Secondary Refrigeration: A Viable Alternative

Secondary Refrigeration: A Viable Alternative

Our Industrial Product Manager, Fraser Higgins, discusses the benefits that secondary refrigerations systems can offer.

It is clear low Global Warming Potential (GWP) refrigerants are the future for refrigeration systems as the phase down of HFC gases gathers pace. Preparing to comply with the reduced levels of refrigerant gas carbon emissions to be enforced by 2030, increasingly more businesses are investing in switching to the lower GWP HFOs or natural refrigerants.

With tens of thousands of supermarkets, shops and restaurants using commercial refrigeration affected by the F-Gas regulations, several major retailers have already announced commitments to move away from HFC gases. Aldi has confirmed it will be utilising natural refrigerants in all of its stores, with a transition to CO2 refrigeration units, while Co-op has committed to adopting the HFO R448A as its preferred option for refrigerant needs across its stores.

While natural refrigerants meet the requirement of reducing carbon gas emissions, they are not harmless or non-toxic. This leads to the question of why secondary refrigeration systems are not being widely adopted to comply with the new regulations and reduce environmental impacts.

Traditional direct expansion (DX) systems are still the most widely operated across a variety of industries, but we are advising that adopting a secondary refrigeration system could not only reduce environmental impact, but deliver significant cost savings.

A centralised DX set up is typical for refrigeration systems installed throughout Europe and usually utilises between three to eight compressors, located in a plant room, which are connected to an external air-cooled condenser. High pressure refrigerant is fed directly from the plant room to the chiller units, via a liquid receiver, the refrigerant vapour is then returned to the compressors via a suction line.

The main issue experienced with DX solutions is the leakage rate of refrigerant, due to the large refrigerant charge required; a typical supermarket DX system will use between 1,360kg – 2,270kg of refrigerant. The average annual refrigerant leakage rate experienced in these systems is up to 15%, which can rise to up to 30% in older systems.

In contrast, secondary refrigeration systems use two separate circuits, with heat from the chiller units transferred to a heat exchanger by circulating a cooling medium, where the heat is absorbed by a primary refrigerant. Typically, the cooling medium used is a water and either glycol or hycool mixture, with propylene glycol being the most popular, particularly in supermarket applications, due to its non-toxic properties.

Due to the primary circuit being confined to the plant room, up to 90% less refrigerant is needed for operation of the secondary refrigeration system, significantly reducing the risk of leaks and completely eliminating the opportunity for leaks near food chillers as the refrigerant does not leave the plant room.

There is a common misconception that secondary refrigeration systems have a higher installed cost, due to the additional expense of the pumps and heat exchanger, however these initial costs can be offset against other savings over the lifetime of the system. The pipework requirements are less demanding within a secondary loop solution, helping to bring down the initial set up costs. The pipe network for a DX system needs to be designed to ensure oil returns to the compressor, which is eliminated within a secondary loop as there is no need for an oil return.

Secondary refrigeration systems also boast a lower cost of operation due to the increased energy efficiency, resulting in average energy savings of 4.9%, compared with DX systems. Less maintenance requirements also add to the operational cost savings, as a simplified pipe network, reduced number of leaks and a more easily accessible primary circuit all add to a reduction in maintenance costs of up to 20%.

Due to the changes in pipework requirements, secondary loop systems can be delivered as a factory-assembled unit, which can be connected easily to the pipe system on-site, offering further installation time and cost savings. However, if this option is pursued, it is important to select a pipe network that can mirror these installation savings to help meet budget and project constraints.

A reliable pipework system is integral to transfer the cooling medium around the refrigeration circuit, with single thinwall steel the most widely installed for this application. However, glycol and hycool solutions can be highly corrosive, and if a corrosion inhibitor is not added to the solution, they can begin to corrode metal materials very quickly.

Due to its corrosion resistant properties, our SuperFLO ABS pipework system is increasingly being utilised as a more effective and durable solution for secondary refrigeration systems. Its wide operational temperature range of -40°C to +60°C makes it ideal for a secondary refrigeration application, which typically operates at -15°C to -17°C.

In addition to the performance benefits, SuperFLO ABS can also aid the installation process; at 1/6th the weight of steel, its lightweight nature makes it easier to handle on site, while its quick and simple solvent weld jointing technique significantly reduces installation time. Taking all these factors into consideration, and when compared with single wall steel, SuperFLO ABS pipe offers an installed cost saving of 30%, making it a more cost effective option.

For further information on our SuperFLO ABS pipe click here


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