CASE STUDY: Don’t give up on those older buildings! Energy efficient conversions and upgrades are still possible…

With the industry under the cosh for much of the post-Covid period, it is perhaps not surprising that growers have been forced into a defensive position when it comes to potato storage in recent seasons.

There are a few green shoots of recovery coming to light but, with new storage costs sky-rocketing to north of £400 per tonne. the focus for growers for now seems to be very clearly on directing any improvements towards what already exists rather than starting from the ground up.

An example of this approach provides a case study we visited recently. It is a store upgrade carried out this summer at Drayton Farms at Little Plumstead on the outskirts of Norwich, Norfolk by North Walsham-based suppliers Crop Systems Ltd. A pair of rather tired 1980s-built stores became the subject of an upgrade proposal with the objective of converting them to provide around 1500 tonnes of high quality, pre-pack storage.

The buildings themselves were metal-clad portal frame units with a modest amount of spray-foam insulation that was cosmetically damaged. Crop Systems proposal was to remove a central, non-structural dividing wall and a couple of existing fridges which were well past their use-by date. The installation would repair and renovate the spray-foam to provide around 85 – 90mm of good quality insulation across the newly-created, larger store. The doors were also a weak point in the store’s overall integrity, as is so often the case, so these were to be replaced with new Hormann up-and-over units with 40mm insulation.

Box stacking in older buildings can often be a challenge so this required some flexibility of thought but Drayton Farms gave the project the go-ahead based around the promise of close store control from the new SmartStor® controller and a state-of-the-art cooling and ventilation system designed and installed by Crop Systems’ directors, Ray Andrews and Richard Cook (right).

Boxes are stacked in a reworked but largely conventional format away from a full-width, but open-fronted, plenum chamber which allows the store to flex around a couple of differing box sizes on the production unit.

The store has an ambient, inverter-controlled drying system with full dew-point control to prevent condensation. The airflow is rated at ~0.03 m3/s/t (65 cfm/t) with the fans running flat out and that is at a nominal 150 Pa pressure. The store pairs the ‘free cooling’ option with a 90kW, glycol-based 4-compressor refrigeration unit which is fully speed-controlled. It is linked to a large, 6.4 metre wide refrigeration coil providing a big interface for efficient cooling to minimise weight loss. The indirect system uses around 600 litres of glycol (running at -2.6 to -3°C) but just a 16kg charge of refrigerant.

When PSI visited, the store had completed the drying/curing phase, when it was held at a target temperature of 8°C, and was in the process of pulling down to holding temperature. Pull-down rate was close to 1°C/day even with the system running at just 80% on the inverter, which offers a 50% reduction in power consumption compared with running at ‘full chat’.

That figure includes the all-important controlunit which provides real-time information and data not only for the store conditions but also power use.