Across the United States, cities are facing the challenge of an aging infrastructure. Atlanta experienced this firsthand in 2020, when a cabinet that housed critical electrical equipment at one of its larger pumping stations burned up following a lightning storm. The City had already made major repairs to the station after a flood six months earlier. The electrical accident and the fact that the aged electrical distribution was original to the building led the City to declare the station unsafe.  It was clear the nearly 50-year-old station would need to be rebuilt, but with the work not scheduled to begin for several years, a solution needed to be found that would enable the station to maintain its critical function.

Rich Pearlstein, managing consulting director for the City of Atlanta Department of Watershed Management, decided an eHouse – a pre-fabricated walk-in enclosure that houses electrical equipment – would be the most cost-effective solution. But since the drives that power and control the electrical components generate a great deal of heat, the air inside the eHouse must be kept cool in order to preserve the electrical components. With the need to conserve space, minimize energy expenses and meet the City’s sustainability goals, Pearlstein and his team needed a cost-effective way to keep the structure cool, preferably without an HVAC system.

Back-Channel Cooling Provides an Innovative Approach

To create an eHouse that would meet the pumping station’s needs, Pearlstein turned to Goforth Williamson, Inc (GWI), a pump and controls supplier for the city. The company is a partner of Danfoss, with a long history of collaboration, and knew that Danfoss offered variable frequency drives with back-channel cooling, which removes heat through the back channel, or building panels, to the outside. This innovation would allow for operation in a structure without HVAC.

Electrical contractor WWPS was also part of this highly collaborative effort. WWPS handled meticulous specification of a precast vault [all holes for pipes pre-drilled], which was dropped in below the eHouse. The company also installed dozens of 3” & 4” PVC pipes through the vault to connect the utility transformers, 5kV switches, generator, eHouse and building, before the concrete pour.

Additionally, the FC202 AQUA Drives, which GWI chose, contain a Smart Logic function in their software, which allows them to monitor the indoor temperature and when necessary, switch between recirculating air inside the eHouse and venting heat to the outside. That meant that in the winter, the heat rejected by the drives could be used to heat the eHouse, compensating for the lack of an HVAC system.

“Danfoss has a proven track record as an industry leader in pumping applications, said J. Boudoin, head of GWI’s controls division. With the back-channel cooling, they were able to provide a green solution. Plus, their 10-year warranty with on-site repair was a valued bonus.”

Back-channel cooling, available with all Danfoss VLT® (low voltage) drives, is based on a unique heatsink design, with heat pipes that conduct heat 20,000 times more efficiently than traditional solutions. Using a minimal amount of energy, the concept exploits the heat differentials in materials and air temperature to effectively cool high performing electronics. In VLT® drives, there is total separation between cooling air and the internal electronics to protect them from dust-borne contaminants.

Efficient heat removal helps prolong product life, increases the overall availability of the system, and reduces faults related to high temperatures. Up to 90% of heat losses are exhausted directly outside the enclosure. The drives’ zero-clearance, side-by-side mounting decreases the amount of space required and the energy consumption related to cooling is brought down to an absolute minimum. Combined installation and energy savings result in up to 30% cost savings in the first year of operation.

Another benefit offered by Danfoss VLT® drives is that they operate in conjunction with harmonic filtering. Installed as a stand-alone solution at a common point of coupling, the filter ensures optimal harmonic suppression, independent of the number of loads or their individual load profiles. In addition, the active filter corrects the power factor and balances the phase load, providing an optimal energy utilization. This improves the system efficiency and increases the grid robustness to avoid downtime. Installing a harmonic filter in the eHouse allowed GWI to keep the cabinets that contained the drives to the smallest size possible, helping to keep the structure compact and lower total energy costs.

Pearlstein affirmed that the equipment was an ideal solution: “The back-channel cooling fit with what we wanted to do, along with the city’s goal of going green and lowering our energy consumption.”

Drives Bring Dividends

Design by Initiative (dB(i)), an enclosure manufacturer, built the eHouse with their propriety EXOACM system, integrating the Danfoss drives to work in conjunction with the forced air enclosure. EXOACM is stronger, lighter and UV-resistant compared to current market enclosures, making this next-generation system possible. The collaboration between dB(i) & Danfoss created a modern efficient solution to cooling that allowed the ability to remove HVAC.

“The EXOACM panels are UV-resistant aluminum composite with a fire-resistant core that provides a thermal break,” explained Sam Vill, dB(i)’s vice president of sales. “Our eHouse works very well with Danfoss’ back-channel cooling system. Our engineers communicated with Danfoss engineers throughout the process to ensure the system would work flawlessly. The overall project was a great success and should pave the way for an energy-efficient and climate-friendly system that can be replicated worldwide.”

The eHouse was shipped from dB(i) to the pumping station where the on-site contractors connected it to the existing wiring. The drives were programmed so that their network communication cards would interface with both the eHouse control panel and external controls and after several weeks of testing, the drives were brought online.

Since the eHouse began operating in December 2021, Pearlstein has been completely satisfied and reports that the electrical equipment has had no problems, a relief for his department. He estimated the drives have resulted in significant energy savings, helping the city fulfill its goal of improving its energy efficiency and lowering costs.  With the exception of a smaller motor control center and 2 panels, all electrical distribution equipment is located in the eHouse, so when the pumping station is fully rebuilt, the electrical contractor can tie to existing piping to the eHouse, keeping total electrical costs for the job very modest.

Joe Hammack, senior application engineer at Danfoss Drives, who designed the configuration for the drives and filter and wrote the programming scripts for the drives, is excited about the potential to use back-channel cooling with the Smart Logic feature to allow the drives to function in environments without HVAC. “The drives are very usable in many applications. They can alleviate the need for extra cooling, save money, and the drives can also be used to heat the surrounding area or other spaces in a building. If you can reuse the heat, why not?”