US20100273412A1

US20100273412A1 - Ventilation System for a Perishable Goods Store

Info

Publication number: US20100273412A1
Application number: US12/767,223
Authority: US
Inventors: Thomas Geoffrey Coxon Kerr Will
Original assignee: VEGETABLE CONSULTANCY SERVICES Ltd
Current assignee: VEGETABLE CONSULTANCY SERVICES Ltd
Priority date: 2009-04-27
Filing date: 2010-04-26
Publication date: 2010-10-28
Also published as: GB2463747A; GB0907152D0; GB2463747B

Abstract

The present invention provides a ventilation system for a perishable goods store and a method of operating a ventilation system for a perishable goods store. The system of the present invention may monitor and control the temperature and humidity of the goods within the store and comprises a controller for automatically operating the system, a duct through which air is propelled into the store, pressure control means for controlling the pressure within the duct and a pressure monitoring means for measuring the pressure within the duct. The controller monitors the pressure within the duct and controls the pressure control means ensure the air pressure within the duct is maintained within a defined pressure range. The pressure control means may comprise at least one variable speed fan. The present invention is advantageous in that it optimises the back-pressure within the duct, against which the at least fan must act, thereby providing a more efficient ventilation system.

Description

FIELD OF THE INVENTION

The present invention relates to the storage of perishable goods and provides a ventilation system for a perishable goods store and a method of operating a ventilation system for a perishable goods store.

BACKGROUND TO THE INVENTION

Perishable goods are often stored in large quantities within stores. The storage of perishable goods requires control of the environmental conditions in which those goods are stored. For example, in order to maintain the lifespan and quality of many food items it is necessary to store those items within certain humidity and/or temperature limits. Therefore, stores are typically large purpose built or suitably modified buildings that include a ventilation system in order to provide the necessary conditions. A ventilation system may only control the humidity within a store and not the temperature. Similarly, a ventilation system may only control the temperature within in a store and not the humidity. However, most ventilation systems control both the temperature and humidity within a store and are heating and ventilation systems.
There are two main types of storage for perishable goods: bulk storage and box storage. In bulk storage the items are simply stored loose within the store, while in box storage the items are stored within boxes that are then stacked within the store. Heating and ventilation systems for both of these types of stores operate in substantially the same manner, as described below.
A typical heating and ventilation system of a perishable goods store comprises at least one fan located within a fan housing, at least one heater also located within the fan housing and exhaust louvers located around the store. The fan housing has a closable air inlet to the outside of the store such that air may be drawn in from the surroundings when the inlet is open. Furthermore, the fan housing is formed such it may draw air in from the store when the air inlet is closed. To achieve this the fan housing may also have a second closable air inlet to the interior of the store or may be formed such that when the air inlet to the outside of the store is closed air is drawn into the housing from the interior of the store. A second closeable air inlet may be formed as a recirculation louver. Heating and ventilation systems are normally automatically controlled by a controller in order to ensure the conditions within the store remain within defined temperature and humidity ranges.
The fan or fans of a typical heating and ventilation system can be operated to recirculate air around the store and/or to draw in air from the surroundings. This is done in the following manner. Air is drawn into the fan housing from the surroundings and/or from the interior of the store depending upon the degree of opening of the air inlet or air inlets. This air is then blown down a main duct and distributed either into under-floor lateral ducts (in bulk stores) or into plenums aligning the bases of the boxes (in bulk stores) and then into the crop. The opening of the exhaust louvers is controlled to allow the amount of air escaping the store through the louvers to be equal to the amount of air being drawn into the store from the surroundings so to avoid pressurising the store. For example, if air is only being recirculated within the store the exhaust louvers will be closed. Similarly, if air is only being drawn in from the surroundings the exhaust louvers will be open.
The amount of air being recirculated and the amount of air being drawn in from the surroundings is controlled by the controller in order to ensure the perishable goods are stored within a pre-defined humidity range. This is done by monitoring humidity within the store and within the duct. Generally, a heating and ventilation system will comprise a humidity sensor positioned within the duct and a number of humidity probes placed in random positions within the stored goods. The reading of the sensor and the probes is fed to the controller in order to provide a measure of the humidity within the store and the duct. The controller uses the information from the sensor and the probes to control the ratio of the volume of air that is recirculated within a store to the volume of air that is drawn into the store from the surroundings by controlling the degree of opening of the air inlet or air inlets of the fan housing. At the same time, the degree of opening of the exhaust louvers is controlled in order to ensure that the store is not pressurised. Generally, if the humidity within the store is too high the amount of air drawn in from the surroundings will be increased and the amount of air recirculated about the store will be reduced in order to reduce the humidity. Similarly, if the humidity within the store is too low the amount of air drawn in from the surroundings will be reduced and the amount of air recirculated about the store will be increased in order to increase the humidity. This is, of course, dependent upon the humidity of the air surrounding the store. When the air surrounding the store is more humid than this the heater or heaters may be used to reduce the humidity of the air drawn from the surroundings before it is blown into the store. The degree to which the surrounding air can be dried by the heaters depends upon the temperature difference between the set store temperature (as discussed below) and the temperature of the surrounding air. In particular, if the heaters are not operating to heat the store the heaters can be set to heat the air to or below the set store temperature to reduce the humidity of the inlet air. However, this is dependent upon the air surrounding the store also being below the set store temperature. In order to monitor the humidity outside the store a heating and ventilation system may further comprise external humidity monitoring means e.g. one or more external humidity sensors.
The heater or heaters are controlled to maintain the temperature within a store. Specifically, the heater or heaters are turned on when the air temperature within the store duct falls below a set duct temperature such that air being propelled into the store via the duct is heated to at least this set duct temperature. The set duct temperature ensures that excessively cold air is not blown into the store. The heater or heaters are also turned on when the temperature within the store falls below a set store temperature such that air being propelled into the store via the duct is heated to the set store temperature. When the temperature within the duct exceeds the set duct temperature and the temperature within the store exceeds the set store temperature temperature the heaters are turned off. Generally, the temperature within the duct is monitored by means of a temperature sensor placed in the duct and the temperature within the store is monitored by a number of temperature probes placed within the crop in random positions. The set store temperature and the set duct temperature may be the same or the set duct temperature may be lower than the set store temperature.
In order to distribute heat evenly throughout a store, when the heater or heaters are operating the fan or fans are also operated, even if the humidity within the store is within the defined humidity range. However, if the temperature within the store is above the set store temperature and the temperature within the duct is above the set duct temperature but the humidity within the store is outside the limits of the defined humidity range the fan or fans are operated, as described above, but the heater or heaters are not operated unless they are operated to dry the air entering the store.
Importantly, a heating and ventilation system, as described above, operates to maintain the conditions in the store only within a defined humidity range and at the set store temperature. The system is used, and the fan or fans are turned on, only when the humidity falls outside of the relevant range or the temperature in the store or duct falls below a set temperature. When the conditions within the store are within the defined humidity range and the crop is at the set store temperature the heating and ventilation system is not used. It is these defined limits that dictate when the fan or fans and heater or heaters are switched on and switched off. For example, typical limits that are used when storing onions are 65% to 75% relative humidity and a set store temperature of 27° C.
Store heating and ventilation systems function well in that they allow for the relatively long-term storage of perishable goods in a climate controlled environment. However, they use a lot of power and are expensive to run. Additionally, due to the intermittent use of high capacity fans it is often difficult to obtain a uniform temperature and humidity throughout a store. Furthermore, the fan or fans can generate high back pressures within the duct and working against these back pressures can significantly reduce the efficiency of the heating and ventilation system Therefore, there is a need for an improved heating and ventilation system for a store that is more power efficient and that can provide a more uniform temperature and humidity distribution throughout the store.

SUMMARY OF INVENTION

The present invention provides a ventilation system when used with a perishable goods store comprising:
a controller for automatically operating the system;
a duct through which air is propelled into the store;
a pressure monitoring means for measuring the air pressure within the duct; and
pressure control means for controlling the pressure within the duct;
wherein when air is propelled through the duct the controller monitors the duct pressure, as measured by the pressure monitoring means, and controls the pressure control means to ensure that the air pressure within the duct is maintained within a defined pressure range.
The present invention can operate significantly more efficiently than heating and ventilation systems according to the prior art. In particular, the present invention allows the working pressures of a ventilation system to be optimised such that the back pressure within the duct is at an optimal level and the amount of energy wasted operating against the back pressure is minimised. Furthermore, the defined pressure range, and resulting optimal duct pressure, can result in the air being distributed from the duct into the store more uniformly.
Preferably, the pressure range for a specific ventilation system according to the present invention is set such that the pressure within the duct is optimal for the store. Specifically, the pressure range may be defined such that the ventilation system works at optimum efficiency by minimising back-pressure within the duct but still providing good air distribution, thereby allowing relatively quick adjustments to the temperature and humidity of the store. Therefore, the defined pressure range of the present invention that is set is dependent upon the specific heating and ventilation system and the goods being stored. Generally, the optimum pressure range is dependent upon the power of the system, the size of the store and the size and dimensions of the duct and any associated lateral ducts. The goods being stored also affect the optimum defined pressure range. For example, the tolerance of the goods to variations in temperature and humidity and the mode of storage (e.g. curing or simple storage) will affect the pressure range. The pressure range will be between a set upper pressure and a set lower pressure.
In the same manner of as heating and ventilation systems according to the prior art, air is propelled through the duct and into the store if the conditions within the store are outside of the desired parameters, for example if the humidity is outside of the defined range and/or the temperature is too low. However, when system of the present invention is operated and the pressure within the duct falls below the set lower pressure of the pressure range the pressure control means is operated by the controller to increase the pressure within the duct. Similarly, when the system of the present invention is operated and the pressure within the duct rises above the set upper pressure of the pressure range the pressure control means is operated by the controller to decrease the pressure within the duct.
The pressure range of the present invention may be automatically set by the controller based on monitored variables such as the air speed through the goods in the store, the power used by the system, the rate of change of humidity and/or temperature within the store and how full the store is. Alternatively, the pressure range may be manually input into the controller by an operator based upon an assessment of the store and the heating and the ventilation system. Preferably, the controller of the present invention allows manual and automatic alteration of the pressure range during operation of the ventilation system in order to optimise that operation. Manual and/or automatic alteration of the pressure range may be used to ensure there is good air flow through the crop.
A ventilation system according to the present invention will typically run slower and longer than heating and ventilation systems according to the prior art wherein the air pressure within the duct is disregarded and the system is simply turned on or off when necessary without any control of the pressure within the duct. Despite running longer than prior art ventilation systems, the present invention may provide significantly higher energy efficiency and improved air distribution
The pressure control means of the present invention may comprise at least one variable speed fan for propelling air through the duct and into the store. By controlling the speed of the variable speed fan the pressure within the duct may be controlled. Specifically, by increasing the speed of the at least one variable speed fan air will be propelled into the duct at a higher rate thereby increasing the pressure within the duct and by decreasing the speed of at least one variable speed fan air will be propelled into the duct at a lower rate thereby decreasing the pressure within the duct.
The pressure control means of the present invention may comprise a plurality of fans for propelling air through the duct into the store. By operating the plurality of fans individually the pressure within the duct may be controlled. Specifically, when the system is operated at least one of the fans will be switched on and the remainder of the plurality of fans may be individually switched on or off to increase or decrease or the pressure within the duct respectively.
If the pressure control means does comprise a plurality of fans the fans may be operated substantially independently by the controller. Alternatively, it may be preferable that the controller controls the fans to operate in series. That is, when it is necessary to increase the pressure within the duct an additional fan is switched on when all the currently operating fans are operating at maximum speed, rather than operating all of the fans simultaneously and increasing their operating speed. Similarly, when it is necessary to reduce the pressure within the duct individual fans are switched off in turn, rather than operating all of the fans but reducing their operating speed. The skilled person will appreciate that a plurality of fans can be operated in this manner whether they are fixed speed fans, variable speed fans or a mixture of both types.
If the system of the present invention comprises a plurality of fans those fans may be arranged in any manner that is apparent to the person skilled in the art. For example, the fans may be arranged in series in the direction in which air is propelled such that the propelled air passes through each fan. Alternatively, the fans may be positioned substantially adjacent to one another.
It is to be understood that if the present invention comprises a plurality of fans those fans may all be variable speed fans or the plurality of fans may all be fixed speed fans or the plurality of fans may comprise a mixture of fixed and variable speed fans. Any fan of the present invention may be an axial fan or a centrifugal fan or any other type of suitable fan. If the system comprises a plurality fans they may all be the same type of fan or may be a mixture of types of fan. As will be understood by the person skilled in the art, the number and type of fans will be largely dependent upon engineering considerations including energy efficiency, the volume of air required per tonne of crop, the size of the store, the goods that are being stored, the size of the duct, the available power supply and the size of any housing in which the at least one fan is housed.
Additionally or alternatively, the pressure control means of the present invention may comprise controllable openings from the duct. These openings may lead from the duct into lateral ducts (in a bulk store) or into plenums (in a box store). By controlling the degree of opening of the openings the pressure within the duct may be controlled. Specifically, by increasing the degree of opening of the openings the pressure within the duct may be decreased as air will be allowed to escape from the duct at a higher rate and by decreasing the degree of opening of the openings the pressure within the duct may be increased as air will be allowed to escape from the duct at a lower rate.
The present invention may be used in storing any perishable good. The present invention may be used for the long-term storage of food items such as root vegetables e.g. onions, potatoes, red beet etc.
The pressure monitoring means may be any means that is suitable for monitoring the pressure within the duct. Preferably, the pressure monitoring means is a pressure sensor positioned within the duct about one third of the length of the duct from the at least one fan. Positioning an air pressure sensor at this position within the duct provides the best measure of the back pressure within the duct. However, it is to be appreciated that the pressure in the duct may be monitored at any point within the duct and/or at more than one point within the duct.
As will be understood by the person skilled in the art, the control means of the present invention may be a computer control unit that is in electronic communication with the components of the ventilation system. The control unit may be automatic. Additionally, the controller may include manual input means for allowing an operator to vary the operation of the heating and ventilation system. The manual input means may allow an operator to vary the operation of the system for the specific goods being stored or the storing regime being operated (e.g. curing or storing) or for any other storing variable.
The present invention may further comprise a plurality of air speed probes positioned within the goods stored within the perishable goods store for monitoring the air speed through the goods. The information from the air speed probes may be used to ensure that air is being circulated through all of the goods within the store. Additionally or alternatively, information from the air speed probes may be used to control the system. For example, the controller may operate the system to ensure is a specific minimum average air speed through the goods. The air speed probes may be positioned randomly throughout the goods or they may be positioned at regular intervals throughout the goods.
Preferably, the present invention further comprises a fan housing in which any fan is housed. The fan housing may be substantially external to the store, substantially internal to the store or formed as part of the structure of the store. Advantageously, the fan housing will comprise a closeable air inlet that allows air to be drawn into the housing from the surroundings when air inlet is open and wherein the fan housing may draw air into the housing from within the store when the air inlet is closed. This may be achieved by having a second air inlet to the interior of the store. The second air inlet may be a recirculation louver. It is to be understood that, alternatively to having a closeable air inlet to the surrounding formed as part of the housing, a closeable air inlet to the surroundings may be provided away from, but in communication with, the fan housing.
Preferably, the present system may form part of an otherwise conventional heating and ventilation system according to the prior art. In particular, the system of the present invention may include any or all of the following features: humidity monitoring means for monitoring the humidity within the store, humidity monitoring means for monitoring the humidity outside of the store, at least one heater, temperature monitoring means for monitoring the temperature within the store. It is to be noted that a ventilation system according to the present invention may be a ventilation only system that does not monitor or control the temperature within the store. Such a system would not comprise temperature monitoring means or at least one heater. Similarly, a ventilation system according to the present invention may be a heating and ventilation system that monitors and controls the temperature within the store but does not monitor or control the humidity within the store. Such a system would not comprise any humidity monitoring means. Preferably the system of the present invention is a heating and ventilation system and is capable of monitoring and controlling both the humidity and temperature within a store.
If a system according to the present invention does monitor and control the humidity within the store the humidity monitoring means for monitoring the humidity within the store may comprise a humidity sensor positioned within the duct and/or a plurality of humidity probes positioned within the perishable goods within the store. Such a is controlled to operate when the humidity within the store is outside of a defined humidity range such that the humidity within the store is corrected to within the defined range in the same manner as the prior art.
Similarly, if a system according to the present invention is a heating and ventilation system and monitors and controls the temperature within the store the temperature monitoring means for monitoring the temperature within the store may comprise a temperature sensor positioned within the duct and/or a plurality of temperature probes positioned within the perishable goods within the store. Such a system, including the at least one heater, would be controlled to operate and thereby raise the temperature within the store when the temperature within the store is below a set store temperature in the same manner as the prior art. The at least one heater of a heating and ventilation system according to the present invention may be a modulating burner.
It is to be understood that the system of the present invention may be used in the same manner as heating ventilation systems according to the prior art for storing goods for extended periods at a constant temperature and within a constant humidity range or for storing goods within controlled but varying conditions. For example, the system of the present invention may be used for cooling products after an extended period of curing. This can be done by reducing the store set temperature and the store duct temperature at a controlled rate such that the goods within the store are cooled.
A system according to the present invention may further comprise data storage means for recording data from any monitoring means and for recording when and how the components of the system are operated. This is beneficial as analysis of the recorded data may allow optimisation of the system. Furthermore, recorded data is beneficial should the system, for any reason, fail to properly control the environmental conditions within the store, as a failure analysis may then be carried out on the basis of that data.
Preferably the present invention will comprise a plurality of exhaust means located around the store for controlling the exhaust of air from the store such that when the system is in use the volume of air being drawn into the store is substantially equal to the volume of air leaving the store. In the same manner as the prior art the exhaust means may comprise exhaust louvers. Advantageously, the exhaust means are automatically controlled by the controller when the system is operated.
The present invention also provides a method of operating ventilation system of a perishable goods store comprising a duct through which air is propelled into the store, wherein the air pressure within the duct is monitored and pressure control means are used to control the pressure within the duct such that it remains within a defined pressure range.
The method of the present invention is particularly advantageous as it may enable a ventilation system for a perishable goods store to be significantly more energy efficient that was previously possible. It is to be understood that the method of the present invention may further comprise operating any or all of the features of the system of the present invention that are described above. These features may be operated in the manner described above or in the conventional manner that will be immediately apparent to the person skilled in the art.

DRAWINGS

FIG. 1 is a schematic plan view of a bulk onion store including a heating and ventilation system according to the present invention; and

FIG. 2 is a schematic cross-sectional view of the bulk onion store of FIG. 1.

A bulk onion store 1 is shown in FIGS. 1 and 2. Although a bulk store 1 is illustrated it is to be understood that the present invention is equally applicable to box stores. The store 1 has a fan housing 2 located substantially external to the store at a first end of the store. The fan housing 2 contains an axial fan 3 and a main duct 4 extends from an inner end of the fan housing along the centre of the store 1. A modulating burner (not shown) is also positioned within the fan housing 2. A plurality of lateral ducts 5 extend laterally outwards from the main duct 4 under a floor 10 of the store 1.
Temperature, humidity and pressure sensors 7 are positioned within the main duct 4 about one-third of the way along the length of the main duct. Four exhaust louvers 6 are positioned on the side walls of the store 1 near the top of the store. The store 1 has two loading doors 8, one either side of the main duct 4, at a second end of the store opposite the fan housing 2. An onion crop 9 is piled on the floor 10 of the store 1 either side of the main duct 4. Temperature, humidity, and air speed probes 11 are randomly positioned within the crop 9. The store 1 illustrated in FIGS. 1 and 2 is full and the onion crop 9 reaches the top of the main duct 4 but lies below the level of the exhaust louvers 6 such that an air space 12 is provided above the crop 9 and below the roof of the store 1. However, it is to be understood that the store 1 need not be full for the heating and ventilation system to operate. The heating and ventilation system may be operated when the store 1 is only partially full or even when the store empty.
The heating and ventilation system of the store 1 comprises the fan housing 2, the axial fan 3, the modulating burner, the exhaust louvers 6, temperature, humidity and air speed probes 11 and the temperature, humidity and pressure sensors 7. All of these components are in communication with an automatic controller (not shown) of the heating and ventilation system. The probes 11 and sensors 7 communicate their temperature, humidity, pressure and air-speed readings to the controller. The controller uses this information to operate the fan housing 2, the axial fan 3, the modulating burner and the exhaust louvers 6 appropriately. In particular, the fan housing 2 can be controlled to allow air to be drawn in from the surroundings and/or allow air to be drawn in from the store 1. Specifically, the fan housing 2 includes an air inlet from the surroundings and an air inlet from the store 1. The degree of opening of these inlets is controlled to control the proportion of air drawn into the fan housing 2 from the surroundings and from the store 1. The axial fan 3 is a variable speed fan and can be controlled to operate at a suitable speed to draw air in from the surroundings and/or the store depending upon the state of inlets of the fan housing 2 and propel that air along the main duct 4. When the ventilation system of the store is operated, air from the main duct 4 is propelled through the lateral ducts 5 and passes up through the crop through holes formed through an upper side of the lateral ducts 5 and corresponding holes formed through the floor of the store 1. The degree of opening of the exhaust louvers 6 is controlled to ensure that the store is not pressurised and remains at substantially the same pressure as the air pressure outside the store. The flow of air through the store 1 is illustrated in the Figures by the broad arrows. The modulating burner can be operated to heat the air being propelled by the axial fan 3 through the main duct 4 in order to heat the store 1. The controller includes data logging means which stores the readings from the sensors 11 and the probes 7 and records when and how each of the other components is operated over time. The data in the data logging means can be extracted from the controller by a user in order to analyse the operation of the heating and ventilation system.
The modulating burner, the fan housing 2 (including the air inlet from the surroundings and the air inlet from the store 1) and the exhaust louvers 6 are operated by the controller in a conventional manner, as will be immediately understood by the person skilled in the art. The modulating burner and fan housing 6 are operated to ensure that the humidity within the store I remains between 65% and 75% relative humidity and the temperature within the store remains at the store set temperature of 27° C. The axial fan 3 is a variable speed fan and is operated by the controller in the same manner as the prior art in that it is operated when the humidity falls outside of the defined range and/or the temperature falls below the store set temperature of 27° C. However, when the axial fan 3 is operated the controller monitors the air pressure with the main duct 4, as measured by the sensors 7, and the air speed through the crop 9, as measured by the probes 11. The speed of the axial fan 3 is controlled to ensure the optimum pressure within the main duct 4 and a minimum air speed through the crop 9 is attained. This is done by maintaining the air pressure within the main duct 4 within a defined range i.e. below a set upper pressure and above a set lower pressure and by ensuring the air speed through the crop 9 is above a minimum limit. The pressure limits within the main duct 4 depend upon the axial fan 3 and the dimensions of the main duct 4 and lateral ducts 5, as will be understood by the person skilled in the art. In particular, it is advantageous to optimise the back pressure acting against the operation of the axial fan 3. The minimum air speed through the crop 9 is set to ensure good air distribution through the crop 9 and thereby ensure that the whole of the crop is being ventilated.

Claims

1. A ventilation system when used with a perishable goods store comprising:

a controller for automatically operating the system,

a duct through which air is propelled into the store,

a pressure monitoring means for measuring the air pressure within the duct; and

pressure control means for controlling the pressure within the duct;

wherein when air is propelled through the duct the controller monitors the duct pressure, as measured by the pressure monitoring means, and controls the pressure control means to ensure that the air pressure within the duct is maintained within a defined pressure range.

2. The system according to claim 1, wherein the pressure control means comprises at least one variable speed fan.

3. The system according to claim 1, wherein the pressure control means comprises a plurality of fans.

4. The system according to claim 3, wherein the pressure control means comprises a plurality of fans operated in series.

5. The system according to claim 2, wherein the at least one fan is an axial fan.

6. The system according to claim 2, wherein the at least one fan is a centrifugal fan.

7. The system according to claim 2 further comprising a fan housing in which the at least one fan is housed.

8. The system according to claim 7, wherein the fan housing comprises a closeable air inlet that allows air to be drawn into the housing by the at least one fan from the surroundings when air inlet is open and wherein the fan housing may draw air into the housing from within the store when the air inlet is closed.

9. The system according to claim 1, wherein the pressure control means comprises at least one controllable opening from the duct.

10. The system according to claim 1, wherein the pressure monitoring means comprises a pressure sensor positioned about one third of the length of the duct from the at least one fan.

11. The system according to claim 1, further comprising a plurality of air speed sensors positioned within the goods stored within the perishable goods store for monitoring the air speed through the goods.

11. The system according to claim 1, further comprising humidity monitoring means for monitoring the humidity within the store.

12. The system according to claim 11, wherein the humidity monitoring means comprises a humidity sensor positioned within the duct.

13. The system according to claim 11, wherein the humidity monitoring means comprises a plurality of humidity probes positioned within the perishable goods within the store.

14. The system according to claim 1, further comprising humidity monitoring means for monitoring the humidity outside the store.

15. The system according to claim 10, wherein the system is controlled to operate when the humidity within the store is outside of a defined humidity range such that the humidity within the store is corrected to within the defined range.

16. The system according to claim 1, further comprising at least one heater.

17. The system according to claim 16, further comprising temperature monitoring means for monitoring the temperature within the duct.

18. The system according to claim 17, wherein when the system is operated and the temperature within the duct is below a set duct temperature the heater is operated to thereby raise the temperature within the duct.

19. The system according to claim 16, further comprising temperature monitoring means for monitoring the temperature within the store.

20. The system according to claim 18, wherein the temperature monitoring means for monitoring the temperature within the store comprises a plurality of temperature probes positioned within the perishable goods within the store.

21. The system according to either claim 19, wherein the system, including the at least one heater, are controlled to operate and thereby raise the temperature of the air within the store when the temperature within the store is below a defined store temperature.

22. The system according to claim 1, further comprising data storage means for recording data from the monitoring means and for recording when and how the components of the system are operated.

23. The system according to claim 1, further comprising a plurality of exhaust means located around the store for controlling the exhaust of air from the store such that when the system is in use the volume of air being drawn into the store is substantially equal to the volume of air leaving the store.

24. The system according to claim 23, wherein the exhaust means comprise exhaust louvers.

25. The system according to claim 23, wherein the exhaust means are automatically controlled by the controller.

26. A method of operating a ventilation system of a perishable goods store comprising a duct through which air is propelled into the store, wherein the air pressure within the duct is monitored and pressure control means are used to control the pressure within the duct such that it remains within a defined pressure range.

27. A The method according to claim 26, wherein the air speed through the perishable goods is monitored and when the system is operated it is controlled to provide at least a minimum air speed through the goods.