Monday, June 28, 2010

Sustainable vs Green

"Green" and "Sustainable" seem to be used as if they mean the same thing in mainstream media. However they are not the same:

Green but not sustainable:
Michael Pollan has a good example of this in his book The Omnivore's Dilemma: industrial organic food. The food is raised without artificial fertilizers or pesticides. However, it is raised in a giant monoculture. This means that a single disease could wipe out the entire crop. It also means that the land is not replenished by the crop growth so more and more fertilizers are needed to keep up yield.

Another example is in the common complaint about LEED not being green enough. I think, this could be a complaint about LEED not being as strong about sustainability as some might like. A recycled, refurbished, bright and airy building with solar panels constructed in the middle of nowhere is not sustainable to operate or for occupants to get to... yet it can still be LEED certified - a "green" building.

Sustainable but not green:
A small community raises pigs and chickens in a factory farm in addition to having a number of farms to supply food to the animals and people. The waste is rotated between a number of storage ponds where the land is severely polluted but the waste is broken down at a rate such that additional land is not required to contain it. The water supply is contaminated but sufficient rain falls that cachement supplies the required amount year-round. By having multiple animal types, a cull due to disease outbreak in one population does not result in a total loss of income or food supply.
This is, I will admit, a bit contrived but is within the realm of possibility for a small enough community without economic growth as a primary goal. It would be impossible to call this situation green but it, arguably, could be sustained.

The relationship between sustainability and green does exist. Namely that it is very hard for a planet of 6.8 billion people to be sustainable without being green because the environmental impact of our current technology is too high. To ensure that we can continue to live here, for human life to be "sustainable", our impact needs to be moderated. The best way we know to do that is by being "green."

It also highlights that "sustainability" is about the entire system. There cannot be "waste" and inputs cannot come exclusively from limited supplies when the population is too large. Or, as William McDonough puts it, "Waste equals food."

Maybe it is fair to say that the missing distinction is that sustainability requires systems thinking while green is about point solutions?

Friday, June 25, 2010

Lighting Labels coming in 2011

Better information for comparing light bulbs is coming next year.

Read this this earlier post to understand what these terms mean.

  • Brightness = Luminous flux
  • Brightness / Energy Used = Efficacy
  • Light appearance = Color Temperature

Wednesday, June 23, 2010

Comparing Light Sources - LEDs vs Fluorescents vs Metal Halide HID

From the previous post, one could conclude that LEDs, Fluorescents and Metal Halide HIDs were all pretty much the same: High efficacy, OK to good CRI and good color temperatures.

Yet what we see are fluorescent bulbs everywhere.

One way to compare these light sources is by bulb life vs cost per lumen output with efficacy taken into account. That looks like this: "Good" is high and to the left with a larger bubble.

One conclusion that immediately stands out is how expensive LED lights are relative to the alternatives. They may be 2x as efficient and last 5x as long, but they are ~38x - 175x the price. That makes adoption of LEDs very difficult for most applications that don't have some other needs specifically met by LEDs.

Some of those special needs:
  • LEED certification 
    • LED lighting is more efficient so it can be used towards energy efficiency credits (EAc1). If 25% of a commercial building's electricity usage goes towards lighting and you can cut that by 50%, that's a 12.5% reduction in electricity cost.
    • LED lighting is more easily controlled (dimmable) to allow for controllability of systems - lighting (EQ6.1).
  • Flicker
    •  For some tasks and working conditions, 60Hz cycling from fluorescents can cause eye strain, especially if it is used with other visual equipment that runs off 60Hz AC. LED lighting has a 120Hz cycling which means it is much more difficult to detect flicker and it is less likely to beat with other equipment running at 60Hz.
  • Dimming
    •  Commercial use fluorescent bulbs (T8, T10 and T12) are not easily dimmable due to the construction of the ballast that keeps them lit. LEDs are dimmable using standard dimming equipment. This is important for applications where light level control is desired.
  • Directionality
    •  LEDs are point sources that can be configured more easily to provide a variety of lighting patterns (focused to diffuse) while fluorescent bulbs are generally quite long making it more difficult to use as task lighting or for other special lighting purposes.
  • Toxic waste disposal concerns
    • Fluorescent bulbs contain mercury which is a hazardous substance. LEDs do not contain mercury, though they are still eWaste and need special handling for disposal.
  • Low temperature operation
    • LED lighting performs better at lower temperatures. In fact, life time if greatly reduced if they operate at too high temperatures (hence all the heat sinks on the LED bulbs). This makes LED lighting a natural fit for lighting refrigerated displays.
  • Green image
    • The current perception of LED lighting is that it is the next big thing in energy efficiency and is, therefore, green. Using this perception to advertise your greenness is good marketing.
While Metal Halide HID compares well on the cost/lm vs lifetime graph, it does have a major strike against it, besides the borderline CRI: restrike time. This is the time it takes for the bulb's arc tube to cool sufficiently to restart the plasma. This can be several (1 - 15) minutes. A long restrike time makes such bulbs very difficult to use in locations where individual light control is required (e.g. office spaces or residential). Using fast starting HIDs greatly shortens the life of the bulb.

So as the cost of LEDs drop (cost comes in line with alternatives), energy costs rise (efficacy difference becomes more important) and green building codes become more prevalent (raising the minimum energy efficiency requirements for new buildings), the ROI of LED lighting will rise vs fluorescents until LED lighting makes economic sense. 

It's just not quite there today.

Sunday, June 20, 2010

Comparing Light Sources

One of the low hanging fruit in energy efficiency is replacing incandescent lights with fluorescent ones.
Then there is much news about how big LED lighting, outside of TV and LCD monitor back-lighting, will be:
So LED lighting is where it's at.
So which is it and why?

First some terms:
How lighting is measured:
  • Photometry: The science of radiated energy as observed by the human eye. Metrics of photometry incorporate wavelength and sensitivity of the human eye at various wavelengths (luminosity function).
    • vs Radiometry, which is the science of radiated energy without regard to human perception of the radiated energy.
  • Luminous Intensity: measured in Candela (cd). Defined as:
    • The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz (~550 nm) and that has a radiant intensity in that direction of 1683 watt per steradian
  • Luminous Flux: measured in Lumens (lm). The light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian. Light bulbs usually label the output of the bulb in Lumens somewhere on the package.
  • Illuminance: measured in Lux (lx) or Foot Candles (fc). The total luminous flux incident on a surface, per unit area.
    • For metric units: Lux = lm/m^2
    • For English units: Foot Candles = lm/ft^2
How light sources are characterized:
  • Efficacy: The amount of illuminance generated per watt of energy input.
  • Color Temperature (CT) / Correlated Color Temperature (CCT): The "whiteness" of light generated from a source. Correlated to the color of light produced by a radiating black body of that temperature (K).
  • Color Rendering Index (CRI): The ability of a light source to correctly reflect accurate colors in the environment. CRI = 100 is perfect reproduction. CRIs in the range of 75-100 are considered excellent, while 65-75 are good. The range of 55-65 is fair, and 0-55 is poor.
I plotted the source characteristics for some common light sources below to show how they relate to each other. "Good" translates to high, to the right(ish) and with a large sized bubble.

What does that mean?
  • Incandescent and halogen bulbs are what most homes use today so they are the baseline against which all other lighting is most easily compared. 
    • It has good CRI, medium-low CT and very low efficacy. 
    • i.e. objects appear to be the "right" color when illuminated and the light itself is "warm (reddish)" but takes significant energy to produce very much of.
  • Fluorescent lights are very common, particularly in commercial lighting and are the other light source which you've probably encountered frequently. There is large variation in the characteristics available depending on phosphors used but:
    • Newer bulb types have reasonably good CRI, a wide range of CCTs (med - high) and high efficacy.
    • i.e. objects appear to be nearly the right color, light can be anywhere from "warm" to "cool (white)" (depending on the bulb) and energy is efficiently converted to light (~5x incandescent).
  • Metal Halide High Intensity Discharge (HID) are more common as outdoor lighting (and a variant - Xenon HID in car headlights).
    • It has borderline good CRI, medium CT and high efficacy. 
    • i.e. objects appear to be the "almost right" color when illuminated, the light itself is "cool (white)" and energy is efficiently converted to light (~7x incandescent).
  • Low Pressure Sodium lighting is the the yellow street lamp you've probably seen in the parking lot that made it impossible to figure out which car was yours because they all looked grey.
    • It's very good at converting energy to light, but it's not light you want to look at... unless you are an astronomer and want to filter out the city of San Jose's light pollution from your observations...
  • LED lighting is still fairly rare but is starting to show up in some more efficient building designs,  vending machines and refrigerated display cases.
    • Newer LED types have reasonably good CRI, a wide range of CCTs (med - high) and high efficacy.
    • i.e. objects appear to be nearly the right color, light can be anywhere from "warm" to "cool (white)" (depending on the phosphor used) and energy is efficiently converted to light (~10x incandescent).
Conclusion: modern fluorescents are quite good from a light quality standpoint, modern LEDs are similar as are (some) HID lamps. LEDs are clearly more "efficient" but adoption is still low. From this basic data one would expect that HID penetration would be higher too. Why is it not?

I'll get into more characteristics of these light sources later to better understand why the lighting situation looks like it does today, but hopefully this post went a good way towards explaining why the forerunners are what they are.
At least this proposed light bulb label should now makes sense:

Tuesday, June 15, 2010

Interesting Mixed Metaphor - BP Oil Spill and Energy Efficiency

This story from Treehugger highlights an interesting quantification of the BP Oil Spill in terms of energy being wasted.
  • The estimated cost to clean up the oil spill ($40 B) is many times greater than the cost to retrofit 75,000 houses ($1 B) and save the energy equivalent of the gulf oil spill every year.
  • 75,000 houses = mid-sized U.S. city or large suburb of a major city, like Chattanooga, Tenn. or Providence, R.I.
  • A typical home energy retrofit costs around $10,000 per house -- before any utility or governments energy rebates are applied.  
Of course, wasted energy is only a small part of the problem. There is the matter of millions of barrels (>114 million gallons = ~2.7 million barrels in worst case estimate or ~30M gal for a more conservative estimate) of crude oil in the water:
  • Oil washing up in coastal habitats killing animals, destroying ecosystems and heading towards Florida and the Atlantic Ocean.
  • Tons (>1.2 Million gal) of toxic chemicals being sprayed on it (dispersants) with unknown long term impact
  • The effect of the dispersed oil droplets sinking in the water column impacting sub-surface life.
  • Tons of methane, >20x more potent than CO2 as a green house gas, that have been released (around 2900 cu ft of methane per barrel of oil = 7.8 billion cu ft = ~112,000 metric tons = ~ equivalent to green house gas effect of emissions from 20,400 cars)
  • Increased hyopxic "dead zone" in the gulf (between 8% and 30% larger than normal) possibly from all the methane being pumped into the water along with the oil, further impacting the ecosystem.
  • The short and long term cost of health effects from the oil, chemical and gas exposure on clean up volunteers.
  • The resulting economic and job loss throughout the market chain as people cannot catch fish, sell fish, buy fish, so fishermen can't buy things thereby hurting local businesses which rely on the fishermen's income. (1% of Lousiana's economic output according to NPR)
  • More economic loss from the moratorium on deep water drilling (16% of the economic activity of Louisiana according to NPR).
  • The loss in stock value of BP impacting the retirement income and viability of retirement portfolios for large numbers of people, bringing further economic hardship on people already in the middle of one of the worst recessions in recent history.
So interesting comparison: yes... but sort of missing the big picture.