2.3 International Treaties: The Montreal Protocol, Kigali Amendment, & TEWI

The refrigeration and air conditioning industry operates under strict international laws designed to protect the environment. As scientific understanding of ozone depletion and climate change has evolved, so too have the international treaties dictating which refrigerants can be produced, sold, and utilized. Understanding these frameworks is vital for contextualizing national F-Gas regulations and calculating the true environmental impact of a system.

The Montreal Protocol

Adopted in 1987, the Montreal Protocol on Substances that Deplete the Ozone Layer is widely considered the most successful environmental treaty in human history. Prompted by the discovery of a massive "hole" in the ozone layer over Antarctica, the treaty established legally binding, time-targeted phase-out schedules for ozone-depleting substances (ODS).

The primary targets of the initial protocol were CFCs (like R-11 and R-12). In developed nations, CFC production was completely halted by the mid-1990s. The protocol later targeted HCFCs (like R-22) as a secondary phase-out. In the UK and the European Union, the use of virgin HCFCs was banned in 2010, and the use of even reclaimed or recycled HCFCs was fully banned at the end of 2014. Thanks to the Montreal Protocol, the stratospheric ozone layer is currently healing and is projected to recover to pre-1980 levels by the middle of the 21st century.

The Kigali Amendment

While the Montreal Protocol successfully solved the ozone crisis by forcing the industry to adopt HFCs, it inadvertently exacerbated a new crisis: global warming. Because HFCs possess zero ODP, they were not restricted by the original Montreal Protocol, despite having exceptionally high GWPs.

To correct this, the international community adopted the Kigali Amendment to the Montreal Protocol in 2016. The Kigali Amendment is a landmark agreement that legally binds nations to drastically phase down the production and consumption of HFCs. Unlike CFCs, which were "phased out" (banned entirely), HFCs are being "phased down" (gradually reduced to a fraction of historical baselines).

In the UK and EU, the Kigali Amendment is implemented via the F-Gas Regulations, which employ a quota system to forcefully reduce the availability of high-GWP HFCs, driving up their price and forcing the market to transition to low-GWP alternatives like HFOs and natural refrigerants (CO2, ammonia, and hydrocarbons).

Total Equivalent Warming Impact (TEWI)

When assessing the environmental impact of a refrigeration or air conditioning system, looking solely at the GWP of the refrigerant inside the pipes is insufficient. A system impacts the climate in two ways: through the refrigerant it leaks, and through the electricity it consumes.

Total Equivalent Warming Impact (TEWI) is an engineering metric that calculates the comprehensive lifetime greenhouse gas emissions of a system. A TEWI calculation is broken down into two distinct components:

1. Direct Emissions: This is the climate impact caused directly by the refrigerant escaping into the atmosphere. It is calculated by multiplying the refrigerant's GWP by the mass of refrigerant leaked over the system's operational lifetime, plus the refrigerant that is lost and unrecovered during final end-of-life disposal.

2. Indirect Emissions: This is the climate impact caused by the energy consumption of the system. Refrigeration systems use vast amounts of electricity to power compressors, fans, and pumps. This electricity is typically generated by burning fossil fuels at a power plant, which releases massive amounts of CO2. Indirect emissions are calculated by multiplying the system's lifetime energy consumption (in kWh) by the CO2 emission factor of the local electrical grid (kg CO2 per kWh).

The TEWI Equation

To calculate TEWI precisely, engineers use a standardized formula that separates direct leakage, recovery losses, and operational energy consumption:

$\text{TEWI} = \text{Direct Emissions} + \text{Indirect Emissions}$

$\text{TEWI} = (\text{GWP} \times L \times n) + (\text{GWP} \times m \times (1 - \alpha)) + (E_a \times \beta \times n)$

Direct vs. Indirect Comparison

Understanding the balance between direct and indirect contributions is essential for sustainable system design:

In almost all traditional refrigeration and air conditioning systems, Indirect Emissions account for the vast majority of the total TEWI. This means that while selecting a low-GWP refrigerant is legally necessary and environmentally responsible, ensuring the system operates with high energy efficiency is mathematically the most effective way to reduce its carbon footprint.

For example, if an engineer replaces a high-GWP refrigerant with a low-GWP alternative, but the new refrigerant is highly inefficient and causes the compressor to run 30% longer, the massive increase in indirect emissions from the power grid could actually result in a higher overall TEWI, worsening the system's climate impact. Conversely, implementing variable-speed compressors, optimising setpoints, and ensuring regular coil cleaning directly reduces $E_a$, driving down the dominant indirect term.