[Bldg-sim] Equest: ERU with added heat and vfd's

Tue Jan 8 12:32:28 PST 2008

Short answer: Yes. 

The temperature & humidity of the dummy/duct zone is used in place of the outside air to the system/zones which include the OA-FROM-SYS command. With no loads in this zone, its conditions should be the same as the supply air. To simulate proper dehumidification when modeling a DOAS as PSZ, the zone cooling setpoint schedule would need to be set to 55F or so, and the real DOAS capacities should probably be entered manually. Other model system/zone combinations generally better represent actual DOAS operation, and should be provided as discussion or example by the program authors.

Fred Porter
AEC

>>> "Kevin Kyte" <kkyte at robsonwoese.com> 1/8/2008 10:02 AM >>>

I understand that doe2.2 cannot accurately model energy recovery in these conditions.  Would the zones receiving the outside air from the system at least receive the same tempered air as the dummy zone in the system?  
Kevin

From:Fred Porter [mailto:FPorter at archenergy.com] 
Sent: Friday, December 14, 2007 3:30 PM
To: bldg-sim at lists.onebuilding.org; Kevin Kyte
Subject: Re: Equest: ERU with added heat and vfd's

Folks;

Whatever else maybe wrong or right with these approaches, eQ/DOE-2.2 cannot generally correctly model energy recovery in the OA-FROM-SYS.  This is because the exhaust/return air to the OA-FROM-SYS in a DOE-2 model is NOT from the occupied spaces, it is from the dummy/duct zone, which should never be at the room/return air conditions in either the model or reality. (It will usually be substantially cooler.) Too bad, because many real DOAS systems, (which would appear to be best represented with DOE-2's OA-FROM-SYS) include heat recovery and pre-conditioning.

Anyone know if any of the other "typical" simulation programs (TRACE, E+) represent a DOAS supplying zonal HVAC more correctly? Obviously one could model them in TRNSYS, and IES-VE.

Fred Porter

AEC

P.S. I did actually once whip up a convoluted DOE-2.2 "workaround" for this arrangement. But I will not post it here because it really does not qualify as "simulation;" calling it a brittle kludge would be charitable. 

>>> "Kevin Kyte" <kkyte at robsonwoese.com> 12/14/2007 11:59 AM >>>

I am attempting to model an energy recovery unit (ERU) supplying outside air
for 5 air handling units (AHUs).  I have attempted to do this thus far by
making the ERU a separate system PSZ with dumbo zone and the AHUs use ERU
for OA-FROM-SYSTEM.  

The problem lies within energy recovery capacities, the ERV report
capacities are nowhere near as high as the designed energy recovered so the
coiling coil is undersized and I am getting a lot of inadequate cooling
capability warnings.  The ERU has an additional gas furnace but no
additional cooling.

This is where I may be getting it mixed up because I set the
COOLING-SCHEDULE flagged to off for the entire year and I end up with no
energy recover on the cooling side.  Even if I were to change the ERU to
type PVAVS or SZRH it shows minimal or no recovery.  How should I schedule
cooling?

Are any other parameters that I may be missing, I have included the enthalpy
wheel effectiveness and a control sequence.  How about humidity controls?
Since this suppose to be a LEED certified building will ECMs be necessary?
Or should I go back to doing individual heat recovery for each AHU?  So many
questions.

Kevin

From: Brian Fountain [mailto:bfountain at greensim.com] 
Sent: Wednesday, November 21, 2007 11:27 AM
To: kkyte at robsonwoese.com; BLDG-SIM at gard.com 
Subject: RE: [BLDG-SIM] Equest: ERU with added heat and vfd's

The way I would do it is to use the OA-FROM-SYSTEM keyword and add the ERU
as a separate system with ventilation heat recovery.  In this way, you can
define the heat recovery and power and flow characteristics of the ERU
explicitly.  

I usually do this by first creating a very small (1 sq-ft) dummy space, then
a dummy thermal zone for that space.  Then, create the ERU as a 100% OA
constant volume system serving that thermal zone.  Now comes the fun part.
You close eQUEST, open the .inp with a text editor and cut the new system
and all its keywords from the bottom of the list of systems and paste it to
the top of the system list.  If you don't do this, when you run the
simulation, it will complain that the OA-FROM-SYSTEM system referenced does
not precede the current system and will abort the sim.  Now, reopen eQUEST
and in your 6 systems, use the OA-FROM-SYSTEM keyword on the system, OA tab
to define that the ventilation air is coming from your ERU.  

Hope this helps.

-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Kevin Kyte
Sent: November 21, 2007 10:55 AM
To: BLDG-SIM at gard.com 
Subject: [BLDG-SIM] Equest: ERU with added heat and vfd's

Simulating an energy recovery unit which serves six air handling units.  I
suppose this is simply enough, I split the total cfm into percentages for
each unit and incorporate into each unit's heat recovery, yes?  Is there any
way to include additional heat from the energy recovery unit? Perhaps split
the total heat into percentages and include this in each unit's heating
capacity.  How about variable frequency drives on supply and exhaust fans
for energy recovery unit?  Perhaps this could be modeled as a 10% reduction
in the fan power similar to occupancy sensors on lights?  Regarding LEED,
would usgbc need a credit interpretation request for something like this or
maybe just mentioning it as a default overridden in the submittal would
suffice.  Would anyone who has encountered this care to chime in?  Any
suggestions would be forthcoming.  Thank you.

Kevin Kyte, LEED AP

Jr. Mechanical Engineer

RobsonWoese, Inc.

T:  716-636-1800

F:  716-636-1856

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Zhen Tian
Sent: Tuesday, November 20, 2007 5:38 PM
To: BLDG-SIM at gard.com 
Subject: [BLDG-SIM] add ceiling in eQUEST

Dear all,

When I model a one-floor building in eQUEST, I found that adding the "lay-in
acoustic tile" ceiling (no insulation added) will cause the peak load
through roof to zero. When eliminate the ceiling, a large part of the
building heat flow will go through the roof.

I also tried several buildings. When added ceiling, then the heat flow
through roof turns to zero. Does anyone have an idea why this happens? 

Thanks a lot.

Regards,

David

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