Largest Lowland Farm in the UK,
Norfolk

The client

The client is the largest lowland farm in the UK, growing over 75,000 tonnes of potatoes, onions and carrots. Well known for the quality fresh produce, the farm estate works with neighbouring growers to grade, wash and pack their crops as close to the source as possible.

The brief

The client took on a main contractor to design and build eight new potato stores. JD Cooling designed, installed and commissioned a secondary cooling system to four of the stores, in addition to system components and infrastructure to allow the ease of expansion to the remaining four stores (future Phase II).

The solution

Based on JD Cooling’s experience and understanding of crop storage, a secondary cooling system was selected to offer improved crop storage conditions over the more traditional methods. The benefits of the secondary cooling system will optimise the quality of the stored crop and reduce weight loss – key to the client’s reputation of fresh and quality potatoes. The secondary cooling system consists of:

Glycol Coolers (four in total – one in each store) – Configured with draw-through airflow through a vertical cooling coil located within the plenum wall, the units have duct extensions that discharge air at high level above the box stacks and sufficient velocity to throw the air the full length of the store. The coolers are complete with warm glycol defrost to allow low temperature operation and includes air activated dampers to prevent warm air rising up the ducts during defrosting.

Packaged Chillers (Two 220kW) – Utilising propane as the primary refrigerant, the hydrocarbon chillers contain a compartment for the compressors – classed as an ‘ATEX Zone 2 Area’ and is completed with a 3-stage leak detection system. Propane was selected as the primary refrigerant due to its natural and ‘HFC Free’ form, which will in the longer-term, provide the client cost savings and avoid any F-Gas phase down issues.

Thermal Buffer Vessel (One) – Providing additional fluid temperature stability at the entry point of the chillers, the thermal buffer vessel prevents any short cycling of the compressors, thereby increasing the efficiency and lifespan of the plant.

Primary and Secondary Glycol Pump Circuits – Using a split tank buffer vessel, the total system is split into primary and secondary loops. The primary loop between the chillers and the tank use small power, primary pumps to provide the minimum flow through the chillers. The larger secondary ring main pumps that deliver to the room coolers utilise inverter driven, variable speed drives. Using a pressure transducer, these larger motored pumps automatically match the glycol flow rate to suit the varying demand from the room coolers so that as this demand drops off, the pumps will ramp down and in doing so save up to 80% of their normal power usage during holding conditions.

EC Fans to Coolers – The coolers are complete with EC fans, thereby reducing energy consumption and allowing fan speed modulation based on the temperature difference across the coil. This allows the fans to operate at a reduced speed once the stored crop is down to temperature, reducing the drying effect.

Automatic Air Venting & Top-Up System – Incorporating automatic air venting and a pressurisation unit to maintain operating pressure and to provide a charging point for glycol. The result – reduced subsequent maintenance and repair work times throughout the lifespan of the plant.

Run and Standby Pumps – Ringmain pumps were provided as ‘run and standby’ to allow full system operation in the event of pump failure.

Inverter Drives for Pumps – Ringmain pumps are fitted with inverter drives to reduce energy consumption and provide stable operating conditions.

Foodsafe Glycol – The heat transfer fluid used as the secondary coolant was Coolflow DTX – a non-toxic variant of ethylene glycol with reduced viscosity compared to propylene glycol, thereby reducing pump power. In addition, Coolflow DTX is formulated with corrosion inhibitors to prevent corrosion in the event of leakage.

Warm Glycol Defrost – Local inline warm glycol defrost heaters were utilised to apply heat to the tubes within the cooling coil. This applies the heat to the first point of formation of the ice – reducing defrost time and in turn the energy required.

Control Panels – A new purpose-built electrical control panel was provided for each glycol cooler, consisting of control cooler fans, defrost and valve operation. A second control panel is contained within the packaged chiller itself.

Control Wiring – All wiring and connections from the main electrical supply to all chillers, panels and coolers was installed, tested and commissioned by JD Power.

Pipework – All glycol pipework has been installed using thin wall stainless tubing and fittings. This will allow easy modifications and repairs without delay and ensure reliability and long-term performance – with the allowance of the introduction of alternative chiller technology in the future without any need to modify or change any other part of the cooling installation.

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