The dry coil indirect evaporative cooler has a rigid media pad, similar to the direct evaporative stage, where the adiabatic cooling takes place. The secondary air enters the evaporative cooler at ambient conditions, is passed into the rigid media pad and enters an air to air heat exchanger where it cools the supply air flowing through the heat exchanger tubes (see diagram below). The moist secondary air is then exhausted to the environment. The secondary air stream has its own fan and consists of a rigid media evaporative pad with water recirculated from a reservoir. The water is pumped from the reservoir to a water distribution header for water feed by gravity from above the media. The evaporative pad provides the area for the adiabatic saturation of the air.
The process that the secondary air goes through, A to C to D, is shown by the dashed lines in the following figure. Process A to C is adiabatic cooling in the rigid media pad. Then the air enters the shell side of the heat exchanger and is sensibly heated from C to D by the warm supply air passing through the tube side. The secondary air inlet is modeled as a separate stream of outdoor air and the user has the option of defining the name of an outdoor air node.
The advantage of the dry coil heat exchanger is that the heat exchanger does not have the evaporation taking place on the outside of the tubes, thus no mineral deposits are left on the heat exchange surface to reduce the efficiency of the heat exchanger. The rigid media pads are designed to flush the mineral deposits to the sump, so the saturation efficiency of the pad stays relatively constant.
A unique name for an instance of an evaporative cooler which is predetermined by DesignBuilder.
The face area of the evaporative pad (in m2 or ft2). With the area and mass flow rate, the air velocity is calculated and is used to determine the saturation efficiency on the secondary side of the evaporative cooler.
The depth of the evaporative pad in meters. The pad depth is used to determine the saturation efficiency on the secondary side of the evaporative cooler.
This field is used to specify the effectiveness of the indirect heat exchanger between the primary and secondary air flow.
This field is used to specify the power consumed by the evaporative cooler recirculating pump (in W).
The secondary flow is sourced from outside air and blown over the
This field is used to specify the secondary fan flow rate and is specified in m3/s or ft3/min.
This field is used to specify the total efficiency of the fan and is used to calculate the power consumed by the evaporative cooler secondary fan. Input values should be between 0 and 1.
This field is used to specify the delta pressure across the secondary stage of the evaporative cooler (in Pa or in H2O).
Schedule that defines when the coil is available, i.e. whether the evaporative cooler can run during a given time period. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during a given time period. A value less than or equal to 0 (usually 0 is used) denotes that the unit is off.