Chilled Water Modeling - Secondary Condenser Water Loops

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Hi Everyone,

I am having difficulty setting up this part of my model & looking for some direction. Pls be forgiving as I?ve never seen this design before (likely very common though!). I?ve attached the chilled water schematic.

This hospital has a modular chiller (CH-1,2,3) that serves the bldg?s cooling needs with the exception of the AHUs. I?m good on that side of things.

On the condenser side, a secondary condenser loop serves terminal reheat and there are also dry coolers that serve the condenser loop. First off, just want to confirm I know how this system works. Please correct me if I?m wrong.

So the chiller is working to provide cooling to the bldg. On the condenser side, one secondary loop provides reheat as required. The dry coolers provide additional cooling to this loop as required. Is it as simple as this? Please provide any or all insight that you can!

If I am correct on how this system works ? if so, any suggestions on how do I model it? It does not look like I can add two secondary condenser loops attached to a chiller.

Thanks!
Darryl Kasun

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Hi David - thank you for the reply! Again I have very little experience
with these systems so far so please bare with me!

I went through the heating schematic and there are a lot of reheat coils
this loop serves. I don't know how to hook up this heating demand to the
condenser water loop and maybe that's not directly possible in eQuest?? If
I add up the heating load, I guess I'll have to make some assumption as to
what that load will be and what it's schedule would be. Is that what you
meant?

Now regarding the dry cooler, looks like that loop doesn't activate until
entering condenser water temp hits 100 degF. Any thoughts on how to model
this?

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Fun stuff - You didn?t even mention the snow melt!

What novel/nifty/weird here is that the CW loop is also the terminal reheat heating loop (Note: condenser temps are boosted up with steam HX?s ? critical point), before coming back to hit the dry coolers tasked with bringing things down to within reason for the chillers? ECT. To my own terminology? I might consider your chillers ?preheat? for your steam HHW reheat loop.

As an aside, this is NOT common to my personal design experience and I wouldn?t feel shy about sharing that with the designers to open up a conversation and be sure everyone is on the same page. Even if this is standard practice in your region/company, it never hurts to review the intent and function of the mechanical design with those putting it together & simulating performance. You might both learn something!

There are a number of hard stops bounding this problem for doe2/eQUEST. Airside reheat coils can only be assigned to circulation loops of type HW and PIPE-2. From context and a few more clues in the diagram, I suspect you have a bunch of simultaneous heating/cooling to deal with, so 2-pipe is probably out of the running (can only deliver heating or cooling any given hour, and has lots of other attachment limitations regardless).

I toyed in a dummy model with a possibility for re-purposing a GLHX of type ?Lake/Well? to force-feed a ?return from the reheat? temperature profile to the dry coolers on a CW loop ? but some piece of that Frankenstein?s monster (when I gave it a temperature schedule of straight 140?s) resulted in negative cooling consumption in the outputs? Here?s a picture if anyone is interested in carrying that ball further ? it might actually work if you built this from scratch:

Now I?m going to do something VERY WEIRD from my typical contributions here on [eQUEST-users]: Frankly, this may be a case where eQUEST/doe2 simply isn?t a workable platform. I?m really stretching my brain here and having trouble coming up with something that wouldn?t involve a very complex set of intermediate and post-simulation output processing assumptions?

How bad would it be to suggest no simultaneous heating/cooling? That could open up some doors for specific circulation loops & plant equipment? I gather however you probably have a bunch of cooling+heating happening from clues in the shared sequencing.

The only other hypothetical path I might consider is some odd approximation using LOOP-TO-LOOP-HP chillers? but then my brain starts to hurt?

I?d be very interested to hear if anyone else would come to a different conclusion!

~Nick

Nick Caton, P.E.

Senior Energy Engineer
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
E nicholas.caton at schneider-electric.com
F 913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

Nick Caton, P.E.

Senior Energy Engineer
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
E nicholas.caton at schneider-electric.com
F 913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

As Nick pointed out, I don?t think eQUEST can model this particular case without some intermediate processing or post-processing.
My first idea would be to try to model loads on the condenser water loop to simulate the real terminal reheat return temperature (right before it goes to the dry cooler exchangers). That way the dry cooler would see the real load.

Here?s my take on the problem:

1- Model the reheat coils on its own hot water loop and plus a steam meter to it, along with a dummy pump. Now I?m not sure if the flow going into the coils is variable or constant.. the loop?s pumps have VFD but it seems like the reheat coils have a bypass with a 3-way valve (so constant gpm flow?). Either way can be modelled but it?s important to model to right case.

2- Look up the supply temperature of the steam heat exchanger feeding the terminal reheat coils (i.e. 120 F).

3- Here?s the intermediate processing step (on an hourly basis):

a. Using the terminal reheat load (1), the actual loop?s flow and the steam exchanger supply temperature (2), calculate the global return temperature of the loop after the reheat coils. (A)

b. Using the actual condenser leaving temperature and the actual flow, calculate the energy required to increase the condenser leaving temperature to the steam exchanger supply temperature (2). (B)

c. Calculate the energy required to bring the actual condenser leaving temperature to the calculated (A) global return temperature of the loop after the reheat coils. (C)

d. Using EMIT, create an hourly load schedule for (B) and (C).

4- Plug the load schedule (C) on the condenser water loop as process load.

5- Plug the load schedule (B) on the steam loop.

If all goes well, step (4) should simulate the real terminal reheat return temperature so that the dry coolers see the real load and step (5) should get you your real steam demand for the terminal reheat.

All in all this strategy requires intermediate processing but no post-processing. It?s not too complicated either but you?ll need to update the 2 hourly schedules every time you make a change to the model.
That is unless I missed something.. it happens to all of us sometimes! Don?t hesitate to comment/edit the strategy if that?s the case.

[Bouthillette Parizeau]

Patrick Lapierre_ing.
plapierre at bpa.ca

De : Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] De la part de via Equest-users
Envoy? : 16 ao?t 2016 18:24
? : darryl.kasun at gmail.com; DEldridge at grummanbutkus.com
Cc : equest-users at lists.onebuilding.org
Objet : Re: [Equest-users] Chilled Water Modeling - Secondary CondenserWater Loops

Fun stuff - You didn?t even mention the snow melt!

What novel/nifty/weird here is that the CW loop is also the terminal reheat heating loop (Note: condenser temps are boosted up with steam HX?s ? critical point), before coming back to hit the dry coolers tasked with bringing things down to within reason for the chillers? ECT. To my own terminology? I might consider your chillers ?preheat? for your steam HHW reheat loop.

As an aside, this is NOT common to my personal design experience and I wouldn?t feel shy about sharing that with the designers to open up a conversation and be sure everyone is on the same page. Even if this is standard practice in your region/company, it never hurts to review the intent and function of the mechanical design with those putting it together & simulating performance. You might both learn something!

There are a number of hard stops bounding this problem for doe2/eQUEST. Airside reheat coils can only be assigned to circulation loops of type HW and PIPE-2. From context and a few more clues in the diagram, I suspect you have a bunch of simultaneous heating/cooling to deal with, so 2-pipe is probably out of the running (can only deliver heating or cooling any given hour, and has lots of other attachment limitations regardless).

I toyed in a dummy model with a possibility for re-purposing a GLHX of type ?Lake/Well? to force-feed a ?return from the reheat? temperature profile to the dry coolers on a CW loop ? but some piece of that Frankenstein?s monster (when I gave it a temperature schedule of straight 140?s) resulted in negative cooling consumption in the outputs? Here?s a picture if anyone is interested in carrying that ball further ? it might actually work if you built this from scratch:
[cid:image002.jpg at 01D1F857.60111330]

Now I?m going to do something VERY WEIRD from my typical contributions here on [eQUEST-users]: Frankly, this may be a case where eQUEST/doe2 simply isn?t a workable platform. I?m really stretching my brain here and having trouble coming up with something that wouldn?t involve a very complex set of intermediate and post-simulation output processing assumptions?

How bad would it be to suggest no simultaneous heating/cooling? That could open up some doors for specific circulation loops & plant equipment? I gather however you probably have a bunch of cooling+heating happening from clues in the shared sequencing.

The only other hypothetical path I might consider is some odd approximation using LOOP-TO-LOOP-HP chillers? but then my brain starts to hurt?

I?d be very interested to hear if anyone else would come to a different conclusion!

~Nick

[cid:image003.png at 01D1F857.60111330]
Nick Caton, P.E.
Senior Energy Engineer
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
E nicholas.caton at schneider-electric.com
F 913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image001.png at 01D189AB.58634A10]

[cid:image003.png at 01D1F857.60111330]
Nick Caton, P.E.
Senior Energy Engineer
Energy and Sustainability Services
Schneider Electric

D 913.564.6361
M 785.410.3317
E nicholas.caton at schneider-electric.com
F 913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image001.png at 01D189AB.58634A10]

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Clever! ?I really like the idea of dumping a process load onto the CW loop, and am curious how this might report as an enduse. ?This would result in appropriate loop temps for the coolers and chillers, but be mindful in output post processing to not double count the artificial "process" energies.

Also I could see your intermediate processing growing more complex if considering reheat temperature resets and/or seasonal HX bypass... ?I would want to quiz the designer(s) thoroughly to ensure nothing like this that would affect my calculations is missed. ?

Keep us posted - you might yet be covering new ground with this project!

~Nick

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Thank you very much Nick and Patrick for your responses!

So I've gone thru the steps suggested by Pat. I've attached a little
diagram to help me figure this out. Again, my experience with hydronic
systems is limited so just let me know if I'm missing something.

I am good with formulas (A) & (B) but am having a tougher time with (C).

Pat you wrote "Calculate the energy required to bring the actual condenser
leaving temperature to the calculated (A) global return temperature of the
loop after the reheat coils. (C)".

Is it possible that instead of actual condenser *leaving* temperature you
meant actual condenser *entering* temperature? That seems to make sense to
me, but again I could be missing something.

I've also attached the heating and chilled water flow diagrams if anyone is
interested.

Thanks again for your help everyone!
Darryl Kasun

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

It?s a pleasure to help. I?m always greatful when the community solves one of my problems so it?s only natural to help out in turn.

The idea with the load (C) as I described it below is that once you plug it as a process load on the condenser water loop, it will change the condenser water loop temperature entering the dry coolers.
In the schematic you?ve drawn, what you want to calculate is Qc = 500*GPMscnd1/2*(T3-T1) and add that load to the condenser water loop.
In other words, you want the condenser leaving temperature calculated by eQUEST to become T3 instead of T1. For that to happen, you plug Qc on the condenser water loop. That way, the flow going to the dry coolers heat exchanger will be at the right temperature.

As Nick mentioned also, be mindful that plugging a load on a loop as process load will be reported as an endues (in the misc equip category I believe.. not 100% sure on this). You?ll need to manually subtract it from your results.

Don?t hesitate if something?s still fuzzy.

[Bouthillette Parizeau]

Patrick Lapierre_ing.
plapierre at bpa.ca

De : Darryl Kasun [mailto:darryl.kasun at gmail.com]
Envoy? : 17 ao?t 2016 18:02
? : Nicholas Caton
Cc : Lapierre, Patrick
; equest
Objet : Re: [Equest-users] TR: Chilled Water Modeling - SecondaryCondenserWater Loops

Thank you very much Nick and Patrick for your responses!

So I've gone thru the steps suggested by Pat. I've attached a little diagram to help me figure this out. Again, my experience with hydronic systems is limited so just let me know if I'm missing something.

I am good with formulas (A) & (B) but am having a tougher time with (C).

Pat you wrote "Calculate the energy required to bring the actual condenser leaving temperature to the calculated (A) global return temperature of the loop after the reheat coils. (C)".

Is it possible that instead of actual condenser leaving temperature you meant actual condenser entering temperature? That seems to make sense to me, but again I could be missing something.

I've also attached the heating and chilled water flow diagrams if anyone is interested.

Thanks again for your help everyone!
Darryl Kasun

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Darryl, I made a quick test to figure out about how the process load on the condenser loop reports as a endues and it seems like it does not report at all.
I?m quite surprised but it?s the result I got? In any case, just double check to make sure the artificial process load (C) doesn?t get counted in your results.

[Bouthillette Parizeau]

Patrick Lapierre_ing.
plapierre at bpa.ca

De : Darryl Kasun [mailto:darryl.kasun at gmail.com]
Envoy? : 17 ao?t 2016 18:02
? : Nicholas Caton
Cc : Lapierre, Patrick
; equest
Objet : Re: [Equest-users] TR: Chilled Water Modeling - SecondaryCondenserWater Loops

Thank you very much Nick and Patrick for your responses!

So I've gone thru the steps suggested by Pat. I've attached a little diagram to help me figure this out. Again, my experience with hydronic systems is limited so just let me know if I'm missing something.

I am good with formulas (A) & (B) but am having a tougher time with (C).

Pat you wrote "Calculate the energy required to bring the actual condenser leaving temperature to the calculated (A) global return temperature of the loop after the reheat coils. (C)".

Is it possible that instead of actual condenser leaving temperature you meant actual condenser entering temperature? That seems to make sense to me, but again I could be missing something.

I've also attached the heating and chilled water flow diagrams if anyone is interested.

Thanks again for your help everyone!
Darryl Kasun

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

I also did a test. Add a positive process load to the condenser loop increases the heat rejection energy ? the process load itself is not reported as misc. energy ? as expected. In the case of the condenser loop serving the reheat coil loop, you would need to enter a negative process load to reduce the cooling tower load/energy. Unfortunately, Equest/DOE22 thinks it is smarter than you so it changes the sign of the load to positive if you enter a negative load. Therefore, this idea won?t fly.

Christopher Jones, P. Eng.
Rowan Williams Davies & Irwin Inc.
Consulting Engineers & Scientists
901 King Street West, Suite 400, Toronto, Ontario, M5V 3H5
T: (519) 823-1311 ext 2052
M: (416) 697-0056

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Well, I guess from a logical point of vue, a negative load on the condenser water loop doesn?t make much sense.. can?t really blame eQUEST on this I guess.
At this point the only way I see left is to post-process all that?s happening on the condenser water side.. which is not really ideal.

[Bouthillette Parizeau]

Patrick Lapierre_ing.
plapierre at bpa.ca

De : Chris Jones [mailto:Christopher.Jones at RWDI.com]
Envoy? : 18 ao?t 2016 09:03
? : Lapierre, Patrick
; Darryl Kasun ; Nicholas Caton
Objet : RE: [Equest-users] TR: Chilled Water Modeling - SecondaryCondenserWater Loops

I also did a test. Add a positive process load to the condenser loop increases the heat rejection energy ? the process load itself is not reported as misc. energy ? as expected. In the case of the condenser loop serving the reheat coil loop, you would need to enter a negative process load to reduce the cooling tower load/energy. Unfortunately, Equest/DOE22 thinks it is smarter than you so it changes the sign of the load to positive if you enter a negative load. Therefore, this idea won?t fly.

Christopher Jones, P. Eng.
Rowan Williams Davies & Irwin Inc.
Consulting Engineers & Scientists
901 King Street West, Suite 400, Toronto, Ontario, M5V 3H5
T: (519) 823-1311 ext 2052
M: (416) 697-0056

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

If this approach is reasonable, the CW loop can perhaps be defined as a WWHP loop, and then it will accept a scheduled process ?heating? load.

A ?virtual? boiler might need to be added to that loop make it work, but if your loads are reasonable then it shouldn?t activate, or maybe you want it to activate to ?simulate? this series or seasonal steam heat. I?m not sure if there would be other ?side effects.?

And then there is also the heat-recovery chiller option. The CW and HW loops won?t be the same, but perhaps it might better represent the action better, and will certainly allow supplementary heating of the reheat/etc. loop based on some criteria, though perhaps not the exact criteria in the real building.

Good Luck,
Fred
Fred Porter, BEMP, LEED? AP
Principal Engineer
Sustainability Services
NORESCO

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Anonymous
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Joined: 2016-07-15
Reputation: 400

Darryl,

I?ve been following this thread and the configuration described by your colleague makes a lot more sense to me. I can understand the initial confusion because the heat rejection side of the heat recovery chiller acts as the condenser, but also as the heating source for the terminal unit reheat.

We do a lot of HRC models, so I just wanted to throw in a few words of advice:

? Make sure that the Max Recovery T is compatible with the supply temperature of your hot water loop. For example, if the max recovery T is only 100?F, but your hot water loop is configured to supply 180?F water with a 40?F delta, you will never recover any heat from the HRC in the model. We?ve done multi-stack projects with recovery temps up to 140?F, have not gone higher than this. The hot water system needs to be designed to be able to make use of this heat. It?s especially beneficial in this case to have a hot water reset schedule that lowers the supply temp during milder outdoor temperatures, as the HRC will get more efficient the lower the recovery temp is.

? Do you have standard, non-heat-recovering chillers on this project as well? If so, you?ll need to pay special attention to the equipment control (EQUIP-CTRL) sequences in your model, to make sure you prioritize the HRCs when there is a heating load.

? Do you have condenser relief on the HRCs? This is an option on multi-stacks. If you don?t have condenser relief, you?ll need to pay even more attention to the EQUIP-CTRL sequences. To my knowledge, eQUEST can?t model HRCs without condenser relief, but you can make more detailed control sequences to limit relief in the model.

Thanks,

Coles Jennings, PE, BEMP, LEED AP BD+C
Sr. Energy Engineer, Building Sciences Manager | Mason & Hanger (formerly Hankins & Anderson)
A Day & Zimmermann Company
D 804.521.7045 | O 804.285.4171 | F 804.217.8520
4880 Sadler Road, Suite 300 | Glen Allen, VA 23060
ha-inc.com (soon to be masonandhanger.com)
We do what we say.?

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400
via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Darryl,

Max Recovery T is the maximum temperature at which the HRC can contribute heat to the system. In the situation you described below, you can set this to 110 and rest assured that all available heat from the HRC can be recovered to the HWS loop.

Condenser relief indicates how the balance of heat is handled. For the majority of the year there will be an imbalance between the heating load and cooling load in the building, so the load needs to be balanced (either via air-cooled or water-cooled condenser). Let?s say on a mild day, you have 2x building cooling load as compared to the heating load. If you only have an HRC supplying chilled water for the cooling load, it?s going to be generating more than twice the heat you need to meet your heating load (more than twice because the compressor heat is also contributing to the heat available to the condenser). So you need somewhere for this extra heat to go, which is what condenser relief accomplishes. Multi-stack makes HRCs that have air-cooled condenser relief, or water-cooled condenser relief which would have six piping connections (two for chilled water, two for hot water, and two for condenser water to relieve the balance of heat).

If you don?t have any other chillers attached to this cooling system, my strong hunch is that you do have condenser relief. I would check the equipment schedules to confirm, or best case if you have a cut-sheet it should be clearly indicated.

Luckily eQUEST models condenser relief fairly readily. It?s when you don?t have it that things get tricky.

FYI the relief valves noted in the spec excerpt you sent are for pressure relief (e.g. safety valve). Different type of relief.

Thanks,

Coles Jennings, PE, BEMP, LEED AP BD+C
Sr. Energy Engineer, Building Sciences Manager | Mason & Hanger (formerly Hankins & Anderson)
A Day & Zimmermann Company
D 804.521.7045 | O 804.285.4171 | F 804.217.8520
4880 Sadler Road, Suite 300 | Glen Allen, VA 23060
ha-inc.com (soon to be masonandhanger.com)
We do what we say.?

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Hi Coles,

So I'm good on the Max Recover T now.

I have not found anything that would indicate that the HRCs have condenser
relief. There are dry coolers on the condenser side of the HRCs that
operate when entering condenser water temperature is above 100 degF (design
entering water temps of the HRC). The dry coolers would take provide the
function of a condenser relief correct?

Thanks
Darryl

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Darryl,

I agree the dry coolers will provide the function of condenser relief, though I haven?t seen condenser relief accomplished this way before. I?m used to seeing either a completely separate condenser water loop, or an air-cooled condenser for relief. As such, I can?t speak from direct experience as to the best modeling approach. My initial thought is that you would still model a water-cooled HRC, which requires a separate condenser water loop, and assign the dry-coolers to the condenser water loop. This is an approximation, but the closest readily available that I can think of.

Thanks,

Coles Jennings, PE, BEMP, LEED AP BD+C
Sr. Energy Engineer, Building Sciences Manager | Mason & Hanger (formerly Hankins & Anderson)
A Day & Zimmermann Company
D 804.521.7045 | O 804.285.4171 | F 804.217.8520
4880 Sadler Road, Suite 300 | Glen Allen, VA 23060
ha-inc.com (soon to be masonandhanger.com)
We do what we say.?

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400