There are different ways of storing potatoes: bulk storage, box storage with a suction wall, box storage with a pressure wall etc. The storage way choice depends on the store type, potato tuber condition, sale timeline and technical feasibilities of the firm. In practice, any storage type requires a climate control system. This automatic system would be supposed to provide appropriate relative humidity and temperature, removing surplus of CO2 generated by the live tubers and other conditions.

Potato storing technology

Different storage phases assume maintenance of special microclimate parameters that is temperature and relative humidity. There are the following storage phases of seed and table potatoes: drying, healing, cooling, holding and warming before unloading out of the storage.

When all potatoes have been completely loaded to the storehouse, the healing period comes, beginning with ventilation of tubers and their drying. Duration and intensity of this process depend on the crop quality, tuber surface moisture, and temperature during harvesting. Here it is substantial to constantly check the tubers condition because they can lose weight and get dry rot if over ventilated. On the other hand, high humidity of tubers requires intensive ventilation.

After healing phase it is necessary to cool the potato to provide long-term storage. This is a very important period when it is required to avoid significant product temperature variations. In this case, refrigeration equipment is very often the only way to perform cooling in time.

During the holding phase, optimal temperature and humidity must be maintained as optimal conditions for preventing natural tubers-germination.

In any particular case it is needed an individual temperature and humidity mode, subject to the potato variety and further utilization of the potatoes. The germination rate of most potato varieties is noticeably decreased when the storage temperature is lower than 5 °C. Periodic ventilation would maintain the set temperature value and provide enough O2 ingress.

Sometimes, it is not easy to foresee weather conditions, potato tuber condition (and quality), store particularities and other factors which have an influence on the product safekeeping. Automatic systems can easily meet such challenge, maintaining any preset parameters of temperature, humidity, duration of ventilation, heating or cooling and any other.

Climate control system

A typical vegetable store for 100 – 2000 t is shown in Fig. 1 and the suggested functional scheme in Fig. 2.

potatoeStoringFig. 1

The automatic climate control system can be based on the following devices:

The system which includes the listed above equipment can provide the following functions:

  • Supervision of: indoor and outdoor air temperature and humidity, temperature in air distribution ducts, and product temperature
  • Control of fans and inlet and outlet air dampers
  • Control of air conditioning
  • Heating control
  • Alarm.
potatoeStoring_fig_2Fig. 2

The SPK207 control panel serves as the main system unit. The panel displays set point values and current values of the system parameters. Manipulating with touch screen, the operator can switch operation modes, supervise system parameters and get information about both the status of individual units and the system status in general.

Due to the input modules MV110-24.8A, the signals from temperature and humidity transmitters are amplified, filtered and converted into digital form to be sent to the SPK207 through the RS485 interface. Robust RTD temperature transmitters with different probe length can be used for measuring product temperature and DTS125L – for outdoor temperature. PKG100-CO2 carbon dioxide transmitter can be used to provide an optimal CO2 concentration in the room. The quantity of modules depends on the storehouse capacity and on the quantity of the involved transmitters. The larger is the storehouse, the more modules are required.

On the basis of information received from the transmitters, the system switches operation modes. There can be several operation modes available in the system: recirculation, airing, cooling, air humidifying or drying, heating and ventilation. Each mode is represented on the control panel screen in the form of a signal lamp or in a text form.

Position of inlet and outlet dampers in the main air channel and EC fans frequency in the air-ventilation chamber are controlled in accordance with PID mode of control, which implements the user program on SPK207, depending on the temperature in the air channel. This temperature can be measured with PVT100 humidity and temperature transmitters (wall mount). The damper actuators and the EC fans are controlled by analog output modules MU110-24.8I and MU110-24.6U.

If there are not enough outputs of these two modules, additional output modules MU110-24.16R can be involved in the system to control other equipment (see Fig. 2).

The most efficient practice is to install the input modules directly in the storeroom, the output module – in the air-ventilation chamber beside the power and actuated equipment, and the control panel – at the entrance to the storehouse.

Often, there are two storehouses raised beside each other. In this case, it is better to organize a separate control room for both control panels. For this purpose, it is recommended to use RS485 interface and twisted pair cables as connection lines.