Re: [EnergyPlus_Support] Re: Heating/Setpoint Controller

Karen

On Sat, Apr 14, 2012 at 6:02 AM, ecoeficientees <ecoeficiente@xxxxxxxxx> wrote:

Thanks Karen for your answer, I agree with your description. I will try to explain the problem better (I think the key is in the dual setpoint).
When you have two coils, you can have a setpoint manager at the outlet (as you say) that works for both or a setpoint manager at the outlet of each coil that controls each of them independently.

If you need to mantain a constant setpoint at the outlet, there is no problem. You specify, for example, 14ºC and both coils work together to get that temperature. The problem is that, when you have, in the same day, a cooling demand (which you can offset with the 14ºC supply air) followed by a heating demand (eg. at night), you still have the 14ºC setpoint which is useless.

For that situation, I tried to specify one setpoint for each coil (eg. 14ºC for cooling and 30ºC for heating) hoping that depending on the final demand in the zone(s) one of the coils would shut off.
The result, however, is that both coils are on, each of them trying to reach its setpoint and you end up with both coils opposing each other.

It seems to be impossible to use the AHU for both heating and cooling unless you specify availability schedules for the coils. The problem is that you cannot predict when you will be needing each load.
Am I right?

Regards,

Germán.

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Karen Walkerman <kwalkerman@...> wrote:
>
> German,
>
> I think you are mistaken that the AHU heating and cooling coils always
> oppose each other. I am not familiar with the templates as I always work
> directly with the idf file, but if you run the expidf file, and then review
> the full idf file created you should see a few things:
>
> 1. There should be a setpoint manager that controls the temperature of the
> air supplied to the zones. Usually it is placed on the AirloopHVAC supply
> outlet node. What type of setpoint manager is it?
> 2. The heatin and cooling coils on the supply side of the air handler loop
> should both have controllers.
> 3. The controllers will have a reference node. Is the reference node the
> same for both controllers? Is the reference node the same as the setpoint
> node for the setpoint manager you found in answering question #1? If so,
> the two controllers will work together to maintain the conditions at that
> setpoint.
>
> What I've described above is a pretty simple system. You could also have a
> setpoint manager at the outlet o each coil specifying the temperature in
> multiple places. In this case you can force the coils to operate
> simultaneously.
>
> I hope this description helps. Good luck.
>
> --
> Karen
>
> On Friday, April 13, 2012, ecoeficientees <ecoeficiente@...> wrote:
> >
> >
> > Dear James,
> > I am afraid that Energyplus does not control heating and cooling coil
> operation for a dual setpoint, at least when they are water coils (not sure
> about DX Coils). Even VAV HVAC Template says so in the help file (that you
> need to use availability managers to control when the coils are operating).
> >
> > It is frustating, as I have said in another reply, because it seems that
> EMS is the only solution to the problem.
> >
> > Regards,
> >
> > Germán.
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Jim Dirkes" <jim@> wrote:
> >>
> >> Dear Germán,
> >>
> >> EnergyPlus will automatically control the operation heating and cooling
> coil
> >> according to your SetpointManagers. It will not operate cooling and
> heating
> >> simultaneously unless you have some sort of CoolReheat control. (You can
> >> see this is you create output variables for the temperature node
> downstream
> >> of each coil)
> >>
> >> Regarding the frost warnings, you can:
> >>
> >> · Ignore the warnings (probably this does not affect accuracy too
> >> much, but you will get a lot of warnings!)
> >>
> >> · Create a two-speed DX coil (This will probably reduce the number
> >> of warnings)
> >>
> >> · Employ EMS to prevent DX coil operation below a certain outdoor
> >> temperature (e.g. 10-12C)
> >>
> >>
> >>
> >> The Building Performance Team
> >> James V. Dirkes II, P.E., BEMP , LEED AP
> >> 1631 Acacia Drive NW
> >> Grand Rapids, MI 49504
> >> 616 450 8653
> >>
> >>
> >>
> >> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of ecoeficientees
> >> Sent: Friday, April 13, 2012 9:30 AM
> >> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >> Subject: [EnergyPlus_Support] Re: Heating/Setpoint Controller
> >>
> >>
> >>
> >>
> >>
> >> Hi, I am stuck on the same problem.
> >> Is Energyplus EMS the only way? Or which 4-5 variables can you adjust?
> >> Also, what do you mean by not using VAV? I am using an AHU and VAV or
> not,
> >> there is the same problem, since you have to use a Setpoint manager for
> the
> >> coils.
> >>
> >> It is a very common HVAC configuration, which I cannot find how to
> >> configure...
> >> Any idea?
> >>
> >> Regards,
> >>
> >> Germán.
> >>
> >> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> >> <mailto:EnergyPlus_Support%40yahoogroups.com> , YuanLu Li <yli006@>
> >> wrote:
> >> >
> >> >
> >> > If yu do not have pre-heat and reheat and there is not need to use VAV,
> >> you should not model using VAV. The zone thermostat should be used to
> >> control the cooling and heating coils directly. When you use VAV dampler,
> >> the theremostat controls the damper which change the flow rate which
> results
> >> in different zone temperature. The process is more complex. You need to
> >> adjust four or five variables to work together to make the system work.
> >> ============================In a real VAV system, a computer control
> system
> >> is used to control the fan speed. Pressure sensors are also required.
> Duct
> >> temperature, diffuser temperature and room temperature are modified to
> make
> >> the desission on whaat to do. Dr. Li
> >> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >> <mailto:EnergyPlus_Support%40yahoogroups.com>
> >> > From: matthew.sverre.anderson@
> >> > Date: Thu, 10 Nov 2011 15:13:58 +0000
> >> > Subject: [EnergyPlus_Support] Heating/Setpoint Controller
> >> >
> >> > Hello Everybody, I have a question that likely (or at least hopefully!)
> >> has an easy answer and I am simply too foolish to know it.
> >> > So I have a building which I modeled as a VAV with no reheat, and no
> >> preheat coil. I want the coils to operate as needed and simply ignore any
> >> frost warnings. However, I currently have no schedule for either since
> there
> >> will be many times during the fall/spring where we might need to
> heat/cool
> >> during the same day or during the week.
> >> >
> >> > The problem I am currently having is that the heating/cooling coils are
> >> operating year long at the same time. I want the HC to operate when the
> >> building needs heating, the CC to operate when the building needs cooling
> >> (neither to operate at the same time). Am I thinking about this
> incorrectly?
> >>
> >> >
> >> > Also is there a way to implement a dead band above/below the set point
> >> where the system is "satisfied" to prevent the system from "slamming"
> >> on/off?
> >> >
> >>
> >
> >
>