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Re: [EnergyPlus_Support] Warnings in the HVAC simulation
Sizing:Plant with "Ventilation Rate" vs "Sensible"
EnergyPlus by default will try to heat and cool all loads including zone loads with air equipment. The zone sizing also happens with an ideal load hvac which is air based. You tell it a air delivery temperature(s), it looks what the zone load is and calculates the air flowrate required to match the load (at the delivery temperature that you specified). This rate (once for cooling design and once for heating design) get passed to the sizing:plant object from all zones' sizing:zone objects.
If you're in Europe, and you want to deliver air at within 2 - 5 K of room setpoint temperature. Obviously, if you were going to try and heat and cool only with air at such a small dT, the airflow rates required will be huge! Mostly, the idea is to then do the zone cooling or heating with zone equipment, whilst the air only brings in fresh outdoor air minimums.
Therefore, to stop the Sizing:Plant object sizing all the central and terminal equipment on HUGE airflow rates, you tell it to ignore the required flow rate needed to meet the the zone loads, and only use the ventilation outdoor air requirements.
Mit freundlichen Grü�en- Sent from my iPhone (excuse the brevity)
i. A.
Jean Marais
b.i.g. bechtold
Tel. Â <tel:%2B49%2030%206706662-23>+49 30 6706662-23
On 15.05.2014, at 15:53, "<mailto:luca.guj@xxxxxxxxx>luca.guj@xxxxxxxxx [EnergyPlus_Support]" <<mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx>EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
> Â
Hi Jean,
>
> I have checked my model and I think that you are actually right, in fact i have found found the following:
> Sizing:System,
  Air Loop HVAC 1,     !- AirLoop Name
  Sensible,         !- Type of Load to Size On
  Autosize,         !- Design Outdoor Air Flow Rate {m3/s}
  0.3,           !- Minimum System Air Flow Ratio
  7,            !- Preheat Design Temperature {C}
  0.008,          !- Preheat Design Humidity Ratio {kgWater/kgDryAir}
  12.8,           !- Precool Design Temperature {C}
  0.008,          !- Precool Design Humidity Ratio {kgWater/kgDryAir}
  12.8,           !- Central Cooling Design Supply Air Temperature {C}
  16.7,           !- Central Heating Design Supply Air Temperature {C}
  NonCoincident,      !- Sizing Option
  Yes,           !- 100% Outdoor Air in Cooling
  Yes,           !- 100% Outdoor Air in Heating
  0.0085,          !- Central Cooling Design Supply Air Humidity Ratio {kgWater/kgDryAir}
  0.008,          !- Central Heating Design Supply Air Humidity Ratio {kgWater/kgDryAir}
  DesignDay,        !- Cooling Design Air Flow Method
  0,            !- Cooling Design Air Flow Rate {m3/s}
  DesignDay,        !- Heating Design Air Flow Method
  0,            !- Heating Design Air Flow Rate {m3/s}
  ZoneSum;         !- System Outdoor Air Method
> Since I'm running another model I cannot check if the solution works but I'll do as soon as possible!!!
Moreover since I'm trying to learn how to model an HVAC system can you explain me what is the difference between "Sensible" and "Ventilation Requirement"?
> Thanks and ciao
> Luca
> Â
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