ACR Journal

August | September 2021 REFRIGERANTS 36 A-Gas managing director John Ormerod explains how an engineer can face a series of problems beyond the challenge of lowering GWP when designing with alternative refrigerants. Operational properties: why they are key Volume 7 No.5 The refrigerant is the main working fluid of any cooling system, and most equipment is designed around specific refrigerants. Therefore, everything relating to this, including the pressures and temperatures the equipment operates at, is connected, and this introduces the concept of volumetric capacity. Volumetric capacity A compressor is no more than a pump that moves a particular volume of refrigerant through it. Different refrigerants have different properties, and if you are moving a constant volume of gas, you may be operating at a different cooling or heating capacity as a result. Volumetric capacity is a key issue for the engineer if they are considering changing refrigerants. Take, for example, R404A. If the compressor has been designed around R404A and the engineer wants to switch to a lower GWP, the most important aspect of the job is the replacement gas. So, the engineer will be looking for a similar volumetric capacity as R404A. The principal question behind this is will it do the same cooling job as R404A? A close match on volumetric capacity is at least halfway to solving the problems facing the engineer, but it is not the only challenge that has to be dealt with. Compressor pressures and system temperatures will also have a considerable impact on how the system operates. This means, and it’s been said many times before, there really is no such thing as a drop-in refrigerant. No such thing as a drop-in refrigerant Refrigerant manufacturers go out of their way to try and match new refrigerant properties with legacy refrigerants. It’s a difficult task and, generally speaking, they can get close, but the new gas won’t be absolutely identical. If you are changing a refrigerant on a system, I would urge the engineer to engage with their refrigerant supplier. There are likely to be various software models available to allow the engineer to find the best match for the application in question. This will cover everything from the volumetric capacity to overall system efficiency, temperatures and pressures involved. With the growing focus on reducing carbon footprints, it’s one thing to change to a lower GWP alternative, but it’s another to factor in energy consumption. The latter is critical in determining the carbon footprint of a typical air conditioning or refrigeration system. Bear in mind that the GWP can only be taken into account if the system leaks. The most noticeable effect on the environment comes from the amount of energy consumed. Does one refrigerant use less power for the same duty? Is it more efficient in this respect? These aspects are key to understanding the whole picture. Natural refrigerants can bring further complications. Although naturals have lower global warming potential than HFCs, it does John Ormerod