COMPRESSORS


answers in the abstract. Therefore, refrigerant selection should be considered carefully alongside compressor selection for each application, with due regard to environmental performance and safety considerations. There is also the 'life-expectancy' question to consider in relation to refrigerant choice. The F-Gas regulations are currently under review, and while a final decision has not yet been made, it seems likely that the current phase- down timetable will be accelerated, and stricter controls introduced on even medium and relatively low GWP fluids.


This combination of factors can make quite a complicated decision matrix. Our advice is, if in doubt, consult the supplier – we can provide guidance on the most efficient solution for a given application, given the conditions and priorities for a project. Selecting the right compressors and


refrigerant are only half of the story, of course. While compressors are the biggest consumer of power, they obviously don't operate in isolation, but as part of an integrated system. It is essential to ensure the overall system is designed and operated to maximise energy efficiency. With energy back at the top of the agenda, it is worth reminding ourselves of the foundational principles. The golden rule is – minimise the cooling load, and minimise the 'temperature lift'. This means providing cooling at the highest possible temperature consistent with quality and safety requirements for a given application, and rejecting heat at the lowest possible temperature.


All things being equal, the amount of energy consumed by a refrigeration system depends on the temperature difference between the product being cooled and the ambient. The bigger the temperature lift, the more energy required. Small changes in either side of the equation can have a dramatic impact on energy efficiency. For example, according to UNEP just 1°C of additional temperature lift can add between 2-4% to the amount of energy used by a system. Poor plant design or a badly managed system can easily add an extra 10 to 15 degrees to the temperature lift – which would equate to an additional 20% to 40% on the total energy bill. This is a colossal waste, financially and environmentally, and entirely avoidable. Another important aspect to consider in


relation to system design is of course peak load. Few refrigeration systems operate at peak load for more than a few hours each year, and spend most of the time operating at part load, at ambient temperatures well below the design


peak. With energy a priority, it makes sense to design for maximum efficiency at part load conditions, where it will be operating the majority of the time. Inverters have come to the fore recently as a means of reducing energy consumption, by matching refrigeration output to load by controlling the speed of the compressor and/or fans. Properly implemented and matched to the system, inverters are very effective and significantly improve refrigeration efficiency and performance. The downside is that inverters can be


expensive and add a significant additional upfront cost when purchasing new equipment. If poorly implemented, they can also cause interference problems with electrical equipment on a site. A lower-cost alternative to inverters for cooling capacity control, developed by my own company, is highly effective and without the high capital cost and potential interference issues. The CRII–Varistep control system enables proportional modulation of compressor output in response to changes in load and system conditions, giving stepless capacity adjustment from 50% up to 100% as standard, and 10% to 100% as an option. It uses a different approach to managing capacity, based on the principle of incrementally blocked suction. This uses control pistons in combination with a bespoke algorithm to enable fine, fast-reacting control of compressor output. Recovering heat from refrigeration systems that would otherwise be wasted also presents further opportunities to enhance efficiency. Following successful field tests, we recently added a new heat recovery option to Ecolite, which further boosts efficiency. The design enables end-users to harness heat from the condenser that would otherwise be wasted to air, to heat water. In addition to careful equipment selection and system design, higher energy costs highlight the importance of planned service and maintenance. In this regard, ensuring correct system charge is a key area.


Systems operating with a reduced charge are a double whammy in terms of energy: they are


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It is essential to ensure the overall system is designed and operated to maximise energy efficiency.


less thermodynamically efficient, and consume more power to achieve the same refrigerating effect. As well as increasing running costs, they also produce more carbon emissions, which obviously has a negative impact on the environment. Estimates vary, but UNEP’s calculation is that when the refrigerant charge is reduced to 85% of the correct amount, then annual running costs are increased by around 10%. The running cost penalty is non-linear, so that at 60% of the correct charge, the running cost penalty is around +45%.


This is a huge surcharge on the cost of running cooling equipment, and entirely avoidable by regular service and maintenance. Operators who have taken a decision to cut back on regular servicing as an economy measure in the past should urgently review their approach. It is never a wise decision to withdraw regular maintenance, and even more of a false economy with today's high energy costs. The hikes in energy prices are clearly unwelcome, adding pressure to businesses and further fuelling inflation. However, if there is an upside it is that they force us to consider again what we can do to improve energy efficiency. Fortunately, as we have highlighted, there


are plenty of no-cost or low-cost options to help reduce consumption and mitigate the impact on the bottom line.


www.acr-news.com • May 2023 23


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