Technical
Figure 3 - Trans-critical system diagram
Image credit : https :// betterbuildingssolutioncenter . energy . gov / sites / default / files / attachments / Transcritical _ CO2 _ Supermarket _ Refrigeration _ Systems . pdf
Condensed high-pressure liquid will drain from the GC outlet into the liquid receiver ( flash tanks ) in sub-critical operation with the HPV valve open . Installation of the GC should ideally allow condensed liquid to drain from the GC with the GC outlet positioned above the flash tank inlet . This would also allow any compressor oil that might end up in the GC to constantly drain from the GC during operation .
This is not essential and many installations have the GC outlet below the flash tank inlet due to site limitations , but it does increase the system charge in such cases . If possible , plan to have the GC one level above the plantroom , where the flash tank is positioned , and route the drainpipe in such a way as to allow the condensed R744 to drain out the GC . Shopping malls , for example , have strict rules regarding pipe routing so start planning early and avoid p-traps for the condensed liquid to accumulate on the way to the liquid receiver .
In most cases the ambient air would also cool down the further the GC is from the ground level , potentially reducing energy usage . Having the GC installed as high as possible pays back long term . Your installation should also reduce the likelihood of warm discharge air from the GC being drawn back into the GC inlet . Should the air onto the GC be warmer that the ambient you might have warm air recirculating , so this is something to check during commissioning .
Adiabatic pre-cooling walls installed in the airstream prior to the gas cooler face area can reduce the ambient temperature airflow the gas cooler receives . This is an option in areas with extremely high ambient conditions making a trans-critical system viable where it would otherwise not be suitable .
Adiabatic pre-cooling walls are used to reduce the dry bulb air temperature onto the gas cooler face area . The energy savings are undeniable , but the regular maintenance required by adiabatic pre-cooling systems seems to be a deterrent and such applications remain limited . The moderate water consumption during high ambient conditions also being a limiting factor to some sites . RACA
" A trans-critical system would be designed and built capable of transcritical operation , but it is far more likely to operate in sub-critical mode for the greater number of hours each year ."
RECOMMENDED RELATED READS
1 . https :// r744 . com / gas-cooler-control-needed-for-efficienttranscritical-co2-says-australian-contractor / 2 . https :// baltimoreaircoil . co . za / en / media / 745 3 . https :// core . ac . uk / download / pdf / 42131256 . pdf 4 . http :// www . scielo . org . za / scielo . php ? script = sci _ arttext & pid
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RACA Journal I April 2023 www . refrigerationandaircon . co . za