Evaporative Cooler - Direct CelDekPad

EvaporativeCooler:Direct:CelDekPad

Used in:   Air Handling Units

The direct stage, shown in the figure below, 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. While the process provides a lower dry-bulb temperature, the moisture content of the leaving air is higher than the entering condition. The direct stage is used for comfort cooling in a building where adding humidity to the air can be tolerated.

Direct Stage Evaporative Cooler

The thermodynamic process is a simultaneous heat and mass transfer, or adiabatic cooling, and follows a constant enthalpy line on the psychrometric chart, it is shown in the figure below as a process from A to B. Since the deviation of the constant wet-bulb line and the constant enthalpy line is small, it is assumed that the wet-bulb temperature is constant across the direct evaporative stage.

Psychrometric Chart - Constant Enthalpy

If the direct evaporative process were 100% efficient, the leaving dry-bulb temperature would equal the entering wet-bulb temperature. The efficiency of the direct evaporative process is less than 100% and by defining saturation efficiency (ε_se) for the direct stage or evaporative pad, the leaving dry-bulb temperature can be expressed by the following equation.

General

Name

A unique name for an instance of an evaporative cooler which is predetermined by DesignBuilder.

Type

Select the type of evaporative cooler from the list of options:

• 1-Direct CelDekPad, the cooler described here, a direct evaporative cooler with rigid media evaporative pad and water recirculated from a reservoir.
• 2-Direct Research Special, similar to 1-Direct CelDekPad but with methods to specify variable effectiveness based on primary air flow rate and a way to control the cooler operating range based on temperature limits.
• 3-Indirect CelDekPad, an indirect evaporative cooler with a rigid media pad, similar to the direct evaporative cooler.
• 4-Indirect Wet Coil, an indirect evaporative cooler where water is sprayed directly on the tubes of the heat exchanger.
• 5-Indirect Research Special, similar to the other indirect evaporative coolers, but it provides additional flexibility including a way to specify the source of secondary air.

Settings

Direct pad area

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.

Direct pad depth

The depth of the evaporative pad (in m or in). The pad depth is used to determine the saturation efficiency.

Recirculating water pump power consumption

This field is used to specify the power consumed by the evaporative cooler recirculating pump (in W).

Operation

Availability schedule

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.