Analog Angle Blog

Beware the unintended consequences of more-efficient design

I‘m a big believer in the “law” of unintended consequences, having been its “victim” many times. Our actions, however well intentioned, often have follow-on implications that may actually be contrary to that original intention and, in fact, undermine it. It's a consequence of the impossibility of fully seeing the ripple effect of our actions, of feeling that the original goal as stated is so important that any unforeseen consequences don’t matter, or of that eternal vice of hubris.

I saw this again the other day, when a friend’s electric water heater began to show signs of age and wear-out after about 15 years of service. No big deal, he thought; just get a new one of same capacity rating. Yes, there’s the expense, but other than that, it’s a straightforward -replacement operation.

Except it is not straightforward, and here’s why: new energy-efficiency regulations recently went into effect in the U.S. and to meet them and as a first step, these water heaters are being jacketed with few extra inches of insulation. The most-common sized water heaters at 55-gallons (210 liters) and below are only slightly affected, but above that size the changes are significant.

This increased diameter due to insulation means that a 70-gallon heater which previously measured about 23 inches (60 cm) across now measures about 27 inches (about 70 cm). Two immediate problems: first, it may be hard to get that new heater to whatever room or basement corner it needs to go to, as the access to the heater area is often full of twists, turns, narrow doorways, and steep stairs. Second, once you get it there, the new and improved heater may not fit into the available space since these units were often stuffed into a very tight corners or closets. So now, the homeowner has to somehow make a bigger place for the new heater, a costly and often very difficult process.

The unintended consequences don't end there. For the larger non-electric heaters, the exhaust manifold outlet is raised a few inches to improve combustion efficiency, a laudable goal. Problem is that, again, many actual installations have no headroom, and changing the path is difficult or nearly impossible—and certainly costly. Electric water heaters also have new requirements which increase their height, as well.

Long story short: any potential energy savings due to the increased efficiency of these units may be completely “wiped out” or worse by the physical installations issues, and that doesn’t include the headache and hassle issues associated with “reconstruction.” Those are unintended consequences, for sure.

Fortunately, for most electronic systems, circuits, and especially power supplies, higher efficiency may come with an increase in BOM cost but not physical size. In fact, most higher- efficiency designs are smaller than their lower-efficiency predecessors, for various reasons—but there are exceptions, of course. Further that new switching supply may be a form, fit, and functional replacement for an existing unit, but operate at a different frequency and so have a new set of system-level EMI/RFI issues.

What's the next “unintended consequence” scenario I am looking at? New York City passed new rules mandating that all battery-powered smoke detectors must have a sealed, 10-year battery, rather than user-replaceable ones, see here and here. The reason given is that homeowners let the batteries go bad, but then don't replace them. Seems like a good idea, but still, so do many other things which have unforeseen consequences in the real world.

[On the other hand, I never understood the public-service announcement reminding everyone to change smoke-detector batteries every six months with the roll-back/turn-ahead of the clocks—that always seemed quite excessive to me. Fresh batteries last two to three years at a minimum, so I wondered if this “change your batteries” admonition was a contrivance spurred the battery vendors.]

What been your experience with and exposure to the “law of unintended consequences” in technical areas? Have you ever had to live with – and perhaps fix – the results of those well-intentioned but naïve decrees of others?


Where’s your inefficiency?

How-are-you-measuring-that-power-consumption ?

When conventional power supply wisdom isn’t so

Can we all afford the cost of energy-efficient design?

Does reducing power consumption actually save energy?

2 comments on “Beware the unintended consequences of more-efficient design

  1. Hughston
    February 2, 2016

    I might have mentioned a few of these before.  I wouldn't list my mistakes.   A few of them would be just as embarrassing as these were.

    I worked on a project where the antenna was changed to a quarter wave antenna on a radio to save money.  But, the ground on a quarter wave is the other radiator, so that was probably the reason the RF started to get into all the analog circuitry.   This was very hard to fix and probably saved very little money compared to the effort.

    A mechanical boss was added to the housing to make the design stronger. But a ferrite in the radio receiver was moved closer to the input power transformer and the 60 Hz got magnetically coupled into the receiver and rectified.

    There was a design where an op amp was changed to another because it was thought the new amp would be better and the design was sent to the customer.  The new op amp had a greater gain bandwidth product and oscillated in the application and it was never noticed.   Sometimes slower amps are more stable and maybe make sure you don't use a digital scope on a setting that filters out high frequency oscillations.

    A company I worked for switched to cheaper keypads but they unfortunately the ESD immunity was never considered. Consider the ESD immunity from a mechanical standpoint first, then from the electrical standpoint.

    A company I worked for decided to take advantage of very cheap labor in a foreign island and manufacture keypads there. Unfortunately, the favorite lunch there was greasy fish sandwiches and the people don't wash their hands often.   The grease got into the keypads and they had a high failure rate which was never noticed until final assembly.


  2. jnissen
    February 3, 2016

    Almost started to laugh with the water heater examples given. Had a recent experience with an older water heater being upgraded to a new “efficient” design. Luckily the location for mine did not require major rework of the framing or drywall. A piece or two of trim had to be removed to account for the larger girth. A co-worker had to endure thousands in upgrade costs as his space was not as lucky. He calculated the savings in $$$$ would require the new water heater to be used for at least 30 years before he would see any savings. BTW – That new heater only has a 10 year warranty!

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.