Food manufacturer FJ Need’s brief was to ensure efficient and accurate temperature management of their goods-in, despatch, and production areas. Careful consideration had to be given to energy consumption due to the site’s semi-rural location and existing demand. Another primary objective, for independent contractor Personal Refrigeration, was to deliver immediate value for money while also providing long-term financial and environmental benefits.
Centred on two independent refrigeration packs, the bespoke system design incorporates inverter technology, all with programmable logic control (PLC) software written in-house by Personal Refrigeration, using Resource Data Management’s (RDM) license inclusive PLC editing software, TDB,
to independently control the two packs and associated evaporators, via Intuitive TDB controllers. Multiple control algorithms were written, including inverter rest condition upon detection of stable load, auto balance of fixed speed compressor run hours, floating head pressure, and also adaptive suction pressure, when necessary; and compressor envelope monitoring, including evaporating temperature/pressure, and discharge temperature.
To facilitate refrigerant control, RDM’s electronic expansion valves (EEV) package was selected to provide individual evaporator satellite control, along with evaporator EC fan modulation, using the TDB software, to help save energy under varying loads. All of the above equipment interacts and communicates seamlessly, and each fully independent system features Intuitive TDB and Mercury controllers, a 3 x semi-hermetic compressor pack, complete with lead compressors, which are inverter driven, and individual compressor de-super heater heat exchanger, for hot water recovery; a three fan condenser with inverter driven condenser fans, four MT evaporators (+3/+5*C) with modulating EC fans, split across two areas, and an HT evaporator (+6/+8*C) with modulating EC fans.
RDM’s DMTouch acts as the control system front end, providing communication across all controllers via an integral TDB program. This ensures that critical alarms are detected, and that the necessary reactive action is taken to maintain stable operation of the system(s). One feature of this is to ensure that the EEV is driven closed, should a failed fan be detected, preventing any “liquid” flood back to the pack(s).
Monitor temperature sensors and pressure transducers analyse system conditions to maintain optimum design evaporator and condensing criteria, using Intuitive TDB controllers. The RDM microprocessor responds to information provided by the sensors and transducers, loading or unloading the compressor(s) as required, therefore optimising design conditions. The refrigeration pack(s) lead compressor is inverter driven for speed modulation, to enhance energy efficiency at variable load conditions. Control algorithms are also provided, for additional energy efficiency, to implement floating evaporating and condensing temperatures to adapt, and control, to real-time refrigeration demands. This control technique allows system pressures to automatically adjust and regulate to suit low or high load conditions.
Each evaporator EC fan(s) speed is independently managed within the PLC software. The fan speed modulates to match the refrigeration duty required for each zone of the refrigerated areas; as a result, energy consumption is reduced when low loads are detected. Independently managed, each evaporator satisfies the temperature set point, minimising defrost clashes. Real-time defrost strategies are also employed. Sporlan EEV’s are controlled, ensuring that the evaporators are efficiently utilised under varying loads by controlling the flow of Refrigerant 407F.
A major consideration for the installation was environmental impact. With this being a high priority, high-efficiency heat exchangers were selected (evaporators and dual circuit condenser) and therefore with reduced refrigerant charge. Refrigerant charges are therefore minimised, and in the event of a leakage, reduced volumes of refrigerant are lost and the impact on the environment reduced. As a result, the environmental impact is also reduced in the event of refrigerant charge loss. An additional precaution is the fixed gas leak detection system installed in the compressor pack plant room, which possesses the highest risk area for refrigerant leakage.
Custom PLC software for the Intuitive controllers communicates with the fixed leak detection sensors and the DMTouch to warn of any increased levels of refrigerant within the plant area. Numerous parameters are adjusted through the software to help prevent any false alarms. Parts per million (PPM) levels for delayed and immediate alarms are built in, along with a knock system, if refrigerant levels are raised intermittently over a period of time.
It was noted that, before the construction of the new factory, the main’s distribution maximum demand (MD) was 125KVA. The existing facility is served by four ‘fixed speed’ scroll condensing units providing a total of 115kw of cooling.
The new factory, which is double the size of the previous cold store and has the capacity to cope with nearly twice the throughput, was designed for an MD contingency of 300KVA. Personal Refrigeration supplied and installed two independent 105kw refrigeration packs complete with inverter driven lead compressors. In conjunction with EC evaporator fan modulation, off cycle defrost, inverter driven condenser fans, heat recovery for the provision of hot water and the flexible but highly intuitive RDM hardware, operating costs have been impressively low.
40% Like-for-like Energy Reduction
Total electrical loading for both sites is registering 200KVA. Therefore, despite the doubling of capacity and throughput, the total electrical loading is only 60% of the figure that the previous site demanded.
The clients and Project Manager are delighted about the 40% energy saving against the previous site usage, of which refrigeration will be a major contributor. When presented with the energy savings the Project Manager Alistair Clark, of Clark Solutions said “It’s impressive. Max demand before the new site was 125KVA and we are running at 200KVA at the moment which is amazing.”
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