Handbook of air conditioning and refrigeration / Shan K

3. Evaluate the error � between the calculated o on and the selected training output (target output)
o t by:
(5.18)
4. Adjust the connection weights from W j to W j�1 to minimize the error by using the following
rule:
Wj�1 � Wj � ��oon (5.19)
where� is the learning rate whose value lies between 0 and 1.
5. Repeat the previous steps for all the input/output pairs in the training set until the error for the
entire training set is lower than the preset training tolerance. The training set should cover the
operating range of the inputs and outputs.
Applications. An ANN can model multiple parameters simultaneously for nonlinear systems. It
can also be periodically trained to update the weights. ANNs are now widely used for predictive
control, such as energy use prediction, energy optimization, adaptive control, data trending, and
optimum start and stop.
5.11 PROGRAMMING OF DDC SYSTEMS
Evolution of DDC Programming
Graphical Programming
ENERGY MANAGEMENT AND CONTROL SYSTEMS 5.53
� � o on(1 � o on)(o t � o on)
The EMCSs having more complex functional controls are heavily software-driven. From the 1960s
to the 1970s, the software for HVAC&R control was mostly performed in a workstation computer
and programmed in the control manufacturer’s factory. Because of the trend to use distributed
microprocessor-based DDC units in the late 1970s, many EMCS manufacturers provide some type
of operator control language (OCL) for field-programmable line programming in the controllers using
BASIC-type language. This meets the requirements of computer program development, periodic
updating, and necessary modifications and improvements.
Since the late 1980s, there is a trend toward the function and object-orientated graphical programming
to provide software for DDC units and the PC in the operator’s workstation. Today, both
traditional line programming using BASIC-like language (sometimes Pascal and C++ languages are
also used) and graphical programming are used in DDC systems.
Davison (1992) described that graphical programming is a schematic drawing of a desirable control
scheme (functional control), such as mechanical cooling or economizer control, using symbols
called templates. The templates are displayed on the computer screen interconnected by lines that
direct the flow of data. The control scheme shows the inputs, through control operations, to outputs.
After the diagram of the graphical programming is completed, it is converted to a program usable
by the DDC units and PC through a computer program.
Compared with traditional line programming using a BASIC-like language, graphical programming
has the following advantages: First, it is intuitive and easier to use and understand by field
HVAC&R engineers and operators. Second, the user is more familiar with it because of meaningful
visual symbols represent functions and devices. It is simpler in documentation and easier in troubleshooting.
Third, it provides a time-saving tool for the specification and documentation of the
HVAC&R energy management and control systems. Finally, graphical programming enables one to
improve programming quality at a reduced cost. The limitations of graphical programming are that