In my experience, the impact of a green roof on the building energy is
pretty small. In the winter, the soil layer is reasonably saturated so
isn't adding much insulation. In the summer, there is some shading
effect to reduce solar but it is difficult to quantify.
Attached is "Greenroofs in Canada" which includes a look at the energy
impact of a greenroof on a building. It does discuss some modelling but
the increase in insulation value seems excessive to me.
The following paper, which might be useful, describes outdoor thermal
comfort of green roof (not necesseceraly building performance)..
"Thermal Comfort Assessment of a Green Roof at the College of
Architecture and Landscape Architecture in Tucson, Arizona
Uttara Patil and Nader Chalfoun, University of Arizona, Arizona, USA
The main difference in winter insulation between green roof and the
standard roof is the extra 1 1/2" expanded polystyrene panel
"drainage layer" in the green roof. If you add that to the standard
roof and assume it is dry (as the analysis does) then it adds the
extra R value and makes the comparison more equal.
I haven't come across the Pilkington Profilit glazing before. I am
modelling a project that uses this glazing. Has anyone come across
thermal performance information for this type of glazing?
Profilit and Reglit (datasheet for Profilit attached) is a U shaped glazed
wall element.
The last time we modelled this for a project we modelled it as a glass block
rather than a piece of glazing as the properties when you see it physically
are much more like a glazing brick. It's translucent, but quite opaque.
I am interested in attending a building energy performance modeling
workshop, in particular with DOE Energy Plus. Is there any suggestions
on training sources?
This is a channel glazing system. Using it with nanogel infill gives you
a slightly better r-value.
http://www.tgpamerica.com/structural-glass/pilkington-profilit/Profilit.
pdf
On 13.09.2010 21:01, bldg-sim-request at lists.onebuilding.org wrote:
Some points without any warranty ;-)
- It is an open system, you cannot evacuate it or fill it with any
special gases
- There are several options to improve perfomance like reducing solar
transmission or adding e.g. translucent insulation, coating inside
surfaces,...
- For double-glazing, the heat transfer should be about 2.8 W/m2K in a
simplified model. However, it may be interesting to have a closer look
at the non-homogenous facade structure.
- Visible light transmission in the double-glazing setup could be
assumed to be about 75% - however be aware of scattering, this is not
clear glass and thus cannot be treated as such when you look into
daylighting.
That's exactly why we modelled it as a glass brick. To be fair it's often
used outside of the conventional glazing system to provide architectural
features or in place of an opaque wall to gain areas of translucency into
deep plan areas where they would otherwise suffer from being miserable dark
corners.
Ah, yes I see what you mean. We of course did a number of different studies
and so had to of course treat each study differently.
In terms of the thermal modelling, we looked at the glazing being
essentially a transmissive shading device - the "wall" we modelled was in
front of a curtain wall and so didn't effect the thermal performance of the
building too much, it was an architectural feature wall largely, but
obviously caused a major effect on the shading and also the airflow which we
had to account for as well. Essentially we built an opaque shading device,
applied those properties of a glass brick to that device which would in
essence as you point out would see it as being fully opaque and therefore
light and solar transmission as being nil, but then we applied a
transmissivity profile relating to the small fraction of light/solar gain it
would allow through it. This is relatively easily done in EnergyPlus. The
other way to do it of course would be to make it glazed and apply a shading
coefficient or similar, based on the assumption you can't get the actual
breakdown of the glazing properties.
The other daylighting simulation required more careful treatment of the
specularity and light transmission values etc and essentially making it
diffusive, a bit like a ceiling light diffuser. I'll see if I can find
copies of the models we built and the figures we used. One was for a
previous employer so I'm not certain I have that model.
Hope that makes more sense
Paul
Paul,
You keep saying you modeled it like glass brick but what does that mean?
Did you consider its visible light transmission, its solar transmission or
both to be negligible?
I believe that NRCan did some initial work on the impact of Green Roofs, the result was a reduction of heat island effect rather than building energy savings.
You could use EnergyPlus' ecoroof model to either determine an effective seasonal heat transfer rates with a basic setpoint controller, and incorporate that into eQuest somehow. You may find that the inputs for the E+ green roof model itself may be a bit of guess work. It might be more work than it is worth.
Chris,
In my experience, the impact of a green roof on the building energy is
pretty small. In the winter, the soil layer is reasonably saturated so
isn't adding much insulation. In the summer, there is some shading
effect to reduce solar but it is difficult to quantify.
Attached is "Greenroofs in Canada" which includes a look at the energy
impact of a greenroof on a building. It does discuss some modelling but
the increase in insulation value seems excessive to me.
Cheers,
Brian
The following paper, which might be useful, describes outdoor thermal
comfort of green roof (not necesseceraly building performance)..
"Thermal Comfort Assessment of a Green Roof at the College of
Architecture and Landscape Architecture in Tucson, Arizona
Uttara Patil and Nader Chalfoun, University of Arizona, Arizona, USA
Nader V. Chalfoun, Ph.D., LEED AP, CEA
The main difference in winter insulation between green roof and the
standard roof is the extra 1 1/2" expanded polystyrene panel
"drainage layer" in the green roof. If you add that to the standard
roof and assume it is dry (as the analysis does) then it adds the
extra R value and makes the comparison more equal.
Chris Jones
I haven't come across the Pilkington Profilit glazing before. I am
modelling a project that uses this glazing. Has anyone come across
thermal performance information for this type of glazing?
Chris Jones
I did not find it in Window 5's library just now. I trust you've checked
the Pilkington Web site? They're probably the best source!
James V. Dirkes II, P.E., LEED AP
Chris
Profilit and Reglit (datasheet for Profilit attached) is a U shaped glazed
wall element.
The last time we modelled this for a project we modelled it as a glass block
rather than a piece of glazing as the properties when you see it physically
are much more like a glazing brick. It's translucent, but quite opaque.
I hope this helps.
Dr Paul Carey
Thanks! That help!
Chris Jones
Hello,
I am interested in attending a building energy performance modeling
workshop, in particular with DOE Energy Plus. Is there any suggestions
on training sources?
Thanks in advance,
Dr. Na (Luna) Lu
This is a channel glazing system. Using it with nanogel infill gives you
a slightly better r-value.
http://www.tgpamerica.com/structural-glass/pilkington-profilit/Profilit.
pdf
On 13.09.2010 21:01, bldg-sim-request at lists.onebuilding.org wrote:
Some points without any warranty ;-)
- It is an open system, you cannot evacuate it or fill it with any
special gases
- There are several options to improve perfomance like reducing solar
transmission or adding e.g. translucent insulation, coating inside
surfaces,...
- For double-glazing, the heat transfer should be about 2.8 W/m2K in a
simplified model. However, it may be interesting to have a closer look
at the non-homogenous facade structure.
- Visible light transmission in the double-glazing setup could be
assumed to be about 75% - however be aware of scattering, this is not
clear glass and thus cannot be treated as such when you look into
daylighting.
Cheers, Lars.
Lars,
That's exactly why we modelled it as a glass brick. To be fair it's often
used outside of the conventional glazing system to provide architectural
features or in place of an opaque wall to gain areas of translucency into
deep plan areas where they would otherwise suffer from being miserable dark
corners.
Paul
Paul
Ah, yes I see what you mean. We of course did a number of different studies
and so had to of course treat each study differently.
In terms of the thermal modelling, we looked at the glazing being
essentially a transmissive shading device - the "wall" we modelled was in
front of a curtain wall and so didn't effect the thermal performance of the
building too much, it was an architectural feature wall largely, but
obviously caused a major effect on the shading and also the airflow which we
had to account for as well. Essentially we built an opaque shading device,
applied those properties of a glass brick to that device which would in
essence as you point out would see it as being fully opaque and therefore
light and solar transmission as being nil, but then we applied a
transmissivity profile relating to the small fraction of light/solar gain it
would allow through it. This is relatively easily done in EnergyPlus. The
other way to do it of course would be to make it glazed and apply a shading
coefficient or similar, based on the assumption you can't get the actual
breakdown of the glazing properties.
The other daylighting simulation required more careful treatment of the
specularity and light transmission values etc and essentially making it
diffusive, a bit like a ceiling light diffuser. I'll see if I can find
copies of the models we built and the figures we used. One was for a
previous employer so I'm not certain I have that model.
Hope that makes more sense
Paul
Paul,
You keep saying you modeled it like glass brick but what does that mean?
Did you consider its visible light transmission, its solar transmission or
both to be negligible?
Paul Riemer
Thank you, I hadn't found that information yet!
http://www.tgpamerica.com/structural-glass/pilkington-profilit/Profilit.pdf
Chris Jones
I believe that NRCan did some initial work on the impact of Green Roofs, the result was a reduction of heat island effect rather than building energy savings.
You could use EnergyPlus' ecoroof model to either determine an effective seasonal heat transfer rates with a basic setpoint controller, and incorporate that into eQuest somehow. You may find that the inputs for the E+ green roof model itself may be a bit of guess work. It might be more work than it is worth.
Cheers,
Phylroy Lopez B.Eng LEED A.P.