Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.SingleZone.SetPoints

Output setpoints for AHU control

Information

This package contains sequences generating setpoints for single zone VAV AHU control.

Package Content

Name	Description
ExhaustDamper	Control of actuated exhaust dampers without fans
OutsideAirFlow	Output the minimum outdoor airflow rate setpoint for systems with a single zone
VAVSupply	Supply air set point for single zone VAV system
Validation	Collection of validation models

Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.SingleZone.SetPoints.ExhaustDamper

Control of actuated exhaust dampers without fans

Information

Control sequence for exhaust dampers without fans. It is implemented according to ASHRAE Guidline 35 (G36), PART5.N.8.(for multi zone VAV AHU), PART5.P.6 and PART3.2B.3 (for single zone VAV AHU).

Single zone VAV AHU: Control of actuated exhaust dampers without fans (PART5.P.6)

1. Exhaust damper position setpoints (PART3.2B.3)
   • minExhDamPos is the exhaust damper position that maintains a building pressure of 12 Pa (0.05 inchWC) while the system is at minOutPosMin (i.e., the economizer damper is positioned to provide minimum outdoor air while the supply fan is at minimum speed).
   • maxExhDamPos is the exhaust damper position that maintains a building pressure of 12 Pa (0.05 inchWC) while the economizer damper is fully open and the fan speed is at cooling maximum.
2. The exhaust damper is enabled when the associated supply fan is proven on and any outdoor air damper is open uOutDamPos > 0 and disabled and closed otherwise.
3. The exhaust damper position is reset linearly from minExhDamPos to maxExhDamPos as the commanded economizer damper position goes from minOutPosMin to outDamPhyPosMax.

The control sequence is as follows:

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.SingleZone.SetPoints.OutsideAirFlow

Output the minimum outdoor airflow rate setpoint for systems with a single zone

Information

This atomic sequence sets the minimum outdoor airflow setpoint for compliance with the ventilation rate procedure of ASHRAE 62.1-2013. The implementation is according to ASHRAE Guidline 36 (G36), PART5.P.4.b, PART5.B.2.b, PART3.1-D.2.a.

Step 1: Minimum breathing zone outdoor airflow required breZon

• The area component of the breathing zone outdoor airflow: breZonAre = AFlo*outAirPerAre.
• The population component of the breathing zone outdoor airflow: breZonPop = occCou*outAirPerPer.

The number of occupant occCou could be retrieved directly from occupancy sensor nOcc if the sensor exists (have_occSen=true), or using the default occupant density occDen to find it AFlo*occDen. The occupant density can be found from Table 6.2.2.1 in ASHRAE Standard 62.1-2013.

Step 2: Zone air-distribution effectiveness zonDisEff

Table 6.2.2.2 in ASHRAE 62.1-2013 lists some typical values for setting the effectiveness. Depending on difference between zone space temperature TZon and supply air temperature TDis, Warm-air effectiveness zonDisEffHea or Cool-air effectiveness zonDisEffCoo should be applied.

Step 3: Minimum required zone outdoor airflow zonOutAirRate

For each zone in any mode other than occupied mode and for zones that have window switches and the window is open, zonOutAirRate shall be zero. Otherwise, the required zone outdoor airflow zonOutAirRate shall be calculated as follows:

• If discharge air temperature at the terminal unit is less than or equal to zone space temperature: zonOutAirRate = (breZonAre+breZonPop)/disEffCoo.
• If discharge air temperature at the terminal unit is greater than zone space temperature: zonOutAirRate = (breZonAre+breZonPop)/disEffHea

• If discharge air temperature at the terminal unit is less than or equal to zone space temperature: zonOutAirRate = breZonAre/disEffCoo
• If discharge air temperature at the terminal unit is greater than zone space temperature: zonOutAirRate = breZonAre/disEffHea

For the single zone system, the required minimum outdoor airflow setpoint VOutMinSet_flow equals to the zonOutAirRate.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.SingleZone.SetPoints.VAVSupply

Supply air set point for single zone VAV system

Information

Block that outputs the set points for the supply air temperature for cooling, heating and economizer control, and the fan speed for a single zone VAV system.

For the temperature set points, the parameters are the maximum supply air temperature TMax, and the minimum supply air temperature for cooling TMin. The deadband temperature is equal to the average set point for the zone temperature for heating and cooling, as obtained from the input TSetZon, constraint to be within 21°C (≈70 F) and 24°C (≈75 F). The setpoints are computed as shown in the figure below. Note that the setpoint for the supply air temperature for heating and for economizer control is the same, and this setpoint is lower than TMin when the heating loop signal is zero and the economizer is in cooling mode, as shown in the figure.

For the fan speed set point, the parameters are the maximu fan speed at heating yHeaMax, the minimum fan speed yMin and the maximum fan speed for cooling yCooMax. For a cooling control signal of uCoo > 0.25, the speed is faster increased the larger the difference is between the zone temperature minus outdoor temperature TZon-TOut. The figure below shows the sequence.

The output TCoo is to be used to control the cooling coil, and the output THeaEco is to be used to control the heating coil and the economizer dampers.

Note that the inputs uHea and uCoo must be computed based on the same temperature sensors and control loops.

Parameters

Connectors

Modelica definition