energy saving

guest; light bulbs, resistance loads less voltage, would save, but output would be less, motors would draw more current under load, harder on motors perry

GA to you too, not because you gave me GA, but you pointed out few more points, which I missed.

What you say over comfort, is not really over comfort. I am not well aware about the cold countries, but here in tropical countries, Air Conditioning means Air cooling necessarily. We do not need heating at any point of time. If we set thermostat at 24 deg C, it is not over comfort, but for many people, who are born and lived here only feel it cold. But if thermostat is at 26 to 27 deg C, it is comfortable to 95% people. Energy saving is great with this small setting.

This should apply to room heating also.

As you say the energy required to do a work remains same. But the fictional losses in any machine can be reduced by proper maintenance of the machine, reducing effective energy consumption.

I also forgot capacitor for power factor.

One more point please:

See that the motors used are being used at its maximum efficiency point, pumps are being used at its maximum efficiency point.

If pump is always under utilized, replace pump by appropriate capacity pump.

The only thing to add to your GA is install good VSDs where actual studies determine significant energy savings, for instance pumps.

Time-switches too!

Well freind, only those loads which follow Ohms law, will show energy saving. But you have to check if reduction in its output (due to lower V) is within acceptable levels.

Current (I) = Voltage / Resistance. So, if V reduces, I will also reduce. Input will reduce & hence output will also reduce.

For example, incandescent bulb will consume less power with lower V - but light emmited by it will also reduce. (other benifit --life of incandescent bulb will increase if used on lower voltages!!)

Thus for loads following Ohms law, if reduction in output is acceptable, you can save energy by reducing V.

But for loads not following Ohms law (e.g. motor), the current drawn by it is more a function of load on it. Hence, you may not be able to save energy with reduced V.

Again let us take the example of motor.

For the constant load, reduced V can in fact increase I, & may harm the motor.

If the 3 phase motor is running on no load, running it in star may help in reducing the energy.

All the Best !!

Friend,

As others have posted, the answer depends on the type of equipment in the plant. Loads which are resistive or mostly resistive will have their power consumption reduced. Otherwise, you have to look at each load. SB noted that for resistive lighting (incandescent), the light output decreases by V². The power consumed does decrease this way, but since the filament temperature has decreased its visible light production has shifted towards the infrared so its visible energy radiation has decreased even further. This is an example of an unwanted result of decreasing the voltage. For the voltage change you suggest, motors which are rated for 415V will most likely be within their design specifications, but the current will increase to compensate for the lower voltage. Therefore, resistance losses on the feeders and circuits would increase, so the overall effect is harmful. Electronic equipment will probably be fine, but the power supplies will be stressed a little more and the harmonic currents reflected by them back onto the distribution equipment will change. I'm not sure if HID lighting will keep the same current, because the ballasts are designed to limit the voltage to the lamps once the arcs have been struck, so with lower voltage you can expect about the same current (for relatively small changes in input voltage, the ballast will feed the same output to the lamps).

Electric utilities frequently use a voltage reduction to shave peak load when they are close to the limit of their generating capacity. In the USA this is usually called a "brownout". However, whether it is the utility or the customer, the best approach is to analyze your plant and take the steps necessary for saving energy with each piece of equipment.

Too often, the purchase price of equipment is the primary consideration, installed of the installed operating cost of the equipment. Therefore, high-efficiency motors often are not purchased. Any motor which has been rewound will be less efficient than it was before the rewind, if even only by a fraction of a percent. That is because the burnout process of removing the old windings from the steel degrades the steel's magnetic properties. (This is true even with very carefully controlled work in a highly competent shop.) Therefore, I suggest using a policy which replaces motors with high-efficiency ones when they fail if they have already been rewound once or are over 15 years old.

The overall topic of energy audits and energy efficiency in a plant is very large and is often complex. Many of the things one finds depend on "human factors" as much as equipment characteristics. Back to your original question: Yes, you can save energy, but its effects on your plant are likely to be harmful in the long-run. Other steps to save energy are probably more desirable.

--JMM