What is a Rule?
This guide provides information about how analytic rules in the Resolute software work in identifying equipment performance issues and provides operational parameters for each rule currently available through the Resolute platform.
What is a Rule?
A Rule is a function that takes time-series data from at least one input point to determine if a fault condition exists. A Rule is always attached to a particular piece of equipment but can accept inputs from other portions of the building hierarchy when determining if a fault condition exists. For example, a Rule attached to an AHU may use input points from VAVs that are serviced by the AHU to determine whether a given fault condition exists. Another Rule attached to the same AHU may use a scheduled occupancy point defined as a child of the building that the AHU resides in.
Rules are designed to be applied to a particular type of equipment. Certain Rules also require specific tags associated with the piece of equipment. If the equipment is the correct type but missing the required tags, the Rule cannot be applied. Such requirements for additional equipment tags are referred to as Equipment Tag Constraints.
What are the Inputs to a Rule?
While each rule is defined to accept a different set of inputs, all inputs to rules fall into two broad categories:
- Time series data in the form of input points.
- Configurable constants
What are Standard Input Points?
Every Rule requires at least one Input Point. An Input Point uses a Resolute connector (Such as Niagara) to retrieve time series data at regular intervals. A standard Input Point can also be a Computed Point. Some Rules also use Input Points with values that are generated by defining a schedule within the Resolute application.
When a Rule is applied to a given piece of equipment, the Input Points for that Rule are selected based on the following criteria:
- The tags associated with a given point. For instance, a Rule used to detect whether a Zone Temperature Sensor failure has occurred will require an Input Point with the ZoneTemp point template assigned to it.
- The position of the point in the building hierarchy relative to the piece of equipment that the Rule is attached to. Most Rules stipulate that an Input Point must be a child of the equipment the Rule has applied to. In the case of a Zone Temperature Sensor Failure Rule, we would look for a point with the ZoneTemp point template assigned to it, but not just any point with the ZoneTemp point template—the point in question must also be a child of the VAV unit that the Rule is attached to. Note that some Rules have more complex positional requirements for their input points. A Rule applied to an AHU may require input points from the VAVs that it serves. In this case, the input points are not children of the AHU itself but are instead children of the VAVs that are attached to the AHU through an equipment relationship hierarchy.
What is Input Point Multiplicity? Scalar Versus Vector
A Scalar Input Point is defined that there is only a single match that can exist. A Vector Input Point can have more than one match and all matches are used to calculate the output point.
Most Rules are defined in such a way that only a single match can exist for a given input point. For instance, if a Rule expects that a VAV will have a single child point with the “ZoneTemp” point template applied to it, and if more than one “ZoneTemp” point is found for a given VAV, then the Rule cannot be applied to the VAV in question. This is because the Rule was expecting a single “ZoneTemp” input point, and it does not know what to do with multiple “ZoneTemp” points.
What are Configurable Constants?
When a Rule is attached to a piece of equipment it uses one or more constants to customize the behavior of the Rule. An occurrence when two constants would be used to customize a Rule would be when a Rule is used to detect Zone Temperature Sensor failures. One constant would be used to represent the high-temperature threshold and another constant used to represent the low-temperature threshold. The sensor would be in fault if the temperature went out of the range of these two constants. A default value is automatically assigned but can be overridden by the user to customize the behavior of the Rule for that equipment.
What are Mandatory Versus Optional Input Points?
For Rules to be attached to a given piece of equipment, it must have at least one input point defined as Mandatory. For example, if a Rule is attempting to attach to a particular VAV and the Rule requires the VAV to have a child point with a ZoneTemp point applied to it, then that point must be tagged before the Rule can apply to that VAV.
Optional Input Points are typically used to refine the accuracy of the fault detection algorithm. The Rule is still able to attach to the equipment if the criteria for these points are not met.
Certain Rules will have more complex requirements around the presence or absence of different input points. For example, a Rule might stipulate that it requires either an ‘EffCoolSp’ point or an ‘EffHeatSp’ point. Taken by themselves each of these points are optional, but the Rule cannot be applied unless at least one of these input points is present. These requirements are known as Tuple Constraints and define the presence or absence of more than one Input Point.