|
 Editor's Note: CR4 would like to thank Jean-Paul Thierion for contributing this fourth installment in GEA Consulting's Refrigerant series. Click here for Part 3.
The Refrigeration
and the Air Conditioning industries brought substantial progress to the mankind
allowing healthier sanitary standards for food conservation and better thermal comfort
for human beings in homes and working places. Unfortunately, like many other
human activities, refrigeration and air conditioning systems can present the
risk to negatively affect the environment either directly and/or indirectly. It
is therefore important when working on the design of new hvac or refrigeration systems
or when retrofitting existing ones for new refrigerants, to consider both the
direct and the indirect effects in terms of magnitude and time.
 Direct
effect on the environment when Ozone Depletion Substances (ODS) and Global
Warming Potential (GWP) refrigerants are released in the atmosphere. This may occur
when small leaks of the equipment are left undetected for long periods, or more
rarely in case of large accidental released. Both situations are abnormal and
are generally the consequence of poorly maintained equipment or improper
service practices.
This was very critical
for the ozone layer depletion when refrigerants containing chlorine atoms where
widely used, such as ChloroFluoroCarbon (CFC's) and this until the Montreal protocol in 1987
voted the phase out of these refrigerants. To a lesser degree but widely used
worldwide, HydroChloroFluoroCarbon (HCFC's) refrigerants also with chlorine
atoms can be used until 2020 in the E.U and 2030 elsewhere. The latest chlorine
free HydroFluoroCarbon (HFC's) refrigerants, although without direct impact for
the ozone layer, have a direct effect on the environment because of their GWP.
It must be
emphasized that the direct effect of the refrigerant substances occurs only
when the refrigerants are released in the atmosphere, which is not normal and which can be almost
completely eliminated with modern equipment incorporating latest technologies,
and with good maintenance and service procedures.
In normal
situations, the direct impact of refrigerants on environment should be very
small.
Indirect effect on the environment with the
emission of carbon dioxide (CO2) from power plants generating the electricity used
to power these HVAC and refrigeration systems during their lifetime. This indirect
component varies from one country to another depending with the types of power
plants, their emission rates, and with the source used to produce electricity:
coal, lignite, oil, gas, nuclear plants, wind mills, etc… On average in western
countries calculation for comparison can be based on 0,5 kg of CO2/kWh,
slightly more in the United States
and slightly less in Europe.
It can be easily
foreseen that the indirect impact is a very significant factor, depending of
the running time of the equipment and its efficiency.
It must be noted
that in plant rooms, it is not only the replacement or retrofit of the largest
pieces of equipment (chillers, air handlers, boilers) which can generate big
savings of energy; kWh usage for pumps, fans, cooling towers, controls etc…must
also be taken into account. For instance significant savings can often be obtained
by reducing the water flows using higher fluid temperature differences and
variable speed pumps (except for process applications, chillers usually clock less
running hours than the associated circulating pumps, and pumping power varies
in cube relation to flow; 20% flow reduction means 49% less power ).
To facilitate the
comparison between systems using different refrigerants, and to determine the
global impact on the environment during the lifetime of the equipment, a
methodology called TEWI is being used. TEWI is defined as follows:
(TEWI = Total
Equivalent Warming Impact = Direct warming impact + Indirect Warming impact).
The formula to calculate TEWI is the following:
TEWI = (GWPr x Qr x
Lr x Year) + (GWPr x Qr x (1 - Rr)) + (Year x E x Emco2)
_________Direct impact__________Direct
impact_________Indirect impact
with:
TEWI - expressed in kg
CO2
GWPr - Global Warming
Potential of the refrigerant substance expressed in equivalent kg of CO2 (100
years integrated time)
Qr - Charge of refrigerant in the
system expressed in kg
Lr - Leak rate of refrigerant
per annum expressed in % of the charge
Year - Life time of the equipment
Rr - % of refrigerant recovered
at the end of lifetime
E - Annual energy consumption
of the equipment in kWh/year
Emco2 - Emission of CO2 in power plants to
produce the energy
In Japan
an alternative method is sometimes used called LCCP which adds to TEWI the
direct impact on environment of the production process producing the refrigerant.
It is interesting
to consider the relative weight of the direct and indirect components in the
TEWI equation.
In the early 70's
although there was no real statistical information at the time, it was common
practice to release some refrigerants into the atmosphere during installation
and service operations; added to the fact that refrigerants commonly used at
the time presented high GWP characteristics, the direct impact on environment was
significantly high and could be estimated around 30% of the total impact, the
other 70% being due to the indirect effect. Later in the 80's when scientists
began to raise the alarm of the risk associated with the usage of halogen
refrigerants
(initially for the depletion of the ozone layer), the balance between the
direct and the indirect effects quickly dropped to approximately 10% direct vs 90%
indirect. Nowdays with the strong focus on global warming, and thanks to the progress
of technologies (better tightness of the equipment and fittings, more sophisticated
purge systems, sensitive leak detection alarms, etc…) and with more ecological
service procedures, the range is close to 1% or even less for the direct impact,
vs 99% for the indirect impact (of the equivalent kg of CO2 released in the
atmosphere).
It is therefore
obvious that in terms of global warming and protection of the environment, (safety
and cost being other factors to take into consideration), the effort and
attention should be given in priority to the efficiency of the new or
retrofitted systems. The indirect effect of the efficiency being far more
significant than the environmental properties of the refrigerant.
| 
