The total equivalent warming impact (TEWI) takes into consideration both the direct and indirect global warming effects of refrigerants.
In addition to the direct impact of the refrigerant (which is conveniently estimated by GWP), any system or process, which requires energy input, indirectly affects the environment. This impact is originated from CO2 emissions from the energy production processes.
TEWI can be calculated using the equation below:
TEWI = direct emissions + indirect emissions = (GWP×L×N)+(Ea×β×n),
where
L – annual leakage rate in the system, kg (3% of refrigerant charge annually),
N – life of the system, years (15 years),
n – system running time, years (based on weather data, 4910 hours),
Ea – energy consumption, kWh per year (modelled for each refrigerant),
β – carbon dioxide emission factor, CO2-eq. emissions per kWh (165 g CO2/kWh).
