Insuring Controlled Comfort and Energy
In many historic buildings across the country—including schools, offices and hospitals—occupants are discovering that their HVAC system is incapable of meeting the modern standard for a healthy building environment. On top of that, fluctuating utility rates are forcing more and more building owners to consider innovative, conservation-based systems for their buildings.
In many historic buildings across the country—including schools, offices and hospitals—occupants are discovering that their HVAC system is incapable of meeting the modern standard for a healthy building environment. On top of that, fluctuating utility rates are forcing more and more building owners to consider innovative, conservation-based systems for their buildings. Owners also need to be able to monitor and control these systems to maximize performance. This exact scenario played out recently for a major New England insurer.
The Bristol, Conn.-based company, occupying the majority of a 130,000-sq.-ft. building originally constructed as a manufacturing plant circa 1919, wasn't satisfied with its internal atmospheric conditions. Served by cooling towers and boilers—and fitted with water source heat pumps and fan coil units throughout—the building's HVAC system worked relatively well in terms of its maintaining temperature. The distributed type of mechanical equipment, however, created an intensive maintenance load. Additionally, poor ventilation raised health concerns.
The owners of the building agreed to upgrading the HVAC, but the insurer desired controls that would not only provide improved environmental conditioning, but flexibility in terms of scheduling, adjusting setpoints and problem notification as well.
The HVAC design
JP Engineering, Windsor, Conn., was retained to design the HVAC system. Their initial recommendation included a pair of unusual technologies for the region: a central partial-ice thermal storage plant and a web-based building control system that would allow the user to take full advantage of the ice storage system's capabilities.
As the construction was funded between the owner and the primary building occupant, both parties were acutely interested in the cost of construction. By request, JP Engineering was asked to compare the system to a conventional central plant. The firm's initial designs helped demonstrate that a partial ice-thermal storage plant, if incorporated into the total system, could be constructed with no incremental difference in first cost. This, factored along with the potential energy savings, made the thermal storage application an easy choice.
Not so simple was the decision as to what to do about the control system. The team decided something was needed that not only suited the complexity of the project, but also offered interoperability between multiple component vendors. Real-time access to information for the occupant was also necessary.
"We knew we were pushing the envelope a little bit," says Joseph D'Amico of JP Engineering. "So in doing so, we limited the field in terms of equipment, manufacturers and representatives. Internet compatibility was key. Until you can connect people through the Web, you can't achieve or realize the true value of a system."
Ultimately, a BACnet-based system was selected. Because of its built-in interoperability and web-based user interface, it met the occupants' need for flexibility. In addition, a big factor for the specifiers, according to D'Amico, was the local control contractor's reputation for product installation and support.
The system's remote-control capability was another primary factor because there would be no on-site maintenance personnel to monitor the HVAC system.
"You can access the system from anywhere, and the alarm capabilities take the alarm to where the personnel are at," continues D'Amico.
He was comfortable with this decision because the role of facility personnel has changed drastically. "The new generation of maintenance personnel are coming in as computer literate, and are comfortable with the Internet," he says.
According to D'Amico, the control-system design had an overall cost benefit as well. The controls needed to integrate with variable-frequency drives on air handlers and chilled-water pumps, so by networking each VFD, the control contractors were able to eliminate a number of physical points, eliminating costs.
The partial ice-thermal storage plant uses the chiller plant to make ice from 11 p.m. until 7 a.m.—when electric rates are lower—and then uses that ice to supplement peak chiller loads during the day. As a result, energy cost savings are expected to immediately be recognized. In addition, Connecticut Light and Power offers an incentive based on the anticipated energy savings from VFDs on the chilled water plant pumps and air-handling units, and the controls strategy utilizes free economizer purge and precooling of the building when weather allows. Other energy conservation strategies include optimal start and night setback setpoints on the zones throughout the building.
So far, the energy savings on the building have exceeded expectations. Electrical savings exceeded $7,000 a month last summer and, as the building experiences a year-round cooling load, this has increased during the fall and winter because the building is now equipped with economizer cooling. These savings are especially impressive in light of an increase in occupancy during the retrofit and the addition of exterior lighting and elevator loads that were previously billed separately from the building.
To better meet full ASHRAE ventilation standards, carbon-dioxide demand strategies are used to increase ventilation over ASHRAE's minimum requirement, if necessary. Additionally, the night precooling algorithm will often completely purge the building with outside air before occupants arrive.
As the facility manager observed, "In an office that employs nearly 1,000 employees, the task of maintaining consistent comfort levels throughout large open spaces is always a challenge. The old system could not meet those challenges because of its limitations and need for costly maintenance. We are just beginning to see the true value of the ice storage system and it's potential capabilities for which it was designed."