Determine if Unit Heaters are Operating when Temperature is Above Setpoint

Applicable Systems

• Primary: UH

Objective/Method/Outcome

• Objective: Determine if unit heater is running unnecessarily, as room temperature is already above the setpoint

• Method: Examines zone temp, setpoint, and the heating command trend. If the zone temperature is above the setpoint, the unit command trend is examined, and the time the unit is on under such conditions is accumulated.

• Outcome: An insight is generated if the unit is overheating for more than 1 hour per week.

Logic

Normalized (15 min) room temperature and room temp setpoint trends are compared, and if the room temperature is above the deadbanded (1 °C) setpoint, the UH command trend is examined. The number of hours in which the heater is engaged under these conditions is accumulated over a week, and if the weekly total number of hours exceeds the threshold (1), an insight is triggered.

IF(RT > RT_SP + Deadband){
   IF(UH >1){
            Time_out_of_range +1
      }
   IF(Time_out_of_range > 1){
            INSIGHT
      }
}

Description / Method

Monitors room temperature, room temperature setpoint, and Unit Heater fan status. Calculates the amount of time (weekly) when the temperature was above the setpoint, and the fan was running. {UH}

Diagnosis / Recommended Action

1. Review UH sequence of operation.
2. UH Fan might be manually overridden.

Message

Unit Heater (UH) has been running when Room Temperature is above Room Temperature Set Point. Please review UH sequence of operation.

Notes

Generates a CTL named ‘WeeklyHours_RT>SP_FanON’.Notes: This rule template could be used for Forced Flow units as well.Default Values for Constants

• Weekly Threshold: 1
• Deadband: 1

Rule Template Type

• Insight Type: Fault Detection
• Trigger Type: Active High

Default Priority

Low

Inputs

Inputs	Units	Tags	Description
Room Temperature	°C/°F	room|zone,temperature,sensor,air	Room Temperature being Examined
Room Temperature Set Point	°C/°F	room|zone,temperature,sp,air	Setpoint of room in question
Fan Status	0/1	fan,status|cmd	Status of the unit heater

Constants

Inputs	Units	Default Value	Description
Weekly Threshold	hr	1	Number of hours condition can persist in order for insight to trigger
Deadband	°C/°F	1	Amount the room temp is allowed to rise above the setpoint without condition becoming true

Output Calculated Trend Logs

Output CTL	Units	Frequency	Description
WeeklyHours_RT_Greater_Than_SP_FanON	hr	weekly	Weekly number of hours unit is over-heating