Complex Office Building Retrofit
Integrating Lighting and HVAC Retrofits: Case Study
Originally constructed in 1905, 33 N. High St., Columbus, Ohio, is a 10-story, 77,000-sq-ft high-rise in the heart of downtown. The building was recently purchased by the Central Ohio Transit Authority (COTA) to serve as its corporate office. The project involved almost completely gutting all electrical and mechanical equipment on seven of the 10 floors and in the basement. During construction, the three floors not renovated remained occupied, creating some difficult design challenges.
The existing HVAC system consisted of 65 heat pumps located in various closets throughout each floor. All the heat pumps have been replaced with modern, high-efficiency units and new ductwork has been installed to reconfigure thermal zones according to new architectural plans. (Several walls were added to configure spaces per the owner’s requests.) A new fluid cooler was added on the roof, in addition to a dedicated outdoor air system necessary to meet current ventilation code requirements. The BAS is capable of monitoring all heat pumps and their respective zones. By replacing the existing heat pumps (circa 1982 with an EER of 9) with high-efficiency units that have an EER of at least 14.2, the energy consumption of these units has been reduced by more than 35%. In order to keep occupants of the three floors warm, an alternate boiler location was necessary to maintain heat to the building. The old boiler was not removed until the new unit was up and running.
The lighting system prior to renovation consisted primarily of T12 fluorescent parabolic luminaires and some incandescent down-lights. Control was by local wall switches. All the luminaires were replaced with a variety of T8 and T5 luminaires. The primary open office spaces use Corelite Class R2 recessed “volumetric” type fixtures with T5 lamps and Lutron EcoSystem dimming ballasts. The open office areas on each floor share a south-facing wall with windows so daylight harvesting has been incorporated to automatically dim the nearest two rows of luminaires based on daylight infiltration. The photocell communicates directly to the EcoSystem ballast and adjusts the light output accordingly. This allows the space to evenly illuminate from the windows into the interior wall. The dimming ballasts and photocell constantly work together, raising and lowering light levels at 1% increments that cannot be perceived by the occupants.
Local dimming overrides also are provided in the event occupants require lower or higher light levels than the 40 foot-candles programmed into the daylight harvesting system. The daylighting system in the open office areas has reduced lighting loads in that space by about 20% by dimming half the luminaires (the two rows nearest the windows) as daylight penetrates the space. This 20% reduction is based on if they would be left full on all the time. The overall savings in consumption are staggering on a per fixture basis.
The lighting load in all open office spaces (about 40% of the COTA building) was reduced from 150 W per luminaire to a mere 48 W per luminaire on average with the daylight harvesting system while maintaining light levels with more efficient luminaires, lamps, and ballasts. This is nearly a 70% reduction in energy costs for this particular application.
This retrofitted building will be U.S. Green Building Council LEED-certified once all closeout and commissioning documentation is completed. Here is a breakdown of the lighting system for the entire building with respect to current power density codes:
- Power density of renovated spaces allowed: 59,663 W (ASHRAE 90.1 2007)
- As designed and installed: 50,071 W
- Power reduction from current code:16%
- Percent of luminaires controlled via occupancy sensor: 76%
- Percent of luminaires controlled by daylighting system: 57%