The Total Equivalent Warming Impact (TEWI) rating measures the
efficiency of a refrigerant by combining its direct and indirect
global warming contribution. Direct contribution is the Global Warming
Potential (GWP) of a substance leaked into the atmosphere, compared to
the GWP of CO2. The indirect contribution is the greenhouse effect
generated by the electricity needed to run an appliance during its
lifetime.
It is well known that the GWP of hydrocarbons is insignificant compared
to the high GWP of HFCs and HCFCs. The producers of HFCs dismiss the
high global warming potential of their products by claiming that in
optimized equipment the TEWI of HFCs is lower than that of natural
refrigerants, such as hydrocarbons. This claim is incorrect. In both
domestic and commercial refrigeration the TEWI of HFC-134a, for
example, is actually higher than its natural refrigerant alternatives.
A 1994 UNEP Information Paper on the "Elimination of CFCs from Domestic
Refrigeration Manufacture" writes: "Testing to date shows that
refrigerators with HC-600a [isobutane] systems are nearly always more
efficient than equivalent ones using HFC-134a and often more efficient
than those using CFC-12. " *
In supermarket refrigeration Westward Refrigeration of Gloucester
conducted TEWI tests for the major UK retailer Sainsbury. Two HFC &
HCFC systems were compared with an ammonia based secondary cooling
system. The tests concluded that the overall TEWI of the system using
ammonia was 5per cent less than that of a HCFC 22 / HFC-134a system,
and 17 per cent lower than the system using HFC-404a. ** These tests
convinced Sainsbury to install an ammonia based secondary cooling system
in a new superstore in Horsham, Sussex, even though just 18 months
earlier the company stated "it is madness to suggest that a modern
supermarket might equip with ammonia". ***
** ENDS Report 236, September, 1994, p.28 [return]
*** ENDS Report 236, September, 1994, p.28 [return]