Computer cooling equipment for computer equipment comprises: a primary heat transfer circuit; a secondary heat transfer circuit containing a secondary heat transfer fluid, a secondary condenser cooled by the primary heat transfer circuit and a secondary evaporator for cooling the computer equipment; and is characterised in that the secondary heat transfer fluid is a volatile fluid. The secondary heat transfer fluid may be carbon dioxide. The cooling system is of particular use in power hungry applications such as cooling of computer servers, particularly of blade servers as it can produce a heat load dissipation of up to 100 kW, compared to 10 kW or less using conventional systems. Heat exchange cabinets, air conditioning systems and building elements using a secondary heat transfer fluid which is a volatile fluid are also disclosed.