Jeffrey Plutz |
Your organization completed a $2 million HVAC renovation project, which included rebuilding three chillers and installing new cooling towers. How did retrocommissioning help determine the chillers were not reaching benchmarks set by your department?
Retrocommissioning allowed us to discover the lack of performance. We implemented a building tune-up, where we looked at the original factory specifications of the chillers. Then we measured all flow rates for the ancillary equipment and evaluated the cooling-tower performance.
After collecting all of the data, some definite deficiencies surfaced. Cooling towers were old and inefficient, and flow rates between the primary and secondary chilled water were not matched correctly. Predictive maintenance, which included vibration and oil analysis, indicated the chillers were in need of major overhaul or replacement.
Preventive maintenance, which included water treatment, monthly inspection, and eddy-current testing, helped determine the future direction for our department.
What factors helped you decide to rebuild, rather than replace, the chillers?
After a careful review of all of the data, the predictive maintenance told us the rotor bars on the motors were at the end of their useful lives and needed to be refurbished or replaced. The preventive maintenance data told us the tubes and internal components were in excellent condition.
The original design data was energy efficient, and this type of machine was not being manufactured any longer. More studies were done on improving the chillers’ efficiency, as well as removing the CFC-R500 refrigerant and replacing with the more environmentally friendly HCFC-134A. We improved chiller efficiency by replacing the refrigerant and installing variable-frequency drives (VFDs).
By replacing the cooling towers, we increased capacity by 300 nominal tons, implemented a new energy-efficient design, and specified VFDs, all of which improved condenser temperatures – kilowatts per ton is down to 0.38 at 50 percent load, compared to 0.587 before the project. We also were able to reduce fan-motor horsepower (hp) by 400 hp.
Lastly, cost factored into the repair-replace decision. New equipment was about $3.2 million, while rebuilding was $850,000, excluding potential downtime and the potential need for rental equipment. Our team completed the project without disrupting our customers and business operations.
What impact did the chiller renovation have on the hotel’s indoor air quality?
We improved the consistent delivery of chilled-water temperature and, by doing so, improved indoor relative humidity. All of those improvements also helped preserve the owners’ asset. Decreasing the potential for mold in a hot, humid Florida climate, as well as customer comfort, also were important factors.
How has the project affected the way your department maintains the chillers?
Fundamentally, the maintenance aspects stay the same. Our department is taking baseline vibration measurements, and eddy-current testing will continue with the same frequency. Removing mineral oil and replacing it with synthetic oil will allow us to sample, analyze, and replace it with less frequency, due to durability.
Can you talk about the savings in both utility costs and energy use since your department completed the project?
This is the best part of the project. Energy use decreased substantially. We were able to save about 8.25 million kilowatt hours, based on a previous four-year average per occupied room. This translated to $825,000 in savings from an $850,000 investment, along with another 20 years of useful asset life.
Certainly being more environmentally conscious also speaks to the success of the project. Minimizing oil disposal, using a green refrigerant, and reducing the hotel’s carbon footprint is priceless.
posted: 2/9/2009
