app_sensor_suitcase

Sensor Suitcase Diagnostic Suite

Introduction

This diagnostic suite includes a variety of analytics:

• Economizer
• Excessive Daylight Lighting
• Excessive Nighttime Lighting
• Setback Points During Unoccupied Hours
• Comfort Optimizations
• Short Cycling
• Too Narrow Room Temperature Setpoint Thresholds

## Pseudo-code: Economizer

This Economizer algorithm checks if the economizer is being used when the roof top unit (RTU) has the potential to be be economizing. Air side economizers take cooler air from outside to cool the air indoors. Optimal usage of the air side economizer is called "free cooling". This happens when the outside air is sufficiently cool and dry enough to be used for indoor cooling, consequently leading to no additional conditioning. In addition to free cooling, there is evidence of indoor air quality improvement by using an economizer.

The economizer should be used when the outside air temperature (OAT) is less than or equal to 65◦F and the diffuser air temperature (DAT) is less than 70 degrees F. The RTU is considered to be ”economizing” if the unit is in ventilation mode and the zone is being cooled– that is DAT is less than 70 degrees F. If it is not being used under these conditions, the building is losing potential "free cooling." Savings due to proper use of economizer operations are about 10%.

Savings are calculated as follows: Percentage of energy due to heating and cooling * 10% * total energy use

Percentage of energy going towards cooling is determined by values in the U.S. Energy Information Administration’s (EIA) Commercial Buildings and Energy Consumption Survey (CBECS).

Program economizer

• Get inputs:

  • DAT, 2-D array with date-time and discharge air temperature data (float)
  • OAT, 2-D array with date-time and outdoor air temperature data (float)
  • HVACstat, 2-D array with date-time and HVAC status data
    • HVAC: 0 - off 1 - fan 2 - compressor
  • ele_cost, electricity cost (float)
  • area, area of the building (float)

• Assume:

  • times, OAT, HVACstat have the same number of data points and date-times must match up

• Iterate through the data points:

  • Get periods when RTU is on:
    • Count when HVAC is not off, DAT < 70, and OAT <= 65 and set to a variable, countOn
  • Get periods when economizer being used:
    • Count when HVAC ventilation is on, DAT < 70, and OAT <= 65, countEconOn

• Check if issue should be flagged:

  • Calculate the percentage of when the economizer is on: countEconOn / countOn
  • If the percentage < 0.7, flag the problem.
    • Problem: "Under use of 'free cooling', i.e., under-economizing."
    • Diagnostic:"More than 30 percent of the time, the economizer is not taking advantage of ’free cooling’ when it is possible to do so."
    • Recommendation: "Ask an HVAC service contractor to check the economizer control sequence, unless the RTU does not have an economizer."

• Savings:

  • Use area to look up percentage due to HVAC according to CBECS.
  • Percent due to HVAC * 0.1 * ele_cost