Question 1: There are 5 fields that apply to the amount of outdoor air.
1) Minimum Outdoor Air Flow Rate
2) Maximum Outdoor Air Flow Rate
3) Minimum Outdoor Air Schedule Name
4) Minimum Fraction of Outdoor Air Schedule Name
5) Maximum Fraction of Outdoor Air Schedule Name
Since this is a 100% outdoor air unit, I assume the minimum and maximum outdoor air flow rate fields are set to the same value. Try using the same schedule for 4) and 5) above and see if you get the variation needed. 3) above is used to modify the minimum and maximum outdoor air flow rate input field fraction to dynamically adjust the minimum outdoor air quantity. The reason there is a check for an air loop is because the actual system flow rate may be different than the maximum outdoor air flow rate specified in 2).
The Minimum Outdoor Air Schedule, 3) above, is used to modify the fraction of outdoor air based on the inputs in 1) and 2) as follows:
// set OutAirMinFrac
if ( AirLoopNum > 0 ) {
if ( AirLoopFlow( AirLoopNum ).DesSupply >= SmallAirVolFlow ) {
OutAirMinFrac = MinOAMassFlowRate / AirLoopFlow( AirLoopNum ).DesSupply; (kg/s)
} else {
OutAirMinFrac = 0.0;
}
} else {
if ( OAController( OAControllerNum ).MaxOA >= SmallAirVolFlow ) {
OutAirMinFrac = MinOA / MaxOA; (inputs in m3/s)
} else {
OutAirMinFrac = 0.0;
}
}
if ( OAController( OAControllerNum ).MinOASchPtr > 0 ) {
MinOASchedVal = GetCurrentScheduleValue( OAController( OAControllerNum ).MinOASchPtr );
MinOASchedVal = min( max( MinOASchedVal, 0.0 ), 1.0 );
OutAirMinFrac *= MinOASchedVal;
}
The flow fraction schedules in 4) and 5) are used to limit outdoor air flow rate:
if ( OAController( OAControllerNum ).MinOAflowSchPtr > 0 ) {
MinOAflowfracVal = GetCurrentScheduleValue( OAController( OAControllerNum ).MinOAflowSchPtr );
MinOAflowfracVal = min( max( MinOAflowfracVal, 0.0 ), 1.0 );
if ( MinOAflowfracVal > OutAirMinFrac ) {
OutAirMinFrac = MinOAflowfracVal;
}
OASignal = max( MinOAflowfracVal, OASignal );
}
if ( OAController( OAControllerNum ).MaxOAflowSchPtr > 0 ) {
MaxOAflowfracVal = GetCurrentScheduleValue( OAController( OAControllerNum ).MaxOAflowSchPtr );
MaxOAflowfracVal = min( max( MaxOAflowfracVal, 0.0 ), 1.0 );
if ( MaxOAflowfracVal < OutAirMinFrac ) {
OutAirMinFrac = MaxOAflowfracVal;
}
OASignal = min( MaxOAflowfracVal, OASignal );
Question 2: Regarding MAU, I assume this refers to the ZoneHVAC:OutdoorAirUnit. I would expect this system type to control using the zone outdoor air flow rate specifications.
I've ran into these kinds of issues before. Have you tried specifying the
Outdoor Air Flow Rate Fraction Schedulein theDesign Specification Outdoor Airobj?Maybe it would be better to post two separate questions here.
So using the
Outdoor Air Flow Rate Faction Scheduleand theMaximum Fraction of Outdoor Air ScheduleI can finally get the OA damper to modulate to 50% at night. I am not able to get the fan to turn down to 50% though, the unit just does 50% OA and 50% RA. Any ideas on forcing the fan to turn down? Also, the 50% modulation of the OA damper doesn't work if I put in a lot of OA (say 2 cfm/sf). It seems like there is a point at about 1 cfm/sf where this works, and then if the OA goes above that it stops working. Any ideas on that, it is very weird.