3.3. Energy consumption optimization
To optimize LR of the OAP unit, the first step is to minimize the
objective function, i.e., total energy consumption (Wtotal) of
the combined system, which is a sum of that of the VRF unit
and the OAP unit:
Wtotal ¼ WVRF þWOAP
3.4. Logic for determining OA supply temperature setpoint
It is not difficult to imagine the complex relationship between
LR and the OA supply temperature, since the capacity ratio of
each unit is determined by not only outdoor temperature, but
also internal loads, control strategy, etc. It is reasonable to
reduce the complexity of the problem to transform LR to OA
supply temperature only considering the decisive variable,
i.e., the outdoor air temperature.
For the combined system in cooling mode, the higher the
LR is, the more loads the OAP unit takes and the lower OA
supply temperature should be. In contrast, in heating mode,
the higher the LR is, the higher OA supply temperature should
be. Therefore, the LR can be transformed and used for the OA
supply temperature control by rules depicted as follows.
For cooling mode,