Meditech's six story office complex, Corporate Place, is Located at 550 Cochituate Road, just off of the Massachusetts Turnpike.
Meditech is a software company specializing in medical information systems
The building's major mechanical systems include:
Corporate Place was initially equipped with an ice bank system for cooling the building. Ice was harvested during off-peak hours and used during the day in addition to chilled water provided by the ice harvesters to provide cooling for the building. Over the years, the electric rates changed as did the building's tenant needs. The heat load increased making the ice bank system severely undersized. In the early 1990's, the York chiller was added to provide additional cooling capacity. The ice bank system continued to degrade over the years due to the unavailability of parts.
During the first quarter of 1997, Meditech removed the ice bank system and added a new Trane centrifugal chiller. At that time, the decision was made to control the chiller plant with a computerized control system. R. L Shields Associates, Inc. was chosen as the controls contractor. Delta Controls was the manufacturer chosen for the controls.
A Delta Controls ORCA series DCU was chosen to control the chiller plant. Meditech received the second DCU sold in the United States (NORAD Headquarters in Colorado received the first). The DCU ran from the first day on with no hardware problems and has proven to be very reliable.
The building operating software, created by R. L. Shields Associates, has been upgraded several times since the first days of operation. Sequencing valve operations and controlling flow rates were very important issues. Additionally, chiller capacity control was required to keep the temperatures inside the building at specification. Chiller sequencing is accomplished based on outside dry bulb and wet bulb temperatures. The cooling tower has two setpoints, one to provide free cooling using tower water circulated through a heat exchanger in the cooling loop. The second setpoint provides the proper water temperature for chiller operation.
A special piping arrangement allows the use of the free cooling heat exchanger and the York chiller simultaneously. If the temperature and dew point are suitable, the building's cooling needs can be met with the cold water from the cooling tower. If more cooling is required, the York will start and provide additional cooling capacity. If more capacity is still needed, the York Chiller and the free cooling heat exchanger are shut down and the Trane chiller is started. If additional capacity is still required, the York is restarted and run together with the Trane.
During chiller startups, the electrical demand is monitored carefully to prevent demand spikes. When starting the chillers, the ramp up time is adjusted to be approximately 20 minutes. When a second chiller is start, the first is capacity locked at 40% prior to the second one starting. This also helps prevent demand spikes.
Special software was written by R. L. Shields Associates, Inc. to accomplish several of the tasks designated as goals. Custom software included:
As previously mentioned, the Delta ORCA DCU Panel is connected to a color host PC. The host system features Delta's IGRAPHW software. This "state-of-the-art" software package provides the user with both text information as well as providing a graphical interface. The maintenance staff has the ability to view all data and graphics from their home computers as they would see from their on-site computers.
Future phases of this project may include controlling the air handlers, automating the tenant Variable Air Volume (VAV) Boxes and adding Carbon Dioxide sensors to monitor indoor air quality.
CHILLER CONTROL GRAPHIC
ELECTRICAL DEMAND TREND LOG
For more information on this project or Delta Controls, contact:R. L. Shields Associates, Inc.
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