By John Ackermann
An existing warehouse situated in the Parow Industrial Area, Cape Town, has been converted to an energy efficient Lactalis distribution centre (DC).
Lactalis is the largest dairy products group in the world, and is the second largest food products group in France, owning brands such as Parmalat and Président.
The refurbished 14m-high chill cold-store with an ammonia/glycol refrigeration plant boasts eight dispatch/receiving bays to receive and distribute the extensive range of dairy products, cheeses, yoghurts and flavoured milk drinks.
The long-standing relationship between Parmalat and Energy Partners influenced the latter’s appointment to design the DC with a focus on energy efficiency, productivity, use of natural refrigerants, compliance with SANS10147 and the high safety standards of Lactalis Group. Wherever economic, decommissioned plant and existing equipment on the site were utilised.
The 3.8-hectare site originally featured a refrigerated DC commissioned in 1991, with various additions and replacements made over the years until 2017. Multiple ageing R22 refrigerant plants serviced several cold stores distributed around the site.
The existing warehouse was repurposed for the new DC. As with any project in an existing facility, careful planning and design were required to identify and mitigate risks and optimise the new facility within the constraints of the existing infrastructure.
To improve the efficiency and reduce complexity, a single large high-rise warehouse was proposed. The high-bay warehouse was important for energy efficiency, as it reduced the ratio of the exterior surface area to the cold store’s volume, thereby minimising the amount of energy absorbed through the walls, floor and ceiling. To complement this, polyisocyanurate insulated panels were chosen for their low thermal conductivity and fire resistance properties.
Additionally, insulated docking cubicles with contact cushions were installed to minimise the heat load from ambient air entering the cold room at the dispatch/ receiving bays. High-traffic doors leading from ambient areas into the cold room were also installed with automated high-speed insulated doors that reduce the infiltration of hot air.
For the refrigeration system, Energy Partners designed an ammonia refrigeration plant with a propylene glycol secondary refrigerant to provide cooling to the store.
A low-temperature circuit was also required for frozen products and a CO2 system was designed to condense on the glycol secondary refrigerant. The combination of ammonia and CO2 met the client’s requirement of natural refrigerants.
The ammonia system designed included a gravity- fed plate heat exchanger and HP-float without a receiver. This design minimised the ammonia charge.
Two evaporative condensers from an old plant were refurbished and used for the system to reduce the capital input required. The condenser fans were installed with variable speed drives to enable floating condensing control and improve the system efficiency.
For the ammonia circuit, two new direct-driven MYCOM piston compressors and an existing belt-driven piston compressor were used. Both new compressors were installed with variable speed drives to enable all operating conditions to be covered, and the belt-driven compressor was used for added redundancy. The combination of the variable speed drives and the piston compressors ensure that all operating conditions are efficiently maintained.
Safety was a high priority for the design; therefore, additional measures were taken to reduce ammonia release from relief valves by installing an absorption tank. A standby stainless-steel tank was installed for this purpose.
The secondary glycol circuit pump was also installed with a variable speed drive to modulate the flow capacity according to demand and thereby maintain energy efficiency. A standby pump was also installed for redundancy. The reticulation of the secondary circuit was designed and installed as a reverse return system for effective distribution irrespective of the differences in the cooler distances. As part of improving the lifetime of the system components, the secondary circuit was pressurised to minimise corrosion of the components in the system and no open expansion tank was used.
For the low-stage CO2 system, two piston compressors were also installed with variable speed drives for load modulation. The condensing temperature control is achieved by modulating the flow rate of glycol through a CO2 glycol plate heat exchanger. The low temperature CO2 system is a direct- expansion system with desuperheater.
Crucial to the operation is visibility of the system and measurement of performance for continued efficient operation after commissioning. A monitoring system was installed, allowing key performance indicators of the plant to be monitored and reported remotely.
Technicians and maintenance staff can remotely change control parameters and be alerted timeously. To facilitate this, flow and energy meters were installed on the main fluid lines and main components to monitor consumption and efficiency.
Once the design was completed, the project was executed in two phases.
The high-stage and main large high-bay insulated panel structure was installed first, followed shortly by the low-stage CO2 system. The project has resulted in an average saving of over 30% on the client’s refrigeration energy consumption, alongside an increase in storage volume of over 150%. (Refer to table 1)
Following the commissioning phase, Energy Partners ensures continuous performance monitoring and reporting of the system. This comprehensive approach encompasses performance metrics such as the efficiency, or Coefficient of Performance (COP), utilisation rates and system stability, all aimed at minimising the total lifecycle cost. Additionally, critical process parameters, including glycol and room temperatures, are systematically tracked, reported and analysed.
To further enhance operational reliability, Lactalis benefits from Energy Partners’ 24/7 remote plant monitoring service. This service promptly identifies, reports and addresses alarms and alerts, ensuring early detection and resolution of potential issues.
“Working within existing structures presented unique challenges but was overcome by Morne de Kock, Lactalis project manager, being on site every day. His personal involvement in the removal of old equipment and the required diversion of electrical and water services proved invaluable.
During the entire construction Morne was also on site daily and any unexpected problems could be resolved promptly,” commented Hougaard Langeveldt, head: Energy Partners Engineering.
