Has there been any information released on the differences between energy simulation programs? We have a bid requirement with a certain percentage listed and we have been asked to address the differences between the bid model and the newly proposed model.
Thanks in advance -
John Peterson, PE, LEED AP
John,
It is like buying a car. Do you want a truck, manual/automatic, something
fast....... You are asking for information overload. If you know exactly
what you want it may be easier for us (in this list) to help guide you to the
best option.
I also was once curious and found the link below. The end of the paper has
charts comparing different features.
http://apps1.eere.energy.gov/buildings/tools_directory/pdfs/contrasting_the_c
apabilities_of_building_energy_performance_simulation_programs_v1.0.pdf
Another sight.
http://www.wbdg.org/resources/energyanalysis.php
I use Trace 700 (v6.2.4). Why? Because the first, second and third company I
worked for used it. It is good for running loads, but so-so for energy
modeling. Also I have never used anything else. I have looked at equest and
DOE, they both look like learning a completely new programming language.
I wouldn't mind hearing other people's brief views of the programs they use.
Equest, DOE, HAP, ect.
John Eurek LEED AP
This is something that I took from another resource and have been
editing. There are many moving targets relative to the release of
software updates etc., and may not be completely accurate, but the core
information is there
Hope this helps
Mike Travers, LEED AP
All,
The original document (Simulation Tool Comparison.doc) had dated information regarding TRACE 700. We have updated the document to reflect current and accurate information and added a few capabilities that have been added to TRACE within the past several years. With the additional capabilities added, the document should be updated to reflect the current capabilities of DOE 2.2, eQUEST, and HAP.
Regards,
Eric Sturm
I know a couple of the eQuest/DOE2.2 guys watch this list - can you
double check this document and make sure it is up-to-date from your
side? One thing I saw is that many people on the lists here report
successfully modeling chilled beam systems in eQuest and this document
shows that to not be a capability.
JEREMY R. POLING, PE, LEED AP
I was at an Equest seminar the other day. Equest does not have direct
chilled beam modeling capability right now. Those algorithms are due to be out in an update issued later this year(?).
Up till now, a work around has been used.
FYI, another comment on TRANE Trace 700: the modeling engineers I hired
told me, after consultation with TRANE, that exposed interior concrete
floors, when modeled against the ASHRAE baseline of carpeted floors,
showed a reduction in the cooling load, but an increase in the heating
load. An increase in the heating load was contrary to my reading in
passive solar books. I used a simplified simulator for lay people, and
it showed exposed interior concrete floors improved cold-weather
performance over carpeted concrete (HEED, www2.aud.ucla.edu/heed).
I have since heard that TRANE does not model thermal mass well. I have
also not been able to find anyone with experience modeling the thermal
mass of interior exposed concrete floors using any simulation tool.
Paul Grahovac, LEED AP
Hi Paul,
My experience on EnergyPlus with this question led me to the conclusion that
the time-delayed release or gain of heat in interior concrete walls or
floors is a bit of a fiction. Virtually all of this heat is picked within
the first hour by the mechanical systems. Exterior concrete, likewise, had
very little impact on the occupant comfort and interior temperatures simply
because of the presence of insulation. However, remove the cooling systems
(we do that here in Canada, particularly in residential high-rises) and the
picture is very different.
It would be interesting to repeat the same analysis on a building that is
fully designed to take advantage of passive heating and cooling. Few are, of
course. I suspect even partially passive buildings (mixed/hybrid mode) don't
experience even a fraction of the purported benefits of thermal mass.
The increase in the heating load is because the assembly is treated as one
R-value. Removing the carpet decreases the R and increases the heating load.
Shaun Martin LEED AP
Shaun
Certainly a reasonable conclusion -- if you assume the DOE software is
infallible. I worked at a DOE national lab for 10 years. They put
their pants on one leg at a time just like the rest of us. That's where
I learned that engineers don't make mistakes. They just have "events"
from which they "recover." In the modeling study I commissioned after
leaving the DOE contractor job, we got the same result regardless of
whether we insulated the slab -- which was curious. With the UCLA HEED
simulator, I got the best results with significant southern glazing --
which would support the passive solar idea.
Paul Grahovac, LEED AP
The way I understand it, the effect of thermal mass is all in how the
heating/cooling loads are calculated. TRACE is unique from many other
programs in that the user can choose the heating/cooling load
methodology that will be used. Depending on your choice, thermal mass
will be calculated differently. Most incorporate some kind of Transfer
Function Method (TFM), and each method is based on calculations and
algorithms from ASHRAE publications such as the 1972, 1985, and 2001
ASHRAE Fundamentals Handbooks, ASHRAE Research Project #359, and the
ASHRAE Toolkit for Building Load Calculations.
So the question of "What are the differences between TRACE and Energy
Simulation program 'X'?" is complicated by the additional question,
"Which Load Calculation Methodology in TRACE did you select?"
Clark Denson, PE
You need to have some mechanism for passively charging your mass to really
get the major energy benefits of the mass. If you have a building that's
being actively heated and cooled all the time, with no passive inputs, then
the mass won't do much except reduce your peak thermal load some, provided
you get an actual temperature differential between the mass and the space
(i.e. the system is sized correctly and the space temperature exceeds the
typical set point at the peak hour).
So, you can couple passive solar input to your mass, and use that mass to
sink heat for later (rather than having the space temperature rise). The
passive solar input to the space has to be higher than the thermal load on
the space for a while to get in energy benefit from the mass storage. Or
you can use passive night cooling to cool your mass for later.
There are many situations where a building would not be able to take
advantage of mass, so anecdotes of one particular building model not
realizing savings from increased proves that not all buildings will see
improvements with increased mass, not that increased mass has zero savings
in all cases. My personal experience in modeling mass shows that mass
makes a huge difference in the efficacy of passive heating and cooling
strategies. I think this paper talks about some of what we found:
http://www.ibpsa.org/proceedings/BS2007/p120_final.pdf
Erm, what passive solar books have you read?
Basically a layer of insulation (carpet) will reduce startup loads
when the thermostat switches from, say, 15 degC setback to 21. Trane
(although i cannot speak of the quality of its algorithms) is probably
right.
It may be better to be uncarpetted if your heating doesn't have a
setback. You don't get any startup heating load spikes then.
I don't know what methodology my people used. I appreciate everyone's
input. I am concerned I should remain a viewer and not a participant on
this listserv since I am not a modeler -- only a consumer of modeling
services. One data point that is not data, but confirmed to me that
thermal mass is real: I brought an energy auditor to an
minimally-heated greenhouse at night and asked him to point his
thermographic gun at everything --including the concrete blocks holding
up the planting platforms. Everything was blue and cold except the
concrete blocks which were yellow-red warm.
Paul Grahovac, LEED AP
Just what is on the shelf at the University of Kansas School of
Engineering. I was just surfing, so did not take notes.
The heat balance switches direction at night. From the blocks
absorbing heat in the day to giving it off at night. A trombe wall
also works this way.
In reference to your last question, where a building is designed to
maximise passive solar then yes exposed concrete could work better.
For a traditionally serviced building, if it's heating intensive but
also intermittently heated, go lightweight and well insulated. If it's
cooling intensive maximise exposed thermal mass.
Paul, back to your original question, this document may help. There is also
a document with a side-by-side comparison table, somewhere. I'll see if I
can find it and send it to you.
If you've been reading through bldg-sim, you'll find modellers tend to get
sidetracked easily.
Shaun Martin LEED AP
I would like to know the meaning of modelers getting sidetracked easily....
Paul,
I would like to console/assure you of something, just because any given
energy model doesn't show specific behavior doesn't mean it's not real,
and it doesn't mean the person who put that model together doesn't
"believe" in it. More often than not, the program simply can't handle
what we're trying to model explicitly/cleanly, if at all! The science
of building energy modeling is ever-developing. Every month new
software and methods are developed that allow us to grow and accurately
model more things.
Speaking specifically to eQuest, I can't purport to be an expert - as
I've yet to be tasked to model thermal massing options comparatively,
but I'm aware explicitly modeling the thermal massing qualities of any
given zone's contents/floor constructions is a possibility (see attached
screengrab - rightmost inputs). The constructions you define for your
envelope walls/floors/roofs and interior walls also defines the mass
properties that, by default, will account for the storage and transfer
of heat over time - though users can and often do choose to model such
elements without heat storage/transfer if necessary for tangent reasons.
That said, my general impression from reading others' discussions on the
topic (in the eQuest mailing list), is that when it comes to comparative
modeling of specific constructions (i.e. carpeted SOG vs. bare slabs),
it does become fuzzy as to how to accurately model both cases.
John,
If I can venture a guess for Shaun... I think it has something to do
with long hours, caffeine overdosage, deadlines, model reviewers, and
the quirky but pleasant company/support available through these mailing
lists... Also, what was the question? =)
NICK CATON, E.I.T.