I assume you will be doing HVAC and Plumbing:
For "applied HVAC piping" (boiler/hydronic, chilled water): get all of John Siegenthaler's books. Also he has a CD, which has dozens of his excellent articles.
For fluid flow fundamentals: get "Cameron Hydraulic Data". It may be out of print, but find a used one online (ebay, etc.) It is the most practical fluids text I have ever seen.
HVAC Cooling/Heating Fundamentals: Trane and Carrier used to publish handbooks - approx 1-inch thick. These books are very practical, but also well grounded in theory. Maybe they are available used, or you could check with Trane & Carrier sales representatives. Also, you might get a used copy of Faye McQuiston's HVAC textbook. It is (was?) a text used for undergraduate, but it is superior: many clear problem examples, reference charts & tables, etc. - a must-have book.
Study all these books. Read them from cover to cover. Then you'll know where to go when you're on a deadline.
Plumbing: check out the books on the ASPE website. They are the best.