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Free blow across the box tops ventilation has been the norm for UK Potato Growers
for well over 30 years now. Farm Electronics alone has been responsible for the ventilation design for many hundreds of these stores across the country. Producers have been achieving successful storage year in, year out. Based on the industry norm of a minimum of 40 cfm or air per ton of potatoes stored, these systems perform perfectly well.
Strangely in the last couple of seasons growers have been bombarded with advice saying they now need 100cfm per ton to successfully dry and store potatoes. This is not just a small airflow increase – it is two and half times greater than the previously accepted norm. Puzzlingly over the last thirty years we have not been inundated with calls from our store owners complaining that they have serious problems and their potato stores need to work better.
So what Problem is this airflow increase meant to be solving?What you can say is it will add a serious amount of money to the initial cost of the ventilation equipment. Larger fans, bigger (more) air ducts, larger intake and exhaust vents. Also bigger motors with inevitable higher running costs. Having to make more and larger openings in the building to cope with the increased airflow also comprises the overall insulation performance of the store.
The only times a Free Blow system will struggle to perform is where the building is too long (100ft ideal) or the doors are badly located and the loading pattern visa are vie the pallet ways are compromised. It should be noted that the higher airflow systems are still liable to be unable to overcome these sorts of deficiencies. These unnecessary issues reinforce our mantra that store design should start with the ventilation system (not the building). The building is the outer envelope of a well-designed ventilation system only.
There are also very low tech (cost) ways of improving the performance of any free blow box store. Blocking the side gangways at the end near the ventilation unit(s) will force the air path more under the box pallet openings thereby making the most of the air flow available.
In 2013 Farm Electronics were asked to design a Free Blow Ventilation system for a converted building to store 418 tons of Potatoes in 1 ton boxes. A single free blow air mixing cooling unit was chosen using a 4.4kw fan giving a ventilation rate of 56cfm per ton. The fan was frequency inverter controlled to allow adjustment to lower speed for gassing the crop. Two exhaust louvres were used and also 4 roof circulation fans (2 with 10kw heater banks for condensation control). The well proven Cropscan 16mc4 controller provides the system with accurate and ultra-reliable auto control. The building (an old grain store) was spray foam insulated.
This Simple and straightforward design provided the grower with an effective ventilation system at a realistic price per ton for the stored crop.
We ask again – why does a system like this need 100cfm per ton???
Not quite "Cheap as Chips” but well up to the ventilation task required.
We are more than happy to quote for 100cfm per ton systems if that is the desired ventilation rate. Our experience would indicate however that in most instances more than satisfactory results are achievable at the lower airflow of 40 cfm per ton.