The mechanical design chosen for the school is representative of a growing trend in multi-zone applications — one that varies and distributes refrigerant, rather than water or steam, to multiple zones. VRF systems are efficient, flexible, and almost entirely ductless, which make them easy to install, particularly in existing structures where space may be lacking, said Al Cook, design engineer, Beardsley Design Associates, Syracuse, New York.

And, the Systemair Topvex offers a suitable complement, he added, stating the ERV incorporates a means for fresh-air supply, offering a decentralized fresh-air solution by design.

The Right Fit

Beardsley Design Associates was selected to design the mechanical renovation at the Stanley campus, but there were challenges. The “D” wing of the Stanley facility included conference rooms and other spaces with outdated baseboard heating and no cooling or means for fresh air. Built nearly a half-century ago, the building had rooftop load restrictions that eliminated the option of installing conventional air handlers to supply fresh air. Furthermore, a traditional ducted system would have been difficult, if not impossible, to discreetly install given the existing walls and layout.

Beardsley chose a zoned VRF heat pump system for heating and cooling and Topvex ERVs for fresh-air supply. The latter was small enough to install above the ceiling, where it was ducted directly to the VRF indoor split (terminal) units that were also installed above the ceiling. An outdoor VRF heat pump is piped to the indoor split units, supplying refrigerant as needed to the individual zones. This combination of space-saving and energy-efficient equipment not only brought the spaces up to code, but introduced a new level of comfort and control to the building spaces.

“As a firm, we’re very efficiency conscious. We always use energy recovery ventilation on our projects, but it’s hard to find any ERV that delivers cfm in the 750-1,000 range. These units can do that,” said Cook.

Enhanced Longevity, Efficiency

The fresh-air challenges at the Stanley campus are common to many K-12 renovations. Space limitations and rooftop load restrictions often rule out more conventional, centralized HVAC solutions. These are the primary reasons a school might typically opt for a solution like the Topvex, which actually fits within the building envelope. But, many other benefits apply, such as longer equipment life, part-load efficiency, and serviceability.

ECMs help provide Topvex part-load efficiency and increase the overall longevity of the unit. ECMs are designed for highly efficient operation during low-rpm periods. The motors are standard on all Topvex units and require no separate variable frequency drives (VFDs), which reduces wiring at the job site. The motors do not require any greasing and are virtually maintenance-free. They are also quiet, which makes them particularly appealing for above-ceiling installations in classrooms and conference rooms.

Bag filters are another unique standard feature of the Topvex unit. The filters are designed with greater surface area, so they last longer. When a replacement is required, a built-in pressure transmitter that measures the filter pressure drop alerts personnel via the control panel or building management system (BMS). The filters are mounted on guiderails for easy removal and replacement. This is the only maintenance procedure required for the Topvex ERVs, which is a big plus for K-12 campuses where maintenance staff is often limited.

Design and Control

The setup and installation of the ERVs, including the connections to the indoor split units, were extremely straightforward, since all Topvex units arrive at the job site pre-programmed for the specific project. Operating parameters, including cfm, temperature set points, etc. are already programmed into the controller.

Topvex installations can be designed to work in concert with a VRF system or operate independently. At the Stanley campus, each of the three Topvex units is ducted to individual indoor split units serving the various zones. Fresh outdoor air passes through the ERV, where it is preconditioned with return air, and then enters the indoor split units, where it may be heated or cooled depending on whether the space temperature is satisfactory. During shoulder seasons, the VRF system operates very little, with the ERV providing ample fresh air and temperature maintenance. During cold-weather operation, the ERV has an exterior-mounted, electric pre-heater that heats outdoor air as needed to keep the internal heat wheel from freezing. On the supply side of the ERV (but still internal to the unit), there is a hydronic reheat coil and modulating valve that modulates flow as needed to heat the supply air if the heat wheel cannot recover enough energy from the exhaust air.

Both ERV and VRF systems have user interface and remote controllers, which are connected to the campus’ BMS.

Size, Quality, and Capacity

Schools are expected to provide many decades of service, so investing in high-efficiency equipment that also meets stringent IAQ standards makes sense. Topvex ERVs are the perfect complement to VRF systems, as they provide the necessary ventilation in an energy-efficient package that can be located in spaces where most ERVs cannot.

Benjamin Hardy, service technician for Modular Mechanical Service, Syracuse, New York, oversaw the HVAC startups at the Stanley campus and agrees the combined systems provide an excellent solution for schools and other light commercial projects.

“I think the greatest advantage to this ERV is the slim design,” said Hardy. “Other ERVs tend to be much taller and wider because of how their heat wheels are designed. But the Topvex can fit above a drop ceiling, so you can install them in close proximity to the indoor split units. And there’s very little ductwork to be installed.”

Cook appreciates the space efficiency, quality, and capacity of the Topvex units, which led him to select the product. “They are very nice, well-built units,” said Cook. “It’s what we’ll use on our next VRF project.”

Publication date: 3/9/2015

Want more HVAC industry news and information? Join The NEWS on Facebook, Twitter, and LinkedIn today!