ASHRAE Journal - October 2012 - 44

to persuade anyone to install a chilled beam system using carbon dioxide. Using carbon dioxide for air conditioning does not significantly reduce the charge of primary refrigerant compared to use of systems that circulate chilled water. However, the charge is significantly reduced compared to direct expansion systems of the variable refrigerant flow type where the refrigerant is circulated to the spaces that require air conditioning.

• Carbon dioxide is the most efficient and effective secondary refrigerant so far discovered. • Carbon dioxide secondary is already being used for air conditioning. • Carbon dioxide secondary systems can be more efficient than direct expansion systems because of the effects of pressure drop around the system.

References
1. EPA. 1990. Clean Air Act. Section 112 (r)(7). U.S. Environmental Protection Agency. 2. EPA. 1986. Emergency Planning and Community Right-toKnow Act 40 CFR 355. U.S. Environmental Protection Agency. 3. Pearson, S.F. 1993. “Development of improved secondary refrigerants.” Proceedings of the Institute of Refrigeration. 4. Quack, H., et al. 2007. “The Extraordinary Properties of Carbon Dioxide as a Secondary Refrigerant.” Proceedings International Congress of Refrigeration. 5. Pearson, A.B. 2007. “Possibilities and pitfalls in carbon dioxide refrigeration.” Proceedings of the Institute of Refrigeration. 6. Clodic, D. 2008. “Latest HVAC&R development trends in Europe in response to HFC regulations.” 12th International Refrigeration and Air Conditioning Conference.

Conclusions
• Compelling reasons exist for reducing refrigerant charge in all refrigerating systems. These include the relationship between refrigerant charge and possibility of leakage, the cost of synthetic refrigerants, the possible environmentally damaging effects of refrigerant leakage and the risk to health from leakage of toxic refrigerants. • Secondary refrigerating systems can produce significant reductions in primary refrigerant charge as is obvious in the case of supermarkets where conventional direct expansion system circulate refrigerant throughout a large building.

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ASHRAE Journal - October 2012

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