Greenhouse temperature regulation and control system based on low-grade heat source

Abstract

The invention discloses a greenhouse temperature regulation and control system based on a low-grade heat source, which comprises a geothermal system and a greenhouse heating system which are arranged in a greenhouse, and the geothermal system comprises a soil heating coil installed on a soil layer in the greenhouse. One end of the soil heating coil is connected with a low-grade heat source through a water pump, and the other end of the soil heating coil is connected with a water storage tank which is communicated with a tail water treatment area; the greenhouse heating system comprises a greenhouse heater, one end of the greenhouse heater is connected with a low-grade heat source through a water pump, and the other end is connected with a water storage tank. According to the invention, the utilization of low-grade energy in the greenhouse can be realized, the growth temperature requirements of crops under the conditions of low air and soil temperature in winter and at night are met, and a feasible technical support is provided for the utilization of the low-grade energy in the greenhouse and the heating of a soil layer in which main root systems of the crops are distributed.

Description

Technical Field

[0001] The present invention relates to the field of temperature regulation in greenhouse greenhouses, and particularly to a temperature regulation system for greenhouse greenhouses based on low-grade heat sources. Background Art

[0002] In the context of the global energy system upgrade and agricultural production safety, climate change has posed new challenges to the energy and agricultural fields. Extreme climate events have led to temperatures exceeding the suitable range for crop growth, resulting in reduced yields of agricultural products such as grains and affecting food security.

[0003] Appropriate space and soil temperatures can both increase crop yields. During the day, greenhouse greenhouses adjust the air temperature by utilizing and storing solar energy to promote crop yield increase; however, the temperature at night is often relatively low. Relying on the energy stored during the day to adjust the greenhouse temperature cannot meet the suitable growth requirements of crops, and other energy sources often need to be used to provide suitable growth temperatures for crops; especially at night in winter, a large amount of energy is required. Traditional greenhouse greenhouses use coal combustion, electric heaters, heat pumps, etc. to achieve heating, which not only increases the carbon emissions in the agricultural production process but also leads to an increase in energy costs.

[0004] The total amount of recoverable waste heat resources in China has been increasing year by year, but the proportion of energy recovery and utilization is still relatively small, and a large amount of industrial waste heat in various forms is directly discarded. For example, the waste heat of cooling water higher than the ambient temperature is generally directly treated as wastewater without waste heat recovery and utilization. At the same time, China is one of the countries with the richest hot spring resources in the world. In hot spring baths, the waste heat of the tail water discharged after bathing is also very rich. Although the application of this low-grade waste heat in other fields has certain difficulties, in the greenhouse system, greenhouse greenhouses have relatively low temperature requirements, and their temperature is sufficient to supply heat to the greenhouse at night. Therefore, this part of waste heat can be used for greenhouse energy supply through appropriate heat recovery methods, and can also heat the root soil area of crops to provide a suitable growth environment for crops, thereby promoting high yield and early maturity of crops.

[0005] Currently, in the methods of greenhouse microclimate regulation and soil temperature regulation, although the existing regulation methods have significantly reduced energy consumption, the degree of temperature control is limited. For example, in the regulation using solar energy and shallow geothermal energy, due to the intermittency and discontinuity of solar energy and the low outlet temperature of the buried pipe system, the temperature in the greenhouse cannot reach the optimal growth temperature of crops. If relying on coal, electricity or other high-grade energy sources to meet this condition, the cost is high. Moreover, in soil temperature regulation, the design of heaters lacks scientificity, and unreasonable buried pipes cause waste of too many resources. Summary of the Invention

[0006] In view of the above deficiencies of the prior art, the present invention provides a temperature regulation system for greenhouse greenhouses based on low-grade heat sources.

[0007] To achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0008] Provide a temperature regulation system for greenhouse based on low-grade heat source, which includes a geothermal system and a greenhouse heating system arranged in the greenhouse. The geothermal system includes a soil heating coil installed in the soil layer of the greenhouse. One end of the soil heating coil is connected to the low-grade heat source through a water pump, and the other end is connected to a water storage tank. The water storage tank is communicated with the tail water treatment area; the greenhouse heating system includes a greenhouse heater. One end of the greenhouse heater is connected to the low-grade heat source through a water pump, and the other end is connected to the water storage tank.

[0009] Furthermore, a temperature sensor is arranged in the temperature greenhouse, and a heat exchange fan is arranged on the wall of the temperature greenhouse.

[0010] Furthermore, the design method of the pipe size in the greenhouse heater is as follows:

[0011] S1: Calculate the heat exchange quantity Q of the greenhouse at night heat ;

[0012] Q heat =(Q s3 +Q 4 +Q s6 +Q s8 )-Q s2 ;

[0013] Among them, Q s8 is the heat exchange quantity between the north wall of the greenhouse and the internal space, Q s3 is the lateral heat transfer quantity from the soil in the greenhouse to the outside, Q 4 is the heat exchange quantity between the greenhouse and the environment at night, Q s6 is the permeation heat transfer quantity of the greenhouse, Q s2 is the convective heat exchange quantity between the ground in the greenhouse and the indoor air;

[0014] S2: Calculate the heat transfer coefficient k based on the inner side area of the pipe in the greenhouse heater 0 ;

[0015]

[0016] Among them, η 0 is the efficiency of the heat exchange fins in the greenhouse heater, β 0 is the finning coefficient of the heat exchange fins, λ p is the thermal conductivity of the pipe in the greenhouse heater, d i1 is the inner diameter of the pipe in the greenhouse heater, d o1 is the outer diameter of the pipe in the greenhouse heater, h i1h is the heat transfer coefficient of the pipeline in the greenhouse heater 0 h is the heat transfer coefficient of the heat transfer fins;

[0017] S3: Establish the heat transfer equation of the pipeline of the greenhouse heater according to the heat transfer coefficient k 0 ;

[0018]

[0019] where A is the inner cross-sectional area of the pipeline in the greenhouse heater, and Δt m is the average temperature difference of heat transfer in the greenhouse heater, t 1 ' is the fluid temperature at the inlet of the greenhouse heater, t 2 ' is the fluid temperature at the outlet of the greenhouse heater, t 2 is the target temperature to be regulated, ρ i1 is the density of the fluid in the pipeline of the greenhouse heater, v i1 is the velocity of the fluid in the pipeline of the greenhouse heater, μ is the dynamic viscosity of the fluid, λ f is the thermal conductivity of the fluid in the pipeline of the greenhouse heater, l i1 is the length of the pipeline in the greenhouse heater, Nu f is the Nusselt number of the fluid in the pipeline of the greenhouse heater, Re f1 is the Reynolds number of the fluid in the pipeline of the greenhouse heater, Pr f1 is the Prandtl number of the fluid in the pipeline of the greenhouse heater, and T is the thermodynamic temperature of the greenhouse;

[0020] S4: Determine the inner diameter d i1 and outer diameter d o1 of the pipeline in the greenhouse heater, as well as the pipe length l i1 .

[0021] Furthermore, the method for calculating the convective heat transfer amount Q s2 between the ground and the indoor air in the greenhouse is as follows:

[0022] Q s2 = h s2 L w (t s1 - t s2 ), h s2 = 3.4(t s1 - t s2 ) 0.33 ;

[0023] where t s1 is the soil surface temperature in the temperature greenhouse, t s2 is the gas temperature in the temperature greenhouse, and h s2 is the convective heat transfer coefficient between the ground and the indoor air in the greenhouse;

[0024] Divide the ground of the greenhouse into different areas, and calculate the lateral heat transfer quantity Q from the soil inside the greenhouse to the outside s3 The method is as follows;

[0025]

[0026] Wherein, si is the area number, W is the number of areas, and k si is the thermal conductivity of the soil in the area, and l si is the size of the area;

[0027] Calculate the heat exchange quantity Q between the greenhouse and the environment at night 4 The method is as follows;

[0028]

[0029] Wherein, h in2 is the indoor heat transfer coefficient of the single-layer plastic film, and h out is the convective heat transfer coefficient between the outside of the heat preservation cotton quilt and the outdoor air, and δ n1 , δ n2 are the thicknesses of the plastic film and the heat preservation cotton respectively, and λ n1 , λ n2 are the thermal conductivities of the plastic film and the heat preservation cotton respectively, and l c is the length of the south and north roof of the greenhouse;

[0030] Calculate the infiltration heat transfer quantity Q of the greenhouse s6 The method is as follows;

[0031]

[0032] Wherein, f c is the sealing coefficient of the temperature greenhouse, C w is the average wind pressure coefficient of the outdoor, f t is the temperature difference correction factor, v 0 is the outdoor wind speed, L a is the infiltration air flow rate, ρ 1 is the air density, c 1 is the specific heat capacity of air, f c is the sealing coefficient of the temperature greenhouse, C w is the average wind pressure coefficient inside and outside the greenhouse;

[0033] Calculate the heat exchange quantity Q between the north wall and the greenhouse space s8 The method is as follows;

[0034]

[0035] Wherein, h in1The convective heat transfer coefficient between the north wall and the greenhouse space, H n1 The height of the north wall of the greenhouse, t n3 The surface temperature of the north wall, pr is the Prandtl number, λ a The thermal conductivity of air, Gr is the Grashof number, β is the coefficient of thermal expansion, v is the kinematic viscosity, ΔT is the temperature difference between the north wall and the greenhouse space, L is the characteristic height of the north wall, and g is the acceleration due to gravity.

[0036] Furthermore, the method for setting the working state of the heat exchange fan includes:

[0037] A1: Calculate the cooling heat Q of the greenhouse during the day cool ;

[0038] Q cool =Q s1 -(Q s2 +Q s3 +Q s4 +Q s5 +Q s6 +Q s7 +Q s8 );

[0039] Among them, Q s1 is the solar radiation heat received by the greenhouse, Q s4 is the heat exchange amount between the covering material of the greenhouse and the environment, Q s5 is the ventilation heat exchange amount of the greenhouse, Q s7 is the heat exchange amount between the plants in the greenhouse and the internal air;

[0040] A2: When the cooling heat Q cool >0, the heat exchange fan rotates forward to introduce the cold air outside into the greenhouse for cooling. When the cooling heat Q cool <0, the heat exchange fan rotates in reverse to introduce the hot air outside into the greenhouse for heating. When the cooling heat Q cool =0, the heat exchange fan does not work.

[0041] Furthermore, the method for calculating the solar radiation heat Q s1 received by the greenhouse is:

[0042] Calculate the dimension parameters of the greenhouse according to the construction location and structural characteristics of the greenhouse, specifically including: the ridge span ratio λ w : λ w =0.4301 + 0.0006249t swb +0.007702I s ; Among them, t swb is the average outdoor temperature in winter, I sis the average daily solar radiation irradiance in winter;

[0043] Span L of the greenhouse w :

[0044] Dimensions of the north roof and north wall:

[0045]

[0046] Among them, C w is the horizontal projection length of the north roof, L p is the height of the vegetation in the greenhouse, P is the width of the aisle in the greenhouse, H w is the ridge height of the greenhouse, H n1 is the height of the north wall, h s is the elevation angle of the sun's rays at noon in summer, h c is the elevation angle of the sun's rays at noon in winter;

[0047] Calculate the solar radiation heat Q received by the greenhouse according to the calculated dimension parameters of the greenhouse s1 ;

[0048] Q s1 = Q s11 + Q s12 ;

[0049] Among them, Q s11 is the solar radiation heat received by the greenhouse in the horizontal direction, Q s12 is the solar radiation heat received by the greenhouse in the vertical direction;

[0050] The method for calculating the solar radiation heat Q s11 is: Q s11 = I h1 L w where I h1 = τkI 0 ·cos(θ), where I h1 is the solar radiation heat flux density per unit length received by the greenhouse in the horizontal direction, I 0 is the solar constant, τ is the penetration ratio of the atmosphere, and k is the penetration ratio of the covering film on the greenhouse;

[0051] The method for calculating the solar radiation heat Q s12 is: Q s12 = I n1 H n1 where I n1 = τkI 0 ·sin(θ);

[0052] Among them, I n1is the solar radiation heat flux density received per unit height in the vertical direction of the greenhouse

[0053] The method for calculating the heat exchange quantity Q between the covering material of the greenhouse and the environment is as follows s4 :

[0054] Q s4 = k c l c (t s2 - t 0 )

[0055] where k c is the thermal conductivity of the covering material

[0056] The method for calculating the ventilation heat exchange quantity Q of the greenhouse is as follows s5 :

[0057]

[0058] where ρ 1 is the air density, c 1 is the specific heat capacity of air, G is the ventilation volume, c d is the resistance coefficient of ventilation heat exchange, g is the acceleration due to gravity, h t is the height of the ventilation opening

[0059] The method for calculating the heat exchange quantity Q between the plants in the greenhouse and the internal air is as follows s7 :

[0060]

[0061] where M T is the moisture transfer rate between the plants and the air is the latent heat of vaporization during the moisture transfer process, w ps is the enthalpy humidity ratio of saturated moist air, w a is the enthalpy humidity ratio of the air in the greenhouse, R a , R s are the air resistance and the stomatal resistance respectively, v i is the indoor air velocity, τ c is the penetration ratio of the covering material

[0062] Furthermore, the method for designing the size parameters of the soil heating coil is as follows

[0063] C1: Establish a soil heat balance model during the heating process of the soil by the soil heating coil

[0064] Let Then

[0065]

[0066] Among them, δ 1 is the distance from the soil surface to the soil heating area, d 1 is the thickness of the soil heating area, Φ is the total heat dissipation of the soil, Φ 2 is the heat loss of the soil upward, Φ x＝0 is the heat loss of the soil laterally, λ s is the thermal conductivity of the soil, H is the lateral influence distance of the soil heating coil on the circumferential soil, t is the lateral soil temperature outside the heating area, x is the lateral distance between the soil and the heating area, t sb is the target temperature of the soil heating area, m is the heat dissipation scale coefficient of the soil heating area;

[0067] C2: Take the total heat dissipation of the soil as the heat exchange quantity Q heat , input it into the heat transfer equation of the greenhouse heater pipeline, replace the pipeline parameters in the heat transfer equation of the greenhouse heater pipeline with the pipeline parameters of the soil heating coil, the heating effect of the soil heating coil is equivalent to the heating effect of the pipeline in the greenhouse heater, and output the inner diameter, outer diameter and pipe length of the soil heating coil.

[0068] The beneficial effects of the present invention are as follows: The technology of using low-grade heat sources to regulate the temperature of the greenhouse space and soil proposed by the present invention systematically sorts out the implementation methods of using low-grade heat sources to adjust the greenhouse space and soil, including constructing a greenhouse heat balance model and a soil heat balance model, and realizing the regulation of the greenhouse environment temperature and soil temperature by designing a greenhouse heater and a soil heating coil. The present invention can realize the utilization of low-grade energy in the greenhouse, and meet the requirements of the growth temperature of crops under the conditions of low air and soil temperatures in winter and at night, providing a feasible technical support for the utilization of low-grade energy in the greenhouse and heating the soil layer where the main roots of crops are distributed. Description of the Drawings

[0069] Figure 1 is a schematic diagram of the principle of a greenhouse temperature control system based on low-grade heat sources.

[0070] Figure 2 is a schematic diagram of the structure of the temperature greenhouse.

[0071] Figure 3 is a schematic diagram of the heat exchange during the day in the temperature greenhouse.

[0072] Figure 4 is a schematic diagram of the heat exchange at night in the temperature greenhouse.

[0073] Figure 5 is a schematic diagram of the heat exchange of the soil in the temperature greenhouse.

[0074] Among them, 1. greenhouse, 2. heat exchange fan, 3. low-grade heat source, 4. water pump, 5. greenhouse heater, 6. soil heating coil, 7. thermal insulation cotton, 8. temperature sensor, 9. water storage tank, 10. tail water treatment area, 11. soil layer. Detailed implementation manners

[0075] The following describes the detailed implementation manners of the present invention to facilitate those skilled in the art of this technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed implementation manners. For those of ordinary skill in the art of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0076] As Figure 1 shown, a temperature control system for a greenhouse based on a low-grade heat source includes a geothermal system and a greenhouse heating system arranged in the greenhouse 1. The geothermal system includes a soil heating coil 6 installed in the soil layer 11 in the greenhouse 1. A layer of thermal insulation cotton 7 is arranged in the soil layer 11 in the greenhouse 1. The soil heating coil 6 is arranged in the thermal insulation cotton 7. One end of the soil heating coil 6 is connected to the low-grade heat source 3 through the water pump 4, and the other end is connected to the water storage tank 9. The water storage tank 9 is communicated with the tail water treatment area 10. The greenhouse heating system includes a greenhouse heater 5. One end of the greenhouse heater 5 is connected to the low-grade heat source 3 through the water pump 4, and the other end is connected to the water storage tank 9. A temperature sensor 8 is arranged in the temperature greenhouse, and a heat exchange fan 2 is arranged on the wall of the temperature greenhouse. The temperature sensor 8 monitors the temperature in the greenhouse 1 in real time, providing data support for temperature control.

[0077] The geothermal system and the greenhouse heating system are respectively provided with a water pump 4 and a valve for control to realize separate indoor and soil heating. After the medium carrying the low-grade heat source releases heat in the geothermal system and the greenhouse heating system, it is discharged into the water storage tank 9 and the tail water treatment area 10 for treatment to avoid direct discharge into the environment.

[0078] The design method of the pipe size in the greenhouse heater 5 is as follows:

[0079] S1: As Figure 4 shown, calculate the heat exchange quantity Q of the greenhouse 1 at night heat ;

[0080] Q heat =(Q s3 +Q 4 +Q s6 +Q s8 )-Q s2 ;

[0081] Among them, Q s8The heat exchange quantity between the north wall of the greenhouse 1 and its internal space, Q s3 The lateral heat transfer quantity from the soil inside the greenhouse 1 to the outside, Q 4 The heat exchange quantity between the greenhouse 1 and the environment at night, Q s6 The infiltration heat transfer quantity of the greenhouse 1, Q s2 The convective heat transfer quantity between the ground inside the greenhouse and the indoor air;

[0082] S2: Calculate the heat transfer coefficient k based on the inner surface area of the inner pipe of the greenhouse heater 5 0 ;

[0083]

[0084] Among them, η 0 is the efficiency of the heat exchange fins inside the greenhouse heater 5, β 0 is the finning coefficient of the heat exchange fins, λ p is the thermal conductivity of the pipe inside the greenhouse heater 5, d i1 is the inner diameter of the pipe inside the greenhouse heater 5, d o1 is the outer diameter of the pipe inside the greenhouse heater 5, h i1 is the heat transfer coefficient of the pipe inside the greenhouse heater 5, h 0 is the heat transfer coefficient of the heat exchange fins;

[0085] S3: Establish the heat transfer equation of the pipe of the greenhouse heater 5 according to the heat transfer coefficient k 0 ;

[0086]

[0087] Among them, A is the inner cross-sectional area of the pipe inside the greenhouse heater 5, Δt m is the average temperature difference of the heat transfer of the greenhouse heater 5, t 1 ′ is the fluid temperature at the inlet of the greenhouse heater 5, t 2 ′ is the fluid temperature at the outlet of the greenhouse heater 5, t 2 is the target temperature to be regulated, ρ i1 is the density of the fluid inside the pipe of the greenhouse heater 5, v i1 is the velocity of the fluid inside the pipe of the greenhouse heater 5, μ is the dynamic viscosity of the fluid, λ f is the thermal conductivity of the fluid inside the pipe of the greenhouse heater 5, l i1 is the length of the pipe inside the greenhouse heater 5, Nu f is the Nusselt number of the fluid inside the pipe of the greenhouse heater 5, Re f1 is the Reynolds number of the fluid inside the pipe of the greenhouse heater 5, Pr f1 is the Prandtl number of the fluid inside the pipe of the greenhouse heater 5, T is the thermodynamic temperature of the greenhouse;

[0088] S4: Determine the inner diameter d and outer diameter d of the pipe in the greenhouse heater 5, as well as the pipe length l, according to the heat transfer equation. i1 and outer diameter d o1 、as well as the pipe length l i1 .

[0089] The method for calculating the convective heat transfer quantity Q between the ground and the indoor air in the greenhouse 1 is as follows: s2 :

[0090] Q s2 = h s2 L w (t s1 - t s2 ), where h s2 = 3.4(t s1 - t s2 ) 0.33 ;

[0091] where t s1 is the soil surface temperature in the greenhouse, t s2 is the gas temperature in the greenhouse, and h s2 is the convective heat transfer coefficient between the ground and the indoor air in the greenhouse;

[0092] Divide the ground of the greenhouse 1 into different areas, and the method for calculating the lateral heat transfer quantity Q from the soil in the greenhouse 1 to the outside is as follows; s3 :

[0093]

[0094] where si is the area number, W is the number of areas, k si is the thermal conductivity of the soil in the area, and l si is the size of the area;

[0095] The method for calculating the heat exchange quantity Q between the greenhouse 1 and the environment at night is as follows; 4 :

[0096]

[0097] where h in2 is the indoor heat transfer coefficient of the single-layer plastic film, h out is the convective heat transfer coefficient between the outside of the insulation cotton 7 and the outdoor air, δ n1 , δ n2 are the thicknesses of the plastic film and the insulation cotton 7 respectively, λ n1 , λ n2 are the thermal conductivities of the plastic film and the insulation cotton 7 respectively, and l c is the length of the south and north roof of the greenhouse;

[0098] Calculate the infiltration heat transfer quantity Q of the greenhouse 1s6 The method is as follows;

[0099]

[0100] where f c is the sealing coefficient of the temperature greenhouse, C w is the average wind pressure coefficient outdoors, f t is the temperature difference correction factor, v 0 is the outdoor wind speed, L a is the infiltration air flow rate, ρ 1 is the air density, c 1 is the specific heat capacity of air, f c is the sealing coefficient of the temperature greenhouse, C w is the average wind pressure coefficient inside and outside the greenhouse

[0101] The method for calculating the heat exchange quantity Q between the north wall and the space of the greenhouse 1 is as follows; s8 The method is as follows;

[0102]

[0103] where h in1 is the convective heat transfer coefficient between the north wall and the space of the greenhouse, H n1 is the height of the north wall of the greenhouse, t n3 is the surface temperature of the north wall, p r is the Prandtl number, λ a is the thermal conductivity of air, Gr is the Grashof number, β is the thermal expansion coefficient, v is the kinematic viscosity, ΔT is the temperature difference between the north wall and the space of the greenhouse, L is the characteristic height of the north wall, and g is the acceleration due to gravity.

[0104] The method for setting the working state of the heat exchange fan 2 includes:

[0105] A1: As Figure 3 shown, calculate the cooling heat quantity Q of the greenhouse 1 during the day cool ;

[0106] Q cool = Q s1 -(Q s2 + Q s3 + Q s4 + Q s5 + Q s6 + Q s7 + Q s8 );

[0107] where Q s1 is the solar radiation heat received by the greenhouse 1, Q s4 is the heat exchange quantity between the covering material of the greenhouse 1 and the environment, Qs5 The ventilation heat exchange quantity of the greenhouse 1 is Q s7 is the heat exchange quantity between the plants in the greenhouse 1 and the internal air; due to the irradiation of sunlight during the day, the outdoor temperature is relatively high, and the working state of the heat exchange fan 2 is controlled according to the cooling heat quantity of the greenhouse 1 during the day, and the heat exchange fan 2 is used to regulate the temperature of the greenhouse 1.

[0108] Convective heat transfer between the ground in the greenhouse and the indoor air, lateral heat transfer of the soil to the outside, heat exchange between the covering material and the outside, ventilation heat transfer, permeation heat transfer, heat exchange between the plants and the greenhouse air, convective heat transfer between the north wall and the indoor air.

[0109] A2: When the cooling heat quantity Q cool > 0, the heat exchange fan 2 rotates forward, introducing the cold air outside into the greenhouse 1 for cooling. When the cooling heat quantity Q cool < 0, the heat exchange fan 2 rotates in reverse, introducing the hot air outside into the greenhouse 1 for heating. When the cooling heat quantity Q cool = 0, the heat exchange fan 2 does not work.

[0110] The method for calculating the solar radiation heat Q received by the greenhouse 1 s1 is as follows:

[0111] As Figure 2 shown, the size parameters of the greenhouse 1 are calculated according to the construction location and structural characteristics of the greenhouse 1, specifically including:

[0112] The ridge span ratio λ w : λ w = 0.4301 + 0.0006249t swb + 0.007702I s ; where, t swb is the average outdoor temperature in winter, and I s is the average daily solar radiation illuminance in winter;

[0113] The span L of the greenhouse 1 w :

[0114] The dimensions of the north roof and the north wall:

[0115]

[0116] Among them, C w is the horizontal projection length of the north roof, L p is the height of the vegetation in the greenhouse 1, P is the width of the aisle in the greenhouse 1, H w is the ridge height of the greenhouse 1, H n1 is the height of the north wall, h sis the elevation angle of the sun's rays at noon in summer, h c is the elevation angle of the sun's rays at noon in winter;

[0117] Calculate the solar radiation heat Q received by the greenhouse according to the calculated size parameters of the greenhouse s1 ;

[0118] Q s1 = Q s11 + Q s12 ;

[0119] Among them, Q s11 is the solar radiation heat received in the horizontal direction of the greenhouse, Q s12 is the solar radiation heat received in the vertical direction of the greenhouse;

[0120] The method for calculating the solar radiation heat Q s11 is: Q s11 = I h1 L w , I h1 = τkI 0 ·cos(θ), where I h1 is the solar radiation heat flux density per unit length received in the horizontal direction of the greenhouse, I 0 is the solar constant, τ is the penetration ratio of the atmosphere, and k is the penetration ratio of the covering film on the greenhouse;

[0121] The method for calculating the solar radiation heat Q s12 is: Q s12 = I n1 H n1 , I n1 = τkI 0 ·sin(θ);

[0122] Among them, I n1 is the solar radiation heat flux density per unit height received in the vertical direction of the greenhouse;

[0123] The method for calculating the heat exchange amount Q between the covering material of the greenhouse 1 and the environment s4 is:

[0124] Q s4 = k c l c (t s2 - t 0 );

[0125] Among them, k c is the thermal conductivity of the covering material, l c is the length of the covering material;

[0126] Calculate the ventilation heat exchange amount Q of the greenhouse 1s5 The method is as follows;

[0127]

[0128] where ρ 1 is the air density, c 1 is the specific heat capacity of air, G is the ventilation rate, c d is the resistance coefficient of ventilation heat transfer, g is the acceleration due to gravity, h t is the height of the ventilation opening;

[0129] The method for calculating the heat exchange quantity Q between the plants and the internal air in the greenhouse 1 s7 is as follows:

[0130]

[0131] where M T is the moisture transfer rate between the plants and the air, is the latent heat of vaporization during the moisture transfer process, w ps is the enthalpy-humidity ratio of saturated moist air, w a is the enthalpy-humidity ratio of the air in the greenhouse 1, R a and R s are the air resistance and the stomatal resistance respectively, v i is the indoor air flow velocity, τ c is the penetration ratio of the covering material.

[0132] The method for designing the size parameters of the soil heating coil 6 is as follows:

[0133] C1: As shown in Figure 5 , according to the temperature of the soil area where the root system is mainly distributed, analyze the heat loss of the main soil area of the root system, and establish a soil heat balance model during the heating process of the soil by the soil heating coil 6;

[0134] Let Then

[0135]

[0136] where δ 1 is the distance from the soil surface to the soil heating area, d 1 is the thickness of the soil heating area, Φ is the total heat dissipation of the soil, Φ 2 is the heat loss of the soil upward, Φ x＝0 is the heat loss of the soil horizontally, λ s is the thermal conductivity of the soil, H is the horizontal influence distance of the soil heating coil on the circumferential soil, t is the horizontal temperature of the soil outside the heating area, x is the horizontal distance between the soil and the heating area, t sb$T_0$ is the target temperature of the soil heating area, and $m$ is the heat dissipation scale coefficient of the soil heating area;

[0137] C2: Take the total heat dissipation of the soil as the heat exchange quantity $Q$ heat , input it into the heat transfer equation of the pipeline of the greenhouse heater 5, replace the pipeline parameters in the heat transfer equation of the pipeline of the greenhouse heater 5 with the pipeline parameters of the soil heating coil 6. The heating effect of the soil heating coil 6 is equivalent to the heating effect of the pipeline in the greenhouse heater 5, and the soil layer between the soil surface and the soil heating coil 6 is equivalent to the heat exchange fins in the greenhouse heater 5, and output the inner diameter, outer diameter and pipe length of the soil heating coil 6.

[0138] The technology for regulating the temperature of the greenhouse 1 space and soil by using the low-grade heat source 3 proposed by the present invention systematically sorts out the implementation methods for regulating the greenhouse space and soil by using the low-grade heat source 3, including constructing a greenhouse heat balance model and a soil heat balance model, and realizing the regulation of the greenhouse environmental temperature and soil temperature by designing the greenhouse heater 5 and the soil heating coil 6. The present invention can realize the utilization of low-grade energy in the greenhouse, and meet the requirements of the growth temperature of crops under the conditions of low air and soil temperatures in winter and at night, providing a feasible technical support for the utilization of low-grade energy in the greenhouse and heating the soil layer 11 where the main roots of the crops are distributed.

Claims

1. A greenhouse temperature control system based on a low-grade heat source, characterized in that: It includes a geothermal system and a greenhouse heating system arranged in a greenhouse. The geothermal system includes a soil heating coil installed in the soil layer in the greenhouse, one end of the soil heating coil is connected to a low-grade heat source through a water pump, and the other end is connected to a water storage tank. The water storage tank is connected to a tail water treatment area; the greenhouse heating system includes a greenhouse heater, one end of the greenhouse heater is connected to a low-grade heat source through a water pump, and the other end is connected to a water storage tank.

2. The greenhouse temperature control system based on low-grade heat source according to claim 1 is characterized in that: A temperature sensor is arranged in the temperature greenhouse, and a heat exchange fan is arranged on the wall of the temperature greenhouse.

3. The greenhouse temperature control system based on low-grade heat source according to claim 2 is characterized in that: The design method of the pipe size in the greenhouse heater is: S1: Calculate the heat exchange Q of the greenhouse at night heat ; Q heat =(Q s3 +Q4+Q s6 +Q s8 )-Q s2 ; Among them, Q s8 is the heat exchange between the north wall of the greenhouse and the interior space, Q s3 To calculate the lateral heat transfer from the soil in the greenhouse to the outside, Q4 is the heat exchange between the greenhouse and the environment at night, Q s6 is the infiltration heat transfer of the greenhouse, Q s2 Provides convection heat exchange between the ground and indoor air in the greenhouse; S2: Calculate the heat transfer coefficient k0 using the inner area of ​​the inner tube of the greenhouse heater as a reference; Among them, η0 is the efficiency of the heat exchange fins in the greenhouse heater, β0 is the finning coefficient of the heat exchange fins, and λ p is the thermal conductivity of the pipe in the greenhouse heater, d i1 is the inner diameter of the greenhouse heater pipe, d o1 is the outer diameter of the pipe inside the greenhouse heater, h i1 is the heat transfer coefficient of the pipe in the greenhouse heater, h0 is the heat transfer coefficient of the heat exchange fins; S3: Establish the heat transfer equation of the greenhouse heater pipe according to the heat transfer coefficient k0; Where A is the internal cross-sectional area of ​​the pipe in the greenhouse heater, Δt m is the average temperature difference of the greenhouse heater heat transfer, t1′ is the fluid temperature at the inlet of the greenhouse heater, t2′ is the fluid temperature at the outlet of the greenhouse heater, t2 is the target temperature to be regulated, ρ i1 is the density of the fluid in the greenhouse heater pipe, v i1 is the velocity of the fluid in the greenhouse heater pipe, μ is the dynamic viscosity of the fluid, λ f is the thermal conductivity of the pipe fluid in the greenhouse heater, l i1 is the length of the pipe in the greenhouse heater, Nu f is the Nusselt number of the fluid in the greenhouse heater pipe, Re f1 is the Reynolds number of the fluid in the greenhouse heater pipe, Pr f1 is the Prandtl number of the fluid in the greenhouse heater pipe, T is the thermodynamic temperature of the greenhouse; S4: Determine the inner diameter d of the greenhouse heater inner pipe according to the heat transfer equation i1 and outer diameter d o1 , and tube length l i1 .

4. The greenhouse temperature control system based on low-grade heat source according to claim 3 is characterized in that: The calculation of the convection heat transfer Q between the ground and indoor air in the greenhouse s2 The method is: Q s2 =h s2 L w (t s1 -t s2 ),h s2 =3.4(t s1 -t s2 ) 0.33 ; Among them, t s1 is the soil surface temperature in the greenhouse, t s2 is the temperature of the air in the greenhouse, h s2 is the convection heat transfer coefficient between the ground and indoor air in the greenhouse; Divide the greenhouse floor into different areas and calculate the lateral heat transfer Q from the soil in the greenhouse to the outside s3 The method is; Among them, si is the area number, W is the number of areas, k si is the thermal conductivity of the soil in the area, l si is the size of the region; The method for calculating the heat exchange Q4 between the greenhouse and the environment at night is: Among them, h in2 is the indoor heat transfer coefficient of a single-layer plastic film, h out is the convection heat transfer coefficient between the outside of the thermal insulation quilt and the outdoor air, δ n1 , δ n2 are the thickness of plastic film and thermal insulation cotton, λ n1 , n2 are the thermal conductivity of plastic film and thermal insulation cotton, l c It is the length of the south and north roof of the greenhouse; Calculation of greenhouse infiltration heat transfer Q s6 The method is; Among them, f c is the sealing coefficient of the temperature greenhouse, C w is the average wind pressure coefficient outdoors, f t is the temperature difference correction factor, v0 is the outdoor wind speed, L a is the permeation air flow rate, ρ1 is the air density, c1 is the specific heat capacity of air, f c is the sealing coefficient of the temperature greenhouse, C w is the average wind pressure coefficient inside and outside the greenhouse; Calculate the heat exchange Q between the north wall and the greenhouse space s8 The method is; Among them, h in1 is the convection heat transfer coefficient between the north wall and the greenhouse space, H n1 is the height of the north wall of the greenhouse, t n3 is the surface temperature of the north wall, pr is the Prandtl number, λ a is the thermal conductivity of air, Gr is the Grashof number, β is the thermal expansion coefficient, v is the kinematic viscosity, ΔT is the temperature difference between the north wall and the greenhouse space, L is the characteristic height of the north wall, and g is the acceleration of gravity.

5. The greenhouse temperature control system based on low-grade heat source according to claim 4 is characterized in that: The method for setting the working state of the heat exchange fan comprises: A1: Calculate the cooling heat Q of the greenhouse during the day cool ; Q cool =Q s1 -(Q s2 +Q s3 +Q s4 +Q s5 +Q s6 +Q s7 +Q s8 ); Among them, Q s1 is the solar radiation heat received by the greenhouse, Q s4 is the heat exchange between the greenhouse covering material and the environment, Q s5 For ventilation and heat exchange of greenhouse, Q s7 It is the heat exchange between the plants in the greenhouse and the internal air; A2: When the cooling heat Q cool >0, the heat exchange fan rotates forward, introducing outdoor cold air into the greenhouse for cooling. cool <0, the heat exchange fan reverses and introduces outdoor hot air into the greenhouse for heating. cool =0, the heat exchange fan does not work.

6. The greenhouse temperature control system based on low-grade heat source according to claim 5 is characterized in that: The calculation of the solar radiation heat Q received by the greenhouse s1 The method is: Calculate the size parameters of the greenhouse according to the construction location and structural characteristics of the greenhouse, including: ridge span ratio λ w :λ w =0.4301+0.0006249t swb +0.007702I s ; where t swb is the average outdoor temperature in winter, I s is the average daily solar radiation in winter; The span of the greenhouse is L w : Dimensions of the north roof and north wall: Among them, C w is the horizontal projection length of the north roof, L p is the height of the vegetation in the greenhouse, P is the width of the aisle in the greenhouse, H w is the ridge height of the greenhouse, H n1 is the height of the north wall, h s is the elevation angle of the sun's rays at noon in summer, h c is the elevation angle of the sun’s rays at noon in winter; Calculate the solar radiation heat Q received by the greenhouse based on the calculated size parameters of the greenhouse s1 ; Q s1 =Q s11 +Q s12 ; Among them, Q s11 is the solar radiation heat received by the greenhouse in the horizontal direction, Q s12 It is the solar radiation heat received by the greenhouse in the vertical direction; Calculate solar radiation heat Q s11 The method is: Q s11 =I h1 L w , I h1 =τkI0·cos(θ), where, I h1 is the solar radiation heat flux density per unit length received by the greenhouse in the horizontal direction, I0 is the solar constant, τ is the penetration ratio of the atmosphere, and k is the penetration ratio of the film covering the greenhouse; Calculate solar radiation heat Q s12 The method is: Q s12 =I n1 H n1 , I n1 =τkI0·sin(θ); Among them, I n1 It is the solar radiation heat flux density received by the greenhouse per unit height in the vertical direction; Calculate the heat exchange Q between the greenhouse covering material and the environment s4 The method is: Q s4 =k c l c (t s2 -t0); Among them, k c is the thermal conductivity of the covering material; Calculate the ventilation heat exchange Q of the greenhouse s5 The method is; Among them, ρ1 is the air density, c1 is the specific heat capacity of air, G is the ventilation volume, c d is the resistance coefficient of ventilation heat exchange, g is the acceleration of gravity, h is t is the height of the vent; Calculate the heat exchange Q between the plants in the greenhouse and the internal air s7 The method is: Among them, M T is the rate of water transfer between plants and air, is the latent heat of vaporization during water transfer, w ps is the enthalpy and humidity of saturated moist air, w a is the enthalpy and humidity of the air in the greenhouse, R a , R s are air resistance and pore resistance, v i is the indoor air velocity, τ c is the penetration ratio of the covering material.

7. The greenhouse temperature control system based on low-grade heat source according to claim 6 is characterized in that: The dimension parameter design method of the soil heating coil is: C1: Establish a soil heat balance model during the soil heating coil heating process; make but Among them, δ1 is the distance from the soil surface to the soil heating area, d1 is the thickness of the soil heating area, Φ is the total heat dissipation of the soil, Φ2 is the heat loss from the soil upward, and Φ x＝0 is the lateral heat loss of the soil, λ s is the thermal conductivity of the soil, H is the lateral influence distance of the soil heating coil on the circumferential soil, t is the lateral temperature of the soil outside the heating area, x is the lateral distance between the soil and the heating area, t sb is the target temperature of the soil heating area, m is the heat dissipation scale coefficient of the soil heating area; C2: The total heat dissipation of the soil is taken as the heat transfer Q heat , input the heat transfer equation of the greenhouse heater pipe, replace the pipe parameters in the heat transfer equation of the greenhouse heater pipe with the pipe parameters of the soil heating coil, the heating effect of the soil heating coil is equivalent to the heating effect of the pipe in the greenhouse heater, and output the inner diameter and outer diameter of the soil heating coil, as well as the pipe length.

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