Heat recovery and energy efficiency go hand in hand

In this installment of What Works, an HVAC contractor designs and builds industrial ventilation system for Iowa manufacturer.

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A mechanical contractor's industrial ventilation design has provided significant energy savings for Mi-T-M, an industrial power equipment manufacturer in Peosta, Iowa. The system provides indoor air quality (IAQ) for quality assurance painting, welding, and laser-cutting production line processes, as well as employee air comfort.

Mi-T-M retrofitted a 420,000-sq-ft former warehouse into an HVAC-controlled industrial production facilities. However, it wouldn't have been possible without a design team consisting of Mi-T-M's former director of operations, Patrick Siegert; Daniel Fens, design/build engineer at project mechanical contractor, All Seasons Heating & Cooling in Dubuque, Iowa; factory engineers at fabric HVAC duct manufacturer, DuctSox; and mechanical equipment manufacturer, Titan Air Inc.

A rooftop ventilation system and exhaust fans with spiral metal duct would have been a conventional solution, but All Seasons, a 30-year-old industrial/commercial/residential mechanical contractor that specializes in design/build geothermal, industrial, and custom home HVAC, turned to some out-of-the-ductwork thinking and took advantage of recent HVAC technology advancements.
The design team used the first industrial application of DuctSox's new Skelecore FTS fabric ductwork in-duct cylindrical tensioning system and combined it with high-efficiency TA Series make-up air units from Titan and industrial filtration systems by Donaldson.

The uniqueness of the system is derived from All Seasons’ division of the concrete tilt-up facility into six zones, each having its own make-up air system that's activated for partial or comprehensive ventilation or heating only when the respective production lines are operating. The design's efficiency is facilitated by variable frequency drives (VFDs), modulating natural gas valves, and a variety of building pressurization sensors and controls overseen by the Metasys building automation system manufactured by Johnson Controls.

VFDs with fabric duct

what works heat recovery energy efficiencyThe 42-year-old Mi-T-M, which manufactures a host of industrial and residential gas-powered and electric equipment such as air compressors, generators, and pressure washers, has used conventional fabric duct in two of its other six buildings on its nearly 20-acre campus. Mi-T-M is a fabric duct advocate, according to Mi-T-M’s Siegert, because of its light weight, superior air distribution, and labor-saving installation time of up to 60% versus spiral metal duct. "I think a factory without previous experience might have been skeptical of fabric ductwork, but our last two systems have performed great for years," says Siegert. “We’ve been using the DuctSox product for about six or seven years. We used it in our original factory, and then, when we moved up the street to the new facility, we decided to once again do the install. One of the advantages we’ve seen from the DuctSox system is the dispensing of the air evenly throughout the shop.”

However, if not for the Skelecore FTS concept, which maintains a 100% fabric inflation, the project would have necessitated metal supply duct and its comparatively exorbitant installation costs. “One of the features we like most is the ease of installation, especially when we have a whole bunch of equipment of the shop floor. For the contractors to work around it with the cable system and then put the SkeleCore through the center, it was a piece of cake to install. It offered a much faster installation, and we were on a really tight timeline to get this new factory up and running.”

Skelecore FTS, which was originally designed to appease architects and building owners that didn't like all fabric duct's inherent deflated appearance or wrinkling during idle or throttled air handler periods, makes textile duct and the design team's variable speed airflow possible. The rule of thumb on VFD use with conventional textile duct is static pressure loss will occur if the fabric is deflated 30% or more during operation. Therefore, the in-duct tensioning system's ability to maintain a 100% inflation, regardless of airflow, enables any airflow dictated by the BAS and eliminates the need of metal ductwork.

Consequently, using fabric duct also reduced ductwork installation costs by 75% versus metal duct, explains Jerry Tigges, All Seasons' project supervisor. Hanging six 180-ft runs, ranging from 32- to 60-in. diameters, would have taken four times longer with metal. Instead, Tigges and just one other crew member hung one duct run per day, which weighed a total of 400 lb versus 1,800 lb of metal.

Conventional fabric ductwork, without an in-duct tension system, wouldn't have been a good choice, explains Siegert, because HVAC system startups and the duct inflation process would have dislodged settled ductwork surface dust down onto the dust-free paint environment of the powder coat production lines equipped by Midwest Finishing Systems of Hartland, Wisconsin, and Nordson of Westlake, Ohio.

VFDs and heat recovery

The variable airflow is key to the building's efficiency. The ventilation system exhausts heat and airborne byproducts of nine Mitsubishi lasers and 50 Genesis Systems Group welding stations via metal duct to three 22,000-cfm and one 30,000-cfm outdoor Donaldson Torit air cleaners. “We have an isolated welding cell out in the factory and when we’re putting the DuctSox through that particular cell area we could not afford to have the DuctSox collapsing and let air seep around the inside part of the cell and creating a negative pressure inside the weld cell,” says Mi-T-M’s Siegert. Building pressure sensors and the BAS offset the exhaust with outdoor air to maintain a positive building pressure and optimum space temperature.

Bringing in a capacity of nearly 100,000 cfm of outdoor air is expensive to heat during Iowa's winters. Therefore, heat from the powder coat ovens and the other heat-producing processes is recovered by the Torit air cleaners and then filtered, cleaned, and ducted to any of the six make-up air systems to energy-efficiently preheat outdoor air. "Another reason, in our powder coat area when it inflates and deflates there’s a potential for dust getting airborne. The SkeleCore product eliminates that,” explains Siegert.

The heat recovery saved Mi-T-M tens of thousands in energy last winter because it never needed to fire up auxiliary furnaces for heating the space, says All Seasons’ Fens. "Over the lifespan of the building the potential energy savings could amount to tens of thousands of dollars," he explains.

Although little fine-tuning was done on the original project design, Fens admits the aftermarket programming of all operational sequencing has been challenging due to the many production line variables. Thus, Fens and Siegert continue tweaking the system to fit Mi-T-M's evolving production schedules and to perfect building pressure while maintaining the highest degree of space temperature and IAQ through the least amount of energy use.

"We think we've combined a cutting-edge HVAC system with the greenest production equipment such as top-of-the-line ovens and highly insulated powder coating equipment and built one of the most innovative and efficient industrial production facilities in the world," says Siegert.

View a complete interview with Patrick Siegert, Mi-T-M’s former director of operations

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