DAYSIM to EnergyPlus - Solemmasolemma.net/img/Events/2012/DD2012_Sargent_DaysimtoEnergyPlu… · As...
21
DIVA Day | October 19, 2012 | M.I.T. DAYSIM to EnergyPlus in Grasshopper
Transcript of DAYSIM to EnergyPlus - Solemmasolemma.net/img/Events/2012/DD2012_Sargent_DaysimtoEnergyPlu… · As...
DIVA Day | October 19, 2012 | M.I.T.
DAYSIM to EnergyPlus in Grasshopper
DIVA Day | October 19, 2012 | M.I.T.
EnergyPlus has native methods for calculating the radiation that falls on building surfaces and nodes. These are important for understanding solar gains and internal lighting loads. So, we ask:
-How accurate are these native calculations?
-When does it make sense to use Radiance/DAYSIM instead?
-How can DAYSIM results be linked to EnergyPlus in DIVA for Grasshopper?
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance: To compare EnergyPlus and DAYSIM, we start with the simplest case: An exposed façade with no obstructions.
Exposed Façade
Typical office zone
DIVA Day | October 19, 2012 | M.I.T.
total irradiance over each subsurface
Façade Irradiance: To calculate irradiance with Radiance/DAYSIM, we use the DIVA Radiation Map component (WIP), which automatically subdivides surfaces and generates vectors and nodes, while keeping track of subsurface areas.
16 analysis nodes
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance: To calculate irradiance with EnergyPlus, we use the Viper component, and sum all incident radiation on the exposed face.
Ext Solar Beam
Ext Solar Sky Diffuse
Ext Solar Ground Diffuse
Ext Solar Sky Diffuse Refl
Ext Beam Sol Refl
Ext Diff Sol Refl exterior wall
adiabatic
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance – Results for Simple Case: When no shading obstructions are present, the differences in annual irradiance are relatively small.
No Ground Plane with Ground Plane (20% reflectance)
-1% +1%
kWh/m2-yr (DAYSIM)
kWh/m2-yr ( EnergyPlus)
South Facade Boston, MA
N 1000
DIVA Day | October 19, 2012 | M.I.T.
N
No Ground Plane with Ground Plane (20% reflectance)
West Facade Boston, MA
Façade Irradiance – Results for Simple Case : Some orientations show greater variance than others (in general, the less the direct irradiance, the greater the sensitivity to the difference in sky models).
-5%
1000
kWh/m2-yr (DAYSIM)
kWh/m2-yr ( EnergyPlus)
-9%
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance – Urban Canyon: What if shading objects are present?
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance – Urban Canyon:
EnergyPlus is not adept at handling scenes with significant interreflections. Theoretically, results should begin to diverge from Radiance/DAYSIM as shading complexity increases. We begin with a simple group of diffuse-reflecting neighboring buildings.
35% refl
20% refl
DIVA Day | October 19, 2012 | M.I.T.
0
50
100
150
200
250
300
2 3 4 5
DAYSIM
Façade Irradiance – Urban Canyon: What radiance parameters to use?
N
Radiance ambient bounces
kWh/
m2-
yr
with context modeled, DAYSIM irradiance results taper off after ~ 3 ambient bounces.
DIVA Day | October 19, 2012 | M.I.T.
1300
0
kWh/m2
100 simulations at different context heights -ab 3 -ad 1000 -as 20 -ar 300 -aa 0.1
DIVA Day | October 19, 2012 | M.I.T.
% Context Height
kWh/
m2-
yr
Façade Irradiance – Urban Canyon: As context grows, DAYSIM and EnergyPlus remain fairly close.
0
200
400
600
800
1000
1200
1 5 9 13
17
21
25
29
33
37
41
45
49
53
57
61
65
69
73
77
81
85
89
93
97
101
DAYSIM
EnergyPlus
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance –Shading Screen
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance – Shading Screen: In this case, we increase the node density in response to the smaller scale of the shade.
256 analysis nodes
-ab 2
-ab 3
-ab 4
-ab 5
-ab 6
N
DIVA Day | October 19, 2012 | M.I.T.
0
100
200
300
400
500
600
700
2 3 4 5 6
DAYSIM
Façade Irradiance – Shading Screen:
N
Radiance ambient bounces
kWh/
m2-
yr
We also up our ambient bounces, since more are needed for results to level off.
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance – Shading Screen:
DIVA Day | October 19, 2012 | M.I.T.
0
200
400
600
800
1000
1200
1400
0.00 0.07 0.13 0.20 0.27 0.33 0.40 0.47 0.53 0.60 0.67 0.73 0.80 0.87 0.93 1.00
DAYSIM
EnergyPlus
Façade Irradiance – Shading Screen Results:
N
Shade Screen Growth
kWh/
m2-
yr
DIVA Day | October 19, 2012 | M.I.T.
0
200
400
600
800
1000
1200
1400
0.00 0.07 0.13 0.20 0.27 0.33 0.40 0.47 0.53 0.60 0.67 0.73 0.80 0.87 0.93 1.00
DAYSIM
EnergyPlus
Façade Irradiance – Shading Screen Results:
N
Shade Screen Growth
kWh/
m2-
yr
Results are same without screen
As shade grows, disparity between Radiance and EnergyPlus quickly jumps to ~25%
- 25%
- 25%
DIVA Day | October 19, 2012 | M.I.T.
Façade Irradiance – Shading Screen Results: For complex shading geometry, EnergyPlus not only diverges from Radiance/DAYSIM, but also becomes very slow. Using v7.0, the above annual simulation took five times longer than a Radiance/DAYSIM run with –ab 6. DAYSIM (-ab 2): 4 min DAYSIM (-ab 3): 7 min DAYSIM (-ab 4): 8 min DAYSIM (-ab 5): 8 min DAYSIM (-ab 6): 8 min EnergyPlus: 40 min *The DOE is in the process of updating its shadowing algorithm to decrease processing times in upcoming releases of 7.x.
DIVA Day | October 19, 2012 | M.I.T.
Conclusions: -EnergyPlus produces similar results to Radiance/DAYSIM in simple shading environments
-Results begin to diverge only when scene becomes quite complex*
-Use the tool that’s right for your geometry, and the question being asked. *Complex materiality could produce differences as well
DIVA Day | October 19, 2012 | M.I.T.
Implementation: Linking Radiance/DAYSIM to EnergyPlus in Grasshopper….
