2. Description and simulation of the
combined system
2.1. Description of the combined system and control
designing
A schematic of the combined system is shown in Fig. 1. The
combined system includes VRF part and VAV part. The VRF
part consists of one outdoor unit and multiple indoor units
(IDU). The VRF part maintains the zone temperature at the setpoint
by variable refrigerant flow with the variable speed
compressor in the outdoor unit and electronic expansion
valve (EEV) located in each IDU. The VAV part mainly consists
of a DX-oriented OAP unit, VAV boxes, supply fan and air duct.
The OA conditioned by OAP unit is supplied into zones by the
supply fan through the VAV boxes. The VAV box regulates the
conditioned OA flow based on demand-controlled ventilation
strategy corresponding to CO2 contaminant concentration for
maintaining indoor air quality (IAQ). The reheat coil is not
always needed. It is designed for the comparison operation