skip to Main Content

Must the 3 Little Pigs Die?


Building Science Summer Camp was last week. That means I was in Massachusetts with 500 of my closest friends, staying up too late, talking building science out the wazoo, and attending some great presentations from leaders in the world of building science. My big takeaways from Summer Camp this year were Marty Houston’s “hairy hand of quality,” Robert Bean’s three little pigs, and a black toenail. The first was a striking image, the second is the topic of this article, and the third will probably fall off in a few days. (Sorry. If that makes you squeamish, just be glad I didn’t tell you how I relieved the pressure.)

Building Science Summer Camp was last week. That means I was in Massachusetts with 500 of my closest friends, staying up too late, talking building science out the wazoo, and attending some great presentations from leaders in the world of building science. My big takeaways from Summer Camp this year were Marty Houston’s “hairy hand of quality,” Robert Bean’s three little pigs, and a black toenail. The first was a striking image, the second is the topic of this article, and the third will probably fall off in a few days. (Sorry. If that makes you squeamish, just be glad I didn’t tell you how I relieved the pressure.)

The customization & complexity pigs

The 3 little pigs Robert Bean was referring to are combustion, customization, and complexity. I’ll save combustion for last because that’s where he used his most sophisticated arguments, including a term you may not be familiar with. Customization and complexity are similar but independent. A customized building can be simple, and a complex building could be standardized. Both customization and complexity, however, end up making sustainability a harder goal to reach.

Customization, Bean said, is the opposite of standardization. If a mechanical contractor, for example, provides customized heating and air conditioning systems for every house he works on in a 40 year career, he may be leaving a lot of little nightmares for the service contractors who have to go in later and figure the system out. Here’s how Bean described it:

You can take a contractor and plop a box full of parts in front of him, and he will interpret in his own mind with his own creativity how those parts should look when they’re assembled. So what happens is that if you go back twenty years or so, contractor A did it in contractor A’s way for that day on that jobsite. In today’s time, he’s done that for 20 years, and so have millions of other contractors, which means you can’t walk into a mechanical room and find the same system. It’s virtually impossible to go into any mechanical room, if it’s hydronic specifically, and find any standardized method.

If you continue that process into the future – 5, 10, 20 years…over a 40 year period you have this smorgasbord of mechanical systems owned by consumers who haven’t got a clue what this is about. If you’re a contractor and get a call to service this system, where do you even begin?…And the sin in all of that is that the guy who did the customization, when he retires, he walks away from the system and he doesn’t care. He’s retired. The person he did the customized work for, they own it for life.


Complexity, likewise, creates problems for the end users. I thought he was going to talk about how difficult it is to get a good building enclosure or mechanical system with a complex design. More than most of us in the industry, though, Robert Bean has a laser focus on the people who live in, work in, and otherwise occupy buildings, so he sees the problem of complexity all the way down to the occupant. It’s certainly important for all the people who work on the building, but as Bean said about operating the systems in a home, “If it’s so complex the consumer has to actually learn the designer’s profession, they won’t use it.”

The combustion pig

OK, let’s tackle the tough one now. You may be thinking he said we’ve got to get rid of combustion because of air pollution or because it’s mainly from fossil fuels. You’d be wrong if so. His argument was efficiency…but not energy efficiency. He introduced a quantity that not too many people have heard of – exergy – and said exergy efficiency is more important than energy efficiency in analyzing how we use energy.

I have to admit I don’t understand exergy well. I’ve seen it mentioned in the past but have never jumped in to see what it’s all about. Since catching the presentation last week, though, I’ve been reading about it more and also spent an hour on the phone with Robert trying to get a handle on it. Since Bean is known as “The Exergist” in the building science world, I know of no one better to learn this stuff from. (Well, all right. He’s not really known as The Exergist…yet. With your help, though, we can make it happen!)

A little bit about heat and efficiency

It’s hard to talk about exergy without at least dipping our toes into the thermodynamics pool, but I’ll try to keep this at the 3000 meter level. (That’s ~10,000 feet for you civilians.) First, exergy is generally defined as the maximum amount of useful work (energy) you can get by moving heat from a higher temperature source to a lower temperature sink.

For example, you can burn a fuel like coal to create a high temperature, converting chemical to thermal energy. Then you can use the heat to make high-pressure steam, converting the thermal energy to mechanical energy that can be used to turn a turbine that generates electricity. As the energy moves through the system, it does work and the temperature drops. A real power plant doesn’t extract the maximum amount of useful work from the energy because real systems are always less efficient than the ideal.

Sadi-CarnotAnd that, of course, brings us to Sadi Carnot and the maximum theoretical efficiency of heat engines. Carnot came up with the idea of an upper limit for energy efficiency, which is now called the Carnot efficiency. That theoretical efficiency depends only on the temperatures of the source and the sink. (For the record, it’s calculated as 1 – (TC/TH), where TC is the sink temperature and TH is the source temperature.) The bigger the temperature difference between source and sink, the higher the theoretical efficiency.

When you multiply the Carnot efficiency by the amount of heat available, you find the maximum amount of useful work you can get from those two temperatures. Go back to the first paragraph of this section and you’ll find that this is exactly what we defined as exergy.

Bean’s take

In his presentation (which you can download from the BSC website), Bean showed calculations of exergy efficiencies for different fuels with different temperatures. For example, natural gas combustion results in an exergy efficiency of 6.1% (slide 172), whereas using solar thermal energy can be done at an exergy efficiency of 20.1% (slide 174). Those are all based on the temperatures of the source energy: 3400° F for natural gas and 220° F for solar thermal.

Based on those calculations, Bean says we should opt for lower temperature sources of fuel. The way he put it is that it doesn’t make sense to create heat at a temperature of 3400° F when we’re trying to heat our homes to temperatures on the order of 100° F. If we used sources with temperatures closer to 100° F, we’d be doing the job with a much higher exergy efficiency.


According to Bean, using combustion to heat our homes is like doing backyard gardening with a trackhoe. It’s like hammering in finishing nails with a sledgehammer. It’s like using a Turbo-Thermo-Encabulator Max to harvest dental floss! (OK, he didn’t really say that last one.)

My take on Bean’s take is that the temperature of the fuel is the main thing you need to look at because it governs the exergy. Rather than using high-temperature sources of energy, he thinks we need to leave the combustion for industrial processes and let the lower-temperature “waste” heat filter down to the low-grade uses like space heating.

My difficulties with the exergy analysis

I’m far from the smartest person who goes to Summer Camp. In fact, I was in the bottom half of my class in graduate school and usually have to work hard to understand the more abstract concepts. If I were a Richard Feynman or a Lise Meitner, the deep ramifications of exergy would probably be immediately obvious to me. But I’m not and they aren’t, so I’m still sitting here trying to figure it all out nearly a week after Robert gave his presentation. 

One thing Robert and I went back and forth on when I spoke with him about this was his use of temperatures to draw conclusions. The trackhoe versus trowel contrast above works because of the vastly different capacities of the two tools. But temperature isn’t energy. A burning match at 1400° F has a lot less energy available for heating than a 10,000 gallon tank of water at 100° F.

Who cares, I said to Robert, that a gas furnace burns at a high temperature if it’s a condensing furnace and you’re extracting 96% of the BTUs and using them to heat the building? After spending an hour talking with him on the phone, the best I could make of this is that an exergy analysis doesn’t really help you when you’re looking at a single building. Its best use if for deciding how to use energy on a large scale.

In Bean’s view, the best use for high-temperature fuels is for industrial purposes. Then you use the moderate temperature “waste” heat for processes that can’t use lower temperatures. Only at the bottom of the chain do you use what’s left for heating buildings.

Now my mind is wandering to entropy and air conditioning and the distribution of electricity. I’m thinking about thermodynamic potentials, statistical mechanics, and the words of David Goodstein:

Ludwig Boltzmann, who spent much of his life studying Statistical Mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the work, died similarly in 1933. Now it is our turn to study Statistical Mechanics. Perhaps it will be wise to approach the subject cautiously.

My brain is hurting and my self-esteem is waning. But at least I can read the shirt Marc Rosenbaum was wearing on the last day of Summer Camp!


Can you? (Hint: It’s his alma mater.)


Related Articles

Mr. Bean Proposes a Radical Change to Energy Codes

Thermal Comfort: Everyone Wants It but Few Know the ASHRAE Standard

What Is the Difference Between Energy Efficiency and Efficacy?


Photo of 3 little pigs by liz west from, used under a Creative Commons license. Sadi Carnot image in the public domain. Trackhoe and gardening image from Robert Bean’s 2015 Building Science Summer Camp presentation. Other images by Energy Vanguard.


NOTE: Comments are moderated. Your comment will not appear below until approved.

This Post Has 16 Comments

  1. Nice explanation, Allison.
    Nice explanation, Allison. But does exergy apply when filling my reservoir of knowledge with information from really smart folks? If so, then I should be learning from people that are just a little smarter than me rather than from geniuses in order to improve exergy efficiency.

    Can Marc from MIT explain how exergy applies to heat pumps? I suspect it depends on the source of electricity to run the heat pumps. is doing some impressive work on exergy and global warming. The charts are impressive even though I don’t have a full grasp on them yet.

    Keep the great articles coming, it helps me raise my TC (Technical Cranium).

  2. Great add and AdMIT for Grate
    Great add and AdMIT for Grate MIT HVAC Guys, like the Great MIT Car Guys, keep it running!

  3. I enjoyed the article and my
    I enjoyed the article and my head started to hurt like the ol’ days at Ga Tech. Love the T-shirt – clever.

  4. Robert will probably shoot me
    Robert will probably shoot me for saying this, as he’s mostly a wethead (hydronics) while I lean towards being an airhead (buh, dum, bum), but don’t forced air systems, which can easily have the ‘box’ changed out on duct systems that can be sealed from the inside (Aeroseal) fit the less complexity and customization argument better than hydronics systems? The boxes can be easily upgraded as new technology comes out, and they are simple and similar enough that most techs can work on most pieces of equipment.

    There is a fellow here in Cleveland who looked up all of the patents on steam systems and understands what all the doohickies do on various systems. He knows what he can replace with what. All because the guys who invented the systems are dead, but the systems live on a hundred years later.

    Like you, though, I’m not smart enough to totally understand the exergy thing yet, I keep feeling like there’s a big piece I don’t get. That said, I push clients towards heat pumps all the time. My reasoning is two fold – I see our economy heading quickly towards electrification and the energy can be produced without burning anything i.e. wind and solar.

    Thanks for the great article, and I love Robert’s three little pigs thing!

    1. When I first I heard Ted Kidd
      When I first I heard Ted Kidd saying “combustion must die”, my scope of what he meant by that was at first confined to a residence: getting rid of combustion appliances in turn eliminated CAZ concerns. When Ted got excited about electric cars and a road trip in a Tesla Model S, my scope widened to internal combustion engines (ICE).

      Robert Bean’s presentation at summer camp widened my scope to include the entire energy generation and distribution infrastructure (aka “grid”). While I had considered it in this fashion before, it was Mr. Bean’s presentation that turned the illumination on it up to 11. I can’t say I have a fantastic grip on the matter of “exergy” as he so eloquently does, but it’s sinking in, with time.

      One of Robert’s points during the exergy presentation was “heat exchanger size”. To heat a space of a given size and calculated heat loss, a small heat exchanger must be very hot and a large one not so hot. The incoming energy to create the heat will be more efficiently used if the delta between the input heat source (natural gas, propane, etc.) and the substance being heated (water for hydronic systems) is further apart. Therefore, on an efficiency basis, the large heat exchanger wins.

      In the spirit of killing the three little pigs of combustion, customization, and complexity, I like your heat pump statement. In my climate (Climate Zone 3) it’s a home run with a good thermal enclosure, properly sized and installed ducts, and proper air distribution room to room. My instinct when it comes to residential building science is to move the proportion of comfort management as far over to the envelope side of the equation as practically possible, with the mechanical systems filling the remaining percent.

      Robert’s emphasis on understanding mean radiant temperature, along with humidity, air speed, and temperature control, for me binds together many things we discuss about building performance.

  5. How about using fuel cell
    How about using fuel cell technology to convert natural gas to electricity?


    “Using ceramic fuel cells, BlueGen® electrochemically converts natural gas into electricity at up to 60 per cent electrical efficiency. Electricity is consumed locally, with unused power being exported to the grid.

    When the integrated heat recovery system is connected, the waste heat from BlueGen can be used to produce hot water – which improves the total efficiency to approximately 85 per cent. You can also monitor and control BlueGen remotely via the internet.”

  6. Red pill or blue pill?
    Red pill or blue pill?

    Once you go Bean, there is no turning back. And the thought shift makes the rest of the world appear insane.

    Very excited you’ve taken the blue pill Allison.

    1. @Tedd Kidd:
      @Tedd Kidd:

      I think I was born with the contents of the blue pill already in my system, as how many things are done in this world, on an accepted basis, strike me as insane.

      Hearing Robert speak at summer camp was the highlight of the daily speaker series for me, along with befriending and hearing David Hill speak on moving air quietly.

      Robert has the right focus, as Allison addressed above: human comfort is why we build buildings and fill them with complex systems. How we design and operate buildings is where the heart of the energy/exergy discussion resides.

      My takeaway from the exergy presentation is that heat equates to energy, and heat wasted is energy wasted. If it takes 3400°F of heat to create energy in order to maintain my home at 70°F when it is 20°F outdoors, where is the 3,330 degrees going?

      Robert’s first presentation of the day was on HVAC in the real world. If ever there was a “blue pill” held forth for one to consume, that presentation was it. Once digested, the way we build and operate buildings and mechanical systems often is insane. Especially in my spot on the planet.

  7. Let it be known I’m
    Let it be known I’m just an eXergy amateur! I know once Allison gets his head around this (took me 2 to 3 years) he’ll do marvelous things with it…

    In the meantime I would encourage those with a ‘burning’ desire to learn about this oh so important way of looking at energy sustainability – study the information below…

    See Annex 37 and 49

    See Annex 59 and 64

    See also

    Re: Allison, “ exergy analysis doesn’t really help you when you’re looking at a single building.”
    When it becomes clearer you’ll see it especially applies to single buildings [:@) If you’re coming to ASHRAE in Florida drop by our small band of eXergy folks at our T.C.7.4 meetings…

    Re: Nate, “…shoot me”
    That would be eXergy inefficient…swords would be much better [:@) only ½+ a wethead still need air for decontamination, dehumidification, and deodorization…and yes air based systems are more standardized than hydronics but not immune to repetitive creativity and customization…just on a much smaller scale.

    Re: Nate, “ …electrification and the energy can be produced without burning anything”

    Yes! Furthermore in many climates with proper architecture and mechanical systems there is no (or little) need for compression or combustion (ref.: Carnegie Mellon Study et al)

    Re: Sean, “fuel cell”
    Yes…and gas micro CHP units…the challenge is economics – the technology is already proven.

    Re: Ted, “world appear insane” and “pills”
    Yup…time for a new prescription starting with a “Porky must die” campaign.

    eXergyly yours,

  8. Thanks for your comments
    Thanks for your comments Cameron – was great to meet you.

    David’s presentation was awesome! Just when one thinks one knows all there is about duct design he comes along and snaps the ears to attention.

    Here’s to putting people at the center of the design process.



  9. Glad I’m one of your 500 best
    Glad I’m one of your 500 best friends Allison.

    The point from Bean’s presentation, that people get old and sick in their homes, and that sick people don’t experience thermal comfort the same way healthy people do, I thought was really important. A lot of my clients swear they want to build their own homes and fiddle and geek out with their systems, and yet a lot of my clients want to age in place in their homes too. There are building envelope examples of this too. For the past three years I’ve gone into my grandparents’ crawlspace twice a year to selectively remove or install temporary crawlspace vent covers. Grandaddy doesn’t see the point in wasting money on silly things like a sealed crawlspace or automatic vents and still thinks he’ll be the one to just crawl around real quick and move covers around…

    On eXergy: You were right Allison, this is the kind of thing I love! I take the concept of eXergy as a reminder that in the big picture a part of using energy efficiently is not just to reduce fuel consumption point blank, but to conserve fuel by using the type of fuel most appropriate to the task you need energy for. Even if a building needs little combustion to provide heating energy and does that combustion very efficiently, that combustion fuel could still have been used for an industrial process that requires high temperatures and can’t currently get those high temperatures except through combustion, while in many cases there are ways to heat a home other than combustion. Which in turn reminds me to think about peak oil sometimes and the appropriate use of a finite resource, not just the air pollution and climate change that I usually end up focusing on–a subject you’ve written well on in the past! Heh, I wonder how well it will work to break out eXergy when I talk to clients about ditching their beloved gas ranges with 900+ CFM range hoods in favor of induction, since that whole line of arguments about indoor air pollution and backdrafting and installing make-up up air (you know, ADDING complexity) does not seem to deter them…

    1. Re: Leigha, “people
      Re: Leigha, “people get old and sick in their homes, and that sick people don’t experience thermal comfort the same way healthy people do, I thought was really important.”

      Very pleased to hear this resonated with you…it’s a project that is on the top of our priority list. By all means stay in touch and share what you experience and learn in this subject matter. My 2015 Healthy Buildings America slides and paper on this topic are available online if anyone wants them. We also maintain a list of over 450 resources addressing aging and IEQ.

      Re: Leigha, “…is not just to reduce fuel consumption point blank, but to conserve fuel by using the type of fuel most appropriate to the task you need energy for.”

      The Stanford University resources that Dale suggest are very good for fleshing this out further.

      Glad you were in the audience.


  10. You can burn natural gas in a
    You can burn natural gas in a home furnace and get 97% of its energy as heat.

    Or you can burn natural gas in a turbine, then use the exhaust gases to make steam and put it through a steam turbine. The electricity from the combined-cycle plant can be used to run heat pumps at a COP of 2 to 3.

    But we’re still not done. The remaining steam is still hot enough to run a steam-driven heat pump. The resulting low-temperature steam can be sent into radiators, and eventually it changes phase. The condensate can be used for domestic hot water.

    When we optimize the whole system, we can do a lot better than a 97% efficient furnace.

    1. Re: Tom, “When we
      Re: Tom, “When we optimize the whole system, we can do a lot better than a 97% efficient furnace.”

      Yes…a whole lot better.

      Am loving how this exergy topic is getting digested – good to be an exergist (credit to Doc. Bailes III)



  11. My Grandfather was a General
    My Grandfather was a General Contractor, he used to hire my Dad in the summers. Of course my Dad’s pay was Room and Board for the rest of the year, because as a small GC he couldn’t afford luxuries for things like pay. One other thing to know about my Dad is that he is legally blind, so swinging a hammer is probably not the best idea for him. Never the less that is what my Dad did and of course the inevitable happened, he whacked his thumb. Whacking the thumb with a hammer ruptures the capillary bed under the nails if you do it correctly, which of course my Dad, being the perfectionist he is (at least when it comes to hurting himself) did.

    My Grandfather took my Dad to the Osteopath (because in those days DOs were cheaper than MDs). The DO took out a drill with a bit and drill through the nail, relieving the pressure and pain. The DO of course charged something like $20, which caused my Grandfather to complain about it to no end.

    From that day on whenever that happened to my Grandfather he drilled his nail himself. This taught my Dad a very valuable lesson: “Don’t tell your Dad when you hit your thumb.” That work though instilled a love of carpentry in my dad that he passed down to me. My Dad taught me the basics, though I can’t tell you the relief I felt when an epiphany struck me when I first started working with professionals. That was “Holy Crap! I don’t have to hit my thumb when I’m driving in a nail!”

Comments are closed.

Back To Top