I really don't think that personal computer choice is relevant to your course or to your future job prospects. If you really need a personal computer for your coursework then just get the cheapest model available and spend the rest on books that are required reading for your course. You wont be...
http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/Ethylene_Vapor_Pressure.GIF
The vapour pressure graph at the end of this link should help illustrate Sheiko's point.
If you are using refrigeration then watch out for the phasing out of R22 refrigerant. Make sure you have a system that can eventually use something else. A new system is unlikely to get a supply of R22 (in the UK anyway).
Correction - The Barrow-in-Furness outbreak was 2002 and not the late 1990s.
http://en.wikipedia.org/wiki/2002_Barrow-in-Furness_legionellosis_outbreak
I think you need to consider getting an external contractor in who specialises in Legionella control ASAP. If you have biofilm developing and also have water spray then you are at serious risk of causing deaths among your workforce or the public due to Legionnaires disease. This happened in...
