Wednesday, July 30, 2008

Panel-Level Dimming

This strategy involves installing a control system at the electric panel to uniformly control all light luminaires on the designated circuits.

You can control circuit dimming, manually or by inputs from occupancy sensors, photosensors, timers, or energy management systems. Panel-level dimming is a method for dimming HID systems as well as both electronically and magnetically ballasted fluorescent systems.

Continuous dimming is accomplished using a variable voltage transformer that reduces the voltage to the HID or fluorescent circuit.

For example, suppose you are using photosensors in a warehouse with skylights. The high-pressure sodium lighting system could be uniformly dimmed in response to the available daylight from the skylights, saving substantial amounts of energy.

Another application would include a wholesale merchandising outlet that requires higher light levels during normal business hours and reduced light levels during routine maintenance and stocking operations. The scheduling control system would automatically adjust the light levels based on the business-operating schedule.

Although slight improvements in efficiency can result from the dimming of fluorescent systems, slight reductions in efficiency result from the dimming of HID systems. Light output reductions are about 1.2 to 1.5 times the power reduction in metal halide systems and about 1.1-1.4 times the power reduction in high-pressure sodium systems. Manufacturers can provide the specific lumen-wattage performance curves for the specific systems being controlled.

Note that some panel-level dimming systems are incompatible with electronic ballasts. Check with the manufacturer to find out if their variable voltage system is compatible with electronic ballasts and whether the system introduces harmonic currents.

Be forewarned that dimming HID lamps below 50% power may result in a significant reduction in lamp life.

Friday, July 25, 2008

Do Energy Saving Motors..Always Save Energy?

This is an interesting phenomenon. Many types of energy efficient motors have a higher inrush current simply because they are manufactured with a lower rotor and stator resistance. This means that many types of energy efficient motors have a higher full load speed than their standard counterparts. This could be significant when these specific motors are utilized for continuous centrifugal loads such as in pumping and fan operation.

In centrifugal loads, speed changes greatly effect the required energy input, since variations in speed effect the required shaft power as the cube of the speed, while the flow of the air or liquid actually varies directly and linearly with the shaft speed.

Therefore an increase in the load of the driven equipment such as the fan or pump, can result in the increase of the kilowatt usage, despite the overall lower losses of the energy efficient motor.

There will actually then be a cost penalty of going to the energy efficient motor, since the equipment may have to operate at a higher full load speed. This will depend on the type of service the motor is actually utilized for. For example. If you are going to utilize the energy efficient motor on a pump which is used to fill a tank or similar usage where the service is more or less a start - stop type, the higher speed at full load will develop a greater flow. This will simply cause the tank to fill faster and cause the pump to be shut down faster. In this type of usage, the energy efficient motor will generate a cost savings. Although the input to the motor may be greater, the operating time will be shorter. This is where the cost savings can be developed.

If however, the motor is utilized in a system where there is continuous operation, as in a cooling or heating system where the extra flow developed by the faster speed is wasted and where it will often be throttled down by the balancing process, the actual system may generate an increase in energy usage by the installation of the energy efficient motor.

For the above reasons, the entire system must be evaluated when considering the installation of an energy efficient motor; not just the motor itself.