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Beyond the Nine Dots of Refrigerant Environmental Properties

Part 4 of the Series: Keys to a Successful Refrigerant Transition

By Jean- Paul Thierion – GEA Consulting, Andernos les bains, FR

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 theMontrealprotocol 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 theUnited States and slightly less inEurope.

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 Japanan 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.