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[EnergyPlus_Support] Re: SetpointManager:MixedAir and Economizer question
Sorry, the connection dropped out on mid post. Here is my last post again.
On a coil outlet? Coils usually need setpoints on the outlets for the controlers. This would give me a SetpointManager conflict! The exit of the mixingbox would make more sense to me.
Also, if I assign a setpoint to the fan inlet (for a blow through config.), I would set it to equal room air exhaust temp, say 22 deg for both heating and cooling modes. But I feel this is a "looser" control, because the air will be "preconditioned" with ODA mixing always to 22 deg, even if it would be more advantages if it were closer to the best achievable delivery air temperature. I guess this I a gap between theory and practise. In practise it may well be the case that the return air temperature is monitored and mixed with ODA as appropriate to achieve a mixed air temperature of roughly 22 degC after the mixing box (with taking onto account fan heat).
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad <RRaustad@...> wrote:
>
> The reference node must have a setpoint assigned to it by another
> setpoint manager.
>
> Of course it does, that's why it's called a reference. Use a different
> type of set point manager to put a set point on a node (remember, the
> fan inlet node, return node, etc.). Then used the mixed air set point
> manager to read the reference node set point, adjust for fan heat, and
> place a new set point anywhere you need it (usually at a coil outlet node).
>
>
> On 12/1/2011 1:43 PM, Jean marais wrote:
> >
> > After reading the io Ref. your suggestion did not make much sense. I
> > applied it anyway and got the errors that I thought I would get.
> >
> > The reference node must have a setpoint assigned to it by another
> > setpoint manager.
> >
> > The setpoint nodes are all the nodes to which the
> > SetpointManager:MixedAir will assign the new calculated setpoint to.
> >
> > This means the Reference Node should have a setpoint assigned by
> > another manager = air delivery temperature (which should change for
> > the heating and cooling case), as this is the setpoint which you are
> > trying to hit.
> >
> > And none of the nodes in the SetpointNodeList may be set by other
> > setpointmanagers as they will conflict.
> >
> > In my current configuration I have Mixingbox,[Fan,dx cooling coil],hot
> > water coil. With setpoint managers for cooling at the dx outlet node
> > (12°C) and at the heating coil outlet (-99 to 34°C). The Setpoint
> > assigned at the exit of my htg coil doubles as my delivery air
> > setpoint temp and serves as the reference node for the
> > SetpointManager:MixedAir. My SetpointManager:MixedAir Setpoint is only
> > assigned to the exit of the Mixing box (but could also be assigned to
> > the exit of the fan.)
> >
> > I think James and I understand this object differently.
> >
> > Pointers? Comments?
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > <RRaustad@> wrote:
> > >
> > > 1) put the reference node on any node that will not be controlled, use
> > > the return node if you have to, or the fan outlet would also work
> > > 2) don't worry about upstream and downstream, just enter the fan
> > > inlet/outlet node names and the manager will do the rest
> > >
> > > What you are basically doing is calculating a set point at the
> > reference
> > > node, and then using the mixed air manager to adjust that calculated
> > set
> > > point by the fan heat. So when all is said and done, the outlet of the
> > > air loop is at the same temperature as the reference node set point
> > > temperature
> > >
> > > On 11/29/2011 11:50 AM, Jean marais wrote:
> > > >
> > > > Thanks James. A few more questions, if you'll indulge me...
> > > >
> > > > The referance node:
> > > > I assume one must be quite careful as to what setpoint is used on the
> > > > reference node (usually the last node on the supply side). For
> > > > example, if my last componant is a heating coil, I can't assign a
> > > > fixed schedule 32degC with a setpoint manager on the htg coil exit
> > > > node, if I plan heating and cooling all year round. I need to use, in
> > > > this case a setpoint manager that can decrease the setpoint on this
> > > > node during times of cooling. Right?
> > > >
> > > > The other setpoint nodes in the list:
> > > > How does the MixedAirSPmanager "know" on which node the fan sits, to
> > > > deturmine upstream and down stream from it? I don't have it here. Is
> > > > it an input field? I ask, because not just the fan takes or adds to
> > > > the air stream. Maybe, it just looks at the setpoint on each node in
> > > > the list (not the airstream temp), checks if it must be applied (eg.
> > > > clg sp not applied if in heating mode), and estimates the energy put
> > > > in or out at these nodes. Using this information, it sets the
> > setpoint
> > > > at the exit of the mixing box, then the controller tries to control
> > > > the damper to match. Right?
> > > >
> > > > Please explain "exception 1". My guess is that if the downstream htg
> > > > coil exit node was included, the manager would see it as a second fan
> > > > and (if outside had cold air) possibly introduce more than nessecary
> > > > ODA, which the poor htg coil would have to heat up. This all becomes
> > > > hellishly complicated considering econimizers and other factors.
> > > >
> > > >
> > >
> > > --
> > > Richard A. Raustad
> > > Senior Research Engineer
> > > Florida Solar Energy Center
> > > University of Central Florida
> > > 1679 Clearlake Road
> > > Cocoa, FL 32922-5703
> > > Phone: (321) 638-1454
> > > Fax: (321) 638-1439 or 1010
> > > Visit our web site at: http://www.fsec.ucf.edu
> > >
> > > UCF - From Promise to Prominence: Celebrating 40 Years
> > >
> >
> >
>
> --
> Richard A. Raustad
> Senior Research Engineer
> Florida Solar Energy Center
> University of Central Florida
> 1679 Clearlake Road
> Cocoa, FL 32922-5703
> Phone: (321) 638-1454
> Fax: (321) 638-1439 or 1010
> Visit our web site at: http://www.fsec.ucf.edu
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
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