Designing A New Potato Store

Energy & Emissions:

Current energy costs and global political trends means that energy consumption and greenhouse gas emissions are key factors when designing a store. Consideration of the different technology available when selecting a cooling and ventilation system is important. Systems should be designed to run as little as possible to avoid excessive running hours, which increase moisture losses. The option to bring in cool night-time air to supplement mechanical cooling is an essential energy saving process to lower the carbon footprint.

Additionally, fans are necessity to ensure premium air flow and temperature regulation in store. During a storage season, fans will run multiple times per day, meaning that it is important to select an energy efficient fan. The rpm of EC fans is electronically controlled, allowing the speed of the fan to vary automatically during the different phases of storage. This is important because different phases of storage require different air speeds. An added benefit of EC fans is that when operated fan at 80% capacity they consume 50% less energy.

Efficiency of Electronically Commutated (EC) Motors

Global Warming Potential (GWP) is high on the agender of many governments. GWP is a measure of the potency of a greenhouse gas, (i.e. the length of time it remains active in the atmosphere). GWP ratings setpoint is based on CO₂, which is given a rating of 1. The use of HFC refrigerants (F-gases) is limited, and legislation to reduce or ban their use is increasing worldwide. Following the ban of HFC’s in Europe, the use of natural refrigerants, ammonia, carbon dioxide and hydrocarbons such as propane are frequently used.

GWP Rating of Refrigerants:

·     R134A – 1430 (common HFC refrigerant used in Australian)

·     Propane - 4

·     CO₂ - 1

·     Ammonia – 0

Utilising solar energy is important as we move towards a carbon neutral society. A product such as the Tolsma ‘Energy Management System’ allows users to prioritise cooling with solar energy over mains power. Understanding the energy requirements of cooling and ventilation systems, alongside real time solar energy production allows variables to be set in the climate control computer to minimise the use of mains power.

Store Materials

 The cooling and ventilation system should be designed to operate as little as possible. That is why it is important to have a well-insulated store. In a well-insulated store, product is able to maintain a stable temperature for a longer period of time without impact from external influences. Therefore, reducing ventilation and refrigeration operating hours, which has two main benefits.

·     Reduced airflow disturbance, allowing the potato to maintain homeostasis through reduced respiration

·     Decreased energy consumption

High insulation rating materials are a must to prevent external heat entering the store, or the formation of cold bridges which cause instore condensation. Insulation is categorised by two values.

·     K-value - the thermal conductivity of a product. The lower the K-value, the less ability a material has to conduct heat

·     R-value - the capacity of an insulation material to resist heat flow. The higher the R-value, the greater insulation power

The fire-retardant properties of the insulation material used must also be considered for insurance and longevity purposes.

Climate Conditions

Regardless of location, potatoes should be treated in the same way. The aim is to keep the moisture inside the potato and avoid evaporation. This can be done with ventilation, refrigeration, or a combination of the two, depending on the regional climate, store insulation rating and condition of the incoming potatoes. With a well-designed cool store solution, internal climate requirements can be easily met.

For financial risk management, store flexibility to overcome poor harvest conditions where potatoes may enter with wet soil and/or low core temperature should be considered. A storage solution that uses ventilated outside air to dry is essential in this case. A heating system can also be added to facilitate faster drying capabilities and improved wound healing (suberization).

In hot climates, the primary challenge is to maintain a constant temperature in store. Again, the key factors are a well-insulated building and adequate cooling and ventilation capacity. Additionally, CO₂ refreshment, where hot air is cooled before being ventilated throughout the store is important in maintaining a low internal store temperature and high humidity.

A low potato core temperature is a key factor to increase dormancy periods, reduce tuber respiration rate and limit weight loss. Less respiration means smaller weight loss. The grower must have knowledge of the specific needs of the variety, and the duration of storage to set accurate minimum storage temperatures. With a well-designed ventilation and refrigeration system including temperature measurement sensors and product probes, a climate control computer can easily maintain accurate storage conditions.

Fight Against Diseases

 The best option to stop moulding and pathogens that affect potatoes is to keep the tubers dry - pathogens like humidity. Ventilation using internal and external air is an essential first phase of storage. High-quality drying and suberization capability before cooling will significantly decrease the risk of pathogen growth and spread instore. To maintain the ideal store environment, internal and external temperature, and relative humidity measurement sensors are used to gather information and determine system operations.

Equipment for Storage Facility

 Must Haves:

·     Climate control computer

·     Ventilation and refrigeration control from computer and online

·     Recording of data for ease of post season analysis to improve the system operation for following season.

·     Ability to utilise outside air

·     Sensors - Temperature, Relative Humidity, and CO₂

·     CO₂ refreshment

·     Well insulation store

Text -  Jan van Maldegem, Tolsma-Grisnich B.V., The Netherlands

Tolsma Team Australia