I have a system which has a tempered air damper and a heat exchanger. The system does not have an dedicated outdoor air system (DOAS) which is confusing me. I am under the assumption that a heat exchanger requires a DOAS.

How can I have a heat exchanger without a DOAS? The image below includes the components of the system.

Is the tempered air damper a part of a make up air system (MUA)?