[Equest-users] Can't get unmet hours under control for cooling

[Dana Etherington]

Jamie,

I ran into this same issue recently. You can use the same OA for all but set the 'ON' hours to -999. This will ignore the schedule for that hour and the zone calculations and inputs will control.


FRAC/DESIGN              accepts a value which is the fraction of the design quantity. Typical values range between 0.0 and 1.0. An entry of -999 causes the schedule to be ignored for that hour.

                                  For example, in the SYSTEM:MIN-AIR-SCH, an entry of 0 or 1 will force the outdoor-air ratio to be 0% or 100% respectively. A value of -999 will cause the schedule to be ignored for the hour, and the outdoor-air ratio will be set by other calculations.
Dana

Mr. Dana Etherington, E.I.T., LEED AP BD+C | CRB | One Kendall Square Ste B2202 | Cambridge, MA 02139
Main: 617-475-3050 | Direct: 617-475-3061 | Mobile: 617-583-3009 | Fax: 617-475-3052 | Ext: 6061
Email: dana.etherington at crbusa.com<mailto:dana.etherington at crbusa.com> | www.crbusa.com<http://www.crbusa.com/>
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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Armstrong, Jamie
Sent: Thursday, June 07, 2012 6:20 PM
To: Howe, Timothy; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Can't get unmet hours under control for cooling

In regards to OA for PSZ RTU's.

When allowing eQuest to autosize the airflow to each space if you set a ratio of OA to supply air whatever eQuest calculates the supply air needed for that space will vary the outside airflow.

If I enter the OA at the zone level to each space how do you set up a schedule for the OA?  Based on Timothy's answer I would need a different schedule for each RTU with its ratio of OA to supply air.  I wanted the MinOA schedule to be an on/off flag to deliver the OA that I put in at the zone level according to the occupied schedule.



Jamie Armstrong P.E.
Mechanical Engineer

[cid:image001.jpg at 01CD44DC.0533B0E0]

v. 210.546.0200 | www.dbrinc.com

From: Howe, Timothy [mailto:Timothy.Howe at stantec.com]
Sent: Thursday, June 07, 2012 3:51 PM
To: Armstrong, Jamie; equest-users at lists.onebuilding.org
Subject: RE: Can't get unmet hours under control for cooling

Jamie,

You have some inconsistencies in your inputs for the OA on system RTU-2 (and all the rest).  See highlighted area below.  You are saying that the system is 100% recirc by setting the Minimum Outside Air ratio to 0.00, but your Minimum Air Schedule (note that this is a fraction of the design supply CFM type of input) is saying otherwise and takes precedence causing it to be a 100% OA system.  See my snip from the hourly reports below too.  You need to develop the proper ventilation rates for each system and verify with hourly reports.  Do not rely on the summary tab in the air side system tab of eQUEST to give you correct data at all times.   If you just define the OA by using the Minimum Outside Air ratio, you will be supplying OA every time the fan operates.  To prevent this you need to set up Minimum Air Schedule for each system which is based upon the proper fractions for that system.

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Timothy Howe, MS, LEED® AP BD+C
Mechanical Engineer
Stantec
61 Commercial Street
Rochester NY 14614
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Fx:   (585) 272-1814
Cell: (585) 330-8681
stantec.com<http://www.stantec.com>

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From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Armstrong, Jamie
Sent: Thursday, June 07, 2012 4:23 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Can't get unmet hours under control for cooling

I need some help getting these cooling unmet hours under control.  I have to get this model complete and submitted by tonight.

We've tried multiple things to try to get the model to work out.

We've tried the following:

·         Letting eQuest autosize the heating and cooling for the PSZ units

·         Verified that the schedules are consistent with both cooling, heating, and occupancy.

·         On the baseline building we have the min cfm set to 0.5 for most spaces and 1 cfm/sf for some of the larger spaces.

·         We set the PSZ -fan - flow parameter - indoor fan mode to intermittent to get the unit to show partial capacity thru out the days.

One item is RTU-2 in my model.  It serves only one space.  We have a high amount of unmet hours on this and we are letting it auto size the capacity and airflow and it still says its not staying under control.  We're assuming that we are missing one small check box that's somehow causing these unmet hours.

I've attached the pd2 files for both baseline and proposed along with weather data and inp files.

Thanks in advance for any help!


Jamie Armstrong P.E.
Mechanical Engineer

[cid:image001.jpg at 01CD44DC.0533B0E0]

v. 210.546.0200 | www.dbrinc.com<http://www.dbrinc.com>

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