From the June 2017 issue
Advanced ductwork, system designs, and fan technology increase efficiency.
HVAC duct systems play a key role in indoor air quality and comfort as they serve the functions of supplying, returning, and ventilating air. The type of system can underscore its efficiencies. Case in point: the shape of the duct always makes a difference in terms of efficiency, notes Roger Coday, product manager for duct and acoustic products for SEMCO. The company designs air climate and air movement systems.
“The design of the system itself makes a huge difference,” he says. “Round and oval shapes are the best in terms of efficiency of air flow—rectangle would be after that.” That’s due to the properties of air flow through a particular shape configuration, Coday adds. “There is less air loss because of friction loss of the duct,” he says. “It is a more efficient method of transferring the air.”
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One of SEMCO’s newest products is its MD-PANL Modular Duct System with acoustical panels, designed for an easier and more affordable alternative to making a double wall rectangular duct in the field.
The MD-PANL Modular Duct Systems are designed with an integrated structure, combined with “no screws,” tongue-and-groove joints to eliminate the required structural steel and labor of fabricating large field-built, dual-wall ducts.
The product is eligible for AVRON46 coating to protect the HVAC system from mold and other fungi. Mold is an increasingly concerning issue, says Coday.
“A lot of people would argue that the coating isn’t needed if the system is designed right and the humidity and other factors are correct,” says Coday. “But if it’s not and you get dust accumulation in the duct and some moisture, you do have a problem with mold growth. There are arguments both ways, but it’s safe to have protection in both directions in terms of the system and the duct.”
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The AirPear from Airius
Officials at Saint Thomas West Hospital in Nashville, TN, sought to retrofit the facility’s HVAC exhaust air system for more cost-efficient energy recovery and enhanced indoor air quality (IAQ). The hospital sought a solution that would not take up limited indoor space in the manner of conventional indoor HVAC ductwork.
The approach: mechanical contractor Nashville Machine Company would use SEMCO acoustical panels to fabricate a support mount system hidden from the building façade that would meet project goals while providing aesthetic appeal that could not be derived by external conventional sheet metal ductwork with visible support brackets.
“It’s not something that we always use, but when the situation arises, it’s a good system for a specialty need,” notes Travis Hughes, project manager for Nashville Machine. “It fit real well into what we had to do, specifically for the St. Thomas project. In that environment, it saves money, fabrication, and installation costs.
“It can be used a number of places, such as health care facilities and where there is exposed duct work,” he adds. “It’s a great system and the structural integrity of this system makes it easy to mount. We had some unique circumstances on this project—attaching it directly to the side of a shear wall straight up—so the structural integrity of this system worked far better than anything else we could come up with.”
The HVAC project was part of a four-year, multi-phase $95 million renovation of the 2.1 million-square-foot, 550-bed hospital campus. It was a collaborative effort of the Nashville Machine Company, architecture firm Freeman White, and consulting engineer TME.
After arriving at Nashville Machine, the panels were assembled into 12.6-foot long sections, shipped to the job site, and hoisted into place with 460-ton rental cranes for the top floors and 120-ton cranes for lower floors, notes Hughes.
The retrofit project created return air distribution through ducts constructed of the SEMCO acoustical panels on the hospital’s exterior. Three HVAC exhaust air distribution risers reach to the new rooftop energy recovery ventilators (ERV) in an aesthetically pleasing fashion on three sides of the hospital’s exterior, notes Hughes.
The estimated savings for recovering exhaust air energy in the ERVs offers a return on the investment in a short time frame, notes Don King, CEO, Saint Thomas West and Saint Thomas Midtown.
The HVAC retrofit brings the building, constructed in 1973, current with ASHRAE Standard 170—Ventilation for Health Care Facilities—by enhancing IAQ for patients and employees and helping to ensure future high hospital industry ratings, says Hughes.
Prior to the HVAC retrofit, return air was exhausted outdoors, as was customary in 1970s-style building HVAC designs. Currently, the three 4-inch thick, 5 foot by 5 foot rectangular, R-16 insulated, seven-story-high acoustic panel risers each deliver 45,000 cfm of return air from the wings to their respective single-wheel desiccant ERV to precondition outdoor air, Hughes says.
While supply air continues to be delivered through an existing chase inside the building, the acoustical panel riser is internally divided into two 2.5-square-foot sections delivering general exhaust and isolation exhaust separately, he adds.
Nashville Machine—which has previous experience using acoustical panels as plenums and ductwork—pressure tested both passageways to ensure no future contamination could occur between isolation and general exhaust.
The panels’ airtight tongue-and-groove design eliminated commonly required air leak repairs following conventional ductwork fabrication and installation, says Hughes.
Ductwork at the Museum of Flight
The outdoor air and heat recovery and existing variable air volume system supplied by three Johnson Controls chillers, one Carrier chiller, and three boilers by Cleaver-Brooks are all controlled by the facility’s JCI Metasys building management system. The project also incorporated three isolation fans by Twin City Fan.
An additional aesthetic benefit is that the panels’ custom factory powder-coated sandalwood color matches the building’s exterior and blends into the facade’s exterior.
The panels also have custom, factory-designed 12.6-foot lengths that—combined with a 6-inch wide metal support band—matches up with the building’s pre-cast concrete seams at 13-foot increments, providing an appearance of continuity, says Hughes.
While the risers only service the second through seventh floors as they ascend to the rooftop ERV plenum, Nashville Machine fabricated an awning that offered a finished, complementary appearance at the bottom of each riser at 8 feet above exit doorways.
The riser suspension system was custom-designed by Nashville Machine engineers to allow for seismic and wind loads.
It gives the appearance of no visible support structure due to the use of hidden wedge anchors drilled into the precast concrete. Also unseen are 5-inch by 5-inch tubular steel stubs connecting to the wedge anchors and incorporated into the building side of the panels, says Hughes.
Collecting the exhaust air from each wing riser is a plenum constructed of acoustical panels measuring 6 by 12 by 63 feet. The plenum is designed to appear as a rooftop architectural façade, concealing the three packaged ERV units from street level view, says Hughes.
In drier winter operations after recovering heat and moisture, the ERV return air is exhausted as needed into another acoustical panel plenum traveling 77 feet in the opposite direction from an additional 90-foot long extended plenum collecting outdoor air on the opposite side of the tower for ERV conditioning, he adds. The separation of exhaust and outdoor air prevents cross contamination, Hughes points out.
The project would have cost 20% more to utilize a sheet metal duct with visible welded supports anchored to the exterior of the duct riser and the building’s wall due to the costs of the required painting and insulation, plus SMACNA code-mandated interior supports to meet structural requirements when using ductwork beyond 4 by 4 feet, says Hughes.
Furthermore, the ductwork would also have required a shop-painted exterior coating with a job site touch-up to mitigate nicking the surface during shipping and installation in contrast to factory powder coating, which offers cost savings in longevity, durability, and labor, he adds.
Additional costs come into play when sheet metal ductwork dimensions exceed 5 by 5 feet, with an accompanying increase in worker handling and safety, structural steel costs, field-installation time, more building anchoring, welding or support fasteners, and extra labor rigging the ductwork into position, says Hughes.
That’s in contrast to the more constant costs of the modular assembly of panels, which does not change significantly in proportion to the size of the duct, and are engineered for job site installation and snap together, he adds.
Hughes notes exterior-mounted acoustical panels ductwork as the wave of the future for older hospital buildings with space restraints for returning air to ERVs as a “great way to bring buildings into compliance of updated codes.” He also notes a trend toward utilizing 100% outdoor air in the health care industry.
SEMCO offers a variety of choices in duct systems, such as its spiral round and flat-oval ducts that are designed to be custom built and industrial ducts that feature the necessary fittings to prevent clogging or congestion via the transfer and collection of particulate matter.
The company’s manifold ducts are designed with pre-assembled duct and tap fittings that are custom-built to enable installation of a system that is pressure tight with fewer field joints.
The Velocity self-sealing, gasketed joint system is designed for ease of installation of the single-blade technology. It offers joint connections without the visual distractions of tape or sealer and is often used for concealed and architecturally exposed applications.
Some building owners and operators look beyond traditional duct systems to achieve their goals, such as through the use of destratification fans as manufactured by Airius. The ceiling fans work together to balance the temperature within a space.
“We work with designers to minimize and reduce the amount of ductwork typically used in a system and use our fans in favor of mixing and distributing the air within the space,” notes Christian Avedon, director of sales and marketing for Airius, adding that the fans reduce upfront material costs by reducing the number of branch circuits that come off of the duct system.
In contrast to a traditional duct system, the Airius system picks up ambient air within the space and continuously rotates it, notes Avedon.
“Sometimes you get stratification—that’s temperature layering—and you get some short cycling with those supplies and returns up at the ceiling and get all of that heat stacked,” says Avedon. “Using a system of the Airius fans along with that distribution system helps bring that heat back down to the floor and keep it circulated.”
Each of the fans resembles a miniature jet engine, Avedon says. “The fan works with a completely enclosed blade system. The axial fan sits above a stator, a reverse set of fins that remove the rotational component to the air flow,” he says. “When the air leaves the nozzle of the fan, if you didn’t have this system in there, it would want to spread as it traveled the distance to the floor and that’s a problem with getting the throw that’s needed to continuously mix that air.”
Each of the installed Airius fans works in concert to project the air from the ceiling to the floor, Avedon adds.
Airius does a great deal of retrofit applications of its fans, notes Avedon. “A lot of the times when you have a supply and return in the ceiling or a poorly-designed or old HVAC system that’s not quite doing what you need it to do, the addition of the fans can help increase the efficiency of that existing system and make it work a lot better,” he points out.
The company is presently doing an installation at a medical office with HVAC challenges in the lobby.
“The supply and return is in the ceiling,” says Avedon. “The floors are freezing cold, but they have 100 degree ceiling temperatures, so they are using a series of Airius fans to capture that air and raise the floor temperature to balance the temperature out. One benefit is that it reduces the amount of heating energy being used and secondly, it increases the comfort.”
Avedon says the general rule of thumb on a typical level of stratification within a space is about a half a degree to a degree per vertical foot above the thermostat.
“Based on the ceiling height and the amount of stratification, a 30-foot tall building with a 15 degree difference from the ceiling to the floor would equate
to a 20% savings if you were to de-stratify that space,” points out Avedon.
With supply ductwork at eve height, the Airius fan system continuously mixes the upper volume down to the playing field at CU’s indoor practice facility.
The company’s website features a graph illustrating potential savings based on those variables.
The Airius fans meet ASHRAE Standard 62, which specifies the minimum ventilation rates and other measures for new and existing buildings, notes Avedon, adding that there are ratings for air distribution effectiveness depending on how a facility is set up, such as a building with rooftop HVAC units.
“A lot of big box stores use those with a drop-down diffuser and what happens is that you have the supply and return located in the ceiling and you get penalized because of that for air distribution effectiveness in terms of the standard,” he says.
The addition of the Airius fans enable building operators to capture the air being distributed at the ceiling level and project it down to the floor at the specified flow rate within the standard to help it increase the effectiveness of the air distribution, “so it can actually help reduce the amount of ventilation energy that’s needed for a space by up to 20%,” says Avedon.
Airius fans are designed to save end users energy costs and increase comfort by mixing the air gently and continuously, balancing temperature destratification from ceiling to floor and wall-to-wall to help the HVAC system maintain the desired temperature and avoid overheating or over-cooling a space.
The system is expected to derive a typical ROI of between 12 to 36 months, with a reduction of up to 35% in heating costs and up to 30% in cooling costs.
Credit: Aerial Innovations
A color-matched galvanized duct from SEMCO was used in areas visible from the street that required the structural stability for mounting purposes. The duct was a double-wall, round duct that was fabricated to allow for easier connection to round exhaust fans and relief dampers.
Airius fans are engineered to maximize the efficiency of all types of HVAC systems and utilize process heat, lighting, and solar gain. The fans also are designed to offer reductions in run time on existing HVAC equipment, internal condensation and wet floors, and ceiling temperatures, which increase lighting lifespans.
The combination of housing shape, stator, and energy efficient motors is the driving factor behind Airius fans’ delivery of air over long distances using minimal power. Airius fan models are available for ceilings from 8 to 125 feet.
A destratification system is designed to throw air the full distance from ceiling to floor where people are and to the thermostat location. The stator system is designed to ensure a laminar non-turbulent column of air is delivered from ceiling to floor.
In contrast to axial fans that feature a radial component to the air flow that causes it to spread laterally and lose velocity when leaving the nozzle, Airius’ fixed blade stator sits below the fan to transfer rotational energy into linear motion exiting the nozzle.
Having the airflow energy in line with the fan axis is designed to promote a tight air column and maximize the throw. The slightly tapered nozzle increases the exit speed, enabling the air throw to be maximized even further.
One of many installations of the system is at Van Engelen in Bantam, CT, a company that sells more than 800 varieties of Dutch flower bulbs and herbaceous peonies; thus, it is very important that they are kept at temperatures that help sustain them longer.
Eleven Airius Air Pear 45-P4 fans and five Airius Air Pear 25 fans are being used to help keep the warehouse temperature and humidity at the required level.
Company officials report their installation of Airius Air Pear Model 45 fans was doing a “spectacular” job of moving air from their warehouse ceiling and keeping it circulating around pallet racks full of millions of flower bulbs.
Alexander VandenBerg notes that company closely monitors temperature and humidity, which is critical for the bulb inventory that comes from the Netherlands in climate-controlled containers and that the fans play a crucial role in keeping those factors close to ideal levels.
The company installed the 11 Airius Model 45 fans in the warehouse, which has a 22.5-foot ceiling. The five Airius Model 25 fans were placed in an area of the warehouse with a lower 10-foot ceiling.
The air circulation is not only ideal for the bulb inventory, but also keeps warehouse staff comfortable as they get shipments ready.
After evaluating the fans’ performance, VandenBerg expected to order a few more Airius Model 45 fans to continue to improve airflow throughout the warehouse.