System autosizing shows zero room load
when autosizing an ApacheHVAC network the room loads show zero load for heating or cooling so sizing is not adequate for system setpoints
When autosizing an ApacheHVAC system via the HVAC toolbar or VE Navigator the first step required is to run the room loads calculation, this runs for the room design day a heating loads and cooling loads calculation to produce the demands for each room that are then written back to the HVAC system parameters and appear on the Room Loads and Supply Airflows tab to update coil sizes and feed into the system sizing calculations.
If the loads for heating or cooling unexpectedly show zero sensible load then this is likely because the room has not exceeded the setpoint threshold that is applied in the space data. The room can be interrogated in VistaPro using the heating or cooling setpoint and looking at the relevant results file (.htg or .clg) to understand why the heat balance did not result in a demand on the system. The gains and loads can then be checked against the space thermal template data for the relevant model (i.e. in apache view for design, 90.1 PRM view for Proposed or baseline, NECB view for Proposed or Reference etc) i case there is a problem with the settings.
If the template data is correct then have a look at the room loads calculations settings in the ASHRAE or CIBSE Loads dialog to check if gains were saturated, included in the heating loads calculation, schedules used in the calculation, time used for the heating loads calculation design day.
For ApacheHVAC method it is common to use a two value schedule with system hours setpoint and then a setback for out of hours. Check the heating or cooling setpoint variable (note for ApacheHVAC linked system sizing or simulation runs then it will be the HVAC zone heating setpoint and HVAC zone cooling setpoint variables you have to check, only room loads uses heating setpoint and cooling setpoint variables as described here), if the setback value has been applied then this may be the reason. You can check on ApacheHVAC system parameters to ensure the relevant schedule has the correct active hours set, in particular pay attention to the room design days schedule to ensure it has active hours which are applied at the time of the heating and cooling loads calculation as this determines whether the system is active or in setback.
