Archive for March, 2009

LED life

March 27, 2009

LED lumen maintenance and mortality needs to be understood in similar terms to those of conventional incandescent and gas-discharge lamps.

Incandescent lamps display little change in light output until the bulb fails catastrophically. In large lighting installations, each lamp failure reduces the overall light output of the system, and in many such installations, a minimum illumination level is mandated by prevailing codes. When the light level falls below the code minimum, relamping is required. This is an expensive process involving administrative and manual labor. The total cost of relamping can be 16 times higher than the purchase cost of the lamp, particularly for high bay or municipal lighting installations. The issue is magnified when both lamps and ballasts are systemic.

090327-ave-rated-life-all-lamp-types-defines-b10-and-b50-valuesThe graph above is generic to conventional lamp types and illustrates the definition of B10 and B50 lamp failure for any multiple lamp installation.

LED sources do not tend to fail catastrophically, the light output degrades gradually over time. The level of degradation can be controlled by two variables available to the design engineer, input current (how hard the chip is driven), and junction temperature at the LED, a function of heat sink design and other variables. The power source can be selected to control the forward DC current, and resulting thermal management controls the operating temperature, yielding extended LED life.

The useful operating life of a power LED is extremely long, and often exceeds the lifetime of the product in which it is embedded. In a large installation, the effect of lumen degradation over time may be to reduce the overall light output level below a specified minimum. However, as relamping is so infrequent, the total cost of ownership is reduced.

The power LED industry group, the Alliance for Solid-State Illumination Systems and Technologies (ASSIST), has found that 70% lumen maintenance is close to the threshold at which the human eye can detect a reduction in light output for isolated light sources. For side-by-side lamps compared one to the other, the ASSIST threshold figure is 80%. ASSIST maintain that 30% reduction in light output is acceptable to the majority of users for general lighting applications. ASSIST propose that two co-ordinates be used to express the useful life of an LED component. These are L70, the time to 70% lumen maintenance, and L50, the time to 50% lumen maintenance.


The graph above illustrates how varying the forward current from the power source will affect LED life. 700 mA is a good reference for power sources used to drive retrofit LED fixtures, although in the graph below, we see the junction temperature stress tests have been run at 1500 mA. Note that driving the LED at a level below its maximum rated forward current will extend its useful life, thereby increasing the quoteable L70 and L50 lifetimes.

090327-how-changes-in-junction-temp-affect-useful-life-of-an-led1In the graph above we see that limiting junction temperature to 115C will greatly impact LED life. Using the ASSIST L70 parameter, the LED lasts 80,000 hours without detectable lumen degradation.

To ensure that designers meet established criteria for light output and relamping intervals, ASSIST recommend understanding that LED performance depends on many parameters, including heat sink design, ambient temperature, thermal resistance of package and leads, and voltage and current applied to the fixture.

To enable a simplified graphical approach, more information than that expressed by the L70 or L50 figures is required. An equivalent to the traditional B-lifetime figure (illustrated at the top of today’s post) is necessary for engineers to understand the percentage of LED in which the lumen output falls below threshold, remembering that an LED exhibiting “lumen failure” below L70 still provides illumination.

To ease the challenge for design engineers who need to factor drive current and thermal management needs, testing data should be expressed in terms of L-lifetimes and B-lifetimes and presented graphically with reference to driving current and junction temperature. That graph is illustrated below, the B50 (equivalent) limiting the LED “life” to 60,000 hours.

090327-b50-l70-how-changes-in-both-tj-and-current-affect-life-of-ledFrom a design engineer’s perspective as it relates to product design for real-world customers, the data is most usefully expressed as functions of LED life as junction temperature and forward current are varied. The heat sink design and the AC-DC power supply choices become critical. Factors of thermal performance, first-cost, and weight and size of both heat sink and power supply become key to successful fixture design, low cost of installation, and low life-cycle cost.

The photo at the top of Dean Kamen’s folly illustrates an RGB LED application; testing was all performed on white LED.

ASSIST is sponsored by NYSERDA and Sylvania.


March 24, 2009


NYSERDA have traditionally funded demand reductions (kW) in preference to usage reductions (kWh), the theory being that reduction in use of transmission and distribution infrastructure, obviating T&D build-out, was more important to the participating utilities than reduction in generation.

NYSERDA have now reversed that bias.

Below is a letter we received last week from NYSERDA related specifically to LED retrofits, some of which involve exterior lighting, never a peak-demand reduction energy conserving measure. The bracketed words and designations are added for clarity.

“As per our conversation, this is our current stance on LEDs:

“LEDs are now eligible technology and they are being aggressively adopted by many of our lighting contractors.  This is exciting for everyone, but we want to make sure that applicants are installing reliable technology.  As a result, we are requiring the criteria listed below for performance projects including kWh savings from LED lighting.

“These criteria are based upon the standards addressed by the DOE’s Energy Star program for solid-state lighting.  (The applicant will probably need to request this info from the LED manufacturer(s))

  1. Independent IESNA LM-79 test data to verify Light Output, Luminaire Efficacy, CCT, and CRI
  2. Independent LM-80 test data from LED Manufacturers at 55 C, 85 C, and a 3rd temperature of the manufacturers choosing, usually higher temp.
  3. IES File in LM-63 format to verify photometrics.

“Note:  The DOE actually has a 4th criteria, but this is not required under our (NYSERDA) program.

  1. L(M)-70 Lifetime and written explanation of how it was determined, and a complete description of the thermal management of the luminaire, or something similar

“Here’s a link to the (DOE) Energy Star page for Commercial LED Lighting:

“As the Energy Star standards evolve, it is likely that our requirements will as well.  In general, please discuss any planned LED projects with us and expect that these applications may take more time to process than usual.

“Related to run hours, as we discussed, our programs are now entirely kWh based.  The run hours (do) not have to coincide with (facility) peak demand to receive incentives (cash rebates).”

This is a very encouraging development. The caveat related to “more time to process than usual” is the one hindrance to LED deployment with NYSERDA assistance.

Photo of Dean Kamen’s retreat in Long Island Sound lit with LED


March 19, 2009


Ground Source Heat Pump is one of the most efficient heating and cooling systems available. The Coefficient Of Performance of closed loop systems in southern New York State will vary but may be assumed to be approximately COP 5.0.

Employing the insulative properties of the earth as a heat exchanger, GSHP is a combination heating and cooling system. Transition from heating to cooling mode is done at the indoor unit or thermostat. Systems include an electric coil at the indoor unit to supplement the heating cycle as necessary.

A federal tax credit of 30% exists for systems exceeding COP 3.3 and SEER 14.0.

NYSERDA provides $600. per ton. for capital costs as well as 50% of feasibility study costs.

Closed loop systems are more expensive than open loop to install but provide the greatest carefree operation. Open loop is not recommended in ecologically sensitive sites near water courses; filtration is required for open loop.

Current construction market conditions in the northeast provide aggresive pricing opportunities for drillers.



March 18, 2009


NYS has a cash rebate program to assist local government, schools and non-profits install PV. US$13.8 Million is currently available.

The rebate is $5,000. per kW for the first 25 kW, $4,000. per kW after the first 25 kW up to a total of 50 kW per site or meter. The rebate is limited to 110% of the facility load; systems larger are eligible for rebates only on the first 110% of load, to prevent giving incentives to Distributed Generators in an era of net metering.

Rebates are paid in two increments and are tied to specific installation milestones. A payment for 75% of the total amount approved is paid after system components have been delivered to a customer’s site, permits have been obtained, and the necessary state application is completed, submitted, and approved. The customer has 90 days from the date that the initial invoice is approved to complete the installation.

The second rebate for the remaining 25%  is paid after the PV system has been connected to the utility grid, inspected by an electrical inspector, and additional paperwork has been completed, submitted and approved. Installers must provide a list of names for all primary crew members working on the installation with the final payment. Documentation for utility and town inspections must be provided.

No local, state, or federal taxes are used to pay for the rebates because it is the Systems Benefit Charge collected on NYS ratepayers’ bills that pays for the NYS PV program. Take a look at your utility bill to see your contribution.

There are additional benefits for PV related to NYC real estate taxes and federal taxes, but as local government, schools and non-profits are not subject to taxes, the ability of these users to benefit (by sale of tax credits, for instance) is not clearly evident.

Further benefits related to RECs and carbon credits will the subject of a future post.


Photo courtesy Sunpower Corporation, module layout and payback analysis at Norwalk Aquarium, MeXSI Inc


March 16, 2009

untitled_rev_tms-so-elThe Edison Electric Institute granted access to the membership portion of their site where I found “Summary of Select Provisions of Interest to the Electric Utility Industry from H.R. 1 American Recovery and Reinvestment Act of 2009”.  This report saves me from reading the remaining 407 pages of the Stimulus Bill. I was on page 24. Thank you, EEI.

Under State Energy Programs, the report summarizes:

“$3,100,000,000. is allocated for State Energy Programs authorized under Part D of Title III of the Energy Policy and Conservation Act. As described below, Section 410 of this Act makes a portion of these funds available only to states that update their residential building codes, commercial building codes, create plans for enforcing building codes, and update regulations on utility energy efficiency programs.”

This is a tall order for the states: meet all four stipulations to receive money. It is heartening to see the emphasized phrase  included. I have contended that Energy Efficiency is misunderstood by practicing professionals and (particularly) non-professionals responsible for the major part of new and renovated construction. The need is not for more stringent codes but rather for unbiased interpretation and compliance with codes in place. This is not a task that a building department review can accomplish, but rather a set of tasks that should be performed by an impartial third party professional. General certification by the filing professional in regard to compliance is vacuous, and construction not under the supervision of professionals is even more at risk of being energy inefficient and illegal.

Third party review is deemed necessary and now DOE is providing an incentive. States and municipalities: take note.

mvc-878x3Rendering of Toyota Motor Sales facility and photo of field verification work: Salvador Behar Architects


March 12, 2009

mastheadsubI attended National Facilities Management & Technology conference at the Baltimore Convention Center on Wednesday. The theme for the show was “going green”, from health of cooling tower water to workings of Power Purchase Agreements, the two best presentations witnessed.

Solar tri-generation was my best-of-show for most exotic building technology. Try this: an exoskeleton of piping carrying glycol or water sent to small gallium PV collectors on which tracking mirrors have concentrated sun rays. The exoskeleton and rows of mirrors are constructed over roofs of parking decks at a height 48″ off the roof surface. The glycol cools the back of the collectors, the heat carried away is sent through a heat exchanger to either heat or cool the interior of an adjacent structure. The technology is Canadian and reportedly guaranteed by its government. The licensee is NJ-based for US deployment.

Solar tri-generation is new to me; conventional tri-generation (combined heat and power) takes natural gas as fuel to fire absorption chillers which heat, cool, and make electricity. Tecogen makes such a chiller, applications generally limited to large facilities such as hospitals with constant need for “waste” heat, here used to heat DHW. Tri-generation for small facilities makes sense only when the cost of natural gas is extremely cheap, or power expensive. Solar tri-generation may have its applications, architects will be challenged to deploy it if the US states provide incentives. I would be concerned about panel life and ease of replacement and graceful integration of the exoskeleton into the structure.



Toyota Motors was at the show. TM continues to lead its industry in alternative energy implementation both in cars and buildings. 2008 saw the completion of their roof-mounted PV installation for a site in Ontario, California, the largest roof-mounted PV system in North America. Sunpower’s Powerlight fixed mounting system was deployed.


Six football fields of silicon



March 10, 2009


Hydrogen is discussed as a fuel for next-gen automobiles, but it’s primary use as a fuel is in the U.S. Space Program. Liquid hydrogen and liquid oxygen are combined as propulsion fuel for the space shuttle. On board, fuel cells using hydrogen and oxygen provide most of the shuttle’s electric power. Fuel cells were developed under NASA contract.

Hydrogen also has use in terrestial generation. The major fuel cell manufacturers are headquartered in Connecticut, but neighboring NYS has the most generous programs to support their implementation.

NYSERDA has a US$11.M program in place, non-competitive, first-come, first-served. Large projects generating in excess of 25 kW are provided cash rebates of $1000./kW for capital improvements which include new gen-sets, and qualify for an additional $0.15/kW-h of “performance-based” incentives. The capital incentive is capped at $200,000. per site.

Small projects generating less than 25 kW are provided cash rebates of $2000./kW for capital improvements, capped at $20,000. per site.

Essential public service sites qualify for an additional $500./ kW. These include hospitals and police stations.

The clean “burn” provided by fuel cell units make them ideal for stand-by power for sites under strict environmental oversight, including all of NYC.

The technology is proven but not widely implemented, such that the enterprise marketing value of a broadcasted installation should not be discounted.

Photo of shuttle courtesy NREL, photo of 400 kW unit courtesy United Technologies



March 9, 2009

35699275fenwayparkThe power industry is one of the world’s largest industrial segments. With a market share of approximately 25%, the United States is the leading producer of electricity, followed by China, Japan and Russia. Global electricity consumption grew at an annual rate of 3.1% from 1980 to 2006, according to the Energy Information Administration of the DOE. Over the same period global installed capacity increased at a slower rate of only 2.8%.

Recent figures are not as robust. Last quarter, Centerpoint in Houston reported a 1% increase in residential electricity use, but an overall 8% reduction in electricity use in their service area, attributed to a slowdown in new construction and a similar retrenchment in the local oil and gas business.

Transmission upgrades provide the best area of growth for electric utilities, as the investment has a guaranteed rate of return and location of new supply and load are divergent.

National Grid and Bangor Hydro-electric are investing US$2.0B in joint venture to bring renewable resources to eastern Massachusetts from supply in Maine and Canada. National Grid has 5,565 MW of renewable energy projects in the interconnection queue: 4,617 MW of wind, 113 MW of biomass, and 835 MW of hydro, of which 666 MW consists of new pump storage.

The Northeast Energy Link would comprise 220 miles of 660 MW High Voltage Direct Current (HVDC) transmission from Orrington, Maine to eastern Massachusetts. The project would include a phase shifter and AC-DC converter at Orrington and a DC-AC converter at the Massachusetts terminal. The project is designed to be expandable to 1,200 V DC, with an in-service date of 2012. Recovery approval for the investment has not yet been sought by the joint venture.

Once built-out, the project will facilitate fuel diversity and greatly increase supply of northern New England generation into the eastern Massachusetts zone, including Boston. Transmission thermal losses will be minimized by the use of HVDC.



March 6, 2009


Light-emitting diodes (LED) are compound semicondutor devices that convert low-voltage electricity to light. General Electric scientists invented the first application of LED in the 1960s. Unlike conventional lamps that can shatter,  LED are resistant to shock and vibration. The solid-state nature of LED means no filaments to break or moving parts to fail.

The advantages of the technology vary with the application. Features of LED include 90% energy savings over similarly-bright incandescents, lamp-life minimum of 50,000 hours, and excellent cold weather start-up and performance. The disposal issue faced with mercury vapor and fluorescent lamps and ballasts is obviated.

Early applications included traffic signals replacement; the technology offers color rendering choices and significant lamp replacement and energy usage advantages over legacy incandescent traffic signals.

Applications have expanded to include parts for televisions, building interior and exterior lighting, signs, focused retail displays, flashlights, elevator call buttons, commercial and residential fixtures (those changing colored lights in your hot tub are LED), and transportation and street lighting.  The LED industry is estimated to have grown 50% year on year between 1995 and 2004, and for the period 2004-2009 the US market is expected to grow from US$3.7 B to US$7.3 B, the highest growth being in transportation uses (projection courtesy Oppenheimer research).

Use in transportation infrastructure continues, South Korea and Los Angeles, Califonia having recently announced major LED initiatives.

Remote monitoring capability facilitate “smart grid” applications; flashing street lights on the curb will one day signal emergency responders regarding the location of a call.

Photo of exterior fixture


March 2, 2009


Electric utilities make transmission and distribution investments. A shift to night-time use of this infrastructure by rate payers increases the utility’s return, as the transmission and distribution system is designed and sized for the daytime peak load. Load shifting is the common name applied to this concept.

Con Edison has started an excellent voluntary program called time of use metering. The utility reduces the kW-hour charge for night-time electric energy while raising the daytime kW-hour charge. The meter has to be switched out, the utility does this free. This is a good way to get return on investment for the customer as it is a savings realized with no capital investment on their part. A certain amount of rate analysis is required on the part of the customer to project the usage pattern for any one meter.

Generally the program would yield savings for stand-alone meters such as you find at a golf-cart facility or a municipal electric vehicle garage. Another application would be a thermal storage (ice plant) run from a chiller system operating at night, an application which would also realize a significant demand charge reduction.

Con Edison’s on-peak period is 8 AM to 10 PM Monday to Friday. The off-peak is all other hours.

SC9 time of use customer rate has a one-year term. SC2 time of use customers can go off the rate at any time.

Interval meters such as those for the ICAP and other demand response programs are not able to be used as time of use meters.

Con Edison’s time of use meter program is an economical step towards the “smart grid” much discussed today.