4 FM quick reads on Chillers
1. 5 Steps to Chiller Efficiency
When developing a PM plan for chilling equipment, maintenance and engineering managers should consider five essential areas.
- Maintain a Daily Operating Log: This process allows the operator to assemble a history of operating conditions, which can be reviewed and analyzed to determine trends and provide advanced warning of potential problems.
- Keep Tubes Clean: One large potential hindrance to desired chiller performance is heat-transfer efficiency. Chiller performance and efficiency relate directly to its ability to transfer heat, which begins with clean evaporator and condenser tubes
- Ensure a Leak-Free Unit: Manufacturers recommend quarterly tests of compressors for leaks. Low-pressure chillers using either CFC-11, which has been phased out, or HCFC-123 have sections of their refrigeration systems that operate at subatmospheric pressure. Although these chillers are the most common in today's facilities, it is difficult to create a perfectly sealed machine, and leaks allow air and moisture, commonly referred to as non-condensables, to enter the unit.
- Sustain Proper Water Treatment: Most chillers use water for heat transfer, so the water must be properly treated to prevent scale, corrosion and biological growth. A one-time chemical treatment is required for closed-water systems, which are typical of chilled-water systems connected to the chiller evaporator.
- Analyze Oil and Refrigerant: Annual chemical analysis of oil and refrigerant can aid in detect chiller-contamination problems before they become serious. Testing consists of spectrometric chemical analysis to determine contaminants, including moisture, acids and metals, which hamper performance and efficiency. A qualified chemical laboratory specializing in HVAC equipment must perform the analysis. Most manufacturers provide annual oil and refrigerant analysis services.
2. Project Management: Chiller Challenges
The process of installing high-efficiency HVAC equipment in institutional and commercial facilities is rarely without complications, challenges or problems. One case in point is the construction of a 174,109-square-foot addition to Advocate Condell Medical Center in Libertyville, Ill., in 2011. The project included two new high-efficiency chillers, and it incorporated the installation of two new high-efficiency boilers in the existing hospital.
Successful installations often depend on the ability of maintenance and engineering managers and their staffs to troubleshoot the problems and make the needed changes quickly.
"As far as the issues with the new building, the commissioning and the involvement of the operations staff had a lot to do with minimizing the problems we had," says Joseph Buri, the medical center's manager of energy solutions.
Advocate Condell, with 281 beds, opened in 2003. The level-one trauma, acute-care facility with 745,034 total square feet sits on a 72-acre campus and is the largest health care provider in Lake County, Ill.
One goal of the 2011 addition was patient comfort.
In addition to allowing the expansion of outpatient services, Buri says, "The other piece to it was to allow the hospital to become all single-occupancy rooms." The addition featured two 600-ton centrifugal chillers, both with variable-frequency drives, which brought additional benefits to the hospital's maintenance and engineering department.
"We chose them because they matched our current chiller plant, which were centrifugal, as well, from the same manufacturer," says Buri, who was the medical center's director of facilities and construction at the time of the project. "We were looking to maintain some equipment uniformity. That was the one piece to it. We also wanted some flexibility in operations. We were looking for efficiency to be able to take advantage of the utility rebates.
"Because we went with a high-efficiency chiller, we received some rebates on the motors. So because of the higher efficiency, we received rebates of about $48,000 from the utility."
3. Solid Maintenance Programs keep Chillers Operating Efficiently
As chillers age, their components wear, heat transfer surfaces become fouled with scale, and breakdowns become more frequent. Solid maintenance programs that address tracking performance, conducting regular inspections, and performing all scheduled maintenance activities can extend system life while maintaining the performance of the system, but they can not completely eliminate the impact that time has on the chiller. Eventually simple wear and tear will cause maintenance costs to increase and system reliability to suffer.
To evaluate system reliability, start with a review of the chiller's operating log. Operating logs track data related to the operation of the chiller, including drive motor current and voltage, condenser water supply and return temperatures, evaporator and condenser pressures, and oil temperature and pressure. Additional information, such as the need to add oil to the system and scheduled and unscheduled maintenance activities, should be recorded in the chiller log.
Reviewing this information on a regular basis can identify trends that may be negatively impacting system performance and reliability. Are the maintenance requirements and breakdowns increasing? Is the length of time that the chiller is out of service the result of a breakdown increasing?
Another reliability factor that must be taken into consideration is the availability of replacement components. While chiller manufacturers maintain an inventory of replacement components for practically all of their models regardless of their age, it does become more difficult to get replacement components for older models. Time delays in locating and shipping these components result in longer outages for managers and building occupants.
4. With HVAC Upgrades, Look Beyond Like-Kind Replacement
Today's tip from Building Operating Management magazine: When replacing elements of the HVAC system, evaluate whether to replace units with a like kind or not.
Say you're replacing a chiller. Because chillers can easily last 30 years or more, the odds are good that the needs of the building and its occupants have changed since it was installed. In that case, it probably isn't a good idea to replace units with like kind.
For one thing, chillers with older technology are not as energy efficient as units made today. What's more, you might find out that the size of the existing unit may not meet the needs of current and future occupants. There's also the question of how much redundancy you have and need. Questions like those are why bringing in an outside engineer, while an added expense, is probably a good idea.
The result of not replacing in kind can be significant. Two Shell Plaza in Houston was formerly outfitted with four 500-ton chillers. As a result of an upgrade by Hines, two of those chillers remain, but only in a backup role. The cooling is now provided by a pair of 680-ton chillers with variable frequency drives. That approach not only allows for more efficiency, but also gives more flexibility when it comes to providing cool air during off-peak hours when only a limited number of tenants need it. Changes like that can only come about if a project is properly evaluated beforehand and the building's use is carefully examined.
In some cases it might be preferable to replace with similar units. Kirk Beaudoin, territory facilities manager, North American retail operations, Nike, says that tracking service calls, breakdowns and temperature complaints helps his company identify problems that would prevent the organization from being able to replace old units with similar new units. "Our assumption is that our stores were properly designed when built. So unless we have identified ongoing comfort issues that are related to sizing of equipment, or if there have been any modifications to the store which would require a review of the systems, we generally replace with the same tonnage," he says.
This has been a Building Operating Management Tip of the Day. Thanks for listening.
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