For years, I worked for a mechanical contracting company that shifted its business plan from design-bid-build (DBB) project delivery to design-build (DB) project delivery. The move became very obvious as the optimum way to provide HVAC services. The company believed it could provide a better product, establish repeat business opportunities, achieve job satisfaction, and be more profitable than chasing the very competitive and not very rewarding plan and spec DBB arena. The same can be said for consulting HVAC engineers who receive their contracts via an architectural firm rather than be the lead on projects.
To just highlight why DBB is not rewarding to an HVAC contractor and HVAC engineering firm, one can list the following negative points: