Businesses that rely heavily on refrigeration for their day-to-day operations are painfully aware that even the slightest inefficiencies can make a significant impact on their electricity costs, which is why ensuring these systems always perform at an optimal level must be a priority. But what many businesses don’t realise, is that the refrigeration infrastructure also presents opportunities for additional cost savings. Recovered waste heat can be used to provide energy to run other operational elements within the business at a fraction of the cost.
Dawie Kriel, Head of Business Development at EP Refrigeration – a division of Energy Partners and part of the PSG group of companies – explains that the waste heat produced by a refrigeration system’s compressor units can in fact help to further reduce electricity and other energy costs. “If a business is not capitalising on the opportunity to recover waste heat to provide energy, they are also losing the opportunity to increase their refrigeration plant’s efficiency and resultant savings.”
Kriel explains that refrigeration systems work by compressing and expanding gas in a closed system. “As the refrigerant gas is compressed, its temperature increases, and it is that heat that can be captured at various points in the system and can be used at a low cost in one’s operation.”
He says that in industrial applications, heat is classified as either low quality-, medium- or process heat. “Low quality heat is close to ambient in temperature, meaning it is 5 to 10 degrees warmer than the surrounding air. Medium heat is commonly the temperatures that you will see in geysers (around 55℃), and process heat is used in operations like cooking or pasteurising (which is hotter than 70℃ and up to 200 ℃).”
Kriel adds that the two lower grades of heat are typically produced by a refrigeration system and that process heat is possible when a heat pump section is added. “If the system’s compressor is water or oil cooled, you can easily recover heat from that part of the system that is well within the medium heat range. Where the gas is compressed in the system, temperatures can reach over 100℃ in some systems (superheat), which can also be recovered for process heat. This only makes up about 10% to 15% of the total heat that the system generates and is easy to capture. Lastly, the condensing stage rejects most of the heat, which just above ambient temperatures at around 35℃ to 40C.”
He notes that recovering even the 10% of easily accessible medium quality heat from a refrigeration system can make a significant difference to a business. “The medium quality heat can be used directly to heat water up to around 55℃, for lower-order applications such as washing. As for the low-quality heat, keep in mind that this makes up nearly 80% of the heat produced by the system. By adding a heat pump to re-compress the low heat gas, you can bring its temperature up to the process heat range of 90℃ to 100℃, while still saving a significant amount on energy costs.”
Of course, investing in a heat pump to bring this low-quality heat to a useful temperature is an additional cost, but Kriel argues that the capital expenditure of this is justifiable. “If you use electricity to bring water up to process heat in the conventional manner, it costs the operation an average of R1,50 (depending on the local electricity tariff) per kilowatt-hour. Using a coal-fired boiler to produce steam brings this cost down to around R0,30 per kilowatt-hour. By comparison, harvesting medium-quality waste heat from an existing refrigeration system, can bring your average cost down to R0,19 per kilowatt-hour.” By adding a heat pump to increase the quality and amount of heat, the price will go to R0,40 (depending on the local electricity tariff) per kilowatt-hour which is competitive with coal and much more sustainable.
Beyond the cost saving, installing a heat pump is a far more convenient solution as it requires less oversight, maintenance and manpower than operating a coal boiler. But most importantly, recovering waste heat to generate hot water can significantly elevate a company’s carbon emission avoidance figures. “According to our findings, one of our client’s that uses waste heat reduced their carbon emissions by nearly 1200 tonnes per year, just by switching from electricity to waste heat recovery.”
Kriel asserts that there are scores of businesses that can benefit from waste heat recovery. “In the food processing industry, businesses can use the process heat produced from heat pumps for cooking, sterilising and drying. Abattoirs, food processing facilities and dairies are just some examples that can integrate their utilities and benefit significantly from waste-heat recovery. These types of operations have both heating and cooling requirements, the majority of which keep the two functions completely separate. Most of the heat-related processes in these settings require heat that is just below boiling point (90℃ to 100℃). In this case it just makes financial sense to obtain this heat from a waste heat recovery system. Processes that need more heat (over 100℃) might be hard to power directly with a waste-heat system, but you can still use this configuration to pre-heat your process feedwater.”
He goes on to explain that waste-heat recovery even has a place in non-industrial settings. “Businesses that use regular warm water for things like employee showers, basic cleaning or under-floor heating, can take that heat directly from the refrigeration system. This means that even retailers, hotels and shopping malls can meaningfully reduce their costs by redirecting waste heat.”
Kriel notes that waste heat recovery is not a one-size-fits-all approach. “Depending on the layout of an operation, the specific heating requirements and the refrigeration system being used, the way in which waste heat is harvested and used will be different. It is therefore important to partner with a service provider that has an intimate understanding of both refrigeration and heat recycling. If you already have an outsourced contract for your refrigeration, it is very possible for your service provider to include the installation and operation of a heat capture system into your contract, provided your partner has the technology and expertise to facilitate it,” Kriel concludes.