[Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

[Nathan Miller]

Many of the projects I model have 100% outside air corridor units that only deliver tempered air (60-70 degrees, year round. It is easy to check the total annual heating energy (or cooling I suppose, but I primarily do work in heating driven climates) of the system against a bin-calc.

I’ve found that when I give system t-stat control to one of the corridors, the amount of annual heating energy comes up way short. Seems to be some combination of heat gain from the adjacent spaces (fully conditioned) and lighting gains, etc. Additionally when I check the hourly reports, I can see that the supply air temperature is bouncing around, even if I’ve specified max and min supply temps, etc. When I use the dummy-zone approach, my total annual heating use pretty much lines right up with my bin calcs, and I can verify in the hourly reports that SAT stays right where I want it.

Nathan Miller, PE, LEED AP BD+C – Mechanical Engineer/Senior Energy Analyst
RUSHING | D 206-788-4577 | O 206-285-7100
www.rushingco.com<http://www.rushingco.com/>

From: Bishop, Bill [mailto:bbishop at pathfinder-ea.com]
Sent: Monday, December 08, 2014 11:40 AM
To: Julien Marrec
Cc: Nathan Miller; Nicholas Caton; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

I honestly don’t know, which is why I asked. I have never needed to use a dummy zone, but am always open to the possibility that it is a useful workaround for (something). I’ll check out the video.
Thanks,
Bill

From: Julien Marrec [mailto:julien.marrec at gmail.com]
Sent: Monday, December 08, 2014 11:33 AM
To: Bishop, Bill
Cc: Nathan Miller; Nicholas Caton; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

I'm in no way an expert here, otherwise I wouldn't be asking for help.

But I don't think it does anything you can't do otherwise. Last time I switched between a PVAVS and PSZ and was able to recreate the same results (PSZ with dummy zone, and PVAVS with some more complex steps to set discharge temp correctly. The PVAVS solution is more flexible though).

It's just easy to use a dummy zone, it's what comes up mostly when searching for "equest" and "doas" keywords, and there's even a tutorial video<http://energy-models.com/make-air-equest>.
Do you think differently Bill?


--
Julien Marrec, EBCP, BPI MFBA
Energy&Sustainability Engineer
T: +33 6 95 14 42 13

LinkedIn (en) : www.linkedin.com/in/julienmarrec<http://www.linkedin.com/in/julienmarrec>
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr<http://www.linkedin.com/in/julienmarrec/fr>

2014-12-08 17:16 GMT+01:00 Bishop, Bill <bbishop at pathfinder-ea.com<mailto:bbishop at pathfinder-ea.com>>:
How does using a dummy zone give you extra capability and/or accuracy modeling discharge air temperature control, and how is the simulated energy consumption more accurate?
Thanks,
Bill

From: Julien Marrec [mailto:julien.marrec at gmail.com<mailto:julien.marrec at gmail.com>]
Sent: Monday, December 08, 2014 11:06 AM
To: Nathan Miller
Cc: Bishop, Bill; Nicholas Caton; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>

Subject: Re: [Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

Bill,
There is nothing fancy in my AHU. Just a fan and a coil. Always 100% outside air, the same amount of CFM (no economizer), and no return airflow. Discharge temperature is fixed (Tstat in discharge air stream is controlling a three way valve on the coil). The system doesn't know and doesn't care about what's happening in the space it serves.
As Nathan was saying, I was thinking about using a Dummy zone to control the discharge temp indeed, like I usually do with PSZ systems: you have to give it a control zone, and the dummy serves this purpose.
But as I'm trying to switch from VAVS to 2pipe FC right now, I realize this isn't the way it works with FC. I think I'll keep my VAVS solution for now. It seems too cumbersome to change it now and I'd have to attribute an outdoor air CFM numbers to all my zones served by the system.
Thanks all,
Julien

--
Julien Marrec, EBCP, BPI MFBA
Energy&Sustainability Engineer
T: +33 6 95 14 42 13<tel:%2B33%206%2095%2014%2042%2013>

LinkedIn (en) : www.linkedin.com/in/julienmarrec<http://www.linkedin.com/in/julienmarrec>
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr<http://www.linkedin.com/in/julienmarrec/fr>

2014-12-08 16:38 GMT+01:00 Nathan Miller <nathanm at rushingco.com<mailto:nathanm at rushingco.com>>:
I personally use dummy zones on corridor units when I’m trying to model a system that uses discharge air temperature control rather than one that responds to a thermostat in the corridor. On single zone systems with control given to a dummy zone (with no internal or envelope loads), you can force the system to discharge air with-in a specific temperature band year-round. Of course you then have to give the actual corridor spaces a t-stat schedule that is rather accommodating or else you might end up with lots of unmet load hours.
Nathan Miller, PE, LEED AP BD+C – Mechanical Engineer/Senior Energy Analyst
RUSHING | D 206-788-4577 | O 206-285-7100
www.rushingco.com<http://www.rushingco.com/>

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Bishop, Bill
Sent: Monday, December 08, 2014 10:28 AM
To: Julien Marrec; Nicholas Caton
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

Julien,
Why would you model this with a dummy zone? If your DOAS is only supplying the corridor, just model the corridors as separate zones and assign the DOAS system to them.
You didn’t say whether or not the DOAS has heat recovery. That will further dictate which system type you select. FC does not allow heat recovery, but VAVS and Single Zone Reheat do.
Regards,
Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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134 South Fitzhugh Street                 Rochester, NY 14608

T: (585) 698-1956                        F: (585) 325-6005

bbishop at pathfinder-ea.com<mailto:wbishop at pathfinder-ea.com>             www.pathfinder-ea.com<http://www.pathfinder-ea.com/>

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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Julien Marrec
Sent: Monday, December 08, 2014 9:58 AM
To: Nicholas Caton
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

Thanks for your message Nick.

I now have a 2-pipe loop with the SNAP-T, thanks for pointing it out.

David Elridge also wrote that I could just subsitute PSZ for a 2pipe FC.

I've got something working right now that is based on VAVS.

I have read the help file before posting.I understand there are many ways to skin a cat in eQuest, but I'm still confused what fundamental difference it would make between using a VAVS or using a 2pipe FC with a dummy zone. Aside from the fact that the dummy zone setup is easier to implement I guess... Is there a wrong way to do this? Or just a better way?
Thanks,
Julien

--
Julien Marrec, EBCP, BPI MFBA
Energy&Sustainability Engineer
T: +33 6 95 14 42 13<tel:%2B33%206%2095%2014%2042%2013>

LinkedIn (en) : www.linkedin.com/in/julienmarrec<http://www.linkedin.com/in/julienmarrec>
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr<http://www.linkedin.com/in/julienmarrec/fr>

2014-12-08 13:20 GMT+01:00 Nicholas Caton <ncaton at catonenergy.com<mailto:ncaton at catonenergy.com>>:
Hi Julien,

I think there are multiple options that could fit the criteria you’ve provided, more than one could work depending on circumstances of your project…

General advice for “what system should I use” queries follows.

1.       Ask a few questions of the system equipment/design:

-          How the actual system is controlled – is it constant volume with heating/cooling triggered via one space/duct thermostat only, or something more complex?

-          Do you have just one central fan or additional fans in each zone for independent circulation?

-          One set of central heating/cooling coils or are there separate reheat / cooling coils occurring at individual zones?

2.       QC your work:

-          Answer for yourself how the system’s fans/cooling/heating should operate, and when/to what degree ventilation OA is delivered

-          After initially setting up your systems/zones (or perhaps the first set of many), perform some test runs to QC your efforts

-          Verify each intended behavior/output via hourly reporting

Considering you can generally force 100% OA and constant volume  with system and/or zonal minimum OA/flow ratio inputs, as appropriate, peruse the help file diagrams for systems of interest that include features of interest.  You probably want to consider/review the articles for FC, VAVS, and PIU.

From your coil description, you may further consider an airside system type to leverage a 2-pipe loop set to an outdoor snap temperature (or perhaps a seasonal schedule) – see the operation tab under the loop in detailed edits.

Hope that helps get you started!

~Nick

NICK CATON, P.E.
Owner

Caton Energy Consulting
  1150 N. 192nd St., #4-202
  Shoreline, WA 98133
  office:  785.410.3317
www.catonenergy.com<http://www.catonenergy.com>

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Julien Marrec
Sent: Monday, December 08, 2014 3:29 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] How to model a DOAS serving corridors with a Chilled Water Coil

Hi,
I've got a building with a DOAS (AHU with 100% outside air) serving corridors (no reheat, no fan in there, just ventilation grilles). The DOAS has one coil, served by hot water in winter and cold water in summer.
There is no economizer, and the supply temperature is simply set by a thermostat set as 70°F year round.
I have modeled DOAS before but I was using a PSZ or a PVVT. Those have DX cooling coils, so it's not an option.
Seems like I could use MSZ or VAV for example, but I'm not sure which would be more appropriate.

What type of system do you recommend using in my case?
How would you control it in order to get the proper supply temperature (70°F) and avoid simultaneous heating and cooling (Is using an availability schedule the only option?)?


Also, if you have an .inp snippet I could use to set it up correctly, I'll greatly appreciate it!


Thanks,
Julien
--
Julien Marrec, EBCP, BPI MFBA
Energy&Sustainability Engineer
T: +33 6 95 14 42 13<tel:%2B33%206%2095%2014%2042%2013>

LinkedIn (en) : www.linkedin.com/in/julienmarrec<http://www.linkedin.com/in/julienmarrec>
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr<http://www.linkedin.com/in/julienmarrec/fr>



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