Open GoogleCodeExporter opened 9 years ago
GoogleCodeExporter
commented
9 years ago Changing this to high priority since the Large Office model updates for the
Reference Test method relies on this.Original comment by chitra.nbr on 17 Mar 2014 at 5:19
GoogleCodeExporter
commented
9 years ago Chitra, please upload your cibd file. Original comment by rhedr...@archenergy.com on 17 Mar 2014 at 5:23
GoogleCodeExporter
commented
9 years ago Roger, see attached.Original comment by chitra.nbr on 17 Mar 2014 at 5:34
Attachments:
GoogleCodeExporter
commented
9 years ago Changing owner to Kyle.
I see no difference in the simulation xml files other than the change in
<FluidSys>/<FixedSupTemp>. But I am seeing nearly constant operation of the
cooling tower fan in the 81F supply temp case. I also don't see any change in
the idf file other than the supply temp setpoint, although it is hard to tell
with all the naming differences from OS. I've attached a screenshot from
ResultsViewer of Cooling Tower Fan Electric Power, with the blue line from the
lower temperature case, the black from the 81F case. Original comment by rhedr...@archenergy.com on 17 Mar 2014 at 8:47
Attachments:
GoogleCodeExporter
commented
9 years ago Original comment by rhedr...@archenergy.com on 17 Mar 2014 at 8:47
GoogleCodeExporter
commented
9 years ago Kyle,
I think this issue stems from the fact that the pump on the CT branch is
VariableSpeed. We are testing some alternate combinations that make more sense
to see if this is the root cause. If it is, we'll add some checks on our side
to ensure that variable speed CW pumps are used appropriately. Will report
back here with what we find.Original comment by da...@360-analytics.com on 20 Mar 2014 at 10:21
GoogleCodeExporter
commented
9 years ago I just ran cases with the CW pumps switched to constant speed with fixed CWST
at 76F and 81F, and the results are as expected. I think we are OK, and adding
checks in the rules will be adequate. Original comment by rhedr...@archenergy.com on 20 Mar 2014 at 11:50
GoogleCodeExporter
commented
9 years ago The little bit of testing I did with variable speed pumps on the loop (as
opposed to branch) also don't control properly. The pump does operate between
50% and 100% flow with chillers staging, as expected, but the flow rate is 50%
of the expected rate at each operating point. this leads to the CW temp
floating upward, well beyond the control temp, and the CT fan runs nearly
constantly trying to compensate.
I'd like to experiment with variable speed pumps on the loop more to see if we
can figure out a way to make that work, but for now, I will add a CHECKSIM rule
that checks for and disallows variable speed pumps on the CW loop.Original comment by da...@360-analytics.com on 21 Mar 2014 at 2:27
GoogleCodeExporter
commented
9 years ago I'm going to post some images in a minute, but I also believe this is more of
an defect (or at least limitation) of EnergyPlus.
Some take aways which I will try to support are:
Temperature might not be controlled correctly.
Changing ONLY the setpoint yields the strange outcome. That is I took the 81F
model (idf) and adjusted only the schedule down to 71F and got (almost) the
exact same results as from the original 71F SDD.
Mass flow through tower based on request from the chillers appears extremely
close.
Some SDD inputs will result in a Design Inlet Air Wet-Bulb Temperature below
20C which is an E+ lower bound. In this case the value will stick at the OS
default 25. Suggest a translator change to set the floor at 20 even if the SDD
tries to set it lower. Keep in mind that this is a calculation based on supply
temp - wet bulb approach.
Original comment by kbe...@gmail.com on 21 Mar 2014 at 1:46
GoogleCodeExporter
commented
9 years ago The following change was motivated by my investigation of this ticket, but has
very little impact on what is being discussed here.
https://github.com/NREL/OpenStudio/commit/4d995832f54c1e2b52127febba63978ef57e5a
01
I don't consider it a critical change and can simply be picked up in the next
build, whoever that is.Original comment by kbe...@gmail.com on 21 Mar 2014 at 3:26
GoogleCodeExporter
commented
9 years ago Roger, I suggest we make the SDD property for Design Wetbulb Temp
(HtRej:DsgnWBTemp property an explicit input in the input and sim XML model.
This way we can check and warn users on the limit.Original comment by da...@360-analytics.com on 21 Mar 2014 at 4:11
GoogleCodeExporter
commented
9 years ago Here are some images to try to explain what I see.
First of all the flow request moving through the towers seems almost identical
between the two models. See the "flow comparison" attachment. This is a flood
plot of the difference in flow between the models over the entire annual
simulation. You can see it is awash in 0.
Now look at "flow". This is flow for the 81 model but it doesn't really matter
since I just showed that they have the same flow rates. It looks pretty
reasonable to me, unless I missed something. Nice swing throughout the year
with peak in the hot summer days.
Then look at tower temps coming out of the 71 model in "71 temps" Looks pretty
decent to me. We seem to be pretty much under control during the times when
the tower actually has water moving through it. Sure it gets crazy and floats
around when the tower is not moving fluid but I don't think that is a concern.
In fact if you look at the "71 power" fan power used by the tower has a pretty
normal looking profile too.
Now look at "81 temps" Crazy town here. I don't know what is going on but the
tower seems to be completely out of control, even though we are asking less of
it. I can't explain it except E+ is weird. I verified that we don't have some
other inadvertant property besides the setpoint schedule messing with things.
I did this by taking the perfectly good 71 idf and modifying the setpoint
schedule value (1 field) and got the same crazy outcome.
Just for completeness a attached the 81 power so you can see the tower running
like crazy while still not achieving setpoint. You might think, well, ambient
conditions just aren't allowing for it, but the same tower seems to have no
problem maintaining 71. ???
I didn't try this with a constant speed pump, but the above reports suggest
this issue goes away. Seems weird since the flows are the same if you ask me.
I'm interested in seeing this same plots with the constant pump, but patience
is running low.
Original comment by kbe...@gmail.com on 22 Mar 2014 at 1:48
Attachments:
GoogleCodeExporter
commented
9 years ago 
A few additional observations to add to last few comments:
As mentioned in #8, the CW loop flow was observed to be about 50% less than the
capacity of the CW pump. Comment #9 indicates the tower mass flow is consistent
with the chiller condenser request, which is a good clue.
This is now starting to make sense..,
In the IDF, the Chiller:Electric:EIR !- Reference Condenser Fluid Flow Rate
{m3/s} is set to 0.05165 m/s, or ~820gpm/chiller, or 1640gpm total for the 2
chillers. The CW pump capacity is 0.21217 m/s, or 3363gpm, roughly double the
specified Chlr condenser flow rate. My guess is that the chiller condenser flow
rate is being calculated based on the design heat rejection of the chiller and
the ChW delta T (20F), as opposed to the CW delta T (10F). This would explain
why the CW loop flow is roughly 1/2 what I expect it would be.
I wasn't sure if this explains the strange CW supply temps. I first iterated
the CW setpoint temp from 70F to 80F in 2F increments, and found that the
control goes "crazy town" when the setpoint temp is somewhere between 76F
(24.4) and 78F (25.5C) (see image 1). I ran a model @ 25C and CWS temps still
are erratic in June and Sept (see image 2). Not sure if this is a climate
specific issue (all runs using Blue Canyon epw), but reinforces what Kyle
indicated.
The last thing I tested was revising the chiller condenser flow rate to be
consistent with the flow needed to reject the heat @ design conditions. I ran
the same model with both 70F and 80F setpoints. As shown in the images below,
the fan energy and CWS temps are as expected (see images 3 and 4)
Keep in mind, for the model results described in this comment, I moved the pump
from being a child of the CT (i.e upstream of CT on a branch) to being a child
of the FluidSeg (i.e upstream of the splitter). I think this should actually be
equivalent to having the pump as a child of a single CT. I think that Eplus is
hard-programed to not allow CW flow to vary through the chiller condenser, so
really, I don't think we need to have a check for VariableSpeed pumps, but
rather, that the condenser pumps are consistent with both CT capacity and
chiller condenser required flow.
Here is the proposed resolution:
Add a property to the SDD to describe the Chiller Condenser Flow Rate
Update reverse translator to set reference the new property.
Add CHECKSIM rules to make sure pump flow rates (within a certain tolerance)
are consistent with primary component capacities.
This resolution will be reflected in a new GC issue so it is address separately
after Add/Alt rule syntax updates are complete.
One other observation in this model: There are two chillers, each with
constant speed primary ChW pumps. Chiller 2 operates much fewer hours than
Chiller 1, yet the pumps for each chiller operate the same number of hours, as
evidenced in image 5 and 6. Not sure what the cause of this control issue is,
but I will create a new GC to investigate it.
Original comment by da...@360-analytics.com on 22 Mar 2014 at 7:08
Attachments:
GoogleCodeExporter
commented
9 years ago Original comment by cnambiar@archenergy.com on 20 May 2014 at 9:18
Original issue reported on code.google.com by
chitra.nbron 11 Mar 2014 at 7:54Attachments: