LEED Issue with EQuest Software's Ability to Model Boilers on Ground Loops

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Everyone, I have received a snarky comment from the LEED reviewers regarding eQuest and not being able to model back-up boilers on a ground heat pump loop. See below. The ground loop is large enough not to generate any temperature low alarm messages, the ground loop pump flow never reaches 100% flow except for 1 hour and the ground loop heating capacity is never exceeded. These facts do not appear to be a good enough explanation not modeling the back up gas boiler.

My questions for the group are:
1. Is there a way to add a boiler or some additional heat source to a ground loop in eQuest? As far as I know the only work around I have discovered is to represent the ground loop by creating a water loop and adding a magical no energy consuming boiler and fluid cooler to a heat pump water loop and change the water loop parameters to match ground loop parameters. Then you can add normal boilers that will start if the non-energy consuming ground loop boiler is too small for the building heat load. I offered this option to the LEED reviewer and they replied that it was not an established work around.

2. If there is no way to attach a boiler to a ground loop in eQuest, is there some established work around that somebody has used that was accepted by a LEED reviewer?

3. Is there anything in the reports that lists the maximum and minimum ground loop temperatures? I have been unable to locate it.

4. Does anyone have an written explanation to answer "If this [the boiler] is not being modeled in the energy modeling software then provide a thorough explanation for why it cannot be modeled. "?

5. Does this sound like LEED is trying to eliminate eQuest software, and if so, is there anything we can do about it? "in the future the software selected to simulate the building components must be able to model those components "

The project team could possibly demonstrate that the boiler would not operate through a series of engineering calculations, some other software that could possibly simulate the building's loop temperatures, or through a thorough explanation of how the system operation prevents the boiler from operating. In short the project team must demonstrate that the boiler will not operate, not just say that is the case without presenting some evidence. If this is not being modeled in the energy modeling software then provide a thorough explanation for why it cannot be modeled. In the future the software selected to simulate the building components must be able to model those components or use an exceptional calculation (work around) to do so (G2.2).

Kathryn Kerns's picture
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You can absolutely add a boiler to a GSHP loop. Just add a boiler, and
when asked which HW loop to assign it to, you can pick the GSHP Loop (as
long as that loop is a "Water Loop HP" loop).

I think more than likely this is the reason you are getting the comments
you are. This reviewer may know that you CAN add a boiler to a GSHP
loop, which is the reason for comment #4.

I doubt GBCI is trying to eliminate eQuest as a modeling option.

Also, printing out hourly reports from an eQuest run is often helpful in
proving your case (whatever case that may be). If you can show, via
hourly reports, that the heat picked up by the GSHP heat exchanger
exceeds the heating load for all 8,760 hours of the day, then case
closed...that's all you need to submit.

James Hansen, P.E., LEED AP

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If it were me, I'd just add the inconsequential boiler, state/show I did so, and move on. Typically less effort than building an impenetrable case to someone being contrarian.

To bullet #3: I think not for the standard output reports, but loop entering and exiting temperatures are options in the custom hourly output report dialog, which I believe you can assign to any loop type. This will put out a CSV you can use with a spreadsheet software of your choosing to quickly come up with minimums/maximums over the simulation.

Attached is a past thread with a spelled out / illustrated procedure for setting up a custom hourly report, in case that's helpful.

Best regards,

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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Unless you have a trick I don't know, no you can't, not without creating a fatal error that says "cannot combine a boiler with a ground loop HX" and having the program not run. Please, if you have a successfully running model with a ground loop HX and a boiler on the same Water Loop HP, please send me the input file.

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Nick if you have some way of adding a boiler to the HP Water Loop containing the Ground Loop HX without getting the "cannot combine a boiler and a ground loop HX" fatal error, please show me. I must be missing something.

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When do you get the fatal error?
[Capture.PNG]

Thanks,
Matthew J. Baron

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When do you get the fatal error?
[Capture.PNG]
Thanks,
Matthew J. Baron

Matthew Baron's picture
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Sorry, I assumed since you could add a boiler to a WSHP loop that you
could run it too :)

Indeed there is an error when processing.

You could always add the boiler load as a process load (in order to get
unmet load hours down).

However, you don't have an issue with unmet load hours right? If there
is a boiler that shows up in your proposed design (ie contract
documents) that is there for backup, but your hourly reports show that
you don't need one, just submit hourly reports and explain this.

James Hansen, P.E., LEED AP

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Try running the model. You won't complete the run.

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How confident are you that the GSHX is actually large enough to meet all
of the annual heating loads? Depending on the building type, size, and
climate, seems like it is reasonable for the reviewer to be skeptical.
I've worked on a LEED-Nc v2.2 commercial building project where I
arrived at the same conclusion, but it took a lot of extra work to
convince myself that the GSHX model inputs, loop/equipment controls, and
overall outputs (including hourly results) were all reasonable (LEED
reviewer didn't seem to have an issue with it in this case). Have you
tried clearly illustrating/justifying the inputs for the DOE-2 GSHX
model? There are other programs available that you can input loads and
GSHX performance parameters, and it will tell you what the average loop
temperatures are over time. I typically use these for
comparison/validation of the DOE-2 model results. Perhaps providing a
secondary analysis of the GSHX would support (or potentially rebuke)
your conclusion?

-David

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James and Nick and everyone,

I have already explained to LEED that the proposed energy model has no error messages, no unmet hour issues and showed them the BEPS and PV-A reports.

Maybe if I printed out all the other PV reports that show the ground loop and ground pump part load performance and point out that the ground loop never reaches 100% part load and the pump only reaches 100% part load for 1 hour? Maybe I could generate the custom report for the ground loop temperatures and attach all this information to the exceptional calculation block?

The problem is, I am not sure adding more reports fits with their demand for either a modeled boiler or an exceptional calculation.

So back to the first question- does anyone know how to attach a boiler to a HP Water Loop that also has a ground loop HX and run the model successfully?

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If you start your system in DD wizard and make it a ground source heat pump your air side system should end up being a PVVT. You can create a separate heating loop with the boilers and then in the air side system go to the heating tab-> Supp heat/defrost tab then add the supplemental heat source as your boiler loop then set your max-hp-t to the outdoor temp you want your boilers to start. Have not personally done this but see post http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/2010-February/003399.html

Thanks,
Matthew J. Baron

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eQUEST itself states that ground-loop heat-exchangers can't be integrated with boilers in the DOE-2 help file "Ground-Loop Heat-Exchangers and Fluid Coolers in parallel on WLHP loops"

Also see:

http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/2010-May/004306.html

Best,
Amalia

Amalia Hicks PhD, LEED GA
Sustainability Consultant | ahicks@sustaineng.com
901 Deming Way, Ste. 201
Madison, WI 53717
608.836.4488 ext. 22| Fax: 608.836.4477
www.sustaineng.com

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I think part of the problem is that the reviewer is wondering if the ground loop is designed to be sufficient during all seasons, why is the project putting in a backup boiler?

If you can explain the motivation of the owner to include a boiler that isn't needed to meet the load, it might help the GBCI understand why you don't need to model it.

Maybe the owner wants to be able to service the ground loop pumps/piping while maintaining heating in the building and the emergency generator can only carry the building pump, not the ground loop pump. Maybe there is a local requirement due to the occupancy to have an alternate fuel source installed, etc.

If the design team and/or commissioning authority has any documentation included within the owner's project requirements or basis of design describing a redundant boiler it might help.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

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Sorry, I didn't mean to suggest there's a definite/easy/established procedure earlier.

Something I've seen pop up before is that you can "fake" a GLHX loop booster boiler's effects with a scheduled process load on the loop. In effect, if you can establish an annual schedule of operation by spoon-feeding the boiler's contributions. In coming up with that schedule, you would have to assess when the loop isn't keeping up, so you're back full circle to making that assessment one way or the other.

Note such consumptions added as loop process loads will fall into the "misc" enduse category if/when you need to document for LEED, if you should choose this path.

Gotta catch a meeting - hope you can come to a quick resolution!

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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Kathryn:

You can add Process/DHW loads to your WLHP as Mbtu/h.? The schedule needs to be a fraction so you can't maintain a certain loop temperature, just a fraction of the Mbut/h per hour based on time of year..? I did one project where I need to add heat to the loop and I wrote a summer/winter schedule.? The boiler/Process Load was off during the summer and I adjusted the winter fractions to eliminate loop errors.

This job was in Boston.? I ended up with a summer schedule starting April 15 (no aux heat) until December 31, when the fractional schedule kicked in until April 14.

?
Paul Diglio

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Hi I recently went thru this too.

If you go through the usual steps to create a GCHP loop, do these steps next:

- Create a hot water loop (and leave it as primary)

- Go back to the GCHP loop and call it secondary

- After doing so close out of that loop and go back into it and indicate that the primary loop is the HW loop

- Create a boiler and put it on the HW loop

- After this you have 2 options:

1) Use equipment controls/load management and flag schedules to allow one loop to be on and the other off seasonally as you see necessary

2) Create an availability schedule in the loop's control tab for the HW loop to suggest a high degree of diversity or off seasonally as mentioned

I prefer step 2 above and I know there are some issues when you don't have a tower, like below, but I've made it work previously.

[cid:image001.jpg at 01CE99D1.D7ACBE40]

MATTHEW HIGGINS
CEM, ASHRAE-HBDP, LEED-AP (BD+C)

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Bill found some issues in the PS-H with this methodology (Thanks Bill!). I'm going to look at it again and may be able to provide some more feedback. I should have noted that the availability schedules don't get around your problem, they just allow for that equipment to be on the loop and unused/sparingly-used.

MATTHEW HIGGINS
CEM, ASHRAE-HBDP, LEED-AP (BD+C)

Matthew W. Higgins's picture
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Thanks so much for trying this out. I was looking at it last night and
realized the same thing. What we really need is to have the ground loop
primary, the boiler secondary, and activate the boiler when the loop
drops below a temperature or maybe when the ground loop HX exceeds its
ability to provide heat. Thanks again.

Kathryn Kerns

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