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Re:[EnergyPlus_Support] Re: ASHRAE 90.1 - VAV with reheat will overheat zone at very high ODA

Okay. The AHU (when in cooling mode and in heating mode) delivers air at (Cooling Setpoint Temp - 11 deg C) to the terminal unit as per G3.1.2.8. If the zone requires heating, the rest of the heating is done by the reheater (delivery air temp @ Heating Setpoint Temp + 11 deg C). If the zone requires cooling, the reheater coil must not operate. 

e+ by default will try and bring the delivery air temperature to the same temparature as the zone heating setpoint temperature. 

Therefore, "if the zone requires cooling, the reheater coil must not operate" presents a problem. Currently, the best way to do this is to schedule the availability of the electric or water heater to OFF. This can be a timed schedule, EMS controled or AvailabilityManager:HighTemperatureTurnOff monitoring the zone exhaust node temperature.

Please note the earlier mentioned delivers air at (Cooling Setpoint Temp - 11 deg C) to the terminal unit as per G3.1.2.8. must include a OutdoorAirReset as per G3.1.3.12 for some system types 5 through 8, which is realised with SetpointManager:OutdoorAirReset.

Note also G3.1.3.13 when setting terminal unit settings.

Kind regards,

Jean Marais

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Gloria  <bankcommhr@...> wrote:
>
> I don't know either.
> Even I don't control the indoor air humidity, the reheat still exist and the reheat consumption is even larger than the heat consumption in winter. (Climate 3A)
> I don't know how to explain this.
> Jean, any idea?
> Gloria
> 
> 
> 
> 
> 
> 
> At 2012-10-13 00:40:47,Ooi <ooi_kb3@...> wrote:
>  
> 
> Hi,
> 
> i do not understand why there has to be a Reheat. i think it wastes energy.
> 
> ooi
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jean marais" <jeannieboef@> wrote:
> >
> > Dear group,
> > Until now I have used the following interpretation of Appx G.
> >
> > The supply air temperature to the zone is defined as the "design supply air temperature"..."design" meaning for the design day or worst case. To me this is a maximum, not a constant. Therefore, the reheating coil should try and maintain the room temp, not the outlet coil temp, but the outlet coil temp may not exceed the maximum of the "design supply air temperature". This way you can avoid overheating a room that has very high ODA requirements.
> >
> > Do you follow?
> >
> > Regards,
> >
> > Jean.
> >
>




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