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In the first two parts, I gave a description of light sources and power distribution.  Now I will give a little more of a description on the newest form of lighting, LEDs, and the technical hurdles that we'll need to mount to increase their market penetration and decrease their costs.

To recap
Part 1:
Part 2:

Light Emitting Diodes turn DC current into light.  When first invented, they were limited to red, and then in time green, and amber colored light.  Very poor in terms of lumens per Watt, they spent most of their first 35 years as either instrumentation, or a way to display information.  As their efficiency improved, and their colors were broadened to blue and then finally white, their ability to produce light that did not change color with respect to intensity made them almost unique in terms of lighting technology.  But they still have drawbacks which continue today, in terms of their being a part of mainstream lighting.

Why would you want to use LEDs?

Light output is measured in lumens .  The efficiency of a lighting source can be measured as lumens/Watt )"lm/W", and the efficiency of a 100W incandescent bulb is about 17 lm/W.  The bigger the bulb, the more efficient, but since most people don't use 1000 W bulbs (I do, but that's for testing switches) they pay a huge penalty. In fact a 40 W bulb is generally about 12.5 lm/W.

Some of the LED's I'm describing claim to have an efficiency of 160lm/W, which would permit you to (in a lossless system) use about 10% as much energy to achieve the same light!

  1. LEDs are semiconductors.  So their "Current vs. Voltage" curve isn't simple like a light bulb, or a resistor- in order to get even the most microscopic amount of light out of them, you need to go beyond their initial operating voltage.  For most LEDs, this is in the low 2 volt range, but some require as much as 4 volts before they turn ON.  And once they are on, it isn't a simple equation, such as twice the voltage giving you twice the current and four times the output.  Their current goes up disproportionately with respect to voltage.  To put is simply, they operate on a very small range of voltages.
  1. Putting multiple LEDs in parallel, that is connecting them together where  both leads are tied to each other, causes imbalanced light output.  You will never get the same amount out of each, because one will always give off slightly more light than the other.  In some cases, as when the batteries are dying on your LED flashlight, one or more "bulbs" might die out on their own, just because the voltage is too low for them "fire".
  1. So if you try to use them on household line current, you get a few little problems.  First they'll burn to a crisp as the high voltage turns them from semiconductor to smoking heaps of melting plastic, possibly scattered all around the room.  Second, they'll only conduct electricity half of the time.  (That's not what the "semi" in semiconductor means, but in some ways it is an adequate description.  They will only conduct in one direction, as long as their threshold voltage is met.)  Now we can put two LEDs in series with each other, so the current flowing through one flows through both, and the voltage needed to make them work is twice as much as the earlier voltage.  Put 50 LEDs in series (making sure they are all lined up in the same direction, and that they all work- like the old Xmas lights, one dead one prevents them all from working!) and you would be able to plug it into the wall socket, and see a flickering light.

Now there are ways to make them work.  Remember in my earlier diary I discussed how you can turn AC voltages into DC; to recap, this is called rectification.  The best way to do it is to take 4 diodes, arrange them in what is called a bridge and that will give you a choppy sine wave, with two positive half cycles, instead of one positive, one negative.  Now the LEDs will turn ON 120 times a second, instead of only turning on 60 times a second, for 1/2 the time.  But this is still not what you want- we still have to convert the ~173 Volts to a voltage low enough to keep the LEDs from melting.  And we'd like some way to turn that sine wave into something easier on the eyes, a flat line.

To the rectifier we add a voltage regulator.  This is now a ubiquitous device, inside of almost every device known to mankind.  They come in several different electronic shapes and sizes, not to mention physical ones!  Obviously, we want it to be small, and we want it to work for a very long time.  And we also want it to be cheap- we're all unreasonable people here!  I'll skip all of the variations and instead stick to the most popular and smallest, a switching voltage regulator.

This consists of a few small high voltage capacitors, an inductor, and a chip, along with a smattering of resistors.  Capacitors store electrical charge, which is a good thing it you want to turn your sinusoid into a straight line.  The inductor stores magnetic energy, and it doesn't like to have any changes in current.  So we turn the current which passes through that inductor on and off a few tens of thousands of times a second, and have the resulting current try to keep the voltage on that capacitor the same, no matter how much we draw out of it.

I can see this being very confusing, so I'll try to make an analogy.  The chip and the inductor act like a spigot and a hose.  The capacitor is like a bucket, with a hole in it.  Our load which in this case is the LED lamp, takes the power coming out of the hole in the bucket.  The chip and the inductor try to make sure that the level of the bucket is the same at all times, to keep the flow going through the LED to be roughly the same.

The bigger the LED, the bigger the flow.  Now if we want to build one big enough to replace a 50 watt bulb, you will need about 6 or 7 watts of LED light, which requires a power supply that can at least handle that much power.  As of now, that's going to be bigger than 4 or 5 quarters stacked together.  And you will need heat sinks to draw the heat out of the regulator (not to mention the LED, they aren't 100% efficient, and trying to generate that much light will also generate a lot of waste heat.)

So how do you do this, while permitting the LED light bulb to work in existing low-profile sockets and lamp holders?

I say, we don't.

Instead of using the standard light switch, the kind you buy at Lowes or Home Depot for $0.36 we design a new light switch.  One that has the rectifier, voltage regulator, and heat sink built IN TO THE SWITCH.  And since we want this fancy new LED to be dimmable as well, instead of a simple "ON/OFF" switch we'll use a rotary dimmer, or a sliding dimmer.

No more $0.36 light switch... I haven't done the pricing, but assuming that what I'm using in our 5 Watt devices doesn't go up too dramatically, it should cost about $6 to make it work for 20 Watts in serious quantities.  Maybe more if we want to use a really good dimmer, with no dead spots and a good feel.  So if it costs about $6 in parts to make in China, it would cost about $15 to $50 at the DIY store, depending upon how many people are willing to spend that much.

Now to get that much light you'll need an expensive LED, not a cheap little $0.05 job, and not even 100 of them.  You'll need a killer, like the Cree XR-E (in fact, you'll need a few of them) for about $6 and change in high volume.  Or you can use the Lamina NT-42D0-0426 (again, you'll need a few, but fewer than the Cree) and you'll need a radically different bulb architecture, more like a PAR parabolic reflective lamp than a round globe, and that too will require more money.

Hey, luxury and doing what's right for the planet ain't cheap.  It will take you around $100 to replace that $1 light bulb.  But it will last you for 20 years at least, so its $100 to replace $20 or more dollars in bulbs, plus for each year you'll save (assuming the bulb being on 4 hours a day) more than $10 a year in electrical bills.

Assuming $0.10/KWhour at 1460 hours a year, 100W bulb uses 146 KWhours per year, $14.60 per year, per bulb.

LED bulb and power supply will use about 20KWhours per year, maybe a little less, maybe a little more.  That's $2.  So that will save you about $13/year, add in the cost of the new bulb to about $14/year.  Time to return on investment, about 7 years.

(Note: I'm currently paying about $0.18 KWH in the suburbs of NYC.)

In time, the costs will get cheaper, the return time smaller.  But this is a start; we are on our way!

Originally posted to Dcoronata on Sun Feb 25, 2007 at 02:17 PM PST.

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Comment Preferences

  •  Tip Jar (24+ / 0-)

    Let some current flow between the anode and the cathode.  That's the positive and the negative sides...

  •  sucks no one has commented (3+ / 0-)
    Recommended by:
    cathy b, maybeeso in michigan, norahc

    on this diary.

    It's over my head, but I read your work.
    I do know LED lighting is expensive. I bought those lights for a trailer I built & they cost me some 350 bucks !

    Have A Bloggy Day :)

    by eeff on Sun Feb 25, 2007 at 06:10:05 PM PST

  •  We need to change the infrastructure (10+ / 0-)

    I've thought for a long time that homes should be wired with low-voltage DC in addition to AC. It simply makes no sense to provide a transformer and power supply for every little tiny device, even a digital clock that uses maybe a watt or so. (Power over Ethernet has some possibilities in this area, but it's very new and expensive.)

    Also, the ceramic sockets we screw light bulbs into are exactly wrong for LEDs since they are great heat insulators. LEDs need a heat sink to conduct the heat away and keep them cooler, extending their life and increasing maximum light output.

    News is what they don't want you to know. Everything else is publicity. --Bill Moyers

    by RobLewis on Sun Feb 25, 2007 at 09:41:51 PM PST

    •  I-squared R (1+ / 0-)
      Recommended by:

      Wires are not perfect conductors, they are really very low value resistors. And as resistors they have voltages drops corresponding to the current flowing through them. The voltage drop is power dissapated - lost - in the wire. The shorthand notation for this is the current times itself - I squared - times the resistance R ; if I is measured in amps and R in ohms the result is in watts.

      Much of the low voltage stuff is also fairly high current. Twelve watts at LED voltages of 4 volts is 3 amps, at 120 volts it's 0.1 amp.

      OK, the low voltage line at 3 amps must have 1/30 of the resistance of the high voltage line at 0.1 amp in order to waste no more power in transmission. Resistance is proportional to the square of the cross section area of the wire, this means the low voltage line would need to be roughly 4.5 times as thick.

      Now most house wiring is rated for 20 amps, even though the line may have a circuit breaker of lower rating. So the 3 amps vs 0.1 amps isn't a real big issue. But put several 12 watt loads on the same line and you get closer to the ratings.

      Another aspect is the wire loss in terms of percentage of power getting to the load. Run 120 volts through a wire that drops 1 volt at the normal current load; power loss is a little less than 1% of the total power in use. Drop 1 volt on a 5 volt line and you've lost 20% of the power.

      Plug in a low voltage feed computer, drawing 300 watts at 5 volts and you're now looking at 60 amps (computers use a mix of voltages, nowdays most of the current draw is at voltages of 3.3 volts and lower, it's less efficient to convert 5 volts to say 1.8 volts than it is to convert 120 V to 1.8 volts for the same output current - IsquaredR in the conversion curcuits)

      So going back to the wire diameter issue above. Half the voltage, double the current to deliever the same amount of power. Double the current means twice the voltage loss on the same size wire, so we need to half that loss by doubling the wire cross section. But because the same voltage loss amounts to twice the percentage loss of delievered power - 1 in 120 vs 1 in 60, we need to half the voltage drop, going to 4 times the wire cross section or twice the thickness.

      Now LED lamps need much less power overall than incandescents, the delievered power at the socket is much less. But consumer electronics are already solid state and will pull the same amount of power, or even a bit more (conversion loss), if powered from low voltage mains. So you end up making the wiring thicker to handle that, or running two sets of power mains with outlets for each.

      The issue of voltage drop is much more important on long lines than the short ones in homes. But it still should be considered in the overall efficiency of an approach to energy savings.

      •  And at $3.25/#, copper ain't cheap! n/t (0+ / 0-)
      •  You misunderstood (0+ / 0-)

        I wasn't talking about powering large loads with low-voltage DC. I gave the example of a digital clock that uses a watt.

        I simply don't believe your assertion that "it's less efficient to convert 5 volts to say 1.8 volts than it is to convert 120 V to 1.8 volts for the same output current." High-efficiency DC to DC converters are so small and cheap now that they're being used at the so-called "point of load", that is, right next to the component that needs the reduced voltage. Can you offer any proof of your claim (and don't spare the equations--I'm an electrical engineer)?

        The current practice, using dozens of "wall warts" to power small household devices from 120VAC, is hugely wasteful: the EPA estimates that, as currently designed, they waste 32 billion KWH per year. I did a whole diary on this; have a look. By contrast, a single large DC supply in your basement could be over 90% efficient.

        And if the whole concept is such a bad idea, why is Power over Ethernet catching on? (It's based on telco-style 48VDC so the currents are low enough to travel over Cat 5, even with 20-30W loads.)

        News is what they don't want you to know. Everything else is publicity. --Bill Moyers

        by RobLewis on Mon Feb 26, 2007 at 01:35:31 PM PST

        [ Parent ]

        •  OK (0+ / 0-)

          charge pumps are very efficient, 90 to 95 percent. But they don't handle large loads well, although there are some that can handle a quarter amp or so. The MAX682 can, but its efficiency is in the 70 to 80 percent range. Switchers can also be rather efficient and can handle higher currents.

          If you are after X watts out, you need to switch more current when running off a low voltage than a hig to reach that power level. And more current means you're running inth the I^2R problems, and the voltage drop across the semiconductors is a larger percent of the working voltag, meaning more power loss.

          Wall bugs have not been designed for efficiency in most cases. There are exceptions, I have a 'wallbug' supply that puts out 4 amps at 22 volts with a rated efficiency of 92 to 94 %, as good as most charge pumps.  Bt most are designd for low cost.

          I was going to suggest that if a lower voltage distribution were to be used, it should be 36 or 48 volts. High enough voltage that you can drive TVs and what not without too much drop, low enough that lower cost conversion can be done.

          Power of Ethernet, and what should have been in USB V1.0, is a much better ideas. A computer's power supply can deliever the power for smaller external devices that don't pull too much. That makes more sense than the forest of wallbugs that happens now.

          But there's been comments in diaries along the lines of "why don't we wire houses with 12/5/3.3 volts because that's what the chips use" They ignore how much power is used by consumer electronics, and are thinking in terms of a single 100 ma LED, not the 10 to 30 watts array needed to give good working lighting. Put several of those on their idea of a low voltage line and you're looking at significant amperage; don't even think of their state of the art gaming computer, big screen TV, or exercise treadmill.

          But you're talking about something different than those people, a mid-range voltage at the house level. Pulling accessory power into the computer box is something that should have happened a decade ago

  •  Calculating return against incandescents (8+ / 0-)

    makes LEDs look attractive - against CFLs, not so good.

    The other consideration is cashflow/opportunity cost. If you can only budget a few hundred dollars for energy reduction measures, LEDs right now will consume most of that, whereas CFLs (especially if you find a cheap source online) won't - leaving you money to invest in insulation, doors, windows, a setback thermostat or other things that provide a good or better energy return on investment dollars than the difference between CFLs and LEDs.

    On the other hand, if you're in a position to achieve the absolutely lowest energy consumption, or trying to reduce your consumption to get off the grid (or paying $0.18/kWh - yikes! - I pay between 2.1 and 2.85 cents/kWh), then the newer LEDs coming on the market now make more sense. There are places where LEDs can make sense now, but generally I think CFLs are a good solution for most people.

    Good engineering always tries to look at and optimize the entire system, not just particular features, and the problem you're trying to solve influences the approach you take.

    There is no more New Frontier - we have got to make it here - Henley/Frey

    by badger on Sun Feb 25, 2007 at 10:46:28 PM PST

    •  I agree that CFLs are the better solution today (2+ / 0-)
      Recommended by:
      mataliandy, jcrit

      These diaries are based on a series that have been done by other Kossacks recently on the subject.  I decided that it needed to go into much greater detail, for it to have a more descriptive dialog.  

    •  But the budget problem is a finance problem, ... (3+ / 0-)
      Recommended by:
      SarahLee, mataliandy, Dcoronata

      ... not a real problem. That is, it is something that the government can simply fix if it wishes to.

      The trade offs between LED's and CFL's are real problems ... which is more efficient. We don't want to have "pick this technology" type policies precisely to allow the best solution to be used for the particular situation ...

      ... but if something has a payoff within 10 years, there is no reason that people should not be seeing some college students earning summer money from the local power company knocking on their door, saying, "we are in the neighborhood doing lighting audits, to see whether you qualify for installation of these high quality light bulbs, paid for out of the savings on electricity".

      •  This is part of the problem/solution (2+ / 0-)
        Recommended by:
        SarahLee, mataliandy

        I'd love to see a real energy program in this nation, where trained professionals can audit a home free of charge, and make recommendations on what repairs/retrofits can be performed to improve the home's efficiency.

        Give tax rebates for every single device or improvement in the audit, and give a double tax break for all components made in the US.  So if you are in the 27% tax bracket, a $1000 in repairs would "cost" $730 if using foreign equipment, $460 for American.  It would help dramatically reduce reliance on foreign sources, reduce GW footprint, and help American businesses.

        Is there a downside? No?

        Then why aren't we doing it!

        •  they have them in some places (2+ / 0-)
          Recommended by:
          SarahLee, mataliandy

          In Massachusetts they have a program like that.  All utilities must participate, they offer free energy audits, and there are ~25% rebates on all measures. The audit and rebates cover all energy sources (gas, oil, electric, propane, doesn't matter).

          I'm not sure about the need for sa special buy American angle - how much insulation do we import each year?

          •  Just an "angle" to push legislation (1+ / 0-)
            Recommended by:

            seeing how the Republicans can't possibly imagine how we can cut greenhouse gases without killing the economy. This would give an incentive for American companies to invest in green enterprises.  

      •  No (3+ / 0-)
        Recommended by:
        SarahLee, AlanF, NRG Guy

        I don't know many people who can say "finance is not a real problem", and certainly the government doesn't have the ability to say that.

        This is way too complicated to develop a realistic example, but here's the kind of situation, although contrived, that you always face. Suppose that you have $300 for energy improvements, whether strictly from your personal budget or via some kind of government incentive. Suppose your monthly energy budget for a winter month is 3000kWh, and that 600kWh is lighting (incandescent) and 1500 kWh is heating (you can convert gas, oil or wood heat to kWh for comparison purposes).

        Now I can spend the entire $300 to convert all of my incandescents to LEDs and save 550kWh. Or I can spend $100 on CFLs and save 450kWh and $200 to insulate my attic and save 20% or 300kWh on heat, for 750kWh total. In the latter case I save 200kWh more (36% more) for the same investment. Which is a better solution for problems of dependence on foreign oil, air pollution, or globabl warming?

        The cliche is "the perfect is the enemy of the good" - every system analysis involves those kinds of tradeoffs.

        Now you can argue that the individual should just spend more money, but in the wider system of a family budget, there are other tradeoffs. The extra money comes from somewhere - health care, better diet, tuition, political donations, clothing, entertainment - something. Energy isn't the only thing people spend money on.

        You can also argue that the government should spend more money, but the situation isn't any different. For example, should the government spend the extra money so everyone can afford LEDs by taking funds away from renewable energy research? Healthcare? Tuition aid? Welfare? Just increase the deficit?

        Nobody here would argue that the War in Iraq is a sufficient excuse to abandon sound fiscal policies or to abrogate indvidual freedoms. There isn't any reason I know of to argue that global warming is any different - the challenge in dealing with global warming is to do it in ways that are fiscally responsible and consistent with democracy and freedom. In fact, trying to do it any other way is almost guaranteed to fail, either through the re-election of a GOP majority and President, or through resistance to change in other ways - the same situation as Bush and the GOP find themselves in now (or the energy policy changes going from Carter to Reagan).

        There is no more New Frontier - we have got to make it here - Henley/Frey

        by badger on Mon Feb 26, 2007 at 09:01:59 AM PST

        [ Parent ]

        •  Connie Mae finance would not be an ... (0+ / 0-)

          "incentive", as in:

          Suppose that you have $300 for energy improvements, whether strictly from your personal budget or via some kind of government incentive.

          It would be a financial instrument based up the financial savings from carbon-reducing capital spending. If you have $1,000 that could be spent in a self-funding way, then it would be $1,000.

          Certainly an individual has a financial constraint, certainly local and state governments have financial constraints, but the constrain on lending by the federal government is the impact of the creation of that purchasing power on the economy. The constraint is real ... and I would argue that for any self-funding cabon-reducing capital spending by anybody in the economy, if there is a problem caused by creating too much purchasing power as a side-effect of the program, that the reduction should come from somewhere else, and not from the Connie Mae program.

          •  Well (0+ / 0-)

            I don't know what Connie Mae is - perhaps I should.

            My point was simply a) there are real financial constraints, and I can't imagine a program that eliminates them, and b) needs another example.

            Assume that for $4 I can save 45W with a CFL, or for $20 I can save 55W with an LED. The savings cost me about 9 cents/watt with the CFL and  about 36 cents/watt with the LED. On a global scale, I can save 4X the energy per dollar spent by using CFLs (and the example is extremely favorable to LEDs - the real numbers won't be that close for a while).

            The extra 10W savings per LED vs CFL on a global basis is an illusion, because there isn't an infinite amount of resources, and resources are not only money, but also the increased use of physical resources, maybe even energy, that an LED takes vs a CFL based just on their price difference.

            In all likelihood, you won't save as much energy globally switching to LEDs vs CFLs, because you won't be able to spend 4X or more the amount of money. We'll be lucky if we can afford to spend enough to solve the problem with the most cost-effective solutions.

            There is no more New Frontier - we have got to make it here - Henley/Frey

            by badger on Mon Feb 26, 2007 at 04:05:00 PM PST

            [ Parent ]

            •  Yes, individuals have a finance constraint ... (0+ / 0-)

              .. but not the federal government. The federal government can "afford" to spend as much money as it wants to ... money is, after all, either government liabilities or bank liabilities that leverage government liabilities. The government is always able (though not always willing) to finance in US$.

              As to the energy cost of the CFL and the LED itself, that has to be included when determining whether something qualifies as a carbon reducing investment. The basic idea of a Connie Mae financial instrument is to finance the self-funding portion of any carbon reducing investment. It does not impose technological choices ... but obviously, if other policies, like carbon taxes, shift the balance of financial advantage, more carbon reducing investment would become eligible for Connie Mae financing.

    •  but doors and windows aren't a good altenative (0+ / 0-)

      I agree that LEDs don't appear to be nearly as cost-effective when compared to lots of other things we can do to save energy, but I wouldn't put windows or doors on that list.  
      In retrofit situations, window and door replacements save very little energy -- most likely less than 5% of heating usage.  Replacing all of your windows with brand new Energy Star windows in a cold climate state will typically pay for themselves with energy savings in about 100-200 years.  Windows might be a great home improvement, but they are not a large energy saving measure. Insulation, air sealing, equipment efficiency,a nd temperature control (setback thermostats) are where the real savings  are for heating usage.  

      Where do you pay 2 cents per kwh for electricity???  I pay nearly 20 in Boston...

      •  Cheap electricity (2+ / 0-)
        Recommended by:
        SarahLee, mataliandy

        I live in E WA State - we have county-owned hydro. I think the county across the river from us is even a little bit cheaper. We pay 2.1 cents for the first 1000 kWh, 2.7 cents for the next 1000, and 2.85 cents after that.

        In a lot of older home retrofits, new doors or windows aren't a benefit only for the increased R value - they often solve significant problems with infiltration (out of square jambs, no seal between jamb and wall, leaky openable windows in exterior doors, no storm window/door, leaky double-hungs changed to tight casements, etc.).

        I'd really want to sit down and do a calculation before I wrote off doors/windows completely just on insulation value - it makes a difference whether you're in Boston or where I am now, both at about 5000 degree-days, or WI where I used to live at 8000 degree-days, or International Falls, MN at over 10,000 degree-days. And of course the window area as a percentage of total wall area makes a difference too.

        I spend less than $200/year on heat (about $120 for electric and maybe $75 for wood) - the payback for anything at all is pretty long under those circumstances. I actually have some leaks around windows right now (due to settling - I have a log home), but the annual savings from fixing them might come to $25 if I'm lucky - probably a lot less. Even the energy return on investment isn't that big.

        There is no more New Frontier - we have got to make it here - Henley/Frey

        by badger on Mon Feb 26, 2007 at 09:29:45 AM PST

        [ Parent ]

        •  more windows and doors (0+ / 0-)

          Window and door replacement won't save much energy in most homes because very few homes in cold climates actually have just single pane aluminum framed window (if they were common, then my conclusions would change).  Instead, the existing conditions are more efficient than usually assumed and real savings fall far short (on average)

          In cold climates, virtually every window has at least a storm and older wood prime windows.  The new Energy Star window will lead to some air leakage reduction (but not that large on average as blower door testing has repeatedly found), a modest reduction in conduction losses (less than the standard equations typically show due to glass vs. sash area, lower true wind speeds, and other factors), but also a reduction in solar gain due to the low e coating, that can offset up to half of the conduction savings or more in cold climates.

          In some homes, you may be able to get decent savings, but in most homes you won't and in virtually no homes will there be a payback of less than 30 years.

          I've actually done some pre/post usage data analysis for window replacements for a bunch of homes upstate NY and found typical savings less than 5% and no home saving more than 10%.  

          •  Lots of older homes out there! (1+ / 0-)
            Recommended by:

            Mine was built in 1967, which isn't that old at all, probably younger than the median.  Had singles that were leaking and rotting, and it was the first major renovation we did.

            I'm sure, many more out there like that.

            •   I agree, but many doesn't mean typical (0+ / 0-)

              It's true, there are lots of older homes out there -- many many older than 1967.  Most older homes in cold climates have storm windows.  In really older homes (pre-1960) the prime windows were usually made with fairly wide wood sashes.  Your 1967 vintage is pretty close to the bottom in terms of window efficiency because that's when they weren't using double pane windows yet, but aluminum frames and other less material-intensive sash and frame designs were more common.  That vintage holds the most promise for window replacements, but still a large proportion of those homes have storm windows now.  Just because your home may have achieved good savings from window replacement (and you haven't actually claimed that it has, yet) doesn't mean that most homes will get good savings or that it is a generally cost-effective retrofit.  

              The analysis of actual usage data I was referring to previously was from older homes --  that's where most window replacements are going and that's where the simple payback on investment is averaging longer than most peoples' lifetimes.  

              I'd love to see anyone find a single study that shows measured (not projected or calculated) reductions in average whole house energy usage from window replacements in a group of homes that are close to cost-effective or that save more than 10% of heating usage.  Strangely, I know of no studies    of measured window energy savings.

              •  There's a good reason (0+ / 0-)

                it wouldn't help the replacement window industry!

              •  From VPIRG (1+ / 0-)
                Recommended by:

                Vermont’s housing stock is old. About 50 percent of the state’s homes pre-date any energy efficiency standards for buildings.

                [emphasis mine]

                The majority of houses in Vermont have single-pane windows, drafty (as in: you can feel an active breeze) doors, and little or no insulation at all.

                In 2005, Vermont residents spent an
                estimated $250 million on residential


                Home weatherization and heating system improvements to Vermont homes from 1999 to 2000 required an average investment of $2,027 per home. Through reduced home heating bills, the investment was recouped in under four years and is today providing hundreds of dollars of annual savings per homeowner.

                With fuel prices even higher today, greater improvements would be cost effective and the payback time on weatherization efforts may be even shorter.

                Beware the everyday brutality of the averted gaze.

                by mataliandy on Mon Feb 26, 2007 at 03:58:47 PM PST

                [ Parent ]

                •  Vermont homes... (0+ / 0-)

                  I've been to Vermont and know people who run energy retrofit programs there and I know the person who wrote the report you cited and have read the full report.   The vast majority of homes there have storm windows and insulation -- even the older low income housing stock.  I do agree that there are lots of worthwhile energy savings investments to be made there,  but those investments are primarily in insulation, air sealing and equipment efficiency on the heating side, plus lots more on the electric baseload side.  

                  The program you cite does very little window work -- less than 6% of total retrofit spending.  Also, the 4 year payback is not accurate -- savings were about 20 MMBtu/yr at an energy measure cost of more $2,000 per home (but full program cost of $3,227) meaning a 4 year payback would require oil heat at more than $3.50/gallon even excluding non-energy measure program costs.  

              •  Marginal (0+ / 0-)

                I did a rough calculation (1500 sq ft, about 12% glass, R30 ceiling, R15 walls, R10 to 55F floor) and if you assume R2 for window + storm and R1 for a 45" X 42" single-glazed picture window vs R3 for low E/double-glazed all around, you save about 11% of the annual heat energy. The payback is probably out past 20 years even for 8000 degree-days, depending on what you pay per window, who does the retrofit, what you pay for energy - there are some cases where it makes sense.

                That doesn't account for infiltration, which can make a substantial difference (although a lot of times that can be dealt with without replacing the entire window or door). It also doesn't account for maintenance costs (sashes and storms) and putting up/taking down storm windows, which is a pain in the ass. Poorly maintained or even missing storms are pretty common, which makes the R2 assumption questionable.

                For new construction, however, the payback period isn't too bad - but there you're only looking at the cost difference between a good window and a poor window (if any), and the labor cost drops out.

                Windows are still a big energy waster though - roughly between 25% and 30% of the total heat load for my rough calculation - the big single-glazed picture windows can account for 5% of the heat load by themselves.

                There is no more New Frontier - we have got to make it here - Henley/Frey

                by badger on Mon Feb 26, 2007 at 04:06:41 PM PST

                [ Parent ]

                •  rough estimates are very rough... (0+ / 0-)

                  The type of calculation you did is quite common but not very accurate.  You did not account for reduced solar gain through the new window and you assumed going from R-2 to R-3 when really it's more like R-2.3 to R-3.3 (R2/3 assume a constant 15 mph wind on the window) -- this change reduces the window savings by 21%.  Also, the picture window is a big part of it (which really should be closer to R-1.3)

                  Here's a link to a Wisconsin window study (warning .doc file) which estimates the net present value of 30 years of savings from window replacement at $4-$8 per square foot --- far lower than the installed cost.  You can expect the typical private contractor to charge maybe 10 times that much.  This calculation is for Wisconsin (quite cold) and assumes low-income housing stock.  

                  Your rough calculation of 25%-30% of heating load is also pretty far off.  Did you include infiltration?  Foundation heat loss?  Also, R15 walls are too high for older homes.  I've been doing detailed simulation modeling of buildings for 20 years -- enough time to realize that back of the envelope calculations always overestimate savings.  

                  I've also been analyzing the actual energy usage in thousands and thousands of homes and assessing the statistical relationship between retrofits and real usage.  

                  I do agree that things look much better for the incremental change from regular new windows to more efficient new windows.

                  •  Forgetting something (1+ / 0-)
                    Recommended by:

                    People like to live in nice houses.

                    And there is the assumption of simple window R value, when the wood will more than likely have shrunk with time, and the caulk will no longer be seamless.

                    •  Not forgetting.. (0+ / 0-)

                      I never said that people shouldn't replace their windows -- I said that they shouldn't expect the cost of the window replacement to payback with energy savings any time soon.  It's great to have screens, nice looking windows, easy cleaning tilt-in features -- but that's not the point of my posts.  I'm just saying that window replacement is not a high priority energy saving retrofit in cold climates.  

                      I also did not base my conclusions on any simple R-value calculations but on a combination of things including actually looking at the monthly gas bills for homes before and after they replaced their windows.

                      I am also aware that air leakage through windows is usually not that significant in the overall air leakage rate of a house as measured by blower door testing, regardless of what peoples anecdotes and feelings may be.

                      •  Is it possible that people (1+ / 0-)
                        Recommended by:

                        when they've redone their homes subconsciously feel that they are more efficient, and therefore they bring the thermostat UP thinking that they are already paying less, so they might as well be comfortable?

                        Just throwing it out there, kind of like the idea of drivers being more reckless when they have ABS and air bags!  I think it's human nature to want to be more profligate when you believe your paying less for it.

                        BTW part of the reason (if not most of it!) we redid the windows was because the old ones were rotting away.  That happens in a 35 year old home.  I'd bet those leakage tests would have shown up with a higher loss figure in This Old House.

                        (BTW, I've finished part 4 on the Sun, but I'll wait until tomorrow to publish as I've been up since 4AM eastern, and I'm going to turn in soon.)

                        •  take-back is not the cuplrit (0+ / 0-)

                          The behavior you are talking about is referred to as takeback in the energy literature.  The few studies to examine it have found no evidence of takeback -- people keep their thermostats where they want them and no systematic changes have been found after energy retrofits.  

                          There really isn't much of a mystery here -- a closer look at the building science indicates that window replacements won't typically save a lot of energy and the usage data supports that analysis.  Let's look at it another way -- the cost side.   It's not uncommon for a whole house window replacement job to cost about 10 times the annual heating bill.  Even if the windows saved 50% of the heating usage (absurd), the payback would still be 20 years.  If they saved 10% of the usage (higher than typical, but certainly not impossible), then the payback would be 100 years.    

                          Also, even 80 year old windows (many of which are not rotted) that are in poor condition and very loose typically account for less than 20% of whole house air leakage (often because the rest of the house with such poor windows is also quite leaky).

                          •  Not in our case (1+ / 0-)
                            Recommended by:

                            Total window cost- $5600

                            Annual heating bills- $3000 (2004-2005 winter). Bear in mind this is the northeast, and we have Con Edison the most expensive energy provider in the continental US.  All of these have to come to bear to determine the real cost of improvement.  I have little doubt that our ROI will be measured in the ~10 year time frame, not 100!!!

                            Now we have increased our temperature significantly, mostly due to our aging cats but I think that this isn't as uncommon as thought.  Even thought energy costs are higher AS PEOPLE AGE they bring the heat up.

                            I can't honestly say how much we've saved because the last two winters have been relatively mild, and the cost per KWH has gone up.  The house itself was well insulated- not as much as I'd like, and I'm working on that but for a nearly 40 year old house it was done well.  

                          •  the plural of anecdote is not data (0+ / 0-)

                            Your $3000 heating bill certainly makes many potential retrofits more cost-effective -- that's very high even for a cold climate.  Your $5600 window cost is also on the low side.  As I have said repeatedly, in typical heating climate situations, window retrofits have very long paybacks.  In some extreme circumstances the paybacks might dip down to something more reasonable -- maybe even 20 years, though they still probably provide a much longer payback than other retrofit opportunities.  You can feel good about your windows all you want and people should replace their windows whenever they want, but that doesn't make them a generally effective energy retrofit.  

                  •  Well (0+ / 0-)

                    The article you reference uses U values pretty much equivalent to R2/R3 - the difference, if I plug in 2.3/3.3 is about 10%, which is lot less of an error than I'd expect a crude model to have in the first place - an order of magnitude would be fine. You're quoting as authoritative an article that doesn't get any closer than 100% ($4 to $8).

                    If you read the post, you'd notice I did include foundation loss (R10 to 55F floor - basically 2 inches of styrofoam under a slab where the heat loss out the ends isn't significant - or at least is ignored; and no, it doesn't make any difference that old homes aren't slab on grade with insulation), and I said I didn't include infiltration, which is reasonable for two reasons - the first being infiltration overall varies hugely from building to building and the second being it'd be pretty foolish to worry about replacing the windows before taking care of air leaks not caused by the windows. That leaves only the window leaks and therefore makes the estimate somewhat conservative. The article you referenced says I was conservative by as much as a factor of 2 - again, an order of magnitude would be fine.

                    It makes no difference if R15 is too high for older homes, because the savings doesn't depend on the total heat loss, just the absolute change in heat loss due to the windows (over time) vs the cost of replacement.

                    I thought it was interesting to see what contribution each subsystem contributed (again, roughly) in a moderately insulated house. In most older homes, getting them up to R15 is going to be major surgery. But at any rate, someone looking at this seriously should consider the costs and energy savings from correcting all of the buildings defects before settling on a single course of action, like replacing windows. Cost/benefit analysis only makes sense.

                    So in summary, while I generally agree with your original statement that windows probably aren't the highest priority item for energy savings (then again, I only included them as one option in a range of options), I don't see any problem with a "back of the envelope" calculation to arrive at that conclusion, once again, within an order of magnitude. Given the variability in scenarios where somone might consider replacing windows, I don't think a general discussion would benefit from any greater accuracy, and in fact I don't think it's possible to be much more accurate in the general case because of the high degree of variability. I don't see how your comment changes the fact that I pretty much agree generally with what you're saying after playing around with a few numbers and crude assumptions.

                    There is no more New Frontier - we have got to make it here - Henley/Frey

                    by badger on Mon Feb 26, 2007 at 06:20:44 PM PST

                    [ Parent ]

                    •  few more thoughts (0+ / 0-)

                      I agree that the article is actually not authoritative, but one of the few places where a slightly more sophisticated model was used.  The reason the range of projected savings is so wide ($4-$8) is because it includes variability in fuel prices.  Also, the percentage uncertainty doesn't really matter, it's that the HIGH end of the savings is still far below the window replacement cost, even when the work is done by non-profit agencies (vs. more expensive private contractors).  If a window retrofit costs $30/sqft it doesn't really matter whether the savings over 30 years are worth $4 or $8, it's still not a good payback.  

                      I agree that even a back of the envelope calculation will usually show that window replacement has a very long payback and those sorts of calculations may be fine for an individual homeowner to make.  I'm more used to working with large scale retrofit programs where more careful analysis makes a difference in what things are promoted and can have a substantial impact on the success of the retrofit programs.  

                      In one recent analysis, I found that the contractors that did the most window and door work had the highest retrofit costs and lowest energy savings of all contractors.  Their work did not pass cost-effectiveness criteria.  If all contractors had taken that approach, the entire program would have been deemed a failure.  These decisions matter to me.

                      I mentioned the other aspects of home heat loss (like wall R value) because you estimated window heat loss as 25%-30% of total heating load, so obviously the size of the total heating load matters in that calculation.  Also, you may want to double check your math -- the difference in conductive heat transfer savings going from R-2.3 to R-3.3 is 21% less than going from R-2 to R-3:  1/2-1/3 =.166 and 1/2.3-1/3.3=.132, .132/.166=79%

                      •  asdf (0+ / 0-)

                        On the calculation - yeah, the 2.3 vs 2 makes a 21% difference on that item (at about 127 sq ft of glass), but I also had a little over 13 sq ft of fixed, single-pane going from R1 to R3.8 (didn't keep a link to which window mfg claims R3.8 for a fixed window - probably one of Andersen, Pella or Harvey - whichever I found first). That limits the change in savings to 10%, which is the number I was looking at. But the total glass area was a pretty wild-assed guess to begin with.

                        I've only worked up new home designs for myself and friends, so there's always the factor that you have to spend something, and only differences make the choices - as opposed to retrofit, where you have the option of doing nothing. Building codes also tend to force more glass for new construction - for example on north walls - when they have requirements for window area/floor area ratios for natural light, ventilation and fire exit. In those cases, or any specific case, I'd agree that accuracy matters.

                        I would agree strongly on cost/benefit analysis (I argued that in some comments above), which is what this amounts to.

                        Contractor variability is another big issue - both in what work they sell, and in how they do the work. Of course the same applies to owner-installed stuff, but we won't get into that.

                        There is no more New Frontier - we have got to make it here - Henley/Frey

                        by badger on Mon Feb 26, 2007 at 11:12:16 PM PST

                        [ Parent ]

                        •  calcs (0+ / 0-)

                          If I add the single pane picture window at R-1, I get a 14% reduction in savings from the 2.3/3.3.  But I would also change the picture window to R-1.3 (that wind speed assumption).  With that change, I get a 24% reduction in projected savings overall.

                          Just to put all of these calculations in perspective and to show how much we agree, I calculated the annual natural gas savings for a home using all of your base assumptions about R value, ignoring solar gain changes, and assuming a very cold 8000 HDD climate and an 80% efficient furnace. I get annual gas savings of 74 therms per year, which is worth somewhere around $74 at current rates or maybe $100+ in places with higher gas rates.  If the window replacement job cost $5,000, that's a simple payback of 50 years or more.  That 74 therms is also probably less than 10% of annual gas usage.

                          If you make the various calculation changes I suggested, the savings drop in half (to less than 5%) and the payback hits about 100 years.  If we re-do this calculation for a more typical heating climate of 5000 HDD then the simple payback is more than 150 years.

                          •  Problem is, not everybody uses nat gas (0+ / 0-)

                            many have oil, many have electricity.

                            That's the problem with assuming that everyone pays the same for their energy, has the same basic layout, buys the same windows.  The plural of anecdote is often REAL WORLD and you've failed to address the millions of homes that do not meet your calculations.

                          •  doesn't really matter that much (1+ / 0-)
                            Recommended by:

                            I am not assuming that everyone is the same, I am illustrating a point.  It's amazing how defensive people get about window replacements.  Sure, there are some circumstances where window replacements might pay for themselves in 20 years and perhaps even less -- someone living off-grid, remote Alaskan villages, a house with all jalousie windows in a cold climate (even I would replace those...), homes with electric resistance heat in a cold climate with metal frame single pane windows and no storms...  My point has been that, for the vast majority of homes in the US, window replacements are not a very cost-effective energy retrofit, especially when you compare them to other opportunities.    

                            Now for the calcs you seem to need.  If the home is heated with oil at $3 per gallon (kind of high),  you now drop that 100 year payback to 50 years in the very cold climate and drop the 150 year payback to 75 years in the more typical heating climate.  If we go with electric resistance heat at 10 cents per kwh, then the payback drops to about 40 years in the 8000 HDD climate (but electric heat is less common in colder climates).  If the electric cost is much higher and you are one of the unlucky few who have high kwh costs and electric heat in a very cold climate, then the payback could head closer to 20 years.  Meanwhile, that same home probably has a dozen more cost-effective things that could do first.

                            If you really want new windows -- then buy them.  Just don't pretend that they are your best energy retrofit in anything but unusual circumstances.      

                          •  Didn't mean to imply that it was the best choice (0+ / 0-)

                            purely in terms of energy vs. $ improvements.  There are times when a repair is needed, and you might as well take advantage of the other benefits!  Most older (and again, here in the near suburbs of NYC there are hundreds of thousands of homes such as this) homes have been renovated in some ways here and there, yet some of the elements are still very inefficient.  If I may repeat something I've said in the past, and neglected to mention once more if you really want to improve your home energy efficiency buy an inexpensive IR thermometer!  You can get a decent one for less than $50, and at the very least you can use it to temper chocolate.  It will help you find all of the areas in the house that are significantly colder than the others, and that can help you fix the more immediate problems.

                          •  IR thermometers are fun, but IR cameras are great (0+ / 0-)

                            The IR thermometers are fun and useful, although it can be tricky sometimes to track down why an area may be cold (infiltration and convective vs. conductive heat loss)

                            If you really want to have some fun, get access to an IR camera (they cost about $10,000 or more). They can really show you what's going on.  It would be great if they came down in price further to make it more viable for every home energy auditor to have one.  When combined with a blower door you can really figure out what's going on with the building envelope.  Then you just need to find a contractor who can really fix it ;)  Lots of older homes like the ones you talk about could really benefit from a blower door / infra-red audit.

  •  Could what you decribe be used w/ these modulars? (3+ / 0-)

    A company has designed "green" modular interiors that have a ton of upside. I heard about it from an interior designer who couldn't say enough good things about 'em.

    It's called DIRTT (Doing It Right This Time) and they do Walls, Floors and Power.
    (And check out their slick designer software demo too).
    Because they're modular it seem like this would be the perfect venue to introduce LED compatible power components. Does that sound right?

    Just looking at their site makes me want to buy a "fixer-upper" to install their stuff. :)

    The meaning of life is LOVE (-5.13, -5.95) 1st-Clark 2nd-Edwards

    by B12love on Sun Feb 25, 2007 at 10:46:41 PM PST

  •  Start small with nite lights (4+ / 0-)
    Recommended by:
    mataliandy, Simplify, norahc, Dcoronata

    I replaced all 7 of the nite lights in our house with 1 W LED lights.

    Went from 5 Watts each down to 1 Watt - an 80% saving for $1 each.

    •  I got some neat nightlights from Lowes (1+ / 0-)
      Recommended by:

      they have motion detection, so they don't stay on all the time.  Only when they sense movement.  Not LED's but I figure I will stay with them until I find an LED with a motion sensor.

      I love them on moonless nights when it is pitch black and I don't want to run into the woodstove.  Also great when I have guests who don't know their way around the house,, but for whom having a light on all the time would make it harder to get to sleep.  

      I had to move one that the cats kept setting off to a higher spot, but otherwise they work great and keep from having to turn on full lights at night.

      •  Motion detectors (1+ / 0-)
        Recommended by:

        funny you mention them, as I'm not the product manager for our line of motion detectors.

        Three basic types, PIR (passive infrared light) ultrasonic, and combination of the two.

        IR can be "shielded" by blocking parts of the sensor.  US and the combination sensors generally are more sensitive.  I'm assuming this is a wall mount IR, not a ceiling mount- they generally have a small cross-section, only 4 or 5 degrees.  While not very pretty, you can cut a piece of electrical tape (or masking tape) and place a thin strip of it on the bottom half of the detector.  It would make it much harder to detect motion near the ground.

        So unless your cats like to fly (mine are lazy) it would block out their detection.

  •  what great timing (2+ / 0-)
    Recommended by:
    mataliandy, maybeeso in michigan

    i'm making some of these (tentative) decisions right now as i embark on a major redo of my house, chronicled here:

    meeting with the lighting guys this week.  i want to do LED but have many needs--can they dim?  can i use them to change color? are their energy use costs really more efficient?

    so the question is, what products are out there NOW, or at least in the next year?


    "there is only one plot - things are not what they seem." Jim Thompson

    by robert green on Sun Feb 25, 2007 at 11:00:48 PM PST

    •  Upscale (1+ / 0-)
      Recommended by:

      There are full-blown systems (must search for them later) that are very expensive, which have full color control over soft interior lighting panels. Imagine entire 12"x12" sections of glass tile, with several LEDs behind them, controlled by a separate control panel which permits total near-infinite color control.

      I saw them two years ago at LightFair, the annual lighting convention (which will be at NYC early this May) and I'm sure they've progressed significantly since then.  But don't expect this to be cheap!

  •  "lifetime" assumes light bulbs don't break (4+ / 0-)
    Recommended by:
    SarahLee, AlanF, mataliandy, Dcoronata

    One issue that I've always had with costs analyses of light bulb technologies (in this diary and elsewhere) is the discussion of light bulb lifetimes.  There is just no way that any bulb in my house is going to last for 20 years.  Random juggling balls, klutzy kids, wayward pets all combine to impose strict limits on the life of a bulb.

    I'm not really comfortable assuming a lifespan of more than 5 years for any light emitting device, unless its made of the same stuff they make airplane Black Boxes out of.

    ...of course, none of this is meant to detract from this diary, which is excellent, nor from the fact that I've replaced most of the lights in my house w/ CFLs.

    •  PAR (Parabolic Aluminized Reflector (2+ / 0-)
      Recommended by:
      AlanF, mataliandy

      bulbs are much more durable, and LED bulbs will not really need the glass to either protect the vacuum, or to hold in the ionizing gas.  To get them right, you'll need reflectors and mounting hardware, which would still be susceptible to impact but otherwise they would be able to withstand the most harsh environments and operating conditions WITHOUT FAIL due to mechanical shock.

      I hadn't even thought of that as a selling point; I mean yes I have for automotive and marine, but not for home!

  •  What about mercury in flourescents?? (2+ / 0-)
    Recommended by:
    mataliandy, Dcoronata

    When weighing LED's vs compact flourescents, I am not comfortable with the fact that the CFL's contain mercury, and we KNOW a lot, if not most, will end up in landfills, thus contaminating the environment even more than it already is being. I know that many places already have laws banning dumping them in the trash, but few cities have a decent hazardous waste disposal program, so most folks just trash them.

    I know this is not strictly an energy efficiency issue, but it certainly pops into my mind when I think about how to replace incandescents.

    •  Much lower now than before (1+ / 0-)
      Recommended by:

      they're using different fluorescing chemicals which rely less on mercury.

      Bear in mind that the mercury in the coal being burned to light the incandescent is much much more than that in the fluorescent bulb!  While not ideal, it is still much better to replace the tungsten as soon as possible

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