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[EnergyPlus_Support] Re: Zone will not reach setpoint
Dear Richard,
Getting better and better! I'll appreciate some clarification,
though, regarding the autosizing limitations that I am encountering.
1) If I have defined a "Zone heating design supply air temperature",
what prevents E+ from just calculating the necessary airflow for the
load and specified supply air temp? That seems pretty
straightforward...since the fan airflow is also autosized.
2) When you refer to "cut-outs for resistive heating coils", do you
mean a high limit temperature safety on an actual electric heating
coil? or something that E+ is using (that I don't know about)?
I very much appreciate your help here! and I'm trying to get
knowledgeable enough to become a net contributor to the Forum.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
<RRaustad@...> wrote:
>
> Because the terminal units are at max capacity. Try increasing the zone
> heating supply air temperature in the zone sizing object to force more
> capacity in the terminal unit heating coils. I think I saw 50C supply
> air temp off the terminal unit heating coils in the last run I made.
> This was not enough capacity. This is getting pretty hot, but you might
> try 55C. The cut-outs for resistive heating coils is somewhere between
> 49C (120F) and 60C (140F). If the supply air temperature is getting
too
> hot, you need to increase the supply air flow rate. You might have to
> manually size the air flow rate if "tweaking" the autosize inputs does
> not get the job done.
>
> ZONE SIZING,
> Floors 3thru5, !- Name of a zone
> 12.78, !- Zone cooling design supply air
> temperature {C}
> 40.56, !- Zone heating design supply air
> temperature {C} <------
>
>
> JV Dirkes II wrote:
> >
> > Dear Richard,
> >
> > I ran the model with the revised "Central heating design supply air
> > temperature". Lo and behold, it does a much better job of heating the
> > zone. Nonetheless, it's still 2C lower than the setpoint, which is
> > generally considered unacceptable for "real" buildings and won't be a
> > good representation of actual energy use. Do you have any ideas why
> > it won't reach the setpoint?
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
<jvd2pe@>
> > wrote:
> > >
> > > I'll try it!
> > >
> > > FYI, ... back earlier in May I posted a problem (Forum message
11377)
> > > noting that I had non-zero loads in the zones, but the system was
> > > calculated to have zero flow / load. That file was uploaded and
> > > called something like "Non-zero loads". Fred Buhl worked on it and
> > > recommended that I change (guess what?) the "central heating design
> > > supply temp" from 12.8C to the value it's now at. I sent him an
> > > e-mail on 5/27 asking about it, but haven't heard back. Fred has the
> > > "non-zero" file (so do I), but I deleted it from the Forum
upload area.
> > >
> > > In short, your fix counters an earlier fix. There may be other
factors
> > > which I've inadvertantly altered since the original problem, but I
> > > want you to be aware of the history....
> > >
> > > Also, regarding your last message about using a higher discharge
> > > setting in the wimter: Good call! That will be one of the savings
> > > strategies employed for the real building model. This model is a
> > > "Baseline" for an ASHRAE 90.1 analysis, so I am using the
> > > ASHRAE-specified HVAC and controls (which do not call for winter
reset
> > > of discharge temp)
> > >
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > > <RRaustad@> wrote:
> > > >
> > > > You might also consider using the main air loop heating coil to
> > pick up
> > > > more of the load. Why did you choose to heat the air to 12.8C
in the
> > > > main air loop during the winter design day?
> > > >
> > > > Richard Raustad wrote:
> > > > >
> > > > > Change your "Central heating design supply air temperature
(C)" to
> > > match
> > > > > what is entering the zone terminal unit heating coil. In
this case
> > > it is
> > > > > 12.78 C. The zone now maintains 18-20C.
> > > > >
> > > > > SYSTEM SIZING,
> > > > > AirLoop_AH1, !- name of an AIR PRIMARY LOOP object
> > > > > sensible, !- type of load to size on
> > > > > Autosize, !- Design (minimum) outside air volumetric
> > > > > flow rate {m3/s}
> > > > > 1, !- minimum system air flow ratio
> > > > > 4.44, !- Preheat design temperature {C}
> > > > > 0, !- Preheat design humidity ratio
> > > > > {kg-H2O/kg-air}
> > > > > 12.78, !- Precool design temperature {C}
> > > > > 0.0087, !- Precool design humidity ratio
> > > > > {kg-H2O/kg-air}
> > > > > 12.78, !- Central cooling design supply air
> > > > > temperature {C}
> > > > > 12.78, !- Central heating design supply air
> > > > > temperature {C} <--------
> > > > > coincident, !- Sizing Option
> > > > > no, !- Cooling 100% Outside Air
> > > > > no, !- Heating 100% Outside Air
> > > > > 0.0087, !- Central cooling design supply air
> > > > > humidity ratio {kg-H2O/kg-air}
> > > > > 0, !- Central heating design supply air
> > > > > humidity ratio {kg-H2O/kg-air}
> > > > > design day, !- cooling design air flow method
> > > > > , !- cooling design air flow rate {m3/s}
> > > > > design day, !- heating design air flow method
> > > > > ; !- heating design air flow rate {m3/s}
> > > > >
> > > > > JV Dirkes II wrote:
> > > > > >
> > > > > > Dear E+ Forum,
> > > > > >
> > > > > > I've tried using V2.2.026, since that version addresses a
known
> > > reheat
> > > > > > problem, but the model still reflects the problems noted in my
> > last
> > > > > post.
> > > > > >
> > > > > > Can anyone help?
> > > > > >
> > > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
> > > > > <jvd2pe@>
> > > > > > wrote:
> > > > > > >
> > > > > > > Dear E+ Forum,
> > > > > > >
> > > > > > > I am still hoping for some help with this problem. I've
added
> > > report
> > > > > > > variables, tried different settings, double and triple
checked
> > > all th
> > > > > > > input, and still cannot get the zone to warm up.
> > > > > > >
> > > > > > > Thanks in advance.
> > > > > > >
> > > > > > > p.s., The uploaded file is called "ZoneTooCold.zip"
> > > > > > >
> > > > > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, "JV Dirkes II"
> > > <jvd2pe@>
> > > > > > > wrote:
> > > > > > > >
> > > > > > > > Dear E+ Forum,
> > > > > > > >
> > > > > > > > My current model includes a variable volume air handler
> > and VAV
> > > > > boxes
> > > > > > > > with reheat coils. The zone which represent 90% of the
> > building
> > > > > never
> > > > > > > > reaches its setpoint on the Winter Design Day.
> > > > > > > >
> > > > > > > > Per report variables, the air handler has proper
temperature
> > > heating
> > > > > > > > hot water (82C) and the discharge temperature is at the
> > expected
> > > > > > > > setpoint (12.9C). Air flow is autosized.
> > > > > > > >
> > > > > > > > The zone reheat coil is also autosized and has the same
> > > heating hot
> > > > > > > > water temperature as the air handler. Per report
> > variables, the
> > > > > > > > reheat coil has water flow and is using energy, but only
> > > heats the
> > > > > > > > zone to 5C instead of the setpoint (21.1C).
> > > > > > > >
> > > > > > > > I've tried manually sizing the reheat coils much
larger than
> > > the
> > > > > load,
> > > > > > > > but they continue to use only a small fraction of their
> > > capacity and
> > > > > > > > the zone stays too cold. Please let me know what might
> > > prevent the
> > > > > > > > reheat coils from warming the zone properly. Thanks!
> > > > > > > >
> > > > > > > > p.s., I've uploaded the file in case it will be helpful.
> > > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > > --
> > > > > 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
> > <http://www.fsec.ucf.edu>
> > > <http://www.fsec.ucf.edu <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
> > <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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