Handbook of air conditioning and refrigeration / Shan K

5.54 CHAPTER FIVE
Templates
Zone
temperature
west
10K
Zone temperature
east
10K
Outdoor
temperature
10K
Zone schedule
Cool SP
74 T
Time
1
clock
0
85 T
�
SP
Cool
Average
�
I
temperature DB
2
SO
Cooling control
0.5
Outdoor temperature
lockout
SP
Cool
I
Templates DB Dead band
SP Set point
it is bulky to display on screen and that it is new to us and needs to develop required supports such
as a portable interface that acts directly to the DDC units.
In Davison’s (1992) paper, a template is a graphical symbol (icon) in graphical programming that
describes a single or combined control scheme (specific functional control), as shown in Fig. 5.26.
A template consists of input and output connections, a small section of computer code, and private
data storage registers. A template is function- and object-oriented. Each template performs a small
portion of a specific functional control. If several templates are connected by lines, they form a
complete computer program for a specific functional control. The template symbol provides a
visual reminder or memory of the function that the template accomplished.
A template maintains its own set of private data and variables that cannot be altered by the action
of any other template. The state of an instance of a template is contained in its private variables. They
can be only modified by the program code contained in that instance. The private variables of an instance
of a template are hidden from the action from other templates.
In a template, inputs are used to receive data from other templates or constants. Outputs are used
to send data to other templates. Inputs and outputs between two or more templates are connected by
lines that direct the data flow between the templates. An input may receive a value from only one
output in order to prevent overwriting of data at the input. On the other hand, an output data may be
sent and used by any number of inputs.
For a more complex control function that needs several templates, a combination of templates
called a macrotemplate is often used to simplify a graphical programming diagram.
Min
Min
180
Economizer
on Min off
on Min off
FIGURE 5.26 Graphical programming for mechanical cooling control in a small packaged unit.
3
DB
T
Compressor