Think before you buy energy-saving equipment
Before installing energy-saving drives and high-efficiency motors, you need to examine carefully the system in which they will be used. Frank Griffith, a drives consultant with ABB in the UK, offers advice on what to look for.
Installing high-efficiency motors and drives can result in great energy savings, providing that the installation works as intended in its current setup. But frequently, users, eager to benefit from energy savings, fit drives in installations that are not properly set up. This may well lead to some energy savings, but the savings achievable by putting the process right would be much greater.
To optimise energy use, it is necessary to look at the system as a whole: what is the installation designed to achieve?; how well is it doing this?; what components are involved?; how do they interact?; on which grounds were the components selected in the first place?; and is the application still doing what it once did?
For instance, a pump at a sewage works may not be the ideal size for energy-efficient operation if it was dimensioned also to handle volumes of stormwater that may occur once every 20 years. Here, a set-up with several smaller pumps using speed control may be more economical.
The key to getting the process right is to understand where losses occur. Sub-metering may be a useful way to get information on how different parts of the system are performing. It is also a good idea to look at any other measurements that are available and to listen to feedback from users.
To optimise performance, it is necessary to understand the process and how the different parts interact. For example, if the pump is far away from the measuring point, flows and pipework along the way may impact in such a way that the output becomes something different from what you were expecting.
Another major consideration is the way the system is used. If a system – a conveyor belt, for instance – is frequently running empty, it may be useful to be able to start and stop it according to demand, using a variable-speed drive, without having to think of start-up. This could be a great boost to energy savings. If an application runs frequently with a low load, it can be a good idea to look at synchronous reluctance motors, which can often halve losses in low-load conditions.
Optimising energy use is about identifying when energy is used for a purpose, and when it’s not. A professional energy appraisal is a good first step towards ensuring that your plant is operating efficiently.