3 Minute Read

| How it Works

The VAV Fully Modulating AHU System profile uses advanced sequences that are fully outlined in ASHRAE GPC 36. For a comprehensive understanding of how GPC 36 works, please read the document in full. Here we will discuss some basic field level understanding for a quick and dirty understanding of what should be expected.

Cooling Mode - The system will call for cooling when there are enough requests for it. The AHU will maintain a SAT which is reset based on OAT. So in the fully modulating profile the AO1 will modulate up and down to maintain the cooling SAT that is set by the # of requests. 

Heating Mode - The system will only go into heating mode if all zones are requiring heating. This will typically be during the morning warm up or after any major setpoint changes. When the unit needs heating AO3 will scale up due to the load and follow the heating sequences as if it were a Fully Modulating DAB unit. 

Recirculation Mode -AO2 will modulate up and down to maintain the static duct pressure setpoint based on the number of requests received from the zones. 


For the basics on Trim and Respond logic, please reference either GPC36 or our outline here: Trim and Respond Overview


| Wiring

| Configuration

Once you've configured the system profile as a VAV system, the sequences for VAV applications in GPC36 will be followed. What you will need to do is select a few specific configuration parameters that define the physical characteristics AHU. 



Relay 3 -Fan Enable. Closes when the Fan is set to circulate at any speed. If your fan needs a dry contact, please review the notes for the dry contact jumper. 

Analog-out1 -Cooling output scaled to the cooling load. 0Vdc = No cooling demand. 10Vdc = Max cooling demand. 

Analog-out2 -Fan Speed. Scaled based on the demand for pressure. 

Analog-out3 -Heating. Output scaled to the heating load. 0Vdc = No heating demand. 10Vdc = Max heating demand. 

Analog-out4 -Composite. This assumes no demand at the mid point. Very configurable. (E.g. 5Vdc = No demand. 0Vdc = Max Cooling demand. 10Vdc = Max Heating Demand) 

Analog-out1-3 at Min and Max -Set the minimum output at minimum load or maximum load. Typically synced with your equipment. 

Analog-out4at Min and Max Here you need to be careful because it is so customizable. Your Min can be more than the max values depending on unit configuration. What you need to know is that however you set this up, must be matched up with your unit. (A common example would be an RTU where you are setting up a DAT reset. AO4 @ Min Cooling = 5, AO4 @ Min Heating = 5, AO4 @ Max Cooling = 0, and AO4 @ Max Heating = 10V. Then you'd need to sync your DAT setpoints at the RTU to match. 0Vdc = 55F and 10Vdc = 100F)

Test Signal - This is used for troubleshooting and testing the equipment if the configuration and the field setup are in sync, and CCU is communicating properly with the controlled equipment. Also at any point, you can override the value of the output the algorithm decides. 

We can use the test signal for relays to turn them on or for analog out to ramp up and see if the equipment works according to commands from CCU.

Test Signal Time Out - once enabled it will be active for an hour if the screen is not changed, after an hour of no interaction on the screen.  zone screen displays and the test signal will be OFF.

If the screen changes from the test signal configuration screen it will be timed out in one minute (time for the algorithm to run next).

Note: The test signal for modulating output is in deci volts ranging from 0.0dV to 100.0dV.




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