Energy Savings Study for Daylighting Application
Bordewich Bray Elementary School-Carson City, Nevada
June 2004
An energy savings study for a daylighting application at Bordewich Bray Elementary
School (Carson City,
Nevada) was performed in 2004 in order to apply for a NevadaSureBet customer
rebate. NevadaSureBet is a program sponsored by Nevada Power and Sierra
Pacific Power and administered by KEMA. This program provided a cash rebate
to the school upon evidence of energy demand and consumption savings obtained
by installing the daylighting system throughout the school.
Daylighting is a state-of-the art technology using dome lenses and diffusers
to transmit direct and ambient sunlight through a reflective light shaft
to evenly illuminate an interior space. T-5 lamps are integrated into
the daylighting modules to provide additional staged lighting when ambient
natural lighting is insufficient or unavailable.
The daylighting retrofit at Bordewich Bray consisted of removing 223
original fixtures (192 x Peerless ENM3 332 277V GEB T8 and 31 x 2SP8
G 332 277V GEB T8 fixtures) and replacing them with 59 daylighting units
(46 x passive 4x4’ units and 13 x passive 2x4’ units with integrated
T-5s). This allowed sunlight to illuminate the classrooms and hallways
during daylight hours, thus saving energy. Furthermore, integrated staged
lighting was connected to a control system that sensed lighting levels
and occupancy to determine if and how much additional electric lighting
was needed to maintain comfortable light levels.
The energy savings calculations consisted of a comparison of the estimated
annual energy use of the old fixtures versus the energy use of the new
daylighting systems. The energy use depends on the amount of available
daylight during normal hours of use of the facility. In the Bordewich
Bray study, we assumed 20 days a month of use with an average of 12 hours
a day (nominally from 7 AM to 7 PM), except for months of June-August
inclusive when fewer hours and days per month were used to account for
summer recess. This provided a total of 2480 hours per year. The amount
of usable daylight was based on the hours per day - from 1 hour after
sunrise to 1 hour before sunset - that fell within the nominal usage
window. The calculation was based on astronomical data for the year and
yielded a total usable daylighting availability of 83% (or 97% during
the peak demand times of June-Sept) (1,2).
Additionally, historical weather data was gathered for the region, to
include climatic conditions – such as the number of cloudy and clear
days – in the daylight availability calculation.
The Carson City area receives sunny or partly cloudy days 68% of the
time during the 83% daylight period, for a total of 57% sunlight availability
(3).
This means that for 57% of the school’s operational time, daylighting
is sufficient to provide all the lighting needs and electrical lighting
is not required. Of the remaining 43% of the time, it is assumed that
half of this time will require half the staged lights to be turned on,
and the other half of the time all the lights will need to be turned
on.
Additionally, accommodation is made for the occupancy sensors. Based
on numerous studies, it is conservatively estimated that the school will
save 40% from the use of occupancy sensors (4).
The end result for Bordewich Bray is that an annual consumption savings
benefit of 41320 KWH or 78% is
obtained from the daylighting application. This figure was accepted by
KEMA in the NevadaSureBet application and was used to calculate the school’s
subsequent rebate.
PRINTABLE PDF VERSION - CLICK HERE
References
(1) Astronomical data:
For Reno, NV area. Astronomical Applications Dept., Rise and Set
for the Sun for 2004.
http://aa.usno.navy.mil/
(2) Power Company:
Average Peak Demand defined as June-Sept inclusive 1-7 PM (as per
Kema, based on Power Company policy for the rebate program).
www.sierrapacific.com
www.nevadapower.com
http://www.nevadasurebet.com/ProjectCenter/
(3) Weather data:
Historical weather data for Reno and Carson City, from Western
Regional Climate Center.
Data is based on daylight hours only. A clear day denotes zero
to 3/10 average, sky cover. Partly cloudy is 4/10 to 7/10 tenths.
Cloudy is 8/10 to 10/10 tenths.
www.wrcc.dri.edu/htmlfiles/westcomp.ovc.html
www.wrcc.dri.edu/htmlfiles/westcomp.clr.html
(4) Lighting, occupancy sensors, etc.:
From FPL study, classroom energy savings of 40 to 46% due to occupancy
sensors.
Occupancy sensors can reduce energy waste by as much as 68% and
increasing energy savings by as much as 60%, according to a new
study conducted by the Environmental Protection Agency (EPA)
Nema study (2001): Occupancy sensors in classroom application,
energy savings of 52% using a 20 minute time delay period.
http://www.nema.org/energy/demandreduction.pdf
http://www.fpl.com/savings/energy_advisor/PA_10.html
http://ateam.lbl.gov/Design-Guide/DGHtm/occupancysensors.htm
http://www.ecmweb.com/news/electric_epa_study_shows/
(5) Daylighting Applications:
Daylighting is a state-of-the art technology using dome lenses
and diffusers to transmit direct and ambient sunlight through a
reflective light shaft to evenly illuminate an interior space. Daylighting
provides indoor full-spectrum, natural daylight which:
- Saves electricity: It greatly reduces the need to use electrical
lighting during daylight hours.
- Maximizes color perception: It has a color rendition of index
of 100 (compared with cool-white fluorescent lighting which has
an index of 67). So colors are rich, true and vibrant.
- Enhances object definition: Improves visual acuity by providing
superior recognition of surface detail, text and graphics.
- Is cooler: Daylight contains half as much heat per unit of illumination
as other sources.
- Is easy on the eyes: Daylighting creates no harsh glare, intense
brightness, hot spots or flicker.
http://www.daylighting.com/
http://windows.lbl.gov/
http://www.pge.com/003_save_energy/003c_edu_train/pec/daylight/daylight.shtml
