[BLDG-SIM] Day-Lighting and DOE2.1E

[Jon McHugh]

Varkie,
 
California's Title 24 energy code has established values of energy
credits for daylighting controls.  These credits are used in both the
prescriptive approach and the performance method which is based upon an
energy simulation.  For the LEED credits the performance method would be
used as you are trying to estimate the energy consumption as a fraction
of the consumption of a minimally compliant building. The current tool
is EnergyPro which is DOE-2.1E with a user interface that places some
limits on inputs and automatically creates a reference or minimally code
compliance comparison case.  
 
The lighting power of controlled lighting that is in the daylit zone (no
more than 15 feet from a window and currently no more than 1 ceiling
height horizontally from a skylight) is reduced by a Power Adjustment
Factor (PAF).  The factor is a function of the visible transmittance and
the fraction of wall area for glazing.  Though this doesn't capture peak
reduction effects, the simplicity of the method provides some confidence
in the results.  Sensor placement has a huge impact on the results.
 
The Title 24 standards can be downloaded from:
http://www.energy.ca.gov/title24/
 
I don't know what rule set is involved for daylighting in DOE-2 when a
geometry is not described.  I wouldn't expect that this would be an
acceptable method since you really do not know what you are modeling.
The bottom line is that your model approximates what your daylighting
design does and that the design would reasonably save energy - thus a
lighting design that does not provide the desired light levels in all
the task locations would not likely provide maintained savings.
Modeling two sensors does not make any sense if your control system has
only one sensor and is designed to switch or dim lights evenly across
the entire control zone.  "Virtual" sensors are usually placed in a
relatively dark spot in the controlled zone so that electric lighting
provides sufficient light in the entire zone on the lighting control not
just next to the window or directly under a skylight.  
 
Modeling two sensors would make sense if the amount of dimming or
fraction of switched lights were segregated by how close they were to
the window or skylight.  In that case you really have two separate
control zones.
 
 
Jon McHugh, PE, LC
Heschong Mahone Group Inc.
11626 Fair Oaks Blvd #302
Fair Oaks, CA 95628 (Sacramento)
(916)962-7001 ext 38
(916)962-0101 FAX
e-mail: mchugh at h-m-g.com
URL: www.h-m-g.com 

 
 
-----Original Message-----
From: Varkie Thomas [mailto:Varkie.Thomas at som.com] 
Sent: Wednesday, January 21, 2004 1:37 PM
To: BLDG-SIM at GARD.COM
Subject: [BLDG-SIM] Day-Lighting and DOE2.1E



Can day-lighting controls be considered for LEED certification under
"Energy & Atmosphere - Optimize Energy Performance"?  If so where should
the light sensor be located in the space?  Is there any energy code that
allows credit for day-lighting controls? The DOE2 program allows two
light sensors per space.  Supposing the two sensors are located 5 ft and
10 ft from the window.  Is the average daylight at these two points used
in determining the reduction in artificial lighting?

 

The DOE2 program expects zones to have 6 surfaces defined with X,Y,Z
coordinates and reflectance values for day-lighting analysis.  Ignoring
this produces warning messages but the results show a reduction in
artificial lighting energy.  For day-lighting analysis we only enter
into DOE2 the X,Y coordinates of the window origin relative to the wall
and also the wall and window dimensions.  Can we assume that the energy
savings results from the DOE2 program are on the safe side (the actual
energy saved is more) when we use the program without all the surfaces
and coordinates?

 

Are there any rules for day-lighting analysis for establishing energy
savings and for comparing the results from different studies?

 

Varkie Thomas

Skidmore, Owings & Merrill LLP

Tel: (312) 360-4467 (direct)


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