TEWI - STULZ answers

Cooling systems and heat pumps have an impact on the greenhouse effect. To ascertain the amount of carbon dioxide that has been released into the environment during its lifetime, the Total Equivalent Warming Impact (TEWI) has been developed. This formula determines the direct and indirect greenhouse effect of the cooling systems and heat pumps.

Direct and indirect effects
In the case of direct greenhouse effects, consider possible leaks and recovery losses when recycling refrigerants. An indirect greenhouse effect is the emission of carbon dioxide through the use of energy. An example of this is the burning of fossil fuels for the energy required for cooling systems.
 
Calculating the Total Equivalent Warming Impact (TEWI)
The Total Equivalent Warming Impact is calculated as follows: firstly, the sum is calculated of the direct Global Warming Potential (GWP). This concerns the leakage rate, recovery factor and indirect effects of the total energy consumption. This is multiplied and measured over the service life of a cooling system and/or heat pump.

TEWI = (GWP x L x n) + (GWP x m x (1- α_R)) + (m x E_a x ß)

GWP: Global Warming Potential
L: Leak rate in %/(kg∗a)
m: Refrigerant charge in kg
n: Operating time of the system in years
β: Carbon emissions per kWh (CEF)
E: Energy consumption in kWh/a
αR: Recovery factor on demolition and disposal of the system in kgCO₂/kg