FEATURE
INCORPORATING COLD CHAIN
500kPa but 14 000kPa is possible in some instances . When released at these pressures to the atmosphere , CO 2 can change phase to solid form , causing restrictions in the flow that can lead to a buildup in pressure . The concern remains that a large leak of
CO 2 can displace existing air in a space , reducing the oxygen levels . If the oxygen levels are reduced considerably , this can lead to health hazards up to and including asphyxiation / death . Average outdoor air consists of around 400 parts per million ( 0.04 %) of CO 2
. The details below list some additional concentration levels and the effects on the human body .
EFFECTS
• 0.1 %– 0.2 %: Breathing rate increases slightly .
• 0.3 %: Breathing rate increases to 50 % above normal level . Exposure can cause headaches , tiredness , weak narcotic effect , impaired hearing , and increased blood pressure and pulse rate .
• 0.5 %– 1 %: Characteristic sharp odour noticeable . Breathing increases to approximately four times normal rate and can be very laboured . Symptoms of intoxication become evident , and slight choking may occur . Visual impairment , headache , and ringing in the ears . Judgment may be impaired , followed within minutes by loss of consciousness .
• Unconsciousness occurs more rapidly above 1 % level . Prolonged exposure to high concentrations may eventually result in death from asphyxiation .
© Cold Link Africa © Cold Link Africa
A rapt audience at the April SAIRAC Johannesburg Tech Talk hosted at ACRA .
SAIRAC Johannesburg President , Robert Fox , delivered a presentation in a previous Tech Talk , addressing the crucial topic of ‘ Climate Change and Challenges for the HVACR Industry ’.
“ Perhaps we should at this point note that as CO 2 at ambient pressure is heavier than air , leak detection systems should be placed low , approximately 200mm from the floor . Let us have a look at the pressures expected when using CO 2 as a refrigerant .
We know that CO 2 operates at higher pressures than typical HCFCs or HFCs , due to the inherent thermodynamic properties of the substances . HFC direct expansion ( DX ) refrigeration systems mechanical safeties and control set points shut the system down around 2 400kPa ( depending on the refrigerant ) discharge pressure . The entire piping system is rated for safe working conditions above this maximum pressure , so no secondary relief devices are necessary .
“ In addition , if the fluorinated refrigeration system shuts down due to power outage or servicing , the internal pressures do not climb any higher to exceed the maximum system design pressure . In fact , the pressure tends to fall as temperatures drop and equalisation occurs .
“ In the case of CO 2 , the high saturated pressure of CO 2 at summertime ambient conditions exceeds the pressure rating of type K copper piping , along with most standard DX refrigeration valves . This requires the “ high side ” of the CO 2 system to be constructed using higher pressure rated materials and installation practices , at a higher cost .
“ To reduce overall system installation cost , the ‘ low side ’ portions of a CO 2 system are designed for the lower operating pressures , allowing copper to be used for
14 www . coldlinkafrica . co . za COLD LINK AFRICA • June 2024