ACR Journal

CMYK / .ai CMYK / .ai CMYK / .ai acrjournal.uk 17 REFRIGERANTS For example, using theoretical cycle calculations for medium (-8°C) and low temperature (-35°C) refrigeration conditions it can be seen in Table 2 that most of the lower GWP alternatives for R-404A have a higher energy efficiency. It can also be clearly seen in Table 2 that low GWP does not necessarily mean good energy efficiency. The lowest GWP refrigerant in table 2 is R-744 (GWP=1), but the energy efficiency of a basic booster system compared to other refrigerants in basic direct expansion (DX) systems, delivering the same cooling capacity, is much lower which will lead to higher total emissions and higher energy costs. The energy efficiency of R-744 systems is often enhanced by using internal heat exchangers, parallel compression, and ejectors, but the energy efficiency of normal DX systems can also be improved by using internal heat exchangers or mechanical subcooling. This however, is often not considered for these types of systems even though the cost is likely to still be less than that for a basic R-744 system. Heat recovery This is a hugely underutilised technique that has the potential to greatly reduce energy usage by re-using the waste heat produced from the refrigeration system, or indeed any process that produces excess heat, that in the past has been expelled to the environment. A white paper published by Chemours in July 2021 considered heat recovery from a supermarket of approximately 2300m² sales floor area using either R-454C or R-744 and compared the results to a basic R404A refrigeration system with either a gas boiler or air source heat pump (AS HP) supplying all the heating requirements. Numerous (62) heat recovery scenarios were considered and the results for a typical UK climate (Leicester) demonstrated the huge potential for lowering total system emissions and life cycle costs. The majority of savings are achieved by reducing energy consumption, with the top 4 scenarios (all using R-454C) reducing emissions by 66-70% compared to the gas boiler baseline and 44-50% compared to the AS HP baseline. It is clear from the results of this study that heat recovery will greatly decrease the energy consumption with any refrigerant but also clearly shows that the lowest GWP refrigerant does not necessarily give the best result. With governments setting targets for reduced emissions and energy usage, it is clear the refrigeration industry has an important role to play. To achieve the maximum reductions available, it is important to thoroughly investigate all the options and not just make decisions on a single parameter, such as refrigerant GWP. As shown in this article, low GWP does not necessarily mean high energy efficiency and a poor choice of refrigerant technology may even lead to an increase in lifetime emissions, energy usage and operating cost. Advice on which solutions best fit your requirements is readily available and the team at Climalife have the tools and knowledge to lead you to an eco-efficient future. *Theoretical calculations made for a 4kW LT, 10kW MT cooling load, comparing a basic flash gas bypass R-744 (i.e. no internal heat exchangers, parallel compression or ejectors) system with 2 individual systems for the other refrigerants. Superheat (12K), subcool (2K) and compressor efficiency (0.65 MT and 0.64 LT) values were the same for all refrigerants . Neil Roberts