Resolved. I removed the Unit Type input field from OS:ScheduleTypeLimits object when creating the schedules for People, Lights and ElectricEquipment objects.

Why not we use key input value of Fraction for this input field when creating lighting, people, and electric equipment schedules? I was expecting the Dimensionless key input value to work with this objects but it did not. This schedule values are dimensionless multipliers of the peak value. Just a thought!

I don't think "Unit Type" is at fault here for Number of People Schedule, as long as you use either empty, dimensionless, availability or controlmode, you're fine.

Since this can be confusing to track down for anyone who's first digging in the source code, these kind of rules are defined in ScheduleTypeRegistry.cpp. Here's an extract circa L273:

// className, scheduleDisplayName, scheduleRelationshipName, isContinuous, unitType, lowerLimitValue, upperLimitValue;
{"People","Number of People","numberofPeopleSchedule",true,"",0.0,1.0},
{"People","Activity Level","activityLevelSchedule",true,"ActivityLevel",0.0,OptionalDouble()},
{"People","Work Efficiency","workEfficiencySchedule",true,"",0.0,1.0},
{"People","Clothing Insulation","clothingInsulationSchedule",true,"ClothingInsulation",0.0,OptionalDouble()},

So here, you might get that you need a number of people schedule that is Continuous, no Unit Type, and between 0 and 1. Not that simple!

Then it gets a bit trickier, and I'll give you the semi-short story. ScheduleTypeRegistry > isCompatible will:

• Ignore the Numeric Type (Discrete or Continuous)
• Check the unit type which in turns calls ScheduleTypeLimits::units, esp L310, which is where you'll see that here really since the ScheduleTypeRegistry is expecting empty for unit type, you could use Dimensionless, availability or controlmode as well. If you use say "Temperature", it won't work.
• Check the lower and upper limit values, that must be included in the [0;1] interval ([0.3;0.7] will work). They MUST be set!

Here's some code to play with and to demonstrate what I'm saying:

# Initialize an empty model with a people object
model = OpenStudio::Model::Model.new
people_def = OpenStudio::Model::PeopleDefinition.new(model)
people = OpenStudio::Model::People.new(people_def)

# Create a sch type limits
sch_limit = OpenStudio::Model::ScheduleTypeLimits.new(model)

# THE LIMITS MUST BE SET.
# Above 0.0 included
sch_limit.setLowerLimitValue(0.3)
# Less than 1.0 included
sch_limit.setUpperLimitValue(0.9)

# Whether you include the following two statements or not, it doesn't care
# If you put "Temperature", it'll fail
sch_limit.setUnitType("Dimensionless") 
# It should be Continuous but it is ignored...
sch_limit.setNumericType("Discrete") 

# Create a schedule and set the schedule type limit
sch = OpenStudio::Model::ScheduleRuleset.new(model)
sch.setScheduleTypeLimits(sch_limit)

# Assign the schedule, and check what the result is:
people.setNumberofPeopleSchedule(sch)

=> true