Over the last year we have been busy as usual, servicing and repairing lifts. Whilst on their travels, our engineers have encountered a number of new Energy Saving Units (ESU’s). These are units that are designed to reduce voltage (usually via a reduced voltage tapping on a transformer), therefore reducing energy usage. Whilst we at ACE Lifts are all for green technology and are currently in the process of developing our own ‘Green Lift’, experience has led us to ask what are the effects of ESU’s on lifts? And are they always the best energy saving solution?
To begin with, how do ESU’s work? As previously mentioned the ESU reduces voltage. In a lift, a reduction in voltage means that the current is increased to compensate. Therefore, the power demand remains constant regardless of whether the voltage is higher or lower (this is because rotational speed is mostly determined by frequency, rather than voltage). The lift load however is variable, and when the load it is lifting is heavier, the power requirement is increased accordingly. Also, the motor torque (effort needed for turning) is proportional to the square of the voltage for an induction motor. This means that if the voltage is reduced by 10%, which doesn’t sound like a lot, it is actually the square of this number that is used, and therefore has a much stronger effect than may be expected (nearer to 18%).
There are a few ways this may influence the effectiveness of the lift. Firstly, there is a danger that if the voltage reduction is too severe, the lift will simply switch off. Another potential outcome is the lowering of the voltage may cause relays to either just partially energise, or not energise at all. At best, this could result in lift performance being unreliable, but may even be dangerous. Another problem (and one we have recently experienced) is that this may decrease the life expectancy of certain components, such as the motor or drive control. It is important that any ESU that is installed is properly configured to avoid the malfunctioning of certain lift controls.
Overall, it seems that there are many potential stumbling blocks when installing an ESU to a building. One vital point to consider is how much energy is actually being saved? The answer to this question is none, due to the fact that the voltage reduction leads to an increase in the current, and therefore about the same amount of energy is still being used. When taking into account this, along with the dangers to the lift and its performance, there is evidence against using this method of energy saving technology in lifts and instead bypassing the lift from the energy saving circuit.