Why selecting the right pump for projects is crucial
One needs to look beyond a manufacturer’s specification to know which pump is right for an application, says Balagopal Nair
If you need to learn about pumps, Balagopal Nair, marketing and business development manager at Faisal Jassim Group, is the man to go to. From using the right type of pumps to focusing more on energy efficiency, Nair hits the nail in the head when it comes to understanding the philosophy behind pumps.
Nair says: “Everyone is aware of what pumps are. The technology is very well known to everyone. Pump is just used for pumping a media; the media can be water or oil. We should enrich and enhance the knowledge of pumps and understand how we can make pumps more efficient. This is how the market should be thinking about pumps.”
However, Nair is annoyed that people do not ask the right questions. People are only concerned about what the kilowatt and footprint of a pump are, he says, adding: “No one has ever asked me what the best pump is to use for a particular application, for the given capacities or for the given hydraulics. Usually the designers will give us the hydraulics, and based on the hydraulics we select a pump.”
He says that there are several factors to consider when selecting a pump such as efficiency, footprint, and ease of maintenance.
A building may have several pumps performing various tasks. Although pumps do not represent a large fraction of the total building cost, careful selection of the pump type and size will reduce the first cost and the cost of operation of the building over the years. In addition, proper selection of the pumps in terms of project specification and requirements will also make the building more valuable by providing reliable service at a low cost.
According to a text book definition: pump selection is the process of matching the characteristics of the pump to the requirements of the system. In order to do that, we must know what kinds of pumps are available for use in building service systems.
Nair said that the the thought process has to change. “Just copy-pasting the specifications which was there for the last 20 years and complying with the same thing, is not going to work,” Nair says.
There are several consultants that are based in Europe or the US, and they follow the same specifications here as are in those countries. He says: “It is not adjusted to the situation in the Middle East. So you will find a lot of contradictions in the specifications and this will call for unwanted arguments with respect to consultants and contractors.”
He says that European consultants prefer to go follow the standards set by European manufacturers and that they use certain standards in the construction material. But in the US, they follow the Hydraulic Institute Standard, where they specify a certain criteria of performance as well as certain type of material to be used.
All about efficiency
However, Nair says that the end game is about efficiency.
He says: “When I talk about understanding a pumping application, one of the biggest things to consider is efficiency.” He reminds us that now with the Dubai government focusing more on sustainability, green buildings, and retrofitting, a pump manufacturer and a consultant should know how to get a better efficient pump. He says: “They have to come up with innovative ideas or use some special controls to achive efficiency at an optimum level, irrespective of the fluctuation of the load.”
Highlighting more on the innovation aspect of pumps, Nair says: “People should focus on intelligent pumping applications like providing digital sensors with a variable speed drive, and which will be connected to the building management system, so that we can monitor what exactly is happening on the pump operation and where to balance the pump if there is an issue with the performance in the efficiency level. They can re-tune the system or rebalance the system to get a better result.” He says that some of the pumps in existing projects lack intelligent controls.
However, Nair does admit that the efficiency levels of pumps have been increasing over the years. “Five years ago, pump manufacturers used to talk about an efficiency level of 80-82%, and that too you will not be able to get for all the hydraulics. I still remember when the consultant used to write saying that the pump efficiency should be in the range of 75% and that was an acceptable level at that time. But today the pump manufacturers are providing pumps with efficiencies above 90-92%. So you can say in another couple of years, an average efficiency level of pumps at most of the hydraulics, will be in the range of 90%.”
Another fact to consider when it comes to pumps is the design point. It is the point at which a pump operates at maximum efficiency. It is determined by the flow rate and the total head at the respective pump speed. Nair asks: “What are the conditions of these pumps in actual operations? Because only 1% of the total 365 days, the pump will run at the design point.”
He explains: “We are designing a pump at a certain capacity, and at that design capacity, the pump will not run for 365 days, because this is the maximum demand. So the demand will fluctuate. For example, during winter, the demand is less, the pump will run at a low speed. But what will be the efficiency level when it runs at low flow or low demand? This is what people should look for.”
District cooling plants are very keen on such numbers, Nair says, adding: “They look at all specific points at different levels. But there are not many district cooling plants, only three or four. However, there are hundreds of buildings and shopping malls, residential buildings and hospitality buildings and all of them use chilled water pumps because there they have standalone chillers.”
According to the HVAC pump design objectives, a modern design will utilise computational fluid dynamics design tools available to improve the efficiency in three aspects of the pumps.
One is higher efficiency levels, second is wider efficiency range for flow rate perspective at constant diameters, and third is sustained efficiency levels as impeller diameters are reduced.
In this context, Nair says, the pump manufacturers have come out with a selection criteria called part load efficiency value (PLEV). “PLEV is a calculation that represents the efficiency of the pump at partial flow rates, and can be used to measure true pump performance within a hydraulic system. When you have this selection criteria, which was not there before, you can measure the pump efficiency at different percentages of operation. This is a good tool for the designers and also for the end users to measure the efficiency levels.
“Sometimes people use oversized pumps to meet the various demand fluctuations leading to inefficiencies. A pump is considered oversized when it does not operate at about 20% of the best efficiency point. So if it is plus or minus 20%, we say that the pump is not operating at its best efficiency point.”
Thinking outside the specification
Finally, Nair says that several consultants ask him to provide them with a list of pumps that can be used with a specific set of pump capacities. Although such a list can be provided, it will be generic, he says.
Nair explains: “There are some technical and engineering reasons why we are using certain types of split case pumps. If you go for larger capacities, you will use horizontal split case pumps, and there are certain engineering reasons behind this. The type of pumps has to be selected based on the hydraulic, your application, materials, etc.”
However, Nair says: “When the designer says he/she needs to use an end suction pump because of what it says in the specification, but the pump characteristics might be better with a multistage pump, then the designer or consultant who is reviewing the pump proposal should have the courage or openness to accept that a multistage pump could be better.”
Therefore, it is very important to think different and outside the range of specifications provided by the manufacturer in order to choose the right pump.