By Andrew Perks
During June 2019, the Western Cape Government Environmental Affairs and the Bavarian State Ministry of the Environment and Consumer Protection, hosted a technical workshop in Stellenbosch on ‘Green Cooling Solutions’.
It was well-attended and there were some interesting and knowledgeable participants. We have a long way to go in the struggle for an environmental solution. The cooling industry is one of the major energy users and we need to really do something to improve the overall energy usage. There are solutions, but again it needs the industry and users to buy into them.
Some of my thoughts are as follows…
Contribution to the implementation of green cooling technology / best practices
Green technology not only refers to the refrigerants but the energy efficiency of the next generation of systems. This will involve each and every component to reduce the use of electricity, and where possible, water. While the following are being implemented on ammonia systems throughout the world, the principles can be applied across the spectrum on larger installations.
- Use of evaporative condensers – lower power usage.
- For freezer applications use of two-stage ammonia systems using reciprocating compressors (cascade NH3/CO2) – best efficiency.
- Use of economised screw compressors where we can enhance the specific power consumption characteristics improving the COP of the system.
- Use of Variable speed drives (compressor motors and fan motors). By reducing the speed of the drive, we can keep screw compressors operating at peak efficiency, while halving the speed of a fan reduces the absorbed power as much as 75%.
- Using all of the above with the use of smart PLC controls optimising plant capacity control will have a potential cumulative energy saving of 14%.
- Further use of thermal storage or ice bank systems to act as a system buffer when the main cooling system demand is reduced, leaving excess cooling capacity that can be further utilised. Especially relevant on air-conditioning of buildings.
thermal storage panels are used extensively in the dairy industry when peak loads are experienced when pasteurising milk. They are also being used in cold stores in the US where energy savings of up to 35% and more stable freezer room conditions are claimed.
There is a lot of work to do in just looking at existing plant and equipment configurations to optimise plant control and energy efficiency. This is a no-brainer, since not only will it be environmentally efficient, but it will also reduce running costs – a win-win situation.
When Eskom initially had its problems, industry was told to reduce power consumption by a minimum of 10%. Sounds like a lot, but, for example, by re-engineering the high-pressure side of the system at a plant in Ceres, this was easily achieved. By replacing a leaking condenser with a larger model and doing some re-piping of the condenser/liquid receiver pipework, the head pressure dropped from 37°C to 34°C – a significant improvement in the systems operating conditions.
Advantages of Green Cooling Technologies
What are the advantages of currently available technology?
- Semi hermetic R717 compressor – reduced leaks.
- Variable speed drives – better control / energy efficiency especially with screw compressors.
- Lower energy and water usage on modern evaporative condensers.
- Adiabatic pads on dry air condensers for lower water usage.
- Screw compressors with higher running speeds – larger ranges of capacity.
- Composite valve blocks for minimising leaks.
- Welded valves instead of previously used flanged valves (three seals to one) – reduced leakage potential.
- Development of CO2-safe refrigerant with a global warming potential (GWP) of 1.
Ammonia is a standalone refrigerant whose economic advantage, energy efficiency and environmental friendliness have made it one of the refrigerants of choice for many applications. Last time I looked at a report from A Gas there were a major number of other refrigerants in the market with eight being phased out, 12 intermediate solutions and 17 long-term replacement refrigerants. Do we really know what’s coming next?
With ammonia being hazardous and toxic, there are certainly challenges to be addressed. But Ammonia is not alone in this, R600a and R290 Propane all have their issues when it comes to flammability. It would appear that all-natural refrigerants have their issues too. Ammonia’s distinctive odour is seen as advantageous, it is commonly known as self-alarming at extremely low parts per million (PPM) concentrations.
There are of course challenges still to come, but I will be looking at that in next month’s article…