| Software Issue Notes AHUNV4c1 |
| Natural Ventilation AHU Controller |
The functionality of the standard AHU controller has been extended to allow this controller to be used for Natural Ventilation control.
Note this controller is NOT AVAILABLE in the system Master version because space used for system master code has been utilised for the Natural Ventilation additions.
Read these note in conjunction with the standard AHU issue notes, only the differences are documented here.
The conditions required to run the night purge have been extended to include checking that the Outside temperature exceeds a configurable set value (POUT found at C185 default 18.0 degC) at a configurable time (PHRS found at C183 default 16.0 hrs). This requirement is defined in the Max Fordam specification for Granta Park. Setting PHRS to zero disables this feature.
If night purge has run then the heating can be Held Off until after a specified time (HHRS found at C184 default 10.0 hrs) the next day. Setting HHRS to zero disables this feature.
The supply setpoint calculation is changed from that of a standard AHU, zero demand produces a setpoint equal to the space setpoint. The setpoint is modified from this value based on demand and MINS (cooling) and MAXS (heating). If driver rescale is set on the AHU the supply setpoint will modulate between 0 and the minimum rescale value. For example if the cooling is set to be rescaled from 50% to 100%, the valve will only operate for the latter half of the cooling demand, then the supply setpoint will vary between space setpoint and MINS for cooling demands from 0 to 50%. This is done so that the Damper Controller can be used to attempt to match the supply temperature requirements before the mechanical plant is utilised.
The Supply setpoint and the supply temperature are passed to the Damper/Fan controller which attemps to control both air flow and air temperature as best it can.
The AHU has a new configuration variable CMDE control mode, this is used to force the Supply Loops off (bypass), in this mode the Output equals demands from Space Loops which in turn in SPTY2 are the received demands from the Zone. CMDE can be set to 0 both loops Bypass; 1 heating controlled, cooling by passed; 2 Heating bypassed cooling controlled; 3 both loops in controlled mode.
This has been done to attempt to separate the room temperature control from the tempered air flow and temperature. The AHU acts essentially as an actuator to the Zone, with redirection to the heating driver in cooling. Note the valve will not open if the medium temperature is not suitable.