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Modular Building Institute

DDC Energy-Management System Controls Plant's New Rooftop Units

March 1, 2008
In 2005, the HVAC equipment serving its 60,000-sq-ft facility in Plainville, Conn., outdated and in disrepair, Gems Sensors & Controls formulated a plan

In 2005, the HVAC equipment serving its 60,000-sq-ft facility in Plainville, Conn., outdated and in disrepair, Gems Sensors & Controls formulated a plan to replace four rooftop units (RTUs) a year over a five-year period. But after discovering The Connecticut Light and Power Co.'s rebate program for companies needing to upgrade their facilities, Gems decided to replace all of the equipment at the same time.

PPL SavageALERT Inc., an energy-services company, and B-G Mechanical Service Inc., a Trend Technology Center, worked closely with Gems' facility director and power-company representatives to ensure compliance with the rebate program.

An important challenge for Gems was maintaining company operations and building temperatures during the transition to the new equipment. Between maintaining comfort in the administrative and sales areas and cooling the manufacturing shop and small data center, satisfying all areas was important.

B-G Mechanical Service installed a Trend direct-digital-control energy-management system to control new, more-efficient RTUs within the updated central heating plant. In all, B-G Mechanical Service installed:

  • 18 high-efficiency RTUs with two-stage cooling and economizer.

  • 18 Honeywell electronic actuators on existing reheat coils for each RTU.

  • One Trend IQ-212 controller with RD space sensors for each RTU.

  • One Trend IQ-204 controller for the central heating plant, which consisted of two new high-efficiency pumps; two existing HB Smith boilers; one existing 5-in., three-way mixing valve; and one demand pulse for kilowatt load shedding.

Four units were replaced at a time. B-G Mechanical Service ordered all of the new RTUs and, during the shipping period, began installation plans. Trend communication lines and sensor cables were roughed in, and new Honeywell valve actuators were installed on the reheat coils of each RTU.

When the new equipment arrived, B-G Mechanical Service disconnected and removed the old units. New curbs were installed and new RTUs dropped on. Startup would take place immediately, with a temporary thermostat operating the units while B-G Mechanical Service installed the Trend controls.

B-G Mechanical Service verified the performance of the Trend system under the observation of an engineer selected by Connecticut Light & Power and then again with one of the power company's representatives present.

The Trend system controls all HVAC and central-heating-plant functions. With graphics from the 963 Supervisor operator workstation, the Gems staff is able to view and adjust the system at will. The central heating plant provides hot water for a radiation loop in the two-story administrative area and the reheat coils in each RTU. The Trend system monitors all temperatures, effectively reducing heating-plant operation for improved comfort and savings.

The reheat coils in the administrative- and sales-area RTUs allow ventilation without discomfort from cold drafts. The manufacturing area is heated by the reheat coils when necessary. Kilowatt demand is monitored and load shed to meet predetermined target savings.

As a participant in the New England Demand Response Program, Gems receives financial rewards for reducing energy usage during emergencies. The Trend system plays a key role in this, allowing an operator to raise cooling set points 7° for all RTUs with one keystroke.

Whenever an out-of-limit condition occurs, the system sends e-mail alerts to the facility manager. A virtual private network enables remote access to the system, saving Gems on service calls.

Over the first year, the Trend system performed flawlessly.

Aside from power-company rebates of approximately 50 percent of the project costs, Gems' incentives will be around $90,000 a year. Additionally, the project met the power company's benefit cost ratio, earning Gems an incentive in the amount of $151,972, which equals 29 percent of the total project cost.

Information and photograph courtesy of Trend Control Systems.
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