[Equest-users] Fwd: no heating loads to systems --part II

[John Aulbach]

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




________________________________
From: Pasha Korber-Gonzalez <pasha.pkconsulting at gmail.com>
To: eQUEST Users List <equest-users at lists.onebuilding.org>; Vikram Sami <vsami at lasarchitect.com>
Sent: Sat, March 6, 2010 9:30:09 PM
Subject: [Equest-users] Fwd: no heating loads to systems --part II


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 ----------
From: Seun Odukomaiya <sodukomaiya at laceindy.com>
Date: Sat, Mar 6, 2010 at 4:59 PM
Subject: RE: [Equest-users] no heating loads to systems --part II
To: Pasha Korber-Gonzalez <pasha.pkconsulting at gmail.com>



Pasha,
I took a look at your model. When employing a VAV-Reheat System as you have in your model, you must also specify the reheat Delta-T for the zone heating coils attached to the units (see attached screenshot). If this is not done, the program assumes that the zones have no reheat, and thus will never put a load on your hot water loop. This, in turn, causes the error that you've seen. The DOE-2 documentation describes it as follows:
 
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.
 
According to your model, the maximum zone entering supply air temperature is 105 degrees. I also noticed that your zone minimum entering supply temperature is 55 degrees. As such, you need to specify your reheat delta-T as 50 degrees (as in the screenshot). This ensures that your zone coils are able to raise the 55-degree air from the AHU up to the 105 degrees that you have specified. Try that, and your model should run just fine.
 Seun Odukomaiya, LEED AP  -  Mechanical Engineer
L'Acquis Consulting Engineers
9229 Delegates Row, Suite 550
Indianapolis, Indiana 46240
voice:  (317) 706-2075, ext. 255
fax:     (317) 706-2076
email:  sodukomaiya at laceindy.com
web: www.laceindy.com
PPlease consider the environment before printing this e-mail.
 

________________________________
From: equest-users-bounces at lists.onebuilding.org [equest-users-bounces at lists.onebuilding.org] On Behalf Of Pasha Korber-Gonzalez [pasha.pkconsulting at gmail.com]
Sent: Saturday, March 06, 2010 4:26 PM 

To: eQUEST Users List
Subject: [Equest-users] no heating loads to systems --part II


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


      
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