We're in the process of putting together a proposal to retrofit 3 rooftop mounted 35 ton DX AHUs with economizers. The system will be converted to operate with a new air cooled heat recovery chiller and chilled water coils will replace the DX coils in the AHUs.
This is a VAV with HW reheat system, so the recovered heat will be used throughout much of the year in place of or as a supplement to the boiler. Now what I'm wondering is if in lower ambients there's any point at which it would make sense to shut down the mechanical cooling in favor of free cooling (but no heat recovery).
I did some looking online and found some mention of heat recovery and economizer coordination but no specifics of how this would be implemented.
Anyone have experience with this?
Let me know if more detail is needed regarding the existing and proposed system arrangement.