[Equest-users] Power induction unit/ reheat delta T

[John Shen]

Thank you for the response, couldn't have asked for a better explanation.
 I was able to get the heat unmet hours down to a reasonable range. However, I am having difficulties with the Cool unmet hours. It appears I am unable to acquire any cooling capacity which is resulting in a few unmet hours (~150). As mentioned the heating capacity is dependent on the reheat delta t and airflow. I can't seem to find a place to enter delta T for cooling, I have coil delta T set along with an appropriate CHW loop. Yet I don't get any cooling in any of my zones in the SS-G section of the report. Any further help would be appreciated.
John

Date: Fri, 24 Aug 2012 09:57:49 -0400
From: bruce5 at bellnet.ca
To: johnshen1 at hotmail.com
CC: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Power induction unit/ reheat delta T


  
    
  
  
    You can
        try changing your interior control zone as this will effect the
        base capacity that the AHU will supply to the floor.  As for the
        exterior zones your heat/cool capacity is based on the delta-T
        and the airflow.  You said you specified the air flow.  Let
        eQuest auto-size the flow.  By specifying the air flow you have
        removed most of eQuest's ability to adjust capacity.  One other
        thing to remember is eQuest is working on the maximum flow as
        well as all the intermediate conditions as well.  It is these
        intermediate loads which will trigger most of your unmet hours. 
        As the sun moves across your exterior zones through the day the
        peak load will be shifting through the exterior zones as well. 
        So a zone which was the peak at 10 am won't be the peak at 3
        pm.  eQuest will count an unmet hour if you are high or low on a
        zones temperature.  By specifying the cfm to the zone I would
        guess you may be over cooling some of the zones and triggering
        unmet hours.  eQuest, if allowed, would reduce the airflow to
        the 10 am zone later in the day and shift the CFM to the 3 pm
        zone.  This is mostly under the hood stuff and you have to drill
        pretty deep into your reports to have an idea of what is going
        on and you won't find the direct answer as to the lower cfm to
        the zone.  You can get an idea of the heat/cool capacity eQuest
        is dealing with in each and follow it across the building.

        Bruce Easterbrook P.Eng.

        Abode Engineering.

        

      
    On 23/08/2012 01:56 PM, John Shen
      wrote:

    
    
      
      
        Working on a building with an air handling
          unit which serves
          the entire floor. In the exterior rooms there are Fan coils to
          supply further heating
          and cooling to the floor. I have split the floor up into
          interior zones and
          exterior zones (each containing a fan coil unit). The AHU I
          have modeled as a
          power induction unit which serves all the zones on the floor,
          the interior
          zones have terminal type std VAV and the exterior zones have
          series PIU. With
          in the exterior zones I have specified flow rates, heat/cool
          capacity
          reflecting the FC. However I am getting lots of unmet hours
          from these exterior
          zones (~500 hrs each). I inputted a REHEAT-DELTA-T in of 57F
          (based on fan flow
          rates and heat capacity) into each of the exterior zones. This
          greatly reduced
          the unmet hours; however I find it strange because the unmet
          hours are
          completely dependent on REHEAT-DELTA-T and completely
          independent of the zone
          heat capacity. I appear to have a poor understanding of how
          the PIU system
          works, if anyone could provide further insight it would be
          much appreciated.
        

        
        John
      
      

      
      

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