AHU Configuration

This section covers how to view and edit the settings of a typical AHU.

To view and edit an existing AHU's settings, click the AHU icon on the Floorplan, in the Temperature Layer.

The AHU Control Screen will appear.

AHU Info Panel And Advanced Panel

The AHU Info Panel And Advanced Panel are used to manage the AHU setup. The Info Panel is found in the bottom-left corner. The Advanced Panel is accessed via the Advanced button at the bottom of the Info Panel (moderator password required). The Advanced Panel contains all of the settings available in the Info Panel plus some further settings.

The settings of the Advanced Panel are as follows:

Min Fresh Air	Voltage setting on the dampers to ensure that at least some fresh air still comes in
CO2 Min Fresh Air	If CO2 Setpoint threshold is reached, this value sets the voltage to apply to dampers (increase value to open dampers more)
Min Outside Air	Minimum temperature at which dampers can open fully
Max Outside Air	Maximum temperature at which dampers close fully so that internal air can be cooled
Return Air Setpoint	The desired temperature of the air leaving the system
Heating Hold Off	Re-circulation Units: Acts like a deadband and is the number of degrees below setpoint where energy is saved by not allowing the heating element of the AHU to operate. Fresh Air Units: Even within this deadband, a minimum voltage will be supplied (see Fresh Air Min Volts) if the outside air falls below the Fresh Air Min Setpoint (default = 15°C)
Cooling Hold Off	Re-circulation Units: Acts like a deadband and is the number of degrees above setpoint where energy is saved by not allowing the cooling element of the AHU to operate. Fresh Air Units: If the outside air temperature is above the Fresh Air Min Setpoint (default = 15°C,) this setting will act as normal and hold off cooling until required. If the Outside Air Temp is below the Fresh Air Min Setpoint and the return air is within deadband, the system will fall back to Fresh MAir Min Volts until it requires heating or cooling
CO2 Setpoint	Used to control maximum parts per million of CO2 – this determines how the dampers work to make sure that fresh air comes in
Default Ctrl Time	Length of time to wait before making further changes
Air Flow Suspend Time	Shuts unit down if no air flow detected for more than the set value
Fan RunOn	Runs the fans for the set length of time after heating coils are turned off, to avoid overheating
Fan Modulation Delay	When heating or cooling has been enabled, the inverter-controlled fans will run at Fan Max Volts. When the heating or cooling turns off then the ‘Fan Modulation Delay’ time is how many minutes the fan must remain at Fan Max Volts before being allowed to modulate again
Start Up Delay Time	Lets fans run for the set time before control begins
Fan Max Volts	Sets maximum speed for fans (as long as they are controlled via analogue 3-way outputs)
Frost Heater Volts	The value in volts that the AHU Heating will be running when Frost Protection Mode is active
Frost Cooling Volts	The value in volts that the AHU Cooling will be running when Frost Protection Mode is active
Frost Setpoint	The threshold below which frost protection is activated
Fresh Air Min Setpoint	If the outside air is below this setpoint then the AHU will apply the Fresh Air Min Volts rules to Fresh Air Units. This is greyed out in Re-Circ Units
Fan Enable in Frost	Allows the fan to run when in Frost Protection mode
PI Control	PI state (Off, Heating only, Cooling only, or Heating and cooling)
Heating PI Ctrl Controller Gain	A static value that determines the proportional additional value to the running total gain
Heating PI Ctrl Integral Sample Time	How often the PI Ctrl algorithm will be recalculated
Cooling PI Ctrl Controller Gain	A static value that determines the proportional additional value to the running total gain
Cooling PI Ctrl Integral Sample Time	How often the PI Ctrl algorithm will be recalculated

The Advanced Panel also allows the type of AHU to be specified via radio buttons:

• AHU: Re-Circulation Unit
• AHU (Fresh Air): Fresh Air Unit

Edit Points

The main part of the AHU screen contains a diagram to illustrate the setup of the AHU. To edit the reference points that are used to control the AHU, click the Edit Points button in the top-left corner of the diagram. The screen will then change to look like the one shown below.

As shown, a series of dropdown menus appear that allow the user to change the references (or control points) that are used to control the AHU. Although there will typically be no need to change these settings after the initial setup, there may be occasions where changes to the Outside Air Temp reference or the Space Temp references are required.

Control Point Graphs

For fine control over the fan, heating, cooling and dampers, use the relevant Fan Speed Control, Heating Control, Cooling Control and Damper Control buttons in the main diagram. An administrator password (not the same as the login password) is required to change the settings, but it's possible just to view the settings without entering the password, by clicking the View Only button. Some example graphs are shown below.

The graphs can be modified by dragging the control points (black circles). Whenever the cursor hovers over one of the points, the value to which that point refers is highlighted on the graph. The corresponding wait time for that point on the graph is also highlighted in the relevant box below the graph.

Below the wait times is a box that confirms the ranges that apply to the currently highlighted control point on the graph. The values indicate the lowest and highest temperatures that apply to the currently highlighted control point and the resulting voltage that will be used for that control point.

Any inadvertent changes to the settings on these screens can be reversed by closing the window without clicking the Save button. There is also an option to go back to the default settings, via the Reset To Defaults button.