One model

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Hi All,

We currently use TAS for energy modelling and Radiance for daylight
simulation.

Virtually every architect that we work with provides us with 3D models,
but we seem to spend a lot of time re drawing models or fixing 3D models
to be able to work with the software that we use. The ultimate goal for
us would be to use one model for daylight and energy models, but I
haven't found that quite that simple as most software requires varying
drawing techniques.

Has anyone got any suggestions on the kind of software that they use
that could help out with the goal of ours?

We would like to investigate energy plus compared to TAS. Is there an
energy plus preprossor that could export models for radiance as well. I
have sent quite some time trying to do this with ecotect, but ecotect is
not the best software for importing 3D models as it doesn't take IFC
files or even dwg's.

I would be interested in investigating how well sketchup could be the
intermediate pre-processor. I have seen some radiance models that have
come from sketchup direct from an architectural model and they look
great. Has anyone used sketch to provide and energy plus model?

Thanks in advance.

Regards

Ross Harding

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Actually, I'm utilising IES to do HVAC design, Energy Analysis, PMV
calc, lighting lux design, lighting power intensity design and natural
daylight analysis all in line with the Australian Standards and Green
Star (another form of LEED) requirements.

Although the software costs money, I've found it to be worthwhile
battling against it's flaws and it gives us the results which we
require.

Please note, this is a one model approach. It's easy to start a project
at CD (concept design) stage within Google Sketchup and to utilise the
freeware version of IES to do alternate design analysis. However, it's
way better if the full suite is purchases and the model is crossed over
into IES. Within IES multiple analysis and detailed designs can be
modelled quickly and with fantastic final project results. I know, I've
done it.

Also with the daylight analysis, if you've got a detailed building with
over 100000 surfaces, it's going to take forever to do the analysis,
that's my only issue with the software. However, the software is
developing multithreading facility within it's software, therefore
decreasing the time for analysis dramatically.

Should anyone want to discuss my approaches further, and are in
Brisbane, I welcome the opportunity to meet and greet with you.

Regards,
Ronan Carney

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Hi All - again

When I created my long post on the Daylighting models I self-edited because it was looking like going on forever. For example, I stopped short of listing the full range of software that has been subject to validation exercises, and stuck to just those that have been validated against measured data. There is for example the validation suite created by the CIE to be an equivalent for lighting of the IEA BESTEST / ASHRAE 140 validation process for thermal simulation programs. To my knowledge, AGI 32 and the Integra software from Japan have undergone this validation process.

This most recent post returns our focus to energy simulation. I have over the past six months of a sabbatical at the Lawrence Lab in Berkeley CA come to know and appreciate the COMFEN program which is targeted at providing the power of the EnergyPlus program, very early in the design of a building. Programs like EnergyPlus have inbuilt engines for calculating light distributions due to daylight. The COMFEN (http://windows.lbl.gov/software/comfen/2/index.html ) program from LBNL makes some of the daylight calculations within EnergyPlus accessible in these very early phases of the design process. This is fully integrated.

Clearly an add-on for daylighting to a thermal simulation program will not be the best lighting program. However, it should be sufficiently accurate for many purposes where thermal and daylight performance are combined.

Rob, you are correct about the su2rad/OpenStudio plugins for SketchUp. Because the OpenStudio plugin from DOE/NREL will read EnergyPlus input (idf) files, SketchUp is the potential integrator of COMFEN/EnergyPlus and Radiance. It works well here because of the elegance of the underlying template for the COMFEN EnergyPlus model. But even here it has limitations. The thermal simulation model representation of a wall is a set of 3D coordinates locating a surface in space and its orientation to the sun. The thickness and thermal properties are represented mathematically. Reading an EnergyPlus '.idf' file into SketchUp reveals windows with no frame and reveals with no depth - anathema to the good daylight modeler. If one creates buildings with depth for daylighting in SketchUp, one needs to specify thermal zones within the model before exporting to EnergyPlus.

The single BIM model that links to all analytical programs but is independent of them all is an ideal that has been worked on since the days of the COMBINE project in Europe 20 or so years ago. Many are working still on it. Logic suggests it is the most elegant solution to the dilemma of exchange of information between many different analytical programs. But this simple illustration suggests to me that the Building Information Model is not SketchUp. It is merely one on a long line of geometry creation tools. It is unusual in that it can be used to create lighting, acoustic or thermal models. But it merely creates a common starting point for these separate analytical tools.

Michael Donn

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Hi All,

Excellent study assessing commercial programs that have integrated solar
gain and daylighting is already available for those who would like to learn
more. Several programs were validated through experiments under the IEA's
SHC Task 34 / ECBCS Annex 43 Project C, titled "Empirical validations of
Shading / Daylighting / Load Interactions in Building Energy Simulation
Tools," (August 2007).

A short version focusing only on EnergyPlus & DOE-2.1E is also available in
Energy 32(2007): 1855-1870, Loutzenhiser et al., "An empirical validation of
the daylighting algorithms and associated interactions in building energy
simulation programs using various shading devices and windows," Elsevier
Ltd.

Needless to say, commercial programs with integrated daylighting algorithms
should be able to simulate, within a certain confidence level, various types
of shading devices (internal / external; venetian / mini-blinds), glazing
types (wavelength selective), light shelves / wells, dome fenestration and
double-skin facades. Until then, it is best to use separate specialized
programs if you are concerned about rich, quality data.

Best regards,

*Ravi Srinivasan**

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I tried out IES-VE a few months or a year ago with some people because
the potential for this type of integration seemed very exciting.
However, we found the HVAC side to be pretty basic. For a lot of
building types, there are significant savings to be had by changing HVAC
control schemes and/or configurations and using HVAC types that were not
well-represented in IES-VE the last time I saw it. It seemed like a
great interface to use if you were trying to design a building to use
minimal energy due to envelope, orientation, natural ventilation, etc.
In other words, it seems strong on the loads calculation side. On the
system use side, though, it seemed a lot more limited than DOE2 or
EnergyPlus. For that reason, I have also stuck with the multiple-tools
method. I agree with all who wrote that it would be wonderful to have
one integrated tool in the future! Rob does bring up an interesting
point about the resolution of spaces needed for daylighting vs. thermal
vs. architectural modeling. Architects especially have to be so
detailed in their models that I've often just ended up using the floor
plans they provided, deleting a bunch of elements out of those, and
scaling wall heights and windows. Other than that, their 3D models only
serve to help me visualize the building myself. It would be nice if we
didn't end up tripling the effort like we all do now, but so far I don't
see a great way around it (unless you don't need complex system modeling
- then you could use IES-VE as discussed below).

Kristin Field

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According to another Bldg-Sim member, my statement of basic HVAC
calculations could be misleading, so I will clarify in case it bothered
anyone else. If one would describe natural ventilation as an HVAC
calculation, then I would *not* describe IES-VE as "basic" in that
context. That capability seemed very strong to me in IES-VE. However,
if you want to model sophisticated HVAC *mechanical* equipment (yes,
this could be a gray area since HVAC can integrate with NV via controls
on the windows, so suffice it to say that I'm talking about all HVAC
*except* NV and didn't come up with a more bulletproof term), then it
does not have as wide an array of options as DOE2 and EnergyPlus. I
thought I stated that below in the fourth sentence, but maybe it gets
confusing along the way. This is as of several months ago, and I didn't
check out a new version and do a thorough review just to write this
email. So if a bunch of new HVAC capabilities have been added, then
that could date some of my statements. Apologies to anyone who thought
I was trying to trash IES-VE because I definitely did not intend to do
that. I think it's an impressive program and probably useful to a lot
of people.

Kristin

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>From what I know IES-VE is really not an ideal tool if you want to
submit for LEED EAc1. From my understanding you cannot model a chilled
water plant in IES-VE. Has anyone submitted their energy model for LEED
EAc1? If so how was your experience? What type of system did you model?
Our company is looking into this program but this limitations is a HUGE
factor in our decision.

ARTURO HERNANDEZ, LEED AP

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Hi all,

I am also currently working with IES-VE for LEED energy modeling. I am
finding it very efficient to compute the loads on the project I am working
on, which is quite huge and relatively complex in terms of
geometry/envelope.

However, it gets harder to model the water chilling plant as required by
Appendix G, and I am actually doing this part of the modelling with my own
excel calculation sheets and with DOE-2 curves.

I was wondering; how will this approach be received by the USGBC? Could they
possibly require that the whole modeling is carried out with a single
package? Has anyone had problems validating EA1 with part of the energy
modelling being external to the simulation tool?

I have also been thinking of somehow using EnergyPlus or eQuest (preferably
the latter) just for the water chilling plant modeling. Has anyone ever used
one of these two tools to compute the systems energy from a cooling demand
calculated in an other simulation package?

Regards

Mathieu Le Bourhis

_____

De : bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] De la part de Field, Kristin
Envoy? : jeudi 12 mars 2009 21:40
? : bldg-sim at lists.onebuilding.org
Objet : Re: [Bldg-sim] One model

I tried out IES-VE a few months or a year ago with some people because the
potential for this type of integration seemed very exciting. However, we
found the HVAC side to be pretty basic. For a lot of building types, there
are significant savings to be had by changing HVAC control schemes and/or
configurations and using HVAC types that were not well-represented in IES-VE
the last time I saw it. It seemed like a great interface to use if you were
trying to design a building to use minimal energy due to envelope,
orientation, natural ventilation, etc. In other words, it seems strong on
the loads calculation side. On the system use side, though, it seemed a lot
more limited than DOE2 or EnergyPlus. For that reason, I have also stuck
with the multiple-tools method. I agree with all who wrote that it would be
wonderful to have one integrated tool in the future! Rob does bring up an
interesting point about the resolution of spaces needed for daylighting vs.
thermal vs. architectural modeling. Architects especially have to be so
detailed in their models that I?ve often just ended up using the floor plans
they provided, deleting a bunch of elements out of those, and scaling wall
heights and windows. Other than that, their 3D models only serve to help me
visualize the building myself. It would be nice if we didn?t end up
tripling the effort like we all do now, but so far I don?t see a great way
around it (unless you don?t need complex system modeling ? then you could
use IES-VE as discussed below).

Kristin Field

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USGBC does allow calculations outside the model for end uses which do not
impact other end uses such as exterior lighting or domestic hot water. If
the cooling central plant can be completely isolated and you can demonstrate
that the loads placed on it are exactly the same in both models then it may
be allowed. In order to do this with a high degree of accuracy you may have
to build virtually the same model in both versions of the software. You
would also need to very thoroughly explain your modeling procedures and
calculations. By the time you did all that my guess is that you would be
better off just submitting the whole model in eQUEST instead of justifying
the combination.

So as a LEED reviewer I would be highly skeptical of the scenario you
suggest and would likely scrutinize it to a significantly higher degree
compared to all calculations in one model. As I understand it IES-VE does
not yet model water cooled systems very well so I might suggest that it is
simply not an appropriate modeling tool to use for this particular project.

Marcus Sheffer

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Regarding the modeling of water-cooled chillers, chilled water loops, and HVAC systems in IES :

In response to user demand, IES is expanding the capability for HVAC systems modeling within IES to more thoroughly represent both conventional and unconventional HVAC systems.

While not yet publically released or announced, in-depth capability for modeling water-cooled chillers and chilled water loops within the IES ApacheHVAC application has been developed and implemented. This capability is presently undergoing testing and will be available in the next release later this spring.

The new water-cooled chiller model is described by three performance curves:

1) varies cooling capacity with entering condenser water temperature

2) varies electric input ratio (EIR) with chilled water temperature

3) varies electric input ratio (EIR) with part-load fraction.

These scalable performance curves are pre-defined for common chiller types: screw; centrifugal (hermetic, with or without VSD, and open); and reciprocating (hermetic and open). Where water flow is variable, performance curves are provided for pumps. These include constant-speed/variable-flow "riding the pump curve" and electronically commutated variable speed. For expert users, parameter values are editable in the equations describing the performance curves for chillers and pumps.

In addition to selecting appropriate performance curves, the user is able to specify interconnected performance inputs for capacity, COP, condenser and chilled water temperatures, flow rates, and loop delta-T at both rated and design conditions. An input is provided for the load fraction below which the chiller will cycle on and off. The user also has control of operating parameters such as condenser-water setpoint and variation of this setpoint via a formula profile (which may reference outdoor or indoor conditions and other sensed variables), chilled supply water temperature (SWT), and ramped SWT reset between high and low outdoor temperature setpoints.

The cooling tower and condenser-water loop use essentially the same cooling tower model that is provided for the waterside economizer component in the current version of ApacheHVAC. The cooling tower model presently includes a two-speed fan with flow fraction setting for each speed, approach, range, and electric input ratio. This tower and condenser-water loop model accounts for changes in outdoor conditions, chiller heat rejection, and user-controlled tower operating parameters as described above.

Primary and secondary chilled water loops are modeled for the first release of this new facility in a PRM-compliant "common pipe" configuration. For this configuration, the primary loop uses a constant-speed pump that operates whenever the chiller is running and the secondary loop with flow controlled to maintain the specified CHW supply temperature and loop delta-T. Either a constant-speed/variable-flow pump riding the pump curve or a variable-speed pump with variable speed drive (VSD) can be specified for the secondary (chilled-water distribution) loop. Cooling coils, chilled ceilings, etc. are then assigned to the secondary loop associated with a particular chiller.

The currently available release of the VE uses a simpler model that does provide means of describing the performance of a water-cooled chiller, cooling tower, and pumps in relation to both part-load fraction and outdoor wet-bulb or dry-bulb temperatures. This is presently done via a matrix of user input data points for the chiller COP, condenser-water pump power, cooling tower fan power, and chilled-water pump power. With appropriate inputs, the chiller COP in this simpler exiting model can be thus be varied according to both load fraction and outdoor conditions, while the power for the associated pumps and fans can separately be varied according to load fraction. However, because this simpler model does not use the type of curves that many EnergyPlus and DOE-2 users are accustomed to and does not explicitly model the thermodynamics of the CW, primary CHW, and secondary CHW loops or their controls, the new facilities described above have been developed to do just this.

It is worth noting that the USGBC generally supports the selection of the simulation tool that will most accurately represent what the user is attempting to model, while also suitably addressing the 90.1 PRM requirements for the baseline model. This requires a degree of professional judgment and USGBC approval is on a case-by-case basis. For example, one might be attempting to model a novel air handler configuration, such as a DOAS with indirect evaporative cooling, DX dehumidification, and a desiccant wheel regenerated by waste heat from the DX condenser coil, in a building that uses passive chilled beams fed by a water-cooled chiller. In such a case, it may be that the benefits of added detail in modeling the air handler configuration, desiccant wheel, and the combined radiant and convective effects of the passive chilled beams would outweigh certain limitations with respect to other aspects of the system, such as chiller sequencing. Similar professional judgment may need to be exercised to appropriately account for heat transfer mechanisms and system dynamics when modeling a UFAD system, displacement ventilation, double-skin fa?ade, earth tube pre-conditioning, natural ventilation, mixed-mode operation, or highly customized controls. Ultimately the energy modeler has to make an informed selection of the most appropriate tool for the project at hand.

Finally, with regard to the "One Model" topic that started this Bldg-Sim thread, the IES is intended to address the need for an interdisciplinary range of technical analyses within a single, integrated model. In part, this is provided through interoperability with other tools, such as SketchUp, Revit, and other BIMs, thus minimizing and potentially eliminating the need for preparing a separate 3D model. The also includes a range of applications, several of which were described by users earlier in this thread, for integrated analysis of solar shading, daylight modeling, daylighting controls, thermal mass and dynamic load calculations, natural ventilation, thermal comfort, airflow, IAQ, conventional HVAC systems, building-integrated HVAC systems, etc. The provides a range of tools for analysis appropriate to each stage of the design process, facilitating both quick, early reduction of building loads followed by detailed investigation of technical opportunities.

Hopefully this helps to clarify the capabilities of the VE for those concerned specifically with modeling HVAC systems and more generally with the "one-model" approach.

Timothy Moore
Senior Consultant
Special Projects

Office: 415 983-0603
timothy.moore at iesve.com
www.iesve.com

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