ATB System Case Study – River Boat Casino, Indiana
A major challenge to the Port Engineer and Head of Operations at the largest riverboat casino in the world, located in Indiana, has been the riverboat’s source of condenser water, which is pulled straight out of the Ohio River.
Typical condenser approach temperatures on one of the four 450-ton chillers, fully loaded, would be about two to three degrees with fairly clean tubes. The casino has been able to monitor the condenser approach and, unfortunately, has had to shut down the chillers frequently to clean the tubes when the approach gets up to six or seven degrees.
Depending on the load, water temperatures and the mud or debris in the river, the frequency of the high approach temperatures would vary. In the summer months all four chillers are needed for comfort cooling on the boat, but summer is also when the river is the hottest and dirtiest. The casino would typically have to shut a chiller down about once a month to brush the tubes just to keep the chillers from tripping on high head pressure. The bottom rows of tubes were even completely plugged in some of the condenser tubes.
If the casino lost one chiller during this critical time they would have to start shutting down some of the decks. This would help decrease the load on the remaining chillers, but it would mean thousands in lost revenue for the casino.
The casino installed the Automatic Tube Brushing System on all four chillers in May, 2002. In June, a one-month follow-up showed that the ATB System had not only performed as promised, but had actually improved the chiller performance. At 75% load, one chiller was showing less than half a degree approach temperature. The other chillers were operating at less than two degrees approach.
At the end of July, all four chillers were running at full load. Usually, by this time the chiller operators would have already had to clean the condenser tubes manually because the approach temperatures would have been excessive. With the ATB System installed, approach temperatures on all four units were less than two degrees, which indicates very clean tubes.
In November, another follow-up showed that all four chillers were still operating at less than two degrees on the approach temperatures.
After more than a year of operation, the Head of Operations at the casino claims to have received a payback in less than six months.
ATB System Case Study – Los Angeles VA Medical Center
The West Los Angeles Veterans Administration Medical Center, a 350-bed hospital, has an average patient load of about 300 people. This creates a demand for cooling in the hospital of a minimum 1,300 tons year-round, with an additional 1,300 tons required in the summer months.
In 1998, the Director of Plant Operations and Maintenance purchased two new 1,300-ton Trane chillers with “helix” style internally enhanced condenser tubes for the West LA VAMC. The advanced tube design offers increased heat transfer and therefore decreased operating costs, providing the tubes are kept scale and deposit free. But as with any chiller, when the fouling in tubes exceeds the .00025 design fouling factor, chiller capacity decreases while kw/ton requirements increase. To maximize the benefit of the new condenser tube, the hospital engineer needed to find a solution to tube fouling.
For over ten years, the Washington DC engineering office for the VAMC has included an option in new chiller specifications that is aimed at eliminating tube fouling. The Automatic Tube Brushing (ATB) System, an on-line condenser tube cleaning system that guarantees to maintain condenser tubes at the .00025 design fouling factor, is available to all VA Medical Centers installing new chillers.
The Plant Supervisor at the VAMC states, “Because our chillers have the brush system, the head pressures are as good as when the machines were new four years ago. We automatically clean tubes every four hours, six times a day, instead of once a year manually.”
The Plant Operator says, “I would recommend the brush system to anyone who wants a clean chiller.”
Maintenance savings are obvious at the West LA VAMC. When coupled with the energy savings the system provides by keeping the condenser tubes at their design fouling factor, the ATB System easily paid for itself during the first year of operation.
The heavy load requirements (at least 1,300 tons year round) and high power costs ($0.08/kwh) make the Return on Investment much better at the West LA VAMC than it might be on an average, but most every installation will provide a payback of less than two years. Using average fouling (.0018) as a baseline, compared to the design fouling factor of .00025, the estimated load hours, power costs and kw/ton rating of the chiller are taken into account.
Each system at the West LA VAMC had a material cost of about $33,000, which includes the on-site installation of the nylon-bristled brushes and open catch-baskets in the tube ends by the manufacturer. Adding in a contractor’s costs to install the reversing valve and controls makes the entire system cost just over $50,000 on 1,300-ton units.
This is minimal when compared to the energy costs required to produce the hospital’s load requirements each year, about $350,000 per unit. By keeping fouling factors at the design .00025 rating, the system is able to help the chiller maintain its design kw/ton rating of .56, rather than operating at the .65 kw/ton rating to which it would normally increase with average fouling.
The $350,000 energy cost drops to $293,000 each year, a savings of $57,000 with a total investment of just over $50,000. With these numbers, it is easy to see why the Washington DC VAMC engineering office recommends the ATB System to its hospitals.