AHU lacks Demand Control Ventilation

Objective/ Method/Outcome

Objective: Determines if AHU’s demand control ventilation is operational.

Method: Using the Return Air CO2 level to setpoint to determine if the supply of outdoor air is sufficient

Outcome: This rule generates an insight.

Description

Reference:ASHRAE36-5.16.3.1/ASHRAE 90.1-6.4.3.8

This rule determines if the outdoor airflow is responsible to the return air CO2 level. Oversupply of outdoor air causes unnecessary energy waste(mechanical cooling or heating mode) and short supply of outdoor air causes IAQ(Indoor air quality) issue. Demand Control Ventilation(DCV) is a ventilation system that provides for the automatic reduction of outdoor air intake below design rates when the actual occupancy of spaces served by the system is less than design occupancy.

This rule is not applicable for economizer mode.

This rule is part of the CopperTree Standard rule-set.

Default Priority

Medium

Diagnosis

  1. Check if outdoor air damper is stuck, manually overridden
  2. Check if AHU is in economizer mode
  3. Implement demand control ventilation (DCV)

Message

AHU is lack of Demand Control Ventilation. Outdoor airflow is too high in mechanical cooling or heating mode.

Rule Template

Insight Type: Energy

Trigger Type: Active High

Notes

1. Expected values for “Fan Status” inputs are “0” or “1”.

2. Expected values for “Fan Speed” inputs are “100” if they are constant speed fans or not available.

Default Values:

Const. – Return Air CO2 Limit [ppm]: 1000

Const. – AHU Rated CFM [cfm]: 10000

Const. – Threshold for Faulty Daily Hours [hrs]: 2

Const. – Energy Rate [$/kWh]: 0.1

Const. – Natural Gas Rate [$/mmBTU]: 3

Const. – Weeks of Operation [weeks]: 52