The larger the space to be cooled, the larger the air-conditioning system that’s required, both in terms of number and size of units, plus ducting.
H.T. Lyons (www.htlyons.com), a full-service mechanical contractor and a subsidiary of PPL (www.pplweb.com), an energy and utility holding company in Allentown, Pennsylvania, is designing green HVAC systems to help buildings to become LEED-certified or Energy-Star-rated. K. Scott Sine, chief engineer and director of engineering and energy services for H.T. Lyons and a certified energy manager and LEED AP, knew how energy-efficient, high-volume, low-speed (HVLS) fans could perform, as he had installed them at a previous job in order to help increase ventilation effectiveness.
“It’s well documented that HVLS fans work well with regard to heat destratification — that is, they push heat down,” says Sine. “What I was interested in was applying the technology in a less common fashion to cooling applications.”
Warehouse projects
H.T. Lyons designed HVAC systems for a 125,000 sq ft rented warehouse for Liberty Property Trust and a 95,000 sq ft warehouse for Olympus (www.olympusamerica.com) in Allentown. Air-conditioning systems don’t effectively stir the air in a building, especially in a warehouse that contains closely spaced, large storage racks, explains Sine. To be effective in applications such as these, HVAC engineers typically have to add to the system’s tonnage or duct distribution when selecting equipment.
Sine turned to HVLS technology as a supplement. A 24-ft MacroAir HVLS fan was integrated into the HVAC system on both projects, enabling Sine to space air-conditioning units further apart, a strategy that required fewer units. By incorporating HVLS fans, Sine decoupled fan distribution from the cooling units. The HVLS fan evens temperature distribution across each warehouse; the cooling units simply pump in the necessary air. “I pointed the small AC unit fans toward the HVLS fan, which then efficiently mixed the cool air throughout the building,” says Sine.
In winter, the HVLS fan sequence operates in reverse, pulling warm air down from the ceiling to the floor, which also helps to reduce heating costs.
How HVLS fans supplement HVAC systems
Tonnage refers to the cooling capacity of an air conditioning system. One ton of cooling is equal to 12,000 Btus/hr. “Engineers often think a ton is a ton, so what does it matter if you add fans?” says Sine. “HVLS fans help in areas of ventilation effectiveness, thermal mass, evaporative cooling, energy consumption, and compressor staging.”
The thorough mixing of air helps with ventilation effectiveness, explains Sine, but engineers often don’t consider using the building’s thermal mass when calculating this effectiveness. “Concrete cools due to natural temperature migration from the ground,” he says. “Blowing air directly on to the concrete in large quantities allows for an increase in the transmission of that natural cooling to the interior space.”
HVLS fans also work very well in conjunction with air conditioning systems as they help with the natural evaporative cooling across the skin, the same way a summer breeze on an 80° F day feels cool, says Sine. “Increased evaporative cooling by the amount of velocity generated by HVLS fans allows building managers to raise the air conditioning setpoint by about 4 °F for the same cooling effect,” he explains. “For each increase in degree, the energy savings is reduction in energy consumption. This makes HVLS fans an integral component of LEED-certified or Energy-Star buildings.”
A final advantage of HVLS fans, says Sine, is compressor optimization. In constant-speed compressors, the longer you can make a compressor run, the more optimally it runs. “Since cooling is now decoupled from air distribution, only the cooling units necessary need to be on,” explains Sine. “In other words, if a building is run at 50% in a standard HVAC design, all four air-conditioning units would have to operate, which kicks the compressors on and off, decreasing efficiency. By incorporating HVLS fans into the system, only two of the four installed air-conditioning units need to operate, and each operates at maximum efficiency.”
Results
By supplementing each project’s HVAC system with one 24-ft MacroAir 6ixBlade fan, tonnage was reduced, says Sine. “Where I needed five air-conditioning units, I only had to buy four,” he explains. “This more than paid for the cost of the fans, and, in addition, the air conditioning units I did purchase required less ducting, which also saved on capital costs.”
Lowering tonnage can also save on future heating and cooling costs. In addition, both warehouses can now apply for LEED certification and Energy Star status.
“The movement of HVLS fans is deceptive,” says Sine. Because the fans move so slowly and are so quiet, one building manager didn’t believe they would cool down his space and turned them all off. “He had to turn them on again, once the interior grew too warm,” says Sine.