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IN BRIEF CHILLERS – UNDERSTANDING METRICS FOR TOTAL EMISSIONS

IN BRIEF CHILLERS – UNDERSTANDING METRICS FOR TOTAL EMISSIONS

27.04.2019

The total greenhouse gas emissions due to the operation of a chiller are the direct emissions of refrigerant and the indirect emissions due to energy use. The switch to lower GWP refrigerants for chillers, such as HFC/HFO blends, HFOs and HCFOs, reduces the contribution of the refrigerant emissions and energy consumption is essentially the source of emissions during use for chillers with very low refrigerant emissions.

The total greenhouse gas emissions during operation of a chiller is known as TEWI (Total Equivalent Warming Impact). Refrigerant recovery at end of life is included. A more complete understanding of the emissions related to the manufacture and use of a chiller is the LCCP or Life Cycle Climate Performance. The LCCP models can be extremely detailed, accounting for all CO2 contributions from CO2 emissions from the use of energy (indirect) and CO2 equivalent emissions from other operations (direct CO2eq) from “cradle” (refrigerant and product manufacturing), through use (including servicing and potential leak rates by type of product), to “grave” (recycling and disposal) for a product. For large centrifugal chillers, due to the long use phase (20-40 years) the emissions due to equipment manufacture and equipment disposal are extremely small (<1%) as a percentage of total LCCP. Life Cycle Assessment extends the LCCP approach to the other relevant aspects that concern the environmental impact of a technology.

The main contributor to LCCP is energy use, typically >95% for a HFC chiller with a 5% annual refrigerant leakage rate, assuming effective end-of-life recovery of refrigerant. Reducing the annual leakage rate to 1% reduces the refrigerant contribution to emissions from about 5% to about 1% (but actually dependent on climatic conditions and primary energy source). State of the art chillers may have annual leakage rates as low as 0.1%.

With extremely low refrigerant emission rates, energy consumption is essentially the source of emissions during use, and refrigerant selection takes into account energy efficiency, safety, reliability and technical performance. Lower GWP HFCs or HFC/HFO refrigerants further reduce the contribution due to refrigerant emissions compared to currently used HFCs.

The switch, where technically appropriate, to HFOs or HCFOs with extremely low GWPs, reduces the contribution of the refrigerant emissions to the LCCP to close to zero. Very low refrigerant leakage rates minimise refrigerant use, maximise resource efficiency and help maintain optimum chiller performance. The chiller in use emissions are effectively only from energy consumption, which in turn depends on the chiller design, its energy efficiency with the selected refrigerant, the ambient conditions, the overall installation and control systems, and the primary energy mix used to generate the electricity consumed. When nuclear or renewable primary sources are used to generate the grid electricity, virtually no GHGs are emitted.

References
Assessment Of Life Cycle Climate Performance (LCCP) Tools For HVAC&R Applications With The Latest Next Generation Refrigerant Technology, Purdue University Purdue e-Pubs International Refrigeration and Air Conditioning Conference School of Mechanical Engineering 2014
2018 RTOC Assessment Report