BR112018073759B1 - METHOD FOR AUTOMATED IN SITU DYNAMIC CONTROL OF A METABOLICLY ACTIVE PRODUCT IN A CONFINED ENVIRONMENT THROUGH THE COMPOSITION OF ITS GASES AND PRESSURE - Google Patents

Abstract

A control system for controlling the storage of metabolically active product in a defined confined environment, said control system comprising at least a gas analysis and pressure measuring means comprising a control unit for determining a composition of the medium gaseous adjusted from the confined environment to protect the product from metabolic degradation; at least one operating/actuating means for adapting the gaseous medium in the confined storage environment based on said determined adjusted gaseous medium composition; wherein the control unit is adapted to determine the composition of the gaseous medium adjusted based on a mathematical model of the system which determines a metabolic coefficient of the product by combining the measurement of gas composition changes in the confined environment with dynamic pressure changes in the space confined. The value of the metabolic coefficient is used as input to a control algorithm to continuously adjust the composition of the gas in the confined space in response to the metabolic activity of the product.

Description

A. Field of invention

[0001] This invention concerns a method and dynamic system related to the algorithmic control of the gas composition in the atmosphere of confined controlled environments, for example storage or growth environments, of respiratory products such as fruits, vegetables and plants, and more particularly to a method and apparatus for dynamically controlling the composition of gases in the controlled environment through software-assisted monitoring of rates of change in the composition of gases in a system where the product can be held for extended periods of time. Such a system comprises a mathematical model that determines the actual gas exchange rates of the product as a measure of its metabolic activity, such as respiration and fermentation.

[0002] Several documents are cited throughout the text of this descriptive report. Each of the documents contained in this document (including manufacturer's specifications, instructions, etc.) is incorporated into this document by reference; however, there is no admission that any document cited is, in fact, prior art of the present invention.

B. Description of related technique

[0003] Horticultural products that need to breathe (fruits, vegetables and plants) are commonly stored at low temperature (generally close to 0°C) in combination with a reduced partial pressure of O2 and increased partial pressure of CO2 (the so-called “Controlled Atmosphere Storage (CA)") to reduce its breathing rate and therefore extend its lifespan.

[0004] Metabolically active plants or cultures are plants that undergo active physiological processes of photosynthesis and/or respiration. These metabolically active plants can be grown in a confined environment such as a factory with artificial lighting and very limited exchange of ambient air from the outside environment under so-called Controlled Atmosphere (CA) growth to optimize the basic process of photosynthesis and respiration underlying the pathway. metabolism that produces chemical energy (ie, adenosine triphosphate (ATP) and redox equivalents) to meet cellular energy demands for growth and maintenance of such metabolically active plants.

[0005] However, the optimal gas composition is critical, since a very low O2 partial pressure in combination with a very high CO2 partial pressure induces a fermentative metabolism in the fruit (Beaudry, Postiolvest Biol Technol, 15: 293 -303, 1999). This causes derangements (eg ethanol) and storage disturbances (eg browning and core breakage). For this reason, the partial pressure of O2 and CO2 in commercial refrigerators is maintained at a safe and stable value. Such systems have been developed under US Pat. No. 5,333,394, "Controlled Atmosphere Container System for Perishables", US Pat. U.S. No. 6,092,430, "Oxygen/Carbon Dioxide Sensor and Controller for a Controlled Atmosphere Refrigerated Vessel" and US Pat. U.S. No. 6,615,908, "Method of transport or storage of perishable products". These patents dealt with the control of the atmosphere, the use of membranes and the use of sensors. Patent US070144638 was positioned as an improvement in relation to these systems, being more economical (energy efficiency) and not resulting in increased pressure in the containers (due to the regulation of gases in the methods then in force). European patent EP0457431 describes a system for controlling oxygen and carbon dioxide concentrations in a refrigerated container to make perishable products breathe to dynamically and continuously control gas concentrations. European patent application EP2092831 describes a similar system. All of these methods target predetermined values of gas concentrations. US Patent 5,333,394 describes an AC container with controller that will implement bursts of gas delivery that are pre-programmed based on a particular application; does not use measured gas production and consumption rates.

[0006] Furthermore, US Patent No. 7,208,187 discloses a method of controlling a controlled atmosphere in which at least one residual gas in a concentration of less than 1% is measured at least at two different times, and in which the variables of control are determined on the rate of change in the concentration of the trace gas, which is then used as a measure of the rate of production of the trace gas. The gases referred to are ethylene, ethanol, ethane, acetaldehyde and carbon dioxide. The method does not consider the gases consumed due to breathing, that is, oxygen. The method also does not consider the ratio of the rate of change of two gases as a measure of the physiological state.

[0007] Conventionally, the storage of horticultural products that need to breathe in a controlled atmosphere (AC) thus uses fixed and static setpoints recommended as optimal storage conditions. As concentrations are set at safe levels, significant loss of firmness can still occur. Furthermore, the development of postharvest disorders has been described even under optimal CA (Peppelenbos & Oosterhaven, Acta Hort 464: 381-386, 1998; DeLong et al., Acta Hort 737: 31-37, 2007). Due to the high biological variability of horticultural products, recommended optimal storage conditions may differ from actual optimal storage conditions (Saltveit, Postharvest Biol Technol 27: 3-13, 2003; Veltman et al., Postharvest Biol Technol 27:79- 86, 2003).

[0008] Adaptive CA storage systems (ACA) can adapt the atmospheric gas composition based on the real physiological state of the fruit (Veltman et al., Postharvest Biol Technol 27: 79-86, 2003; Zanella et al., Acta Hort 796, 77-82, 2008) as a function of time and fruit batch, such that variations due to factors such as geographic location, cultivar, mutant, orchard effects, harvest date and storage duration can be taken into account. consideration. ACA storage can maintain fruit quality to a greater extent than conventional CA and Ultra Low Oxygen (ULO) storage facilities (Gasser et al., Acta Hort 796 69-76: 2008; Zanella et al., Acta Hort 796, 77-82, 2008), and has been proposed as a viable option for organic apple growers who are not using preventive chemicals (DeLong et al., Acta Hort 737: 31-37, 2007). Veltman et al. Biol Technol Post 27: 79-86 (2003) showed that ACA resulted in improved quality of 'Elstar' apples, with better firmness retention and inhibition of the 'skin spots' defect. Other ACA applications have been successful for the storage of 'Granny Smith' and 'Delicious' apple cultivars (Hoehn et al., In (MM Yahia): Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities, CRC Press, 42, 2009).

[0009] Monitoring systems for ACA were developed based on chlorophyll fluorescence (Prange et al., Patent No. WO0206795) and monitoring the release of acetaldehyde or ethanol (Veltman et al. Postharvest Biol Technol 27: 79-86 ( 2003)).

[0010] The principle behind ACA storage is the storage of fruit in an atmosphere with the lowest possible level of oxygen that is tolerated by the fruit. Below this level, fermentation becomes important and physiological disturbances such as internal browning can develop. In practice, a fruit response signal that is generated under such conditions is used to monitor oxygen stress. Two systems are already in use. Systems using chlorophyll fluorescence as the fruit response signal have been disclosed in WO-0206795. Controlled Atmosphere (CA) using chlorophyll fluorescence requires several expensive sensors per cold room and has methodological constraints such as measurement position (a constant distance from the sensor to the apples is required). Veltman et al. Postharvest Biol Technol 27: 79-86 (2003) used fermentative ethanol production as the fruit response signal. Ethanol measurements are performed offline on fruits sampled from the storage room or ambient air. The ethanol-based system is disclosed in WO-0206795 and EP-0798962. The first method is a procedure that does not match the characteristics of a dynamic commodity indicator as part of an automated control system. The latter is unreliable due to the possible interaction of the detection equipment with gases such as ethylene, which may be present in the sample air (Hoehn et al., In (MM Yahia): Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities, CRC Press, 42, 2009).

[0011] Both methods were compared with respiration measurements. The appearance of stressful conditions indicated by increased ethanol concentration or chlorophyll fluorescence signal is in accordance with the lowest acceptable respiratory rate, which can be obtained by measuring changes in O2 and/or CO2 concentration in the atmosphere surrounding the fruit (Veltman et al., Postharvest Biol Technol 27: 79-86, 2003; Gasser et al., Acta Hort 796: 69-76, 2008). Measuring respiration rate in storage rooms was not considered practical (Hoehn et al., In (MM Yahia): Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities, CRC Press, 42, 2009).

[0012] Yearsly et al., Postharvest Biol Technol 8: 95-109 (1996) and Gasser et al., Acta Hort 796: 69-76 (2008) demonstrated in small batches of apples in jars that the respiration coefficient RQ ( CO2 production rate per O2 consumption rate) increases dramatically below the lowest respiration rate, due to the onset of fermentation. This demonstrated that RQ matches the fluorescence and chlorophyll ethanol methods.

[0013] The flask experiments in the laboratory, however, exclude important influencing factors of real deposits (room size and shape, leaks, climatic conditions, stacking pattern, gas storage inside the fruits) that prevent the exact determination of the RQ and therefore make precise control of real systems impossible. In particular, the flasks provide an airtight system that excludes leaks and can be controlled to avoid temperature and pressure fluctuations. In containers, chambers or rooms, accurately determining gas leak rates is essential to correct measurements of physiological processes such as respiration and fermentation (Hoehn et al., In (MM Yahia): Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities, CRC Press, 42, 2009). Existing methods use non-reactive trace gases for this purpose in separate tests (Baker et al., Environ Exp. Bot 51: 103-110, 2004) or pressure decay in empty rooms at room temperature (Bartsch, Cornell Fruit Handling and Storage Newsletter, 16-20, 2004; Raghaven et al., In (DM Barett, L. Somogy, H. Ramaswamy): Processing Fruits, CRC Press, 23-52, 2005 ). Leakage depends on room design and construction, weather conditions, load, and changes over time. Annual testing is recommended (Hoehn et al., In (MM Yahia): Modified and Controlled Atmospheres for the Storage, Transportation, and Packaging of Horticultural Commodities, CRC Press, 42, 2009). In heavily used storage rooms, a method for automatic leak measurement is needed to reduce workload, automate storage room management, and implement Dynamic Controlled Atmosphere (DCA). In fact, in the present invention the DCA will be implemented in such a way that the leakage effect can be automatically corrected without additional systems or tests, such as those claimed in EP2816890 A1. To achieve this, the storage room needs to be maintained at an overpressure with respect to its direct environment, which is achieved by injecting expensive N2 gas. In addition, the storage room must meet certain requirements regarding tightness in order to obtain this overpressure. Also with the system described in EP2816890 A1, the respiration of the product is determined only periodically.

[0014] In heavily used storage rooms, a method for automatic RQ measurement is needed to reduce the workload, automate storage room management, and thus implement dynamic AC instead of tuned AC. Instead of RQ-based control, a new control paradigm is also needed that uses the total gas exchange rate (GERQ) quotient in the storage environment and determines through a mathematical model of the system the actual respiratory rate of the product. .

[0015] In patent EP2547213B1 we demonstrated that the dynamic control of AC storage environments not only requires dynamic and accurate measurement of O2 and CO2 levels as a function of time in the room, but also the rate of gas exchange with the external environment and the accumulation of gases. In said patent, a method is presented that estimates a leak coefficient characteristic of the room enclosure to correct leaks. While determining and correcting such a coefficient has been shown to be feasible and advantageous, additional and separate measurement protocols were required.

[0016] The present invention does not require sealing the space from external influences such as leakage during breath detection, which is the basis and restriction of the method claimed in application EP2816890 A1.

[0017] WO2014/066952 A1 describes a system for controlling the gas composition in a fruit storage container. The change in internal pressure is measured to calculate an equivalent leak hole diameter which is compared to a reference flow hole diameter. Based on this, the control system determines the ambient air intake rate to maintain a fixed gas composition in the storage vessel. Disadvantages of the system are that the leakage parameters such as the equivalent leak hole diameter must be calculated, only the leakage of ambient gas directly from the storage vessel to the storage vessel is considered and not vice versa, and that the product is stored at a fixed gas composition and not automatically at the optimum gas composition. Furthermore, the control algorithm is not based and adapted to a metabolic parameter of the product.

[0018] With the present invention, no leakage parameter, such as the equivalent diameter of the leakage hole or the leakage constant, should be determined. The control system uses an internal pressure measurement to determine a metabolic rate of the metabolic product, taking into account leakage from the confined space to its environment and vice versa, and automatically stores the product at the optimum gas composition.

[0019] This invention incorporates a system and associated instrumentation for automatically monitoring a metabolic coefficient, such as RQ, which takes into account room design and operating factors based on internal pressure measurements, rather than measuring leak coefficients. The present invention clearly demonstrates that the evaluation of the gas exchange dynamics of the complete storage system (including the fruit, the storage atmosphere, the room design and the gas leakage to or from outside), considering the climatic conditions, provides a means to monitor the respiratory activity of the product. The present invention also makes it possible to automatically calculate the future gas composition required to keep the product breathing at safe levels. The system can advise storage room operators to adapt the gas composition or apply automated control of the gas composition in the storage environment.

SUMMARY OF THE INVENTION

[0020] The present invention solves the related art problems of accurately controlling a respiratory product in a confined environment by calculating a metabolic coefficient as a function of the gas composition measured in the confined environment and as a function of the pressure in the confined environment, whose metabolic rate is determined by the control unit at least as a function of gas composition and pressure at least two consecutive times during a selective time period in the confined environment, 2) as a function of the metabolic rate calculated to determine a composition of adjusted gaseous medium, 3) generate an output signal that directs the operator/actuator to control the fruit and vegetable product that needs to breathe. This method has several advantages over the technique. It is more accurate than a method by which it is necessary to estimate an equivalent leak hole diameter. It is not necessary to introduce outside air through a diagram (gas inlet) for pressure measurement or to extract CO2 through a semipermeable membrane. By the method of the present invention, the requirement to estimate a leakage parameter (k) is also avoided. This is an improvement as the value of k can vary over time so multiple estimates are needed separated in time as k is a function of the confined space load, temperature and pressure or pressure difference between the confined space and the environment. Another advantage of the system of the present invention is that to detect product breathing in the confined environment it is not necessary to turn off the atmosphere control (AC control) and the temperature control during the measurement and to seal the leak substantially tight during the measurement and/or keep the atmosphere moving and/or adjust the pressure by N2, so that it is only possible to do so at certain time intervals (>1 h). Especially in this classic system, there are several days between measurements.

[0021] The further scope of applicability of the present invention will become apparent from the detailed description herein given below. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, as various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. in the technique from this detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.

[0022] FIG. 1 provides a schematic view of the control system based on a software-assisted measurement system of gas composition and atmospheric pressure in a confined environment and control algorithm. The metabolically active product (a) is contained in a confined environment (b). The pressure is measured with a pressure sensor (c) and the gas composition with a gas analyzer (d). The signals from the pressure sensor and the gas analyzer are used by the control unit (e) to calculate a metabolic coefficient of the product (a) which calculates an output signal as a function of the metabolic coefficient value. The output signal from the control unit triggers the operator/actuator (f) to adjust the gas composition in the confined environment using a gas supplied by a conventional gas treatment unit (g) which may include scrubbers and generators.

[0023] The present invention provides a way to solve related art problems of accurately controlling a fruit and vegetable product that needs to breathe in a closed environment by first calculating a metabolic coefficient as a function of the gas composition measured in the confined environment and as a function of pressure in the confined environment, the metabolic rate of which is determined by the control unit at least as a function of gas composition and pressure for at least two consecutive times during a selective period of time in the confined environment, second as a function of the metabolic coefficient calculated to determine an adjusted gaseous medium composition and, third, generate an output signal that directs the operator/actuator to control the fruit and vegetable product that needs to breathe. This method has several advantages over the technique. It is more accurate than a method by which it is necessary to estimate an equivalent leak hole diameter. Using an inventive system it is possible to protect the fruit and vegetable product that needs to breathe from a metabolic disturbance or against fermentative degradation.

[0024] With regard to protecting the horticultural product that needs to breathe or control its metabolism, it is noted that it is advantageous if these means of the control system are able to accomplish this without the need to introduce air from the outside through a diagram ( gas inlet) for pressure measurement or without the need to draw CO2 through a semipermeable membrane.

[0025] Another advantageous aspect of the method or system of the present invention is also that it is also not necessary to estimate a leakage parameter (k). This is an improvement as the value of k can vary over time so multiple estimates are needed separated in time as k is a function of the confined space load, temperature and pressure or pressure difference between the confined space and the environment. Another advantage of the system of the present invention is that to detect product breathing in the confined environment it is not necessary to turn off the temperature control during the measurement and seal the leak substantially tight during the measurement and/or keep the atmosphere moving and/or adjust the pressure by N2, so that it is only possible to do it at certain time intervals (>1 h). Especially in this classic system, there are several days between measurements.

[0026] The object of the present invention is to provide a method or system for controlling the metabolism of a product, and in particular for protecting it against a metabolic disorder or against fermentative degradation, which is less complex, time-consuming and more accurate.

[0027] According to the present invention, a control system is provided to control horticultural products that need to breathe in a confined environment, said control system comprising an operator/actuator, a gas analyzer and an atmospheric pressure sensor, and a control unit adapted to receive the signals from the gas analyzer and atmospheric pressure sensor and adapted to generate an output signal responsive to a change in gas composition and pressure in the confined environment, which output signal triggers the operator/actuator to adjust the gas composition in the confined environment, characterized by the fact that the control unit is designed 1) to calculate a metabolic coefficient as a function of the gas composition measured in the confined environment and as a function of the pressure in the confined environment, whose metabolic coefficient is determined by the control unit at least as a function of gas composition and pressure for at least two consecutive times for a selective period of time in the confined environment, 2) as a function of the metabolic coefficient calculated to determine an adjusted gas medium composition and 3) to generate an output signal that triggers the operator/actuator to control the breathing product. In this system, the gas analyzer is indicative of a level or composition of the atmosphere in the confined environment and the atmospheric pressure sensor or gas pressure sensor is indicative of an atmospheric pressure in the confined environment. In a particular embodiment, the control unit is adapted to continuously receive signals from the gas analyzer and the atmospheric pressure sensor. Using an inventive system, it is possible to calculate the metabolic rate in real time. A metabolic coefficient, which is a function of the rate of oxygen consumption and the rate of carbon dioxide production of the product, has the inherent ability to characterize respiration and fermentation of the product.

[0028] In this system, the control unit is designed to generate an output signal to control the horticultural product that needs to breathe. This output system is designed to generate an output signal to control the metabolic activity of the product, to protect the product against metabolic disturbances, to protect the product against degradation, to protect the product against fermentative degradation.

[0029] In another aspect, the present invention also provides a temperature sensor and a control unit adapted to receive signals from the temperature sensor and adapted to generate a temperature-responsive output signal.

[0030] In another aspect, the present invention further provides a volumetric sensor and a control unit adapted to receive signals from the volumetric sensor and adapted to generate an output signal responsive to volume.

[0031] In another aspect, the present invention provides a control unit further adapted to continuously receive temperature sensor signals and adapted to generate an output signal responsive to temperature.

[0032] In another aspect, the present invention provides a control unit which is further adapted to continuously receive signals from the volumetric sensor and adapted to generate an output signal which is responsive to volume.

[0033] An example of an atmospheric pressure sensor suitable for the present invention is a barometric pressure sensor.

[0034] Some of the systems described above can be contained as a system, in which the control unit is arranged to determine the composition of the adjusted gaseous medium based on a mathematical model of the system that uses at least the measured gas composition and the pressure at least two consecutive times during a selective time period in the confined environment to calculate in real time a metabolic coefficient; in which the composition of the adjusted gaseous medium is determined as a function of the metabolic coefficient calculated in the confined environment, in which the metabolic coefficient is calculated in real time as the solution of the following system of equations: with the rate of change with time, xa measured mole fraction of gas i in the confined environment, P the measured pressure in the confined environment, V the volume of the confined space, T the temperature in the confined environment, R the universal gas constant, m the mass of the respiratory product in the confined environment, ri is the rate of gas exchange with the metabolically active product, and f(ri) a defined mathematical function of the ri values. The molar fraction is defined by the function H which states that H = 0 when is greater than or equal to 0 and H = 1 when is less than 0.

[0035] In order to overcome the disadvantage cited above, some of the systems described above can be contained as a system in which the control unit is arranged to determine the composition of the adjusted gaseous medium based on a mathematical model of the system it uses, at least the measured gas composition and pressure at least twice consecutively during a selective time period in the confined environment to calculate in real time a metabolic coefficient; in which the composition of the adjusted gaseous medium is determined as a function of the metabolic coefficient calculated in the confined environment, in which the metabolic coefficient is the respiratory quotient of the respiratory product and the gases are O2, CO2 and N2; where the metabolic rate is calculated in real time as the solution of the following system of equations: with the rate of change with time, xi the measured mole fraction of gas i in the confined environment, P the measured pressure in the confined environment, V the volume of the confined space, T the temperature in the confined environment, R the universal gas constant, ma mass of the horticultural product that needs to breathe in the confined environment, is the rate of oxygen consumption of the fruit and vegetable product that needs to breathe and r is the carbon dioxide production rate of the fruit and vegetable product that needs to breathe. The molar fraction is defined by the function H which states that H = 0 when is greater than or equal to 0 and H = 1 when is less than 0.

[0036] In order to overcome the disadvantage cited above, some of the systems described above can be contained as a system in which the control system comprising at least one gas analyzer and at least one atmospheric pressure sensor connected to a control unit disposed to determine a composition of the adjusted gaseous medium of the confined storage environment to protect the product from fermentative degradation; and at least one operator/actuator arranged to adapt the gaseous medium in the confined storage environment based on said determined adjusted gaseous medium composition; in which the control unit is arranged to determine the composition of the adjusted gaseous medium based on a mathematical model of the system that uses at least the composition and pressure of the gas measured on two consecutive occasions during a selective period of time in the environment of confined storage defined to calculate, in real time, a metabolic coefficient - which is a function of the rate of oxygen consumption and the rate of carbon dioxide production of the product that defines respiration and fermentation; where the composition of the adjusted gaseous medium is determined as a function of the metabolic coefficient (MC) calculated in the confined storage environment, where the metabolic coefficient is calculated in real time as the solution of the following system of equations: with the rate of change with time, xi the measured mole fraction of gas i in the confined environment, P the measured pressure in the confined environment, V the volume of the confined space, T the temperature in the confined environment, R the universal gas constant, ma mass of the horticultural product that needs to breathe in the confined environment, is the rate of oxygen consumption of the fruit and vegetable product that needs to breathe and is the production rate of carbon dioxide from the fruit and vegetable product that needs to breathe. The molar fraction is defined by the function H which states that H = 0 when is greater than or equal to 0 and H = 1 when is less than 0.

[0037] In a practical embodiment, these systems according to the present invention control the gas composition in relation to at least one of the following gases: oxygen, carbon dioxide, nitrogen, ethanol, acetaldehyde, ethylene, ethane, acetone.

[0038] In another embodiment of the invention, the function for the metabolic coefficient is a linear or non-linear function of the metabolic exchange rates of different relevant gases with the product.

[0039] In yet another embodiment of the invention, the pressure and gas composition in the defined confined storage environment are measured continuously over a certain period of time.

[0040] In yet another embodiment of the invention, the pressure and gas composition in the defined confined storage environment are measured periodically with a fixed or adaptive time interval over a certain period of time.

[0041] In yet another practical embodiment, the system according to the present invention comprises that the total measurement time and the time intervals between subsequent measurements of gas composition and pressure are optimized so that the gas composition and the pressure signals contain a maximum amount of information on the metabolic rates of respiration and fermentation and the lowest possible measurement noise. In addition, the measured gas composition and pressure signals undergo signal processing to filter out the measured noise.

[0042] In yet another embodiment of the invention, in addition to the metabolic rates of respiration and fermentation, the error of the estimated metabolic rates and the metabolic coefficient is also calculated.

[0043] In yet another aspect, the present invention provides, in the system according to any of the above embodiments, the calculated metabolic rates and/or metabolic coefficient are subject to evaluation based on the validity criteria based on the calculated errors of the metabolic rates, metabolic rate and blood pressure.

[0044] In yet another aspect, the present invention provides, in the system, according to any of the previous embodiments, the flows of oxygen gas, carbon dioxide gas and nitrogen gas, both from the confined space environment to the confined space itself , as well as the confined space to its environment, due to leakage, are considered to calculate the metabolic coefficient.

[0045] The system, according to any of the above embodiments, in which the flux of carbon dioxide, due to leakage from the environment into the confined space, can be neglected by the control algorithm when calculating the metabolic coefficient.

[0046] In yet another aspect, the present invention provides, in the system according to any of the foregoing embodiments, the control system is adapted to calculate the adjusted gas composition as a function of the determined metabolic rates or coefficients.

[0047] In yet another aspect, the present invention provides, in the system according to any of the foregoing embodiments, the control unit is adapted to compare the calculated metabolic coefficient to the starting point value of the metabolic coefficient, its integral or its differential and in which the control unit is adapted to compare the CO2 level to the maximum tolerable concentration of the production, for example fruit or the control unit is also adapted to compare the calculated metabolic coefficient to the starting point value of the coefficient metabolic rate, its integral or its differential and in which the control unit is adapted to compare the O2 level to the minimum tolerable concentration of the production, for example fruit or the control unit is also adapted to compare the calculated metabolic coefficient to the value of metabolic rate threshold and at which the control unit is adapted to compare the O2 level to the minimum tolerable concentration of production, instance fruit.

[0048] In yet another aspect, the present invention provides, in the system according to any of the above embodiments, the determined metabolic rates or metabolic coefficient are used to calculate the adjusted gas composition, wherein the gas composition in the confined space is maintained as a fixed composition.

[0049] In yet another aspect, the present invention provides, in the system according to any of the above embodiments, the control unit comprises a PID controller to automatically calculate the composition of the future gaseous medium necessary to maintain the metabolic coefficient at safe levels .

[0050] In yet another aspect, the present invention provides, in the system according to any of the above embodiments, the control unit comprises a PID controller for automatically calculating the composition of the future gaseous medium required to maintain the metabolic coefficient at a certain reference value.

[0051] In yet another aspect, the present invention provides, in the system according to any of the above embodiments, the control unit comprises a predictive control model (MPC) for automatically calculating the composition of the future gaseous medium required to maintain the metabolic rate at safe levels.

[0052] In yet another aspect, the present invention provides, in the system, according to any of the previous embodiments, the operating or actuation means for adapting the gas composition in the confined storage environment comprising a means for draining at least one gas for said confined storage environment and a means for purifying at least one gas, such as CO2 or Ethylene.

[0053] Some of the systems described above can be contained as the confined space subject to control, can have a constant volume; confined space subject to control, may have a constant temperature; confined space is a reservoir within another confined space, such as a storage room; the control system does not need to seal off the confined storage environment or part of the confined storage environment from gas flow into or out of the confined storage environment to or from the outside environment; control system does not have to estimate model parameters with uncertainty that can lead to introducing errors in estimates of metabolic rates of respiration and fermentation and the metabolic coefficient and the control system does not need to estimate a leak coefficient, equivalent leak diameter, pressure difference or dynamic pressure drop curve.

[0054] The present invention provides a system according to any of the above embodiments, whereby only the internal pressure is used for calculating the leakage flow without an estimate of the leakage parameter (k); therefore, due to the mathematical model of leakage disturbance correction based on pressure-triggered leakage, no equivalent leak hole diameter needs to be calculated or whereby the dynamic control of the relative gas composition in the confined environment is directed rather than the composition fixed relative gas.

Detailed Description

[0055] The following detailed description of the invention refers to the accompanying drawings. The same reference numerals in different drawings identify the same or similar elements. Furthermore, the following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims and equivalents thereof.

[0056] Various documents are cited throughout the text of this descriptive report. Each of the documents contained in this document (including manufacturer's specifications, instructions, etc.) is incorporated into this document by reference; however, there is no admission that any document cited is, in fact, prior art of the present invention.

[0057] The present invention will be described in relation to the particular embodiments and with reference to certain figures, but the invention is not limited thereto, but only by the claims. The figures are only schematic and are not limiting. In the figures, the size of some elements may be exaggerated and not drawn to scale for illustrative purposes. Dimensions and relative dimensions do not correspond to actual reductions for practicing the invention.

[0058] Furthermore, the terms first, second, third and the like in the description and claims are used to distinguish between like elements and not necessarily to describe a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in sequences other than those described or illustrated herein.

[0059] Furthermore, the terms top, bottom, over, below and the like in the description and claims are used for descriptive purposes and not necessarily to describe relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations described or illustrated herein.

[0060] It should be noted that the term "characterized by the fact that it comprises", used in the claims, should not be interpreted as being restricted to the means enumerated below; this does not exclude other elements or steps. Therefore, it should be interpreted as specifying the presence of the aforementioned features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "device characterized by the fact that it comprises means A and B" should not be limited to devices consisting only of components A and B. This means that, in connection with the present invention, the only relevant components of the device are A and B.

[0061] Reference throughout this specification to "an embodiment", "the embodiment" means that a particular feature, structure or characteristic described in relation to the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in a modality" or "in modality" in various places throughout this specification are not necessarily referring to the same modality, but they may be. Furthermore, the particular features, structures or characteristics may be combined in any suitable way, as would be apparent to one of ordinary skill in the art of this disclosure, in one or more embodiments.

[0062] Likewise, it should be understood that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof with the aim of simplifying the description and helping in understanding one or more of the various aspects of the invention. This method of disclosure, however, should not be construed as reflecting an intent that the claimed invention requires more features than are expressly cited in each claim. On the contrary, as the following claims reflect, inventive aspects are found in less than all the characteristics of a single embodiment previously described. Accordingly, the claims following the detailed description are hereby expressly incorporated into the present detailed description, with each of the claims standing by itself as a specific embodiment of the present invention.

[0063] Furthermore, although some embodiments described herein include some but not other features included in other embodiments, combinations of features from different embodiments are intended to be within the scope of the invention, and form different embodiments, as would be understood by those versed in the technique. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0064] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other cases, well known methods, structures and techniques have not been shown in detail so as not to obscure an understanding of this description.

[0065] Other embodiments of the invention will be apparent to persons skilled in the art by considering the specification and practice of the invention disclosed herein.

[0066] It is intended that the specification and examples are considered exemplary only.

[0067] Each and every claim is incorporated in the specification as an embodiment of the present invention. Thus, the claims form part of the description and are a further description and are in addition to preferred embodiments of the present invention.

[0068] Each of the claims establishes a particular embodiment of the invention.

[0069] The following terms are provided only to aid in understanding the invention.

DEFINITIONS

[0070] The metabolically active product is a whole or part (such as organs, tissues) of a living system that has an active metabolism; this product can be from plants, animals, fungi and micro-organisms.

[0071] Fresh produce that needs to breathe is a whole or part (such as organs, tissues) of a living system that has a respiratory metabolism; this product can be from plants, animals, fungi and micro-organisms.

[0072] The closed environment is any physical enclosure into which the metabolically active product can be placed.

[0073] The storage environment is an example of a closed environment that is used for storage of produce that needs to breathe.

[0074] The metabolic coefficient (MC) is a coefficient that is directly related to the rate at which metabolic processes occur in the active metabolic asset.

[0075] The coefficient of respiration (RQ) is the ratio of the rate of carbon dioxide production to the rate of oxygen consumption for the metabolic reactions that convert carbohydrates to water.

[0076] A controller is a device or system that controls the transfer of data from a computer to a peripheral device and vice versa, in particular the controller is the control unit of the system or device that receives and processes data acquired from the environment confined storage.

[0077] Where in the embodiments of the present invention reference is made to "operating/actuating means" or "operating means" or "actuating means", reference is made to a means for adapting or controlling a gas medium in the operating environment confined storage, for example according to a determined adjusted gaseous medium composition. Such a system can be operated in an automated manner based on control signals from the control unit or it can be operated by an operator based on a control signal output from the control unit.

[0078] Where in the embodiments of the present invention reference is made to "food products that need to breathe", reference is made to a complete living system or part thereof, such as organs, tissues, having a respiratory metabolism; this product can be, for example, from plants, fruits, vegetables, animals, fungi and micro-organisms.

[0079] Where in the embodiments of the present invention reference is made to a confined environment, for example a storage or growth environment, reference is made to any physical enclosure in which the respiratory product can be placed, for example an enclosed space for storing agricultural products or horticultural crops in a controlled atmosphere or for growing agricultural or horticultural products in a controlled atmosphere.

[0080] Where in the embodiments of the present invention reference is made to a "control unit" or "controller", reference is made to a device for controlling the transfer and/or processing of data from a computing device to a peripheral device and vice versa, for example, receiving and processing the data acquired from the confined environment, for example, storage or growth environment.

[0081] Where in the embodiments of the present invention reference is made to "operating/actuating means" or "operating means" or "actuating means", reference is made to a means for adapting or controlling a gas medium in the confined environment , for example for storage or growth of the environment, for example according to a determined adjusted gaseous medium composition. Such a system can be operated in an automated manner based on control signals from the control unit or it can be operated by an operator based on a control signal output from the control unit.

[0082] The following detailed description of the invention refers to the accompanying drawings. The same reference numerals in different drawings identify the same or similar elements. Furthermore, the following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims and equivalents thereof.

[0083] In a first aspect, the present invention relates to a control system and method for controlling the storage of horticultural products that need to breathe in a defined confined environment, for example, storage or growth environment.

[0084] The defined confined environment, for example, storage or growth environment, may be, for example, a room, a container, a box, a box, a bag, a bag of pellets, a conditioned storage platform on a ship , a conditioned trailer and a truck.

[0085] The produce that needs to breathe can be any of those described above, such as plant organs such as fruits, vegetables and flowers or whole plants.

[0086] The confined environment, for example, storage or growth environment, may be subject to variation due to a variation factor in the horticultural product that needs to breathe, due to the condition of the confined environment or a variation thereof and/or due to to storage time.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0087] A typical confined space filled with metabolic active products is shown schematically in FIG. 2. The gas mixture inside the confined space consists of n gases with molar concentration ci. The free volume of the confined space is given by V and the internal pressure is given by P. The temperature in the confined space is given by T. The confined storage space environment is assumed to have a known or measurable gas composition.

[0088] Changes in gas conditions within the confined space are mainly caused by the metabolism of the stored product. However, while confined space walls can be considered perfectly watertight, minor imperfections in the confined space seals and seams can allow gases to pass between the confined space and its environment. The rate of change of the number of moles of the n gases in the confined space is then given by: with on the number of moles of the gaseous component i in the confined space, the time derivative [s-1], ri the metabolic rate of the gas component i of the product [mol kg-1 s-1], which is dependent on the concentrations ci of all n gas components in the confined space [molm-3] as well such as the temperature [K] in the confined space, m the mass of the stored active metabolic product [kg] and qi the gas flows between the confined space and its environment due to leaks [mols-1].

[0089] The pressure in the confined space can then be calculated using the ideal gas law: with P the pressure inside the confined space [Pa], R the universal gas constant [J mol-1 K-1], T the temperature of the confined space [K] and V the free volume of the confined space [m3].

[0090] The mole fraction of each of the gases in the confined space and its environment is defined as: with xi the gas fraction of the gas component i in the confined space, the gas fraction of gas component i in the environment and pi the partial pressure of component i in the confined space.

[0091] A leak model that describes the gas flows due to leaks for the gaseous components i = 1 in the confined space, which takes into account the transport of gas between confined space and environment driven by pressure and concentration was developed, based on mass balances for each of gases in the confined space. The total rate of change of the number of moles of the gas component i ... n in the confined leaking space is given by:

[0092] The first term on the right side of equation 4 represents pressure-driven leakage, while the second term represents concentration-driven leakage. In equation 4, k represents the cold room leakage constant [mol s-1 Pa-1], Di the diffusivity of the gas component i [m2 s-1], Al the leak area of the confined space [m2], δ the wall thickness of the confined space [m], is defined by the function H which states that H = 0 when PP is greater than or equal to 0 and H = 1 when PP is less than 0.

[0093] The model given by equation 4 was used to verify the relative contributions of diffusion and pressure-driven flow to leakage.

[0094] If the diffusion-oriented terms can be neglected, the set of equations 4 can be simplified as:

[0095] The sum of the equations of the set of equations 1 using the ideal gas law leads to:

[0096] Combining equation 5 with equation 6 we get:

[0097] The substitution of equation 7 in equation 5 produces the following expression for gas leak flows:

[0098] The molar fraction is defined by the function Z which asserts that Z = 0 when is greater than or equal to 0 and Z = 1 when less than 0.

[0099] Finally, filling in the expressions for the qi gas flows in the equation, set 1 yields:

[0100] Equation 9 allows you to calculate the changes in the number of moles of the relevant gases in the confined space due to leaks when the rate of change of the internal system pressure and the metabolic rates of the stored product are known. When no product is present in the confined space, changes in the number of moles of gases are determined only by the gas leak, so Equation 9 simplifies to:

[0101] The instantaneous metabolic rate can now be calculated by solving the set of equations 9 and is a function of the metabolic rates of the product:

[0102] While the average value of the metabolic rate over a certain period of time, say, It is given by: where is the mean value of the metabolic rate and represents the time integral.

[0103] The control system is robust against complicating factors (such as, but not limited to changes in temperature, humidity, aging of the product).

[0104] The actual implementation of this system is a considerable reduction in the management efforts of environmental control of the confined space, since it only requires dynamic measurement of pressure and gas concentration in the room, instead of measuring a leak coefficient or implementing systems and additional procedures.

[0105] The actual implementation of this control system can be used for all types of storage environments, such as rooms, halls, factories, containers, boxes, bins, bags, pellet bags, conditioned storage platforms on ships, conditioned trailers and trucks of all sizes.

[0106] It will be apparent to those skilled in the art that various modifications and variations can be made in the construction of the system and method without departing from the spirit or scope of the invention.

[0107] Other embodiments of the invention will become apparent to persons skilled in the art by considering the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the spirit of the invention being indicated by the following claims.

Example 1

[0108] This example refers to the control of the gas composition in a cooled storage room (cold room) for horticultural products that need to breathe, in which the adjusted gas composition is calculated based on the respiratory quotient (RQ) as metabolic coefficient . RQ is defined as the ratio of the carbon dioxide production rate to the oxygen consumption rate of the stored product. It is a measure for low oxygen stress. When the stored product does not have low oxygen stress, the RQ has a low value, usually around 1, but when low oxygen stress occurs, the RQ shows a sharp increase, which makes it a good indicator of low oxygen stress. oxygen. The objective of using RQ to control the gas composition in a storage room for fresh produce that needs to breathe is therefore to store the optimum adjusted gas composition, without causing low oxygen stress on the fruit, to preserve quality during the storage.

[0109] A typical RQ-DCA storage room filled with fruit is shown schematically in FIG. 3. It is assumed that the gas mixture inside the room consists only of O2, CO2 and N2 gases with gas partial pressures , respectively. The effect of other gas components on the composition of the gas mixture is assumed to be negligible. Water vapor is excluded, since it follows from the psychrometric chart that the partial pressure of water vapor is in any case less than 0.6 kPa. The free volume of the cold room is given by V and the internal pressure is given by P. The temperature in the cold room is assumed to be uniform and constant. The cold room environment is assumed to be at ambient conditions, with atmospheric partial pressures of O2, CO2 and N2 gases given by . The total atmospheric pressure is given by Pa.

[0110] Changes in gas conditions within the cold room are mainly caused by fruit respiration. However, although the cold room wall panels can be assumed to be perfectly watertight, small imperfections in the seals and joints in the room can allow gases to pass between the cold room and the environment. Gas flows of O2, CO2 and N2 are given by , respectively. The rate of change of the number of moles of the relevant gases in the cold room is then given by: with nt the number of moles of the gas component i in the cold room, the time derivative [s-1], the rate of oxygen consumption by the fruit [mol kg-1 s-1], and the rate of carbon dioxide production by fruits [mol kg-1 s-1], both dependent on partial pressure of O2 gas in the cold chamber [Pa], and the partial pressure of the CO2 gas inside the cold room, m of the stored fruit mass [kg] and the gas flows of O2, CO2 and N2 due to leaks [mol s-1].

[0111] The pressure in the cold room can then be calculated using the ideal gas law: with P the pressure inside the cold room [Pa], R the universal gas constant [J mol-1 K-1], T the air temperature in the cold room [K] and V the free volume of the installation [m3].

[0112] The gas fraction of each of the gases in the room and atmosphere is defined as: with Xi,r the gas fraction of the i gas component in the cold room, Xi,a the gas fraction of the i gas component in the ambient atmosphere and Pi,r the partial pressure of the i component in the cold room.

[0113] A leak model describes gas transport by pressure and concentration between the cold room and the environment based on mass balances for each of the relevant gases in the cold room. The total rate of change of the number of moles of the relevant gases in the cold room per leak is then given by:

[0114] The first term on the right side of equation 16 represents pressure driven leakage, while the second term represents concentration driven leakage. In equation 16, k represents the cold room leak constant [mol s-1 Pa-1], is defined by the function H which states that H = 0 when PP is greater than or equal to 0 and H = 1 when PP is less than 0.

[0115] Di is the diffusivity of the gas component i in air at atmospheric pressure at 274.15 K [m2 s-1], Al is the leak area of the cold room [m2] and δ the wall thickness of the cold room [m ]. The model given by equation 16 was used to verify the relative contributions of diffusion and pressure-driven flow to leakage.

[0116] If the diffusion-oriented terms can be neglected, the set of equations 16 can be simplified as:

[0117] The sum of the equations of the set of equations 13, using the ideal gas law and assuming that the temperature and the free volume in the cold room are constant, leads to:

[0118] Combining equation 17 with equation 18 we get:

[0119] The substitution of equation 19 in equation 17 produces the following expression for gas leak flows:

[0120] The molar fraction is defined by the function Z which asserts that Z = 0 when is greater than or equal to 0 and Z = 1 when less than 0.

[0121] Finally, filling in the expressions for the gas flows of O2, CO2 and N2 in equation 13, we obtain:

[0122] Equation 21 allows you to calculate the changes in the number of moles of the relevant gases in the cold room due to leaks when the rate of change in the internal system pressure and the respiration rates of the fruit are known. When no fruit is present in the cold room, changes in the number of moles of the relevant gases are determined only by the gas leak; therefore, equation 21 simplifies to:

[0123] The respiratory quotient (RQ) is defined as the ratio between the CO2 production rate and the O2 consumption rate. It can be estimated by dividing the change in CO2 concentration by the O2 concentration in the cold room over a certain time interval. As the partial pressure of ambient CO2 and O2 are typically lower and higher than that of the cold room, respectively, leakage causes the RQ to be overestimated and may even become negative. Your estimate can be corrected for measured changes in respiratory gases that are not due to breathing but due to cold room leakage. We start by rearranging the last equation of the set of equations 19, which describes the rate of change of moles of N2 gas in the room and contains only information about the leak:

[0124] Replacing the last equation of the set of equations 19 by the first two equations produces:

[0125] We now rearrange equation 24 and use the ideal gas law to obtain:

[0126] Finally, using the definition of RQ results in:

[0127] Equation 26 is an expression for instantaneous RQ at a given time and is therefore written as a function of time derivatives describing the instantaneous changes in partial pressure of O2, CO2, and N2 in the cold room and total internal pressure . Equation 26 was solved using a Backward Euler numerical scheme to obtain momentary RQ values RQ(t). In practice, one is often interested in the average value of RQ(t) over a certain period of time. For this, we define the mean RQ of the fruit stored, say, in a time interval , which is the measurement period of the RQ, as:

[0128] For validation of pressure-based leakage correction, storage containers and RQ-DCA control units were used for automatic RQ-DCA control. The simplified leak model given by equation 22 was validated using an empty storage vessel with a volume of 0.4 m3. CA conditions were set to typical RQ-DCA conditions of 0.4 kPa O2 and 1.3 kPa CO2. Subsequently, AC and temperature control were disabled for a period of 2 hours, during which O2, CO2 and internal pressure P were monitored. Measurements were performed during 2 h of decrease as well as 2 h of increase in atmospheric pressure. Equation 22 was used to predict changes in gas partial pressures using the measured internal pressure as input. Subsequently, the predicted changes in the gas composition were compared to the measured changes in the partial pressure of the gas. In a second step, RQ estimates of stored product with and without pressure-based leakage correction were compared. Here, real-time estimates of RQ with and without leak correction, the storage container was loaded with 4 European Standard Packaging (EPS) boxes each loaded with 19 ± 0.5 kg of Braeburn apple fruit (Malus x domestica Borkh cv Braeburn). The apples were harvested on October 1, 2014, south of Toulouse (France). Unselected apples were refrigerated and transported by refrigerated transport to the laboratory, where they arrived on October 3, 2014, at a temperature of 6°C.

[0129] O2 control was conducted according to the RQ-DCA control algorithm using RQ estimates with leak correction. In summary, the partial pressure of O2 in the storage vessel was reduced by 0.05 kPa if RQ was less than 2. When the RQ was greater than 2, the partial pressure of O2 was increased by 0.1 kPa. However, for the control system to act, the measured RQ had to be valid. If this were not the case, the O2 recovery time was not adapted. RQ values with leak disturbance correction were used for O2 control. Simultaneously with RQ estimates with leakage disturbance correction, RQ estimates without leakage correction were recorded and compared with RQ estimates with leakage correction.

[0130] FIG. 4 illustrates the results of the validation experiment using an empty storage container. It shows the measured pressure in the empty storage container (full line) and the measured atmospheric pressure (dashed line) as a function of time over a 2 hour time period, as well as the partial pressures of O2 and CO2 measured and predicted using the leak correction model during an increase in internal pressure (Fig. 4 (a)) and during a decrease in internal pressure (Fig. 4 (b)) in a typical ACD condition of 0.5 kPa O2 and 1, 5 kPa CO2. FIG. 4(a) clearly indicates that the pressure inside the cold room increased when the atmospheric air pressure increased. The inner vessel pressure increased from 1006.19 hPa to 1009.28 hPa in response to an increase in atmospheric pressure from 1006.7 hPa to 1009.22 hPa over a 2 h time period. As the storage container used in the validation experiment did not contain fruit, the O2 partial pressure increased as a function of time, from an initial value of 430 Pa to a final value of 490 Pa during the experiment, due to an influx of atmospheric air. of the environment in the cold room, as shown by the light blue line in FIG. 4(a). The full line shows the predicted partial pressure of O2 in the storage vessel as a function of time using the leak correction method developed. The predicted and measured O2 partial pressures differ only within the resolution range of the used sensor (10 Pa). The CO2 partial pressure remained constant at 1330 Pa over the 4 hour time period as indicated in FIG. 4 (a) by the complete line with the symbols o. The full line without the symbols shows the CO2 partial pressure predicted using the leak model developed. Here too, the predicted and measured CO2 partial pressures only differ from each other within the resolution range of the used sensor. The excellent correlation between the measured and predicted partial pressures of O2 and CO2 in the validation experiment indicates that the leak model developed performed well. When comparing the measured changes in partial pressures of O2 and CO2 during the two hours of increase in atmospheric pressure, it can be seen that the change in partial pressure of O2 was significantly greater compared to the partial pressure of CO2 .

[0131] As illustrated in FIG. 4(b), during the decrease in atmospheric pressure, the pressure inside the storage vessel decreased from an initial value of 1022.18 hPa to a final value of 1021.50 hPa in response to a decrease in atmospheric air pressure of 1022.20 hPa to 1021.54 hPa over a time period of 2 h (Figure 4 (b)). The partial pressure of O2 in the storage vessel decreased from a partial pressure of 460 Pa to 450 Pa over the 2 h period. The CO2 partial pressure decreased from a partial pressure of 1010 Pa to 1000 Pa over the 2 h period.

[0132] The excellent fit of the simulated gas composition using the pressure-based leak model to the gas composition measured in the validation experiment can be explained by looking at the physical nature of the processes driven by pressure and concentration. According to state of the art gas tightness recommendations, leakage areas smaller than 2 x 10-5 m2 per m3 of storage volume and preferably smaller than 1.5 x10-5 m2 m-3 are recommended (Veltman , 2013). In addition to the area over which transport takes place, a second parameter that determines the rate of diffusion of respiratory gases into and out of the cold room is the Fick diffusivities for O2 and CO2 in air at atmospheric pressure. These diffusivities are typically of the order of magnitude 10-5 m2 s-1. From eq. 4, it follows that the time constant of the δ diffusion process(es) Filling in the O2 or CO2 diffusivities together with the values for Al and δ gives out a value of 7.14 x 1013 s. This is a very large value, indicating that the diffusion process is very slow.

[0133] Pressure differences between the cold room and the environment due to changes in atmospheric air pressure create a source of momentum, leading to the movement of a large gas flow between the cold room and the environment at a much higher rate . As shown by equation 17, the rate at which gas exchange between the cold room and the environment occurs is proportional to the pressure difference, with the k-value [mol s-1 Pa-1] as a constant of proportionality. The time constant of the V diffusion process(es) Tpres is given by . Filling the used kRT storage container volume (0.4 m3) together with the estimated k-value, gas constant and temperature yields a value of 1.17 s. The time constant of the pressure leak was found to be 13 orders of magnitude smaller, indicating that the pressure triggered leak is much faster. Therefore, leakage from post-harvest storage facilities can be considered a pressure-driven process.

[0134] FIG. 5 illustrates the real-time application of the pressure-based leak correction model to obtain RQ estimates over a 4-day time period in the storage vessel loaded with Braeburn apple. FIG. 5 (a) represents the evolution of the internal pressure in the apple-filled storage vessel as a function of time over a period of 4 days, while (b) shows the corresponding O2 set point and measured O2 partial pressure and (c) the measured RQ values. When atmospheric air pressure remains constant or decreases, the RQ estimates with and without leak correction are nearly equal, as illustrated by the first 4 RQ measurements in Figure 5(c). Subsequently, when atmospheric air pressure increases, the estimated RQ without leakage correction (eq. (17)) suddenly deviates from the estimated RQ with leakage correction (eq. (15)). Depending on the rate of change of pressure, the RQ without leak correction is now negative or greater than the RQ with leak correction. This is illustrated by the 5th to 7th RQ measurement, respectively, in FIG. 5(c). Furthermore, it can be seen that the developed leak correction application provides estimates of RQ during the increase in atmospheric air pressure with the same RQ value as the RQ value obtained during the previous RQ measurement period while the pressure of atmospheric air was decreasing as shown in FIG. 5(c) by the 7th and 8th RQ measurements. This confirms that the developed leak correction is reliable and produces accurate RQ estimates during both decreasing and increasing atmospheric air pressures.

[0135] FIG. 5(b) shows the result of the RQ-DCA control of the partial pressure of O2 in the storage vessel based on the leak corrected RQ estimates obtained. From the first six RQ measurements in FIG. 5(b), the RQ estimates were below the threshold value of 2, the O2 partial pressure decreased by 0.05 kPa after each measurement. This led to a gradual increase in RQ until low O2 tension was detected by RQ estimates greater than 2 by the 7th and 8th RQ estimates. The O2 partial pressure was subsequently increased by 0.1 kPa until the estimated RQ dropped back below 2, indicating relief from the low O2 tension. This process was repeated continuously for a period of 4 d.

[0136] In FIG. 5, it has been shown that large errors occur in the estimation of RQ when cold room leakage is not taken into account. The large errors found offer a plausible explanation for the highly pressure-dependent RQ estimates. Furthermore, they explain the high variation in RQ measurements reported in other recent field surveys, where the RQ of stored fruit was estimated based on measured changes in O2 and CO2 gas partial pressure over a 24 h period and the cold room leakage was not taken into account [1], [2].

[0137] RQ estimates without leak correction tend to overestimate the actual RQ value of the stored fruit, leading to false signals of low O2 tension in the stored fruit. As a consequence, the O2 partial pressure in the cold room will be increased. This leads to an increase in the number of control actions (increased use of O2 and N2 gas) and, therefore, an increase in the variable cost of storage in RQ-DCA. Furthermore, the energy efficiency of RQ-DCA storage will be reduced, since a higher O2 partial pressure in the cold room increases respiration and therefore heat production. Finally, storing fruit at a higher O2 partial pressure can cause suboptimal keeping quality during storage.

[0138] FIG. 5 also showed that a large discrepancy between RQ estimates with and without pressure-based leak correction is observed when internal pressure increases, but not when internal pressure decreases. When atmospheric air pressure increases over time, the cold room is under a small amount of pressure relative to the environment. Ambient air then flows into the cold room, leading to increased internal pressure and can significantly change the internal gas composition. As noted, the effect of the influx of gas with atmospheric composition into the storage vessel had a different effect on the partial pressure of O2 and CO2. The difference in partial pressure between the inside of the storage vessel and the environment is much greater for O2 than for CO2. Therefore, the effect of the inflow of a certain amount of atmospheric air into the storage vessel has a greater effect on the change in partial pressure of O2 compared to the change in partial pressure of CO2.

[0139] During the decrease in atmospheric pressure, both the partial pressure of O2 and the partial pressure of CO2 decreased slightly. Note that the composition of the gas inside the storage vessel has not changed. Because during decreases in atmospheric air pressure, the cold room is at a small overpressure relative to its environment, the air with the composition of the gas mixture inside the storage container flows into the environment and does not affect the composition of the gas mixture inside the storage container. Since the partial pressure is the combined effect of the gas fraction and the total pressure, this led to a slight decrease in the internal gas partial pressure for both O2 and CO2. Therefore, it is shown that RQ estimates without pressure correction are reliable only during the decrease of the internal pressure of the storage facility, i.e., when the composition of the storage atmosphere is not changed by leakage. RQ estimation with leakage correction was able to estimate the stored fruit RQ under all circumstances.

Example 2

[0140] This example concerns an analysis of the error made by the estimated RQ with and without leak correction based on pressure and a comparison of the errors made with the actual RQ value of the stored respiratory products.

[0141] The relative error of the RQ calculation with and without pressure-based leakage correction was calculated using a validated respiration model of the 'Braeburn' apple. Errors were later compared with the actual RQ value of the fruit. The analysis was conducted for a series of monotonic changes in internal pressure between -250 Pa and 250 Pa, due to leak and respiration rates corresponding to values of 1, 1.5, 2 and 2.5, respectively. A time interval of 4 h was used together with a ratio of fruit volume to cold room volume of 0.16 m3 m-3. The temperature was adjusted to 274.15 K. The respiration model parameters used are listed in Table 1. TABLE 1: Respiration model parameters of intact 'Braeburn' apple at 274.15 K, ± indicates the standard error of the value estimate of the parameter.

[0142] A breathing model of the Braeburn apple (Malus x Domestica cv. Braeburn) was developed. Braeburn fruit respiration rate measurements, in summary, were conducted using 1.7 L flasks. A full factorial design was conducted at 0, 1, 3, 5, 10, and 20 kPa O2 in combination with 0 kPa CO2 and a temperature of 5, 10 and 20°C. The CO2 inhibiting effect on respiration rate was determined at 5, 10 and 20°C in combination with 10 kPa CO2. A non-competitive inhibition model was used to describe the O2 consumption rate: with the maximum rate of O2 consumption [mol m-3 s-1], the partial pressure of O2 [kPa], the partial pressure of CO2 [kPa], the Michaelis-Menten constant for O2 consumption [kPa] and the Michaelis-Menten CO2 inhibition constant is not competitive with the O2 consumption rate.

[0143] The CO2 production rate equation consists of an oxidative respiration and a fermentation part: with RQox or RQ at elevated partial pressure of O2 [-], the O2 consumption rate [molm-3 s-1], the maximum fermentative CO2 production rate and the Michaelis-Menten constant of O2 inhibition in fermentative CO2 production. The effect of temperature was described using the Arrhenius law. The parameters of the breathing model were estimated by fitting equations (28) and (29) to the experimental data using a non-linear least squares regression in Matlab R2015b.

[0144] According to FIG. 6 shows, it has been shown that large errors occur in the estimation of RQ when no pressure-based leak correction is applied. Furthermore, the error was shown to increase with increasing RQ. The smallest errors of RQ estimates without leakage correction were found when the RQ of the stored fruit was equal to 1 (up to 139%), while the largest relative errors (up to 746%) were found when RQ had a value of 2.5 , the maximum investigated RQ. Again, this example shows that the large errors found offer a plausible explanation for highly pressure-dependent RQ estimates. Furthermore, they explain the high variation in RQ measurements reported in other recent field surveys, where the RQ of stored fruit was estimated based on measured changes in O2 and CO2 partial pressure gas over a 24 h period and the leakage of the cold room was not taken into account (V. Both, F. Rodrigo, A. Brackmann, R. De Oliveira, D. De Freitas and R. Wagner, “Effects of dynamic controlled atmosphere by respiratory quotient on some quality parameters and volatile profile of ' Royal Gala ' apple after long-term storage,” Food Chem., vol. 215, pp. 483-492, 2017; A. Weber, A. Brackmann, V. Both, E. P. Pavanello, R. D. O. Anese and F. Rodrigo , “Respiratory quotient: innovative method for monitoring ' Royal Gala ' apple storage in a dynamic controlled atmosphere,” Food Science And Technology, February Issue, pp. 28-33, 2015).

Example 3

[0145] This example refers to the calculation of the standard error of the RQ estimates obtained and subjecting them to the test to meet the validity criteria. The standard error of the RQ estimate is calculated each minute based on the estimated standard errors of the time derivative approximations in equation 26, as illustrated in FIG 7. The standard error of the time derivative approximations needed to calculate the RQ estimate are calculated every minute. Standard errors are used to statistically test whether the measured changes in gas composition and pressure represented by approximations of the time derivatives in equation 26 are significant. In this case, the RQ estimates are calculated along with the standard error of the RQ estimate.

[0146] For the control system to take action, the estimated RQ value will be tested to meet the validity criteria. The validity criteria used by the control system are: • The leak-corrected O2 rate change based on pressure as a function of time must be negative, • The leak-corrected CO2 rate of change based on pressure as a function of time must be positive, • The leak-corrected O2 rate change based on pressure as a function of time must be statistically significant, • The leak-corrected CO2 rate of change based on pressure as a function of time must be statistically significant, • The RQ value obtained must be greater than a lower threshold value, • The internal confidence of the RQ estimate must not contain 0. Disclaimer 1. The proposed control method based on the metabolic rate of the product takes into account the gas exchange dynamics of the product as well as the gas exchange dynamics of the storage environment, continuously measuring gas composition and pressure changes. 2. Control is based on a mathematical model that calculates product metabolic rates from measured dynamic changes in gas composition and pressure, without the need to independently determine a leak parameter. 3. The control system does not require that the conditions of the confined system, in particular atmospheric pressure, be modified to compensate for leakage during the measurement period. 4. The control system calculates the metabolic rate error to ensure robust system operation. 5. The control system will automatically adapt the gas concentrations in the storage environment when changes occur in the metabolic activity of the product, when the amount of product in the confined environment changes, when the gas and temperature conditions in the confined environment change, or when the design or structure of the confined environment changes. 6. The control system can be applied to any metabolic product and any confined system. 7. The control system is not limited by restrictions on temperature, humidity, gas concentration, quantity and type of product, or dimensions of the confined space.

Description of Figures BRIEF DESCRIPTION OF THE FIGURES

[0147] The present invention will become more understandable from the detailed description given below and the accompanying drawings which are provided for illustrative purposes only and therefore are not limits to the present invention, and in which:

[0148] FIG. 1 is a schematic view showing the details of the pressure-corrected control system based on a software-aided measurement system and control algorithm. The metabolically active product (a) is contained in a confined environment (b). The pressure is measured with a pressure sensor (c) and the gas composition with a gas analyzer (d). Signals from the pressure sensor and gas analyzer are used by the control unit (e) to calculate a product metabolic rate (a) which is used to calculate an output signal. The output signal from the control unit triggers the operator/actuator (f) to adjust the gas composition in the confined environment using a gas supplied by a gas control unit (g).

[0149] FIG. 2 is a schematic view of a confined space. The confined space contains active metabolic products with mass M. The number of moles of the n different gases present in the confined space is given by n1 to nn. The confined space has free volume V, temperature T and internal pressure P. Due to its metabolic activity, gases are consumed or produced at a rate from r1 to rn. The immediate environment of the confined space is the pressurePa. Since the confined space is not perfectly gas tight, gas flows due to pressure driven leakage as it occurs, represented by q1 to qn.

[0150] FIG. 3 is a schematic view of a cooled storage room (cold room), indicated by a dashed line to emphasize that the cold room is not perfectly gas tight. The cold room contains respiratory products with mass M. The number of moles of oxygen, carbon dioxide and nitrogen is given by nO2, nnCO2 and nN2 respectively. The cold room has free volume V, temperature T and internal pressure P. Due to its metabolic activity, the fruit is breathing and consuming oxygen and producing carbon dioxide at rates of rO2 and rCO2 respectively. The immediate environment of the cold room, in this case atmospheric air, has atmospheric pressure Pa. Since the cold room is not perfectly gas tight, gas flows due to leakage of oxygen, carbon dioxide and nitrogen gas caused by pressure, represented by qO2, qCO2 and qN2 respectively.

[0151] FIG. 4 represents the partial pressures of O2 atmospheric (full line) and internal pressure (dashed line) and measured (full line) and simulated (full line, symbol o), as well as measured (full line) and simulated (full line, symbol o ) partial pressures of CO2 over a time period of 120 minutes with increasing (a) and decreasing (b) internal pressure during the validation experiment in an empty storage vessel. The simulated gas using the pressure-based leak model fits the measured gas composition excellently, indicating the high accuracy of the pressure-based leak model.

[0152] FIG. 5 shows the results of demonstration of leak-corrected RQ measurement based on pressure and resulting control of apple storage gas composition where (a) shows measured internal pressure, (b) measured partial pressures of O2 from point of fit (dashed and full lines, respectively) and (c) estimation of corresponding RQ with (upward pointing triangle) and without pressure based leakage correction (downward pointing triangle). It is shown that leak-corrected RQ estimates provide reliable RQ values of stored respiratory products during both decreasing and increasing internal pressure, while non-leak-corrected RQ estimates provide reliable RQ values when internal pressure decreases. and there is leakage from the storage space to the environment, not significantly altering the internal composition of the gas.

[0153] FIG. 6: Estimated RQ values of stored apples as a function of pressure changes within the room. The leak correction based on the pressure represented by the green line and without leak correction based on the pressure represented by the red line for different real RQ values of the stored fruit equal to 1.0 (a), 1.5 (b), 2(c) and 2.5(d).

[0154] FIG. 7 illustrates the calculated standard errors of real-time RQ estimates in a storage space containing respiratory products. The standard error of the RQ estimate is calculated every minute for a time period of 240 minutes, based on the standard error of the estimates of the time derivative approximations in equation 26.

Claims (13)

1. Method for controlling respiratory products (a) in a confined environment (b), said method comprising the use of a control system comprising an operator/actuator (f), a gas analyzer (d), a pressure sensor atmospheric pressure (c) and a control unit (e), for adapting or controlling a gaseous medium in the confined environment according to a determined composition of the gaseous medium, and adapted to receive signals from the gas analyzer and atmospheric pressure sensor , and to generate an output signal responsive to a change in gas composition and pressure in the confined environment, which output signal triggers the operator/actuator to adjust the gas composition in the confined environment using gases supplied by a gas treatment unit conventional (g) which may comprise purifiers and generators, the method characterized by the fact that the control unit is designed: 1) to calculate a breathing coefficient (RQ) as a function of the gas composition measured in the confined environment and as a function of the pressure in the confined environment, whose respiration coefficient (RQ) is determined by the control unit based on a mathematical model that at least uses the gas composition and the measured pressure of at least two consecutive times for a selective period of time in the confined environment to calculate, in real time, the coefficient of respiration (RQ), where the mathematical model provides the rate of exchange with time of a quantity of gas (ni) as the rate of exchange (ri) with the respiratory product of that gas, times the mass (m) of the respiratory product, and the exchange of the total amount of gases (n) minus the sum of the exchange rates of all gases times the fraction of gas xi* obtained from the output of the gas sensor. atmospheric pressure, where the respiratory coefficient (RQ) is a defined mathematical function (f) of the rate of exchange (ri) of the gas, and where the gas fraction (xi*) is taken as the fraction of the gas in the atmosphere when the pressure atmospheric pressure is greater than or equal to the pressure in the confined environment, or as the fraction of the gas in the confined environment when atmospheric pressure is less than in confined incorporation, where the coefficient of respiration (RQ) is the respiratory quotient of the respiratory product and the gases are O2, CO2 and N2, and which is calculated in real time as the solution of the following system of equations: with being the rate of change with time, xi being the measured mole fraction dt 3.3 of gas i in the confined environment, P being the pressure measured in the confined environment, V being the volume of the confined space, T being the temperature in the confined environment, R being the universal gas constant, m being the mass of the respiratory product in the confined environment, being the rate of oxygen consumption of the respiratory product being the rate of carbon dioxide production from the respiratory product, and where the mole fraction is defined by the function H which states that H = 0 when is greater than or equal to 0 and H = 1 when is less than 0; 2) to determine an adjusted gaseous medium composition as a function of the respiration coefficient (RQ); and 3) to generate an output signal that triggers the operator/actuator to control the breathing product. 2. Method according to claim 1, characterized in that the control system comprises at least one gas analyzer and at least one atmospheric pressure sensor connected to a control unit arranged to determine an adjusted composition of the gaseous medium of the confined storage environment to protect the product from fermentative degradation and at least one operator/actuator willing to adapt the gaseous medium in the confined storage environment based on said determined adjusted gaseous medium composition in which the control unit is arranged to determine the adjusted composition of the gaseous medium based on a mathematical model of the system that uses at least the gas composition and pressure measured twice consecutively during a selective time period in the defined confined storage environment to calculate, in time real, said respiration coefficient (RQ) which is a function of the oxygen consumption rate and the carbon dioxide production rate of the product defining respiration and fermentation; wherein the adjusted composition of the gaseous medium is determined as a function of the calculated respiration coefficient (RQ) in the confined storage environment; where the coefficient of respiration (RQ) is calculated in real time as the solution of the following system of equations: With being the rate of change with time, xi being the measured mole fraction dt of gas i in the confined environment, P being the pressure measured in the confined environment, V being the volume of the confined space, T being the temperature in the confined environment, R being the universal gas constant, m being the mass of the respiratory product in the confined environment, being the rate of oxygen consumption of the respiratory product and being the rate of carbon dioxide production of the respiratory product; and where the molar fraction is defined by the function H which states that H = 0 when is greater than or equal to 0 and H = 1 when is less than 0. 3. Method according to claim 1 or 2, characterized in that the control system further comprises a temperature sensor and a control unit adapted to receive signals from the temperature sensor and adapted to generate a signal temperature-responsive output. 4. Method according to any one of claims 1 to 3, characterized in that the control system further comprises a volumetric sensor and a control unit adapted to receive signals from the volumetric sensor and adapted to generate a signal volume-responsive output. 5. Method according to any one of claims 1 to 4, characterized in that the control system controls the gas composition in relation to at least one of the following gases: oxygen, carbon dioxide, nitrogen, ethanol, acetaldehyde , ethylene, ethane or acetone. 6. Method according to any one of claims 1 to 5, characterized in that the total measurement time and the time intervals between subsequent measurements of gas composition and pressure are optimized so that the gas composition and the pressure signals contain as much information on the metabolic rates of respiration and fermentation and as little measurement noise as possible. 7. Method according to any one of claims 1 to 6, characterized in that the gas composition and the measured pressure signals are subject to signal processing to filter out the measured noise. 8. Method according to any one of claims 1 to 7, characterized in that, in addition to the metabolic rates of respiration and fermentation, the estimated metabolic rates and the respiration coefficient (RQ) are also calculated. 9. Method, according to any one of claims 1 to 8, characterized in that the metabolic rates and/or coefficient of respiration (RQ) calculated are subject to evaluation based on the validity criteria based on calculated errors of metabolic rates , respiration coefficient (RQ) and pressure. 10. Method according to any one of claims 1 to 9, characterized in that the control unit is adapted to compare the calculated respiration coefficient (RQ) with the reference value of the respiration coefficient (RQ), with its integral or with its differential, in which the control unit is adapted to compare the CO2 level with the maximum tolerable concentration of the product, such as a fruit. 11. Method according to any one of claims 1 to 10, characterized in that the control unit is also adapted to compare the calculated respiration coefficient (RQ) with the reference value of the respiration coefficient (RQ), with its integral or with its differential, in which the control unit is adapted to compare the O2 level with the minimum tolerable concentration of the product, such as a fruit. 12. Method according to any one of claims 1 to 11, characterized in that the control unit comprises a predictive control model (MPC) to automatically calculate the future composition of the gaseous medium necessary to maintain the respiration coefficient ( RQ) at safe levels. 13. Method according to any one of claims 1 to 12, characterized in that the confined space is a reservoir within another confined space, such as a storage room.