1.4.5
Dynamic Control
A process that optimizes energy efficiency of HVAC systems (air handling
units, converters, chillers, and boilers) by increasing and decreasing
setpoints or starting and stopping equipment in response to heating and
cooling needs of the facility. A requirement of dynamic control is knowing
the heating/cooling demand status of the process. Therefore dynamic control
requires controllers connected in a communications network.
1.4.6
Firmware
Firmware is software programmed into read only memory (ROM) and erasable
programmable read only memory (EPROM) chips. Software may not be changed
without physically altering the chip.
1.4.7
Hand-Held Terminal
A hand-held terminal is a manufacturer specific device connected directly
to a communications port on a controller, through which the controller is
accessed and, in some cases, programmed.
1.4.8
Input/Output (I/O) Points
I/O points refer to analog inputs (AI), digital inputs (DI), analog outputs
(AO), and digital outputs (DO) in a digital controller. Another term for
digital inputs and outputs is binary inputs and outputs. Inputs are from
analog sensors (temperature, pressure, humidity, flow) and digital sensors
(motor status, flow switches, switch position, and pulse output devices).
Outputs operate modulating and on/off control devices.
1.4.9
I/O Expansion Unit
An I/O expansion unit provides additional point capacity to a digital
controller and communicates with the stand-alone digital controller on a
LAN. An I/O unit is not stand-alone because the control program does not
reside in the I/O unit. An I/O expander which connects directly to a stand
alone controller through a multi-line microprocessor bus is restricted to
reside within 3 feet of the stand alone controller and is considered part
of the stand alone controller.
1.4.10
Local Area Network (LAN)
a.
A communications bus that interconnects digital controllers for
peer-to-peer (see "peer-to-peer" below) communications.
Different levels of LANs are possible within a single DDC system.
In this case, a digital controller on a higher level LAN acts as a
network controller to the controllers on the lower level LAN. The
network controller, then, has at least two LAN communications
ports. One port supports peer-to-peer communications with other
digital controllers on the higher level LAN. The other port
supports communications with the digital controllers on the lower
level LAN.
b.
LANs permit sharing global information. This allows building and
site wide control strategies such as peak demand limiting, dynamic
control strategies, coordinated response to alarm conditions, and
remote monitoring and programming of digital controllers.
SECTION 15910N
Page 12
Previous Page
