The purpose of this guide is to help understand modeling strategies on some common system types. Since similarly named sensor types can exist both within a system and the equipment within that system, it is helpful to distinguish the differences in the application of each. For each system type, we will define the system sensors as well as the equipment for that system. We will further break down the sensors for each equipment and how they may differ from the system sensors if similarly named. For more details on individual sensor types, see the Sensor Type Guide.
Chilled Water System
Chilled water systems typically link together all the pumps, chillers, and associated sensors in the loop dedicated to delivering chilled water throughout a building. Note this is discrete from a Condenser Water System which will be covered later in this guide.
System Sensors
Supply - The supply sensor types will be used to denote a sensor that is independent of any individual equipment like a chiller, but rather the supply portion of the loop as a whole. Supply water is used only in the absence of primary and secondary chilled water loops.
Supply Water
Supply Valve
Return - The return sensor types will be used to denote a sensor that is independent of any individual equipment like a chiller, but rather the return portion of the loop as a whole. Return water is used only in the absence of primary and secondary chilled water loops.
Return Water
Primary/Secondary - Primary and Secondary distinction can be added to both supply and return in the presence of a secondary loop and clarifies that this is the supply of the primary loop. These are often used in applications where a primary loop can maintain a constant pump speed and the secondary loop modulates speed to control flow.
Primary Supply Water
Primary Supply Valve
Primary Return Water
Secondary Supply Water
Secondary Supply Valve
Secondary Return Water
Chiller
Supply - The supply of the chiller is the water that is being supplied out to the loop. This can be discrete from the system supply which is the combination of the supplies from all chillers in the loop.
Supply Water
Return - The return of the chiller is the water that is being returned to an individual chiller from the loop. This can be discrete from the system return, though it often has very similar readings.
Return Water
Diagram
Below is a visual guide on where sensor placement would be in the loop and how they would be assigned to equipment or the system as a whole. System sensors are highlighted blue, and equipment sensors highlighted green.
VAV System
A VAV System links together the AHU and VAVs that work together to control temperature within associated spaces.
System Sensors
Generally, there are few true dedicated "system sensors" and most of the sensors are simply sourced from the AHU or VAVs associated. One caveat to how the sensors are set up is the relationship between "Supply Air" from the AHU and the "Source Air" to the VAV. These are effectively the same data point, and are typically modeled at the AHU. Relationship to the VAV can then be utilized as part of the system.
Equipment Sensors
Supply - The supply of the AHU is the air that is being delivered to a served space. In many applications, this may also be referred to as "Discharge".
Supply Air
Supply Fan
Return - The return of the AHU is the air that is being brought back to the unit from the served space.
Return Air
Return Fan
Exhaust - The exhaust of the AHU is the air that is being exhausted outside from within the served space to depressurize or allow for fresh air intake.
Exhaust Air
Exhaust Fan
Exhaust Damper
Makeup - The makeup of the AHU is the outside air inlet source to add fresh air, make up for the air lost through exhaust, or to repressurize the space.
Makeup Air
Makeup Damper
Makeup Fan
VAV
Supply - The supply of the VAV is the air that is being delivered to a served space. In many applications, this may also be referred to as "Discharge".
Supply Air
Supply Fan