[Equest-users] DOAS in baseline

Nick Caton ncaton at smithboucher.com
Thu Jan 27 12:21:01 PST 2011


Paul,

 

I agree – using a dummy zone approach but without using OA-FROM-SYSTEM is probably inadvisable and difficult at best… certainly not preferable – I was drawn to attempt this once where circumstances prevented me from using OA-FROM-SYSTEM.  

 

I haven’t considered this particular approach in a long while (and hope to not have to), but here’s a few suggestions if you or others are trying to tweak/correct this approach and are encountering those issues listed:

1.       Dummy space volume can be adjusted, and a dummy zone (in my mind) should have zero heat transfer – deleting the offending space surfaces may do the trick ;).

2.       The system exhaust at the ERV components should match the return air stream temperature – perhaps add an internal load using the fractional schedule used for ventilation (remember this isn’t using OA-FROM-SYSTEM) and assigned to a dummy meter (free) to bump the RA into the right range?

3.       ERV-FAN-KW-FFLOW produces a figure that considers both the system’s MIN-OUTSIDE-AIR ratio and the hourly ventilation flow.  It’s possible the hourly flows (re: ventilation schedule), MIN-OUTSIDE-AIR ratio and/or the fan curve used may be throwing the hourly expected power draw off… you’d have to investigate further.

4.       This point – achieving the correct hourly ventilation requirement -  is why in the end, this method avoiding OA-FROM-SYSTEM is such a pain to construct and document.  

 

I also hope DOE2/eQuest may someday have a “parent DOAS” option for airside systems… I’m not privy to exactly how development is funded, but I speculate this issue might fall into the category of “a really big R&D windfall needs to navigate through the state of California.”  (i.e. not anytime soon <http://gov.ca.gov/news.php?id=16872> )

 

~Nick

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Thursday, January 27, 2011 1:31 PM
To: Nick Caton; Susan F; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] DOAS in baseline

 

Nick:

The problems I have experienced with using a dummy zone, without OA From Units, for the DOAS, as confirmed by different hourly reports I input are as follows:
1.    The dummy zone does not equal the size of the conditioned space served and heat loss/gain is not accurate.
2.    The return air temperature is not indicative of what is being returned to the DOAS when a ERV is used.
3.    The fan kW of a variable speed DOAS does not track correctly.
4.    The dummy zone occupancy level and schedule do not equal that of all the systems served.

When using an OA From System, if the system served is not running, eQuest assumes no outside air is being supplied.  The designer needs to specify OA isolation dampers on the systems served.

I recently modeled two projects with DOAS that was conditioning one zone (Corridors) and supplying ventilation air to the other systems.  This design results in more accurate modeling, a dummy zone is not needed, but the same problem of incorrect return air temperatures for an ERV, since only the heat loss or gain from the corridor is included.

DOAS is becoming more and more popular, due in large part to LEED 62.1 requirements, and hopefully the eQuest developers will refine the program to accurately model this system

Paul Diglio

 

________________________________

From: Nick Caton <ncaton at smithboucher.com>
To: Paul Diglio <paul.diglio at sbcglobal.net>; Susan F <modelsenergy at gmail.com>; equest-users at lists.onebuilding.org
Sent: Thu, January 27, 2011 10:55:07 AM
Subject: RE: [Equest-users] DOAS in baseline

Hi Paul!

 

1.       You could specify the DOAS as part of the systems it’s serving (breaking out the fan energies/ERV components/preconditioning and so forth), then the OA and scheduling specified at the zonal level carries through.

2.       If the DOAS has preconditioning/ERV elements maintaining specific temperature setpoints, then those could be specified at the systems being served.  This may not be technically feasible for every system type.

 

I’ve used both approaches in the past: OA-FROM-SYSTEM using dummy zone(s) and integrating DOAS/ERV into the proposed systems served.  I believe both are viable approaches, with the first benefiting from more nuanced control over system behavior (fans, specifically), and the latter being much easier/simpler to set up and troubleshoot.

 

~Nick

 



 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Thursday, January 27, 2011 9:41 AM
To: Nick Caton; Susan F; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] DOAS in baseline

 

Nick:

 

If you do not use the OA From System how will eQuest calculate the CFM required by varying occupancy?  In addition, since the DOAS system might not provide the supply air temperatures required eQuest will not correctly calculate the energy required to condition the OA.

 

Paul Diglio

 

________________________________

From: Nick Caton <ncaton at smithboucher.com>
To: Susan F <modelsenergy at gmail.com>; equest-users at lists.onebuilding.org
Sent: Thu, January 27, 2011 10:21:55 AM
Subject: Re: [Equest-users] DOAS in baseline

Hi Susan!

 

Whether or not a baseline model gets a separate system for a proposed design featuring a DOAS is dependent on a few things, including how you decided to approach modeling the DOAS in the proposed model.

 

-          A clarification first:  Type and quantity of baseline systems is determined first and foremost per Appendix G.3.1.1.  You generally have either one system per floor or one system per zone, depending on the system type.  You never start with “one system per proposed system” except by coincidence.

-          If you use a dummy zone approach (not integrating the DOAS into the proposed systems), and you have one baseline system serving only the dummy zone per G.3.1.1 (or its exceptions), and you have specified the ventilation requirements at that dummy zone (not indirectly from the actual zones - using OA-FROM-SYSTEM for the proposed systems)… then you’ll end up with a distinct baseline system handling the ventilation requirements analogous to the proposed DOAS.  

-          In many/most cases (partially dependant on your preferred strategy for handling DOAS’s in your proposed models), you will not have a dedicated baseline system handling the ventilation air.  That’s okay.

 

~Nick

 



 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Susan F
Sent: Thursday, January 27, 2011 6:11 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] DOAS in baseline

 

This is not exactly an eQUEST question but y'all have been so helpful in the past so I'm hoping you can help here too.  I'm looking for a little clarification.  It was my understanding if you had a DOAS system that heated and cooled the outside air before delivering it to the floor mechanical room to be combined with return air and further conditioned by the AHU in your Proposed building that this system would NOT be modeled separately in the Baseline.  I cannot find anything in 90.1 that would regulate the DOAS system and I'm not sure how you would model it.  (I understand the dummy zone concept for modeling DOAS but not sure that would apply to the Baseline.)

Should it be separate system in the Baseline and would it be VAV or constant volume?  And if it is a separate system what section of 90.1 would you reference for this?


Thanks in advance.

Nick:

 

 

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