[Equest-users] DOAS Dummy Warnings - no problem?

[David Bastow]

I have used the DCV ventilation method with OA from the system and it
has worked great, as long as you have inputs in correctly under the zone
outside air & exhaust.  If you have inputs under the zone incorrectly
then the OA control on the system will be overridden by the inputs under
the zone.

Inputs in the model would be something like this to get it to work:

-Air side HVAC System under outdoor air - vent & economizer:
	-Under Min. outside air (ratio)- set at whatever, such as 0.10
for 10% OSA (if using an economizer the minimum must be set at least to
0.001, or the 		economizer feature will not work in the model).
	-Under Min. OA Method - I always use DCV Return Sensor.

-On each Zone under the system under Outside Air & Exhaust:
	-Under Outside Air Flow/Person - Input CFM required by code or
usually 15 to 20 CFM per person.
	-Under Outside Air Flow - Leave this blank.
	-Under Outside Air Changes - Leave this blank.
	-Under Outside Air/Flow/Area (CFM/FT2) - Normally I input 0.06
here, which is typically the amount required by the code.

As long as you have your hourly occupancy schedule set up correctly with
the % of the number of people that are in each zone then these inputs
have always worked for me.  The Outside Air entering the system will
vary down to as low as 0.06 CFM/FT2 of the area of the applicable zones
depending on how many people your occupancy schedule shows you have in
each of the applicable zones that you have under the HVAC air system.
The Outside air reduction will, of course, also always be limited by the
amount of exhaust CFM that you have input under the zone.  Be careful
with what you enter under the zone regarding the CFM of the ventilation
and the exhaust, as the program will always override what you enter
under the system by what you have entered under the zone.

David A. Bastow 
McClure Engineering, Inc.  
507 Main Avenue West
Post Office Box 1404
Twin Falls, Idaho   83303-1404
Web Site:  www.mcclure-engineering.com
 

-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of R B
Sent: Tuesday, March 23, 2010 5:20 AM
To: Nick Caton
Cc: Jacob Goodman; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] DOAS Dummy Warnings - no problem?

Question - 1: I believe that to be the case. What I had done ususally is
to use the DCV features and proportion the OA and related ERV, fans etc.
if any to the individual systems.

Question #1 - I have used this also but had run into some issue, but
cannot recollect whatthat was. It is a reasonable way to model. The
CO2 usually has a lag of 20-30 minutes, so you could shift your schedule
accordingly. But the DCV model in eQuest anyway does not consider the
lag - it is strictly number of people times the OA cfm required.

-Rohini
On 3/23/10, Nick Caton <ncaton at smithboucher.com> wrote:
> I am revisiting this model and never received a response, and I see 
> another has run into the same warnings.  Reposting/rephrasing for any
> suggestions/input:
>
>
>
> In hindsight perhaps I can phrase a simpler set of questions:
>
>
>
> 1.       True or False: Is it simply impossible in eQuest to
> simultaneously use OA-FROM-SYSTEM and either of the DCV ventilation 
> control methods with the same system.  This appears to be the case.
>
> 2.       Based on #1, I seem to be stuck being unable to modeling the
> savings from DCV at the zonal level (instead forced to use fraction of

> design or the like for my min-OA method)...
>
>
>
> But I've got a crazy idea:  For an alternative way to force DCV 
> behavior, might I define a set of MIN-AIR-SCHEDULE's, using the zonal 
> occupancy schedules as a template, and multiply each fractional 
> occupancy rate by the designed OA ratio?  This would be tied to an 
> assumption that the C02 levels rise and fall instantaneously with the 
> occupancy, which I know is not true but may be an acceptable 
> approximation given #1.
>
>
>
> Example:  A classroom has a daily schedule that looks like this (this 
> is for evening classes, if this looks odd):
>
>
>
> "General Classroom Occup Mon-Thu" = DAY-SCHEDULE-PD
>
>    TYPE             = FRACTION
>
>    VALUES           = ( 0, &D, &D, &D, &D, &D, 0.2, &D, &D, &D, &D,
&D,
> &D,
>
>          &D, &D, &D, 0.6, 1, &D, &D, &D, &D, 0.5, 0 )
>
>    ..
>
>
>
> With the design OA flow being 60% of the design Supply Air flow for 
> that terminal unit, I create a new MIN-AIR-SCHEDULE multiplying
through:
>
>
>
> "General Classroom MinAir Mon-Thu" = DAY-SCHEDULE-PD
>
>    TYPE             = FRACTION
>
>    VALUES           = ( 0, &D, &D, &D, &D, &D, 0.12, &D, &D, &D, &D,
&D,
> &D,
>
>          &D, &D, &D, 0.36, 0.60, &D, &D, &D, &D, 0.30, 0 )
>
>    ..
>
>
>
> For this approach I would tightly control the OA present at each zone 
> specifying MIN-OUTSIDE-AIR and clearing out the zonal-level OA inputs.
>
>
>
> For reference - The system I am trying to model is:
>
> *         Dedicated outside air unit - HW/CHW coils, enthalpy recovery
> wheel, variable supply which effectively sums the terminal fan coil's 
> call for OA over time.  Conditioned OA is supplied to VAV's which 
> modulate based on the terminal fan-coil's DCV sensor.
>
> *         Terminal units of widely varying size:  4-pipe HW/CHW coils
> which handle essentially all the internal/envelope loads, constant 
> volume, local thermostat controlled, conditioned OA from dedicated OA 
> units ties into supply ductwork (not seen by the terminal fan coil 
> units).  OA is modulated down to zero based on a CO2 sensor in return 
> path.
>
> For reference - I'm trying to model the above using:
>
> *         Single Zone Reheat (SZRH) for the DOAS, tied to a dummy zone
>
> *         4-pipe Fan Coil (FC) for the terminal units, system per
zone,
> OA-FROM-SYSTEM
>
>
>
> ~Nick
>
>
>
>
>
>
>
> NICK CATON, E.I.T.
>
> PROJECT ENGINEER
>
> 25501 west valley parkway
>
> olathe ks 66061
>
> direct 913 344.0036
>
> fax 913 345.0617
>
> Check out our new web-site @ www.smithboucher.com
>
>
>
>
>
> From: equest-users-bounces at lists.onebuilding.org
> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jacob

> Goodman
> Sent: Friday, December 18, 2009 3:24 PM
> To: equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] DOAS Dummy Warnings - no problem?
>
>
>
> I saw your question on the warnings from your DOAS model and didn't 
> see any replies. I have some of those same warnings.
>
>
> **WARNING*************************************************************
> **
> *******
>              EL1 Sys1 (PVVT) (G.SW1)          has a MIN-AIR-SCH,
> OA-CONTROL
>              other than FIXED and/or a MIN-OA-METHOD other than 
> FRACTION-OF-DESIGN
>              along with having a specified OA-FROM-SYSTEM. This may 
> cause incorrect
>              OA load/flow calculation for its OA-FROM-SYSTEM.
>
> Shows up for each zone the DOAS is supplying and so does:
>
>
>
> **WARNING*************************************************************
> **
> *******
>              SYSTEM EL1 Sys1 (PVVT) (T.C12)          has zero outside
> air for design calculations
>
> the second one seems normal since I put 0 cfm OA in the DD wiz before 
> I went to detailed edit mode, but I'm not sure about the first one.
>
> Hope your model turned out well, for both of our sakes.
>
> Thanks,
>
> --
>
> Jacob Goodman , LEED AP, Green Building Specialist
> v:509.747.2179  f:509.747.2186  i:www.lseng.com <http://www.lseng.com>

> L&S  Engineering Associates, Inc.
> 'High Performance Design'
>
>
>
>
>
> From: equest-users-bounces at lists.onebuilding.org
> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick 
> Caton
> Sent: Friday, September 25, 2009 2:58 PM
> To: equest-users at lists.onebuilding.org
> Subject: [Equest-users] DOAS Dummy Warnings - no problem?
>
>
>
> Hi everyone,
>
>
>
> I've got what I believe to be a working preliminary model of a DOAS 
> system.  I'm following the DOAS concept (prescribed by previous 
> archived
> discussions) of creating a "dummy zone/shell" to be served by the DOAS

> equipment.  All terminal units are tied to the DOAS via
OA-FROM-SYSTEM.
> My DOAS is based on the system type SZRH ("Single Zone Air Handler 
> with HW reheat").
>
>
>
> This DOAS is assigned to a 1ft-cube "dummy shell" with a single zone, 
> adiabatic ceiling/floor constructions, wall constructions of U=.0001, 
> and zeroed-out internal loads.  Conceptually, I believe the airflow 
> for the DOAS should be calculated as the hourly sum of all the 
> terminal unit's calculated OA needs.
>
>
>
> I've got three basic questions, presented in order of (perceived)
> difficulty:
>
>
>
> QUESTION 1)
>
> As I've set my "dummy" zone's walls to U=0.0001, and of physically 
> tiny dimensions, I don't think there's much to worry about regarding 
> heat gains/losses.  In the interest of doing the intuitively "right" 
> thing however, is there a way to set their "surface type" as adiabatic

> in the same way as roof and floor surfaces?  Is perhaps the cleanest 
> way to deal with all three to create "adiabatic" constructions, and if

> so how do you get around the error (see attached image) when you input
U=0?
>
>
>
> QUESTION 2)
>
> Every system (DOAS and terminal units) currently has the MIN-OA-METHOD

> set as FRACTION-OF-DESIGN, per the warning below.  In reality, the 
> hourly OA supplied by the DOAS will be calculated by summing what is 
> being called for by all of the terminal units, which will be based on 
> local DCV sensors in the return air path of each unit.  Unfortunately,

> setting any of the terminal units' MIN-OA-METHOD to the intuitive 
> DCV-RETURN-SENSOR results in the following warning (typical for each
> system):
>
>
>
> **WARNING*************************************************************
> **
> *******
>
>              EL1 Sys1 (FC) (G.N1)             has a MIN-AIR-SCH,
> OA-CONTROL
>
>              other than FIXED and/or a MIN-OA-METHOD other than 
> FRACTION-OF-DESIGN
>
>              along with having a specified OA-FROM-SYSTEM. This may 
> cause incorrect
>
>              OA load/flow calculation for its OA-FROM-SYSTEM.
>
>
>
> I've gathered that one approach to this problem is to manually define 
> the design airflow of the DOAS, based on summing the critical case of 
> OA required by digging through the reports (not sure where to begin 
> there), but is there any way of tricking eQuest into correctly summing

> the hourly OA CFM required by all terminal units tied to the DOAS, and

> then sizing the DOAS system based on that critical sum?
>
>
>
> QUESTION 3)
>
> The following are the remaining 3 warnings, all referring to this 
> "dummy zone:"
>
>
>
> **WARNING*************************************************************
> **
> *******
>
>              Zone: EL2 Zn (G.1)                     has a design
cooling
>
>              temperature differential of only  1.0F.  This
>
>              may result in an extremely large design airflow.
>
>
>
>
> **WARNING*************************************************************
> **
> *******
>
>              Zone: EL2 Zn (G.1)                     has a design
heating
>
>              temperature differential of only  -1.0F.  This
>
>              may result in an extremely large design airflow.
>
>
>
>
> **WARNING*************************************************************
> **
> *******
>
>              ZONE EL2 Zn (G.1)
>
>              might have insufficient heating capability.
>
>              Check that the SYSTEM or ZONE HEATING-CAPACITY plus this
>
>              ZONEs BASEBOARD-RATING is adequate to maintain the ZONE
>
>              specified DESIGN-HEAT-T for the calculated peak ZONE load
>
>              (see LS-A or LS-B for the ZONE peak load.)
>
>
>
> Which (if any) of these I should be addressing/evaluating, considering

> the modeling function of this "dummy zone?"  In other words, can I 
> ignore these and sleep well at night? =)
>
>
>
>
>
>
>
> NICK CATON, E.I.T.
>
> PROJECT ENGINEER
>
> 25501 west valley parkway
>
> olathe ks 66061
>
> direct 913 344.0036
>
> fax 913 345.0617
>
> Check out our new web-site @ www.smithboucher.com
>
>
>
>
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