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[EnergyPlus_Support] Re: SetpointManager:MixedAir and Economizer question

Dear Richard,
I have a blow through unitary cooling system (dx) followed by an extra hot water coil as the last componant on the supply side of my Airloop (meaning the last node has a setpoint applied as required by the hot water coil controller). So earlier, you suggested using an uncontrolled node for the reference node, and suggested the fan outlet or exhaust node.
1) Would it matter if the fan outlet node is contained in the unitary system?
2) Should I insert a Duct object as the last componant on the supply side, before opting for the exhaust node (this may be important for DOAS).

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, 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
>




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