The variable refrigerant flow (VRF) direct expansion (DX) cooling coil model is nearly identical to the single-speed DX cooling coil model. For this reason, an adaptation of the single-speed DX cooling coil model is used to model the variable-speed compression system used in VRF AC systems. The model inputs are quite similar to the input requirements for the single-speed DX cooling coil model, however, the location of a majority of the inputs have been moved to the variable refrigerant flow air conditioner object since multiple DX cooling coils will use the same DX compression system.
A unique auto-assigned name for an instance of the VRF DX cooling coil. Any reference to this DX coil by another object will use this name.
Select the DX cooling coil availability schedule. Schedule values of 0 mean that the DX cooling coil is off. A schedule value greater than 0 indicates that the coil can operate during the time period.
The air volume flow rate (in m3/s or ft3/s) across the DX cooling coil at rated conditions. The rated air volume flow rate should be between 0.00004027 m3/s and 0.00006041 m3/s per watt of rated total cooling capacity (300 to 450 cfm/ton). The gross rated total cooling capacity and gross rated SHR should be performance information for the unit with at this rated air volume flow rate.
This numeric field defines the gross rated total cooling capacity of the DX cooling coil (in W or btu/hr). The total cooling capacity should be a gross , i.e., the effect of supply air fan heat NOT accounted for.
This numeric field defines the gross sensible heat ratio (sensible capacity divided by total cooling capacity) of the DX cooling coil at rated conditions. Both the sensible and total cooling capacities used to define the Rated SHR should be gross (i.e., the effect of supply air fan heat is NOT accounted for)
Select the curve that defines the cooling capacity ratio modifier as a function of indoor wet-bulb temperature or indoor wet-bulb and outdoor dry-bulb temperatures. This is a linear, quadratic or cubic performance curve if the cooling capacity is solely a function of indoor wet-bulb temperature (i.e., the indoor terminal units weighted average inlet air wet-bulb temperatures). Without specific manufacturers data indicating otherwise, the use of a single independent variable is recommended for this coil type. If, however, the user has reason to believe the cooling capacity is both a function of indoor wet-bulb temperature and outdoor dry-bulb temperature (and has manufacturers data to create the performance curve), a bi-quadratic equation using weighted average indoor wet-bulb temperature and condenser entering air dry-bulb temperature as the independent variables may be used. See the Engineering Reference for more discussion on using this input field.
Select the curve that defines that parameterises the variation of total cooling capacity as a function of the ratio of actual air flow rate across the cooling coil to the rated air flow rate (i.e., fraction of full load flow). The curve must be a linear, quadratic or cubic performance curve. The output of this curve is multiplied by the gross rated total cooling capacity and the total cooling capacity modifier curve (function of temperature) to give the gross total cooling capacity at the specific temperature and air flow conditions at which the coil is operating. The curve is normalized to have the value of 1.0 when the actual air flow rate equals the rated air flow rate.