fan operation of air loop to follow Heating/Cooling Thermostat Schedules

asked 2018-11-29 11:51:32 -0500

updated 2018-11-29 13:55:14 -0500

I'm having a hard time understanding setpoints and Availability Managers for controlling fan operation time in Packaged rooftop or Air loops. There is no fresh air coming into my building, so the fan operation should only work to meet heating/cooling setpoints within zone thermostats. I've played around a bit with AVM temperature Turn Off, this seems to do something, although it is not intuitive which node I should be picking and what temperature the turn off should be set to, in addition the AVM turn off would work for cooling season and not for heating season, or vice versa, depending on which AVM turn off is chosen.

It seems like this would be the simplest operation of a rooftop unit. Example, when there is a call for heat -> turn the fan on, when there is a call for cooling -> turn the fan on, when there are no thermostat calls -> fan remains off.

I've looked through the definitions for Setpoint Managers and AVM, so I am a bit familiar with what they are capable of. Below are some screenshots and my model.

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RTU 8 - Lobby: Air System Fan Energy image description

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This is not an answer to your overall question, but if you plot zone air temperature, supply air temperature, off coil temperature on the same graph as you've shown above, you can determine which node your setpoint corresponds to. Right now you are telling your system to shut off if some temperature exceeds 23.8C...if this is your zone air temperature, that's probably not the control strategy that you want to employ.

When you say there is no fresh air coming into the building, do you mean that you've deliberately set all ventilation rates to 0 cfm of OAV?

jbatt's avatar jbatt  ( 2018-11-29 13:52:09 -0500 )edit

@jmbattis when I say "there is no fresh air coming into the building" I mean that there is no "design spec outdoor air" and therefore no reason for the fan to be running.

re-measure's avatar re-measure  ( 2018-11-29 14:34:00 -0500 )edit

Okay so 0 outdoor air volume - great we are on the same page. Have you confirmed that it's functioning according to your intent? You can call out the mass flow rate at the outdoor air node to see if it's zero at all times.

jbatt's avatar jbatt  ( 2018-11-29 14:41:46 -0500 )edit