Many pumps still waste energy due to oversizing and outdated control strategies, says Peter Wolf from Armstrong. Here he explains how modern intelligent, demand-driven pumps with digital oversight can unlock significant efficiency gains across a building’s lifecycle.
Pumps have come a long way since the days of fixed speed units. The evolution into variable speed pumps, and eventually into fully connected intelligent devices, has given a brain to the heart of a building, becoming an integral part of the design phase as well as contributing towards efficiency targets long after installation.
Pure efficiency hardware gains are still netting huge savings for customers (new DEPM motors are reaching heights outstripping EU efficiency guidelines, for example). However, considerable cost-savings are still being left on the table, especially in four key areas which are all too easy to overlook.
1. Pumps being oversized for their duty
The traditional method of assessing system flow rate, with built-in safety factors, results in an oversized pump that’s regularly running at way under the design flow number, reducing its operating efficiency and its lifetime. A better solution is to split the system flow rate between two or more pumps. Today’s intelligent Design Envelope pumps can talk to each other and stage themselves in and out, delivering higher efficiency across a much broader operating range. So be very wary of ‘like-for-like’ replacement of pumps without reviewing the specific requirements of the application.
Be particularly careful where projects involve incremental expansion, as pumps designed for the peak output at some future date will be forced, in the early stages, to operate far below their ideal capacity, wasting energy, and increasing the risk of technical problems. In these instances, harness the advantages of modular design. The latest generation of packaged HVAC solutions has been 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 avoid costly customisation of existing systems, as well as providing much needed predictability and repeatability of environmental performance.
2. Pumps operating off their natural curve
Perhaps the most important technical issue to address is the choice of 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 a HVAC component such as a pump or fan, there is huge potential to improve part-load efficiency due to the pump affinity laws (change in power is proportional to the change in rotary speed cubed: (P proportional to N³). If a rotating device is allowed the flexibility to operate along its peak efficiency natural curve, this can increase operating efficiency by 400%. These efficiency improvements 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.
3. Inefficient staging of pumps
As well as ensuring the efficiency of each pump, it’s important to make sure the control methodology is in place to effectively balance the different pumps against each other, managing the entire plant room in the most efficient way possible. The latest generation of control technologies can optimise energy efficiency by phasing components such as pumps and boilers in and out more effectively as demand on the system rises and falls. Traditional pump staging strategies, for example, 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%.
4. Operational drift
Operational drift isn’t 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. Today’s pumps provide far greater connectivity, and allow the user or custodian to keep up to date with real time monitoring on browser or even apps.
Armstrong Envelope, for example, is an integrated digital platform that delivers optimisation through performance mapping, advanced analytics and lifecycle services. It can optimise equipment from other manufacturers in addition to Armstrong components. Armstrong’s Envelope Advisor can analyse HVAC system’s operation effectiveness, air and water side, comparing it with industry standard guidelines, and highlight any issues affecting performance to enable them to be rectified.
