Re: [EnergyPlus_Support] Re: Why Autosize does not consider System Outdoor Air Loads

["Jean Marais jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

You are correct. And have brought up an interesting suggestion. I would add this at the helpdesk, however. The forum is more for users.

Sizing uses the idealHVAC szenario, so the zone loads (excluding the energy input from the system) is calculated, and from that the system air flows at specified temperature are deduced (i.e. what air flow is required to meet the load). If the sizing (idealHVAC) supply temperature is such as to add to the load, instead of subtracting from it, rubbish comes out of the simulation. As a work around for you, you could use a ZoneVentilation:DesignFlowRate object where you specify the availability as on only for designdays.

PS don't expect too fast an implementation...the e+ team are transitioning from FORTRAN to C++, so they have this priority to meet before continueing developement of the software. v8.1 is going to be around longer than most versions.

2014-07-02 14:17 GMT+02:00 ecoeficiente@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

 

As far as I know:

Zone:sizing: sizes zone equipment to fight zone thermal load. That thermal load does not include outside air if it is provided by a system. So if you have a system for mechanical ventilation and fancoils in the zone, the fancoils' coils autosized capacity is not enough to counteract thermal losses + outside aire provided by the system.

I know you can autosize your system for ventilation requirement or for zone load + ventilation. That impacts on the capacity of the coils, fans, etc. But for zone equipment, sizing:zone mechanism does not add system load. It works as if air provided by the system is always neutral (preconditioned to zone conditions).

As you say, the load is always calculated for the DesignDay but it does not include outdoor air load provided by a system (only infiltrations or natural ventilation).

Regards.

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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>

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