As part of a CRADA with the Alternative Fluorocarbons Environmental Acceptability Study, BTC researchers evaluated the total equivalent warming impacts (TEWI) of alternatives to hydrochlorofluorocarbon (HCFC) fluids.
The TEWI index was developed by ORNL as a tool to combine the effects of direct refrigerant emissions with those of carbon dioxide emissions from energy use over the lifetime of a given heating, air-conditioning, or refrigeration system. TEWI is gaining international acceptance as the preferred means to evaluate warming impacts: the International Institute of Refrigeration has published an informatory note indicating that TEWI is a better indicator of fluorocarbon climate impacts than global warming potential (GWP) alone, and the British Refrigeration Association has published a document Guideline Methods for Calculating TEWI under the Best Practices Programme of the UK Department of the Environment.
The project examined several alternatives as replacements for HCFC-based systems:
near-zero-global-warming fluid alternatives (hydrocarbons, ammonia, and carbon dioxide), and
emerging nontraditional or not-in-kind (NIK) technology options.
One of the principal conclusions of the study is that for systems with low refrigerant losses (e.g., RFs, heat pumps, and chillers), the best way to reduce TEWI is to increase system energy efficiency. For systems with high refrigerant loss rates (e.g., supermarket refrigeration and car air-conditioners), we must also find ways to reduce refrigerant emissions or to use alternative low-global-warming refrigerants or NIK technology alternatives. A summary of the Phase III study was published recently in a headline article in the ASHRAE Journal (V. D. Baxter, S. K. Fischer, and J. R. Sand, Global Warming Implications of Replacing Ozone-Depleting Refrigerants, ASHRAE Journal 40 [September 1998]: 2330).