Experimental evaluation of advanced features of a modern heat pumping system

Background

The demand in the future on heat pumping systems is to be more environmentally friendly by using natural refrigerants and becoming more energy efficient. One of the key natural refrigerants used in many refrigeration and heat pumping applications today is CO2, the great interest in CO2 led to rapid development on system solution, components, and control strategies. Some of the features of today’s advanced CO2 refrigeration and heat pumping systems are: heat recovery, gas ejector, and liquid ejector.

Extensive research work has been done studying the features of the modern CO2 systems at KTH in the past two decades; however, the last experimental work done in this area at KTH was more than 10 years ago, all the research work done in the past years have been based on modelling and field measurement analysis, where the researchers can only monitor the systems but not change the operating parameters.

There is a need to experimentally investigate almost every feature of the modern CO2 system to refine and verify their performance, also there is greater need to investigate new features that can further improve the efficiency. Therefore, the new cooling system of the renovated climate chambers at our laboratory has been built including some of the latest modern energy efficiency features of a CO2 system, so it will be experimentally evaluated. The system is being commissioned at this stage and will be ready for testing by the end of 2021.

The main objective in this project is to experimentally evaluate features to maximize the energy efficiency of CO2 vapor compression systems and provide very much needed scientifically verified answers to the refrigeration and heal pump industry.

The features that will be investigated in this project are heat recovery, where the performance of the system in the heat recovery mode will be experimentally and theoretically analysed. Refrigeration systems with CO2 can recover heat to cover space heating, domestic hot water, export heat to district heating, and to neighbouring buildings. Different temperature levels and capacities should be expected in each heat recovery application.

Another feature is the ejector, which is a new unconventional component in heat pumping and refrigeration systems. The ejector in this system can act as gas ejector with the function of increasing the suction pressure or as liquid ejector with the function of overfeeding the evaporators, which will also increase the suction pressure.

Preliminary tasks:

• Conduct literature review on refrigeration and heat pumping systems with CO2 as refrigerant, focus will be on the following features: heat recovery, gas and liquid ejectors
• Run the system on the standard operating conditions. This is new system and we need to make sure that the system is operating as it should, at this point we define the reference operation.
• Define the test matrix that is required for the evaluation of the key features.
• Run the system according to the test matrix, collect and analyse the data.
• Compare experimental results with expectations from theory.

Preliminary time schedule

 including milestones and dates for intermediate reports:

The project starts in January or February 2022. The expected thesis period is 5 months. At start of the thesis work the student is expected to submit a detailed work plan and preliminary layout of the thesis report.

No intermediate reports are required; however, the student is encouraged to write the report in parallel to conducting the research.

Besides the final presentation, at least one presentation will be conducted around halfway of the project period in a project meeting with the industrial partners. We have 10 industrial partners in this project.

Supervisor at KTH, Department of Energy Technology