Green Engineering

The very idea of designing "green" productsmay be the kind of thing that keeps you up at night. After all, you might have to reconsider all your time-tested design practices, materials, and manufacturing processes. Maybe you'll even have to replace them all. Sounds expensive and risky. In reality, though, environmentally intelligent design practices can have positive effects on your products. Just ask the engineers at Haworth and Steelcase.

These two office-furniture makers recently developed chairs that are among the first products to win an environmental certification from McDonough Braungart Design Chemistry (MBDC), a leading green design consulting firm. The company's Cradle to Cradle certification scrutinizes every aspect of the design for its environmental impact, focusing not just on what goes into a product but also on the potential to reclaim the products components at the end of its life.

Many industries have been quietly adopting aspects of MBDC's approach to design. The company's client roster spans the automotive, office furniture, appliance, and textile industries. But office furniture makers seem to be leading the charge—and for good reason. "The architects and designers who buy their products care about the environment and base their purchasing decisions partly on their environmental values," says Jay Bolus, an environmental engineer who runs the Cradle to Cradle program for MDBC.

Office chairs, in particular, spark lots of interest in the environmentally conscious design community. "Chairs are iconic," explains Mark Bonnema, senior design-for-environment engineer at Haworth. Chairs should also arouse some interest among engineers. While no one would argue that an office chair is as complex as a car, chairs do require engineers to confront structural problems, develop adjustment mechanisms, pick the right materials, and manage multiple manufacturing processes. And they do all these things with extra constraints imposed by ergonomics and industrial design needs.

In short, chairs aren't exactly easy to engineer, and engineering them with strict environmental goals in mind only increases the difficulty, which is why Haworth's brand new Zody chair and Steelcase's year-old Think chair provide some good lessons for any engineer charged with making products greener.

Recycle Twice

No one will be surprised that recycled materials play a major role in environmentally intelligent design. And both of these office chairs do incorporate about 50 percent recycled content. Yet simply incorporating recycled materials doesn't in itself translate to an environmentally friendly design. "There's a lot of nuance to recycling," says Bonnema.

For example, not all recycled materials are created equal from an environmental standpoint. Mature, efficient recycling markets make it easy to use recycled steel and aluminum, according to Bonnema. "In fact, it typically takes 95 percent less energy to reclaim an aluminum part than produce it from scratch," he notes.

Recycled plastics, though, have a less clear-cut environmental value proposition. Steelcase's chief engineer Kurt Heidmann explains that reclaimed plastics represent something of a crapshoot from both environmental and engineering standpoints. "You just don't know what's in them," he says, citing the wide variety of additives, reinforcements, and colorants that go into typical engineering plastic compounds. Some of these add-ins may reduce performance in unpredictable ways, and some even contain hazardous substances that make them worse for the environment than using a virgin plastic.

Bolus notes that MBDC endorses this view. "It's not a given that a recycled material will be better for the environment than a well-chosen virgin material," he says. For this reason both the Zody and Think primarily use virgin plastic and limit their recycled content to aluminum and steel. Neither Bonnema nor Heidmann rule out using more recycled plastics in the future as reliable closed-loop recycling systems emerge. "In an ideal world, we'd have access to plastics recycled in a 100 percent closed-loop system," Heidmann says. Right now, though, virgin materials often make more sense.

The other, perhaps more important, aspect of recycling involves how much of a product can be reclaimed at the end of its life. On this score, both chairs shine. About 98 percent of both chairs' components lend themselves to recycling, according to their creators. But this ability to recycle so much of the chairs' content creates all sorts of engineering challenges and drives many of the design decisions.

Design For Disassembly

Chief among them is designing for disassembly (DFDA). Both chairs have to hold up to tough working conditions but still break down into recyclable bits and pieces at the end their lifecycles. "One of the driving issues is how you separate all the components," says Heidmann. One strategy that both companies pursued comes down to using fewer types of materials but greater amounts of each type.

A related strategy involves not permanently mixing materials that won't go into the same recycling stream—a tactic that can put green engineering at odds with conventional design-for-assembly wisdom. For example, overmolding plastics may help consolidate multiple components into one. Or adhesive bonding can slash the component count by doing away with mechanical fasteners. But Heidmann points out that these techniques can mix materials in a way that makes it impractical to separate for recycling. "We had to stay away from some of the ways that engineers trust to make things stay together," he says. Steelcase does still look at techniques that permanently mix materials but only as long as those mixed materials go into the same recycling stream—such as a TPO skin on a PP substrate.

Bonnema makes the same point about permanent mixing of disparate materials, noting that engineers shouldn't just assume that parts consolidation techniques will have a positive net effect from an environmental standpoint. "You might use fewer components but reclaim fewer still."

Haworth and Steelcase also rejected another shibboleth of the design-for-assembly movement: They incorporated more mechanical fasteners than they would have used in less environmentally conscious designs. "People get schizophrenic about screws," Heidmann jokes. But screws and their ilk can hold components and subassemblies together both securely and reversibly. Among the mechanical fastening alternatives found on the Think, for example, is a j-channel that allows the seat upholstery to snap in place as an alternative to gluing.

Steelcase also molded another important mechanical fastening feature into the seat back, showing that parts

A lifecycle analysis provides crucial information about the environmental impact of each design and manufacturing decision. In this summary of Haworth’s analysis for the Zody chair, the importance of recycling isn’t just to common sense but quantified. For a larger image, click here

consolidations doesn't have to fall completely by the wayside. Heidmann notes that the chair features a molded-in connection that attaches the back to the bottom of the chair. With a thirty degree rotation, the back flips into place. Steelcase adds a couple fasteners to the molded-in connection to keep it tight. "But the back passes all our testing without the fasteners," Heidmann says.

With Zody, Haworth engineers likewise simplified the way the back attaches to the rest of the chair. "We use just a single bolt," Bonnema says.

The end result of these DFDA efforts are that the chairs not only disassemble fully but also quickly. Heidmann says the Think can be taken apart into its recyclable constituents in about five minutes using common hand tools. Bonnema makes a similar claim for the Zody.

Pick Sustainable Materials

Haworth and Steelcase built their chairs almost entirely from sustainable materials as defined by MBDC's Cradle to Cradle approach. In part, MBDC's idea of sustainability means that the materials lend themselves to recycling using readily available methods. In plastics, for example, this requirement would favor thermoplastics over thermosets.

Sustainability also meant a given material's constituents pass environmental muster from the standpoints of energy consumed and hazardous substances. Bolus notes that MBDC evaluates materials throughout their entire lifecycles—from feedstock all the way to the end of a product's life. Thus, the company would favor steels whose chemistries use no lead, according to Bolus.

Or in plastics, this intensive evaluation takes all the material's monomers and feedstock chemicals into account. MDBC particularly frowns on plastics that it deems harmful at the beginning, middle, and end of its lifecycle. PVC is a prime example, says Bolus. Other plastics occupy a middle-ground. "ABS contains a hazardous monomer, but it may be acceptable to use if that residual monomer is low in the finished component," says Bolus. At the top of heap, MBDC lists plastics, like nylon, that don't require blatantly hazardous ingredients during their manufacturing process and don't release any dangerous substances during their use.

MBDC likewise looks at all the additives that commonly go into a given thermoplastics compounds—things like colorants, flame retardants, and reinforcements. "If the material safety data sheet lists two percent as 'other,' they want to know what exactly 'other' means," says Bonnema.

Using sustainable materials may be its own reward for companies concerned about the environment, but these materials can require some extra engineering effort. And even seemingly simple components can prove troublesome. Haworth's Bonnema recalls that the company had to find just the right alternatives to PVC—previously used on chair arms and on control cable covers. "The reason PVC is used, for better or worse, is that it does a lot of things well and does them at low cost," says Bonnema, citing the material's abrasion, tear, and crush resistance. "But we made the decision not to use chlorinated materials like PVC." So Haworth engineers found a TPU grade that worked for the arms and used a polypropylene to cover the control cables, both choices at the expense of some extra engineering effort.

Heidmann also gives a good example of the price engineers pay to use green materials. Given the structural load on the Think chair's back—a 300 lb pull test 16 inches from the seat—it would have been easier to make the seat back from a long-glass-filled nylon. "But we discovered that long glass, while great for performance, was not so great in its second life," Heidmann recalls. So the design team switched to a short-glass product that has better recycling prospects. The short-glass nylon, however, had a flexural modulus of about 1.5 million versus 2.5 million psi for the long-glass equivalent. So Steelcase engineers had to spend extra time optimizing the frame's geometry.

Early in the optimization process, they had to contended with some failures. "We struggled with whether to upgrade materials and decided not to," Heidmann says. "We decided to not allow ourselves the option of increasing material performance at the expense of our environmental mission." In the end, Steelcase's engineers did manage to meet the structural requirements. In fact, they ended up validating the chair for a 300-lb person, 75 lbs more than industry standards require.

Look Beyond Materials

Both the Zody and Think also embody environmental virtues that go well beyond their use of green materials. Haworth, for example, paid attention to the kind of energy used to make its chairs and ended up buying enough wind-energy credits to offset the energy actually consumed by its assembly plant. Bolus says these credits, rather than inherent design features, earned Haworth a higher level Cradle to Cradle certification than Steelcase.

Steelcase, for its part, came up with some clever design twists that made the Think even more environmentally friendly. Chief among them was a redesigned chair control system. Instead of the linkages used in the past, the Think instead uses a pair of flat springs to control the recline and other chair movements. Calling the spring design "bio-inspired," Heidmann says the springs took their inspiration from a cockroach's forward-bending, bouncy legs. He says the system produces more fluid adjustments than a linkage, and it also saved a lot of weight. The Think weighs about 32 lbs versus 50 lbs for most chairs its class. "Less weight means fewer materials. Period," Heidmann says.

Hayworth’s Zody chair has to hold up in an office environment but disassemble easily at the end of its life for recycling.

Weight savings also reduced the environmental impact of transporting the chair—not to mention shipping costs. What's more, Think's threaded back connection lets Steelcase ship the chair with its back flipped down, which allows more chairs per truckload and further increases the transportation benefits, Heidmann reports.

The way the benefits of green design start to stack up may not be all that unusual. Both Heidmann and Bonnema make the point that green design, while it involves some engineering challenges and design constraints, can pay off in unexpected ways.

Both argue that that DFDA, in particular, tends to result in streamlined, cost-effective manufacturing operations. They both describe the assembly lines that produce these green chairs as less capital intensive than those used for chairs that don't take DFDA to such an extreme. "Design for disassembly and design for assembly tend to go together," says Bonnema.

Stay Committed

Design benefits probably won't be the first thing engineers new to green design will notice. Instead, the temptation to fall back on familiar materials and design practices will arise—particularly when deadlines loom and some prototypes fail. Heidmann has been there and at times felt the pull of proven technologies that lack green credentials. "You don't have all the same ways out of a problem as in the past," he says.

One essential element of green design, then, is ignoring that pull, which takes some commitment. Says Heidmann, "We don't allow ourselves to spend time pursuing technologies that may promise a cost or performance advantage but have a negative impact on the environment." And in today's engineering environment, what's more committed than that.