What is it about?

This article reports a critical review of the CO2 based heating, cooling, and refrigeration system. It presents updated literature along with barriers and challenges on commercial use of Natref-based heating and cooling applications worldwide. This article is about the researcher's work on solar and electricity-powered CO2 heat pump water heaters, CO2 in organic Rankine cycle (ORC), cascade refrigeration ammonia/CO2, and CO2 refrigeration systems. The commercial products and research and development (R&D) of almost 30+ companies working on CO2 are summarized.

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Why is it important?

Refrigerants bearing high global warming potential (GWP) and ozone depletion potential (ODP) were outlawed or facing time-beared permission under the Montreal (1987), Kyoto (1997) protocols, F-Gas law (2015), Paris Accord (2016), and recent Kigali Amendment to Montreal Protocol (2019). In order to modify followed by the paradigm shift of existing heating and cooling systems, the American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) envisaged natural and synthetic refrigerants (Synrefs) are under investigation globally. Carbon dioxide (CO2) is a popular natural refrigerant (Natref) replacing Synrefs used in commercial heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems globally. A rampant rise is observed in markets of Asia (Japan and China), North America (the United States and Canada), the Australian continent, and Africa (South Africa) by reaching 20 000 CO2-stores around the globe. The European markets are leading the utilization of CO2 in the heat pump, and refrigeration, CO2 based markets estimate 14% of the total food retail stores (400 m2). Japan is the second leading market of CO2 heat pump and refrigeration with more than 10200 CO2 condensing units. CO2 transcritical systems have a share of more than 10% in only the European market (large stores); however, their share is less than 10% of total stores in other major markets of the world. New pump and compressor-driven transcritical CO2 systems integrate ejectors, condensers, and booster systems to reduce energy consumption's, enhance efficiency, efficacy, and coefficient of performance.


This work was started from the initial review on solar thermal cooling technologies during my Ph.D. course work under the supervision of co-author Prof. Dr. Nasrullah Khan. Then, Co-supervisor, Dr. Naeem Abas, has provided his insights and helped in shaping this article to only for the Carbon dioxide (CO2) based technologies, which is closely related to my Ph.D. project. Their guidance for improving the quality of the article is highly acknowledged.

Saad Dilshad
COMSATS University Islamabad

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This page is a summary of: Review of carbon dioxide (CO 2 ) based heating and cooling technologies: Past, present, and future outlook, International Journal of Energy Research, December 2019, Wiley, DOI: 10.1002/er.5024.
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