TREATMENTS AND FLUIDS
Secondary cooling: helping to take the heat out of F-Gas phase down
With so much market attention on the switch to lower GWP refrigerants to meet the F-Gas phase down steps, many secondary refrigerants can also offer a quota and GWP free solution, as Climalife explains.
S
econdary refrigerants have long been used in systems in conjunction with a primary circuit and can help to significantly reduce the amount of refrigerant used in a system and also provide the option to consider ultra-low global warming potential (GWP) alternatives.
How and where is a secondary refrigerant used? As its name suggests, a secondary refrigerant can be used alongside a primary circuit but, unlike the refrigerant in the primary circuit, the fluid used in the secondary circuit does not undergo phase change and needs to stay as a free flowing liquid over a wide range of temperatures. The fluid normally performs the function of transferring thermal energy, hot or cold, from one location to another. Simply put, by using smaller quantities of refrigerant to cool the secondary refrigerant via a heat exchanger, the fluid can be pumped around the system rather than vast quantities of refrigerant.
These fluids are used across a range of applications, from small water chillers and heat pumps containing around 10-25 litres, to larger refrigeration plant that transports cooling capacity from the plant room to various points in a system, and which may contain as much as 100,000 litres operating at temperatures well below the freezing point of water.
Secondary refrigerants are sometimes used in conjunction with ultra-low refrigerant options
such as ammonia, which has a GWP of 0, or CO2 with a GWP of 1. For example, ammonia would
normally be too hazardous to pump in volume around an indoor facility, however by installing an outdoor chiller, smaller quantities of ammonia are used to chill the secondary refrigerant which is then pumped around the facility. This process can similarly be followed with refrigerant gases, whereby far less refrigerant charge is required as it simply chills the secondary refrigerant which is then pumped around the system.
F-Gas phase-down
With the impact of F-Gas being felt, hybrid VRF systems and water loop condensing units offer new options to lower GWP and reduce refrigerant charge. The use of A2L, mildly flammable low GWP refrigerants could be very viable in such applications.
Some high temperature applications, such as air conditioning, may only use chilled water as the secondary refrigerant, however its freezing point is a problem and if used without some form of anti- freezing agent or inhibitor package, it runs the risk of freezing or corrosion which can cause costly damage to a system.
Types of secondary refrigerant on the market:
Mono Propylene Glycol (MPG) is probably the most commonly used secondary refrigerant as it is safe to use at food manufacturing sites
Mono Ethylene Glycol (MEG) is used in some industrial applications and is classified as harmful, as ingestion of as little as 90ml can be fatal
Bio glycol is growing in its popularity as a 38 June 2018
www.acr-news.com
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