¿Some of the most common problems we find in the larger systems are related to controls,¿ Hollembeak stated. Controls, he said, can be broken down into:
- The building management system or building controls;
- Cooling tower controls; and
- Chiller controls themselves.
¿Probably the biggest problem we find is matching the controls to system requirements and making everything work together without fighting each other,¿ he noted. Other problems are related to load and to the unit components. But controls typically are the biggest issue.
Chillers aren¿t always tied into building management systems, but building controls often control the air handlers, pumps, primary and secondary loops, and the towers, and ¿if they are not set up to operate within the normal design parameters of the chiller, it can give you a nightmare.¿
With cooling towers, excessive staging can be a problem. Typically, if you¿re operating in mild ambient temperatures, three-way bypass valves are recommended. ¿And they¿re not as frequently used as they should be,¿ commented Hollembeak. Tower problems can cause everything from loss of refrigerant management to complete oil loss on some systems.
¿The tower should be matched to the system,¿ he stated, ¿and the system should have controls to prevent inverted starts.¿ A common scenario, he continued, is where you might be starting up with a hot building with a chilled-water loop at 70°, 80°, or 90°F and you¿ve got a tower basin with 45° to 60° water.
¿Inverted starts are typically a problem on systems where they don¿t have proper controls.¿
Check connections
Regarding electrical problems, the more common are electrical connections and power supply feed.Every manufacturer recommends checking all electrical connections, Hollembeak noted. When copper wires are tightened, there¿s always some relaxation of the torque that can cause them to loosen. Components should also be inspected for arcing or burned contacts.
As for refrigerant leaks, it is definitely easier to pinpoint leaks on positive-pressure systems than on negative-pressure systems, Hollembeak said. ¿But if you use good test equipment and procedures, it¿s usually not a problem finding leaks.¿ You should check all mechanical joints for leaks, and also shaft seals.
When you have dirty filters in chilled-water systems, you aren¿t going to transfer heat as well and you¿re not going to maintain comfort as well as you should. Dirty coils, he added, can also prevent you from reaching design conditions.
Proper water treatment and blowdown are critical with a cooling tower system. Blowdown minimizes solids and water treatment keeps the solids in suspension, prevents scale, and prevents organic growth. If the water isn¿t being treated properly, he said, you¿ll see the effects in the cooling tower first.
You can automatically add chemicals, but you still need to monitor the system regularly and adjust it as needed. ¿Depending on the ambient conditions and the load conditions, requirements vary at different times of the year, so the system would have to be adjusted based on the actual operating conditions.¿
Since most chillers today have microprocessor controls, Hollembeak said the first thing he would look at in troubleshooting a system is the controls status. ¿Is the machine on standby? Is it waiting for load? Is it waiting for interlock? Is it off on a safety or alarm?¿
If it is off on a safety, why did it trip on that safety? ¿You wouldn¿t just reset the button and restart the chiller without trying to investigate what caused the failure.¿
Look at the history
Most microprocessors will have an alarm history that will tell you the conditions at the time of shutdown. That can be a valuable tool in determining what may have led to the problem, noted Hollembeak.¿You have to look at the complete system to determine what the problems are. It¿s not just the chiller itself; it can be a system problem.¿
Probably one of the best tools for troubleshooting that¿s often neglected, he said, is the log sheet. People just don¿t bother to use it.
Hollembeak also remarked that stopping and starting puts a lot of stress on a motor. On systems that have stepped capacity, if the system is not set up properly, you can see a lot more stops and starts and consequently more motor problems.
As far as more unusual problems, he related, ¿You see everything from drink cans to plastic bags in the heads of the chiller and condenser.
¿One thing that more frequently happens, especially with some of the larger systems, is that they seem to generate oil. You¿ll find evaporators that are flooded with oil and nobody ever put the oil in there.¿
They¿ll remove as much as 30 gal of oil, but no one added that oil. So the system somehow must be producing it. (Take note, oil companies.)
In closing, the best troubleshooting tips Hollembeak said he can give are to have a good log sheet, know the design conditions of the system, and know the basics well.
Hollembeak can be reached at 540-248-0711, ext. 204.
