Cooler Capacity Model

[WeiT]

We were recently asked about the cooler capacity model and want to provide some supporting information.

According to our experience with data-center cooling design, the majority of cases are not limited by cooler capacity, but instead the cooling airflow that delivers cooling to rack inlets. So, we recommend first trying the infinite capacity model, which allows coolers to always maintain the supply temperature setpoint. If the rack-cooling checks are green, it is likely that the rack cooling performance is fine. To rigorously verify if a cooler is overloaded, one can compare the actual load to the actual cooler capacity, which can be manually determined from the technical data manual with refence to the return temperature.

In cases where supply airflow rate is low, such as when simulating cooler control, one may consider the specified capacity model. In reality, the cooler capacity linearly increases along with the return temperature. ITA CFD predicts the capacity at a given return temperature with a linear interpolation using two points provided by the user consisting of a return temperature and capacity, both at the same reference airflow. If the actual load is less than the capacity, the supply temperature setpoint will be kept; otherwise, the supply temperature will be above the setpoint.

After the solve, one can always hover the mouse on cooler to find the relevant information, such as actual load, actual cooler capacity, return temperature, and supply temperature.

Terminology:

1. Heat Load, or simply Load, means the amount of heat generated in the whitespace (which is eventually removed by coolers).
2. Capacity means the maximum amount of load a cooler can remove from whitespace to outside at a certain set of operating conditions.
3. Supply Temperature means the average temperature of airflow at the supply terminal(s) of a cooler.
4. Return Temperature means the average temperature of airflow at the return terminal(s) of a cooler.
5. Supply Temperature Setpoint, or simply Setpoint, means the desired supply temperature set by the user for a cooler. It might or might not be maintained, depending on the capacity and load.

Please let us know if you have more questions or comments!