Cold Link Africa July/August 2019 - Page 25

FEATURE INCORPORATING COLD CHAIN Refrigerated warehousing and storage – refrigerants matter By Ilana Koegelenberg COMPARING SYSTEMS With so many different options when it comes to refrigeration solutions for cold stores, how does one choose the right system for your project? It will obviously depend on the type of product being stored, but there are also other considerations. Shane Moodley, cold store manager at Go Chill (part of the Go Global group) in KwaZulu-Natal, explains that plant downtime and ammonia leaks are their biggest concern as the client. So, what do they look for in a refrigeration system when setting up a new cold store? “It must be user-friendly and friendly towards the environment, as well as compatible for our industry,” he says. “Also, it must be able to handle the cooling when the cold store is running at full capacity.” Grant Ford of Matador Refrigeration explains that the following are usually considered before selecting a system: energy savings, eco-friendly requirements, and how user-friendly it must be. Then the usual requirements: insulation thickness, size, lighting, access (manual, forklifts or trolleys). Also, airflow is critical to achieve constant temperature throughout the room. Humidity required depends on product requirements and things like fast chilled versus slow chilled also makes a huge difference. For example: potatoes need to come down at 2°C a day to avoid them going glassy when warmed up. “It’s crucial at all times to avoid having the product integrity compromised,” says Ford. According to Ford, the consideration taking place when choosing a system nowadays is linked to: a. Mechanical systems: i. Simplex – single compressor application ii. Multiplex – multi compressor application b. Or chosen by refrigerant: Hydrocarbons, ammonia, CO 2, or synthetic refrigerants. c. A multi-rack also provides a more controlled temperature range. As mentioned, one of the main considerations for selecting a system relates to the refrigerant used in the system. HFC refrigerants are still the most common solution (and cheapest) but as the imminent global phase-down starts taking effect, many are looking at more natural alternatives such as hydrocarbons, ammonia, or CO 2 systems. Christo van der Merwe of Marine and Refrigeration Engineering (MRE) explains that the most common systems are as follows: • Ammonia systems Industrial ammonia is the most appropriate system for large installations and has the best coefficient of performance (COP) available. These systems are designed for a 30-year or greater life span and offer excellent reliability if maintained correctly. For the smaller sized cold store installations, the first costs can be considerably higher but over a 20-year life cycle costing, which takes into account the total operating cost, the ammonia option can be an interesting proposition. • CO 2 cascade systems CO 2 is established as a preferred ‘green’ solution for supermarket applications and is being considered for certain low temperature applications such as freezer stores. CO 2 (sub-critical) cannot match the COP of ammonia plants though. CO 2 (trans-critical) COPs are just starting to match typical air-cooled R404s COPs and the higher ambients in South Africa must be taken into account when evaluating the total operating costs of this solution. • R404a, R507, and other HFC cocktails Air-cooled synthetic refrigerant systems omeone once told me that no matter how bad the economy gets, people still need to eat. And with more and more people moving to cities, the role of the cold store is becoming more critical than ever to ensure there is enough perishable product where it’s needed most. So, despite many HVAC projects being put on hold and the state of the industry being described as ‘sluggish’ at best when it comes to projects, cold stores are still going up left, right and centre. A vital link in the cold chain, the cold store is crucial for ensuring perishables make it to their fiinal destination in the best possible condition. But not all cold stores are equal and it seems the key distinguishing element has become the refrigerants used in the refrigeration plant. Are natural refrigerants the way forward? We speak to the local stakeholders to find out more. Hydraulically operated dock levellers operate much faster and more reliably than their air- powered counterparts. S We chat to the professionals about all things cold storage – from selecting your refrigeration system to maintenance, and local trends in the market. What are the dos and don’ts of refrigerated warehousing and cold storage? The size of the cold store will influence which refrigeration system should be selected. are the correct solution for small cold storage applications, typically up to 150 or 200 pallets of frozen storage. These systems have a lower first cost but the running costs are higher (due to a low COP and high electrical costs) and often the maintenance costs can be higher due to low quality installations with gas leaks and equipment failures. Marius la Grange of Energy Partners Refrigeration Solutions, who is also the current South African Institute of Refrigeration and Air Conditioning (SAIRAC) national president, goes into a bit more detail. Consider a distribution centre (DC) application. It’s important to calculate the medium temperature (MT) load COLD LINK AFRICA • July/August 2019 required compared to that of the low temperature (MT), advises La Grange. The COP of the LT load is significantly worse than MT applications, regardless of the refrigerant used. “That is an important ratio to consider when comparing one installation with another.” HFC installations are the most common, with the refrigerants being selected based on the planned operating conditions, explains La Grange. These offer a lower capital outlay but with higher operational cost (energy consumption). They are also fairly simple to install in a relatively short time period. “The long-term premium is of course the energy consumed to keep them running and there is not much one can do to make them more www.coldlinkafrica.co.za 25