As 3DDave has pointed out, I think there might be some confusion of the concept of a DOAS system. DOAS usually implies 100% fresh air, which in turn implies that much air being replaced or exhausted. The only possible exception that one could argue to exist would be if the DOAS provided fresh air to multiple spaces and that some spaces exhausted only 90% while some other space (like a restroom) made up the difference in its exhaust. Could you explain the system as a whole a little more?
Unfortunately, I don't have any experience with HAP, so beyond trying to clarify the question, I can't help much.
