Indirect Evaporative
This coil provides a model for a wetted coil evaporative cooler that has water sprayed directly on the tubes of the heat exchanger where latent cooling takes place. The vaporization of the water on the outside of the heat exchanger tubes allows the simultaneous heat and mass transfer which removes heat from the supply air on the tube side. Then the moist secondary air is exhausted. The secondary air stream has its own fan. This indirect evaporative coil can modulate so that the air leaving the cooler just meets a drybulb temperature setpoint. This coil is intended to be able to model indirect evaporative coils that have
1. variable speed tower fans,
2. variable speed pumps for water recirculation and spraying, and
3. ability to operate in a dry mode.
Such indirect evaporative coils can modulate the cooling power during operation by varying either the tower fan speed or the intensity of water spray or both. To simplify the simulation it is assumed that the device’s internal controls are such that, when it is operating as a “Wet” evaporative cooler, tower fan and spray pump operation are linked together so that there is a one-to-one mapping between them at any given part load situation. This allows formulating the fan and pump power performance curves to be based on the same independent variable, tower air flow fraction.
