DENVER, CO — It’s a sunny 65-degree afternoon here. On the Linton Tower building, two rooftop heating and cooling units are keeping the building comfortable.

One rooftop unit is a classic 1970s vintage multizone unit. It’s simultaneously running, one stage of mechanical cooling and one stage of gas-fired forced air heat. It is a multizone system. Typical of multizone units, it is mixing heated and cooled air to satisfy the varying requirements in each zone.

Its recently installed companion unit is supplying cooled air to volume dampers that 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. Both units serve essentially the same amount of space.

“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 passed them by so they’re expensive to operate and maintain today.”

Climate Engineering, based here, is the company that just installed the new system and is responsible for maintaining the equipment in the building. Climate Engineering is also a Honeywell Automation Controls Specialist (ACS) contractor.

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

“Building owners have been finding themselves with aging multizone systems that are beyond repair and with nothing readily available to replace them,” said Nick Bennett, automation sales representative at Climate Engineering. “The difference now is the RapidZone™ control system, recently introduced by Honeywell. RapidZone was a no-brainer; it was just the right retrofit for the job.”


The job was simplified by completing a major portion of the work off site. ThyCurb Company, based in Carrollton, TX, designed and fabricated a Retro-Mate™ adapter curb. According to Doug Hinton, sales engineer at ThyCurb, this is an insulated, structural steel base that mounts on the top of the existing curb. It adapts to the differing configurations of the new unit and to the existing ductwork below.

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 reduces installation time and costs, according to Moody.

On Monday, the installation team finalized the job details. On Tuesday morning, Climate Engineering hoisted and set the adapter curb and the unit. The finishing piece of the job was the new Lennox hvac unit.

“This was a real team effort,” said Lennox district manager, John Neves. “All of the pieces went together beautifully.”

“If planned properly, once we set the equipment all we have to do is terminate the control lines and reconnect the gas line,” said David Hoogendyk, mechanical technician. “In this case, we completed those tasks by Thursday and put the system on line that day. The whole change-out went very smoothly. It was a well-executed team effort, from initial planning through final commissioning.”


“The building occupants will feel a big difference,” said Benny Benson, automation technician of Climate Engineering. “The Honeywell RapidZone™ controls will maintain each zone temperature closely and will respond quickly to temperature changes.”

When the system comes out of night setback, the temperature will be brought up slowly so the whole building is thoroughly warmed without overshooting the setpoint and wasting energy, he noted.

“Built-in intelligence in the automation system determines when the warm-up will start each morning, depending on outdoor and indoor temperatures,” said Benson. “Night setback sensing in each zone will maintain a uniform unoccupied temperature throughout the building.”

“All of this assures the owner that the system saves energy — days, nights, weekends, and holidays,” said Bennett.

The owner stipulated that the building was to remain occupied with no interruption to the tenants’ normal operation during the retrofit. Frank Gostic, design engineer and project manager for Climate Engineering, said, “I knew I had the right selection of controls, equipment, and accessories that would be the least intrusive for our customer’s tenants.”

Publication date: 01/28/2002