Choosing the Right Natural Refrigerant
A-Gas Managing Director John Ormerod explains how to get the perfect mix to protect the environment and be energy efficient.
There’s been much focus on natural refrigerants with their fine environmental credentials. If you know your history, you’ll remember that naturals were the original refrigerants. At the start of mechanical refrigeration 100 or so years ago, ammonia, hydrocarbons and CO2 were among the few available options for the cooling industry to work with.
Natural refrigerants fell out of favour because their physical properties can make them difficult to handle. Ammonia is toxic, hydrocarbons are flammable and CO2 is a high-pressure gas but to their credit they have major plus points. Hydrocarbons and CO2 have a low GWP and ammonia has no GWP value at all.
When HFC refrigerants came under the scrutiny of the regulators the industry once more looked towards naturals as the silver bullet. Each natural refrigerant has its place in the scheme of things and ammonia, hydrocarbons and CO2 are all excellent choices when used in the right application.
Perhaps, it is fair to say that engineers and end users may need to refresh their memories on what are the right applications. Naturals are not the correct fit for all installations and end users must look carefully at what is for each individual project.
The low GWP credentials of natural refrigerants mean that the F-Gas Regulations won’t affect them but it still doesn’t make them a straightforward fit. You cannot replace HFC refrigerants with any of these naturals directly. New equipment is needed but if you are faced with a choice of which refrigerant do I want in new equipment, at that point it is probably worth considering naturals.
Understanding the best application for the job is key. For instance, with ammonia being highly toxic and mildly flammable, this makes it a great refrigerant in industrial applications where the equipment can be located outside the building. Secondary systems like glycol can then be used to take the cooling to where it is needed in the building.
Hydrocarbons are a superb refrigerant in small, integral cabinets in supermarkets and convenience stores. It is worth noting that all domestic fridges in the EU have been running on hydrocarbons for the past 15 years now. This is a classic application illustrating where hydrocarbons fit extremely well.
They have small charge sizes but the high flammability associated with them means that they are difficult to use in large quantities. Small charge sizes allow you to control the risk more effectively and as a result this makes hydrocarbons unsuitable for air conditioning systems where large scale cooling is required.
CO2 works extremely well in low temperatures but the physics can get in the way of making it an efficient refrigerant in warmer climates. CO2 has a low critical temperature and that’s not helpful when it gets hot. High pressures also mean that the capital costs for the equipment are significantly higher than comparable HFC refrigerants.
These are some of the challenges but for the end user it ultimately depends on what is driving the choice of refrigerant. Is it the green credentials? Is it energy consumption? The latter is a key aspect of refrigeration systems particularly if you are a big user of gases. The hotel industry, for instance, is one of the largest consumers of refrigerants through the use of air conditioning systems.
Green-thinking customers are forcing end users to be extremely conscious of energy consumption. Many naturals in the correct application are very energy efficient but outside the correct parameters they can suffer dramatically and in some instances this can make them a worse choice than sticking with an HFC or HFC blend.
If you want to mix environmental credentials with energy efficiency options and arrive at the lowest possible carbon footprint for an application, then the TEWI (Total Environmental Warming Impact) measurement is the answer.
TEWI looks at the leaks from the system and what can be recovered when it is no longer of any use. It also considers the impact of energy consumption during its lifetime. Add the two aspects together and the result is a measurement of the true carbon footprint of the application.
So when looking for a low GWP alternative this can help you compare a natural refrigerant – say CO2 in a supermarket installation – with an HFC gas. Refrigeration suppliers are usually happy to help calculate the figures if necessary, so assistance is on hand if you are finding making the switch a challenge. To help in making the right choice, the A-Gas refrigeration selection form, Refrigerant Suggestions, is available at www.agas.co.uk
Without a doubt TEWI should be in the minds of engineers and contractors if they want to make the correct choice for their customers. In the future we are going to see more fragmentation in the number of refrigerants available. There is now a long list of suitable alternatives available to an industry looking for low GWP alternatives. The key factor is making sure you get the right one for the job you are working on.