Tracking Room Air Temperature Setpoint: The Clockworks Approach
April 4, 2021
by Jaime Gagne
One question that comes up very often is:
Can you describe how the Clockworks approach to fault detection and diagnostics (FDD) is different from other vendors?
This is best explained with an example. Let’s look at the most commonly flagged diagnostic in our system (aside from sensor errors): Room Air Temperature Setpoint Tracking.
A typical FDD “rule” for this diagnostic will usually require 3 points:
The “diagnostic” is simple: identify if the room air temperature is significantly off setpoint during occupied hours.
But when this simple concepts meets real world HVAC systems, we quickly realize that it’s not so simple. Take a few examples:
- If a zone has RoomAirHeatingTempSetpt and RoomAirCoolingTempSetpt instead of a double-sided setpoint, most vendors would require a new rule to be applied.
- If UnoccupiedSetpts are available, yet another rule would be necessary.
- If Occupancy was available as a numerical Mode instead of a boolean, a different rule would apply.
Depending on the vendor’s system, the various sets of rules may need to be created separately per equipment type, which means they would need to be defined separately for a VAV vs a FCU vs a zone with a chilled beam, etc. Some vendors even require the rules to be written by equipment types which have been distinguished by configuration.
For example, a VAV with reheat would have different rules than a VAV without.
In contrast, the Clockworks diagnostic library has a single diagnostic check that can apply to ANY combination of point types, variables, and equipment types. Our diagnostic is also incredibly complex in order to handle the many different controls scenarios that we have seen implemented in real-life BASs.
As you can see below, our “single” Room Air Temperature Setpoint Tracking diagnostic can actually handle a huge number of variations in terms of equipment types and controls strategies. Instead of hundreds of rules necessary for the logic above, we have folded it all into a single diagnostic that is applied across all relevant equipment automatically.
Scenarios that our diagnostic will interpret based on point types alone:
- Single double-sided setpoint tracking, during occupied periods
- Single double-sided setpoint tracking, during occupied and unoccupied periods, based on existence of an unoccupied setpoint
- Heating and/or cooling setpoints, during occupied periods
- Heating and/or cooling setpoints, during occupied and unoccupied periods, based on EITHER an inferred setback on individual setpoints or existence of unoccupied setpoints
- Single double-sided setpoint tracking during occupied periods and heating and/or cooling setpoints during unoccupied periods
- Heating and/or cooling setpoints during occupied periods and single double-sided setpoint tracking tracking unoccupied period (an unlikely scenario, but we would accommodate it)
- A single double-sided setpoint that can turn into a heating or a cooling setpoint based on heating and cooling tracking mode points
- Any of the above scenarios only tracked during certain times using the TempTrackingStatus point
Additional scenarios that we can accommodate by adding equipment variables:
➡️ Adjusting whether unoccupied tracking should occur (can turn it “on” or “off”)
➡️ Changing a single setpoint into heating or cooling setpoint based on heating or cooling plant enables
➡️ Custom tracking using a custom tracking equation
Equipment or building variables” within Clockworks give you the ability to configure inputs to diagnostic algorithms that model expected equipment and system performance.
Point types that will automatically be used in the diagnostic:
- RoomAirTemp – Required
- Room Air Temp Setpt(s) – At least one required, all values are also available as equipment variables
- Occupancy – Optional but preferred, may be given using building/equipment variables
- AHU Status – Optional, will be used if zone is served by an AHU and occupancy info is missing
- Supply Fan points – Status, Run, Amps, Power, Speed (many point types), Mode, Static Pressure
- Supply Air Static Pressure or Flow
- AHUStatus or Inhibit
- Modes – Optional
- TempTrackingStatus – Optional
Point types and equipment variables that will adjust the logic:
- Changing a single setpoint into heating or cooling setpoint based on heating or cooling plant enables
- ZoneConditioningRequiresPlantEnable variable (set to 1)
- Cooling and Heating Plant Enables—looks at both point types (i.e. Outdoor Air Temp) and variables (i.e. CoolingEnableOAT)
Diagnostics and Equipment Types that this check is applied to:
- Zone diagnostic – for any type of zone unit or single room air conditions
- AHU Coil diagnostic – for any type of supply air AHU serving a single zone, or an AHU with multiple supply ducts each serving a single zone (will be performed once per duct/zone)
- Open Floor Plan Zone Group – for common room air conditions in an open floor plan zone group served by multiple zone units
- Room air temp higher than setpoint
- Room air temp lower than setpoint
- Room air temp both higher and lower than setpoint
- Room air temp higher than setpoint while heating is on
- Room air temp higher than setpoint while cooling is on
- Room air temp lower than setpoint while cooling is on
- Room air temp lower than setpoint while heating is on
Possible Cause Considerations:
When determining the list of possible causes for room air temperature deviating from setpoint, the following information and related diagnostic findings are also taken into account:
- Zone unit can heat
- Zone unit can cool
- Zone is served by an AHU
- Zone unit was heating while fault was occurring
- Zone unit was cooling while fault was occurring
- Zone unit has leaking heating or re-heating coil valve
- Zone unit has leaking cooling or re-cooling coil valve
- Zone unit has stuck heating or re-heating coil valve
- Zone unit has stuck cooling or re-cooling coil valve
- AHU serving the zone has supply air temperature above setpoint
- AHU serving the zone has supply air temperature below setpoint
What the Clockworks method does—by being able to process point types, variables, and equipment types in an interconnected way—is avoid false alarms and broken rules, reduce the amount of heavy lifting required to get started, and provide a holistic view across all your buildings and equipment. Because our system understands how one fault might influence another fault, or how one piece of equipment is related to another, we are able to provide true diagnostics information that goes beyond simple fault detection.
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