blockController

Information

Controller for dual-duct terminal unit using mixing control with discharge flow sensor according to Section 5.13 of ASHRAE Guideline 36, May 2020. It outputs discharge airflow setpoint VSet_flow, cold and hot duct dampers position setpoint (yCooDam, yHeaDam), cooling supply temperature setpoint reset request yZonCooTemResReq, heating supply temperature setpoint reset request yZonHeaTemResReq, cold-duct static pressure setpoint reset request yColDucPreResReq, hot-duct static pressure setpoint reset request yHotDucPreResReq, heating fan request yHeaFanReq. It also outputs the alarms about the low airflow yLowFloAla, leaking dampers, and airflow sensor(s) calibration alarm.

The sequence consists of six subsequences.

a. Heating and cooling control loop

The subsequence is implementd according to Section 5.3.4. The measured zone temperature TZon, zone setpoints temperatures THeaSet and TCooSet are inputs to the instance of class Buildings.Controls.OBC.ASHRAE.G36.ThermalZones.ZoneStates to generate the heating and cooling control loop signal.

b. Active airflow setpoint calculation

This sequence sets the active maximum airflow according to Section 5.13.4. Depending on operation modes uOpeMod, it sets the airflow rate limits for cooling and heating supply. See Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctMixConDischargeSensor.Subsequences.ActiveAirFlow.

c. Dampers control

This sequence sets the dampers position setpoints. The implementation is according to Section 5.13.5. The sequence outputs discharge airflow rate setpoint VSet_flow, cold and hot ducts damper position setpoints (yCooDam, yHeaDam). See Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctMixConDischargeSensor.Subsequences.Dampers.

d. System reset requests generation

According to Section 5.13.8, this sequence outputs the system reset requests, i.e. cooling and heating supply air temperature reset requests (yZonCooTemResReq and yZonHeaTemResReq), cold and hot duct static pressure reset requests (yColDucPreResReq and yHotDucPreResReq), and the heating fan requests yHeaFanReq. See Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctMixConDischargeSensor.Subsequences.SystemRequests.

e. Alarms

According to Section 5.13.6, this sequence outputs the alarms of low discharge flow, leaking dampers and airflow sensor calibration alarm. See Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctMixConDischargeSensor.Subsequences.Alarms.

f. Testing and commissioning overrides

According to Section 5.13.7, this sequence allows the override the aiflow and dampers position setpoints. See Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctMixConDischargeSensor.Subsequences.Overrides.

Note that in this implementation, the system request sequence for generating hot-duct pressure reset request needs to know the airflow setpoint. However, the damper control sequence, which is specified in the Section 5.13.5, does not specify the flow setpoint when the zone is in heating state. It directly maps the heating loop output to the heating damper position. To avoid the confusion caused by the wordings in the Section 5.13.5.1.c, the damper control was implemented according to the Figure 5.13.5.

Parameters

Connectors

Components

Revisions

• January 12, 2023, by Jianjun Hu:
  Removed the parameter have_preIndDam to exclude the option of using pressure independant damper.
  This is for issue 3139.
• August 1, 2020, by Jianjun Hu:
  First implementation.