Produced in Association with
SERIES 22 / Module 03 Refrigeration
typical upgrade is to fit electronically commutated (EC) fan units. Water cooled condensers are typically used on larger chilled water and process systems. As with air cooled system uprating the unit may be beneficial. Water cooled system can be susceptible to fouling if the correct water treatment is not used. Unlike the fouling of an air cooled unit, it can be harder to detect. Evaporative cooling (cooling towers) can be energy efficient, but these systems do require adequate controls for Legionella risk.
● Evaporators – as with condensers upsizing can be beneficial. Whilst condensers can become blocked with debris, for evaporators the issue can be icing up. Where de-frosting is part of the system operation ensuring ‘defrost on demand’ as opposed to defrost on a fixed cycle time can lead to savings.
● Expansion valves/devices – ‘smart’ devices can be used on larger systems where they are economically viable. Typically for a large system an electronic expansion valve might have a payback of 1-2 years.
● Heat recovery – given a refrigeration system needs to reject heat, finding a use for that heat can improve overall performance – if an economic use for that heat can be found. The issue with all heat recovery is the time and quality match between the waste heat and its potential use. Refrigeration systems can provide around 10% high grade heat (at 50-60ºC via a de-superheater) and 90% low-grade heat at 20-30ºC. Recovered heat can be used to pre-heat hot water – this could be cost effective in a food processing environment where there is a regular demand for hot water.
● Refrigerant charge – a refrigeration system can operate with a reduced charge and this may not be noticeable, until the system needs to operate at full capacity. However, operating with a reduced charge is inefficient. Systems typically become under charged as a result of refrigerant leakage. Many refrigerants are powerful GHGs adding to the impact of system inefficiency and reduced capacity.
● System monitoring – whilst a domestic fridge is pretty much fit and forget, the same is not true of
larger systems. System monitoring and control can be used to optimise performance and identify operational issues in advance of failure. Here we can expect to see the wider application of digital technology and the possible impact of AI.
● Insulation – this is often overlooked, but poor quality or poor condition insulation can have a significant impact on system performance. Low- temperature insulation needs to be air-tight as well as having good thermal performance. External insulation needs to be weather protected, otherwise it will breakdown over time. Where there is chilled water pipework, poor performing insulation will add to the system load.
Absorption chillers Whilst the majority of systems use the vapour compression process, some systems use the absorption cycle. The difference between the vapour compression cycle and the absorption cycle is that the compressor in the vapour compression cycle is replaced by a chemical absorption process and generator, with a pump to provide the circulation and pressure change. The absorption cycle is referred to as
a heat-operated cycle because most of the energy required to operate the cycle is heat energy. As it uses a compressor the vapour compression cycle is described as a work-operated cycle. Absorption chilling is a relatively
small part of the total refrigeration market. At the smaller end of the market there are absorption fridges/ freezers powered by LPG for mobile applications. Where larger scale units come into play is where there is an available waste or low-cost heat stream. Possible applications include new
CHP plant; existing CHP with spare heat; applications where waste heat is available (e.g., exhaust steam); where a low-cost source of heat is available (e.g., landfill gas, geothermal); where solar energy can be harnessed. Absorption chillers can be part of a
so-called tri generation system – which generate electricity, provide heat and provide cooling. There are various types of absorption
chillers, but they all work on a similar principle. An absorption fluid is evaporated, removing heat from the chilled water. A heat source such as steam, exhaust gas or hot water is then
used to regenerate the absorption solution. Typical absorption solutions are lithium bromide and water, and ammonia and water.
Energy Technology List – the government’s Energy Technology List has a range of refrigeration equipment listed that is within the top 25% of most efficient products in the marketplace. This includes absorption systems, condensers, chillers, cellar cooling equipment, refrigerated storage and display cabinets, accessories for refrigerated display cabinets, compressors, leakage detection and system controls. When designing a system, it makes sense to review these products as part of the equipment selection process.
Choice of Refrigerant Fluorinated greenhouse gases (F gases) used as refrigerants are known to cause significant environmental damage. In particular as some have very high Global Warming Potentials (GWP). These can be as much as 3,000 times greater than CO₂ – which can also be used as a refrigerant. Arguably, with a sealed system, leakage should not be a significant problem. However, the IPCC suggested that globally the average annual leakage could be in the region of 7−12% of the refrigerant charge. Fluorinated greenhouse gases (F
gases) include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6) For this reason, the F-gas regulations were introduced. These regulations place a responsibility on system operators to prevent leakage from their equipment and for contractors to share that responsibility.
NetRegs provides guidance on the F-gas regulations. Great Britain (England, Scotland and Wales) is phasing down HFCs, including mixtures, by 79% by 2030. This is compared to the average use of HFCs between 2009 and 2012. Part of this phase down is the banning of certain F-gases for certain uses. However, the banning of gases does
provide an opportunity to consider an upgrade or replacement of the system. Another option is the use of a so-called ‘drop in’ gas – caution is required as these may have an impact on system performance.
Other refrigerants ● Ammonia, NH3 (R717) is a ‘natural fluid’ with zero Ozone Depletion Potential (ODP) and GWP, however its toxicity, corrosiveness and explosiveness mean it is a niche refrigerant. Typically, it is used in large, industrial refrigeration systems.
● Carbon dioxide, CO₂ (R744) is also a natural fluid with zero ODP and GWP=1, but without the negative effects of some other natural fluids. CO₂ is now being widely used in retail refrigeration systems.
Air Conditioning Inspections The Energy Performance of Buildings (England and Wales) Regulations 2012, as amended in 2020 (the EPB regulations) place obligations on anyone who manages or controls an air conditioning system. The main requirement is for a regular inspection (every five years) of air conditioning systems with an effective rated output of more than 12kW. TM44 is the accepted guidance for the UK for assessing the efficiency of air conditioning units. The inspection must be carried out by an accredited assessor. The assessor’s report will tell you
about the current efficiency of your equipment; suggestions for improving the efficiency of your equipment; any faults and suggested actions and suggestions on how to reduce your air conditioning use. It is aways worth checking on the
‘TM44 status’ of a building as some building operators do not have valid inspection certificates. For England & Wales checks can
be made at
https://www.gov.uk/find- energy-certificate
The future Looking at refrigeration equipment itself, there are two potential future pathways. One is advanced vapour compression systems with low or ultra-low GWP refrigerants and a decarbonised grid, the other with non-traditional technologies. The UN Environment Programme suggests that GHG emissions from cooling could be reduced by at least 60% by 2050 against a 2022 baseline. However, better management and operation of existing systems has a potential that can be exploited today.
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