[Bldg-sim] Daylight saving simulation in eQUEST

[Eleanor Lee]

The numbers seem reasonable but there are a few ways you can check:

1. If you're using DOE-2/ Equest, check the depth of your zone & 
photosensor location against head height of window. Rule of thumb is 
daylit depth is ~1.5 times head height of window so typical zone depth 
for 9-ft ceiling is about 15 ft with sensor at 2/3rds or 10 ft distance 
from window.  DOE-2 has limitations in calc with split-flux method: 
internally reflected component is overestimated for distances greater 
than approx 2 times head height of window which can lead to 
overestimation of lighting energy use savings.   Also, pay attention to 
interior shading schedule/ modeling assumptions.  If you have a bare 
window, you're going to get great savings but uncomfortable occupants.

2. Check results against some other software packages:
DAYSIM or Daylight123 via Christoph Reinhardt, which uses Radiance as 
core engine but friendly user interface
Run your facade design through http://commglazing.datrona.com/facade.php 
in about 5 minutes (database based on DOE-2)
Run SPOT tool  (Radiance with GUI)
Compare switching strategies vs dimming strategies (ballast energy 
consumption differs between strategies), include occupancy-sensors in 
model for base & test cases
 
3. Field data:
New York Times Headquarters monitored data for open plan office with 
actively managed shades:
http://gaia.lbl.gov/btech/papers/56979.pdf
30-48% avg annual lighitng energy savings for west facing windows and
75% for bilaterally daylit SW facing windows
with dimming, setpoint tuning, nighttime occupancy (no occ sensors 
during daytime since open plan).
Owner informally reports an operating avg LPD of 0.35 W/ft2 for May/June 
08 with installed LPD of 1.0 W/ft2. 
http://windows.lbl.gov/comm_perf/newyorktimes.htm

HMG, NREL, Weidt Group reports savings that are significantly less than 
predicted savings depending on attention paid to proper execution 
(reports published on 0-10V systems) & in particular for sidelighting 
applications.  DALI-enabled digital lighting controls (used at NYT) is 
making it easier to achieve more reliable results but still not a slam 
dunk yet.

Hope this helps,
el.

On 6/20/2008 6:19 AM, Lan Hu wrote:
> Hi, all,
>
> I simulated an office building with 49% window on each orientation, and
> compared the results with daylighting and without daylight. The lighting
> energy consumption is 48.5% less with daylighting, and the total energy
> consumption is 18.5% less. I set the only sensor in each exterior zone
> around 15ft from the exterior window and used default values for other
> setup. I wonder if anybody with experience of daylighting think these
> big(?) saving numbers are realistic?
>
> Any input will be appreciated.
>
> Lan Hu
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