ASHRAE Journal - September 2024 - 56

TECHNICAL FEATURE
Listing 1), and it is almost unavoidable to not include
such metadata directly or indirectly. As one can see in
Listing 1, clear names and values are used throughout
the sample, making the code relatively specific to the
system for which it is built.
In other words, the more metadata included in the
code, the less portable and less standard it becomes.
Namely, context of a particular situation is embedded
into the code, making it inapplicable to other contexts.
Even different naming conventions pose a challenge.
Hence, it is typically recommended to make code as
generic as possible and avoid " hardcoding " metadata.
Early and Late Binding of Metadata
The above, in which metadata is directly encoded
and the result is a control system that is tailor-made to
the specific context it belongs to, can be said to rely on
early binding coding principles. All information and
functions are known at compile time, and all metadata
and context is directly embedded in the code. This tends
to result in efficient code for the considered case and
simpler code, yet also low levels of portability-the code
cannot adapt to different systems or different buildings,
for example. In other words, other contexts and other
input data streams are very difficult to support.
def getAllPumps(self,g,hvacComp,atts):
complist=getattr(hvacComp,atts)
for comps in complist:
try:
pump=Pump(name=comps.name,
medium=comps.medium,
massflow=comps.massflow,
port_a=comps.port_a,
port_b=comps.port_b,
localPressure=comps.localPressure,
pipeResistance=comps.pipeResistance)
self.pumps.append(pump)
pump.printSelf()
#Add the connection information to the entire list
if {comps.name+'.port_a',comps.port_a} not in self.connections:
self.connections.append({comps.name+'.port_a',comps.port_a})
if {comps.name+'.port_b',comps.port_b} not in self.connections:
self.connections.append({comps.name+'.port_b',comps.port_b})
except:
print( " Warning: " +pump.name+ " not listed before. Least information missing! " )
56
ASHRAE JOURNAL ashrae.org S E PTEM B ER 2024
This can be alleviated by relying on late binding
coding principles instead and transferring metadata
and context outside the control algorithm. In this case,
code becomes more generic, and context is ported to a
place independent of the applicable code. Therefore, the
code can adapt at run-time to different contexts. This
code is much more flexible, yet also more difficult to
create, as all sorts of contexts (metadata schemas) need
to be considered as potential inputs without breaking
the code. This coding principle also makes the resulting
algorithm less efficient (more time needed) and less
safe (more exceptions possible). In other words, the
portability comes at a cost. While late binding can be
pushed to the extreme, it can also be implemented to a
more limited extent. In our context of control systems,
these principles can be used, for example, simply to
separate incoming data structures from the control
algorithm itself; in other words, the control algorithm
can be applied to multiple data structures.
Listing 2 gives a brief example of how input data can
be divided from the algorithm that processes the data.
This is not a very extreme example of late binding, yet
it does give an impression of what is meant or hinted
at. The first part of this Python snippet lists a query
that retrieves data from an available data set, aiming
LISTING 1-EXAMPLE HARDCODED METADATA FOR MPC (PARTIAL)
http://www.ashrae.org
ASHRAE Journal - September 2024

Table of Contents for the Digital Edition of ASHRAE Journal - September 2024
