Safe use of flammable refrigerants-literature review

In order to achieve the climate neutrality goals and the forthcoming F-gas regulation, it is important to promote the transition toward low-GWP refrigerants. Almost all low GWP refrigerants are flammable and the safety issues of these refrigerants (hydrocarbons and HFOs) prevent them from being used in larger systems. This master thesis is a risk assessment project and the purpose is to develop and improve the knowledge required for the safe use of flammable refrigerants in refrigeration and heat pump systems. The project will evaluate and quantify the refrigerant concentration around a plant in connection with unintentional emissions. In addition, the project will evaluate various available technical solutions for detecting refrigerant leakage, and also the solutions and methods to reduce the risk of occurring flammable concentrations. The overall goal is that the results to be used as a basis for developing new national and international standards.

Tasks:

Review the available academic literature as well as industry reports on the risks of using flammable refrigerants in heat pumps and refrigeration systems with the aim of updating and informing the latest technical solutions of safer use of flammable refrigerants.

 Theoretical studies in following field of the research:

1. Evaluation and quantification of local refrigerant concentrations and ignition risks in case of leakage due to equipment failure or component fatigue. It includes analysis of various parameters such as potential leakage rates and amount, air volume, flame source, etc. The most common A3 refrigerants should be investigated. Evaluate some of the most common HFOs and HFO/HFC blends as A2L refrigerants in order to be able to make a risk assessment of these refrigerants and compare the safety risks between A3 and A2L refrigerants.
2. Evaluation of methods for limiting the risks associated with leakage of flammable refrigerants. This may include, for example:

• Determination and control of the minimum possible room area for the plant with regard to the expected maximum refrigerant emission.
• Separation of spaces with electrical components that can cause sparks
• Minimization of the filling amount
• Sectioning of the refrigerant circuit with quick-closing valves
• Shielding of the system combined with forced ventilation of the shield to keep the concentration of flammable refrigerants so low that ignition is prevented.
• Shielding of the system combined with filling of the shield with inert gases such as nitrogen, carbon dioxide, argon, helium (in case of leakage).

3. Evaluation of various leak detection techniques and sensors. It includes the analysis of each technology's ability to detect refrigerant leakage and potential misplacements of the sensors for different applications, as well as their price.

The outcome of theoretical studies for leak detection techniques should be identified and the most promising techniques for A2L and A3 refrigerants should be evaluated and introduced.

Number of students: one.

Contact person, supervisor and examiner:

Supervisor: