Variable flow rate for AirLoopHVAC:UnitaryHeatCool:VAVChangeoverBypass

[lymereJ]

General Summary

This request adds on to the list of requested improvements provided in #8122. The AirLoopHVAC:UnitaryHeatCool:VAVChangeoverBypass can only run at a constant flow rate. Commercially available systems can run at variable flow rates (down to a specific turndown ratio).

Detailed Description

I tried using an EMS to control the fan flow rate of the existing unitary system, it worked, but the bypassed flow rate was not updated based on that new flow. As an alternative, I setup a model with a "dummy" zone (adiabatic envelope, no internal gains, and no OA requirements) served with a VAV (no reheat) terminal and controlled its minimum air flow fraction using a schedule and an EMS. It worked reasonably well, although I did notice a bit of discrepancy between the dummy zone temperature and the system supply air temperature.

Here's a publication on these systems:
https://www.trane.com/commercial/north-america/us/en/about-us/newsroom/blogs/the-evolution-of-changeover-systems.html

Possible Implementation

No response