Cooling tower calibration error
I am working on a OpenStudio (1.12.0) project which contains a cooling tower that is meant to predominantly operate during winter months. While the specifications of this project describe a 49F design wet-bulb temperature, EnergyPlus requires a minimum "Design Inlet Air Wet-Bulb Temperature" of around 68F. Making this adjustment and an associated change in "Design Approach Temperature" to 3.24R (per the manufacturer's specification), yields the following error.
* Severe * Bad starting values for cooling tower water flow rate ratio calibration. * ~~~ * Design inlet air wet-bulb or range temperature must be modified to achieve the design approach * ~~~ * A water flow rate ratio of 0.500000 was calculated to yield an approach temperature of 1.91. * Fatal * Cooling tower calibration failed for tower VAR SPD COOLING TOWER 1.
Reducing the "Design Range Temperature to around 8R" helps avoid the error but conflicts with the true specifications.
I am looking for help and suggestions for better understanding this error message and how to remedy the situation.
