Re:Re:[EnergyPlus_Support] Re: ASHRAE 90.1 - VAV with reheat will overheat zone

["Jean marais" <jeannieboef@xxxxxxxxx>]

Correction: if you have a terminal unit with the reheater doing the heating, then the AHU can use a setpointmanager:scheduled to set the outlet temp at (zone cooling setpoint - 11 deg C) and don't forget to apply the ODAreset availibility manager mentioned earlier.
Regards,
jean 

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jean marais" <jeannieboef@...> wrote:
>
> 1) as an AHU typically supplies more than one zone, the situation may arise where the one zone requires heating whilst at the same time the other needs cooling. By insuring that the AHU delivers (zone cooling setpoint - 11 deg C) air to the terminal units all the time, you can insure that both heating and cooling can take place at the required delivery air temperatures...in the heating case the air is raised from  (zone cooling setpoint - 11 deg C) to (zone heating setpoint + 11 deg C) by the reheater. In the case where all the zones need heating, your AHU should still deliver (zone cooling setpoint - 11 deg C) to the terminal units as a preheated temperature if ODA temp is below (zone cooling setpoint - 11 deg C).
> 2) this issue has been previously clarified by Richard Raustad on this forum. The documentation perhaps does not capture the details as does his explanation.
> 3) There are a few acceptable ways to do this. Temperature Setpointmanagers can't be applied to terminal unit reheaters. Your control of AHU coils is an important part of getting this right. This topic has been experimented with by myself extensively and mentioned in detail in previous posts. In a nutshell, allowing the coils band width result in best results. I prefer setpointmanager:single(or multi)zone:heating with the lower limit set to  (zone cooling setpoint - 11 deg C) and the upper limit set to (zone heating setpoint + 11 deg C) placed on the last node of the AHU in combination with setpoinamager for the oda mixing duct (I forget the name).
> 
> Kind regards,
> jean
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Gloria  <bankcommhr@> wrote:
> >
> > 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:
> > 1
> > 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.
> > 2
> > 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+?
> > 3
> > 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@> 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.
> > > >
> > >
> >
>




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