[EnergyPlus_Support] Autosizing air and water circuits for zone heating

["Elmer Morrissey" <elmofuddly@xxxxxxxxx>]

Hello all,

I have another autoszing problem. I have 3 zones that are fed with 
heated auxiliary air at 20C supply air. Any additional heat required 
to maintain zone temps should be picked up by convector units. 

ZONE EQUIPMENT LIST,
    Equip:1,                 !- Name
    DIRECT AIR,              !- KEY--Zone Equipment Type 1
    RB:1,                    !- Type Name 1
    1,                       !- Cooling Priority 1
    1,                       !- Heating Priority 1
    BASEBOARD HEATER:WATER:CONVECTIVE,  !- KEY--Zone Equipment Type 2
    HB:1,                    !- Type Name 2
    2,                       !- Cooling Priority 2
    2;                       !- Heating Priority 2

A boiler system supplies hot water to the heating coil in the AHU 
and to the convector units.

(from my interpretation of the EIO file?)
If I fully autosize the system, E+ thinks that it should force: 
Calculated heating design air flow rate [m3/s],   4762.2. 

However, the actual flow rate is constrained by my input in the 
Direct Air objects to no greater than 0.2 m3/s. E+ seems to be think 
the AHU needs to supply all the hot air in the zone. This forces 
mass oversizing of the flowrate in the boiler circuit.

Therefore, I tried to force E+ strain of thought by using this?

SYSTEM SIZING,
    A1:Loop,                 !- name of an AIR PRIMARY LOOP object
    sensible,                !- type of load to size on
    0.05144145,              !- Design (minimum) outside air 
volumetric flow rate {m3/s}
    1,                       !- minimum system air flow ratio
    5,                       !- Preheat design set temperature {C}
    12,                      !- Central cooling design supply air 
temperature {C}
    20,                      !- Central heating design supply air 
temperature {C}
    noncoincident,           !- Sizing Option
    Yes,                     !- Cooling 100% Outside Air
    Yes,                     !- Heating 100% Outside Air
    ,                        !- Central cooling design supply air 
humidity ratio {kg-H2O/kg-air}
    ,                        !- Central heating design supply air 
humidity ratio {kg-H2O/kg-air}
    Design day,              !- cooling design air flow method
    ,                        !- cooling design air flow rate {m3/s}
    flow/system,             !- heating design air flow method
    0.05144145;              !- heating design air flow rate {m3/s}

This corrects the boiler flowrates sizing problems however it means 
that the convector units never turns on. 

Can anyone shed any light on how I might fix things? (or I do I need 
to post some additional information)

Kind regards

-Elmer 







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