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AIRAH
TEWI
Method of calculating
Total Equivalent Warming Impact
This methodology for calculating total equivalent warming impact (TEWI) is for new stationary
refrigeration and air conditioning (RAC) systems that operate on vapour compression principles
and are powered by mains electricity connected to the grid.
The method of calculating TEWI is provided below:
TEWI
= GWP (direct; refrigerant leaks incl. EOL) + GWP (indirect; operation)
= (GWP x m x L annual x n) + GWP x m x (1 – αrecovery)) + (Eannual x β x n)
Where:
GWP
=
Global Warming Potential of refrigerant, relative to CO2 (GWP CO2 = 1)
Lannual
=
Leakage rate p.a. (Units: kg)
n
=
System operating life (Units: years)
m
=
Refrigerant charge (Units: kg)
αrecovery =
Recovery/recycling factor from 0 to 1
Eannual
=
Energy consumption per year (Units: kWh p.a.)
β
=
Indirect emission factor (Units: kg CO2 per kWh)
The TEWI equation provided can be found, amongst other places, in EN 378-1: 2008, Refrigerating
System and Heat Pumps Safety and Environmental Requirements, Annex B. When greenhouse gases
may be emitted by insulation (i.e. display cases) or other components in the cooling or heating system
the global warming potential of such gases is to be added to the above equation.
THE AUSTRALIAN INSTITUTE OF
REFRIGERATION, AIR CONDITIONING AND HEATING
BEST
PRACTICE
GUIDELINES
Methods of calculating
Total Equivalent Warming Impact
The aim of this method is to provide predictive estimates
for the TEWI values of new systems that can be usefully compared
with confidence, even when different estimators have prepared
these. Sensitivity analysis is recommended to calculate lower and
upper threshold TEWI values, which provides an expected band.
(TEWI) 2012
For more information about
TEWI and its applications, visit
www.airah.org.au/Resources to download
AIRAH’s free Methods of Calculating
Total Equivalent Warming Impact (TEWI)
– Best Practice Guidelines.