Controlling relative humidity conditions for stored potatoes

Controlling relative humidity (RH) is fundamental for successful potato storage

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For a couch potato, weight loss can be a desirable goal. For a stored potato, weight loss must be avoided! Weight loss, or shrinkage, can be minimized during the course of storage by achieving the most ideal storage environment conditions possible. Preserving the quality, and quantity, of stored potatoes means gaining the best possible return on a grower’s harvested crop. Of all the factors impacting storage shrinkage, relative humidity (RH) is paramount. RH is the amount of moisture in the air at a given temperature, relative to the maximum possible humidity at that same temperature.

Relative humidity is all relative—to both moisture AND temperature

RH is dependent upon the temperature, with cold air holding less moisture than warm air. In maintaining a consistent, ideal level of RH in storage, the amount of moisture that needs to be provided is higher at a higher temperature. For example, in order to maintain the same level of RH, at a storage temperature of 48°, more moisture would need to be added to the same volume of air, than if the temperature is 45°.

Accurately measuring RH is not a matter of simply measuring temperature. Measurement can be taken at a variety of storage locations, by both portable sensors and ones linked to a control panel. Measurement should occur away from any humidification equipment. The most critical RH measurement is in the plenum air, before it is delivered to the potatoes.

The importance of consistent, controlled RH cannot be overstated

Weight loss in stored potatoes occurs from giving up weight to the surrounding air (transpiration), and also, to a lesser degree, through respiration. Transpirational water loss can be slowed, but not stopped, and this slowing is achieved by maintaining the highest level of RH possible. Ventilation with high RH air is especially critical following harvest and during curing.

Recommendations for a plenum RH minimum is 90%, but preferably greater than 95% throughout storage, for a healthy crop with little-to-no-disease presence. The following graph shows the research results of shrinkage versus months in storage. With a temperature of 45°, the humidity ranged from 80 to 98%.

Affect of relative humidity (RH) on potato weight loss in storage at 45˚F.

Source: University of Idaho, Kimberly and Twin Falls Research Centers & Extension Centers

Affect of relative humidity (RH) on potato weight loss in storage at 45˚F.

The graph right/above shows how 9% in weight loss occurred at 90% RH—nearly twice as much as weight as those stored at 95% RH. Now here’s some important calculations from the research: Given a storage capacity of 100,000cwt, and a value of $5.00 per cwt, the building maintained at 90% RH would return $22,000 less than the storage controlled at 95% RH.

What is the best way to achieve overall, optimal RH?

Optimal RH conditions for stored spuds is best achieved through a combination of centrifugal humidifiers, or spinners, plus media cells. Industrial Ventilation, Inc. (IVI) offers both the Centrifugal Humidifier 30-Series and our Humidicell. We also offer the expertise in set up and system design for new or existing storage buildings. Our service technicians can evaluate the quality of operation of your existing components, as well as monitoring sensors, to ensure optimal performance in advance of harvest. As research has demonstrated, achieving ideal relative humidity is directly relative to any grower’s bottom line.

IVI’s Centrifugal Humidifier 30-Series is the leading, industrial-grade performer


Centrifugal Humidifier 30-Series is the Leading, Industrial-Grade Performer

Dependable humidification comes with high-volume output and economical operation. Our Centrifugal Humidifier also is fast and simple to install. The rugged construction ensures a long service life with very minimal maintenance. With eight models, including portable units as well as ceiling-mounted, humidification can be customized perfectly for your storage space. The efficient 1/2 H.P. motor uses little electricity, yet it is high-capacity, producing up to 30 gallons of atomized water per hour.

Humidicell Evaporative Cooler is low-cost and efficient


Centrifugal Humidifier 30-Series is the Leading, Industrial-Grade Performer

Considered a passive form of humidification, IVI’s Humidicell Evaporative Cooler pairs well with the Centrifugal Humidifier in a complete storage system. The cells are low cost to operate, relying on water and evaporation. The sturdy design is uniquely cross-fluted to minimize debris build up and shorten the replacement timeline. Learn more here.

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Posted on: May 1, 2018