Hello everyone!
I am working on a project, a high rise office building. The architect
added louvers as part of the design which I admire for sophistication.
Attached is a picture that shows the louvers outside for shading. But, when
I did the initial run, the effect of the louvers is only around 1% energy
improvement from the baseline.
Please let me know if there is a better way to do it in eQuest. What I did
was to measure the louver thickness and proportioned it to the glass area
that it covers. I put the fraction as "Transmittance:" in Building and
Fixed Shades properties. Doe 2 help says: TRANSMITTANCE
Fraction of incident solar radiation that is transmitted by the shading
surface. The default value is 0.0, which means the surface is opaque. A
value greater than 0.0 represents a device that passes some solar
radiation, such as a tree, lattice, or fabric. Using SHADE-SCHEDULE allows
seasonal variation in transmittance. Daylighting calculation assumes
TRANSMITTANCE = 0.
The design team quite find it hard to believe that the louvers have very
minimal effect. I told them to consider the window to wall ratio (almost
60%) and that fact that they will be using a clear glass, even with these
louvers partial UV rays still pass through the gaps that spreads allover
the glass surface that adds to the heat load for air conditioning. Ive
noticed to some of my other projects in tropical countries, building shades
don't have much effect to energy efficiency. Did anyone encounter the same
result with building shades?
Thanks,
Bob
Hi there
Has anyone worked out to apply the metric unit to equest?
Thanks
Jean-Luc Godillon
Bobby,
My approach would be (would have been) to model the shades as window overhangs or building shades, or a combination thereof. Based on your sketches this would be a lot of work, but the louvers are obviously an important feature for the design team and will have considerable project cost. You could try replicating the impressive things Nick Caton has done with shades per the attached email. You could try it for a floor or two to get the delta energy improvement and extrapolate for # of floors to get a rough comparison to your transmittance approach. I would think the reduction in cooling energy would be considerable if using clear glass with external shades vs. without. The overall numbers will of course depend on several other things, including the proportion of solar load to overall building cooling load.
Regards,
Bill
[cid:image001.png at 01CD3F0D.CC92CD30]
Bob,
What is the project location and how is the building oriented? Do these
louvers run across the entire height of the building?
If you have a heavily internal load dominated (office) building, the
building skin effect might be minimal, but then again the shading design
you have in this project looks pretty dense and assuming you have a need
for cooling, my gut feeling is that 1% is on the lower side.
Feeling confident in your modeling approach is very much important, but before running deep into alternate methods, I would seek perspective on what % improvement is even feasible. Perhaps a 1% net improvement is quite impressive, all things considered? Considering static shades can be simultaneously helpful and harmful thermally over a year, a few iterations exploring different transmittance values may be enlightening.
Doing so, you might be able to establish a ceiling for maximum possible improvement with such shades, and suggest a more optimized exoskeleton spacing or similar.
There may also be a lesson in here about how to present results in a fashion that both informs and appeases the design team. Perhaps the shades may not have an impressive net annual baseline % improvement, but significant thermal comfort and glare issues are averted, and cooling plant capacities can be lowered by slicing the summertime solar loads.... I would also caution to check the solar loads are indeed cutting down as anticipated if you aren't sure of your approach.
Best of luck!
~Nick
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
Classification: UNCLASSIFIED
Caveats: NONE
1% sounds about right.
This is what we are here for!! Now you can walk back to the architect and let him understand that there louvers will look pretty, but only save 1%. Maybe the money can be saved, or do the liberal things and just find another way to spend it.
If you can, run a quick model with 100% shading to see what a 'perfect' shading case would save.
Before you talk to the architect make sure you can explain why the louvers only save 1%.
1. You are not receiving heat in the winter when you want it.
2. The building energy use is mostly from computers, lights and outside air. Even with 100% shading you only save X%.
3. The outside wall area to the volume of the building is small, so the skin load (insulation, shading) is less important. (Yes it is important but has a quicker diminishing return than a smaller building. See elephant mouse analogy.)
Like I said, this is perfect use of energy modeling. It will show if a 'good' idea is actually a good idea or a feel good idea.
[Now when you try to nail down every since variable and account for every hour of every day for LEED, the benefits of energy modeling get a little more sketchier.]
"Is Freedom a small price to pay to stop Global Warming?"
John Eurek
Have not followed the thread in detail - but here are some things I have
found about windows - first off not a whole lot of saving at the
yearly-building level. If you look at the peak breakdown for a window - the
U-value related conductance is 2/3rds vs the solar radiation (1/3rd) -
atleast for the one model that I was looking at. As others have noted,
almost 40-50% of the energy consumption is from lights/plug loads.
You might want to look at just the perimeter zones and see what happens to
the energy consumption reduction in just those zones?
You can also look at just the LS-D reports to see what the % savings are.
Sometimes it helps in saying that reductions are x% of the cooling load
(without considering the HVAC inefficiencies) - which will be a higher
number.
Classification: UNCLASSIFIED
Caveats: NONE
It is all up to interpretation. The key to interpreting the information is to first know what you want the information to say, then find the data to back it up.
If you want to sell the solar shades, focus on the reduction of solar radiation. (Truth: A small part of the whole)
If you want to talk the architect out of it, highlight that it only saves 1%. (Truth: Energy savings comes from having many small energy savings methods working together.)
1 important question - How much does the architect like the solar shade?
If the solar shades are just an option, the next step is to do a life cycle cost analysis. You already have the energy model which is the hardest part. If you can find the cost of the solar shades and energy costs you could do it in 20 minutes or less.
If the solar shades are his pet, it won't be too hard to find numbers telling him how wonderful they are.
*his/hers
While I wouldn?t expect big savings from the shades, I think it might be a
bit higher than what you?re seeing because of the way its modelled. Using
proportional transmittance doesn?t account for how the shading varies with
sun angle. When the sun is high, less solar will get through. As Bill says,
I would model this as a building shade, actually putting each louver in. It
looks like the louvers are tubular, so you can probably approximate that
with a vertical shade and another one at 45?.
While this sounds like a lot of work, if you use copy and paste in the inp
file it probably isn?t as bad as it sounds. Just need to change the z
coordinate once you?ve put the first ones in. You might consider doing it in
Excel, with a formula for the z, and then copying the results into the inp
file. That would be pretty quick.
Mike
Michael Wilson, P.Eng., Enerficiency Consulting
Bobby, others,
I beg to differ, but I find it hard to believe that a louver system with the density
shown on your picture on a building with a WWR of 60 will have only a 1% impact on the
building energy use.
What is the percent impact on the cooling energy use? In an office building in a tropical
climate, as implied in your post, solar heat gain through windows can easily make up
30-50% of the building's cooling load, so if the solar is reduced by 30-50% due to
louvers, I would expect a cooling load reduction around 10-20%, and maybe total building
energy around 5-10%.
When you interpret the results from eQUEST, remember that the program doesn't model at all
the UV or long-wave interactions, etc., that you've mentioned to explain why the savings are
so low. If you are modeling the louvers as a BUILDING-SHADE, make sure that the shade is
positioned correctly in front of the glazing, that the TRANSMITTANCE and SHADE-SCHEDULE are
appropriately defined, and that you also adjust the SKY-FORM-FACTOR and GND-FORM-FACTOR
for the glazing, since the BUILDING-SHADE affects only the direct solar radiation and not
the diffuse solar radiation. This is particularly important in a tropical location where
there is a lot of diffuse radiation. The form factors are meant to be the amount (solid
angle) of sky or ground
that the glazing "sees". The defaults are 0.50 and 0.50, i.e., half sky and half
ground. If you input only the SFF, DOE-2 would assume 1-SFF as the GFF. I've had
trouble with that recently,
so it's better to also input GFF at 0.50, or a little higher if you think there's
reradiation due to the louvers.
Joe
Joe Huang
One more thought since peak load from windows was mentioned earlier:
In calculating peak cooling loads for sizing equipment (using Trane TRACE),
I have almost always found that the solar gains through windows were more
significant than conductance gains through windows...usually about 1.5 times
greater, sometimes much more. This of course depends on the U-value, SHGC,
and orientation of the assemblies. Unless a building is highly internal
load driven, I generally find that solar gain through windows is one of the
top three driving factors in peak cooling load (including lighting, plug
loads, ventilation, etc). Adding effective building shades can often result
in appreciably smaller cooling equipment, potentially allowing the equipment
to operate under more favorable part-load conditions as well as saving money
up front.
With that said, peak design load and annual energy are two different
animals. I agree that the overall percent energy savings on an annual basis
will be pretty low. Just wanted to mention this peak load side effect.
Christian