Cold Stores

Recent discussions with cold store operators around the question, “Given the difference in capital cost why should anyone even look at installing an ammonia as opposed to a Freon refrigeration system?”, prompted me to quiz SARDA’s John Ackermann on the topic. John started by saying that all the chicken abattoirs, Elgin fruit producers most of the big wine producers were using ammonia. He reckons 90 to 95% of current low temperature freezer space in SA is cooled with ammonia. “On a capital cost basis alone, there is no way that an ammonia (R717) system could compete with a Freon one.” Safeties must be considered and coded welders are required for installation and there is always some level of redundancy built in,” he continued. “You could be looking at R3.9M for an ammonia plant when you would pay R2.4M for a Freon equivalent.  “But that’s just the capital cost. You also have to look at the system’s COP”. (co-efficient of performance). “Clients must compare the COPs for the Freon and ammonia alternatives, calculated as the number of kWR of refrigeration obtained per kW hr of electricity used. This will vary by plant but should be available from the suppliers”. “Hard to say what the exact difference will be but not impossible that the COP for an ammonia plant can be close to double that for a Freon equivalent.” In other words, per month, for the life of the store, you could be paying almost twice as much for running a Freon as opposed to an ammonia plant. The energy cost differential increases with the size of the store. According to Christo van der Merwe, of MRE, (Marine and Refrigeration Engineering), Freon systems can be reasonably cost effective up to about 800 pallets. After that, ammonia becomes increasingly attractive. In fact, Christo says, over the life of a refrigeration system, the initial capital cost can represent as little as 10% of the total plant operating cost. The cost and availability of synthetic Freon refrigerants must be considered. They are all imported so the cost will vary with the value of the Rand. While ammonia is imported too, it can also be sourced locally. Ammonia is relatively cheap at approximately R28 per kg in Cape Town. Freon types are priced differently, but you are looking at an average of R120per kg. Freons are also less dense than ammonia, requiring up to double the weight to reach the same volume in litres. Leakages per year should be zero but practically one can budget at about 25 to 30% of charge. Suppliers of refrigeration systems should separate out the cost of a gas charge for their proposed system. This will give you an idea of what you might pay annually in the future. Being odourless, a lot more Freon can be lost before the leak is identified. With ammonia, you know immediately when there is a problem. Environmentally, the COP 21 summit on climate change in Paris advocated a carbon tax. There is also a move afoot to limit the supply of the Freon gases, because of their GWP (global warming potential.) This is likely to increase prices. Ammonia’s global warming potential is zero. The Freons start at a rating of 1800 and go up to over 3000. Any tax (according to John Ackermann it is inevitable in SA ,the draft bill was issued in November 2015, will  be on the basis of TEWI or “total environmental warming impact”, which takes the following into account; COP or Co-efficient of performance. In this instance it is linked to the amount of carbon used to produce a kW of electricity. In SA it is 0.9 kg as we are predominantly coal based electricity producers. Leakage of refrigerant per year. Ammonia is fine as the GWP is zero. But if you have a 25% leakage rate with Freon and it has a GWP of 2100, then the tax will increase, frighteningly……. Finally, ammonia plants with the correct initial design can be expanded cost effectively if the cold store grows. I personally know of one instance where a Freon system was removed when the store was extended and an ammonia plant installed to cover both stores.