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INCORPORATING COLD CHAIN |
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in production early on and became a pioneer in the field of modern heat pump technology . This provides customers with significant , measurable operational benefits as well as a future-proof solution that helps them to achieve their sustainability-related goals ”, GEA Refrigeration Technology noted in a product update .
Power supply constraints in some parts of the world are putting further emphasis on energy efficiency in the expanding infrastructure of the refrigeration sector and having to use that same power supply .
“ In a study conducted recently in South Africa we aimed to test the energy-saving potential that could be realised by using variable speed technology , specifically focusing on scroll compressors . By quantifying the saving , one can then easily calculate the savings over the full lifecycle cost considering the initial capital outlay and we further aimed to prove that lifecycle cost outweighs initial capital outlay when using energy-saving technology . Based on the results of this study , it is clear that when using even basic technology , a saving could be realised by merely changing one element of the cycle . Further savings could hence be reached by potentially changing , for example , thermostatic expansion to electronically controlled expansion , implementing smart defrost cycles , including defrost on demand and pulsing of fans during the off cycles .
“ Putting the electricity saving aside , further savings and optimisation features to be gained by using this technology include increased food safety due to accurate suction control , which directly leads to an upsurge in food shelf life , reduced sound levels due to compressor technology and EC fans , a smaller footprint – one unit to run several cold rooms – as it can adjust to load , lower maintenance cost due to fewer components , reduced complexity and capital cost on installation . It can safely be said that a minimum of 30 % in electricity savings could be realised in equally sized condensing units , when changing over from fixed speed scroll technology to inverter scroll technology . When looking at the expanded criteria , it is completely plausible to assume that the saving will most likely lead to even greater saving in electricity when sizing the units correctly , and combining the inverter scroll technology with the appropriate energysaving evaporator controls ,” says Danfoss South Africa .
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There are several national and international programmes that regulate refrigerants , one of those being the European F-gas regulation , which was passed in 2006 . The F-gas rule significantly reduces the amount of fluorocarbons that are sold in the European Union ( EU ) by dramatically phasing them down . As a result of the Kigali amendment more and more countries are stepping up legislative efforts to limit the use of HFCs .
WHY USE AMMONIA AS A REFRIGERANT ? Globally , there is an interest in ammonia as a refrigerant , both by itself , and in cascade refrigeration systems with carbon dioxide and other secondary system designs . Regulatory oversight on CFC , HCFC , and other synthetic refrigerants , have re-focused attention on ammonia to emerge as one of the widely used refrigerants that , when released to the atmosphere , does not contribute to ozone depletion and global warming .
New technology and equipment are leading to low and reduced ammonia charge designs . The application of these new low charge systems and packages creates an opportunity to use ammonia systems in a broad range of industrial , commercial , and indirect space conditioning applications that would not have been considered with traditional designs .
These changes will require industry to provide proper recommendations for both design safety and guidance for regulatory and code agencies .
Ammonia is an efficient and popular refrigerant due to its superior thermodynamic properties and low cost . Ammonia is environmentally benign , having zero GWP and zero ODP . It is hazardous when released in large quantities due to its toxicity . However , ammonia does exhibit a unique refrigerant characteristic due to its irritating odour . Persons exposed to an ammonia release will not voluntarily stay near concentrations
BASIC REFRIGERATION SYSTEM TYPES
• Single-stage compression system : This configuration comprises the components of a traditional refrigeration system , as well as a pump and a liquid separator . The high-pressure liquid refrigerant flows from the condenser to the expansion valve , which regulates the pressure and delivers liquid refrigerant to the liquid separator . From there , the refrigerant in the liquid state , is pumped to the evaporator and then back to the separator This ensures that the compressor does not receive any liquid . The refrigerant in the form
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that are health-threatening . Although ammonia will burn in a narrow range of high concentrations , it is difficult to ignite and will not support combustion after the ignition source is withdrawn .
WHY USE CO₂ AS A REFRIGERANT ? CO₂ is chemically stable and at the same time , inexpensive to produce . It is odourless , non-toxic , and naturally occurring in the surroundings and heavier than air ( it will settle at lowest level ) CO₂ is compatible with most materials ( being noncorrosive ). It has a high vapour density ( 700 % compared with R134a @ -10 ° C ) and high evaporating enthalpy ( 125 % of R134a @ – the gradient between velocity of vapour and liquid phase is lower compared to HFCs .
More heat energy ( 10 ° C ) is required to evaporate liquid CO₂ ( liquid sloughing ) and it has a low viscosity in liquid and gas lines ( small pressure losses ) with high heat transfer coefficients and high thermal conductivity > operate with 2K higher evaporating temperature Vs . HFCs operate with small approach on gas cooler and PHE . CO₂ has a high volumetric refrigeration capacity resulting in smaller compressors , components , and pipe work .
CO₂ concentration in ambient air plants should always be well ventilated for regularly air exchange . Airflow of mechanical ventilation shall be at least 15 air changes / hour , or the quantity obtained by the following equation : V = 14x10-3 x m ²/³ Where : V is the flow rate in m ³/ s m is the mass of refrigerant charge in kg in the system . A suitable CO₂ gas detector must be installed in the plant room and various areas on the trading floor .
WHY USE R290 AS A REFRIGERANT ? R290 is a refrigerant-grade propane possible to be used on a wide range of commercial refrigeration units . A highly pure propane , it has a low environmental
of vapour at low pressure rises and is drawn back into the compressor before repeating the entire cycle again .
• Two-stage compression system : This is the next evolution of the industrial refrigeration system , suitable for low temperature refrigeration applications , providing high efficiency and low compressor discharge temperatures . In this type of system , there are two compression stages , as the name implies . There is also a tank , called an intermediate cooler , between the receiver and the expansion valve . There is a coil inside the tank , where the main refrigerant flow passes through before
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impact and nominal global warming potential ( GWP ). It possesses no qualities that can destroy the ozone layer .
In nature , hydrocarbon refrigerants are constituents of oil and natural gas . Hydrocarbon refrigerants have excellent environmental , thermodynamic , and thermo-physical properties ; however , they are highly flammable . As a result of these factors , hydrocarbons are the molecular basis for the halocarbon refrigerants wherein some or all the hydrogen atoms have been replaced by halogens such as chlorine , fluorine , and bromine which reduce flammability but can cause unwelcome effects on the environment .
Hydrocarbon refrigerants provide a range of boiling points with applicability from cryogenics to air conditioning . In the past hydrocarbon refrigerants have had limited applications primarily within the petrochemical industry to provide industrial chilling and process refrigeration . With the phase out of the CFCs , hydrocarbon refrigerants are entering into new arenas . One of the first uses has been as a small quantity constituent in halocarbon blends to provide enhanced thermo-physical properties , such as oil miscibility .
For the last decade , in European and Asian countries , the commercial market for systems using hydrocarbon refrigerants has been growing as a result of concerns about the environmental consequences of the halocarbon refrigerants .
Examples of commercially available equipment using hydrocarbon refrigerants are systems with small charges including domestic refrigerator / freezers and portable air conditioners , stand-alone commercial refrigeration systems including beverage and ice-cream machines , as the primary refrigerant in centralised indirect systems for supermarket refrigeration , transport refrigeration systems for trucks , and chillers in the range 1kW – 150 kW ( 0.3 – 40 tons of refrigeration ).
entering the main expansion valve the refrigerant continues its flow via the separator , the evaporator and back to the separator . Another refrigerant flow comes out of the main line and is sprayed into the tank via an expansion valve to produce a cooling effect : as it is sprayed and evaporates in the tank , it cools the submerged coil . This sub-cools the main refrigerant flow inside the coil before this reaches the main expansion valve . The vapour refrigerant drawn out of the separator flows to the low-stage compressor to increase its pressure . From there , it flows into the intermediate cooler , which helps condense the
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