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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy( ACRA) in Edenvale. He holds a Bachelor of Business Administration and an associate degree in educational administration. He has a National Technical Diploma and completed an apprenticeship with Transnet. He has dual-trades status: refrigeration and electrical. He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018. Currently he is the SAIRAC national treasurer.
WELCOME TO THE SOLUTIONS PAGE
By Grant Laidlaw
Many people ask for assistance in understanding theoretical and practical aspects of the industry. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indicate that the basic understanding necessary to work in industry is not in place.
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Cayla asks: Grant, could you please look into the use of R744 and how these systems work. It is quite difficult to understand the operation of these systems. Also, a particular concern is the high pressures. Thank you.
Hi Cayla. Yes, I can help. Let us begin with protection against excessive pressures and preventing explosions. CO2 systems operate at higher pressures than other systems because of the high triple point of the gas. High pressure can be dangerous if incorrect materials are used or if the system is not connected properly. Pipes or the housing of components might burst, and the resulting energy release can be dangerous for people and / or can cause damage equipment in the area.
Examples of pressure levels:
• High pressure = 12 000 kPa
• Intermediate pressure and medium temperature cooling = 4 500 kPa
• High pressure LT( low temperature) = 4 500 kPa
To prevent accidents due to high pressure, it is important to use the right materials for piping and brazing operation and to install appropriate safety relief valves.
Additionally, CO2 has a high coefficient of expansion. This means that trapped liquid or gaseous CO2 expands quickly at increasing temperatures, leading to extremely high-pressure increases. Trapped liquid CO2 expands much more than other refrigerants. As an example, the pressure of trapped liquid CO2 in an evaporator at-30 ° C will rise to over 10 000 kPa if the temperature rises to-20 ° C. For every 1 ° C rise in temperature trapped liquid pressure CO2 increases by approximately 1000kPa.
To prevent this pressure increase CO2 systems need to be equipped with safety relief valves at every pressure level to secure the system against excessive pressures. Some systems are equipped with additional cooling systems that activate during close down / stand-still of the equipment, so that liquid CO2 will
RACA Journal I July 2025 not increase its pressure. Trapped liquid refrigerant is dangerous. Cayla, we begin with risk assessment. A risk assessment includes analysis and evaluation of risks or hazards. There are generally two important types of risk assessment: one relating to the manufacturing of a system and one relating to hazards for employees working on a system.
RISK ASSESSMENT BY MANUFACTURERS Systems and components shall be designed and constructed with the intention to eliminate possible hazards to people, property and the environment. Both excessive as well as too low pressure can lead to considerable damage to a RACHP system, e. g. rupturing the system with a total loss of refrigerant. The pressure in the system during operation and standstill shall not exceed the maximum allowable pressure of the system. Protection against foreseeable excessive pressure must be included as part of the system.
The maximum allowable pressure for each component shall not be less than the maximum allowable pressure of the system or part of the system. The selection of materials for components shall consider the impact strength at all temperatures to which they may be exposed.
RISK ASSESSMENT BY TECHNICIANS Closely related to the safety of a system declared by the manufacturer, a risk assessment for health and safety of the workers is extremely important. This can also be called a hazard assessment, and it comes, for example, from the Industrial Safety Regulation. A risk assessment must be conducted by the operator / employer to evaluate the health and safety risks to employees resulting from hazards at the workplace. An occupational health and safety system( OHS system) provides a framework for managing the risks and opportunities.
Let us have a look at the correct refrigerant tubing. The standard material is copper with two main copper alloys being
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