A: This is actually a much bigger idea than just psychrometrics — Q = ṀΔH crosses all boundaries: steam, refrigerant, air, whether or not there's phase change. The 4.5 × CFM × ΔH rule of thumb comes from substituting a standard air density of 0.075 lb/ft³ into the foundational equation, so if density deviates from standard (like hot humid air), that rule of thumb can be off. You can always go back to the foundational equation and substitute ρ × Q for mass flow rate to stay precise.

A: Yes, that equation is fine to use — the reference handbook has embedded assumptions about air density that make it work without explicitly using air conditions. I agree it feels odd not to check the air, which is why I solved it differently in the video, but both approaches should give very close answers. Know both methods so you have two options.

A: The magic phrase to watch for is 'cooling tower ton' — only reach for the 15,000 BTU/hr figure if the problem specifically uses that phrase; otherwise stick with the standard 12,000 BTU/hr cooling ton. That 15,000 BTU/hr rule of thumb just scales the cooling load up by 25% to account for compressor heat rejection, and it's a quick industry shortcut for pre-selecting a cooling tower without detailed chiller analysis. For this problem it just says 'tons,' so I used 1.2 million BTU/hr, not 1.5 million.