Support

due to different reasons, such as power outages. The system should be filled with a different refrigerant, such as propane, have a cooling load of about 1 kW and have an evaporation temperature below the triple point of CO2. It should always run on a different power supply.

Sub-critical cascade-systems are often equipped with additional cooling units or safety operation functions. The upper stage is activated in case the pressure in the CO2 system exceeds the limit. The charge of the receiver is limited to 80 % of the receiver volume.

A further option is to limit the charge. Smaller, simple one-stage systems can be designed without additional cooling if the design limits the charge size and pressure in the system below a dangerous level. These systems also do not have safety relief valves.

During the design stage of the total volume, or piping and components, refrigerant charge and maximum pressure for expected ambient temperatures is determined. The receiver of such a system must be in the middle or low-pressure stage.

The filling factor and the ambient temperature determine the pressure in the system. This method may be applied only for the receiver or for a simple one-stage system. The filling factor is the quotient of the charge mass and complete volume of the system. A system with a volume of 2 dm ³ and a charge of 560g carbon dioxide has a filling factor of 280 kg m-3. If the ambient temperature is 40 ° C, the expected maximum pressure is 8 000 kPa( 80 bar). If the filling factor is only 200 kg / m-3, the expected maximum pressure is 7 000 kPa.

As CO2 is not damaging to the ozone layer and does not contain fluorine, regulations on ozone depleting or fluorinated substances do not affect the use of CO2 as refrigerant. SANS 10147 is the primary standard set in South Africa. Additional standards include the OHS Act and the pressure vessel regulation. South Africa follows the ASHRAE classifications for CO2 as a refrigerant( A1). All persons working with refrigerants should have knowledge of SANS 10147.

Cayla, I hope that this assists you with your understanding of R744. We will continue with the thermodynamics relating to CO2 in the next issue. RACA

Technical

By Eamonn Ryan

At an AHI Carrier customer event last year titled‘ Feel the Change’, a bold vision for the future of HVAC technology was unveiled, emphasising a shift towards more environmentally friendly products and solutions.

One of the innovations highlighted was the introduction of the new SHRM Advance( Super Heat Recovery Multi Advance). The presentation also featured the Multi Split System air conditioners, designed specifically for residential applications.

A key focus of the presentation was integrating product efficiencies and capacities into holistic system designs. Prousalogou emphasised the importance of considering not only environmental benefits but also operational and financial gains for end-users and building operators.

Prousalogou highlighted a critical statistic: approximately 40 % of energy consumption in buildings is attributed to heating, ventilation and air conditioning( HVAC)- and process heating.

In terms of the regulatory landscape, there are specific mandates in many countries including South Africa requiring a significant percentage

Harris Prousalogou, product and solutions development manager at AHI Carrier Fzs.

All images by © RACA Journal

RACA Journal I July 2025 www. refrigerationandaircon. co. za