A Drive for All Spaces

By Steve Gonzalez, CEM, Senior Product Manager, Honeywell, Environmental and Combustion Controls Div., Golden Valley, Minn. -- Consulting-Specifying Engineer, 7/1/2006

The biggest challenge with mixed-use facilities is that they employ multiple systems in one building to accommodate different types of space. Commercial facilities run constantly for extended hours, often with different technologies, where residential facilities generally use more localized systems, with limited runtime.

In a mixed-used facility with both of these space types, loads will vary and move around the building throughout the day. The building will experience a large pickup in load early in the morning to accommodate residential occupants getting ready for work. After this spike, loads decrease in the residential space and increase in the commercial space as people begin their workdays. Employing variable-frequency drives (VFDs) for systems in both types of spaces can help regulate mechanical and plumbing systems and accommodate the varying loads, as well as maximize comfort control and office efficiency.

Installing a VFD in a residential space is a relatively new concept, since most don't operate at 120 volts, which residential spaces utilize. But they're just as useful in this type of space, and their residential applications are growing. They're easily applied in a multi-use facility where people move from the commercial space during the day to living space at night. For example, in the evening during winter, when you're turning the temperatures up in the residential space, the commercial space is being set back to 55°F, as is done with tradition commercial office space, in an effort to decrease the temperature in the commercial and retail space while keeping residential space warm. The best way to design a system with a high turndown ratio and run at really low part-load conditions—15% to 25% of full-load capacity—is to install VFDs in the air and water distribution systems. This allows you to slow things down at a system level, provide comfort at the residential level and turn things off in the commercial space at night, creating enormous energy savings.

Do engineers turn to VFDs first? They should and they're starting to. Since VFDs have become more reliable and their quality has improved, engineers have become more comfortable with them. This has helped to bring specification of VFDs from a fringe activity to the mainstream.

Many systems employ zone-level control today, and it's very inefficient to do zoning without VFDs. Zoning gives everyone individual levels of control, but without VFDs, what you're doing is running at full speed and bypassing what you don't need or using dampers and valves to choke off the air or water. While it works, this method wastes a lot of energy and can be hard on the system components. With a zoned system, I might not want to serve a certain space at all, so I'll slow my overall system down. If I slow the system down just a little, I can save a lot of energy. A VFD can provide 80% of design flow with only 50% of the energy. Progressive engineers are looking at these types of things and making our buildings better.

Additionally, the EPA's Energy Star and the United States Green Build Council's LEED programs are helping end users and building owners to become better educated about how to save energy.