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Operations-level processor: A PC or other device used
primarily by building operation personnel for everyday
building operations. This processor can access points
or data in all the lower level controllers.
System-level controller: A microprocessor-based controller
that controls centrally located HVAC equipment such
as VAV supply units, built-up air handlers, and central
chiller and boiler plants. These controllers typically
have an input/output (I/O) device capability, a library
of control programs, and may control more than one
mechanical system from a single controller. In a BMS,
these controllers provide processing of point data for
higher level processors and typically include energy
management programs.
BACKGROUND
The BMS concept emerged in the early 1950s and has since
changed dramatically both in scope and system configuration.
System communications evolved from hardwired (and home-
run piping for pneumatic centralization) to multiplexed (shared
wiring) to today's two-wire all digital system. The EMS and
BMCS evolved from poll-response protocols with central
control processors to peer-to-peer protocols with distributed
control.
ENERGY MANAGEMENT
Energy management is typically a function of the
microprocessor-based DDC controller. Several energy
management applications are described in Microprocessor-
Based/DDC Fundamentals section. In most mid-sized to
large buildings, energy management is an integral part of
the BMCS, with optimized control performed at the system
level and with management information and user access
provided by the BMS host.
Equipment is operated at a minimum cost and temperatures
are controlled for maximum efficiency within user-defined
comfort boundaries by a network of controllers. Energy
strategies are global and network communications are essential.
Load leveling and demand control along with starting and
loading of central plant based upon the demands of air handling
systems require continuous global system coordination.
Energy Management BMS host functions include the
following:
— Efficiency monitoring - recording
— Energy usage monitoring - recording
— Energy summaries
– Energy usage by source and by time period
– On-times, temperatures, efficiencies by system,
building, area
ENGINEERING MANUAL OF AUTOMATIC CONTROL
BUILDING MANAGEMENT SYSTEM FUNDAMENTALS
Zone-level controller: A microprocessor-based controller that
controls distributed or unitary HVAC equipment such
as VAV terminal units, fan coil units, and heat pumps.
These controllers typically have relatively few
connected I/O devices, standard control sequences,
and are dedicated to specific applications. In a BMS,
these controllers provide processing of point data for
higher level processors.
— Curve plots of trends
— Access to energy management strategies for continuous
tuning and adapting to changing needs
– Occupancy schedules
– Comfort limit temperatures
– Parametric adjustments (e.g., integral gain) of
DDC loops
– Setpoint adjustments:
Duct static pressures
Economizer changeover values
Water temperatures and schedules
— Modifying and adding DDC programs
Energy Management for buildings preceded DDC by about
ten years. These pre-DDC systems were usually a digital
architecture consisting of a central computer which contained
the monitoring and control strategies and remote data gathering
panels (DGPs) which interfaced with local pneumatic, electric,
and electronic control systems. The central computer issued
optimized start/stop commands and adjusted local loop
temperature controllers.
FACILITIES MANAGEMENT SYSTEMS
Facilities management, introduced in the late 1980s,
broadened the scope of central control to include the
management of a total facility. In an automotive manufacturing
plant, for example, production scheduling and monitoring can
be included with normal BMS environmental control and
monitoring. The production and BMS personnel can have
separate distributed systems for control of inputs and outputs,
but the systems are able to exchange data to generate
management reports. For example, a per-car cost allocation
for heating, ventilating, and air conditioning overhead might
be necessary management information for final pricing of
the product.
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