However, condenser tube scale buildup on centrifugal chillers at the New Orleans Airport Hilton was creating major operating problems ranging from undesirable compressor surge to rising wastewater and chemical treatment expenses. The Hilton's facility opted to cure their scale blues, enhance chiller efficiency, and lower operating and maintenance costs with the ED2000, a totally non-invasive, electronic anti-tube fouling system from York International (York, PA).
Scale Never Sleeps
The New Orleans Airport Hilton opened in 1989, and since its debut, scale-related troubles have been increasingly problematic.Originally, the hotel's cooling plant was comprised of three centrifugal chillers rated at 135, 185, and 235-tons. The condenser water loop was conditioned using a magnetic water treatment device to prevent scale, while chemical treatment was used for biological control.
As cooling tower water was warmed in the chillers' condensers, dissolved mineral ions precipitated out of the water and adhered to condenser tube walls. Over time, soft deposits formed, and eventually turned into hard scale. This unwanted accumulation decreased the effective heat transfer surface and restricted water flow.
The old magnetic system proved to be an ineffective scale-controlling deterrent. What's more, this system's failure to alleviate scale formation in the condenser tubes resulted in higher-than-design condenser pressures, which created other operating concerns.
"High condenser pressure increases the chiller's energy consumption, and if the pressure increases enough, it will force the compressor into surge. A surge condition limits a chiller's ability to provide cooling, and if left unchecked, can lead to significant compressor mechanical failures," commented Ned Hebert, zone service manager at York's Saint Rose, LA, office.
Chiller tube fouling can also increase chiller energy consumption. For example, with a fouling factor or 0.003 (0.036-in. scale thickness) the additional energy cost per year for a 500-ton chiller is $25,300.
"Energy use was rising and maintenance and water treatment costs were going up as well. The magnetic system just wasn't working, and we had to do something to protect our investment for Hilton and its guests," declared Glenn Ziegler, the hotel's chief engineer.
Traditional Tube Cleaning
Once scaling occurs, traditional tube cleaning involves acid, steel brushes, and abrasive. This method may shorten tube life, resulting in expensive tube replacement. Also, acid disposal may pose environmental concerns.Ziegler acted quickly to halt the creeping mineral deposits. In April 1998, York technicians installed ED2000 units on each of the condenser water supply lines to the three chillers; ED2000 coils were also added to the cooling towers' makeup water supply inlet piping.
The process, called solenoid-induced molecular agitation (SIMA(tm)), induces dissolved mineral ions to precipitate into larger insoluble crystals, which pass through the condenser without adhering to the wall.
"With ED2000 water management, you eliminate the hassles of cleaning tubes with acid, steel brushes, abrasives. You also save the wear and tear on tubes caused by these cleaning methods," Ziegler noted.
The ED2000 system is easily installed, because no welding or other invasive procedures are used. The hardware includes an electronic control box attached to a prewrapped solenoid coil in a weather-resistant enclosure. The solenoid coil is externally (noninvasively) fitted to the condenser inlet pipe. Installation takes about 20 minutes. As a result, there is no downtime and no threat to system integrity.
Flawless Performance
After two years of operation, the ED2000 electronic de-scaling system has exceeded expectations.After installation, a combination of chemicals and the ED2000 treated the condenser water loop for biological control. This was continued for 10 months, and afterward the condenser heads were removed from the three chillers. Inspection revealed no evidence of scale.
A post-installation analysis performed in December 1999 showed a significant increase in the amount of calcium ions precipitating out of the tower water. When compared to the raw makeup water, which was determined to have respective chloride and calcium levels of 84 and 134 ppm, the tower water showed chloride and calcium readings of 500 and 400 ppm.
Herbert said that less calcium in the tower water created a proportional increase in chloride concentration allowing increased concentration cycles from 3.4 to 5.8, saving up to $3,157 per year in water expenses.
All in all, cleaner condenser tubes are predicted to reduce energy usage on the old chillers by about $7,303/year by improving the chillers' efficiency from about .80 to .75 kW/ton. ES
