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The bane of supersizing of HVAC pumps

Is there scope for improving the energy efficiency of pumps through better design or operation approaches? How have changing occupancy profiles in a COVID-19-ravaged world affected building operations? And how can intelligent systems help? Insights from a plenary discussion during
“Heart of the Matter: A Webinar on pumping systems”, presented as part of CPI Industry’s HVACR Virtual Conference series, on August 10…

| | Sep 30, 2020 | 1:31 pm
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Mohamed R Zackariah

Mohamed R Zackariah, Chief Consultant, Suhaimi Design– Protecooling, is convinced that pumps and their components and impellers have quite reached their zenith in terms of design. His focus, hence, is on improving their operation. “If we analyse many of the projects that are currently operational, the pumps are not operating in the best efficiency point or within the preferable operating rate,” he said, adding that building owners are extracting very low operation from pumps, owing to a mismatch between pumping performance and system
performance.

Hassan Younes

Agreeing with this, Hassan Younes, Director & Partner, GRFN Consultants; and President, ASHRAE Falcon Chapter, said that modern impeller designs and availability of IE5 motors have helped reduce power consumption of pumps. Speaking from his experience, he said that most of the problems associated with Delta T can be attributed to the improper balancing of the systems. “Normally, units closer to pumps have more flow, and the ones that are not close – maybe those in the top floors – are not getting anything,” he said. “They get complaints, and the BMS guy increases the pumping, because he doesn’t know where the flow is needed.” Such practice, he said, is quite common and leads to higher power consumption. Younes said the situation underlines the importance of assessing demand from both a cooling and a hydraulic perspective and balancing the requirements while looking at the best efficiency point and adjusting the pumps and VFD speed to attain the best efficiency. He added that ASHRAE encourages having a higher Delta T, even going beyond the nine degrees C typically recommended for district cooling purposes, to 10-11 degrees C, in an effort to reduce the amount of water required to be transported.

Sleiman Dahabra

On cue, Sleiman Dahabra, Senior Operation Manager, Tabreed, highlighted the importance of identifying the best efficiency point, especially with pumps running in parallel in district cooling schemes. “The operator should understand hydraulics and know where the index point is in the network,” he said, adding that it is essential to identify, select and keep the pump running based on the index point to meet the demand of chilled water for all the clients, with minimum power consumption on the motor. The index point, he added, is also integral to controlling the speed. “How can we identify which one is index point?” he said, rhetorically speaking. “For me, it is the farthest point in the network or the highest point or the highest capacity in the network. The operator can select this as an index point to lead the pump to run optimally and efficiently.”

Prabhakar Naik

Agreeing, Prabhakar Naik, Managing Director, Base VASTU and, ENGG Services FZE, said: “The pump is not decided in the first index, or second FCU. It is two-third of the index length, basically. The pump head is calculated on index, so overall operations and Delta T control is very important, but in a district cooling plant, hardly three per cent of energy is contributed to the pump.”

Wading into the discussion, Nimal Amukotuwa, independent consultant, raised the issue of design considerations and the vexingly high number of instances of oversizing of pumps, which he said, affects the overall performance of pumps. “This [oversizing] is a no-no not only because of energy [considerations] – the life of the pump is also reduced,” he said.

Picking up the thread, V Sekhar Reddy, Managing Director, Lexzander, said that despite the best intentions of consultants and designers, a number of challenges invariably crop up when the project takes off. “The contractor’s responsibility is to ensure that all elements are well-integrated and well-coordinated,” he said. “There will definitely be issues if you go for a copy-and paste approach. Normally, the
consultant or designer gives a lot of safety factors for the system, keeping in mind capital cost and also keeping budgets in mind
to ensure the best in the interest of the project, but then it becomes the responsibility of the contractor to ensure that it is properly engineered, sized and then matched to the requirement.”

Nimal Amukotuwa

Reddy said that some contractors tend to cut corners when it comes to the capacity of the motor. “They tend to match the pump to the motor and deliver very little leverage in terms of any changes to system requirement,” he said. “That’s where it affects the performance of the system.” Reddy said that many of the buildings are unable to keep performance levels up due to shortcomings in the pumping system and that this phenomenon has been amplified by a rapidly ageing building stock.

He explained that while its impact on the energy consumption varies from project to project, which means it may not have a significant impact on the running cost, it still has significant implications on the overall performance of the system. “Definitely, the contractor has a huge role to play in terms of ensuring the selected system does its job, and yes, it’s always good to keep it at a right point, but it’s not always practically possible,” he said.

V Sekhar Reddy

THE COVID-19 EFFECT
A shift in occupancy profiles, following COVID-19, has also had a hand at aggravating inefficient operation of pumps. Kandasamy Anbalagan, Managing Partner, Proleed Engineering Consultants, said that a peculiar scenario he has recently observed is that occupancy of residential buildings is now at 80-90%. Pre-COVID, he pointed out, people tended to travel during summer months but that restrictions have forced most residents to stay put and indoors, and this has resulted in an increase in the number of tenant complaints about building performance.

Kandasamy Anbalagan

Anbalagan said a lot of the performance pain points are consequences of improper design. He pointed out that a decade or so ago, constant-speed systems were the norm, and pump selection was a critical scenario. “You needed to have the right calculations,” he said. “Those days, engineers had the time and mind to do proper calculations and come up with index circuit calculation. Valves selection used to be of paramount importance, and we used to spend a lot of time going into it and selecting the right
pump and applying the diversity for larger circuits.” Of late, however, Anabalagan said he has seen depreciation in the design and selection process of control valves. “The risk is becoming a bit less in terms of the selection process, and engineers do not pay enough attention to going in the right direction, because most of the deficiencies are corrected by VFDs,” he said.

Anantharaman Kanagaraman

For Anantharaman Kanagaraman, Discipline Lead – MEP, SSH, the ability of pumping systems to cater to such unforeseen circumstances, such as changing occupancy profiles, following COVID-19, has proven to be tricky. “Usually, pumps are all sized based on peak loads, and there are a lot of safety factors,” he said. However, he pointed out that considering that VFDs are widely used, data is going to be the key that will allow operators to have a better understanding on at what point they should run the system, especially in developments where the index could be changing. “Having multiple information gathered from the network is very important, even with COVID, where operators can see that part load can happen on some sectors of the clusters but not on other segments,” he said. “This type of information is key, and data is essential, because the number of index points cannot be just one – it probably keeps varying.”

THE GAPS IN SMART SYSTEMS

Improving pump efficiency by utilising data extracted from control systems is an approach that Dahabra said Tabreed is adopting. He said that the district cooling utility has implemented smart control systems to prevent the pump from running very fast, and to maintain the stability of the operation and proper flow for the entire network. Dahabra said that Tabreed is also in the middle of discussions to run plants through unmanned operations and that it is implementing a number of smart innovations to collect all historical data for evaluation and analysis. “We have a specialist team for analysis and to give advice to the operator on the ground,” he said, “The philosophy is that you can gain some savings in power or in dollar.” Dahabra said that Tabreed is also utilising systems that will allow it to monitor 20 plants to help operators educate stakeholders on how to efficiently run their systems.

Zackariah was quick to point out that while smart systems are, undoubtedly, vital for improving efficiency, many projects suffer, because
there is often a disconnect between the controls group and the mechanical group. “That disconnect is causing a lot of lost
opportunities, because sometimes, the investment in the control system is heavy and there are a lot of intelligent components
implemented on site, but at the end of the day, the required functionality of controls, pumping and any other systems are not
properly delivered,” he said.

Zackariah also observed that when control teams implement the project on site, often the technicians are not familiar with the old system to the fullest extent. “They are not able to deliver those features and functionality at site,” he said. “These kind of shortcomings need to be addressed. When we are talking about artificially intelligent, machine-learning-enabled type of control systems – the level of skill and understanding among the control implementation team must be increased further.” He emphasised that if there is proper understanding and intersection between control engineers and process engineers, there will be greater and more significant improvement in the overall operations.

Younes, agreeing, said that digitalisation and IoT are both integral to ASHRAE’s global agenda. Currently, he said, there are guidelines published for central plants that provide recommendations on the type of sensors that need to be installed. However, he said, ASHRAE is also working on a set of guidelines for sequence and operation. “Currently, there is Guideline 36, which is mainly on the air-side,” he said. “The purpose of this guideline is that instead of having every consultant write these requirements in terms of sequence and operation in the specs, they can go to this guideline and select what kind of system applies to their own system. The suppliers can then use that. Everyone can use it, instead of reinventing the wheel.”

Younes said that ASHRAE is also working on a new guideline focusing on smoother integration of smart systems in chilled water plants. “What I normally face is that system integrators are not really good at mechanical aspects,” he said. “They know how to control stuff or to build the control philosophy, if you give them the right algorithm. They know how to program, but they don’t know the mechanical part. If we have such standards and guidelines, which is what ASHRAE is trying to do now, it is much more helpful for the industry.”

 


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