Refrigerant – the quiet GHG contributor

Refrigerant leakage from myriad air cooled condensers installed in the windows of a university campus building in Bangladesh is an environmental problem. In this case the leakage has been calculated to contribute 9.6 metric tons and combined with other greenhouse gas emissions each year of 102 tons, making regular maintenance of such systems critical. It’s a problem multiplied countless times globally.

Almost every window reveals an air-cooled condenser (in the featured image). One could almost play a “Where’s Wally” quiz, where the challenge is to find the window that doesn’t have an air-cooled condenser installed. Maybe each of the condensers could be painted a bright colour and follow Paris’ Pompidou Centre’s philosophy with respect to building services, namely “show-off what you cannot hide”.

Buildings in most developing and some developed countries commonly feature airconditioning add-ons. Over time, the need to ensure occupant comfort has led to the haphazard installation of AC units. These units serve a crucial purpose, especially in places such as Dhaka, where high summer temperatures and oppressive humidity during the monsoon season can be unbearable.

Operating these units contributes to greenhouse gas emissions in two ways.

Firstly, through the consumption of electricity when these units are in use. In the university building image, there are about 195 air-cooled condensers, mostly one-ton units (referring to cooling capacity, not weight), which require electrical power to operate.

The energy efficiency of these units, measured as the coefficient of performance (COP), is around 3. If these units run for eight hours each working day during warmer months (they are rarely switched off, even when the room is unoccupied), it results in greenhouse gas emissions of 102 metric tons per annum. To put this in perspective, this is equivalent to planting 4062 trees, with each tree typically absorbing approximately 25 kg of CO2 annually.

The second impact on the environment is leakage of refrigerant – essentially a greenhouse gas (GHG) – from the units.

So, what exactly is a refrigerant? Refrigerant is the gas used in this type of airconditioning unit to transfer energy from outside to inside and vice versa for reverse cycle application.

To understand refrigeration more clearly, go to your refrigerator, open the door, and check the label inside. This will tell you what the refrigerant is that keeps the inside cool and the outside warm (the back of the refrigerator will feel warm).

This demonstrates how heating or cooling energies are transferred from inside space to the outdoor environment using the refrigeration cycle. The energy exchange is a result of the change of phase of the refrigerant from liquid to gas and vice versa. While water boils at 100°C, refrigerants have much lower boiling points. These principles are employed in the humble refrigerator as well as in an airconditioning unit and are known a direct expansion or DX. This is also referred to as the air-cooled version since the operation involves energy exchanges using the atmosphere. Other versions include water-cooled, which uses equipment such as cooling towers, and geo-thermal or geo-change, which utilises the ground as heat source and heat sink.

Some pertinent observations about split airconditioning units are:

• They are rated for certain outdoor temperatures. If there is no cooler outdoor air, such as ambient temperature being above the rated temperature (generally around 48^°C), a split AC unit will cease to work. In other words, it will stop working if the outside temperature is very high – and when it is most needed. Similarly, when there is no warmer outdoor air, as experienced in very cold climates such as Alaska and Canada, the reverse cycle heating function will not work and therefore there is a need for supplementary heating, in many instances using natural gas. Full electrification was not carried out for two projects I was involved with recently in Toronto and Calgary since it was much cheaper to use gas furnace compared to electric heaters.
• Reverse cycle heating is the most efficient (electrical) form of heating. For every kilowatt of power input the unit can generate 4 to 5 kW of heating depending on the type and capacity of the unit.
• As part of the refrigeration cycle, the refrigerant goes through high and low pressures. Together with that there is vibrating equipment (the compressor), which all leads to fittings getting loose over time, resulting in refrigerant leakage. If you have experienced refrigerant leakage, your friendly airconditioning mechanic has probably told you that your split system needs “topping up”.  As the unit gets older the leakage gets worse, and the best way to monitor this is to keep accurate record of the “top ups”.

We can also better understand the different aspects and types of refrigerants by looking at the history. Refrigerants were initially developed in 1840 to create ice in ice machines. They were then adapted for use in airconditioning systems. Early refrigerants were known to be flammable, and it wasn’t until 1928 that non-flammable chlorofluorocarbon (CFC) refrigerants were introduced. Among these was the hydrochlorofluorocarbon (HCFC) R-22, which became the standard refrigerant used in AC systems.

R-22 continued to be famous for many decades until scientists discovered that chlorine in CFCs and HCFCs was damaging the ozone layer. R-22 has been phased down in Australia (since 2018) and globally under the Montreal Protocol (since 2019), as it has a high ozone depleting potential. The phase-out is supported by bans on new equipment containing R-22.

However, when I was in Dhaka for a net zero project, I could not only get R-22 but also get new airconditioning units using R-22. One gets suspicious about the dumping of phased-out products from developed to developing countries.

As part of my research, I obtained the American Society of Heating, Refrigeration and Airconditioning Engineers (ASHRAE) latest Standard 228/2023, titled Standard Method of Evaluating Zero Net Carbon Building Performance (NB: ASHRAE has termed it “Zero Net” rather than the more typically used “Net Zero”).

For the net zero work that I am involved with in developing countries, including Tajikistan, Bangladesh, and Pakistan, I found the Standard 228/2023 not as useful. It is North American (USA and Canada) centric. In parts, it is bordering on misleading.

Refrigerant Leakage. Projects shall account for refrigerant leakage and associated GHG. The unit leakage shall be calculated by taking the manufacturer’s specified charge (approximately 1.4 kg per ton) and multiplying it by the typical annual leakage rate for that unit type as shown in Table 9, and by the global warming potential (GWP) of the respective refrigerant as shown in Table 10.

Tables 9 & 10

There is no mention or acknowledgement of the fact that age of the unit and condition of the installation are vital considerations that influence the leakage rate. In other words, I could apply 30 per cent leakage on a new refrigeration system in a supermarket. That, in my opinion, is misleading. Data collected from several buildings that have undergone GHG and energy audits show higher leakage rate for older and/or unmaintained installations.

The Standard does not highlight the point that a procedure for compiling the refrigerant “top-up” data is a better process to give more accurate refrigerant leakage rate instead of the stipulated fixed rates. Prevention, too, needs to be encouraged with procedures involving tightening of fittings (bearing in mind that typically refrigerant pipework is connected to vibrating equipment as in compressors). Refrigerant leak tests should also be performed periodically.

The Standard makes no reference to refrigerant recovery procedures in the event of replacement of compressors and D/X coils, which is mandated in most countries, including Australia.

How can we ascertain the leakage associated with buildings such as the campus building example?

For the Dhaka campus building with 195 AC units, each with a refrigerant charge of 1.4 kg per ton, applying the leakage rates and global warming potentials from ASHRAE Standard tables nine and 10 results in an estimated annual emission of 9.6 tons of CO2, equivalent to planting 384 trees per year.

In summary, the GHG emissions of just this one building are 111 tons a year, requiring the planting of 4447 trees annually to offset the emissions.

Given that there are numerous similar buildings, the cumulative GHG impact is substantial, emphasising the importance for facility and building managers to ensure efficient operation and regular maintenance of their building’s airconditioning systems.