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MarketManager » Modeling HVAC Systems
Q: I would like to model the addition of a VFD on my AHU, but only want to apply it during night hours. How do I do it?


This is almost what we had in mind when we created HVAC standby. HVAC standby is designed to cycle fans to meet setpoint during hours in which the fans are scheduled off in the HVAC system form. So, instead of a constant volume of supply air during night hours, only a minimum supply air amount will be introduced into the zones.

1. In the System form:

    1. in the HVAC Schedules field, make sure that you have scheduled your day run hours correctly.
    2. in your HVAC Operating Modes fields, make sure that you have the hvac fans scheduled for day only, and off when you want the fan to be on the VFD.
    3. click on the HVAC Standby for summer and/or winter, depending upon which season(s) you want this control strategy to operate.

2. In your Supply Fan | Detail form. Change the Fan Volume Control to Speed. This will change the part load ratios for a VFD. Do the same for your return fan.

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