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

Hi Jean,

Thanks for your answer!

I tried to use the schedule to limit the operation time of cooling coil and heating coil, and it really works! I further have three questions:

You mentioned that the AHU supply air at Cooling setpoint temp minus 11 deg C, then I wonder why it does not supply air at Heating Setpoint Temp + 11 deg C in heating mode? From G3.1.2.8, the 11 deg C temperature difference does not mention that it is cooling mode or heating mode.

Another issue is that: "e+ by default will try and bring the delivery air temperature to the same temperature as the zone heating setpoint temperature". I found it true. In my case, my heating setpoint temperature is 18 deg C, and the AHU supply air at about 17.5deg C. My question is that how do you know the e+ will perform like this? Is it from experience or from its working principle? If it is wrong, how to correct the e+?

when setting the working schedule of cooling coil and heating coil, how shall we separate the cooling coil operation period from heating coil? For example, for a 3A climate, I use Mar 15 and Nov 15 as the separate line. Is there any principle in doing this?

Thanks!

Gloria

At 2013-04-19 19:23:11,"Jean marais" <jeannieboef@xxxxxxxxx> wrote:

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.
> >
>