[Trace-users] Split System with DOAS for LEED (UNCLASSIFIED)

Breese Doug dbreese at beardsley.com
Thu Feb 3 12:00:35 PST 2011


Hello Bob and John,

I am on my 7th Barracks and 10th overall building using DOAS systems
ranging from 2-pipe changeover Fan Coil Units to Geothermal Heat Pump
Systems with scavenger reclaim for dehumidification reheat and
Multistack geochillers for DOAS. 

John is correct, select your primary System (unitary equipment) with
info for the DOAS filled out in the dedicated OA tab, just select that
it is room direct as to model your decoupled ventilation, and make sure
your Fixed-Setpoints are the same as your room setpoints so that you do
not burden the split system or cause need for insulation of the DOAS
ductwork. Remember that you can drag and drop the coils into the
different plants so that a electric back-up htg coil for the splits can
be activated if your split system needs additional heat, and your new
"Opt-Cooling" coil can be attached to your chiller/multi-stack/WWHP and
Opt Vent htg coil can be attached to the boiler/boiler backup.

It's very useful to look at your equipment energy consumption output to
see if the energy is being accounted for correctly. If something isn't
connected properly in the plants or coils assigned incorrectly, the row
of kwh or therms will "disappear" to give you a clue that something is
wrong with this picture. When building the plants always consider back
up heat whether it is boiler or electric reheat coils. 

Also with DOAS in your room airflows, if you have a space that is 45cfm
of ventilation air and you only want to exhaust 30cfm from the toilet
room, that's 15cfm positive pressure, consider only entering 15cfm in
the room exhaust and the 45cfm ventilation air, then do not assign a
room exhaust fan. Your System Checksums will show the ventilation air
and what is being returned back to your DOAS for energy recovery
purposes. 

In the Detailed Reports Tab of you Output refer to the Airflow Balance
at coil peak. Remember that you wanted a decoupled ventilation, so the
Total Outflow will equal your Total Inflow. Back at your System
Checksums add your Main Fan to the Nom Vent minus Rm Exhaust and that
should equal your Return Air quantity. OA+SA-RmEA=RA. Trace will not
allow a building to be positively pressurized, only balanced airflows.

   Doug Breese
Be Sustainable -- Never let today use up tomorrow!.


-----Original Message-----
From: trace-users-bounces at lists.onebuilding.org
[mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Eurek,
John S NWO
Sent: Thursday, February 03, 2011 2:06 PM
To: Robert Arnott; trace-users at lists.onebuilding.org
Subject: Re: [Trace-users] Split System with DOAS for LEED
(UNCLASSIFIED)

Classification: UNCLASSIFIED
Caveats: NONE

Good timing Robert, I am modeling almost the exact same system.

I called Trane, but I still don't like how the system is working.

Under create system, select the dedicated outside air unit and fill in
the
information.  This is equivelant to modeling two separate pieces of
equipment.

I modeled it the way Trane instructed, but I had my doubts.

I also modeled one system like normal but used 0 ventilation and another
system with 1sqft and nothing else but 100% ventilation (7400 cfm in my
case)

The thing I didn't like about the method with 2 separate systems was
that it
showed the return air of the second system to be 14800 cfm, I can't
figure
out why it doubles the return air cfm.


-----Original Message-----
From: trace-users-bounces at lists.onebuilding.org
[mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Robert
Arnott
Sent: Thursday, February 03, 2011 3:46 AM
To: trace-users at lists.onebuilding.org
Subject: [Trace-users] Split System with DOAS for LEED

Hi all,

I am a new Trace 700 user and I'm busy modelling a building for LEED.
I'm
struggling with two fundamental aspects of how the HVAC system modelling
works in Trace.


1. The building uses a split unit heating/cooling system, with a
completely
separate dedicated outdoor air system for fresh air. The fresh air
supply is
constant and does not vary with the heating and cooling load. The split
unit
draws air directly from each zone (recirculating indoor air only) and is
not
at all connected to the supply ducting of the fresh air. Since there are
two
completely independent systems serving the same zones, how should this
be
modelled for LEED? Would it be acceptable to assume that a single system
is
being used, and that the heating/cooling is done directly on the supply
air?

2. All zones receive fresh air, with only the bathrooms exhausting air,
creating a definite airflow network between the zones. If I set every
zone's
"Adjacent air transfer from room" to the passageway connecting all the
zones,
will Trace determine the correct airflow rate and direction between each
zone? Or is the adjacent air transfer directional, so that the bathroom
would
need to be set to have an airflow transfer from the passage, then the
passage
would need an airflow transfer from multiple zones (but trace only
allows a
single zone to be set)?


I'd appreciate any feedback. Thanks in advance!

Regards,
Robert


Classification: UNCLASSIFIED
Caveats: NONE


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