggest fruit production of the world, Chinese fruits also have problems such as low sugar content [13]. As for the sugar content of fruits, according to the literature [14,15,16,17], the crop growth is an energy conversion process, and energy management has an important impact on the quality and yield of crop products. The level and variation of ambient temperature have a crucial influence on the sweetness and quality of crops such as fruits, during fruit growth, carbohydrates are produced during the day by photosynthesis. Under the same conditions as water and fertilizer, high temperatures can enhance photosynthesis to produce more carbohydrates; these carbohydrates are converted into sugars at night. Temperature is the main factor affecting sugar conversion, which is the temperature difference between day and night. The greater the temperature difference between day and night, the more favorable the sugar conversion is, and the sweetness of the fruit is higher.

Spray cooling technology has been widely used in industrial and urban areas to reduce environmental temperature or dust pollution, in the agricultural field has also been used to cool the breeding environment or orchard to prevent frost [18].

To sum up, with the wide application of the Internet of Things in the field of agriculture, how to use the Internet of Things to regulate the environmental temperature of the orchard to achieve energy management of the fruit growth environment and create an environment conducive to the improvement of fruit quality has become a topic worth exploring.

2 The Orchard IoT for Temperature Difference Regulation

2.1 The Cooling Principle of Spraying Water Mist in Orchard

The cooling principle of artificial fog space environment is the double flow of air fog and the principle of evaporation and heat absorption [19, 20]. The sprayer diffuses the fog particles with a diameter of 1–10 μ to the cooling area, evaporates continuously in the diffusion process, and absorbs a lot of heat energy in the area. Scientific statistics of a kilogram of water to stimulate the floating state of artificial fog, the effect is equal to the dissolution of seven kilograms of ice, generally up to 6 ℃–10 ℃ cooling effect, extreme cases can be reduced by 14 ℃. Per gram of water can be for outdoor air cooling, the spray cooling efficiency is very high, in theory, the spray cooling is the amount of energy needed to overcome the surface tension of the water increases, the energy needed to 1 m3 of water into the cube, 10 μ needed by its surface tension, and the latent heat of evaporation is as high as 2.2 billion joules, its theory can effect comparing is as high as 50000, And air conditioning is limited by the law of thermodynamics, 30 ℃ cooling 5 ℃ theoretical maximum energy efficiency ratio is about 60.

2.2 Principle and Process of Temperature Difference Regulation in Orchard

Photosynthesis and respiration occur simultaneously in cells of green plants such as fruit trees. During the day, Photosynthesis is the main process because of the light intensity and the temperature is high. During the photosynthesis process, the chloroplast in the cell synthesizes solar energy, CO2, H2O, and other organic matter, stores energy and releases O2. At night, the light intensity is small, and the respiration is stronger than photosynthesis. Cell mitochondria decompose organic matter produced by photosynthesis and releases energy and oxygen. Respiratory effects include aerobic and anaerobic respiration.

In the summer of temperate plains, temperatures are high during the day and fruits accumulate nutrients. At night, the ambient temperature drops, however, in general, declines less and the decline rate is slower. Therefore, the mist cooling method can be used to accelerate the reduction of the ambient temperature. In summer, the sun enters the sunset point relatively late. In order to make full use of the photosynthesis of fruit trees after the sunset, under non-rainfall conditions, it is generally chosen to spray the water misting in the orchard at 8:00 pm every day. According to the wind direction collected by the wind direction sensor, the data center transmits the command to the sprayer node through LoRa, adjusts the direction of the sprayer nozzle, and sprays water mist.

2.3 Orchard IoT for Temperature Difference Regulation

The proposed orchard IoT scheme is shown in Fig. 1. The basic functions including collection of orchard environmental information, soil temperature, soil pH, soil humidity, carbon dioxide CO2 concentration, air temperature and humidity, light intensity, wind speed and direction, rainfall, etc.; monitoring fruit tree pest by hyperspectral sensors; remote monitoring achieved on a computer or smartphone devices [6,7,8].

According to the three-layer basic architecture of the Internet of Things: the sensing layer, the transmission layer, and the application layer. The sensing layer contains 4 types of sensor nodes and 2 types of actuator nodes. The sensor node mainly implements the orchard information collection. Actuator node 1 completes automatic orchard irrigation. Actuator 2 reduces the ambient temperature of the orchard at night by spraying the mist and increases the temperature difference between day and night in the summer. Water mist is conducive to fruit expansion after the fruit enters the expansion stage [11]. The basic composition of a sensor node is: a sensor, an ARM microcontroller, LoRa module; the basic composition of an actuator node is: a relay, an ARM microcontroller, LoRa module.

Fig. 1.
figure 1

Internet of orchard things system scheme

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The ARM microcontroller is a low power, high-performance embedded system as the node control core. It is an MCU based on the STM32 F401 series ARM® Cortex ™ -M4. It has a 12-bit ADC and a 16-bit/32-bit timer. FPU floating-point unit, communication peripheral interface (USART, SPI, I2C, I2S) and audio PLL. The operating frequency reaches 84 MHz, 105 DMIPS/285 Core-Mark, the flash ROM capacity is up to 256 kB, the SRAM capacity is 64 kB, and the chip’s operating voltage ranges from 1.7 to 3.6 V.

In order to reduce costs, each node is provided with several related sensors. In order to control the day and night temperature difference of the orchard, sensor node 2 collects four orchard meteorological parameters such as air temperature, humidity, CO2 and light intensity, and actuator node 1 executes relevant commands sent by the data center.

Sensor node 2 selects OSA-F7, which can measure four parameters: air temperature, relative humidity, CO2 concentration, and illumination. The measurement range and accuracy of the four parameters are air temperature −30–70 ± 0.2 ℃; relative humidity 0–100% RH ± 3% RH; carbon dioxide concentration 0–10000 ppm (optional 2000, 5000 ppm) ± 20 ppm; light intensity 0–200k lx (optional 2k, 20k lx and other ranges) ±3%.

3 System Software

Based on the functions analysis of the orchard IoT, the system program includes 6 subroutines: parameter collection, irrigation, spraying mist, insect analysis, data server and mobile clients. The display can ensure the normal operation of the orchard’s data access, data storage, and visual display programs; the interactive platform uses the B/S (Brower/Server) mode. Mist spraying operation procedure flow is shown in Fig. 2.

Fig. 2.
figure 2

Orchard mist operation process flow chart

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4 System Experiment and Results Analysis

The experiment was conducted on July 20, 2018 in a Peach Orchard, an area of 1hm2, and an Internet of orchard Things. There is a water well in the orchard with a depth of 30 m. The weather: sunny, temperature 37 ℃–28 ℃, south wind 3–4 level. The water temperature of well is 16 ℃. Mist spraying machine parameters: electric high-pressure remote sprayer, rated flow: 30–40 L/min; adjustable working pressure: 10–40 MPa; horizontal range: up to 100M. The sensor node 2 is shown in Fig. 3, and the pressure spray equipment is shown in Fig. 4. There are five sprayers, one at each corner of the orchard and the center. The temperature data is shown in Table 1.

Fig. 3.
figure 3

Sensor node 2.

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Fig. 4.
figure 4

The pressure spray equipment.

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Table 1. Collected data of temperature
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It can be seen from Table 1 that during the misting operation of the orchard, the ambient temperature in the orchard is reduced by a maximum of 10 ℃ compared with the temperature outside the orchard, and the cooling effect is obvious. Compared with the maximum temperature of 37 ℃ during the day, the temperature difference between day and night reaches 20 ℃.

5 Conclusion

Regulating the ambient temperature of orchards is the key way to realize the energy management of orchards. At present, the research on energy management of orchards by reducing the night temperature of orchards has not attracted enough attention from scholars at home and abroad. The main reason is that the low temperature media with low cost is not easy to be found.

Compared with the simulation of fluent or CFD [19, 20], it’s quite different that this paper has done a beneficial trial to implement orchard energy management based on Internet of Things to improve fruit quality. The Internet of orchard Things was designed and implemented. The experiments show that:

  • (1) The ambient temperature of the orchard at night can be effectively reduced by spray well water mist of perennial constant temperature at 16 ℃, and the maximum temperature reduction can reach 10 ℃ so that the day-night temperature difference of the orchard on that day can reach 20 ℃.

  • (2) Spray cooling system equipment is cheap, simple installation, and at the same time increases the air humidity, and can improve the yield and quality of peaches.