Calculating scheduled solar gains for EnergyPlus' surfaces

Hi German,
If you're okay with spatial averaging of the solar gains over a group of
windows, you could create a BSDF using Radiance to represent the complexity
in E+. The only caveat is that instances where sunlight coming from behind
the facade can enter the facade (reflecting off of buildings across the
street, for example) can not be represented in a BSDF. So you site
obstructions are best represented as geometry in the energy plus model. But
overhangs and undulated microperferated screens can now be represented as
BSDFs.

Now I'll try to compare my approach from 2011 to the approach you detail. I
traced rays from the window into the space to see what surfaces the ray
hit. You're creating sensors on surfaces tracing rays from the surfaces to
most cases, but mine is better :). With your approach you're trying to
calculate the average irradiance over a surface. If you have one sensor
point your estimate of the average will not be very good. So you decide to
use a grid of sensor points, which improves your estimate, but a regular
grid will be biased. So you use random points and your estimate is very
good. Though if you have a complex model, with say furniture, then you need
to know what hits the furniture too. Good luck putting sensor on all the
furniture surfaces. So then the next question is what settings are you
using? where they high enough?

Instead if you send rays from the window into the space, like I did, every
ray is accounted for, so your total solar gains will be accurate. With my
approach, I know that the sum of the energy distributed to the surfaces
equals the sum of the energy transmitted by the window, error in my
approach is limited to relative distribution between surfaces. With you
approach you have to do a lot of work to try to make sure the total energy
in the space is accurate, and I don't know of a simple way to check that
the sum of energy attributed to surfaces equals the sum of energy
transmitted by the window.

So while my approach might be trickier to implement, once it's running you
know you're not destroying or creating energy. Your approach is simple to
set up, but you're never really sure that the total energy in the space is
correct.

Andy

···

On Sat, Feb 27, 2016 at 4:18 AM, Germán Molina Larrain <[email protected] > wrote:

Hi everyone,

I am working on a project that requires calculating solar heat gains
through (very) complex building envelopes. I am pretty sure that EnergyPlus
will not be able to do it...

I know EPlus is capable of dealing with CFS by means of BSDF... but that
assumes that the CFS is an extra layer in the facade. In my case, you could
consider the facade to be just anything.... a moving (ondulated and
microperforated) overhang, a tree, a complex exterior environment, etc.

My plan is to use Daylight Coefficients and use
SurfaceProperty:SolarIncidentInside object in E+. That is, I want to
incident! interreflection will be calculated by EPlus (is that correct?)*

I understand this could be done as:

1. Create an office with black walls, floor and ceiling... the
exterior and the envelope keep their properties.
2. Create a sensor file for each surface... sensors are normal to each
surface, pointing inside
3. Calculate Daylight Coefficients for each wall
Wall.dcmtx
1. cat weather.wea | dctimestep Wall.dcmtx | averageSensors >

Now... I am not sure if this is correct, because what ANDY SHOWED IN 2011
is sort of different. He calculated a wird View Matrix.... is that an old
way of doing this same thing? What am I missing?

Best!

Germán

_______________________________________________
[email protected]

1 Like

Also, if you use your approach and use ab>0 then you need to multiply the
irradiance on the surface by solar absorbance of the surface. If you don't
then you will definitely create energy.

Andy

···

On Sat, Feb 27, 2016 at 1:28 PM, Andy McNeil <[email protected]> wrote:

Hi German,
If you're okay with spatial averaging of the solar gains over a group of
windows, you could create a BSDF using Radiance to represent the complexity
in E+. The only caveat is that instances where sunlight coming from behind
the facade can enter the facade (reflecting off of buildings across the
street, for example) can not be represented in a BSDF. So you site
obstructions are best represented as geometry in the energy plus model. But
overhangs and undulated microperferated screens can now be represented as
BSDFs.

Now I'll try to compare my approach from 2011 to the approach you detail.
I traced rays from the window into the space to see what surfaces the ray
hit. You're creating sensors on surfaces tracing rays from the surfaces to
most cases, but mine is better :). With your approach you're trying to
calculate the average irradiance over a surface. If you have one sensor
point your estimate of the average will not be very good. So you decide to
use a grid of sensor points, which improves your estimate, but a regular
grid will be biased. So you use random points and your estimate is very
good. Though if you have a complex model, with say furniture, then you need
to know what hits the furniture too. Good luck putting sensor on all the
furniture surfaces. So then the next question is what settings are you
using? where they high enough?

Instead if you send rays from the window into the space, like I did, every
ray is accounted for, so your total solar gains will be accurate. With my
approach, I know that the sum of the energy distributed to the surfaces
equals the sum of the energy transmitted by the window, error in my
approach is limited to relative distribution between surfaces. With you
approach you have to do a lot of work to try to make sure the total energy
in the space is accurate, and I don't know of a simple way to check that
the sum of energy attributed to surfaces equals the sum of energy
transmitted by the window.

So while my approach might be trickier to implement, once it's running you
know you're not destroying or creating energy. Your approach is simple to
set up, but you're never really sure that the total energy in the space is
correct.

Andy

On Sat, Feb 27, 2016 at 4:18 AM, Germán Molina Larrain < > [email protected]> wrote:

Hi everyone,

I am working on a project that requires calculating solar heat gains
through (very) complex building envelopes. I am pretty sure that EnergyPlus
will not be able to do it...

I know EPlus is capable of dealing with CFS by means of BSDF... but that
assumes that the CFS is an extra layer in the facade. In my case, you could
consider the facade to be just anything.... a moving (ondulated and
microperforated) overhang, a tree, a complex exterior environment, etc.

My plan is to use Daylight Coefficients and use
SurfaceProperty:SolarIncidentInside object in E+. That is, I want to
incident! interreflection will be calculated by EPlus (is that correct?)*

I understand this could be done as:

1. Create an office with black walls, floor and ceiling... the
exterior and the envelope keep their properties.
2. Create a sensor file for each surface... sensors are normal to
each surface, pointing inside
3. Calculate Daylight Coefficients for each wall
Wall.dcmtx
1. cat weather.wea | dctimestep Wall.dcmtx | averageSensors >

Now... I am not sure if this is correct, because what ANDY SHOWED IN 2011
is sort of different. He calculated a wird View Matrix.... is that an old
way of doing this same thing? What am I missing?

Best!

Germán

_______________________________________________
[email protected]

Hi Andy,

thanks for such a very good answer. It is quite clear, or will be once it
sinks in.

I have one concern though. Let me elaborate.

My intention was to, actually, not use BSDFs at all. I would like to
account for the irradiance caused by the sky and sun, not using the 3-phase
method, but the 2 phase one. Accordingly, I send rays from the walls to the
binned sky, not to the window. In such case, I would say that your method
is impracticable since there is nowhere to send rays from, and with it it
is impossible to account for inter reflections on the (very weird) exterior
environment.

The idea of using black walls, floor and ceiling surfaces was not to
consider inter reflections in the interior space (I understand that energy
plus will account for that...?). Why do I need -ab 0? I actually want to
account for all the optical phenomena on the exterior.

Am I being clear? Am I totally wrong?

Kind regards!

···

El 27 feb. 2016 18:33, "Andy McNeil" <[email protected]> escribió:

Also, if you use your approach and use ab>0 then you need to multiply the
irradiance on the surface by solar absorbance of the surface. If you don't
then you will definitely create energy.

Andy

On Sat, Feb 27, 2016 at 1:28 PM, Andy McNeil <[email protected]> > wrote:

Hi German,
If you're okay with spatial averaging of the solar gains over a group of
windows, you could create a BSDF using Radiance to represent the complexity
in E+. The only caveat is that instances where sunlight coming from behind
the facade can enter the facade (reflecting off of buildings across the
street, for example) can not be represented in a BSDF. So you site
obstructions are best represented as geometry in the energy plus model. But
overhangs and undulated microperferated screens can now be represented as
BSDFs.

Now I'll try to compare my approach from 2011 to the approach you detail.
I traced rays from the window into the space to see what surfaces the ray
hit. You're creating sensors on surfaces tracing rays from the surfaces to
most cases, but mine is better :). With your approach you're trying to
calculate the average irradiance over a surface. If you have one sensor
point your estimate of the average will not be very good. So you decide to
use a grid of sensor points, which improves your estimate, but a regular
grid will be biased. So you use random points and your estimate is very
good. Though if you have a complex model, with say furniture, then you need
to know what hits the furniture too. Good luck putting sensor on all the
furniture surfaces. So then the next question is what settings are you
using? where they high enough?

Instead if you send rays from the window into the space, like I did,
every ray is accounted for, so your total solar gains will be accurate.
With my approach, I know that the sum of the energy distributed to the
surfaces equals the sum of the energy transmitted by the window, error in
my approach is limited to relative distribution between surfaces. With you
approach you have to do a lot of work to try to make sure the total energy
in the space is accurate, and I don't know of a simple way to check that
the sum of energy attributed to surfaces equals the sum of energy
transmitted by the window.

So while my approach might be trickier to implement, once it's running
you know you're not destroying or creating energy. Your approach is simple
to set up, but you're never really sure that the total energy in the space
is correct.

Andy

On Sat, Feb 27, 2016 at 4:18 AM, Germán Molina Larrain < >> [email protected]> wrote:

Hi everyone,

I am working on a project that requires calculating solar heat gains
through (very) complex building envelopes. I am pretty sure that EnergyPlus
will not be able to do it...

I know EPlus is capable of dealing with CFS by means of BSDF... but that
assumes that the CFS is an extra layer in the facade. In my case, you could
consider the facade to be just anything.... a moving (ondulated and
microperforated) overhang, a tree, a complex exterior environment, etc.

My plan is to use Daylight Coefficients and use
SurfaceProperty:SolarIncidentInside object in E+. That is, I want to
incident! interreflection will be calculated by EPlus (is that correct?)*

I understand this could be done as:

1. Create an office with black walls, floor and ceiling... the
exterior and the envelope keep their properties.
2. Create a sensor file for each surface... sensors are normal to
each surface, pointing inside
3. Calculate Daylight Coefficients for each wall
Wall.dcmtx
1. cat weather.wea | dctimestep Wall.dcmtx | averageSensors >

Now... I am not sure if this is correct, because what ANDY SHOWED IN
2011
is sort of different. He calculated a wird View Matrix.... is that an old
way of doing this same thing? What am I missing?

Best!

Germán

_______________________________________________
[email protected]

_______________________________________________
[email protected]

German,
Since you're not using BSDFs, I guess your approach makes sense. Just make
sure you accurately account for all the surface area in your model,
otherwise your total solar gain will be off.
Andy

···

On Sat, Feb 27, 2016 at 4:35 PM, Germán Molina Larrain <[email protected] > wrote:

Hi Andy,

thanks for such a very good answer. It is quite clear, or will be once it
sinks in.

I have one concern though. Let me elaborate.

My intention was to, actually, not use BSDFs at all. I would like to
account for the irradiance caused by the sky and sun, not using the 3-phase
method, but the 2 phase one. Accordingly, I send rays from the walls to the
binned sky, not to the window. In such case, I would say that your method
is impracticable since there is nowhere to send rays from, and with it it
is impossible to account for inter reflections on the (very weird) exterior
environment.

The idea of using black walls, floor and ceiling surfaces was not to
consider inter reflections in the interior space (I understand that energy
plus will account for that...?). Why do I need -ab 0? I actually want to
account for all the optical phenomena on the exterior.

Am I being clear? Am I totally wrong?

Kind regards!
El 27 feb. 2016 18:33, "Andy McNeil" <[email protected]> escribió:

Also, if you use your approach and use ab>0 then you need to multiply the
irradiance on the surface by solar absorbance of the surface. If you don't
then you will definitely create energy.

Andy

On Sat, Feb 27, 2016 at 1:28 PM, Andy McNeil <[email protected]> >> wrote:

Hi German,
If you're okay with spatial averaging of the solar gains over a group of
windows, you could create a BSDF using Radiance to represent the complexity
in E+. The only caveat is that instances where sunlight coming from behind
the facade can enter the facade (reflecting off of buildings across the
street, for example) can not be represented in a BSDF. So you site
obstructions are best represented as geometry in the energy plus model. But
overhangs and undulated microperferated screens can now be represented as
BSDFs.

Now I'll try to compare my approach from 2011 to the approach you
detail. I traced rays from the window into the space to see what surfaces
the ray hit. You're creating sensors on surfaces tracing rays from the
works fine in most cases, but mine is better :). With your approach you're
trying to calculate the average irradiance over a surface. If you have one
sensor point your estimate of the average will not be very good. So you
decide to use a grid of sensor points, which improves your estimate, but a
regular grid will be biased. So you use random points and your estimate is
very good. Though if you have a complex model, with say furniture, then you
need to know what hits the furniture too. Good luck putting sensor on all
the furniture surfaces. So then the next question is what settings are you
using? where they high enough?

Instead if you send rays from the window into the space, like I did,
every ray is accounted for, so your total solar gains will be accurate.
With my approach, I know that the sum of the energy distributed to the
surfaces equals the sum of the energy transmitted by the window, error in
my approach is limited to relative distribution between surfaces. With you
approach you have to do a lot of work to try to make sure the total energy
in the space is accurate, and I don't know of a simple way to check that
the sum of energy attributed to surfaces equals the sum of energy
transmitted by the window.

So while my approach might be trickier to implement, once it's running
you know you're not destroying or creating energy. Your approach is simple
to set up, but you're never really sure that the total energy in the space
is correct.

Andy

On Sat, Feb 27, 2016 at 4:18 AM, Germán Molina Larrain < >>> [email protected]> wrote:

Hi everyone,

I am working on a project that requires calculating solar heat gains
through (very) complex building envelopes. I am pretty sure that EnergyPlus
will not be able to do it...

I know EPlus is capable of dealing with CFS by means of BSDF... but
that assumes that the CFS is an extra layer in the facade. In my case, you
could consider the facade to be just anything.... a moving (ondulated and
microperforated) overhang, a tree, a complex exterior environment, etc.

My plan is to use Daylight Coefficients and use
SurfaceProperty:SolarIncidentInside object in E+. That is, I want to
incident! interreflection will be calculated by EPlus (is that correct?)*

I understand this could be done as:

1. Create an office with black walls, floor and ceiling... the
exterior and the envelope keep their properties.
2. Create a sensor file for each surface... sensors are normal to
each surface, pointing inside
3. Calculate Daylight Coefficients for each wall
> Wall.dcmtx
1. cat weather.wea | dctimestep Wall.dcmtx | averageSensors >

Now... I am not sure if this is correct, because what ANDY SHOWED IN
2011
is sort of different. He calculated a wird View Matrix.... is that an old
way of doing this same thing? What am I missing?

Best!

Germán

_______________________________________________
[email protected]

_______________________________________________
[email protected]

_______________________________________________
[email protected]

Cool, Andy! Thanks very much... I understand why you did what you did when
using BSDFs.

I have just noticed something: This approach does not require WINDOW, thus
it can be scripted...

Best,

···

2016-02-29 16:46 GMT-03:00 Andy McNeil <[email protected]>:

German,
Since you're not using BSDFs, I guess your approach makes sense. Just make
sure you accurately account for all the surface area in your model,
otherwise your total solar gain will be off.
Andy

On Sat, Feb 27, 2016 at 4:35 PM, Germán Molina Larrain < > [email protected]> wrote:

Hi Andy,

thanks for such a very good answer. It is quite clear, or will be once it
sinks in.

I have one concern though. Let me elaborate.

My intention was to, actually, not use BSDFs at all. I would like to
account for the irradiance caused by the sky and sun, not using the 3-phase
method, but the 2 phase one. Accordingly, I send rays from the walls to the
binned sky, not to the window. In such case, I would say that your method
is impracticable since there is nowhere to send rays from, and with it it
is impossible to account for inter reflections on the (very weird) exterior
environment.

The idea of using black walls, floor and ceiling surfaces was not to
consider inter reflections in the interior space (I understand that energy
plus will account for that...?). Why do I need -ab 0? I actually want to
account for all the optical phenomena on the exterior.

Am I being clear? Am I totally wrong?

Kind regards!
El 27 feb. 2016 18:33, "Andy McNeil" <[email protected]> escribió:

Also, if you use your approach and use ab>0 then you need to multiply
the irradiance on the surface by solar absorbance of the surface. If you
don't then you will definitely create energy.

Andy

On Sat, Feb 27, 2016 at 1:28 PM, Andy McNeil <[email protected]> >>> wrote:

Hi German,
If you're okay with spatial averaging of the solar gains over a group
of windows, you could create a BSDF using Radiance to represent the
complexity in E+. The only caveat is that instances where sunlight coming
from behind the facade can enter the facade (reflecting off of buildings
across the street, for example) can not be represented in a BSDF. So you
site obstructions are best represented as geometry in the energy plus
model. But overhangs and undulated microperferated screens can now be
represented as BSDFs.

Now I'll try to compare my approach from 2011 to the approach you
detail. I traced rays from the window into the space to see what surfaces
the ray hit. You're creating sensors on surfaces tracing rays from the
works fine in most cases, but mine is better :). With your approach you're
trying to calculate the average irradiance over a surface. If you have one
sensor point your estimate of the average will not be very good. So you
decide to use a grid of sensor points, which improves your estimate, but a
regular grid will be biased. So you use random points and your estimate is
very good. Though if you have a complex model, with say furniture, then you
need to know what hits the furniture too. Good luck putting sensor on all
the furniture surfaces. So then the next question is what settings are you
using? where they high enough?

Instead if you send rays from the window into the space, like I did,
every ray is accounted for, so your total solar gains will be accurate.
With my approach, I know that the sum of the energy distributed to the
surfaces equals the sum of the energy transmitted by the window, error in
my approach is limited to relative distribution between surfaces. With you
approach you have to do a lot of work to try to make sure the total energy
in the space is accurate, and I don't know of a simple way to check that
the sum of energy attributed to surfaces equals the sum of energy
transmitted by the window.

So while my approach might be trickier to implement, once it's running
you know you're not destroying or creating energy. Your approach is simple
to set up, but you're never really sure that the total energy in the space
is correct.

Andy

On Sat, Feb 27, 2016 at 4:18 AM, Germán Molina Larrain < >>>> [email protected]> wrote:

Hi everyone,

I am working on a project that requires calculating solar heat gains
through (very) complex building envelopes. I am pretty sure that EnergyPlus
will not be able to do it...

I know EPlus is capable of dealing with CFS by means of BSDF... but
that assumes that the CFS is an extra layer in the facade. In my case, you
could consider the facade to be just anything.... a moving (ondulated and
microperforated) overhang, a tree, a complex exterior environment, etc.

My plan is to use Daylight Coefficients and use
SurfaceProperty:SolarIncidentInside object in E+. That is, I want to
incident! interreflection will be calculated by EPlus (is that correct?)*

I understand this could be done as:

1. Create an office with black walls, floor and ceiling... the
exterior and the envelope keep their properties.
2. Create a sensor file for each surface... sensors are normal to
each surface, pointing inside
3. Calculate Daylight Coefficients for each wall
> Wall.dcmtx
1. cat weather.wea | dctimestep Wall.dcmtx | averageSensors >

Now... I am not sure if this is correct, because what ANDY SHOWED IN
2011
is sort of different. He calculated a wird View Matrix.... is that an old
way of doing this same thing? What am I missing?

Best!

Germán

_______________________________________________
[email protected]

_______________________________________________