By: Scott Lance, EBCP, LEED AP O+M, Engineering Manager
Now that winter is close to an end in the norther region of the United States, it’s time to start thinking about entering back into the cooling season.
Many facilities shut down their cooling operations in the winter; this includes items such as draining down cooling towers and exterior condenser water piping, shutting down chilled water and condenser water pumps for the season, and stopping chemical treatment of these systems. Now is the time to start performing some operational checks before that first warm day in late March or early April happens.
The easiest things to do while chilled water systems are shut down, is to start-up pumps and recirculate water through the entire interior chilled water system. This will break-up any rust scale that might have settled in the system throughout the winter and collect this material in wye strainers and suction screens of pumps. Once the recirculation has taken place, clean out the strainers and screens. During the recirculation operation, check motor voltage and amperage for all three phases of power; this will help determine if the pump motor has any issues. You’ll see it in the amperage readings, or it will determine if there is a phase imbalance issue with the incoming power.
Also, look for leaks while the system is running; when pumps sit for an extended period of time and then start back up it may cause a shaft seal to start to leak. Identifying a leak now and repairing it will be more convenient then when chilled water is actually required to be online and stable.
This is also a great time to do a quick check on calibration of sensors. Since the main cooling source will be offline, the supply and return sensors for primary and secondary circuits should be close in regards to measuring water temperature, if the air handling unit coils are piped three way. If the system is piped two way, remove thermostats from wells and insert an electronic calibrated device to verify temperature. Also, flow meters can be verified using a HDM, pressure gauges at the pump, electrical readings and the pump curves. Certain kinds of flow meters lose calibration when they sit for extended periods of time with no water flow. While the system is shut down, look at pressure gauges and sensors. Inlet and discharge sensors for pumps should read the same value when the pump is offline, if the values are off then there is a gauge issue. Gauges are great for operational checks while a system is running, but if they are not accurate then your check is not legitimate.
Look at your chillers; look for leaks, water and oil. Test the refrigerant purge system, if one is present, while the system is shut down. Remember, lots of these systems use a vacuum pump and have been pulling back dust all winter while the system is down. You’ll more than likely have a refrigerant leak when the chiller comes back online because it has been sitting non-operational for an extended period. This is also the last chance to check tubes for leaks, so verify the refrigerant charge throughout the winter.
Cooling towers have been offline and drained all winter. Just because they are empty doesn’t mean they are good to go. Birds might have made a stop by for a while, dust collects in the basin and media and snow and ice melt might be adding some water to the basin which could have cracked tower media or wreaked havoc on the tower fan motors. Bump start the fans and take electrical readings, check the fan blades are balanced and perform a physical inspection of the entire tower.
The other issue is the condenser water system might have been sitting dry all winter. The inside of piping rust slower when water is present and oxygen is low. But when the water is gone and air is in the piping it will start to scale. Look at the weather forecast and toward the end of the season when it’s still too cold to run but not cold enough to freeze give that system a good flush and clean the strainers afterwards.
One other item that gets overlooked are conductivity sensors; these are designed to always be submersed, detecting water conductivity, they don’t like going dry. Make sure these sensors still read accurately to ensure that system blow downs or chemical additions are properly calculated by the water condition controls system. This will save money on chemicals or when buying municipality water for make-up after a blow down has occurred.
Most of these checks are very simple and will take minimal time when the system is not required to be online full time. Finding issues now will cost less to correct and lessen general aggravation, as opposed to finding them when the cooling season is in full swing.
Questions on how to bring your building back in shape? Contact us at firstname.lastname@example.org.