Philadelphia office building liberated from high costs
The upgrade to the cooling system for 1515 Market St., a 40-year-old, mixed-use structure owned by West World Management, Inc., Purchase, N.Y., was completed in 1997 with the installation of new chillers and sophisticated controls.
Now, with more than a year of operating experience behind them, the building’s managers have calculated that the payback will be easily less than eight years, based on the energy savings alone. In fact, on a typical day, this multitenant, 564,000-sq-ft office building requires just one quarter of its former cooling capacity, according to Carrier.
The manufacturer’s “Evergreen” centrifugal chillers are the heart of the system, with its Windows® NT-based building operation-energy management network and control package serving as its central nervous system and brain.
Looking for the right 'fit'Energy efficiency improvements for the building actually began a decade ago, when the building received an exterior facelift.
“Previously, the building had windows that opened and there was a lot of leakage in the shell,” said Bob Freeman, property manager for West World. The windows were replaced with double-glazed, green-tinted reflective glass. Leaks were sealed in the steel-and-limestone curtainwall.
While these exterior changes drastically reduced cooling and heating requirements, the building’s two 800-ton chillers were not changed at that time. Their location, in a 7-ft-deep pit in the 30- by 50-ft mechanical room, sandwiched between the ground floor above and a subway concourse below, was simply not conducive to a retrofit.
Overhead piping further constricted navigating space in the mechanical room, but by 1997, one of the units needed extensive repairs, and it was time to take action.
The old units were at a disadvantage because they were not considered efficient by today’s standards. Moreover, they used R-12, which has been banned from production since 1996.
Because of the tight space, the old units had to be cut apart and removed piece by piece. One doorway had to be widened to accommodate the removal.
The bolt-together design of the Evergreen chillers was especially important for the office building. Carrier installed three 400-ton Evergreen chillers, which can be separated into two components that fit through normal doorways and can be assembled on-site.
Chillers get resultsThe efficiency of the new chillers made it possible to reduce the building’s total cooling capacity from 1,600 to 1,200 tons. And, having three smaller chillers rather than two larger units gives greater flexibility, Freeman said.
Before, even for minimum cooling, an 800-ton unit had to run at full capacity. Now, the building can be cooled efficiently using as little as 400 tons of cooling.
“Normally we don’t need more than one 400-ton unit in operation during intermittent seasons and non-peak times. During heavier-use periods, we never need more than two units running at once,” Freeman said.
“Having a third unit means we always have a back-up in the event that one chiller needs to be shut down for maintenance.”
Product Integrated Controls (PICs) digitally monitor more than 100 functions and display more than 125 operating and diagnostic conditions. For 1515 Market St., PICs were electronically tied together using the Carrier Comfort Control Network (CCN), and linked to a personal computer in Freeman’s office.
There, through the “ComfortWORKS” software interface, Freeman and his associates can monitor and control not only chiller operation, but also chilled water and condenser water pumps, the cooling tower, the system’s four heat exchangers, and all 38 of the building’s air handlers.
Free to be coolOf course, the bottom line for the system is tenant comfort.
As far as the building’s occupants are concerned, the whole project was invisible, Freeman said. They weren’t aware when the retrofit took place, as Carrier handled the eight-week job of demolition and installation in late winter.
And when the warm weather came, tenants apparently never noticed a difference, even though the building was being cooled essentially by half the power of the original unit.