Bi-Level Stairwell Lighting Controls
Stairwell Lighting: Bi-Level with Occupancy Controls vs. Always Full Brightness
Typically combine bi-level LED drivers or fluorescent bi-level ballasts and occupancy sensors to reduce lighting levels in stairwells when the stairwell is unoccupied.
Item ID: 108
Lighting--Sensors & Controls
Technical Advisory Group: 2009 Lighting TAG (#1)
TAG Ranking Date: 11/06/2013
Stairwells are required for emergency exits and, in buildings with elevators or escalators, are mostly unoccupied. Yet fire and life safety codes require that stairwells be lighted at all times, resulting in a large amount of wasted energy. Occupancy sensors can be coupled with bi-level controls so lights are on only at a minimum level whenever the stairwell is unoccupied. As soon as someone enters the space, the light level can be brought up to a useful level (10 footcandles required by Life Safety codes).
Studies (PIER, 2008), (Lutron, 2013), (Ecovation, 2010) have verified energy savings ranging from 40% to 80%, depending on the traffic flow in the stairwell and the technology that was replaced. Lamp life can also be increased as a result of reduced switching, with attendant reduced maintenance and replacement costs.
Although new luminares with bi-level technology may cost two or three times more than standard products, they can be very cost-effective, especially if they are used to replace T12 fluorescent technology (which is now obsolete). Some models also include built-in emergency, battery-powered exit lights. An increasing number of utilities are offering incentives to help offset the cost of the modern equipment. Most of the products that are currently available are linear fluorescent lamps, but LED products now entering the market offer even longer lamp life and greater energy efficiency.
Baseline Description: Uncontrolled Two Lamp T8 32 Watt Fluorescent
Baseline Energy Use: 543 kWh per year per fixture
Baseline energy use estimate is for a two lamp, standard 32W T8 fixture. Baseline assumes lamp will be operational 24 hours per day, 365 days per year, for a total of 8760 hours per year, per assumptions used in (Epstein, 2005). 32 Watt T8 lamps are a reasonable baseline equipment assumption than the 40 Watt T12 examples used by most manufacturers.
Baseline Energy Use = 62W x 8,760 hours/year / 1000 = 543 kWh/year
Manufacturer's Energy Savings Claims:
"Typical" Savings: 50%
Savings Range: From 40% to 80%
Typical savings and saving ranges from an examination of manufacturer websites and brochures (Lutron, 2013), (Columbia, 2010), (Ecovation, 2010). Note that most manufacturers are comparing their products to 40 Watt T12s, which has an impact on the energy savings claims. Some products are capable of dimming to 5% in standby mode (Ecovation, 2010).
Best Estimate of Energy Savings:
"Typical" Savings: 51%
Low and High Energy Savings: 40% to 80%
Energy Savings Reliability: 4 - Extensive Assessment
Energy savings estimates are taken from a survey of 9 case studies of bi-level occupancy controlled stairwell projects in the California University system (PIER, 2008), where 60% savings is the most common and reasonable savings versus the Baseline. High and low estimates are taken from summary of case study results (PIER, 2005), (PIER, 2008).
Occupancy of the stairwell is the primary dependency. Like any occupancy sensor, these fixtures must be properly commissioned to operate as designed. Occupancy for many stairwells has been measured as low as 3.5% (Epstein, 2005), which for a fixture set to 10% of rated output in standby mode, translates to an energy savings of approximately 87% over the 32W T8 Baseline. Case studies have found that actual occupancy rates are between 20% and 33% for a "typical" stairwell, which translates to between 60% and 75% savings as compared to the 32W T8 Baseline.
Not all stairwells in a building receive the same use and controls should be adjusted in relation to actual use. There may be heavy use on the first three floors, while higher floors receive little use. Sometimes there is a lot of traffic between two floors, and little on others.
With the arrival of LED products, the time delay to turn off lights in places where that is allowed, not stairwells, when no occupancy is detected can be shortened to a few seconds, with no harm to lamp life, well below the 15 minutes most fluorescent lamp manufacturers recommend to preserve lamp life, saving even more energy.
Energy Use of Emerging Technology:
266.1 kWh per fixture per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
There are several configurations for fluorescent units, but for this example the 2-lamp 4-foot T8 fixture with bi-level lighting control will have an input wattage of 17W during unoccupied times (70% or 6,132 hrs/yr) and an input wattage of 62W during occupied times (30% or 2,628 hrs/yr).
Emerging Technology Energy Use = 17W x 6,132 hours/year / 1000 + 62W x 2,628 hours/year / 1000 = 267 kWh/year
Potential number of units replaced by this technology:
Assume there is 1 BSF of multi-story commercial space in the CBSA region, which includes the major cities, in Jan 2012. Assume that 5% of this floorspace is stairwells to get 50 MSF. Assume 1 fixture per 15 sf of stairwell = 3333333. This assumption gives us 3.3 million fixtures for Pacific Northwest.
Regional Technical Potential:
0.91 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: fixture
Emerging Technology Unit Cost (Equipment Only): $260.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $50.00
Baseline Technology Unit Cost (Equipment Only): $65.00
Information for cost estimates from Olympia WA. area CED and Platt Electrical contractors for cost to contractors of fluorescent 2-lamp fixtures.
This is dependent on the labor rate and experience of the installing electrician. Some systems like Lutron's have separate control mounting which adds to the cost. A secondary cost sensitivity is the net cost of the fixture, which can be less expensive when purchased in bulk quantities.
LED products are also on the market with costs around $420.
A PIER study for the California Energy Commission in 2004 found that if new luminaire costs drop to double the conventional uncontrolled fixture cost, the payback periods would make the bi-level fixture the obvious choice for all new installations in California where energy costs are high.
Simple payback, new construction (years): 7.8
Simple payback, retrofit (years): 12.4
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Savings of 40-80% on energy costs are likely, depending on which equipment is being replaced, the power consumption of the new system at low power, cost of electricity, and traffic in the stairwell. Demand charges may also be reduced.
Paybacks will be fastest with new installations and when replacing T12 systems, which can have an almost immediate payback.
Bi-level stairwell light fixtures and controls typically combine fluorescent T8 or T5 systems, or LED luminaires with ultrasonic or other occupancy sensors. When there is no activity in the area, lights are set to a lower level of illumination – typically 50% of full lighting, but sometimes as low as 10%. When the occupancy sensors are activated, lighting goes to 100% until “unoccupied” for a specified time period. The same technology could also be useful in other low-occupancy areas such as storerooms, restrooms, corridors, and laundry rooms.
Wireless controls and sensors can be integrated into new luminaires and may reduce installation time, while other systems use separately mounted sensors.
Many of these application-specific luminaires incorporate features to reduce vandalism (especially if they are installed in isolated areas) and minimize damage from damp or wet conditions.
Fixtures with battery packs are UL listed as “emergency lighting and power equipment.” These can be used instead of the common “headlamp” emergency backup lights. Various lamp configurations and strategies for switching include:
• One or two fluorescent lamps on a bi-level ballast,
• Two lamps of high and low wattage, where the low wattage one is used for unoccupied times and both are used for occupied times, and
• A single low wattage 2’ T8 lamp for constant light output and 4’ T8 lamps controlled by an integral occupancy/daylight harvesting sensor.
LED models which change output and can have set-back times as short as a minute- providing additional savings over fluorescents.
Some have adjustable settings to charge photoluminescent products.
Lutron, Stairwell Fixture
Lutron, Stairwell LED Fixture
Columbia, BIL - BI-LEVEL LUMINAIRE
Philips Lightolier, Lightolier Stairwell
Philips Day Brite, 2, 3, or 4 foot Stairwell Luminaire
LaMar Lighting Co, Occu-Smart
LaMar Lighting Co , VOLED Series LED
Cooper, Stairlite Series
What is the standard practice approach to this technology?
Standard practice is to have uncontrolled lighting in stairwell fixtures. Stairway lighting may be incandescent, CFL, or linear fluorescent, on 24/7 hours. Many stairways are unoccupied most of the time. In fact, case studies have shown that stairwell areas in buildings such as hotels, hospitals and offices have occupancy rates on average of 1-7%. http://www.columbialighting.com/products/literature/literature_files/co1042.pdf
Stairwells may be used for regular transit, optional use, or fire escape use only. In tall buildings, stairs may be used more for inter-floor travel rather than transiting the whole stairwell. While stairwell lighting provides visibility, it can also affect the mood or feeling of the stairwell, such as feelings of safety, which could impact usage rates.
Emergency exit lighting is also provided in stairwells. In some places, like New York City, photoluminescent markings are required in stairwells of high rise buildings, which require exposure to light in order to work.
As evacuation routes, stairwells must meet any life safety, building code/fire codes that are in effect concerning emergency light levels and duration. Some codes may allow lights to be completely off when unoccupied, but this would be the exception. The Uniform Building Code currently requires minimal lighting of one foot-candle (fc) for emergency egress in all stairwells. The National Fire Protection Association (NFPA) has already adopted a new minimum illuminance level of 10 fc during all occupied times.
The proposed technology mitigates the energy increase required to achieve such illumination levels while remaining code compliant well into the future (specifically for Occu-smart but could apply to others).
Stairwell fixtures are already a mature technology combining two well-known applications: bi-level ballasts and ultrasonic occupancy sensors. The combination used in this way is still not widespread in the Northwest. The un-amended ASHRAE/IEC 90.1-2010 energy code includes requirements for this practice.
Fixtures have been produced since around 2002. Ballast improvements are ongoing and costs are expected to decrease.
California Lighting Technology Center (CLTC), Pacific Gas & Electric Company (PG&E), California’s Public Interest Energy Research (PIER) Program, and New York State Energy Research and Development Authority (NYSERDA) are just some of the organizations that have demonstrated the energy benefits of this technology. They find that stairways are largely unoccupied, providing plenty of savings opportunities.
Lamp life may be extended with lower, full-power usage.
End User Drawbacks:
First cost and the time required to commission the system.
If photoluminescent markings are installed in a stairwell, the lowest bi-level light level will need to provide adequate light to keep the markings “charged” enough to remain visible for at least 90 minutes without light.
Operations and Maintenance Costs:
Baseline Cost: $6.00
per: fixture per year
Emerging Technology Cost: $7.00
per: fixture per year
This O&M compares a standard T8 lamp on instant start ballast operating 8760 hours per year against a Bi-Level fixture operating at full power 30% of the time( 2628hr/yr), containing 2)32W extra long life (80,000hr) T8 lamps on a programmed start ballast and one 17W long life T8 operating 8760 hours per year. It is assumed cleaning costs are equal and ballasts last 10 years, though they do not have rated lives. Most electronic fluorescent ballasts are warrantied for 5 years and 50,000 starts and in this applications there would be one start for the 24/7 use and a variable amount for the bi-level full power lamps. For ten years of operation using the long life lamps and replacing the ballast at 10 years, the cost of operating the 2 lamp system 24/7, excluding energy use, is $57.21.
To operate the long life Bi-level system for ten years and replacing both ballasts at ten years, the cost, excluding energy use is $72.05. In fact the two full size lamps in the bi-level system may not replacement for 30 years.
Anticipated Lifespan of Emerging Technology: 10 years
The effective life of the proposed technology will depend on the life of the technology is used, how much of the time they operate at the low output level, and if a sensor uses battery power when the battery needs replacement. LED life may extend significantly when operating mostly at the reduced level, fluorescent lamp life is also extended by operating just the low output much of the time, how often the full power lamps are switched could negatively impact lamp life if they operate for less than 15 minutes per use. While standard fluorescent lamp life is in the range of 20-24,000 hours, long life lamps on programmed start ballast (recommended with occupancy sensors) may last up to 65,000 hours depending on the lamp/ballast combination and frequency of switching. If the space is conditioned at 600F or above a 28W lamp might be used and achieve 80,000 hours of life.
By not switching the lamps off and on, and only reducing and increasing the power, the lamp life for bi-level ballast systems is expected to be extended significantly to about 15 years. For systems that involve switching the high power lamp off and on, 10 years might be more accurate; with no switching of the low power lamp, its life could be quite extended. If LEDs live up to expectations, the systems could last even longer.
Daylighting controls plus occupancy sensors and dimming ballasts might be an option in some stairwells.
LED lighting in these products has entered the market. LEDs provide instant on/off and should be a good fit in locations where:
• Light color is not too important,
• Ambient temperature operating conditions vary widely, especially in cold temperatures in unconditioned or exterior stairways, and
• Long equipment life is a benefit.
Reference and Citations:
Life Safety Code
National Fire Protection Association
Bi-level Smart Stairwell Luminaire: Draft Case Study
Public Interest Energy Research Program
Provides quantitative information on a bi-level case study including energy savings, purchase costs and installation costs.
Stairwell Lighting Report - The Fillmore Center, San Francisco, California
Pacific Gas & Electric Company
Provides first cost and installation costs for bi-level systems, as well as energy savings and payback information.
Bi-Level Luminaire: Maximizing Energy Savings with Controlled Light Levels
Energy savings claims of 70%.
Stairwell Fixture T8
TCP/Ecovations Lighting, Inc.
Provides information on dimming levels achievable by the fixture (5% of full output when no occupancy detected).
Stairwell Standard Feature
Lutron product page.
Project 5.1 Bi-level Stairwell Fixture Performance: Final Report
California Energy Commission
PIER Lighting Technology Candidates for 2008 Title 24
Public Interest Energy Research
Presentation which includes some summary stats on occupancy rates and energy savings for bi-level control case studies in California.
Bilevel Stairwell Lighting Promises Up to 70-80 Percent Energy Savings
Lighting Controls Association