A method for determining the optimal ventilation rate in a plant factory

Abstract

The present invention belongs to the field of plant factories, and specifically relates to a method for determining the optimal ventilation volume of a plant factory. The present invention simulates the ventilation conditions of a plant factory, finds that the Reynolds number and the Archimedes number can well characterize the changes in environmental parameters in the plant factory, and selects the specific values ​​of the Reynolds number and the Archimedes number that can balance the distribution of the better environmental parameters of the plant factory and the lower ventilation energy consumption as the basis for calculating and judging the optimal ventilation volume of the plant factory, so as to maximize the guarantee that the cultivation area reaches the ideal cultivation environment, use the minimum ventilation volume to save environmental regulation energy consumption, and ensure the stability of the flow field in the cultivation area.

Description

Technical Field

[0001] The invention belongs to the field of plant factories, and in particular relates to a method for determining an optimal ventilation volume of a plant factory. Background Art

[0002] The vertical plant factory is an efficient agricultural production system that uses artificial light and vertical cultivation racks in a fully enclosed environment to autonomously control plant growth conditions such as light, temperature, water, air, and fertilizer. It subverts the traditional agricultural production model that relies on sunlight and soil, and can achieve continuous and uninterrupted production of plants throughout the year. It has the advantages of no pollution, no environmental impact, high yield, saving arable land, and nearby production.

[0003] The environmental control system of a plant factory, namely the ventilation system, plays a vital role in the plant factory. It optimizes the growth conditions of plants by precisely controlling environmental factors such as temperature, humidity, and carbon dioxide concentration, thereby improving the yield and quality of crops. The design and optimization of the ventilation system of a plant factory involves many considerations, including the selection of air supply and return air positions, air duct design, and air supply parameter settings. Due to factors such as the stacking of multiple layers of crops, the resistance of crops to air flow, and the heat generated by growth lamps, the control and optimization of the plant growth environment in a plant factory face many challenges. If the air circulation system is improperly designed, it may lead to uneven environmental conditions within and between different layers, causing some plant growth areas to overheat or overcool, and humidity to be too high or too low, which in turn affects the growth rate, yield, and quality of crops.

[0004] In common vertical plant factories, in order to facilitate the passage of equipment and personnel, vertical cultivation racks are usually placed in the middle of the room, and there is a corridor between the cultivation rack and the side wall. Side wall ventilation is a common ventilation method in small vertical plant factories, but the existence of corridors increases the difficulty of environmental regulation in the cultivation area. For example, a smaller ventilation volume will make it difficult for dry and cold air to fully reach the cultivation area, while a larger ventilation volume corresponds to a higher cooling load demand, resulting in energy waste. Adjusting the ventilation volume with the help of a limited number of sensor monitoring values ​​is costly and difficult to quickly obtain the optimal value. The ventilation volume setting value is often too high, which will cause a lot of energy waste. Summary of the invention

[0005] The present invention provides a method for determining an optimal ventilation volume of a plant factory, wherein an air supply port and an air return port for allowing air flow to pass through are provided in the plant factory, and the method comprises the following steps:

[0006] S1: Set the target temperature difference between the return air outlet and the supply air outlet of the plant factory ΔT ;

[0007] S2: According to the target temperature difference ΔT Calculate the total ventilation volume for temperature control Q in,1 ;

[0008] S3: Total ventilation volume based on temperature control Q in,1 Calculate the air outlet velocity V in ;

[0009] S4: According to the target temperature difference ΔT , air outlet speed V in And the geometric characteristics of the vertical plant factory are used to calculate the Reynolds number Re , Archimedean number Ar , to determine whether the flow field is stable; Reynolds number Re >4000 and Archimedean number Ar When <0.1, the current flow field is considered stable, otherwise, the flow field is unstable;

[0010] S5: If the flow field is stable, Q in,1 is the optimal ventilation volume; if the flow field is unstable, according to the Reynolds number Re = 4000 Calculate the critical total ventilation volume of Reynolds number Q in,2 , according to Archimedean number Ar = 0.1 to calculate the Archimedean number critical total ventilation volume Q in,3 ,Pick Q in,2 , Q in,3 The larger value is taken as the optimal ventilation rate.

[0011] The present invention analyzes the environmental parameters of the plant factory (wind speed, temperature, humidity, and temperature difference between the supply and return air outlets) and finds that these environmental parameters will achieve better distribution as the hourly ventilation volume per unit planting area increases, but when the hourly ventilation volume per unit planting area reaches a certain level, the degree of change in the distribution of the environmental parameters of the plant factory no longer changes significantly. Therefore, for the plant factory, there is an optimal ventilation volume that can balance the distribution of the environmental parameters of the plant factory and the energy consumption required for ventilation. In further analysis, it is believed that the changes in the Reynolds number and the Archimedes number in the plant factory can well characterize the changes in the environmental parameters in the plant factory. Therefore, the Reynolds number and the Archimedes number are selected as the basis for selecting the optimal ventilation volume of the plant factory, and the Reynolds number is set to 4000 and the Archimedes number is set to 0.1 as the critical values ​​of the two parameters according to the ventilation conditions of the plant factory.

[0012] Furthermore, in S2, the total ventilation volume of temperature control Q in,1 The calculation method is:

[0013] (1)

[0014] In formula (1), q air The hourly ventilation volume per planting area, in m 3 / m 2 h; n is the number of layers in the cultivation area; L is the length of the single-layer cultivation area, in m; W is the width of the single-layer cultivation area, in m;

[0015] q air The following formula is used for calculation:

[0016] (2)

[0017] In formula (2), q sen The sensible heat surplus per unit planting area, in W / m 2 ; ρ air is the air density, take 1.2 kg / m 3 ; c is the specific heat capacity of air, which is taken as 1005 J / kg°C; ΔT is the target temperature difference.

[0018] in, q sen The following formula is used for calculation:

[0019] (3)

[0020] In formula (3), ρ r is the reflection coefficient, which is determined by the type of plants grown in the plant factory; I lighting It is the photosynthetically active radiation (PAR) illumination, which is calculated based on the power and luminous efficiency of the LED plant growth lamp per unit planting area, and the unit is W / m 2 ; CAC is the planting area coverage rate.

[0021] In existing plant factories, corridors are generally set up inside the plant factory to facilitate the passage of equipment and personnel, and air outlets are set on the side walls of one side of the corridor to dehumidify and cool each floor inside the plant factory. Generally speaking, the width of the corridor is set to a degree that can be used by personnel to walk and carry plants, usually within 1.2 m. Inside the plant factory, in the air supply direction, the width of the cultivation area is generally set at 0.5 m ~ 1.5 m. The method for determining the optimal ventilation volume of the plant factory provided in this application can be applied to the above-mentioned conventional-sized plant factories.

[0022] Furthermore, in S3, the air outlet speed V in The calculation method is:

[0023] (4)

[0024] In formula (4), V in is the air outlet velocity, in m 2 / s, Q in,1 is the total ventilation volume, A air is the total area of ​​the air outlet.

[0025] Furthermore, in S4, the Reynolds number Re The calculation method is:

[0026] (5)

[0027] In formula (5), V in is the air outlet speed; D h is the hydraulic diameter of the air outlet, in m; ν is the kinematic viscosity of air, which can be taken as 1.56×10 −5 m 2 / s;

[0028] Archimedean Number Ar The calculation method is:

[0029] (6)

[0030] In formula (6), g 9.81 m / s 2 , β is the thermal expansion coefficient of air, which is taken as 0.0036; ΔT is the target temperature difference; L c is the characteristic length of the air supply direction of the plant factory, and is the total length of the indoor space of the plant factory in the air supply direction.

[0031] Furthermore, in S5, Q in,2 The calculation method is:

[0032] (7)

[0033] In formula (7), Re is the Reynolds number, which is taken as the critical value of 4000; νis the kinematic viscosity of air, taking 1.56×10 −5 m 2 s −1 ; D h is the hydraulic diameter of the air outlet; A air is the total air supply area.

[0034] Furthermore, in S5, Q in,3 The calculation method is:

[0035] (8)

[0036] In formula (8), Ar is the Archimedean number, with a critical value of 0.1; n is the number of layers in the cultivation area; L is the length of the single-layer cultivation area, in m; W is the width of the single-layer cultivation area, in m; q sen The sensible heat surplus per unit planting area, in W / m 2 ; A air is the total air supply area; g 9.81 m / s 2 ; β is the thermal expansion coefficient of air, which is taken as 0.0036; L c It is the characteristic length of air supply direction of plant factory; c is the specific heat capacity of air, which is taken as 1005 J / kg°C; ρ air is the air density, take 1.2 kg / m 3 .

[0037] Further, I lighting The calculation method is:

[0038] (9)

[0039] in q LED is the power of the plant growth lamp, η It is the photosynthetically active radiation luminous efficiency.

[0040] Further, in S1, the target temperature difference ΔT 0.5~5 °C.

[0041] Furthermore, the target temperature difference ΔT 0.5~2 °C.

[0042] Furthermore, in the plant factory, a corridor is provided between the air supply outlet and the cultivation area.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention provides a method for calculating and judging the optimal ventilation volume of a plant factory. By simulating the ventilation conditions of the plant factory, it is found that the Reynolds number and the Archimedes number can well characterize the changes in environmental parameters in the plant factory, and the specific values ​​of the Reynolds number and the Archimedes number that can balance the distribution of better environmental parameters of the plant factory and lower ventilation energy consumption are selected as the basis for calculating and judging the optimal ventilation volume of the plant factory, so as to maximize the guarantee that the cultivation area reaches an ideal cultivation environment, adopt the minimum ventilation volume to save environmental regulation energy consumption, and ensure the stability of the flow field in the cultivation area. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of the air circulation system and indoor space layout of the plant factory in the simulation.

[0046] Figure 2 This is a schematic diagram of the relationship between the simulation of central ventilation volume and the temperature difference between the supply and return air outlets.

[0047] Figure 3 Schematic diagram of the relationship between the simulated ventilation volume and wind speed distribution in the plant factory.

[0048] Figure 4 Schematic diagram of the simulation of the relationship between central ventilation volume and temperature distribution in a plant factory.

[0049] Figure 5 This is a schematic diagram of the relationship between the simulated ventilation volume and the absolute humidity distribution in the plant factory.

[0050] Figure 6 This is a result graph showing the impact of ventilation volume per unit planting area on the mean and standard deviation of environmental parameters of the cultivation layer of the vertical plant factory in the simulation.

[0051] Figure 7 Schematic diagram of the relationship between the simulated ventilation volume, Reynolds number and Archimedes number.

[0052] Figure 8 Logic diagram for determining the optimal ventilation rate for a plant factory.

[0053] Fig. 9 This is a simulation result diagram of the plant factory environmental distribution with optimal ventilation volume in Example 2. DETAILED DESCRIPTION

[0054] In order to make those skilled in the art better understand the scheme of the present invention, the technical scheme of the present invention is clearly and completely described below in conjunction with specific embodiments. It should be noted that the following detailed descriptions are all exemplary and are only embodiments of a part of the present invention, rather than all embodiments.

[0055] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work should fall within the scope of protection of the present invention.

[0056] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the art to which this application belongs. The experimental materials used in the examples of the present invention are all conventional experimental materials in the art and can be purchased through commercial channels. Experimental methods without specifying detailed conditions were performed according to conventional experimental methods or according to the operating instructions recommended by the supplier.

[0057] The present invention uses fluid numerical simulation technology to simulate plant factories, which means using computers to simulate fluid flow and interaction, and predicting the behavior of fluid flow by solving fluid dynamics equations (Navier-Stokes equations). It discretizes the continuous fluid domain into small units and uses numerical methods for calculation.

[0058] The flow field stability mentioned in the present invention means that the spatial distribution of air environment parameters (wind speed, temperature and humidity, etc.) is not affected by small fluctuations in the inlet wind speed and reaches a stable state.

[0059] Example 1 Effect of hourly ventilation volume per unit area on environmental parameters of plant factories

[0060] In this embodiment, if Figure 1 As shown in the figure, the plant factory adopts the side-supply and side-return airflow control method. In order to facilitate the operation of equipment and the movement of personnel, corridors are set between the air supply outlet and the cultivation area.

[0061] The cultivation area of ​​the plant factory is set to 6 layers, the length of a single-layer cultivation area is 6 m, and the width of a single-layer cultivation area is 1.4 m. The corridor width, that is, the distance from the air supply outlet to the edge of the cultivation area, is 700 mm, and the distance from the cultivation area to the return air outlet is 100 mm.

[0062] Each cultivation area of ​​the plant factory corresponds to a layer of air outlets, with a diameter of 40 mm and a spacing of 100 mm. The total air supply area, i.e. the total area of ​​the air outlets, is 0.452 m 2 Supply air temperature 22 °C, supply air absolute humidity 13.5 g / m 3 (Relative humidity 70%). Photosynthetically active radiation flux density PPFD = 200 μmol / m 2s, corresponding to the unit planting area LED plant growth lamp power 66.7 ‍W / m 2 The planting area coverage rate in the cultivation zone is 90%.

[0063] The ventilation conditions of the plant factory were simulated using fluid numerical simulation technology, and the photosynthetically active radiation flux density PPFD was set to 200 μmol / m 2 s, corresponding to the LED plant growth lamp power per unit planting area of ​​66.7 W / m 2 , the planting area coverage rate in the cultivation area is 90%. In the simulation of the ventilation conditions of the plant factory, according to the current technical level, 58% of the power of the LED plant growth lamp is set to be converted into photosynthetically active radiation of the plant.

[0064] In the simulation of the ventilation conditions of the plant factory, the effect of ventilation volume on the temperature difference between the supply and return air flows was investigated. The specific results are as follows: Figure 2 As shown. Figure 2 It can be seen that when the unit planting area is small, the ventilation volume ( q air ) between 15 and 45 m 3 / m 2 h, the temperature difference between the supply air flow and the return air flow exceeds 2 degrees Celsius; when the ventilation volume is 50 m 3 / m 2 h and above, the temperature difference drops below 2 degrees Celsius; when the ventilation volume exceeds 100 m 3 / m 2 h, the temperature difference remains below 1 degree Celsius.

[0065] In the simulation of ventilation conditions in plant factories, the effects of ventilation volume on wind speed, temperature and humidity distribution were investigated. The specific results are as follows: Figure 3 , 4 , as shown in Figure 5.

[0066] The influence of ventilation volume on wind speed distribution is as follows: Figure 3 As shown in the figure, it can be seen that when the ventilation volume per unit planting area is between 15 and 45 m 3 / m 2 h, the wind speed distribution is significantly affected by the ventilation volume. The presence of the corridor and the significant temperature difference cause the delivered cold air to drop from the air outlet. Therefore, not all the supplied cold air can reach the planting area, resulting in stagnation areas in the crop canopy. q air ) equal to or greater than 60 m 3 / m 2 h, the wind speed distribution is no longer affected by changes in ventilation volume.

[0067] The effect of ventilation volume on temperature distribution is as follows: Figure 4 As shown, it can be seen that when the ventilation rate ( q air ) below 60 m 3 / m 2 At 1500 ft, the incoming cold air descended in the corridor due to the influence of thermal buoyancy, and the thermal stratification phenomenon in the cultivation area was significant. The temperature at the bottom of the cultivation area was low and the temperature at the top was high, and the temperature gradually increased with height. As the ventilation rate increased, the temperature in the cultivation area gradually decreased, but under high ventilation rate, the temperature distribution did not change significantly. In the top cultivation layer, as the ventilation rate increased from 15 m 3 / m 2 h increased to 75 m 3 / m 2 h, the air temperature dropped from about 28 °C to 23 °C.

[0068] The effect of ventilation volume on humidity distribution is as follows: Figure 5 As shown, at lower ventilation rates (≤45 m 3 / m 2 h), the air velocity in the top cultivation area is very low, so the absolute humidity (AH) in these areas is high due to plant transpiration. For corridor side ventilation, under low ventilation rate, similar to the temperature distribution characteristics, AH also shows a stratification phenomenon with height, with low AH values ​​at the bottom and high AH values ​​at high levels. Under high ventilation rate, increasing the ventilation rate can reduce the absolute humidity in the cultivation area, but the absolute humidity distribution form does not change, and the reduction is not linear with the ventilation rate. After reaching a certain value, further increasing the ventilation rate has limited effect on the environmental distribution of the cultivation area.

[0069] In the simulation of the ventilation conditions of the plant factory, the effect of ventilation volume on the average environmental parameters and standard deviation of the environmental parameters in the cultivation area was investigated. The specific results are as follows: Figure 6 shown.

[0070] like Figure 6 As shown in (a), the increase in ventilation volume leads to an increase in air supply speed, and the air speed and wind speed standard deviation in the cultivation area also increase accordingly.

[0071] like Figure 6 As shown in b, the air temperature at the fixed air outlet and increasing the ventilation volume can reduce the air temperature in the cultivation area. q air 45 m 3 / m 2 h or higher, the temperature difference between the air supply position and the cultivation area is kept below 2 °C, and when q air 75 m 3 / m 2h or more, the temperature difference remains below 1 °C. There is a nonlinear relationship between the average temperature of the cultivation area and the ventilation volume. Under high ventilation volume, as the ventilation volume increases, the average temperature of the cultivation area is infinitely close to the air outlet temperature, and the temperature variation range and standard deviation of the cultivation area also tend to be stable.

[0072] like Figure 6 As shown in Figure c, the trend of absolute humidity (AH) with ventilation rate is similar to that of air temperature. Higher ventilation rate makes the average AH ​​value in the crop area closer to the supply air value. q air = 15m 3 / m 2 h, due to the effect of thermal buoyancy, the air supply airflow fails to fully reach each cultivation area. Figure 3 and Figure 5 As shown. Therefore, the average AH ​​value is significantly higher than other ventilation rates. Similar to temperature changes, there is a nonlinear relationship between the average absolute humidity in the cultivation area and the ventilation rate. Under high ventilation rates, as the ventilation rate increases, the average AH ​​value in the cultivation area is infinitely close to the humidity at the air outlet, the humidity change range in the cultivation area also tends to be stable, and the standard deviation of the average AH ​​decreases slightly.

[0073] In the simulation of the ventilation conditions of the plant factory, the influence of ventilation volume on the Reynolds number and Archimedes number was investigated. The specific results are as follows: Figure 7 shown.

[0074] like Figure 7 As shown in a, there is a linear relationship between the hourly ventilation volume per unit planting area and the Reynolds number. When the hourly ventilation volume per unit planting area is between 15 and 45 m 3 / m 2 h, the Reynolds number changes from 1191 to 3574, indicating that the flow is in a transitional state from laminar flow to turbulent flow; the hourly ventilation volume per unit planting area exceeds 60 m 3 / m 2 h, the Reynolds number is 4765, exceeding 4000, reaching a fully turbulent state, indicating that this ventilation volume (60 m 3 / m 2 h), the ventilation volume has little effect on the environmental distribution characteristics (manifold).

[0075] like Figure 7 As shown in b, when the air flow rates are 15, 30 and 45 m 3 / m 2 h, by Figure 3 , Figure 4 , Figure 5The environmental distribution shows that the influence of thermal buoyancy cannot be ignored. The corresponding Archimedean numbers are 2.57, 0.32 and 0.095 respectively. When the air flow rate is 45 m 3 / m 2 When h is above, the flow field tends to be stable and the thermal buoyancy effect can be ignored, so the critical Archimedean number can be determined to be 0.1.

[0076] Depend on Figures 2 to 6 It can be seen that the environmental parameters of the plant factory (wind speed, temperature, humidity, and temperature difference between the supply and return air outlets) achieve better distribution with the increase of the hourly ventilation volume per unit planting area. However, when the hourly ventilation volume per unit planting area reaches a certain level, the degree of change in the distribution of the environmental parameters of the plant factory no longer changes significantly. Therefore, for the plant factory, there is an optimal ventilation volume that can balance the distribution of the environmental parameters of the plant factory and the energy consumption required for ventilation.

[0077] Depend on Figure 7 It can be seen that the changes in the Reynolds number and Archimedes number in the plant factory can well characterize the changes in the environmental parameters in the plant factory. Therefore, the Reynolds number and Archimedes number are selected as the basis for selecting the optimal ventilation volume of the plant factory. Figure 3~Figure 6 It can be judged that when the air flow rate is 45 m 3 / m 2 When h is above, the flow field tends to be stable and the thermal buoyancy effect can be ignored. At this time, the corresponding Reynolds number is 3574 and the Archimedes number is 0.095. A certain design redundancy is retained, based on which the critical Reynolds number of 4000 and the critical Archimedes number of 0.1 can be selected.

[0078] Example 2 Determination of the optimal ventilation rate of a plant factory

[0079] The plant factory in this embodiment is configured the same as that in the first embodiment, specifically: the cultivation area of ​​the plant factory is configured as 6 layers, the length of a single-layer cultivation area is 6 m, the width of a single-layer cultivation area is 1.4 m, the corridor width, i.e., the distance from the air supply outlet to the edge of the cultivation area, is 700 mm, the distance from the cultivation area to the return air outlet is 100 mm, the air supply outlet diameter is 40 mm, the spacing is 100 mm, and the total air supply area, i.e., the total area of ​​the air supply outlet is 0.452 m 2 , air supply temperature 22 °C, air supply absolute humidity 13.5 g / m 3 (Relative humidity 70%), photosynthetically active radiation flux density PPFD = 200 μmol / m 2 s, corresponding to the unit planting area LED plant growth lamp power 66.7 ‍‍‍ ‍W / m 2 The planting area coverage rate in the cultivation area is 90%, and 58% of the power of the LED plant growth lamp is set to be converted into photosynthetically active radiation of the plant.

[0080] The present invention provides a method for determining the optimal ventilation volume for a plant factory, and its logic diagram is as follows: Figure 8 As shown, the optimal ventilation volume of the above plant factory is determined, and the specific steps are as follows:

[0081] S1: Set the target temperature difference between the return air outlet and the supply air outlet of the plant factory ΔT .

[0082] In this embodiment, the target temperature difference is set ΔT is 1°C.

[0083] S2: According to the target temperature difference ΔT Calculate the total ventilation volume for temperature control Q in,1 , the specific calculation method is as follows:

[0084] S2.1: Calculate photosynthetically active radiation (PAR) illuminance I lighting , calculated by the following formula:

[0085] (9)

[0086] In formula (9), q LED is the power of the plant growth lamp per unit planting area, η It is the photosynthetically active radiation luminous efficiency.

[0087] S2.2: Calculate the sensible heat surplus per unit planting area q sen , calculated by the following formula:

[0088] (3)

[0089] In formula (3), ρ r is the reflection coefficient. In this embodiment, the plant cultivated in the cultivation area is set to be lettuce. ρ r The value is 0.07; I lighting It is the photosynthetically active radiation (PAR) illumination, which is calculated based on the power and luminous efficiency of the LED plant growth lamp per unit planting area, and the unit is W / m 2 ; CAC is the planting area coverage rate.

[0090] S2.3: Calculate the hourly ventilation rate per unit planting area q air , calculated by the following formula:

[0091] (2)

[0092] In formula (2), q sen The sensible heat surplus per unit planting area, in W / m 2 ; ρ air is the air density, take 1.2 kg / m 3 ; c is the specific heat capacity of air, which is taken as 1005 J / kg°C; ΔT is the target temperature difference.

[0093] S2.4: Calculate total ventilation volume for temperature control Q in1 , calculated by the following formula:

[0094] (1)

[0095] In formula (1), q air The hourly ventilation volume per planting area, in m 3 / m 2 h; n is the number of layers in the cultivation area; L is the length of the single-layer cultivation area, in m; W is the width of single-layer cultivation area, in m.

[0096] S3: Total ventilation volume based on temperature control Q in,1 Calculate the air outlet velocity V in , calculated as follows:

[0097] (4)

[0098] In formula (4), V in is the air outlet speed, Q in,1 is the total ventilation volume, A air is the total area of ​​the air outlet.

[0099] S4: According to the target temperature difference ΔT , air outlet speed V in And the geometric characteristics of the vertical plant factory are used to calculate the Reynolds number Re , Archimedean number Ar , to determine whether the flow field is stable; Reynolds number Re >4000 and Archimedean number Ar When <0.1, the current flow field is considered stable, otherwise, the flow field is unstable.

[0100] Reynolds number Re The calculation method is:

[0101] (5)

[0102] In formula (5), V in is the air outlet speed; D h is the hydraulic diameter of the air outlet; ν is the kinematic viscosity of the air, which is 1.56×10 −5 m 2 s −1 .

[0103] Archimedean Number Ar The calculation method is:

[0104] (6)

[0105] In formula (6), g 9.81 m / s 2 , β is the thermal expansion coefficient of air, which is taken as 0.0036; ΔT is the target temperature difference; L c is the characteristic length of the air supply direction of the plant factory, and is the total length of the indoor space of the plant factory in the air supply direction.

[0106] S5: If the flow field is stable, Q in,1 is the optimal ventilation volume; if the flow field is unstable, according to the Reynolds number Re = 4000 Calculate the critical total ventilation volume of Reynolds number Q in,2 , according to Archimedean number Ar = 0.1 to calculate the Archimedean number critical total ventilation volume Q in,3 ,Pick Q in,2 , Q in,3 The larger value is taken as the optimal ventilation rate.

[0107] In this embodiment, the calculated value in S2 Q in,1 = 5163 m 3 / h, Reynolds number calculated in S4 Re = 8136>4000, Archimedean number Ar = 0.0084<0.1, meaning Q in,1 Meet the requirements of flow field stability and set the optimal ventilation volume for the temperature difference target.

[0108] S6: Based on the calculated optimal ventilation volume, the ventilation conditions of the plant factory are simulated using fluid numerical simulation technology.

[0109] The simulation of the plant factory environment distribution of the optimal ventilation volume in this embodiment is as follows Fig. 9 As shown, it can be seen that when the optimal ventilation volume calculated by the above method is used for ventilation, the temperature difference between the supply and return air outlets of the plant factory can reach the preset value, and the environmental parameters (wind speed, temperature, humidity) of the plant factory are evenly distributed in each layer of the cultivation area, which can ensure that the plants planted in the cultivation area have a better growth environment and make the plants planted in each layer of the cultivation area have similar growth conditions.

[0110] Example 3 Determination of the optimal ventilation rate of a plant factory

[0111] The plant factory in this embodiment is configured the same as that in the first embodiment, specifically: the cultivation area of ​​the plant factory is configured as 6 layers, the length of a single-layer cultivation area is 6 m, the width of a single-layer cultivation area is 1.4 m, the corridor width, i.e., the distance from the air supply outlet to the edge of the cultivation area, is 700 mm, the distance from the cultivation area to the return air outlet is 100 mm, the air supply outlet diameter is 40 mm, the spacing is 100 mm, and the total air supply area, i.e., the total area of ​​the air supply outlet is 0.452 m 2 , air supply temperature 22 °C, air supply absolute humidity 13.5 g / m 3 (Relative humidity 70%), photosynthetically active radiation flux density PPFD = 200 μmol / m 2 s, corresponding to the unit planting area LED plant growth lamp power 66.7 ‍W / m 2 The planting area coverage rate in the cultivation area is 90%, and 58% of the power of the LED plant growth lamp is set to be converted into photosynthetically active radiation of the plant.

[0112] The present invention provides a method for determining the optimal ventilation volume for a plant factory, and its logic diagram is as follows: Figure 8 As shown, the optimal ventilation volume of the plant factory is determined, and the specific steps are as follows. The specific calculation method is the same as that of Example 2:

[0113] S1: Set the target temperature difference between the return air outlet and the supply air outlet of the plant factory ΔT .

[0114] In this embodiment, the target temperature difference is set ΔT is 3°C.

[0115] S2: According to the target temperature difference ΔT Calculate the total ventilation volume for temperature control Q in,1 , is 1721 m 3 / h.

[0116] S3: Total ventilation volume based on temperature control Q in,1 Calculate the air outlet velocity V in = 1.06 m / s.

[0117] S4: According to the target temperature difference ΔT , air outlet speed V in And the geometric characteristics of the vertical plant factory are used to calculate the Reynolds number Re = 2712, Archimedean Number Ar = 0.227; Reynolds number Re <4000 and Archimedean number Ar >0.1, does not meet the flow field stability requirements.

[0118] S5: The flow field is unstable, according to the Reynolds number Re = 4000 Calculate the critical total ventilation volume of Reynolds number Q in,2 , according to Archimedean number Ar = 0.1 to calculate the Archimedean number critical total ventilation volume Q in,3 ,Pick Q in,2 , Q in,3 The larger value is taken as the optimal ventilation rate.

[0119] S5.2: Q in,2 Calculate according to the following formula

[0120] (7)

[0121] In formula (7), Re is the Reynolds number, which is taken as the critical value of 4000; ν is the kinematic viscosity of air, taking 1.56×10 −5 m 2 s −1 ; D h is the hydraulic diameter of the air outlet; A air is the total air supply area.

[0122] Calculated: Q in,2 = 2538 m 3 / h.

[0123] S5.3: Q in,3 Calculate according to the following formula

[0124] (8)

[0125] In formula (8), Ar is the Archimedean number, with a critical value of 0.1; n is the number of layers in the cultivation area; L is the length of the single-layer cultivation area, in m; W is the width of the single-layer cultivation area, in m; q sen The sensible heat surplus per unit planting area, in W / m 2 ; A air is the total air supply area; g 9.81 m / s 2 ; β is the thermal expansion coefficient of air, which is taken as 0.0036; L c It is the characteristic length of air supply direction of plant factory; c is the specific heat capacity of air, which is taken as 1005 J / kg°C; ρ air is the air density, take 1.2 kg / m 3 .

[0126] Calculated: Q in,3 = 2262 m 3 / h.

[0127] Q in,2 > Q in,3 , take the larger value 2538 m 3 / h is the optimal ventilation rate.

[0128] S6: According to the following formula

[0129] (1)

[0130] Available q air,2 = Q in,2 / ( nW ) = 50.4 m 3 / h.

[0131] according to Figure 6 And Example 1 ( Figure 2~Figure 6 ) analysis shows that the flow field is stable at this time, and the ventilation volume can make the temperature difference between the return air outlet and the supply air outlet within the set temperature control target, and the ventilation volume setting value does not cause waste of environmental control energy consumption, which is the optimal ventilation volume within the set target temperature difference range.

Claims

1. A method for determining the optimal ventilation volume of a plant factory, wherein the plant factory is provided with an air supply port and an air return port for allowing air flow to pass through, and the plant factory is provided with a cultivation area for growing plants, characterized in that: The following steps are involved: S1: Set the target temperature difference between the return air outlet and the supply air outlet of the plant factory ΔT ; S2: According to the target temperature difference ΔT Calculate the total ventilation volume for temperature control Q in,1 ; S3: Total ventilation volume based on temperature control Q in,1 Calculate the air outlet velocity V in ; S4: According to the target temperature difference ΔT , air outlet speed V in And the geometric characteristics of the vertical plant factory are used to calculate the Reynolds number Re , Archimedean number Ar , to determine whether the flow field is stable; Reynolds number Re >4000 and Archimedean number Ar When <0.1, the current flow field is considered stable, otherwise, the flow field is unstable; S5: If the flow field is stable, Q in,1 is the optimal ventilation volume; if the flow field is unstable, according to the Reynolds number Re = 4000 Calculate the critical total ventilation volume of Reynolds number Q in,2 , according to Archimedean number Ar = 0.1 to calculate the Archimedean number critical total ventilation volume Q in,3 ,Pick Q in,2 , Q in,3 The larger value is taken as the optimal ventilation rate.

2. The method according to claim 1, characterized in that In S2, the total ventilation volume of temperature control Q in,1 The calculation method is: （1） In formula (1), q air The hourly ventilation volume per planting area, in m 3 / m 2 h; n is the number of planting layers; L is the length of the single-layer cultivation area, in m; W is the width of the single-layer cultivation area, in m; q air The following formula is used for calculation: （2） In formula (2), q sen The sensible heat surplus per unit planting area, in W / m 2 ; ρ air is the air density, take 1.2 kg / m 3 ; c is the specific heat capacity of air, which is taken as 1005 J / kg°C; ΔT is the target temperature difference; in, q sen The following formula is used for calculation: （3） In formula (3), q LED The power of LED plant growth lamp per unit planting area, ρ r is the reflection coefficient, which is determined by the type of plants grown in the plant factory; I lighting It is the photosynthetically active radiation, which is calculated based on the power and luminous efficiency of the LED plant growth lamp per unit planting area, and the unit is W / m 2 ; CAC is the planting area coverage rate.

3. The method according to claim 2, characterized in that In S3, the air outlet speed V in The calculation method is: （4） In formula (4), V in is the air outlet speed, Q in1 is the total ventilation volume, A air is the total area of ​​the air outlet.

4. The method according to claim 3, characterized in that In S4, the Reynolds number Re The calculation method is: （5） In formula (5), V in is the air velocity at the air outlet, in m / s; D h is the hydraulic diameter of the air outlet, in m; ν is the kinematic viscosity of air, which is 1.56×10 −5 m 2 / s; Archimedean Number Ar The calculation method is: （6） In formula (6), g 9.81 m / s 2 , β is the coefficient of thermal expansion of air, which is 0.0036 at room temperature; ΔT is the target temperature difference; L c is the characteristic length of the air supply direction of the plant factory, and is the total length of the indoor space of the plant factory in the air supply direction.

5. The method according to claim 4, characterized in that In S5, Q in,2 The calculation method is: （7） In formula (7), Re is the Reynolds number, which is taken as the critical value of 4000; ν is the kinematic viscosity of air, which is 1.56×10 −5 m 2 s −1 ; D h is the hydraulic diameter of the air outlet; A air is the total air supply area.

6. The method according to claim 4, characterized in that In S5, Q in,3 The calculation method is: （8） In formula (8), Ar is the Archimedean number, with a critical value of 0.1; n is the number of layers in the cultivation area; L is the length of the single-layer cultivation area, in m; W is the width of the single-layer cultivation area, in m; q sen The sensible heat surplus per unit planting area, in W / m 2 ; A air is the total air supply area; g 9.81 m / s 2 ; β is the thermal expansion coefficient of air, which is taken as 0.0036; L c It is the characteristic length of air supply direction of plant factory; c is the specific heat capacity of air, which is taken as 1005 J / kg°C; ρ air is the air density, take 1.2 kg / m 3 .

7. The method according to claim 2, characterized in that I lighting The calculation method is: （9） in q LED is the power of the plant growth lamp, η It is the photosynthetically active radiation luminous efficiency.

8. The method according to claim 1, characterized in that The target temperature difference ΔT 0.5~5 °C.

9. The method according to claim 1, characterized in that: In the plant factory, a corridor is arranged between the air supply outlet and the cultivation area.

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