Evaporator Selection

[US Iceman]

The evaporator coils for NH3 systems are usually selected on kW cooling load and temperature difference (or BTU per hour per degree TD).

The temperature difference (TD) is based on the room temperature minus the evaporating temperature of the refrigerant in the coil.

In effect, you are selecting the evaporator based on it's cooling capacity at a specific TD you will select.

For a given coil capacity, a smaller TD will provide less capacity. A higher TD will provide more capacity for the same coil.

The fan selections are done by the evaporator coil manufacturer. However, in some applications with high static pressure requirements you may have to increase the minimum coil capacity. The higher static pressure systems cause the fan air flow volume to be reduced (axial or propeller fans). The lower volume of air flow reduces the coil capacity.

You should also be aware that some coil manufacturers list their coil capacity as only kW (or Tons). This usually indicates they have selected this rating on a specified TD of their choice. Be sure to check the small print in their catalogs.

Does that help?