As variable refrigerant flow (VRF) systems gain popularity in the U.S., HVAC contractors and engineers are customizing them with designs that provide efficient, aesthetically pleasing HVAC functionality.
The design, installation, and rooftop aesthetics of a recent HVAC retrofit at the four-story Texas State Bank (TSB) in San Angelo, Texas, by mechanical contractor, Air Dynamics Inc., for example, promises to serve as a role model for future U.S. VRF projects.
One challenge contractors face is concealing and protecting VRF’s inherent multitude of line sets, which can look unsightly and fail prematurely when exposed to rain, hail, and the sun’s UV light, according to Cecil Sain, president of Air Dynamics — a company boasting 54 years of HVAC and plumbing experience.
Concerned with the aesthetics of making the project look like a $1 million-plus retrofit, Air Dynamics specified the RD-Series, a VRF-specific line set protection duct line recently introduced to the North American market by RectorSeal Corp. The corrosion- and scratch-resistant zinc/aluminum/magnesium (ZAM)-coated metal duct installed on TSB’s roof protects and preserves line sets from 17 rooftop City Multi Series VRF condensers manufactured by Mitsubishi Electric US Cooling & Heating Division.
The RD-Series comes with a full line of fittings, adaptors, and couplings, such as the 45- and 90-degree elbows that Air Dynamics used in building line set connection chases.
“The building’s owners are very pleased with how the roof looks neatly laid out and professional in appearance, which also reflects on our overall design and Air Dynamics’ installation,” said Paul Wilkerson, owner, PSI Power Systems Inc., the project’s consulting engineer.
The 37-year-old facility has always been an HVAC trendsetter. Its original HVAC concept was one of the nation’s first commercial heat pump applications that recovered heat from lighting and converted it into energy for the chilled water loop system, consisting of a chiller, cooling tower, boiler, and air handlers. While it was state of the art in 1977, the aging system’s escalating expenditures for cooling tower chemicals, repairs, and general system maintenance surpassed $10,000 annually. Replacement parts also became problematic, according to Sain, who began servicing the system annually in 1985 and kept it running well after its useful life cycle had passed.
TSB, which uses the 30,000-square-foot building for its headquarters and leased office space, opted for the inevitable retrofit. An 84-ton Mitsubishi system was specified because it represented no downtime for tenants, and its cost was competitive with other HVAC alternatives when accounting for VRF’s expedited labor advantages. Operating expenses are expected to be approximately 30 percent lower while providing zoned temperature control for occupants.
“We’ve noticed a definite indoor comfort improvement with the VRF system,” said David Harrison, executive vice president, TSB, a single-location institution with more than $235 million in assets.
The building’s original three air handlers were replaced with 32 Mitsubishi VRF-based fan coil units in zones fed by two branch circuit controllers per floor. Eighty percent of the building’s original supply ductwork was re-used for air distribution. The VRF equipment’s sizing was determined by the building’s peak north-side heating load. Sain and Wilkerson’s VRF calculations were assisted by Andy St. John, commercial sales manager at Mitsubishi distributor Robert Madden Industries in Lubbock, Texas, and verified by Power Systems’ in-house computer modeling.
Because it was Air Dynamics’ first major VRF project, Sain was comprehensive in managing and installing the project. He even sent his installation and service crew to a Robert Madden Co.-sponsored VRF school in preparation. Sain also wanted to find the highest-quality mounting system for the rooftop condensers and discovered Big Foot Systems rooftop equipment mounts, also available through RectorSeal. Instead of the conventional poured rooftop concrete pads, and the inherent roofing costs associated with them, Sain specified Big Foot Systems’ tubular, corrosion-resistant, hot-dipped, galvanized, modular steel support frames. The frames were designed by RectorSeal’s in-house engineering team and assembled onsite in various configurations by Air Dynamics’ crew to custom-fit the condensers.
While the Big Foot system is an aesthetically pleasing and fully functional option, Sain also recommended the unit based on its superior sound and vibration attenuation. Previously, he had not been completely satisfied with noise abatement attempts of previous mechanical rooftop systems set on I-beams, even when used with anti-vibration pads.
The mounting system features adjustable legs and 12-by-12-inch anti-vibration nylon feet. When the building is re-roofed someday, roofing can be replaced underneath one leg at a time while the units and piping stay connected and functional.
The system also includes nylon-footed H-shaped stands for the line set ducting. Sain found the mounting systems’ under-unit access very convenient for expedited refrigeration and electrical hookups. The system’s conduciveness to attaching appendages, such as electrical conduit with common hardware clamps, encouraged Sain to innovatively support each condensing unit’s electrical disconnect boxes to the mounting frame. “The mounting system is costlier in materials than I-beams, but it’s really an even tradeoff because installation labor is cut by more than half and it looks so much better,” said Sain, who has more than 45 years experience in the HVAC industry.
Another energy savings built into the design was a 10-ton, 2,000-cfm dedicated outdoor air system (DOAS) by Desert Aire and supplied by Direct Expansion Systems. Previously, space humidity was controlled strictly with air conditioning, which, on hot west Texas summer days, is inefficient and costly in electricity. The DOAS provides outdoor air dehumidification and conditioning, and recovers 95 percent of exhaust air energy. The unit also includes an integral backup gas-fired heater for additional heating capacity.
The real advantage Wilkerson found in the VRF installation was minimal downtime or tenant space disruption. “My cost comparison analysis found that all the HVAC methodology choices for the TSB, including VRF, were within a few percentage points of each other in price,” he said.
Both Sain and Wilkerson plan more VRF system designs in the future and predict VRF will become a factor in U.S. HVAC design as contractors gain more installation experience and costs are reduced due to volume and experience.
Information provided courtesy of John Parris-Frantz, president of JPF Communications Inc. in Chicago. He has written for the HVAC, plumbing, electrical, lighting, and security industries for more than 30 years. Contact him at firstname.lastname@example.org.
Publication date: 1/12/2015