Reference condition – outdoor unit
Figure 3-139: Design parameters tab of the VRF system editing dialog, shown for water-source VRF system with Reference condition – outdoor unit sub-tab selected.
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. For water-source VRF systems, this parameter is defined only for 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.
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.
Entering source loop water temperature: This reference source water temperature (Tewtref) is perhaps the most significant reference condition for the water-source unit, as it is the condition at which the reference COP would have been determined by the manufacturer. This parameter must be entered separately for cooling and heating.
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.
