Reference condition – outdoor unit
Figure 3-133: VRF System > Design parameters dialog with Reference condition – outdoor unit tab selected for an air-source VRF system.
Capacity: Cooling and heating capacity of the outdoor unit at reference conditions (Qcref and Qhref) may be manually entered by the user or autosized as part of the System equipment and plant sizing function.
COP: The Coefficient of performance for cooling and heating at reference conditions (COPcref and COPhref) defines the efficiency of the VRF outdoor unit at the reference conditions indicated on this tab. This value is not autosized and should be edited by the user in keeping with the COP and Reference conditions.
Average indoor unit coil entering wet-bulb temperature: This design entering air condition (Tawbref) is the average entering air wet-bulb temperature seen by indoor unit coils for all indoor units connected to the VRF system currently selected for editing. This value is defined separately for cooling and heating at reference conditions.
Cooling mode: By default, the value for this outdoor unit reference operating condition is a copy of the coil entering wet-bulb temperature set in the Reference condition for the indoor unit (on the next tab). To independently edit this outdoor unit cooling-mode reference operating condition, uncheck the “Use same coil entering wet-bulb temperature as for indoor unit” box.
Heating mode: The coil entering wet-bulb temperature at reference conditions is always directly edited in this tab of the dialog as a reference operating condition for the outdoor unit.
Average indoor unit coil entering dry-bulb temperature: This reference entering air condition (Tadbref) is the average entering air dry-bulb temperature seen by indoor unit coils for all indoor units connected to the VRF system currently selected for editing. This value is defined only for heating mode.
By default, the value for this outdoor unit reference operating condition is a copy of the coil entering dry-bulb temperature set in the Reference condition for the indoor unit (on the next tab). To independently edit this outdoor unit heating-mode reference operating condition, uncheck the “Use same coil entering dry-bulb temperature as for indoor unit” box.
Outdoor air dry-bulb temperature: This is the reference outdoor dry-bulb temperature (Todbref) at which the VRF outdoor unit is capable of providing the reference performance. This value is defined separately for cooling and heating performance.
Combination ratio: This derived parameter describes the capacity of indoor units at the reference condition relative to the capacity of the outdoor unit at the reference condition. It is presented separately for cooling and heating operation, as VRF outdoor units typically have different cooling and heating capacities at reference conditions.
