Heat Recovery Not Working

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I have heat recovery set up on my DOAS air loop.

But when I look at the html report, it is showing no heat recovered.

This has stymied me in the past... sometimes heat recovery works fine in my model and I see numbers in this table, sometimes I can't figure out why its not recovering any heat. I have tried with and without SPMs on the incoming air stream.

Just wondering if anyone has any general guidance on how to set up and troubleshoot heat recovery so I can reliably get it to work.