no heating loads to systems --part II

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Hi all,

okay-I'm back to where I was last time I posted this question: why are
there no heating loads being passed to my systems?

Here's the story: (160,000 sf high school building)

The attached file is my baseline 90.1 model using System 7 (VAV w/reheat)
As the file is now-I have removed the reheat delt-T (30 deg), and removed
any baseboard heating in all /systems/zones and removed any input of heating
capacity of the coils. With this, my file receives the following error:
***ERROR***********************************************************************

Loop: Hot Water Loop has zero design flow.

Check input for consistency, or specify design loads.
Right now I am trying to have DOE2 'autosize' anything it can so that I can
get a good run and go back and adjust equipment capacities....but I don't
know where else I can look further for why the systems aren't receiving the
design loads.---thus creating the above error. Something is stopping DOE
from passing the loads to the systems. When I open my sim file, the only
reports being produced are the L-reports.

If anyone has any hints or can take a look to find what it is I'm missing--I
know it's a simple thing, but can't seem to find why it is doing this.
(I've been staring at these files tooo long...)

---on a side note--after all the help I received with this issue earlier
this week I have input all of the temp schedules that are required, and all
that I know needs to be input to get the systems to run. any help would be
greatly appreciated so I don't have to go back and rebuild this model from
the beginning....I'm too close to the end to go back and rebuild
another file.

Thanks in advance!
Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600

Thank you both for looking at this. I'm a bit dumbfounded that it can't be
as easy as the fact that I need to specify reheat, since I have indicated
that it is a VAV with reheat system, but if that is the case then I will
re-instate the reheat delta t so that I can generate heating energy. (when
I had input a reheat delta t of 30 degrees F, I was able to successfully fun
a simulation, but the heating energy numbers where so high (i.e. 30 kWH/sq
ft or more) that it just didn't seem like this was the correct input for my
model.

I just think that it is a bit weird even for the programming that the only
way I can get heat out of the heating coil is that I have to enlist reheat
or baseboards in order for the system to assume that there is a heating
load.

I understand the logic of why this works, but I don't understand why it is a
requirement in DOE to have some or ll of the heating capacity specified for
it to "autosize" or react to the fact that heating loads need to be passed
to the systems module only if reheat or baseboards are specified.

If it is possible for any of the eQuest programmers to comment on this input
requirement I would like to hear thier feedback. In the meantime, what I am
understanding is that it is a requirement to specify supplementary heating
(i.e reheat or baseboards) in DOE2 for a VAV reaheat system before DOE2
will allow a basic heating coil to assume a heating load...somebody please
tell me I'm wrong-because this doesn't make sense.

Pasha

---------- Forwarded message ----------

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600

Pasha:

I believe the short answer to this is that not all VAV zones have reheat. Therefore, you need to put reheat in the zones that have it. otherwise, all systems would get reheat.

John Aulbach

John Aulbach's picture
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Joined: 2011-09-30
Reputation: 1

Thanks John/Vik- Yes. but when I do put in reheat that is the only way the
systems are receiving reheat, so my question is why are the heating coils
not doing the primary heating wherefore in my case file, all of the heating
is up to either reheat (specified by me) or via baseboards (also specified
by me.)

The big question is: why aren't the heating coils doing the job first, and
then the excess is to be made up via reheat and/or baseboards.

I have not specified any input for humidty control (based on the help file
recommendations--b/c we don't have humidification control in the proposed
building...

The DOE2 help file indicates:
REHEAT-DELTA-T

Maximum increase in temperature for supply air passing through the zone (or
subzone) reheat coils. The value specified here applies to all zones in the
system. This keyword is required in order to simulate heating the air as it
passes through the terminal reheat coil. Note that when very little air is
passed (see MIN-FLOW-RATIO) there may be insufficient reheating.
The highlighted statement is noted, but it still doesn't indicate that this
input is required *in order to simulate any heating requirement.* It only
states it is required to simulate reheat heating requirements. Why don't
the heating coils work in my model is my "black & white" question.... all
in all my space heating energy (with reheat & baseboards) is only 1% of the
total building energy for a climate in Vancouver, BC... why is it so low?

...if I am just really missing something---please don't hesitate to tell me
so. ---- I have also specified the hot deck temp coming off the htg coils
which then gave me some capacity in my heating coils, but unfortunately by
adding this input all of my numbers have dropped instead of increased.

I also looked back into the archives to find an answer to this issue--I
found two others who were having the same problems I have, but they have
responded that they never figured out the problem either...

Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600

sorry all- somehow the last file got corrupt-wrong zones/systems, etc...

please don't use that file.

pk

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600

Pasha,

For VAV systems you also have to specify the HEAT-SET-T (Hot Deck Max
Leaving Temp) to enable the main air handler heating coil. You can't
just leave the field blank. For example, if your room supply air
temperature is 90F and you have 30F reheat, enter 60F for the hot deck
temp.

Regards,

William Bishop, EIT, LEED(r) AP

Bishop, Bill2's picture
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Joined: 2011-09-30
Reputation: 0

Thanks Bill,

I do have specified 105 supply temp, 105 hot deck max temp, 50F reheat delta
T. For some reason my results are very low for my ASHRAE baseline building
& they are showing virtually 1% heating energy consumption overall in my
building, and I have one standard effeicency boiler in the plant side.

This is what I know (by gut feel) the issue is--somewhere in the airside I
have either turned on or off some control or schedule--along with when I set
up the model using the wizard initial inputs they were for the proposed case
(water-to-water heat pumps-geothermal htg/clg & serving all spaces including
thermal displacement vent, natural vent zones (for htg baseboards), FC's
etc. So----I am wondering if when I saved my file for the baseline model
and then switched the plant equip (chiller/boiler) & VAV sys if there is a
carry-over input from the HPsystems (or other) that is affecting the lack of
heating energy with the standard systems.

Not sure how to find a 'carry-over' input. I have compared my input files
with examdiff program and couldn't find anything specific.

I've attached the non-corrupted files to this email...

pk

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600

Try taking your heat control off scheduled and try coldest to compliment your warmest setting on cooling. Also you may need to enter a capacity for your heating coils in order to get them to enable. Ive had this problem in the past, but considering you have 50 degree reheat in your zones this shouldn't be the problem. I would guess it's the schedule setting, Im not sure what schedule that looks at but im pretty sure taking that out should fix your problem.

Charles Land's picture
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Joined: 2011-09-30
Reputation: 0

Dear fellow eQuest-users;

With tremendous support/response from so many of you I have resolved all of
my visible issues--one due to [shameful] personal error & also with
adjusments on some schedules, heat reset control, etc.

I can't express my THANKS loud enough for you to hear my true appreciation
of your immediate help & support. Especially since emotionally speaking I
was in a 'panic' mode b/c of my deadline and a non-working baseline model.

All is well now, I learned a lot of new things about the system controls, so
it was a good 'growing' experience too. It's wonderful to have such a great
support group to turn too. I'm impessed to know that there are many
professionals & simulators who are willing to extend thier experience and
assistance to help each of us become better at what we are doing.
I hope I can repay the favors to all of you.

Cheers,
Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600

This problem isn't completely relevant, but I didn't find anything in the archives about it, so I figured I would pass this along in case someone finds themselves in a similar position:

I was working through a similar problem myself, where I had the AHU heating coils providing heat, but not the zone reheat coils. I found that my problem was the heating availability schedule (HEATING-SCHEDULE). I originally had it set to "S1-(YOUR SYSTEM NAME HERE) Heat Schedule", which is the zone temperature setpoint. After much head scratching, I still kept getting 4,000 hours per year (for each zone) that the heat loads were not met.

The problem is, with a VAV with reheat system, you need heating more or less all year. So, what I was telling equest was the heating is only available when the outside temperature is below a given value, when really you need heat all year. So, my solution was to change my heating availability schedule (HEATING-SCHEDULE) to "Hourly Report Schedule", and the very next simulation I had zero unmet hours.

I hope it helps. thanks.

Daniel I. Deese

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