[BLDG-SIM] Clarification re: Chilled Beams and Radiant Systems in eQUEST

[Timothy Moore]

Shivani,

Indeed the Induction Units (IU), and not Powered Induction Units (PIU), are
what you would use to model active chilled beams so that you could use the
zone coil to represent the chilled beam and associated chilled water flow.
(In my previous post on this topic I inadvertently mixed two conversations
into one---in the midst of related offline discussions of PIU features we'd
like to see in future versions of eQuest.) Anyway, it does appear that the
IUs are limited to using constant-volume primary airflow from the AHU as
Fred suggested, which would typically be 100% OA at some fixed ventilation
rate. If anyone knows a way to make this work otherwise, please chime in.

Using the IU, you would also still need to adjust the Induction Ratio to
correctly represent the relationship between supply water flow and
primary+induced airflow for the particular device and application. If the
zone loop temperatures are to differ substantially from the main loop, as is
often the case, there will also be challenges related to correctly
representing loop pumping power.

If you're modeling a passive chilled beam or radiant panel, you would need
to reduce the total fan static by 1 to 1.5 i.w.c. (per DOE-2 documentation)
below what it would be for induction units. However, if it is an active
chilled beam, depending on the specific unit, the fan static may be much
closer to what it would be for an induction unit, since many active beams
are essentially induction units with an expanded heat-exchange surface area
and radiant cooling effect as a result of limited exposure of chilled
surfaces.

If you want to model radiant panels in eQuest with cooling capacity
decoupled from ventilation air supply, the closest you can get is probably
modeling a Fan Coil with no fan energy. If ventilation air is to be supplied
by a central AHU, set the Outside Air from System to the appropriate system
in your model. Unfortunately, this is pretty fuzzy in terms of how a fan
coil vs. radiant system would interact with space loads, particularly in
spaces also served by an airside system. For example, this would be an
especially crude approximation if using either suspended radiant panels,
suspended passive chilled beams, or a chilled floor while allowing thermal
stratification in the space above, and then exhausting the hot air from the
top of the space: Even if you do the typical workarounds to approximate the
stratification (already very messy), you would still not be modeling
potentially significant radiant interaction between the warm ceiling and the
chilled floor, not to mention where the solar gain is going to end up.

If you simply need to get a approximation of energy consumption for these
systems within eQuest, the approaches above may get you reasonably close, at
least for many situations with simple overhead devices in well-mixed
environments---especially those with active chilled beams. However, as
alluded to above, there is no separate/explicit modeling of radiant exchange
in eQuest/DOE-2. Therefore, to the degree that the system you're modeling
does provide radiant cooling, these methods may be somewhat inaccurate,
particularly in situations with significant radiant asymmetry, and will
provide very limited information about thermal comfort and associated design
considerations. From a design perspective, you may want a tool such as Tas,
EnergyPlus, or Virtual Environment that models surface temperatures, related
thermal comfort parameters, and the radiant exchange between surfaces. These
tools also open up the possibility of more sophisticated analysis of energy
savings related to natural ventilation, which can have significant synergies
with radiant cooling.

Cheers again,
Timothy 

*************************************
Timothy Moore
Center for the Built Environment (CBE)
University of California at Berkeley




-----Original Message-----
From: Shivani Shah [mailto:ss at a10nyc.com] 
Sent: Thursday, April 26, 2007 7:10 AM
To: tcm at berkeley.edu; BLDG-SIM at gard.com
Subject: RE: [BLDG-SIM] Chilled Beams and eQUEST

Tim,
Thanks for your email. If we model active chilled beams as a PIU units, how
does one take account of the chilled water coil in a chilled beam unit? From
my understanding, PIU in eQUEST only has a re-heat coil and no chilled water
coils, which means that all the cooling is being done at the AHU which is
not actually the case. Can you throw us a light on that?

Thanks.

--
Shivani Shah
Atelier Ten



-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Timothy
Moore
Sent: Wednesday, April 25, 2007 9:04 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Chilled Beams and eQUEST

In the case of the PIUs (fan-powered boxes), it is true that both series and
parallel PIUs modeled in eQuest/DOE-2.2 presently assume a constant-volume
fan in the box. For series units the fan is always on per schedule and draws
from both the primary and secondary air streams. For the parallel unit the
fan draws only from the secondary air and runs as needed (on/off only) to
meet zone demands.  

If the terminal unit includes a fan with variable speed drive, the method is
presently the same as for any PIU with a variable speed drive: Run the
model; Then, based upon SIM file bin results for part-load operational
hours, determine the average part-load fraction; Finally, based on
performance curves for the terminal unit, or approximated using peak power
and fan laws, etc., determine an appropriate average kW/cfm for the PIU in
your application.

Timothy Moore
Center for the Built Environment (CBE)



-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Fred Porter
Sent: Wednesday, April 25, 2007 4:28 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Chilled Beams and eQUEST

Correct me if I'm wrong, but the one drawback to the IU SYSTEM in DOE-2.x is
that the supply air volume is constant, or off. A system that varies primary
airflow in response to ventilation needs can't be modeled directly.

--
Fred W. Porter, B.S., LEED A.P.
Architectural Energy Corp.

-----Original Message-----
From: Gerald Pde [mailto:geraldpde at yahoo.com]
Sent: Wednesday, April 25, 2007 2:53 PM
To: BLDG-SIM at gard.com
Cc: Nathan Fleischer
Subject: [BLDG-SIM] Chilled Beams and eQUEST

You can use induction units to simulate a chilled beam system but you might
also need to configure a seperate (or secondary) warmer chilled-water loop
and cooler hot-water loop for the zonal coils. You might also need to check
the induced ratio to scale the capacity of the primary air delivery and the
secondary induced air component.

Hope this helps.

Gerald
 
--- Ryan Hammond <RHammond at gb-eng.com> wrote:

> All,
> 
>  
> 
> Has anyone out there had experience modeling chilled beams with 
> eQUEST?
> 
> 
>  
> 
> How's it done?
> 
>  
> 
> Thanks,
> 
> R. Ryan Hammond, LEED(r) AP
> 
> Designer
> 
>  
> 
> G U T T M A N N & B L A E V O E T
> 
> C o n s u l t i n g E n g i n e e r s
> 
>  
> 
> 2351 Powell Street                  1111 Howe Ave.,
> Suite 155
> 
> San Francisco, CA 94133       Sacramento, CA 95825
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> P  (415) 625-0730                   P  (916)
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> F  (415) 625-0735                   F  (916)
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> E  RHammond at gb-eng.com
> 
> W www.gb-eng.com
> 
>  
> 
> 
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