Allowing the building’s HVAC control system to run the chiller plant is usually the best option to ensure that optimum cooling and energy efficiency are achieved. A properly set up HVAC control system should ramp up/down equipment as a building’s loads change and shut off pieces of equipment when they are not required (such as during a building’s unoccupied periods).
But what happens when the building’s control system is not working properly and fails to turn on pieces of equipment that should be running, such as a chiller? In this situation, you will need to run the chiller plant in hand.
When a chiller plant shuts down due to the failure of one or more things, sometimes the best option to quickly restore cooling to a building is to run the chiller plant in manually. Running a chiller plant manually, or running a chiller plant in “hand” is sometimes required when the building’s control system fails to work properly, or one or more pieces of mechanical equipment fail altogether.
There are many different types of chilled water systems that all have their own intricacies, however, there are a few main steps to take in order to get most chiller plants running in hand.
These steps will not always work, especially if there are one or more mechanical equipment failures.
Step 1: Assess the Situation
Before trying to get the chiller plant running in hand, it can be helpful to look at all pieces of equipment in the chiller plant to check for alarms. If there are alarms on the equipment, what kind of alarms are they? This is important because you will probably need to make adjustments moving forward in how the chiller plant is operated.
Sometimes clearing alarms will allow the building’s control system to take control again, and running the chiller plant in hand will not even be required.
Make a note of which chiller(s) you are going to run in hand. This will be important moving forward because some chillers require specific pieces of equipment to be running before the chiller is started in hand.
If the chiller is water-cooled, make a note of which cooling tower(s) you are going to run.
Step 2: Adjust Valves
In order for a chilled water system to work, there needs to be a load on the building’s space. Ensure that at least a minimum amount of units that demand chilled water are running and have their chilled water valves open – such as air handling units and fan coil units.
In addition, ensure that all isolation valves are open for the pieces of chiller plant equipment that you are going to run. Open the isolation valves for the chiller, chilled water pump(s), etc.
If the chiller is a water-cooled chiller, ensure that the chiller condenser water isolation valves are open, cooling tower isolation valves as well as isolation valves for condenser water pump(s).
Also, remember to check for isolation valves controlled by the building’s control system. These valves sometimes require the power to be disconnected from them in order to be opened manually.
Some chilled water systems have one or more bypass valves that are controlled by the building’s control system. These may require adjustment as well.
This step may not be required if isolation valves are already open or do not exist.
Step 3: Start Pump(s)
The next step is to get water flowing through the building. Chillers will not run if they do not have flow. Start the chilled water pump(s) and ensure that they are running at a proper speed (if they are speed controlled).
Some chilled water systems have different types of pumps (such as primary and secondary). If this is the case, ensure to start only the pumps that are necessary.
If the chiller is a water-cooled chiller, remember to start the condenser water pump(s) as well. This step may not be required if the chiller internally controls the chilled water pump(s).
Step 4: Start Cooling Tower(s)
This step is only required if the chiller(s) are water-cooled.
Start the cooling tower fan(s) and ensure that they are running at a proper speed (if they are speed controlled). Some cooling towers have spray pumps, these may need to be started as well.
Step 5: Start Chiller
Now that all the other required chiller plant equipment is running, the last step is to start the chiller in hand. Start the chiller and wait for it to run. This may take up to a few minutes, depending on the chiller.
If the chiller runs, keep close observation on all chiller plant equipment and how they behave while running. Listen for any unfamiliar or obnoxious sounds such as grinding or banging. This may be an indication of mechanical equipment that is having problems and should be investigated further, and not ran at all.
Sometimes a chiller will run for a few minutes and then shut down due to an alarm. If this happens, investigate the alarm and figure out if you are able to run any other pieces of equipment differently to get the chiller to run properly. Depending on the alarm, the chiller could have a mechanical or internal control system problem that does not allow the chiller to run altogether.
If the chiller doesn’t run at all, go back to step 1, and choose a different chiller to run (if available).