How to increase Energy Efficiency in a System
Exemplified by a temperature control system, you will learn how energy efficiency can be increased significantly by using the built-in functionalities in intelligent pumps.
Far too many industrial applications are characterised by complex system design and pumps that operate at full speed no matter the requirements. One of the downsides to this is unnecessarily high energy consumptions – but it doesn’t have to be that way.
In this tutorial we’ll show how intelligent system design will lead to optimised performance and significant energy savings, using temperature control as an example.
Let’s begin by taking a look at the stats. According to a Europump study, 30% of potential energy optimisation can be found in better system control and better system design. It is, however, possible to go even higher than that. We’ll touch upon that later in the tutorial.
Temperature control is a crucial part of a wide range of industrial applications and an obvious place to look for optimisation opportunities. The operating cost of temperature control depends on a number of things:
• The efficiency of the pump and motor
• The control mode
• The sizing of the system
• The load profile
• And not least the losses in the system.
In this tutorial we’ll be paying primary attention to the control mode and system losses.
Traditionally, there are two ways to design a temperature control system. The one you see here features a constant speed pump, a temperature sensor and a temperature control valve, which controls the temperature on the discharge of the exchanger. It’s a simple system design that gets the job done – but far from energy-efficiently because the pump operates at constant speed even when demand is at a minimum.
A slightly more advanced solution is achieved by replacing the constant speed pump with a variable speed pump and add a differential pressure sensor. Again, the system does what it is supposed to do – but the presence of a temperature control valve still equals pressure losses in the feed pipe, which requires the pump to work harder and increases the energy consumption
Now, let’s take a look at how things can be done much smarter and less complex by applying a different mind-set and a different control strategy.
Because do we really need all the components in the system we just looked at? The answer is no.
By connecting the temperature sensor directly to the pump we are able to control the pump by means of the constant discharge temperature and so make the differential pressure sensor – as well as the temperature control valve – redundant. As you might have noticed, the pump is the same as in example 2 – a variable speed pump; but now we are making use of its integrated control functionalities which allows us to control the pump directly according to the temperature.
As we can see here, at a flow level of for instance 10 m3/h, the energy consumption is low when operating with direct temperature control, as the green line highlights here.
To emphasise the effect of intelligent temperature control, let’s quickly look at 3 typical load profiles and the difference in performance between the 3 system setups. The simple system setup with the constant speed operated pump is set to index 0. As you can see, the system using direct temperature control will outmatch the other two system setups significantly and save up to 70 % of the energy used for pump operation. The 72 % saving is obtained on the system with the most part load.
However, the level of savings all depends on the load profile. The huge savings that can be found in temperature control are because many pumps are oversized. This means that they mostly operate within the first third of the pump curve, where greater savings are made.
So, as we have just seen, applying a different mind-set to the system design and choosing the right control strategy pays off. By doing this the total efficiency will increase significantly and result in tangible energy savings and very attractive life cycle costs.