A cooling system for potatoes or onions: what to consider

By Luuk Salomons, Omnivent

A well-designed cooling system is vital for minimising storage losses and maintaining potato quality. However, achieving this sustainably and energy-efficiently is increasingly challenging. With extreme weather patterns and harvest variations becoming more frequent, it’s essential to ensure a cooling setup is built for long-term resilience. The following are several key considerations when deciding on a cooling system for your storage.

Three questions to determine the right cooling system capacity

To determine the appropriate capacity and setup for a cooling system, it’s essential to answer these three questions.

1. What cooling capacity do your potatoes require?
Consider when and for how long you intend to store your potatoes, how quickly the temperature needs to decrease and the conditions under which you want to store the produce for a specific period. This requires performing a so-called cooling load calculation. Depending on the potato variety, the cooling capacity typically ranges from between 60 – 140 Watts per tonne of stored produce.

2. Do storage cells need to be cooled simultaneously, and when?
Create a cooling schedule to determine which rooms will be cooled at the same time. For example, if a store has three rooms with a combined total cooling capacity of 300 kW, but the plan is to only use two rooms at full capacity simultaneously, the simultaneity factor would be 2/3, or 67%. In this case, a cooling system would only need to provide 200 kW of cooling capacity.

3. At what temperatures will the cooling take place?
Establish the maximum outdoor temperature and the minimum room temperature. With this information, you can determine the condensation temperature and the evaporation temperature of the cooling system. The condensation temperature is typically 10°C higher than the maximum outdoor temperature, and the evaporation temperature is typically 7°C lower than the minimum room temperature. These values are crucial for determining the system’s effective cooling capacity.

Choosing between direct or indirect cooling

Typically, there are two types of cooling systems commonly used for storing potatoes. A direct cooling system (often referred to as DX or Direct Expansion) and an indirect cooling system. In a direct system, a refrigerant evaporates in the cooling coils of the system, cooling the air in the storage rooms. The compressor compresses the gas, raising its temperature, and this hot gas then condenses in the condenser, releasing heat to the outside air.

An indirect system can also be used, where the cold air is not directly released into the storage rooms, but instead it circulates through an intermediary system that uses a mixture of water and glycol.

A direct cooling system is typically more cost-effective in terms of initial investment and generally consumes less energy compared to an indirect system. On the other hand, an indirect cooling system allows for more precise control of the temperature in the coolers, because each storage cell can be cooled individually. This helps tailor the cooling process more precisely to the potatoes and minimizes the risk of dehydration.

Use of efficient natural refrigerants

Cooling with natural refrigerants is not only more environmentally friendly than synthetic alternatives but can also help reduce energy consumption. Depending on the situation, natural refrigerants can reduce energy consumption by around 15 – 30%. The most commonly used natural refrigerants are propane, CO₂ and ammonia. Generally, propane is ideal for smaller cooling capacities up to around 75 kW, CO₂ for capacities up to around 300 kW and ammonia is best for larger capacities. It is advisable to assess your specific situation carefully with an expert before selecting the most appropriate refrigerant.

Peace of mind and certainty thanks to automated systems

When it comes to long-term storage, every degree and every percentage point of humidity counts. A modern control system monitors conditions 24/7 and automatically controls cooling, hatches, and ventilation. This ensures stable conditions and, above all, certainty during storage.

Do you have plans to invest in cooling or would you like to optimize your current cooling system?

Our specialists will be happy to tell you more about the possibilities for your company.