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.

Severe Pitting of Chillers and condensers

On the left is a Photomicrograph showing the corrosion pit that worked itself to the outside surface of the condenser tube. 

Severe pitting of chillers absorber and condenser Tubes. occurred in a system utilizing 4" to 6" steel piping with an open

cooling tower.

It is important to note that badly maintained cooling tower water circuits in a chiller system can cause very rapid corrosion of chiller

absorber and condenser tubing. In fact, it is not uncommon

that even in new installations, such corrosion could

completely destroy a chiller in one to three years. One very

common scenario is as follows:

Algae, spores, sand and other debris builds up to cause

fouling of the absorber and condenser tubes. As the fouling

progresses, localized, differential corrosion cells begin to

form. The differential corrosion cells cause pitting corrosion

and attack the internal areas of the absorber and condenser

tubes.

As the pitting corrosion progresses, it causes wastage of

copper material. Copper then plates out on the interior

surfaces of the steel piping material. A combination of low pH

values (6-7) along with the warm condenser water and the

copper plating out on the steel causes corrosion to then

progress to the steel piping. This corrosion process develops

tubercle material which, due to the water velocity, periodically

breaks off and ends up in the cooling tower water circuit.

The iron oxide that then enters the cooling tower water circuit

begins to work its way to the absorber and condenser tubes,

accumulate with the algae, spores, sand, etc. and begins to

cause increased fouling of the tubes. Once fouling rapidly

accelerates, cleaning brushes utilized in the chillers usually

becomes ineffective. Water flows and water velocities begin to

severely decrease and tends to decrease the effectiveness of

cleaning brushes which may be installed. Therefore, don't

depend upon them in this type of situation.

This type of corrosion cycle becomes self feeding. The more

corrosion, the more you get increased fouling which then

creates increased corrosion and so on and so on. To stop the

process, you must start with a complete system cleaning,

keeping the cooling water clean and making sure that the

water pH stays in the 8 to 8.5 range or at the pH level required,

depending on the water treatment chemicals utilized in the

system.