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Condense drying: common truths and misconceptions:
The experience gained from the systems which we just mentioned has inspired the creation of an all-in-one integrated machine: VaccTek. It is similar to an enormous version of your own tumble dryer at home. It is installed as one single machine, not custom-made.
This machine is difficult to assemble, as its parts have to work in unison, automatically and irrespective of the weather and amount of storage space. The operator can adjust the r.h. and temperature of the drying air by using two remote controls. This technique has been perfected through years of experience and working with dozens of machines.
Having all of the functions integrated into one single machine makes it very easy (for the user) to control the drying air. Simplicity is a key advantage in a storage facility, which at the end of the day is not a factory.
Installation of a VaccTek unit in a storage facility.
We have also designed several accessories to provide the machine with even more applications:
-- Suitable for all types of box storage, with pressure or suction ventilation.
-- Integrated heat pump for extra drying, even if the heat from condensation has been used up.
-- Option to dry at a low temperature, once the produce is cooled.
-- The amount of condensed water which leaves the storage facility is measured, providing even more data for monitoring the drying process.
Investment in these integral units is slightly higher, but in return they offer the following advantages: 100% simultaneous drying of several spaces; more control; a heat pump; considerably lower long-term maintenance; simplified installation and setup (the machine is installed as one unit, it is not custom-made).
We will now apply our knowledge to the debate over the advantages and downsides of condense drying.
This is true if you only need to dry the produce by a small amount. However, if you need to dry the produce well below the humidity level (reducing the r.h. below 65% in many cases), then the ventilated air needs to have a r.h. of less than 65%, making the condense drying technique much more favourable, certainly in terms of energy costs. For example, drying at 30 degrees at 60% r.h., the condensation method works out 70% more efficient (in the Netherlands ?0.004/kg versus ?0.015/kg). It is not worth comparing heat drying at 75% r.h. with condense drying at 50-65%.
It does require a greater investment, but this doesn't necessarily make it more expensive. In many cases the investment proves profitable, even in terms of saving money on your bills. Then there's the pride and peace of mind obtained from always having a good product, year in year out, with a lower percentage of shrinkage and lower energy output.
In certain countries, and if the machine has a heat pump, the investment can be tax-deductible, as it saves energy.
What counts is the drying cost per tonne, rather than the extra investment per tonne. That extra amount, divided over ten years, is equal to just 0.4-1 dollar cent per kilogram, which pays for itself through increased yields (due to less shrinkage) as well as energy savings.
Just as important, if not more important, is the quality and safety of the supply, year after year: the investment will pay itself back. By being able to rapidly and fully dry the produce, you will gain commercial opportunities which are not open to growers or wholesalers who cannot.
In principle this is true: VaccTek merely combines basic refrigeration, dehumidification and heating techniques with cooling circuits, applying common sense. The work of a VaccTek unit can be done "by hand", but only if you know how to expertly manage all of the components, and even so it will not always go to plan. It is difficult: if it were easy, everyone would use the condense drying technique, but that is not the case. In practice, the most effective solution has proven to be integrating all of the functions into one single machine with automated digital control.
This is another half-truth, as we have seen in recent years. While the neck of the onion is open, it can be dried without the risk of over-drying (obviously the drying process always has to be controlled). Once the necks of the bulbs have closed, you can either: increase the r.h. of the air, continue to dry at a higher temperature, or let the onions cool down, and still be able to dry them later on. The user makes this type of decision, no matter which system is used.
The grain of truth behind this assertion is that the technique was first developed for organic crops, reducing shrinkage by 10-30%, reaching the yields of "normal" crops, but without the pesticides, fungicides, etc. However, since then it has been proven that condense drying is also profitable in the majority of box storage facilities with forced ventilation. For example, red onions can now be dried properly every time, which opens the door to higher yields. Ensure all of your produce is dried!
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