Pump pitfalls
Peter Wolff, Global Manager, Ecosystems and Performance Upgrades at Armstrong Fluid Technology, explains how to avoid disappointing pump performance.
Today’s pumps are really impressive pieces of equipment. Improvements in software and machine learning have created advanced control methodologies which result in huge efficiency gains. There are, however, several pitfalls along the path to optimisation. If mistakes are made in system design, pump selection or commissioning, even the pumps with the best raw efficiency numbers could deliver disappointing results.
Here are some common mistakes to avoid, and some practical answers on how to make sure you get the absolute maximum from your investment.
Pitfall 1: Pumps over-sized for duty
Although it does seem to make sense on a logical level to just match sizings with maximum load, we often see that the inflexibility of this approach can undermine efficiency significantly. Take the example of a new or growing district energy network. For much of the time in the early phases of these projects, the pumps (selected to meet peak output at some future date) are required to operate far below their ideal capacity, which means energy wastage every day until capacity is reached.
On top of this, operating with over-sized equipment also means a higher than average potential for technical issues to develop, due to the equipment operating outside the parameters for which it was designed. With stakeholders looking closely at the performance of the district energy network from the outset, these inefficiencies in the early stages could easily undermine confidence in the project and the organisations delivering it.
A solution to this dilemma is utilisation of modular design. The latest generation of packaged HVAC solutions is designed to address projects where scaling-up is the necessity, so look for solutions that are already designed with incremental expansion in mind. This can provide much-needed predictability and reliability of environmental performance. For large and complex projects, scalable energy centres and/or temporary energy centres can also avoid the problems of operating over-sized pumps.
For product selection on all projects, look for tools such as AID (Armstrong Integrated Designer), which can simplify selection and sizing of pumps and accessories, saving time, improving accuracy and enhancing energy efficiency. Selection tools can enable the creation of comprehensive equipment schedules and system layouts with pre-configured solutions, with the benefit of real-time performance estimates.
Pitfall 2: Pumps operating off their natural curve
Perhaps the most important technical issue to address is the choice of pump control strategy. Capacity-based control focuses on the equipment being at its most efficient when operating at 100% design flow. In reality, however, the system will operate at between 10% and 60% of design flow nearly all of the time. So capacity-based control clearly fails to harness the full energy and cost-saving potential.
Demand-based control, by contrast, focuses on operating each component at its most efficient point to meet the actual load. Pumps incorporating sensorless control have significant advantages in delivering demand based control, as they automatically adjust to changing demand whilst reducing system complexity.
When a variable frequency drive is added to an HVAC component such as a pump or fan, there is huge potential to improve part-load efficiency due to the pump affinity laws. If a rotating device is able to operate along its peak efficiency natural curve, this can increase operating efficiency by 400%. This can only be achieved, however, if the pump affinity law relationship between pressure and rotary speed, along the natural curve, is maintained at decreased speeds.
An effective solution is to select intelligent pumps incorporating on-board inverters, capable of adjusting automatically to changes in load. Design point and setpoints can be adjusted to match on-site conditions, and the pumps are sequenced to operate along their peak efficiency natural curve automatically, for all load conditions. Equipment loading can be optimised across the system as a whole, to achieve significant reductions in energy consumption.
Pitfall 3: Inefficient staging of pumps
Traditional pump staging strategies typically turn on the next pump when the existing or current pumps reach 95% of maximum speed. Pumps are typically staged off when the existing or current pumps slow down to 55% of maximum speed. Both of these scenarios (staging pumps on too late, and off too early) involve lost efficiency. The best practice alternative is to adopt efficiency-based staging points (as opposed to staging points based on pump speed). With this control strategy in place, the system ‘surfs’ across the top of the efficiency curves throughout the day, eliminating the wastage inherent in pump speed-based control approaches. This improved strategy can achieve energy savings of over 30%.
Pitfall 4: Operational drift
Operational drift isn’t necessarily an inevitable element of an energy upgrade, but it’s difficult to avoid without oversight. This kind of oversight is made possible by advancements in cloud computing and machine learning, however. Today’s pumps provide far greater connectivity, and allow the user or custodian to keep up to date with real-time monitoring on a browser or even apps.
Armstrong Envelope, for example, is an integrated digital platform that delivers optimisation through performance mapping, advanced analytics and lifecycle services. Importantly, it can optimise equipment from other manufacturers in addition to Armstrong components. Armstrong’s Envelope Advisor can analyse the HVAC system’s operational effectiveness, air and water side, comparing it with industry standard guidelines, and highlight any issues affecting performance to enable them to be rectified.
Remember that you don’t have to replace the complete pump to harness the aspects of functionality mentioned here. Many pump models, for example, enable the pump head/rotating assembly to be updated whilst leaving the pump body in place. This reduces cost and disruption for the upgrade of the pump and can unlock significant savings.
