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Where efficient design meets practical implementation

By Gert van Rooyen, HC Heat Exchangers mechanical engineer, and edited by Eamonn Ryan | All photos by ©Eamonn Ryan Cold Link Africa

HC Heat Exchangers supplied 91 glycol coils to the Pick ‘n Pay Distribution Centre refrigeration project, with 62 of those coils being of the same type in a single area.

The HC Heat Exchangers factory.
The HC Heat Exchangers factory.

Distribution centres in themselves are not novel, says Gert van Rooyen, HC Heat Exchangers mechanical engineer, but improvements in design and improvements in operation are what make them interesting.

He notes that a full set of designs was done on each potential type of refrigerant to find the one that was the best price, the best energy consumption and the best fit for client.

The project was prefaced with multiple design iterations and engineering models to ensure the best fit for purpose solution was proposed and ultimately installed. Design guidelines were centred on product quality, plant efficiency, personnel safety and life cycle cost without deviating from a commitment to minimise the environmental impact and maximise the space utility.

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The solution for this project is a 7.2 MW installed ammonia refrigeration plant divided into two suction regimes to ensure the operating spaces are served by the most appropriate glycol supply. The ammonia plant ensures a high efficiency zero GWP (Global Warming Potential) engine that drives the cooling for the entire facility coupled with a non-hazardous secondary refrigerant loop to maintain highly controlled cooling in all serviced areas. The selection of the glycol option was followed by some further iterations of design to ensure it was as efficient as possible.

Factory large coil assembly.
Factory large coil assembly.

“Due to safety and as a result of the size of the facility the decision was taken early on in the design phase to use secondary refrigerants in the field and limit the ammonia charge to the plant room. Noting the congestion in the roof void and the travel distances it was a prudent decision and greatly increased the safety aspects of the overall facility and roof void,” says van Rooyen.

This project ultimately draws from the best of the available technologies to produce a final product that plays to the strengths of the parts.

The heat from the spaces (with the future ambient area incorporated) is removed by means of 80 coils of 74kWR each in the 2°C space, 24 coils of 76kWR each in the 14°C space, and 4 coils of 73kWR each in the chocolate box. The coils were designed at tight temperatures: larger coils that were aimed at saving on energy usage over the life of the plant.

“The brief called for glycol coils with stainless steel tube and aluminium fins, designed for a big open space with a fair amount of thermal volume and fluid flow with stringent pressure drop requirements through the coil. We consequently had to refine the design of the coils especially considering the flow regimes through the coil whether a turbulent, laminar or transition.

“In this project, we’re using waste heat from the compressors to heat up the glycol to pump through the coils to defrost them for an efficient and quick defrost. The compressors’ energy has to go somewhere, so it might as well as be used to heat water. It’s almost free water heating because you have to have the cooling to run the distribution centre. The waste heat that comes out of that can be efficiently and economically used for other things like crate washing, staff showers or just to wash their hands,” suggests van Rooyen.

Global tender with local solution

Effective cooler design was of paramount importance to ensure the facility is able to operate at its design capacity – allowing for the realisation of the project’s goals. It is with this in mind that the design of the coolers was consistently refined to ensure that they satisfied the load requirements while utilising available resources and fitting within the overall design philosophy applied throughout the entire facility.

The coils are built to work at relatively elevated fluid temperatures which adds size but improves long term plant energy efficiency and therefore operating cost and viability. The detail design done by AMC Engineers was focused on the best overall site solution. Having a view of each part working in conjunction with the others in the system allowed HC Heat Exchangers to design coils that overcame challenges related to pressure drops, laminar flow regimes and defrost energy considerations without compromising on performance.

Based on the scale of the project, the tender for the cooling coils invited submissions from international suppliers but local supply was secured based on product design coupled with the most attractive offering.

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Gert van Rooyen, HC Heat Exchangers mechanical engineer.
Gert van Rooyen, HC Heat Exchangers mechanical engineer.

Van Rooyen says the coils defrost regime was the subject of much discussion and a crucial factor in the design of the units. In place of typical electrical defrost systems these coils make direct use of warm glycol heated by the waste heat recovery from the ammonia plant. This allows for quick defrosts with minimum energy spilled into the cooled space while eliminating risks from possible element failures.

Further to this the cooling units were supplied with ebm Axicool EC fans. This premium range of fans allows for low noise, ultra-efficient operation with long term monitoring and real time feedback on fan data points with protections built in to minimise down time and optimise operating points. There being a total of 104 blower coils and 416 fans with a total peak power consumption of 650 kW, it was important to optimise the fan speed and control to reduce power consumption to an absolute minimum.

“The efficiency of the fans is beyond the current regulatory requirements, even in Europe: for instance, providing for a IE5 energy rating when an IE3 or IE4 rating is sufficient at the moment. The detailed design calls for monitoring, tracking for errors, for restarting and for warning upfront of any maintenance problems,” van Rooyen adds.

The challenge of stockholding ramp up

“As a manufacturer of multiple cogs of the cooling machine that is implemented in various aspects throughout the HVAC&R space, the HC Group is always aware of the role that its units must play and their ultimate wider societal impact.”

The group is comprised of several companies that are all interlinked in the HVAC-R space. HC operates as a product supplier (as in this case) or also as a full solution provider, partnering with contractors to add value to the end users by means of full project implementations. The Pick n Pay distribution centre represents one of its larger contracts.

“We had a design which we tweaked as far as we could to make sure that it satisfied the requirements. The selected coils were efficient units that would last long and be efficient in terms of the operation, accounting for all the various issues such as temperatures and flows  in addition to whatever other challenges every specific design comes with,” says van Rooyen.

“We went to extremes to ensure that the materials we brought in were correct as to gauges, pricing for the specific job, and the correct stockholding – given work commenced just after Covid. We had to increase our stockholding by approximately 40% over our norm to ensure sufficient stock on hand given the various logistics issues, the fact the construction industry was ramping up and there were also strikes in various sectors.”

Van Rooyen points out that projects such as this have many different moving parts, “and you don’t want to get caught without even the smallest part as it can delay the entire project”.

“By the time our manufacturing component was complete, due to the nature of such a massive project there was still a fair amount of work happening on site: electrical work, installation work, fitting various components, adjusting various things during commissioning.

“Having increased our stockholding proved a good move, but coordinating stock levels and work with all the other contractors is the core of managing such a large project. Its scale required intense engagement with all parties. For instance, there was strike action and materials delays in between, affecting a range of items such as tubing and fittings – while ports were closed for several weeks. Even though we pre-ordered supplies of fans, for instance, they still took longer than initially expected. Coordinating all these issues to get them complete at the same time was quite a challenge, requiring constant dialogue with the main refrigeration contractor MRE.

“We were already busy, so taking on another large project was a challenge. We increased manpower in various parts of the factory, and managed the shifts accordingly. On the other hand, the benefit of being a large project was that it was quite repetitive enabling one to get into a routine to run things smoothly: plug in, play and repeat.”

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