EU Energy-Using Products - Environmental disaster?
What's the problem ?
The Energy Using Products directive from the EU implies amongst other things that from 1 January 2015, all electric motors from 7.5-375 kW must either meet the IE3 standard or the IE2 standard equipped with a variable frequency drive (VFD).
Grundfos supported this initiative, as well they might and credit is due (in general).
However, there is also significant scope for this specific requirement to cause an environmental disaster...
This sounds rather alarmist - it is, I am sounding an alarm!
However it also requires that I justify my position.
As we see on the left slowing a pump just a little from 100% - 60% of maximum may reduce energy consumption by 80%
This is not to be sneezed at.
But system efficiency is another question - and it is the only question that matters from an environmental perspective.
If we consider the most common application of pumping it is in the movement of energy contained in hot heating services or cold chilling services water.
A pump capable of moving megawatts of heating water (powered say by gas boilers or furnaces) may be pumped by a few kilowatts.
Under these conditions reducing the pumping rate saves some kilowatts, but may have repercussions on the supply of megawatts of services.
But is this likely?
Lets see what the International Energy Agency have to say on the subject:
IEA (experiences in Swedish District Heating) (Abstract)
In practice, the achievement of large temperature differences is counteracted by mal-functions of consumer stations and their components and often also by short circuits in the distribution network, leading to higher return temperatures and in general also to increased supply temperatures compared to what would be desirable. Additionally, system designers have very often built-in over-dimensioned "reserve capacities" leading to non-optimal functions of control instruments. The results of such malfunctions are higher pumping losses, higher return and supply temperatures and therefore higher heat losses from the net. In the worst case, the net can be choked at the high load times and will not be able to deliver the necessary design power.
What does this mean?
OK - Imagine you are controlling the mixing of hot and cold water running into your bath in some cheap motel. The hot water is scalding hot (unnecessarily) and so you keep the hot tap pretty much closed at all times. All the other guests do the same. So what happens is very little very hot water is used, and as a result the motel saves pumping costs with their new variable speed drive (for the technically alert I am assuming an open system so local pumping is related to water flow delivered).
BUT - a smart new engineer comes along and says,
"HEY - I have a better idea - If we lower the water temperature, we will save on gas, and less heat will leak out of the hot pipes into the areas we are cooling. Naturally, guests will use a bit more water, which will put up our pumping costs, but these are negligible vs our heating costs."
Our new engineer is using the variable speed drive as a feedback mechanism to better control provision of the primary service "heat", by ensuring that the VSD never works as intended (ie operates near maximum rated output - where there are nearly no electrical savings) he maximizes system efficiency and hence environmental impact. In other words, generally the best VSD is one that is not installed as intended !
Where-ever a VSD is fitted, without a smart engineer like our fictional character above, at times of low load, simple thermostatic control efficiency is jeopardized, because the returning temperature of hot or cold water services is no longer indicative of the demand for those services.
Simple return temperature sequencing of boilers and chillers as recommended almost universally for simple system control by Best Practice (to overcome the single weakest point in any building with multiple boilers - the matching of supply to demand), becomes not a simple panacea, but an unstable control system with an inherently non-linear destabilizing positive feedback mechanism built in.
And that is a Environmental Disaster - not one that is waiting to happen, but one that is already well underway !
Update : There is good reason for use of appropriate technologies when adequately understood and outlined here :