How iZone AC Systems Work

iZone Air Conditioning Control Strategies

Developed over 30 years, iZone’s control strategies are designed to deliver optimal temperature control, energy efficiency, and cost-effectiveness.

The various system control strategies are outlined below, each tailored to maximise comfort while minimising running costs.

The zone dampers function in a standalone control system, operating independently as outlined below:

The simplest form of zone control is the basic open/close operation. As the name suggests, when a zone is opened, the damper drives to its maximum (MAX) open position. When closed, it moves to its minimum (MIN) closed position.

If the MAX setting is configured to 100%, the damper will open fully until the actuator motor triggers the MAX microswitch, which then cuts power to the motor. Similarly, if the MIN setting is 0%, the damper will close fully until the MIN microswitch is engaged, cutting power to the motor.

When the iZone system is reset or power is cycled to the C225 module, all zone dampers will cycle fully open and fully closed several times. This process calibrates each damper by recording the time (in milliseconds) it takes to reach both end positions.

These timing values are then used to accurately position the dampers at partial openings-such as 75% open or 25% closed.
For further details, refer to the Damper Timing section.

To achieve different airflow percentages, the dampers operate for varying lengths of time. These percentages are calculated based on the estimated airflow performance of the damper, not the physical position of the damper blade.

As a result, the motor may run for longer or shorter durations to produce a similar change in airflow, depending on where the damper blade is along its operating curve. This is due to the non-linear relationship between damper position and actual airflow.

The iZone system uses the fully open and fully closed microswitches as calibration and reference points to ensure accurate positioning of each damper.

The iZone system includes a technician-level feature that allows balancing of both MAX and MIN airflow settings. These balancing adjustments operate independently from the Zone Air Flow MAX and MIN controls available to end users in the GUI.

For example, if the technician sets the Balance MAX to 75%, the end user can still adjust the Zone Air Flow anywhere between 0% and 100%. However, at 100% user setting, the actual damper opening will be limited to 75% based on the technician’s balance setting, without affecting the user’s control range.

The installer can configure any number of electronic constant zones within the iZone system. However, it is important to note that any zone designated as an electronic constant cannot be used for individual temperature control.

• If the system has no electronic constant zones or uses fixed ducted constants (outlets without zones), the installer can select zero constants.

• When one electronic constant zone is configured, the system ensures that the total airflow across all open zones plus the constant zone equals at least the equivalent of one zone fully open (100%).

For example:

• Zone 1 = 25% open

• Zone 2 = 35% open

• Zone 3 = 10% open

The electronic constant zone will automatically open to 30% to bring the total airflow up to the equivalent of one fully open zone (100%). As the other zones open and close, the constant zone will adjust automatically to maintain this balance.

For larger systems or where more precise control of the electronic constant is needed, two or more electronic constant zones can be configured. Their operation is sequential: Constant 1 activates first, followed by Constant 2; they close in the reverse order.

The system maintains total airflow equal to at least the equivalent of two fully open zones (200%).

For example:

• Zone 1 = 25% open

• Zone 2 = 35% open

• Zone 3 = 90% open

• Zone 4 = 0% open

• Zone 5 = 0% open

• Zone 6 = 0% open

The total open zones equal 150% (1.5 zones fully open). Electronic Constant 1 will open to 50%, while Electronic Constant 2 remains closed to maintain the required total airflow.

Advanced electronic constant control offers more precise management of constant zones, especially beneficial when only one or two small zones are non-constant. To configure this system, the area of each zone must be input along with a minimum area that must always remain open-referred to as the “Area to be covered by constant.” This value is typically calculated as three times the capacity of the AC unit.

For calculation purposes, the iZone system assumes that a zone open to 80% is supplying 80% of its airflow. For example, an 18m² zone at 80% open is considered to be providing airflow equivalent to 14.4m² (18 × 0.8).

Example: For a 14KW ac with 6 zones,

In this example, the total equivalent active area is 18.3m². The minimum area that must be covered by the constant zone is 42m² (determined by the system designer).

Calculation:

• Required area to be served by the constant zone = 42 – 18.3 = 23.7m²

• Percentage constant zone must open = 23.7 / 42 = 0.56 (or 56%)

Therefore, the constant zone will open approximately 56% to maintain the equivalent of 42m² of active airflow.

While this method isn’t perfectly precise, adjusting the reported areas of the zones and constant can help achieve a satisfactory balance.

Zone temperature control requires each zone to be set to "Climate" mode and utilizes iZone wall sensors to modulate the zone dampers in order to maintain the desired setpoint. A key component in this control strategy is the supply air sensor (CDTS), which plays a critical role by reversing damper operation during heating mode. This helps prevent hot or cold air from being blown into a zone when the system initially starts.

The zone temperature control strategies rely on the following parameters for effective regulation:

As selected by the user

As measured by the zone sensor. The displayed value takes into account any calibration offsets from the configuration menu

As measured by the CDTS sensor

Open

Open

By default, the iZone system leverages the residual hot or cold air within the ductwork to help regulate zone temperatures after the AC system has cycled off. This feature assists zones in moving toward their set points more efficiently.

Example Scenario:

In a double-storey home served by a single ducted AC system running in heat mode, when the upper level reaches its set point, its zone damper closes. However, the lower level remains below set point, so the system continues heating the lower level.

Due to stratification, warm air from the lower level rises through the stairwell, causing the upper level ACT (Actual Temperature) to increase above its set point by approximately 2°C. When the lower level reaches set point and the system cycles off, the supply air temperature in the ducts drops below the upper level’s set point.

At this point, the upper level zone damper reopens, allowing cooler supply air to flow through the ducts, helping reduce the upper level temperature back to its set point.

This strategy works in reverse during cooling mode, where the system uses warm air in the ductwork to raise the temperature of any zones that have dropped below their set point.

Disabling In-Duct Energy Use

This in-duct energy utilization can be disabled in the system configuration. When disabled, the iZone system will only open zones during heating if the ACT is below the set point, and during cooling if the ACT is above the set point.

The following description outlines the control strategy for most ducted air conditioning units equipped with C325 AC unit modules.

Please note that control features may vary between brands, and some units may not support the full range of iZone system control options.

The iZone provides and receives the same basic information that is normally exchanged between the proprietary AC unit controller and the FCU 

Based on the output data from the iZone system, the AC unit utilises its own internal strategies to determine how to control the evaporator fan, compressor, inverter, reversing valve, condenser fans, condensate pump and all other peripheral controls and safety systems associated with the AC unit

In addition all delay and run on timers are controlled by the AC unit. iZone plays no part it the control of these sub-systems.

The iSave system cools your whole home using your ducted reverse cycle air conditioner’s fan mode.

Open

Open

Only the air entry point is visible outside.
It is fitted on your roof

The iSave system enhances your ducted reverse cycle air conditioner by efficiently utilizing its fan mode to cool your entire home. It works by drawing fresh air from outside, filtering it, and circulating it throughout your living spaces, while expelling hot air through your roof space or open windows. This creates a cooling effect similar to an evaporative air conditioner-without the need for a bulky rooftop unit or water.

Using the iSave system can significantly reduce your air conditioning costs, as it operates at just a few cents per hour. The more you use it instead of your conventional ducted reverse cycle air conditioner, the greater your savings. Additionally, it helps your primary air conditioner run more efficiently by preventing heat buildup, reducing its workload and operational expenses.

The system also improves indoor air quality by filtering incoming air. It can be installed with both new and existing ducted reverse cycle air conditioners, provided there is sufficient roof space for the extra ductwork and components. Overall, the iSave system offers a practical and cost-effective way to boost your home’s cooling efficiency while lowering energy consumption.

The iZone system provides multiple sensor options to control the AC unit, including:

• R/Air – Return air sensor

• Master – Allows the customer to select any sensor in the system to control the AC unit

• Zones – iZone automatically selects the most suitable sensor for the AC unit

• RF – Uses a single wireless iZone sensor to control an AC unit without zones

The strategies for each sensor type are detailed below:

This option uses the return air sensor built into the AC unit. When selected, the iZone system does not provide an Actual Temperature (ACT) signal to the AC unit.

Note that this option is not available on some brands that do not include a return air sensor. The return air sensor is the factory default on the iZone system.

Since it relies on a single sensing point, the return air sensor provides an approximate average temperature for all zones. As a result, the AC unit operates independently of individual zones and may cycle off before or after certain zones reach their set points.

When controlled via the return air sensor, the iZone system displays the AC unit set point in 1°C increments, and the AC unit’s control behavior remains consistent with that of its proprietary controller.

When Master is selected, the iZone system displays an icon on both the touchscreen and the app, allowing the end user to manually choose which sensor will control the AC unit.

The user can switch the Master sensor at any time by changing the corresponding X on the screen to a ✔.

The AC unit is then controlled based on the set point and actual temperature readings from the selected Master sensor.

If the Master zone damper is accidentally closed, it will be held fully open, ensuring the AC unit continues to be controlled by the Master sensor.

While in Master Sensor mode, the AC unit’s temperature display updates in 0.5°C increments and maintains control within an approximate range of ±1°C, depending on the AC unit brand.

When Zones is selected, the iZone system scans all zone sensors set to “Climate” mode and selects the sensor that is furthest from its set point to control the AC unit.

As zones approach their set points, the controlling sensor may shift among them until the last zone reaches its set point. This scan occurs approximately every three minutes.

If there is a mix of “Open” and “Climate” zones, the AC unit will be controlled by the Climate zone sensor that is furthest from its set point, as described above.

However, if only “Open” zones remain and all Climate zones are closed, the AC unit will default to control via its return air sensor, as explained in the Return Air Sensor section.

If a Climate zone is activated, the iZone system automatically switches back to control based on Zones.

While in Zones mode, the AC unit temperature display updates in 0.5°C increments and controls within an approximate range of ±1°C, depending on the AC unit brand.

Controlling the AC unit from Zones typically delivers the most accurate temperature control and the lowest running costs among all sensor options.

The RF option is designed for ducted systems without zones.

While it is possible to operate such systems using the unit’s return air (RA) sensor, using a wireless sensor (CRFS#) placed within the conditioned space can provide better temperature control and enable in-duct temperature display.

When setting up the CRFS#, set the zone dial to “R” or “F” on the selector switch.

This option is only available with wireless CRFS# sensors.

In RF mode, the AC unit displays temperature in 0.5°C increments and controls within an approximate range of ±1°C, depending on the AC unit brand. Additionally, the sensor’s button can be used to turn the AC system on or off.

On the iZone control panel or app, customers can manually select from the available fan speed settings. These typically include High, Medium, and Low, although some AC brands may offer fewer or more speed options.

When Fan Speed is set to Auto, the iZone system will automatically adjust the fan speed based on the number of zones that are Open or in Climate mode, as well as the percentage each zone is open. This is a dynamic function-fan speed changes in real-time as zone dampers modulate open and closed.

To enable automatic fan speed control, the following must be configured correctly in the iZone setup menu:

• Fan Auto must be enabled

• Fan airflow capacity (in litres per second) must be entered

• Number of fan speeds must be defined (e.g., High / Medium / Low = 3 speeds)

• All zone areas (in square meters) must be set

• Constant area must be configured

Note: The difference in average airflow between fan speeds is not dramatic. Approximate airflow percentages for a typical AC unit are shown below:

The iZone system offers the following operating modes for selection:

In this mode, the AC unit operates in Cooling mode.

• The compressor is managed by the AC unit’s internal control protocol.

• The fan will operate according to the AC unit’s factory default-either running continuously or cycling with the compressor-or as configured in the unit’s field settings.

For optimal performance, it is recommended that the indoor fan runs continuously while in Cool Mode.

In this mode, the AC unit operates in Heating mode.

• The compressor is controlled by the AC unit’s internal protocol and will initiate defrost cycles as required by the condensing unit.

• The fan will operate according to the AC unit’s factory default settings-either running continuously or cycling with the compressor-or as configured in the unit’s field settings.

For optimal comfort and efficiency, it is recommended that the indoor fan cycles on and off with the compressor when operating in Heat Mode.

In Vent mode, the indoor fan runs continuously, while the compressor remains off.

In Dry mode, the AC unit operates similarly to Cool mode, but the fan speed is automatically reduced to low to enhance moisture removal and dehumidify the supply air more effectively.

In Auto mode, the iZone system automatically switches between Cooling and Heating to maintain the desired temperature based on sensor readings.

An Auto Mode Dead Band is applied to prevent frequent mode changes. This setting can be adjusted via the iZone AC unit configuration settings.

It is recommended to set the dead band to approximately ±1.5°C from the set point (SP ±1.5°C) for optimal comfort and system efficiency.

Preventing Mode 'Hunting' (Auto Mode Logic)

To prevent the system from constantly switching between cooling and heating (a condition known as "hunting"), the iZone system uses a majority-based control strategy when operating in Auto mode with "Zones" as the control source.

How It Works:

• The system will operate in Cooling or Heating based on the majority of Climate zones requesting that mode.

• If the majority shifts from one mode to another, the system will only switch modes when at least one zone in the new majority has exceeded the Auto mode dead band.

• If there is no clear majority (equal number of zones requesting cooling and heating), the system will continue operating in the previous mode.

• When zones not aligned with the current mode detect supply air in the opposite temperature range (via the CDTS sensor), those zones will close to avoid discomfort.

Example (See diagram below):

1. Initial State:

   • 3 zones require cooling

   • 2 zones require heating

   • The system starts in Cool mode.

   • The 2 heating zones close when the CDTS sensor detects cold supply air.

2. Majority Shift:

   • One cooling zone reaches its set point and switches to heating.

   • Now: 2 zones require cooling, 3 require heating.

   • The system switches to Heat mode, provided at least one of the heating zones is outside the dead band.

   • The 2 cooling zones now close when the CDTS sensor detects warm supply air.

3. Back to Cooling:

   • The heating zones reach their set points.

   • All 5 zones now require cooling, but remain within the dead band, so the system stays in Heat mode.

   • Once any cooling zone drifts outside the dead band, the system switches back to Cool mode.

   • The heating zones close when the CDTS detects cool air.

Open

The Unit Auto Off feature can be enabled or disabled via the iZone AC unit configuration settings.

Functionality:

• When enabled, the AC unit will automatically turn off after a short delay if all zones are set to Closed.

• If the AC unit is manually turned On while all zones remain Closed, a message will appear on the screen informing the user that all zones are closed and the unit will shut down shortly.

• If a zone is immediately opened or switched to Climate mode, the AC unit will continue to operate normally.

• If no zones are opened or set to Climate within the delay period, the system will proceed to automatically power off the AC unit.

Important Note:

When Unit Auto Off is enabled, the AC unit will not turn off if zones are in Climate mode, even if all zones are satisfied and have temporarily closed. This ensures continued monitoring and readiness to respond to temperature changes.

This is a unique feature of the iZone system and must be enabled in the AC Unit Configuration to operate.

To take full advantage of this feature, the system must include:

• A supply air sensor (CDTS)

• Zones configured for temperature control (Climate mode)

How It Works:

When enabled, the iZone system monitors the temperature of the air in the ductwork and uses it to help bring zones closer to their set points-regardless of the AC unit’s current mode.

Example – Summer (Cooling Mode):

• The system is running in Cool mode.

• All zones reach their set points and the compressor cycles off.

• Over time, the air in the ducts warms up due to the heat in the roof space.

• If any Climate zone is below its set point, the iZone will open that zone and use the warmer duct air to gently raise the room temperature, reducing the need to restart the compressor.

Example – Winter (Heating Mode):

• In Heat mode, once all zones are satisfied, the system cycles off.

• The duct air begins to cool, especially if located in a cold roof space.

• If a Climate zone is above its set point, the iZone may open that zone to allow the cooler air to bring the temperature down.