[Equest-users] Unmet Hours

[Matt Clough]

All,

I just wanted to follow up on this.  I was able to recover the unmet hours by declaring a minimum flow density (cfm/f^2) .  I also implemented John's suggestion of widening the deadband, although I suppose I should have performed each of these changes individually in order to see which one contributes most to an acceptable simulation.

After doing this I began making the system definitions match the equipment specs on the drawings (supply flow rate, outside air flow rate) but now the proposed model reports extremely high energy usage (millions of MBtu).  I'm pretty sure that the baseline design is not more efficient than the proposed.  It seems like the systems run at no less than 50% all the time (per the summary tab).  My hunch is that this is a problem related to schedules, but I'm really stumped and wanted to see if any of you gurus have suggestions.

Regards,
Matt



________________________________
From: John Aulbach [mailto:jra_sac at yahoo.com]
Sent: Friday, March 16, 2012 9:07 AM
To: Matt Clough; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Unmet Hours

Matt:

I will look at your run later. But for the VAVs, make sure your thermostats are reverse acting, then increase the deadband to 4 or even 6 deg F.

John Aulbach
Partner Energy

________________________________
From: Matt Clough <mclough at kme-inc.com>
To: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Sent: Friday, March 16, 2012 8:00 AM
Subject: [Equest-users] Unmet Hours

All right Folks,

It's time to do that thing again where we talk about unmet hours.  I'll give a little background first:  I'm new to equest and to the HVAC industry, so bear with me.  The project is a 1F school building (pre-k) with a clerestory, split into 10 zones and predominantly served by series VAV terminals using chilled water and hot water loops.  It's in Houston , TX so and are no economizers.  I've spent the majority of the past few days reading previous discussions and trying a variety of changes.  I have attached the INP and PD2 for convenience.

I initially tried to represent the system based on the mechanical/electrical schedules, but that yielded many unmet hours (99%), so it is currently set to auto-size, but am still at about 600 unmet hours (7%).  7 of the zones are series VAV, 2 are single-zone with reheat, and one is a packaged single zone for the MDF room.

  *   Changing to an auto-sized system provided a large reduction in UH.
  *   am trying to not manipulate the data by adjusting the cooling/heating ratio.
  *   The setpoints are 75c/72h.  I tried changing them a few degrees in either direction, but did not get a large enough reduction.
  *   have the fans cycling at night (no OA), which did help reduce the hours
  *   switched into DDE and set actual CFM from the mechanical plans.  This resulted in an increase

As I am looking through the LS-B report, it seems like some of my zone loads might be a little high with some of the heat generation loads at about 12kbtu/h.  I think my inexperience hampers my ability to troubleshoot some of the problems because I don't necessarily have a good sense for what a reasonable result/prediction is.

I appreciate any assistance on this matter and am open to suggestions as far as proper modeling techniques and troubleshooting methods.

Sincerely,
Matt Clough
Mechanical Designer
KME Engineering

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