WO2022018744A1

WO2022018744A1 - A process solution thermal control method and a plant for controlled environment aeroponics/hydroponics farm

Info

Publication number: WO2022018744A1
Application number: PCT/IN2021/050679
Authority: WO
Inventors: Prabhu Sankar Krishnan
Original assignee: Iac Krishitech Private Limited
Priority date: 2020-07-19
Filing date: 2021-07-14
Publication date: 2022-01-27

Abstract

The present invention is to create a Process Solution Temperature Control System for aeroponics/hydroponics driven controlled environment grow rooms located anywhere in the tropics and in the temperate climate zones, consuming less power compared to conventional systems by a unique logic making use of thermodynamic principles. The invention provides a system to solve this issue by combining wet cooling tower principle with vapor compression cycle and changing the mode of operation between three functional modes which are evaporative cooling mode, refrigerated cooling mode and refrigerated heating mode dynamically based on the conditions and state of the solution and the ambience.

Description

TITLE : A PROCESS SOLUTION THERMAL CONTROL METHOD AND A PLANT FOR CONTROLLED ENVIRONMENT AEROPONICS/HYDROPONICS FARM

FIELD OF INVENTION

Controlled environment agriculture is expanding at a greater pace globally and it is expected to address the problems encountered by traditional agriculture in terms of food security, resources depletion, nutritive fulfillment, residual toxicity and etcetera.

BACKGROUND OF INVENTION

A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with wails and roof made chiefly of transparent material, such as glass or plastic sheets, in which plants requiring regulated climatic conditions are grown. These structures range in size from small sheds to industrial-sized buildings. A miniature greenhouse is known as a cold frame. The interior of a greenhouse exposed to sunlight becomes significantly warmer than the external ambient temperature, protecting its contents in cold weather.

Many commercial glass greenhouses or hothouses are high tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment including screening installations, heating, cooling, lighting, and may be controlled by a computer to optimize conditions for plant growth. Different techniques are then used to evaluate optimality-degrees and comfort ratio of greenhouse micro-climate (i.e., air temperature, relative humidity and vapor pressure deficit) in order to reduce production risk prior to cultivation of a specific crop.

The warmer temperature in a greenhouse occurs because incident solar radiation passes through the transparent roof and walls and is absorbed by the floor, earth, and other contents, which in turn become warmer. As the structure is not open to the atmosphere, and the air warmed up by infrared irradiation from internal surfaces, cannot escape via convection, so the temperature inside the greenhouse rises. Quantitative studies suggest that the effect of infrared irradiative heating is not negligibly small, and may have economic implications in a heated greenhouse, in any controlled environment agriculture the greenhouse is the primary and most popular grow room. There are other grow rooms, having artificial lighting instead of sunlight may not be termed as greenhouse. But even in such cases the irradiative heating of interiors and contents is unavoidable as artificial light radiation contributing for internal heat buildup.

Such controlled environment grow rooms, even though cooled down by ventilation, evaporative cooling or by refrigerated cooling they still persist at temperature levels, optimum for a crop to grow.

On the other hand the controlled environment grow rooms located in areas beyond 24 Deg N and 24 deg S latitudes are susceptible to very low temperatures during night hours.

Such controlled environment grow rooms are the primary requirement for conducting agriculture driven by soil less technologies like aeroponics and hydroponics employing water recycling technique.

The basic principle of aeroponic growing is to grow plants suspended in a closed or semi-dosed environment by spraying the plant's dangling roots and lower stem with an atomized or sprayed, nutrient-rich water solution. The leaves and crown, often called the canopy, extend above. The roots of the plant are separated by the plant support structure. Often, closed-cell foam is compressed around the lower stem and inserted into an opening in the aeroponic chamber.

Hydroponics is a subset of hydro culture, which is a method of growing plants without soil and by instead using mineral nutrient solutions in a water solvent. Terrestrial plants may be grown with only their roots exposed to the nutritious liquid, or the roots may be physically supported by an inert medium such as perlite or gravel.

In both of these cases, the process solution containing water and nutrient mix is pumped into the root chamber and then sprayed onto the roots in case of aeroponics, or allowed to flow along a channel where roots are contained in case of hydroponics and thereafter returned back to the reservoir for recycling again and again.

Because of this recycling of several times within a day, the process solution tends to gain heat from the wails of crop support platforms of aeroponics and hydroponics. The crop support system walls, due to their exposure to radiation from sunlight, or from artificial light gets heated up and in turn transfer the same to the process solution coming in contact on their inner side. Besides the direct radiative heat gain, the crop support systems also gain convection heat from the atmosphere temperature of the grow room, even though it is at an optimum level only.

During the course of the day, this small amount of heat gain progressively increases the process solution temperature, making it dynamic and further making other process solution characters like electrical conductivity, pH and dissolved oxygen also dynamic towards non permissible levels, in a typical high intensity sunlight zone, the process solution temperature within a few hours shoots up to the temperature in the grow room.

The primary detrimental effect is in reduction of difference of temperature in the grow room and that in the root zone. Plants take cool water from root zone and transpire the same into the grow room to regulate the temperature of themselves. As the difference between these two temperatures gets reduced the plant bio synthetic activity also slows down besides transpiring more water to regulate the temperature of the plants.

When the lights go on, temperatures are low and there is less need for cooling. As the day progresses, the energy and temperature in the air and plant tissues increase, as does the rate of transpiration, which then falls back again as the day comes to an end. These temperatures can, for example, start at around 22°c and reach a peak of 33°c before falling back, an 11 -degree difference over half a day. In the root zone, these temperatures may vary between 22°c and 25°c - only a 3°C difference, but the roots must function well enough in that constant temperature range to provide everything that the top zone needs.

The plant’s root system does not regulate its own temperature, and once temperature in the medium strays outside the optimum zone for reactions to occur, it can no longer supply the rest of the plant with the optimum level of water and nutrients. This is the case whether the temperature is too high or too low. The greater the fluctuation in temperature in a 24-hour period, the more stressed the root system will become, and the more problems a plant will have both physiologically and pathologically, and it will become increasingly susceptible to pathogens and insects. Placing any root system in a medium above ground will increase the surface area from which heat can be gained or lost.

Plants become dormant when the root system stops most of its functions, whether this is a result of too cool or too hot conditions. Even the temperature of the irrigation water or nutrient solution will increase or decrease the root function, and any sudden large temperature change will shock the roots.

The next detrimental effect of increased process solution temperature is reduction of dissolved oxygen in it. Typically 8 to 9 ppm presence of dissolved oxygen in the process solution is optimum for mobilizing nutrients to the plant. Less than 5 ppm dissolved oxygen, gives way for anaerobic pathogens to proliferate. Dissolved oxygen content of water is a function of temperature. Higher the temperature lower the dissolved oxygen.

On the contrary too cool process solution temperature usually slows growth by pushing the plant metabolism to dormancy. Such condition occurs in northern hemisphere climates during the winter. Research has shown that leaf numbers, leaf length and total fresh and dry weight can be affected. Low temperature can affect dissolved nutrients and physiological properties.

The present invention is to create a Process Solution Temperature Control System(PSTCP) for aeroponics/hydroponics driven controlled environment grow rooms located anywhere in the tropics and in the temperate climate zones, consuming less power compared to conventional systems by a unique logic making use of thermodynamic principles.

PRIOR ART Existing Systems

Heat Pumps (Refrigerated cooling/heating)

A heat pump is a device that transfers heat energy from a source of heat to what is called a thermal reservoir. Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses external power to accomplish the work of transferring energy from the heat source to the heat sink by using a vapor compression cycle or by vapor absorption cycle. The most common design of a heat pump involves four main components - a condenser, an expansion valve, an evaporator and a compressor. The heat transfer medium circulated through these components is called refrigerant. While air conditioners and freezers are familiar examples of heat pumps, the term "heat pump" is more general and applies to many heating, ventilating, and air conditioning (HVAC) devices used for heating or cooling. Heat pumps usually can be used either in heating mode or cooling mode, as required by the user. When a heat pump is used for heating, it employs the same basic refrigeration- type cycle used by an air conditioner or a refrigerator, but in the opposite direction - releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground.

In the heating mode, heat pumps are significantly more energy efficient than simple electrical resistance heaters. However, the typical cost of installing a heat pump is higher than that of a resistance heater.

A cooling tower is a heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and coo! the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to coo! the working fluid to near the dry-bulb air temperature.

Problems with Existing Systems

In aeroponics/hydroponics growing, the process solution temperature is maintained within a range of 3 Deg C. For temperate crops the range is 18° C to 20° C, and for tropica! crops it is 23° C to 25° C. A range of 21° C to 23° C for temperate crops and 25° C to 27° C is also required if a tradeoff is accepted by compromising quality and quantity outputs for reduced power consumption. But in ail the above cases, the range is only within a 3 degree variation. in this background, a wet cooling tower functioning on the principle of evaporative cooling and forced air, may fail short of achieving desired results at all times, since its heat removal capacity is dependent on temperature and relative humidity of ambient air. A wet cooling tower, theoretically can cool the process solution down to the wet bulb temperature of ambient air. The heat balance could be equated as under.

{[Wa x (Tamb -Twb) x Hsp.air] + [Ww x (Tw1-Twb) x Hsp.w]}= (Hamb-Hwb) x

Wa x Heva

Where

Wa - Mass of Air in kg/hour

Tamb - Ambient air temperature in Deg C

Twb - Wet bulb temperature in Deg C

Hsp.air - Specific Heat of air in KJ/Kg. deg C

Ww - Mass of water in Kg/hour

Tw1 - Initial Water temperature in Deg C

Hsp.w - Specific Heat of water in KJ/Kg. deg C

Hamb - Absolute humidity of ambient air at Tamb Kg/kg

Awb - Absolute humidity of air at Twb in Kg/kg

Heva - Heat of evaporation of water

Keeping the mass of water (Ww) a constant the following are the limitations * Twb is dynamic depending on Tamb and relative humidity of ambient air. Thus only when these two parameters of ambient air is in combinations permitting Twb is within the required process solution temperature.

* As heat transfer from ambient air and from process solution to vapor temperature, is directly proportional to the temperature differential, either larger sized interaction space or smaller sized water particles or a combination of both required when the equilibrium approaches the Twb. So, in practice, generally cooling towers are designed to achieve a marginally higher temperature than TWB. In the present case the marginally higher allowance is not possible many times as the process solution is kept at narrow band.

* Many a times even if the Twb is achievabie for a given configuration of cooling tower, the value of it may be higher than that of the upper limit of desired range.

* (Hamb-Hwb) is dynamic depending on relative humidity and T amb, and decides the amount of mass of water required, many a times at unacceptable levels even If Twb is within required range.

As such the wet cooling tower will be effective only in cases when Twb is within the desired range or less than the lower limit of desired temperature range.

Table: 1 -Adoptability of Wet cooling towers for a few select ambient conditions

The ambient conditions assumed in Table 1 above tend to happen within a day from morning to evening and across seasons throughout a year. A wet cooling tower is not solving the problem even in 50% of the ambient eventualities. On the other hand in a dry cooling tower, if the ambient air temperature is less than the desired process solution temperature, it is passed through a heat exchanger mounted across the path of process solution spray, removing the heat. The following table shows when it is adoptable for the purpose of aeroponics/hydroponics process solution cooling.

Table: 2-Adoptability of Dry cooling towers for varying ambient conditions

From the Table 2, one can discern that only in temperate locations, a dry cooling tower using ambient air as coolant is adoptable for the purpose of process solution cooling to the desired range. Even in such eventualities, a wet cooling tower itself will do the job so no need of going for a dry one.

In case of refrigerated heat pumps employing either vapor compression or vapor absorption, the power consumption is exorbitantly high rendering the entire aeroponics or hydroponics growing methods cost ineffective or at least reducing the return on investment.

The following calculation shows the power facts. Grow room size = 2500 sqm industry Average Production = 2000 kgs/day Process solution volume = 45000 liters Assumed Day length = 10 hours Average temperature gain/hour = 1 deg C Specific Heat of water = 4,19 kJ/kg°C

Total heat load to be removed in an hour= 45000*1*4.19*0,00118 = 218.72 Kwh Assumed Coefficient of Performance = 4,00

Power Consumed by a Heat Pump = 218.72/4.0 = 54.68 Kwh

Power Consumed/day = 10.00 ^* 54.68 = 546.8 Kwh

Such a high amount of power consumed just for one aspect of aeroponics/hydroponics growing make the entire project unviable.

SUMMARY OF THE INVENTION

The Solution offered In the invention is given below,

It is therefore desirable to provide a system for commercial scale aeroponics farming and the invention has achieved this object.

Based on an universal and novel approach to solve the process solution temperature control issue by combining “wet cooling tower principle” with “vapor compression cycle” so that between 24° N to 24° S, wherever it may be, the system maintains the daytime temperature as well as night time temperature at the desired level and at a substantially reduced power consumption.

The present innovation is to have a mechanical and structural arrangement or configuration of various components and subsystems and a unique algorithm governing the operation to deliver the desired results by” running it in evaporative cooling mode to the maximum possible extent”, and in “vapor compression heat pump mode unless otherwise not possible in the former mode” The Evaporative cooling mode requires only 1/5^th of energy consumed by Heat pump mode for the same amount of heat mitigation in a conducive ambient condition.

DETAILED DESCRIPTION OF INVENTION

The proposed Process solution temperature control plant shall have the following design configuration.

1. A master controller to run the operating logic of PSTCP

2. A pumping system to pump hot process solution returning from grow room and collected at the Return tank, with enough power to develop required pressure and discharge.

3. A micron filtering system to filter the process solution for tiny inorganic and organic debris collected from grow room.

4. A solenoid actuated set of valves to guide the flow normally into the filtering systems in forward direction and in reverse direction automatically whenever the pressure differential is beyond allowable limits between the inlet side and the outlet side.

5. Two numbers of pressure transducers mounted on the inlet and the outlet side of filtering system.

6. A temperature transmitter mounted on the process solution delivery line to grow room, to trigger PSTCP logic in the master controller.

7. A combined temperature and relative humidity transmitter mounted externally to give input value for the PSTCP logic running in the master controller to calculate and to trigger appropriate systems.

8. A combined temperature and relative humidity transmitter mounted at air exit port to verify the performance of evaporative cooling mode.

9. A temperature transmitter at the bottom of the evaporating chamber to verify the process solution cooling level in evaporative cooling mode. 10. An array of misting nozzles mounted at the top of the evaporating chamber to deliver 60 to 80 micron sized water spray in required quantity.

11. An Evaporating chamber erected vertically over the process solution tank allowing misted water and air to pass in counter flow mode.

12. A drift arrester at the top of the evaporating chamber preventing tiny process solution particle getting carried away.

13. A bi-directional heat pump configured with two heat exchangers, one immersed in process solution and the other located externally, along with a compressor, reversible direction valve, expansion device, and refrigerant coils to pump heat out during hot weather and to pump heat in during cold weather.

The schematic diagram is illustrated in Fig. 1.

The Functional Modes

There are three functional modes between which the PSTCP switches actions according to the external temperature, external RH and required process solution temperature range.

1. Evaporative Cooling Mode

This is the lowest power consuming mode for attaining the required temperature range of process solution when the external ambient temperature is above that. The logical program running on the controller calculates the wet bulb temperature from the ambient temperature and relative humidity data input from continuous transmitting sensors and selects the mode only if

* Calculated wet bulb temperature is less than the upper limit of process solution temperature.

* Calculated amount of air within the capacity of air throw fans. Further the logical program incorporates check and correction mechanism, by taking input of RH data transmission from the exiting air at the top. For the calculated amount of air and for the desired process solution temperature the exiting air must attain a relative humidity level of 95% to 100%. If it is less than 95%, the air volume is adjusted by reducing the RPM of the fan motor. If it is equal to 100% the air volume is adjusted by increasing the RPM of the fan motor.

Please refer illustration in Fig. 2. in this mode,

* The PS water supply pump is on and it pumps the warm process solution received from the grow room to micron foggers through Micron filters. The said pump is shown in green colour, the warm water lines in red colour, and cooled water in light blue colour.

* The air blowing fan is on and it sucks air from the external atmosphere through the non-working heat exchanger and throws it in to the evaporating area in a counter flow direction to that of micro fogging water. The arrows in red indicate the warm air and the same in blue at the exit indicate humidified cold air.

* The entire heat pump system in either modes is off and shown in dark blue colour. Refrigerated Cooling Mode

This is the highest power consuming mode for attaining the required temperature range of process solution when the external ambient temperature is above that. The logical program running on the controller calculates the wet bulb temperature from the ambient temperature and relative humidity data input from continuous transmitting sensors and selects the mode only if * Calculated wet bulb temperature is higher than the upper limit of process solution temperature.

* Calculated amount of air above the capacity of air throw fans.

This mode is operational till the lower limit of process solution temperature is reached.

Please refer illustration in Fig. 3. in this mode,

• The Refrigerant compressor, and condenser fan are on and the former compresses the refrigerant into the latter. Air sucked in through the fins of the condenser and removes the heat. The compressor and the fan are shown in green color and the hot liquid refrigerant pathway is shown in red color,

• The evaporator is submerged inside the PS solution, and shown in yellow color. The expanded cold refrigerant in gaseous state is passed through the evaporator where it gains heat from Process solution and thus gets heated before reaching the compressor for the next cycle.

* The entire Evaporative cooling system is off and shown in dark blue colour. , Refrigerated Heating Mode

This is also the highest power consuming mode for attaining the required temperature range of process solution when the externa! ambient temperature is below that. The logical program running on the controller takes input data of external temperature and Relative humidity and selects the mode only if

* The process solution temperature is less than the lower limit of the required range. * The external temperature is less than the lower limit of the required range.

Please refer illustration in Fig. 4. in this mode,

* A reversible valve in refrigerant cycle reverses the refrigerant flow direction in such a way that both condenser and evaporator inter change their role for reverse directional heat flow.

• The Refrigerant compressor, and condenser fan are on and the former compresses the refrigerant into the latter. Air sucked in through the fins of the condenser and supplies the heat. The compressor and the fan are shown in green color and the expanded, cold gaseous refrigerant pathway is shown in yellow color.

• The condenser is submerged inside the PS solution, and shown in red color. The hot liquid refrigerant is passed through the condenser where it delivers heat to the Process solution and thus gets cooled before reaching the compressor for the next cycle.

* The entire Evaporative cooling system is off and shown in dark blue colour.

The Functional Logic

If Process solution temperature is ≥ upper limit * Calculate Twb for the prevailing Tamb and RH o If Twb ≤ upper limit

^* Calcuiate estimated Mass of air required by the equation 1 to cool down to lower limit

^* Calculate estimated quantity of water to be evaporated by the equation 1

^* if both are within allowable limits • Switch on Evaporative cooling mode

• Change Fan RPM to force required mass of air • Verify exit air Temperature o If it is > Twb

* Reduce the Fan RPM to appropriate level

* Loop back to verification of exit air temperature

* If Process solution temperature is = Lower limit

* Switch off evaporative cooling mode

* Go back to the very first step

• if either one is not within allowable limits

• Switch on Heat pump cooling mode • If Process solution temperature is = Lower limit

• Switch off Heat pump cooling mode

• Go back to the very first step o If Twb ≥ upper limit o Switch on Heat pump cooling mode o If Process solution temperature is = Lower limit + 0.5 deg C o Switch off Heat pump cooling mode o Go back to the very first step If Process solution temperature is ≤ lower limit o Switch on Heat pump heating mode o If Process solution temperature is = upper limit - 0.5 deg C o Switch off Heat pump heating mode o Go back to the very first step

The Flow Chart of the Logic is illustrated in Fig. 5. A case study for Coimbatore and Delhi is illustrated in Fig. 6 and 7.

The invention discloses the configuration of all subsystems and components, which arrangement is novel, the operating logic which is novel and the configuration and the operating logic in combination

The embodiments disclosed herein overcome the shortcomings of the prior art by providing an aeroponic chamber incorporating the method of managing the chamber with optimized growth rate.

This invention relates generally to the field of aeroponics, and more particularly to a method and structure which enhances the efficiency of aeroponic farming and the same has been achieved very effectively and simply.

Therefore what was needed is an method and a corresponding plant system that more efficiently and effectively executes aeroponic principals in a specific volume and this solution has been disclosed sufficiently to work the invention.

In one aspect the invention relates to a method of thermal control of process solution in a controlled environment aeroponics and/or hydroponics farm the grow room of which is a greenhouse requires regulated climatic condition within, based on the external ambient state, process solution temperature state and wet bulb state, the said method has the following steps as detailed below :

The method involves providing an assembly of process solution tank configured and dimensioned for achieving desired process solution temperature for aeroponic/hydroponic farming. An operating logic is used to detect the external ambient state, the process solution state, and the wet bulb state. Based on the combination of the three states detected and as per the operating logic, the system actuates one of the three mode in which the system can operate. The evaporative cooling mode is actuated when an operating logic detects that the ambient temperature is higher than desired process solution temperature and wet bulb temperature is lower than allowable highest upper limit threshold temperature of the process solution temperature. Further the method involves actuating refrigerated cooling mode when the operating logic detects that the ambient temperature is higher than desired process solution temperature and wet bulb temperature is higher than allowable highest upper limit threshold temperature of the process solution temperature. Third mode is actuated which is, refrigerated heating mode when the operating logic detects that the ambient temperature is lower than desired process solution temperature. As described above, the method teaches selection of one of three modes dynamically based on the detected the external ambient state, the processed solution state and the wet bulb state and using an operating logic for actuating one of the three modes based on the calculated signal. Accordingly this method is characterized in the dynamic switching between the modes, switching between modes with a master controller based on the operating logic instruction signals. To run this process in another aspect the invention also discloses the arrangement of the process solution tank with all of the corresponding assembly and the same is also illustrated in the accompanying drawings.

Having now described various embodiments of the invention in detail as required in the application, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the claims.

Claims

WE CLAIM :

1. A method of thermal control of process solution in a controlled environment aeroponics and/or hydroponics farm the grow room of which is a greenhouse requires regulated climatic condition within, based on the external ambient state, process solution temperature state and wet bulb state, the said method comprising of :

- providing an assembly of process solution tank configured and dimensioned for achieving desired process solution temperature for aeroponic/hydroponic farming,

- using an operating logic to detect the external ambient state, the process solution state, and the wet bulb state,

- actuating evaporative cooling mode when an operating logic detects that the ambient temperature is higher than desired process solution temperature and wet bulb temperature is lower than allowable highest upper limit threshold temperature of the process solution temperature,

- actuating refrigerated cooling mode when the operating logic detects that the ambient temperature is higher than desired process solution temperature and wet bulb temperature is higher than allowable highest upper limit threshold temperature of the process solution temperature,

- actuating refrigerated heating mode when the operating logic detects that the ambient temperature is lower than desired process solution temperature, and

- the method characterized in the dynamic switching between the modes, switching between modes with a master controller based on the operating logic instruction signals.