Sarfraz H Dairkee on the philosophy of pumping system optimisation
When I am asked to explain pumping system optimisation, I always like to use the analogy of the car engine. Even if a car’s engine operates at a wide range, say between 500-rpm to 5,000-rpm, its optimal performance may be well be within a narrow range of say 2,000-2,500-rpm. Similarly, a pumping system operates and performs optimally only inside a narrow range. Outside that, it doesn’t operate optimally.
Why do you need pump optimisation? In our region, the tendency is to overdesign pumping systems to ‘obese’ levels, so much so that at times it cannot lift its own weight. Removing this obesity is a key benefit of optimisation. Let us go to the root of the problem, which begins at the design stage. The natural human tendency is: when you don’t know, increase the safety margin. Designers of pumping systems always assume the worst case scenario. But there is a huge gap between assumption and reality. In this case, the safety factor is actually ignorance factor. It is more of a psychological comfort around which you design the system. Unfortunately, fat safety margins ultimately destroy the pump.
Basically, any hydraulic system operates in a very narrow range where it delivers its best. While it will operate across a wide range, it will not deliver optimum performance at that range. When the system doesn’t operate optimally, fuel or energy consumption goes up. Energy that doesn’t get converted into useful work manifests itself as heat, noise and vibration. The safety factor thus becomes the cause of destruction of the pump.
There is a difference between merely designing a pumping system and designing an optimised pumping system. More often than not, pumping system design is guided by thumb rules. I call it the AK-47 effect. You fire many bullets in the hope that one of them hits the bull’s eye. The other way round is to know precisely the characteristics of the bull’s eye, do a self-assessment to find out whether you are equipped to hit it and if not, find and learn the methods to redress those gaps, so that you hit the target. The key word here is precision.
Coming back to the car example, if you start the car directly in fourth gear, it will neither start nor stop quickly. If you put the engine in first gear and run the car at a speed of 50-60 km/hr, imagine what your fuel consumption and noise levels will be, and the damage you will be doing to your engine. The same analogy is applicable to pumping systems, where you design it to run at the fourth gear equivalent, but then run it at first gear. At least, in cars, you have the gear box. But in the case of pumps, how do you adjust? Here, you can either carry out proper commissioning of the system or you should have the finesse to understand the system thoroughly.
Just another equipment
Often, a pump is considered only as another piece of equipment or component. Most of the time, you realise your building has a pump only when it gives you a problem. The tendency is to fit it and forget it. You don’t have many operators who truly understand the importance of system integration. Think about airconditioning systems. The temperature varies a lot, so your pump doesn’t run at one constant speed at a time except in the process. Even in the process, it keeps on varying. You cannot address that variation with just one pump, so you put in valves, drives. Once you fit in the pump, how many times will you go and see how it is operating? Say, out of 8,760 hours, the system might be running at its design condition only for 100 hours.
To understand and appreciate that, you need pumping system optimisation knowledge. Otherwise, even if you see the writing on the wall, you are not able to understand because you don’t have knowledge of the language. If you ask me about variable speed drives, they are analogous to the automatic gear box in the car. But even if you have an automatic gear box, you need the skill and knowledge to use it effectively; else, it wouldn’t do much good. Drives will deliver only as much you have in your mind. I always like to emphasise that a computer cannot think for you, it is the other way round. To make an ‘intelligent’ pumping system work, you have to transfer your ‘intelligence’ into it because the system cannot think on its own. This is something that escapes most people. Another good analogy is MS Office Excel, which has an enormous amount of formulas or intelligence built in, but to explore that is an altogether different ball game. Coming back to obesity, I look at it in two ways – In a passive, static system, obesity may not be harmful because it is not subject to a lot of stresses. But in a system which is in motion and consumes energy, obesity can be a disaster. It is equivalent to making a Sumo wrestler run a marathon. To run a marathon, the person has to be agile and light-weight. Any system which is a dynamic system with lots of variants has to be very agile.
Whenever the pump is not operating within its recommended operational range, energy is not being used creatively. This ultimately destroys the pump. A good example is cavitations, which degrades pump performance. Imagine a traffic flow – as long as traffic flow is streamlined, everything moves perfectly. But if there are unanticipated obstructions, there will be chaos. In other words, if you are running the pumping system outside the conditions it was designed for, it goes into that particular random mode, where you don’t know what is happening. The moment that comes in, the pump’s operation is impacted.
When you run the pump beyond its operational values, its reliability comes down drastically. With more wear and tear on parts, your pump only becomes more unreliable. There are many operations where pump reliability is of critical importance. Pumping system design, as it stands today, is more about adding weight to the body. You can add weight to your body through muscles or fat. If you eat without exercise, you accumulate fat. So when we talk optimisation, we are talking about doing exercise, removing excess ‘fat’ and replacing it with muscle.
But optimisation is not at the cost of safety. When you optimise the pumping system, safety comes automatically. With optimisation, you are also able to take informed decisions. For example, when you are putting in safety, you know why it is needed, when it is needed and what the repercussions are. You don’t build in safety blindly. When you design a pumping system, we have to consider three basic parameters – the flow rate, the head and the RPM. When you design an impeller based on that particular design, you work out a streamlined flow without turbulence and you work through mathematical modelling. Having said so, when you fit the pump in its real-life operating environment and it deviates from any of the three parameters, your assumptions will also cease to deliver.
You may overdesign the pumping system in anticipation of the future demands that may be made on it. But can a system designed for the future give you value today? It is akin to making a big-sized suit today anticipating that your girth will grow to that size in the future. The material may be world-class, the tailor very good, but that cannot hide the fact that you are left with an ill-fitting and over-sized suit of little value for today. Operators of pumping systems need to have knowledge about optimisation. Let them be aware of the possible, so that they can understand the ‘writing on the wall’ and take informed decisions. Today, they are left to deal with the impact of decisions taken at the design stage.
As told to Anoop K Menon
(Sarfraz H Dairkee is GM, Corporate Dev. & Engineering, M.A.H.Y. Khoory & Co. He is also a Qualified Trainer for Pumping System Optimisation from Hydraulic Institute-USA)
