Many owners of older buildings today are faced with inefficient, worn 25- to 30-year old hvac systems. They can be costly and time-consuming to replace.

Mounting the ducts to the hvac through a new roof curb made this job at the Linton Towers office building a breeze.
Many owners of older buildings today are faced with inefficient, worn 25- to 30-year old hvac systems. It can be costly and time-consuming to replace whole systems, especially when system replacement represents the potential problem of having to renovate the building's roof to replace older curbs. Many owners have relied on retrofitting their building's existing system to save money and time.

Linton Towers, a 20,000-sq.-ft., three-story office building in Denver, houses insurance agencies and real estate agents, among their tenants. The building had two multizone units on the roof. They were classic 1970s vintage multizone units, simultaneously running one stage of mechanical cooling and one stage of gas-fired forced air heat. Typical of multizone units, they were mixing heated and cooled air to satisfy the varying requirements in each zone - an unnecessary waste of energy.

"Those old multizone systems were state-of-the-art 30 years ago," said Dale Moody, a Climate Engineering mechanical technician. "But technology and time have surpassed them so they're expensive to operate and maintain today."

Climate Engine-er-ing in Denver is responsible for maintaining the hvac equipment in Linton Towers. When one of the multizone units needed replacing, they undertook the job of renovating the new -system.

"Last summer, all three of the compressors in one of the units went out," said Moody. "We were running the last part of the summer on one replacement compressor. Then the heat exchanger went out early this fall."

The building owner wasn't ready to replace both units, so only the failed unit was replaced. A Lennox 30-ton L Series rooftop unit replaced the old multizone unit. It is now supplying cooled air to volume dampers, which regulate the volume of conditioned air to each zone in response to their individual requirements. There is no wasteful mixing with heated air to maintain desired temperatures in the different zones. Climate Engineering expects to replace the other old multizone unit in the coming year.

Replacing the curbs was another task. The owner stipulated the building was to remain occupied with no interruption to the tenants' normal operation during the retrofit.

"I knew I had selected the controls, equipment and accessories that would be the least intrusive four our customer's tenants," said Frank Gostic, design engineer and project manager for Climate Engineering.

ThyCurb Company, based in Carrollton, Texas, was called in to design a retrofit curb - a "Retro-Mate" adapter curb. Retro-Mate is an insulated, structural steel base that mounts over the existing curb. The Retro-Mate curb adapts to the differing configurations of the new unit to the existing ductwork below.

This part of the job was simplified by completing a major portion of the work off site. Climate Engineering sent ThyCurb sales engineer Doug Hinton drawings, measurements, and serial numbers from existing curbs. The RetroMate curb construction began. When it was complete, the curb was simply hoisted onto Linton Tower's roof and fitted over the existing curb.

Another vendor, Honeywell, was selected for its "RapidZone" zoning product. The RapidZone dampers and controls were factory installed in the curb. With no roof patching nor sheet metal modification required and with controls in place, the Multi-Zone Retro-Mate curb significantly reduced installation time and costs.

Each of the building's eight zones is controlled by a sensor and thermostat, which keeps the system operating at a comfortable temperature. Lennox territory manager David Garver said, "The tenants joked the system must not be working, since they couldn't hear it; the new one is quieter. Each zone of the building is always within a degree of the desired temperature."