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Energy Saving Scams And Mis Representations

Posted by marke, 09 September 2007 · 1,897 views

Energy Saving
There are many energy saving schemes promoted in the industry today, some of these work, but many either can not work, or can not work in the manner that they are promoted.

In order to reduce energy consumption, there must first be energy wasted, and second, a means of reducing that energy wastage.
You can only save a portion of the energy that is being wasted.

If you are serious about saving energy, you must:
  1. Establish where energy is being wasted.
  2. Determine how much energy is being wasted
  3. Determine possible means of reducing the wastage
  4. Determine the amount of reduced wastage
  5. Determine the cost and viability of reducing the wastage

Energy wastage generally occurs due to either reduced operating efficiency, or excessive output.
For example, an office is provided with lighting sufficient to light the work areas at night. As the ambient light level is increased, (day time) the supplemental lighting levels required, are reduced, but so often, the full light output is used irrespective of the ambient light levels. The artificial light levels can be reduced, or in some cases totally removed without greatly affecting the light levels at the work area.

It is important that in reducing the energy consumed, you do not reduce the "work" output to a level that it begins to impact on the productivity of the plant. Lighting can often be reduced during the day, pumps and fans can be slowed down when there is reduced flow required.

Energy saving is more commonly related to process control, than to "magic" add on boxes.

Typical add ons for saving energy:

Nola type energy savers for induction motors. - These will save energy if the motor is operating at very light load and is operating inefficiently. Larger and more modern motors are far more efficient than old small motors. There are some applications for saving energy using this technology, but they are very limited.
Motors must be small, operate under very light load for very long periods of time.

Power factor correction. - Power factor correction is a means of reducing the current drawn by an inductive load. This will reduce the line losses in a transmission system, but will have little or no impact on the KWHr meter except where the mater is installed many KM from the connected load and the correction is applied at the connected load.
In the industrial installations, there are usually electricity tarriffs based on KWHrs plus an additional surcharge for poor power factor, or a KVA maximum demand penalty or similar. Money can be saved by a reduction in the penalty, not the reduction in KWHrs.
In the domestic installation, the power is charged for KWHrs used. There is no power factor penalty or KVA maximum demand penalty. There is no financial gain from the addition of power factor correction in the domestic environment.

Lighting Controllers. - Lighting controllers that reduce the level of artificial light during periods of high ambient lighting, will achieve appreciable energy savings. Some controllers permanently reduce the voltage to the lamps, reducing the light output under all conditions. These will reduce the energy saved, but will also reduce the usefulness of the lighting when it is required most.

Variable Speed Controllers. - VSDs can be used to control the speed of a machine. There can be significant energy reduction if the machine is slowed down when it does not need to operate at full speed. For example, pumps operated so that they run at a speed dependent on the flow requirements will reduce the cavitation losses in the pump. If the pump is required to run at constant full speed, the addition of a VSD will actually waste another 5% of energy.




Dear Marke
I do not fully agree with the VSD saving.
In the wholistic view when taking the total energy consumption on a VSD device, it creates more losses & affecting other equipments:
a) There is a double energy conversion with VSD. AC power => DC power, DC => AC (with variable frequency). The front end of the double energy conversion is usually with efficient of only 80%. Depends on makers. Some AC-DC & DC - AC design are event less efficient & losses more power.
So even if we save energy on motor running, we losses power on the front end which is quite substantial.
cool.gif Harmonics generated along power line. This harmonics are usually very high & can impact the performance of other equipments along the line. We improve power consumption on motor load but causing waste on other equipement due to the high harmonics. Many people also realise that VSD causes high harmonics & can be quite difficult for other sensitive or data equipment to function properly.

So in summary, it is OK for small VSD device for some specific applicaiton, but in general, I do not think this is a good solution.
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Hello STARS-5

Yes, I agree that the addition of a VSD does add losses to the system, but, in some cases, by slowing down the driven load, the energy savings are much larger than the additional losses.
For example, if you have a pump operating under variable flow conditions, then the reduced flow will result in the pump being throttled and it will cavitate. This causes high hydraulic losses.
If you slow the pump down, you can increase the operating efficiency at reduced flow and this will result in energy savings that are greater than the additional losses.

There are a number of cases where slowing the load will reduce losses and the use of a VFD does save energy, but there are many situations where the addition of a VFD will reduce the overall efficiency.
Best regards,
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Dear Marke
That's the point...

If Motor or compressor load are running at high efficiency on full/ part load, then who need a VSD (or inverter)?
If Inverter can improve efficiency of load operation, then why the motor control (like the Nola type controller)can't?

My opinions are most motor/compressor suppliers over claim the efficiency performance to make us believe tht higher rating/power motor are very efficient even running on part load situation.
Some 'theory' also proven that 'NO-WAY' you can improve a motor load with motor control.
However, most of us also lead to believe that inverter running at variable speed on part load reduces the loading on motor/compressor.

The aboves are very controvasal & contraditing (we accept inverter but reject motor controller). IN fact inverter systems have for more problem than the simple Nola type motor control, other than cost, implementation. contanminate power line etc.

The only good thing (benefit) about inverter device over motor load (if we can use it properly), is for us to tap inverter power source from renewable energy like Solar.
Because inverter need to convert DC to AC, Solar is the best source of DC power that is currently very green (omit the waste of building Solar panet).
Also, inverter keep the motor/compressor running at all time eliminate the start/stop procecss on motor, eliminate the problem of voltage output fluctuation cause by dynamic load changes. This is the common problem faced with inverter circuit.
Suppliers of inverter device (such as VSD, air-con) should actually work toward this kiind of product to fully enhance the inverter design & not on the current motor/compressor controller, which do not actually benefit to consumers in term of energy saving.

Cheers





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If the motor and compressor are operating at maximum efficiency at part load, then there is no advantage.
If the compressor efficiency can be improved at part load by slowing it down, then there is an advantage. The Nola system does not slow the machine down, it just reduces the voltage and thereby reduces the iron loss in the motor. It does not improve the efficiency of the machine.
Note, frictional losses are proportional to the speed squared. Slowing down a small amount can reduce the losses.

Best regards,
Mark.
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The points is:

Why should a motor/compressor be slowing down to improve the efficiency on part load? If the motor/compressor is already operating on high efficiency even on part load, then it should lower the consumption (current) to the point when efficiency is the still high!
I.e. for a efficient motor load, whether it is running on inverter, Nola technic - there is not improvement at all.
The fact is if you can improve the efficiency by slowing the speed to match this amount of load, there are also other method (like the Nola technic) who will do the similar job (& perhaps better).

Like all mechanism, these controlling devices cannot be perfect with ZERO losses. The only way is to REDUCE the losses & result in IMPROVE the efficiency.
If the Nola method do a better job (by lowering the losses) than inverter system, then it should be a better system to transform energy from one-form-to-another effectively. Vice-verse, for the inverter system.

Iron loss are just part of the efficiency improvement. There are also other reduction if you ride on the constant momentum on energy on rotating motor etc. These are part of the saving you can get on the entire system - not just the iron or core losses.

Good to share these with you on open discussion.
Cheers! wink.gif biggrin.gif


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Hello STARs-5

Firstly, I think that you have a number of misunderstandings about how things operate.
Firstly, a typical VFD has an efficiency in the order of 97% overall. Your comment about the rectifier being on 80% efficient is not correct.
So, at full load, we may have a VFD at 97% and the motor at say 92% (depending on size and design) and the pump (or machine) may have an efficiency of say 80% or even less, so the wasted energy in the VFD is small, The wasted energy in the motor is also relatively small. The major losses are in the driven load an that is why we target the driven load.
If our driven load has an efficiency of 80% and the losses (20% of rating) are essentially frictional, then reducing the load to half load would not alter the frictional losses, so the efficiency would drop to 66%. If we slow the speed of the machine to 70% speed, then the frictional losses are halved, so are now 10% of rating. If the same work can be done at 70% load, then the efficiency is back up to 80%.

You describe the Nola controller as "freewheel" basis. This is not correct, the Nola controller reduces the voltage when the motor (Not the load), is operating at reduced efficiency. The motor and load do not freewheel at any time.

Best regards,
Mark
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Hello STARS-5

I accept that english is probably not your primary language and that can lead to mis understandings, however there are some very fundimental facts that are definitely incorrect. I am assuming from your comments that your background is in low power electronics and switchmode power supplies.
QUOTE
do not agree with you on a 97% efficiency on VSD & I don't think any maker can claim that kind of efficiency. The most you can get from a double conversion system is 85%, with an extremely good circuit design.

Have a look at the data on any VFDmanufactured and you will find that they all quote an efficiency of better than 95% and they are correct!!
The AC - DC power stage comprises a three phase bridge rectifier with a DC Bus choke and a capacitor bank. The voltage across the rectifiers is in the order of one volt, so if we look at each phase on a 400Volt supply, we are effectively losing 1 volt in 230, so 0.5% losses plus a small loss in the DC Bus Choke.
The DC - AC stage comprises 6 x IGBT switching modules. The output waveform is a PWM waveform with the switches either ON of OFF. They are not operated in a linear mode.While a switch is ON, there will be in the order of 1.5 - 2.5 volt drop across the switch and the output current passing through it. If we assume 2 volts, then the static losses in the IGBTs would be in the order of 1 - 1.5%. Now we have the switching losses and these are dependent on the switching speed and the switching frequency.
It is not uncommon for the switching losses to be in the same order of magnitude as the static losses in many drives, so let us assume 1.5%. We now have a total of 3.5%for the power circuitry.we certainly do not have 20% losses in the control circuitry!! I think that you need to do some real research before making such statements above.

QUOTE
Your are right that Nola-type do control the voltage. However, because it allow the motor to rotate using the control & momentum (becase of the speed of motor), the freewheel effect is now taking the role in energy saving.
You obviously do not understand the operation of motors or the Nola system. If you reduce the voltage on the terminals of the motor, you reduce the magnetic flux in the motor core. This reduces the iron loss in the motor and it also reduces the maximum torque that the motor can produce. At a reduced voltage for a given load torque, the slip increases so that the motor can develop that torque. This increases the slip losses in the motor. You can only achieve a reduction in energy consumed when using this technique, at very light load. The load current needs to be equal to or less than the magnetizing current. There is no freewheel effect There would be a freewheel effect if you turned the supply ON and OFF to the extent that there was no flux. This does not happen. Perhaps you have developed this idea because there are SCRs controlling the voltage to the motor. These SCRs are phase controlled, not cycle switched. You can achieve the same effect using a variable transformer to reduce the voltage.

QUOTE
What you mentioned about the frictional loss is actually very negligible unless it is a very old motor with insufficient/ineffective greasing. I would not put the frictional loss into discussion unless they are very signifcant in the equation
I agree, the frictional loss in the motor is low, however I am talking about the frictional losses in machines that can be very high. Have a look at gearbox losses etc.
Have a look at a set of pump curves and see what happens to the efficiency of the pump when you reduce the flow by increasing the head. This is what happens if you restrict the flow by closing a valve. The efficiency of the pump falls and the pump gets very hot. Now look at the efficiency curve when you reduce the impeller size. The efficiency comes back up. Some curves will show you what happens if you change the pump speed. Changing the pump speed gives the same results as changing the impeller size. by matching impeller size and speed to the required flow and head, you get maximum efficiency. If you require a variable flow, then the only way to do this matching for the different flows, is to vary the speed.

Please do some proper research before making such bold statements. You are arguing against well tested and proven FACTs that you can easily prove to yourself in practice.

Best regards,
Mark.
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Dear Marke
I am sure you are a very knowledgeable in technical & good english speaking background.
1. For 97% efficiency - I am also surprise that you are taking these manufacturers' claim seriously on the efficiency but do not study how (under what condition) that they claim 97%. In the matter of practical fact.. there is no way you can tranform energy from 1-form to another with 97% efficiency.
2. You have a good indiction of calculating from AC to DC. However, you do not seem to take into consideration that huge amount of garbage power generated as the bi-products (ripples, harmonics etc) & electrical design has to take care of these garbage to minimse the operation impact. The circuit generate garbage & it needs another circuit design to clean these garbage.
3. On inverter IGBT (or some use MOSFET, with lower in cost), what kind of inverter output signal (PWM) are we referring? Are we seeing a perfect Sine-wave? What is the cost of a inverter output with perfect Sine-wave? How are the Sine-wave affected when driving on difference loading condition? What is the efficiency of power conversion under each loading condition?
If the inverter design do not product a perfect Sine-wave but step-waves, how much of such step-wave power can be effectively driving the motor? What happen to the motor operation if it is being driven by step wave?
So you see how to get a 97% efficiency?
You are mentioning that I am arguing on PROVEN FACT - I would very like to know who has proven these FACT??? Did any institution put these into their R&D lab to prove that Inverter is a very efficient design & Nola-type control is not as good? All these are just speculation from internet with different people's opinion. Some people like me - who has no knowlege of technical - can argue strongly to support inverter design & denies others' techology because they copy what manufacturers making the claim. Many of us are a bunch of COPYCAT!!!
3. On FREEWHEEL - please make some study on the how a fix speed motor can achieve a freewheel effect. In Nola-tyep design, the rotation is vey much a momentum driven, especially significant when motor are taking on very light load. This simply cannot be happening to an inverter design- because inverter are re-generated power & are very sensitive to sudden/drastic load change. This most of the low speed rotation are in fact 'unnecessary'- If you stop the motor completely. It is a 100% saving of power. Beside, the low speed contributes to a lost of wastage power & harmful harmonics are the highest in magnitude, making the power correction much difficult. Such harmonics if untreated properly can transmit back to power line & creates stress & waste on other sensitive equipments working on the same power line. Are you aware you are not able to operates data-machine properly if you are using high power VSD in your operating facilities? You might want to learn about this to understand where are all these losses go!
4. Talking about friction loss.. you are now drifting away... to includes pump & gear... If you talk about the impact of different types of load.. then you are adding more parameter into the design.. we are talking about the motor friction... not the external loading.

I am sorry to learn that you find my opinion BORDING.. Perhaps you are more knowledgeable than me. But I have been working on AC-DC, batter charge, inverter design from the static control, MOSFET, IGBT etc. I have not come across makers who can prove a 97% efficiency in such conversion.

I am writing this reply not to argue on your points (which I think you have a good electrical knowledge) but to point out on my humble opinions & my experience on AC-DC-AC design because these are over-claim data that can mislead & unfair to consumers who do not have technical knowledge & experience. This is not the first product that many manufacturers over-claim & not the last- anyway.
STARS-5







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Hello STARS-5

I have replied to you on the main forum as this thread is getting too long for comments on the blog.
http://www.lmpforum....Blog-t3299.html

Best regards,
Mark.
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