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Don't forget this is a model. It will never actually work the same
as a complex HVAC system. A FCU is a trimming unit, it adds hot or
cold to allow you to differentiate loads or temperatures in
different spaces, it isn't normally used to control fresh air to the
space. It just adjusts what the main air handlers give it. It is a
variable temperature system. But eQuest will treat it like a fresh
air system and all outside air is drawn through the unit. If you
are going to use it that way then have your co2 sensors in the
spaces and get rid of the DOAS. eQuest really doesn't care if one
office has 2 people in it and they have 20 cfm of outside air each.
OA works on a area basis. All equest wants to know is how many
people are in the area, what are the building loads and people loads
on the area, how much OA is being brought into the area and the
loads associated with this air. It will sum all the zones on a
area/system. It does care about the temperatures in a zone. What
you have to do is figure out how to best model your system so you
control the loads not the IAQ, (indoor air quality). Just because
you are told you are using FCU and DOAS doesn't mean you actually
model it this way. Initially you are trying to size your systems
for maximum conditions. Maximum people, maximum OA. Because people
is very variable and OA is very costly to condition, designers are
coming up with ways to minimize OA and co2 sensors are one way to do
it. But this works more in actuality than in modelling and it
doesn't mean you have to use a DOAS. Equest is set up to use
economizers, exhaust air, ERV/HRV systems. DOAS are a way to
separate the outside air control from the temperature control
system, not the only way. In actuality on a complex building they
are not used because money talks. You are adding a separate AHU, a
separate supply and return duct system with all the accessories and
that is expensive. I almost never model a DOAS.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering<br>
<br>
On 06/06/2011 12:08 AM, tiejun hu wrote:
<blockquote
cite="mid:11d03b6.3cad.13063233bd7.Coremail.hutiejun1223@126.com"
type="cite">
<div>if i remove the DCV sensor from FCU. the fresh air of FCU
zoom will be constant i think. and if each room do it like that.
the fresh air from DOAS room will be fixed. so it do not reflect
the change of fresh air according to CO2 concentration. is it
right?<br>
</div>
<br>
At 2011-06-06
00:36:08£¬"Bruce Easterbrook" <a class="moz-txt-link-rfc2396E" href="mailto:bruce5@bellnet.ca"><bruce5@bellnet.ca></a> wrote:<br>
<blockquote id="isReplyContent" style="padding-left: 1ex; margin:
0px 0px 0px 0.8ex; border-left: 1px solid rgb(204, 204, 204);"><font
size="+1">Your DOAS and FCU are separate systems. Remove the
DCV sensor on all the fan coils and just have one on the
DOAS. I can't help much on the DOAS as I haven't modelled on
in a long time and my recollection is fuzzy on the fine
details. There should be lots of information on older posts
if you search the archives.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering<br>
</font><br>
On 04/06/2011 12:09 AM, tiejun hu wrote:
<blockquote
cite="mid:7e3f78d.2668.13058d79280.Coremail.hutiejun1223@126.com"
type="cite">
<div>HI equester:</div>
<div> I am working on project in which fresh air is
controled by CO2 concentration, in my model, every room has
FCU, and all fresh air provied by DOAS controling a dummy
room. so the fresh air volume of this system is sum of all
room served by FCU. and to realize this control , in
every system tab, i choose DCV return sensor, but i don't
kown how to setup the fresh air system(DOAS), if i also
choose DCV return sensor, i think the volume of air
provided by system is unchanged, because people im dummy
room is 0. i tried to input number of people in room tab and
total heat for 0,but is unaccepted by software. so this
method is not ok.</div>
<div> dose any people can guide me? note that:my fresh
air volume of DOAS must reflect requirement of all room
served by FCU.</div>
<div> any words will be apreciated! </div>
<div>BEST
REGARDS!
</div>
<br>
<br>
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