Pump and system in harmony

Much has been written over recent years to both raise the profile whilst explaining the benefits of energy consumption. This debate, which is now backed by a variety of legislation, has also had a significant amount of wordage written relating to commercial building services buildings and products, which of course includes pump solutions. 

We say ‘of course’ because we know pumps are big energy consumers that currently account for 10% of global electricity and many are needlessly inefficient.  In fact by focussing on changing to high efficiency pumps, that incorporate advanced motor technology, companies can reduce the average pump’s energy consumption by up to 60%. 

This makes this no longer simply a moral argument, but one that has significant importance environmentally as well as financially.

What value should we place on efficiency:

To explain a little about how efficiencies are a function of good pump design, and not purely a standalone benefit, it is important to understand the true value of pump efficiency, or wire-to-water efficiency.

An easy way to place a value on efficiency is to discuss operating costs. That approach is looked at here, but it should also be noted that operating costs (which reflect power draw) has a direct link to power generation and environmentally disturbing factors (such as greenhouse gasses).

Simply stated, pump efficiency (Ep) is the ratio of output power (otp) divided by the input power (inp), expressed as a percentage.

Efficiency in pumps, as portrayed on pump curves or stated on pump data sheets, is a calculated value based on test results. The amount of work being done is measured, as is the power consumption by the pump and efficiency calculated from those results.

Many factors impact pump efficiency, but there are three stand-out components:

  • Mechanical Efficiency - This is the energy used in bearings, stuffing box/glands and disc friction losses at the wear rings.
  • Volumetric Efficiency - This is the energy used in bearings, stuffing box/glands and disc friction losses at the wear rings.
  • Hydraulic Efficiency - This accounts for friction and shock losses in the flow paths.

When does a pump achieve ‘high efficiency’ status?

It is difficult to state what is meant by high efficiency in a pump. The variety of pump types and intended duties, the specific speeds, pump size, etc., are so varied, that no “cardinal number” can be set that encompasses these circumstances. However, the following can be assumed:

  • in general, the larger the pump, the higher the attainable efficiency.
  • efficiency should be relative to other, similar, pumps of the same size and type.
  • efficiency is only one aspect of pump performance, and reliability should not be sacrificed for efficiency improvements. Typically, when efficiency is discussed, it refers to efficiency at either BEP or a given operating condition. It does anyone little good to look at a pump with 90% efficiency at design point and hear, “Look how efficient this pump is’ if the point of selection is not at that point.
  • while efficiency of the pump is important, its impact is best totally evaluated by a study of the system in which it is installed. Moving a pump to its BEP by closing valves and “balancing a system” will indeed improve its efficiency, but the system itself may become even more inefficient or worse, less effective and is something we have seen happening in the UK for many years.

This means that to achieve the highest overall efficiency the total system needs to be looked at in terms of the entire system, as opposed to just viewing the pump in isolation.

Looking beyond the pump

Today we are all aware that there is increasing pressure on margins at every point in the value chain. Therefore being able to deliver real energy savings with a short return on investment, of less than 2 years for example, is now a reality.

By thinking beyond the pump and taking the entire pumping system into account it is possible to optimise the way pumps, drives, controls & protection, measurement and communication units work together as part of one system. For example a manufacturer like Grundfos, can incorporate specific demands with our application expertise and then take these requirements and translate them into state-of-the-art pump intelligence - for any application. This approach is both integral as well as encompasses the integrity of the entire system and is called Grundfos iSOLUTIONS.

There are many benefits to adopting such an approach from the obvious savings that will be achieved through improved efficiencies – but also will go much further by ensuring that the pumps, controls, sensors, variable frequency drives, connectivity and software and fully aligned – means these solutions offer the optimal result. 

The need to optimise and control speed is something that will continue to gain in importance within building services therefore the ability for systems to become increasingly synchronised, will continuously play a more major role.