ESL-IE-09-05-29
Utilizing Daylighting Controls in a Manufacturing Facility
Som S. Shrestha
PhD Candidate
som@iastate.edu
Dr. Gregory M. Maxwell
Associate Professor
gmaxwell@iastate.edu
Iowa State University
Ames, IA
ABSTRACT
Opportunities exist to reduce artificial lighting in
manufacturing facilities which have skylights and/or
fenestration that provide sufficient quantities of
daylight to the work space. Using photometric
sensors to measure the illuminance in the space,
artificial lights can be automatically switched off
during periods when sufficient daylight is available.
Daylighting controls used in commercial buildings
often use dimmable ballasts with fluorescent lights.
Most fluorescent lighting used in manufacturing
facilities use high output ballasts which are nondimmable. The preferred method for reducing
artificial lighting output is to switch the lamps off.
For multi-lamp fixtures such as six-lamp Super T8’s,
ballast/lamp configurations are either 2-4 or 3-3, thus
giving rise to various stages of lighting reduction.
This paper examines these lighting control strategies
for a 90,000 square foot manufacturing facility in
Iowa. Using the EnergyPlus building energy
simulation code, annual lighting energy savings
associated with utilization of daylighting were
computed for the building. Results showed that the 24 switching control strategy provided better energy
reduction opportunity compared to 3-3 switching
control.
INTRODUCTION
Artificial lighting accounts from 10 to 20% of
energy consumed by industry (FEMP 2007). When
manufacturing facilities have skylights and/or wall
fenestrations, opportunities exist to reduce the
artificial light power by utilizing daylight. Many
manufacturing facilities in the upper Midwest have
skylights or fenestration, but they are not taking
advantage of daylighting controls to reduce their
lighting energy.
This paper analyzes the lighting energy savings
potential for a manufacturing facility by utilizing
daylighting controls. The 90,000 square foot
production facility has 19 windows along the south
wall, and 24 windows along the west wall. The
window dimensions are 46” x 46”. Figure 1 is a
photograph showing the windows along the west
wall. The facility has 20 roof skylights (46” x 92”)
which are located 25 feet above the floor over the
production area. Figure 2 shows an example of the
existing 400 -watt metal halide lamps in close
proximity to skylights. Currently the facility has 196
metal halide lamps.
Due to long re-strike times, it is not feasible to
use metal halide lamps in daylighting systems where
the lighting level must react to changing ambient
lighting conditions (McCowan and Birleanu 2005).
Hence, these systems are not suitable for daylighting
control. Bi-level metal halide systems are available
that operate at 100 and 50 percent of full power.
When operating at 50 percent power, the lamp
delivers approximately 30 to 40 percent of its full
output (McCowan and Birleanu 2005). Moreover, the
energy efficiency of metal halide lamps are less
compared to that of fluorescent lamps. Typically, a
400-watt metal halide lamp consumes about 460
watts of electric power, as some additional power is
required for ballast.
Improved lighting technology has led to
fluorescent lamps and ballasts that both have higher
efficiency and also give better color rendering to the
objects viewed under their light. While metal halide
lamps suffer from severe lumen depreciation over
time; fluorescent lighting maintains a much more
consistent light output. A 6-lamp fixture with Super
T8 fluorescent lamps and electronic ballasts that use
222 watts of power produces nearly the same amount
of light as a 400-watt metal halide lamp. These
fluorescent fixtures have been designed to be a direct
replacement of the metal halide lamp. In the analysis
presented in this paper, all 400-watt metal halide
lamps in the manufacturing facility were replaced
with high bay 6-lamp Super T8 fixture. Thus, energy
savings not only comes from daylighting controlled
lights, but also a reduction in total installed light
wattage.
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009
ESL-IE-09-05-29
Figure 1. Windows along the West Wall
Figure 2. Sky Lights Surrounded by Electrical Lights
that many utility companies charge less per unit as
the quantity purchased increases. Marginal energy
cost is $0.0476 per kWh and marginal demand cost is
$49.20 per kW-yr for this facility.
Table 1 shows the existing lighting, total
demand, and total annual energy usage. Table 2
shows the proposed lighting system and savings
associated with the retrofit. By replacing existing
metal halide lights with Super T8 lamps 204,971
kWh of energy per year and 46.6 kW of demand can
be saved which will effectively save $12,052 per
year.
ENERGY, DEMAND, AND COST SAVINGS
ASSOCIATED WITH REPLACING 400 WATT
METAL HALIDE LIGHTS WITH SIX-LAMP
SUPER T8 FIXTURES
Electrical bills for 12 consecutive months were
analyzed to calculate marginal rates of electrical
demand and energy for this facility. The marginal
cost of a good is the price paid for one additional
unit. Marginal rates are almost always lower than
average rates. There are two common reasons for this
difference. One is that fixed costs such as service
charges are usually constant each month no matter
how much energy is purchased. The other reason is
Table 1. Existing Lighting
Existing Lighting
System Wattage
Per Lamp (W)
400 Watt Metal
460*
Halide
* Per fixture including ballast power
Number of
Lamps
Total Demand
(kW)
Usage Time
(hr/yr)
Total Energy Usage
(kWh/yr)
196
90.16
4,394
396,163
Table 2. Proposed Lighting Energy and Cost Savings Summary
Proposed
Lighting
System
Wattage
(W)*
Total
Demand
(kW)
Six-Lamp
Fixture With 32
222
43.512
Watt 4 Foot
Super T8 Lamps
* Per fixture including ballast power
Total Energy
Usage
(kWh/yr)
Demand
Savings
(kW)
Energy
Savings
(kWh/yr)
Demand Cost
Savings
($/yr)
Energy Cost
Savings
($/yr)
191,191
46.6
204,971
2,295
9,757
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009
ESL-IE-09-05-29
Table 3 gives the estimated unit costs for the
Super T8 lamps / fixture / ballasts, and disposal costs.
Labor cost is estimated assuming that one worker can
replace one fixture in one hour at $20/hr. The utility
company offers $200 rebate per kW demand
reduction by installing high efficiency lights. The
total rebate is limited to 50% of project cost. When
400 Watt Metal Halide lights are replaced with sixlamp fixture of Super T8 lights, the demand savings
is 0.238 kW per fixture. Hence the utility company
will offer $47.60 rebate per fixture. Table 4
summarizes the estimated cost of removing the old
fixtures and lamps and replacing them with Super T8
fixtures and lamps. From the table the total estimated
implementation cost is $20,552 including recycling
fee. The total cost savings $12,052 per year would
pay for the total implementation cost within 21
months.
Table 3. Materials and Disposal Rate Estimate
Cost Component
Disposal of Metal Halide Lamps
Disposal of Ballasts
Cost of Six-Lamp Super T-8 Fixture, Ballasts, and Lamps
Unit Cost ($)
1.46
1
130/set
Table 4. Estimated Implementation Cost and Simple Payback Summary
Six-Lamp Super T-8
Fixture, Ballasts, and
Lamps Cost ($)
25,480
Lamp
Disposal
Cost ($)
286
Ballast
Disposal
Cost ($)
196
ENERGY AND COST SAVINGS ASSOCIATED
WITH DAYLIGHTING
Various daylighting design and energy
simulation tools have been developed to estimate
lighting energy usage in buildings. The EnergyPlus
energy simulation software (http://www.eere.energy.
gov/buildings/energyplus/) developed by Building
Technology Program of the U. S. Department of
Energy was used in this study to simulate the facility
and calculate the energy savings associated with
daylighting controls.
Two types of daylight control systems are in use
for various spaces: Dimming Daylighting Control
and Stepped Daylighting Control. Stepped
daylighting
control
systems
turn
selected
lamps/fixtures on or off within the daylight control
zone based on the light level as measured by a
photosensor. During the day, as natural light in the
space increases, the light level in the space increases
beyond the preset value and the control system turns
off a portion of the lights. Similarly, as the daylight
in the space decreases, the light level in the space
decreases beyond the preset value and the control
system turns on a portion of the lights to maintain the
desired lighting level. Typically, control devices
consist of photosensors and lighting relays to switch
lights on or off based on daylight availability.
Dimming daylighting control systems use
photosensors to control dimmable ballasts that
gradually dim or brighten lamps to maintain a desired
Labor Cost
($)
Rebate
($)
Implementation
Cost ($)
3,920
9,330
20,552
light level in the space. This type of system will
usually allow the lamps to be dimmed up to 30%
power and then turn the lamps off if further reduction
in artificial light can be achieved. A disadvantage to
dimming daylight controls is that it is a more
expensive and sophisticated control system and not
all lighting manufacturers make Super T8 lights with
dimmable electronic ballasts. Hence, stepped
daylighting control systems are considered in this
study. More information on lighting technology and
control strategy can be found at Lighting Research
Center and its subsidiary National Lighting Product
Information Program website http://www.lrc.rpi.edu.
High bay Super T8 fixtures with six lamps are
available in two configurations. In one configuration,
two electronic ballasts are used where each ballast
powers 3 lamps (referred to as configuration ‘A’ in
this paper). The control is staged allowing lamps to
be turned-off three at a time as daylight increases in
the space. In the other configuration, two electronic
ballasts are used where one ballast powers 2 lamps
and other one powers 4 lamps (referred to as
configuration ‘B’ in this paper). The control is staged
allowing two lamps off four lamps on, four lamps off
two lamps on or all lamps off as daylight increases.
Using EnergyPlus, energy simulations were
performed for each configuration and the results are
described in this section. The following parameters
and control strategies were used in simulation:
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009
ESL-IE-09-05-29
(1) Des Moines, IA weather data
(2) Daylighting control type: stepped
(3) Number of steps (excluding off) for stepped
control: 2 for configuration ‘A’ and 3 for
configuration ‘B”.
(4) Illuminance setpoint at reference point (based
on the existing light level in the facility): 30
foot-candle
(5) Time step: 1 hour
Placement and orientation of the photosensors
depends on the application. For this facility it is
recommended to install three photosensors each
looking at a task surface so that the sensors detect the
combination of daylight and electric light reflected
off that surface. Various options of photosensor
placement are discussed in NBI 2003.
Figure 3 illustrates the proposed lighting layout,
including the proposed photosensor location and
control strategy for the facility. As can be seen from
the Figure, 28 fixtures are controlled by a
photosensor that detects light from windows along
the south wall, 56 fixtures are controlled by a
photosensor that detect light from skylights, and 16
fixtures are controlled by a photosensor that senses
light from windows in the west wall. The reference
setpoint for the photosensors is fixed at 30 footcandles and the sensors are located at about 30 inch
above the floor.
The optical properties of the glass used in the
windows or the skylights will affect the amount of
visible light transmitted into the space and hence the
daylighting energy savings. Table 5 shows the optical
properties of glass used for the EnergyPlus
simulation. The dome shaped skylight was modeled
as a plane sheet of glass.
EnergyPlus use typical meteorological year
(TMY) data for environmental conditions. The data
file contains hourly environmental parameters
including the intensity of diffuse and direct solar
light, and solar angles. Daylight illuminance at
reference point is calculated in a pre-specified time
step using the weather file, the geographical location
and the orientation of the building and windows /
skylights. Figure 4 illustrates direct and diffuse
visible light available outside of the building obtained
from the weather file for one week (August 21 to 27)
for Des Moines. Figure 5 is an example showing
EnergyPlus calculated daylight illuminance at each of
the three reference points for this time period.
Lights and Photosensors Layout
Skylight Controlled
No Daylight Control
Skylight Sensor
300 feet
West Wall
South Sensor Controlled
West Sensor Controlled
South Sensor
West Sensor
South Wall
300 feet
Figure 3. Lighting and Photosensor Layout and Control Strategy
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009
ESL-IE-09-05-29
Table 5. Optical Properties of Glass Used for EnergyPlus Simulation
Property
Solar Transmittance at Normal Incidence
Solar Reflectance at Normal Incidence: Front Side
Solar Reflectance at Normal Incidence: Back Side
Visible Transmittance at Normal Incidence
Visible Reflectance at Normal Incidence: Front Side
Visible Reflectance at Normal Incidence: Back Side
Value
0.775
0.071
0.071
0.881
0.08
0.08
Direct and Diffuse Solar Illuminance
Direct Normal Illuminance
Illuminance, Foot-Candle
8000
Dif fuse Horizontal Illuminance
7000
6000
5000
4000
3000
2000
1000
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
0:00
12:00
0
Time, hrs
Figure 4. Exterior Illuminance from August 21 to 27
Illuminance, Foot-Candle
Daylight Illuminance at reference points
South Sensor
80
West Sensor
Skylight Sensor
70
60
50
40
30
20
10
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
12:00
0:00
0
Time, hrs
Figure 5. Interior Illuminance from August 21 to 27
Table 6 compares the energy savings potential
with lighting configuration ‘A’ and ‘B’. It can be
seen from the table that configuration ‘B’ has almost
63% more energy saving potential compared to that
of configuration ‘A’. This is because configuration
‘B’ offers a finer control on the number of lights
needed to meet the zone light level.
It can also be noticed from the table that, with
configuration ‘B’, the windows along the south wall
have potential to save 1,141 kWh/year of lighting
energy per kW of installed lighting power controlled
by south side photosensor. Similarly, with
configuration ‘B’, West side windows have potential
to save 927 kWh/year of lighting energy per kW of
installed lighting power controlled by the west side
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009
ESL-IE-09-05-29
photosensor and skylights have potential to save
1,215 kWh/year of lighting energy per kW of
installed lighting power controlled by the skylight
photosensor.
Table 6. Energy Savings Potential with Lighting Configuration ‘A’ and ‘B’
Lights
Controlled by
Number
of
Fixtures
South Sensor
West Sensor
Skylight Sensor
Total
28
16
56
100
Total
Lighting
Power
(kW)
6.22
3.55
12.43
22.2
Lighting Energy Savings
(kWh/Year)
Configuration Configuration
‘A’
‘B’
4,453
7,095
1,872
3,293
9,351
15,111
15,676
25,499
Figure 6 compares monthly lighting energy
savings potential of configurations ‘A’ and ‘B’.
Configuration ‘B’ has persistently higher energy
Lighting Energy Savings
(kWh / kW Installed Power / Year)
Configuration
Configuration
‘A’
‘B’
716
1,141
527
927
752
1,215
savings potential for each month compared to that of
configuration ‘A’.
Energy Savings Potential, kWh
Monthly Lighting Energy Savings Potential
Conf iguration 'A'
Conf iguration 'B'
3500
3000
2500
2000
1500
1000
500
0
1
2
3
4
5
6
7
8
9
10
11
12
Months
Figure 6. Monthly Lighting Energy Savings Potential of Configurations ‘A’ and ‘B’
It cannot be predicted whether the lights will be
turned off during monthly demand peak.
Conservative estimate is that the cost savings will
come only from the reduced electrical energy
consumption. So demand savings is not estimated for
daylighting. With the energy cost of $0.0476/kWh,
the annual energy savings of 25,499 kWh
(configuration ‘B’) will save $1,214 per year. The
implementation cost, IC, for installation of
photosensors, relays and necessary rewiring is
calculated as:
IC = ( N )( PSC ) + ( RWC )
where
N = number of photosensors including control system and relays
PSC = photosensor cost including necessary control device and relays, estimated as $600/set
RWC = rewiring cost, estimated as $2,000
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009
ESL-IE-09-05-29
Hence, the implementation cost of daylight
control system is estimated as $3,800. The total cost
savings associated with daylighting, $1,214 per year,
would pay for the total implementation cost within 38
months.
Daylighting energy savings potential is also
subject to the building location. Figure 7 shows the
expected daylighting energy savings for the same
facility if the building was located at cities which are
further north or south of Des Moines. The total hours
of available daylight for each location is dependent
on latitude, but weather conditions (in particular
cloud cover) also impacts the exterior illuminance
available for daylight.
Expected Daylighting Energy Savings
Skylight
West
South
35000
30000
kWh / yr
25000
20000
16810
17482
17722
3499
3789
3950
3807
7538
8159
8252
8150
5
6
15173
15111
15738
10000
3364
3293
5000
7274
7095
15000
Houston,
TX
4
Dallas,
TX
3
Oklahoma City,
OK
2
Kansas City,
MO
1
Des Moines,
IA
Minneapolis,
MN
0
Figure 7. Expected Daylighting Energy Savings for the Same Facility at Various Cities
SUMMARY
For manufacturing facilities that have available
fenestration (both windows and skylights),
daylighting control of artificial lighting can be a cost
effective means of reducing lighting energy costs.
Although dimmable ballasts are often used for
daylighting systems in office space, the higher level
of light output required for manufacturing space
limits the daylighting control to be switched. Of the
switched configurations available for 6-lamp Super
T8’s, the 2-4 combination provides the greatest
opportunity for savings. Although not considered in
this study, a detailed energy model that includes
space conditioning energy costs coupled with
daylighting should be considered. The energy
gain/loss through the fenestration could be a more
important factor in overall building energy use than
the energy savings from daylighting.
REFERENCES
Federal Energy Management Program (FEMP), 2007,
Hybrid solar lighting illuminates energy savings
for government facilities. U.S. Department of
Energy, Energy Efficiency and Renewable
Energy
McCowan, B., and D. Birleanu, 2005, Daylighting
application and effectiveness in industrial
facilities. Energy Systems Laboratory, Texas
A&M University
New Building Institute (NBI), 2003, Advanced
lighting guidelines
Proceedings of the Thirty-First Industrial Energy Technology Conference, New Orleans, LA, May 12-15, 2009