[Equest-users] FC+DOAS

[tiejun hu]

this is a phychrometric chart, y axes is "enthalpy" ；x axes has 145 °angle with the y axis ，stand for "humidity". N stand for indoor Indoor State point; W stand for outdoor state point; S stand for state point which belong to outdoor air processed by DOAS. L stand for state point processed by FCU.; O stand for mix point between S and L.
  S' enthalpy value = N' enthalpy value
At 2011-04-14 22:12:25，"Joe Fleming" <joe at thespinnakergroupinc.com> wrote:


Regarding the fan power.  If we assume that both fans and fan motors have the same efficiency and the units are constant volume, then you will adjust the static pressure of your fan coil units by the current flow over the new flow when you add the outside air. 

 

i.e. if you have two FCU’s current supplying 2000 cfm and you have a 1000 cfm outside air unit delivering 500 cfm to each FCU, then your new FCU supply air rate will be 2500 cfm.  You will build your DOAS as is designed and you will bump up your FCU airflow quantity to the total of the design and the DOAS supply to that space/zone/system.  You will then reduce your static pressure for the FCU by 2000/2500 or 80% of what it is designed at, if the design total static is 4 inches then your new static will be 3.2 inches.  This will eliminate any increase in fan power that you may see to the increased flow.  (If you have ten FCUs at 2000 cfm and a DOAS at 2000 cfm, your numbers with the DOAS would be, DOAS as designed, 2200 cfm for each FCU, and a new total static pressure at 2000/2200 of design or 90.9% of design static).

 

 

As for the process, you say isenthalpic, so to me that means that the air is delivered off of the evaporator coil after the refrigerant goes through an expansion valve? 

Or could you please tell us what N, L, O, S, and W stand for, and what the axes of this chart are, (temperature and entropy?)  It doesn’t look like a psychrometric chart.

 

 

 

Joe Fleming, E.I., LEED AP BD+C, BEMP

 

From: tiejun hu [mailto:hutiejun1223 at 126.com]
Sent: Thursday, April 14, 2011 9:40 AM
To: Joe Fleming
Cc: 'equest-users'
Subject: Re:RE: [Equest-users] FC+DOAS

 

 


At 2011-04-14 21:03:47，"Joe Fleming" <joe at thespinnakergroupinc.com> wrote:



Search DOAS in the user archives and you will find abunch of discussions on this topic.

 

First you need to be in detailed mode, for some reason the DOE engine (maybe just eQuest), doesn’t have the skills to make a dedicated outdoor air system as a drop down selection. 

 

Next, what is the supply air temperature entering the zones from the DOAS?  Cold?  Room temperature? Hot?

What is the process that the DOAS goes through to get the leaving air temperature at set-point?

 

Typically, you need to create a “dummy space” and assign it to a “dummy zone” then assign your first system to this zone.  If you already created systems you can always open your .inp file and cut and paste the DOAS to the top of the systems list so that it will become your first system.  Go ahead and assign all of the outside air to your DOAS “dummy zone” and then choose outside air from system for all of the systems that this DOAS serves.   It will only be able to find OA from systems above it on the component tree, so make sure your DOAS is at the top.

 

 

Joe Fleming, E.I., LEED AP BD+C, BEMP

 

From:equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org]On Behalf Oftiejun hu
Sent: Thursday, April 14, 2011 1:11 AM
To: equest-users
Subject: [Equest-users] FC+DOAS

 

hi equesters

            Dose anybody have experiences for FC+DOAS, in my modle, outdoor air processed by independent air-condition unit, then supplied to room directly, do not go through FC inlet. as far as i kown, outdoor air and return air combined process in FC in some countries,like below picturebut On the upper right corner,i see an outdoor air fan, is it an DOAS? if so ,how to realize it in equest? and how to set in the tab "OA FROM SYSTEM"?

 any words will be appreciated!

                                                                                                                                                yours sincere

 hi joe

       thanks for your reply,this is my Processing,, independent outdoor air from DOAS are processed to S( isenthalpic with room N，H:90%), then mixed with supply air from FC outnet(L), outdoor air doesn't undertake indoor load.  Note that: my outdoor air do not get through FC, delivered to room derectly.

    i doubt that , as your method, Whether outdoor air from DOAS will be delivered to FC, flow through the fan in FC, then increase fan energy?

 thanks again!
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