Plandroid Help Documentation

Evaporative Versus Refrigerative Cooling

An evaporative cooling system works by cooling air by the evaporation of water. The energy required to change the state of water from a liquid to a vapour (the enthalpy of vaporization) is extracted from the air in the form of heat as the water evaporates, thereby cooling the air. Under the right conditions, this process uses much less energy than an equivalent refrigerative system, and allows more fresh air into a building. However, the maintenace requirements of an evaporative system can be significant.

The performance of evaporative cooling systems depend greatly depending on the ambient air humidity. If the ambient humidity is less than 30%, the performance is generally very good, while if it is between 30-50%, the performance can be expected to be reasonable. If the humidity is over 50%, then it is not advisable to use evaporative systems, and a refrigerative system should be used instead.

Finally, it is important to realise that a refrigerative system will recycle most of the same air through the building, while an evaporative system continually supplies fresh air from outside.

Designing an Evaporative Cooling System

Plandroid has a dedicated evaporative design mode (Droplet) that you can select with the Design -> Loads -> Design mode toggle button. The current design mode will also determine whether the Automatic design toolbar tool (automatic design tool) will create a refrigerated, evaporative, gas heating, or venturi design. (There is no automatic design function at this stage for the lighting mode).

Evaporative units are commonly sized solely based on the volumes of air that must be supplied, although they may be sized on the floor area to be serviced. Both of these figures can be shown by Plandroid - in the Options tab you can set the zone properties that you want to see displayed in your design, including the zone area and airflow requirements.

Each load zone can display its required air flow and floor area, while the status bar will show the total requirements for all of the zones that are switched on. The status bar also shows an icon indicating if you are currently in the evaporative (Droplet), refrigerative (Coil), ducted gas heating (Flame), venturi (Venturi Mode), or the Lighting (Lighting Mode) design mode.

Total loads shown in the status bar
Total loads shown in the status bar

An evaporative system requires much higher air flow rates than an equivalent refrigerative system to be effective. While a refrigerated system typically requires at least 8 to 10 air changes per hour, an evaporative system will typically require a minimum of 28 to 35 air changes per hour. You can adjust the air changes settings used for each mode under the Options -> Design -> Design Modes -> Evaporative mode:

Evaporative Design Mode Settings
Settings - Air Changes

An evaporative unit is often selected based on the total air flow requirements of the design only. In the evaporative design mode settings you can select if the automatic designer selects evaporative units based on the airflow requirements only, or if both the airflow and cooling power requirements are used in your designs.

A number of units catalogs supplied with the program contain evaporative units, and likewise a number of parts catalogs include the droppers and chutes required for creating an evaporative system design. Note that when selecting evaporative units from the parts catalog, the units' power rating shown may be the fan motor power, and not the refrigeration power as it is for refrigerative systems.

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