Moving air through spinning parts has been a core capability for Schofield, Wis.–based Greenheck since the company's founding in 1947. Some of its earliest products included rotary turbines built with the knowledge of airflow that Bob Greenheck gained while working on aircraft during an internship at Boeing. Today, in a complex prosaically named Facility One, the 2,600-employee company manufactures an extensive line of commercial and industrial air movement control products, including energy recovery ventilators (ERVs). Available in some form since the 1970s, the ERV is an overlooked technology that offers big energy and cost savings—and LEED credits.
ENERGY RECOVERY VENTILATORS: A SHORT PRIMER All mechanical ventilation systems involve the intake of a certain quantity of fresh outdoor air, balanced with the recirculation of a corresponding percentage of redistributed, preconditioned indoor air. In everyday application, this outdoor air (cold and dry in winter, hot and moist in summer, depending on specific climatic conditions) must be tempered before it can be distributed throughout a building. In a 100 percent fresh-air circumstance, all the energy used to temper this air would be lost when the air is exhausted. An ERV recaptures some portion of the energy previously used to heat or cool the exhaust air and applies it to incoming fresh air to maintain desired indoor temperatures.
HOW THE WHEEL WORKS Two different methods are commonly used for recovering energy within ventilating systems. Many manufacturers use plates that transfer heat between the exhaust and fresh air streams. Greenheck uses the preferred method: an enthalpy wheel that spins between the two air streams, one half through the exhaust air and the other half through the supply stream. “It transfers sensible and latent energy,” explains Dan Jore, Greenheck's sales and marketing manager for energy recovery products. “A lot of devices out there— [those with] just plates—get heat, but not the moisture transfer.” Since maintaining comfortable humidity levels is just as important as maintaining temperature, the wheel method is much more efficient in recovering energy that's already been created within the mechanical system.
The enthalpy wheel typically rotates at a velocity of between 50 and 60 rpm—just a little faster than the old vinyl 45 single recordings. But these platters are considerably larger, ranging in diameter from 25 to 74 inches. Regardless of size, each wheel is configured in six to eight segments that can be individually demounted for easy cleaning. Energy is recovered via plastic polymer infill strips—each paper-thin —packed within each wedge. A desiccant is permanently bonded to each of the literally thousands of strips in each wheel. While the stacks of polymer are relatively tight, it's easy enough to poke a finger between them and even simpler to clean with a stream of water from an ordinary hose. With proper care, the wheel doesn't need to be replaced during the life of the unit. “We weren't the first to use the wheel,” explains Jore, noting, “We got to cherry-pick from the best ideas on how to do energy recovery.” Another advantage is the lightweight nature of the plastic polymer wheel. It doesn't take a lot of energy to rotate it.
THE MANUFACTURING PROCESS Welcome to Facility One. The first two steps in the assembly line are relatively compact and low-key—the raw material staging and controls assembly. Large-scale action begins when the packages of sheet steel are opened. Individual sheets—all galvanized and some powder coated, depending on the particular specification—weigh approximately 88 pounds each. They are individually fed into one of two computerized punch presses that meticulously cut and punch each sheet to size. Every screw hole that will eventually allow the ERVs to be hand-assembled is mechanically punched while the metal is still in sheet form. The next stop, just steps away, is a matching pair of computer-controlled panel benders. These machines shape the sheets into what finally begin to resemble actual parts.