How important is ventilation in a computer room in relation to the workplace?

I am by no means an expert on this topic but much depends on the size of the computer room, the amount of equipment you have in there, and whether you have air conditioning. Obviously, in a confined space with no ventilation or cooling, the temperature of the computer room is likely to rise, and it's the temperature that is the crucial parameter, not ventilation per se; and just as humans function best in an environment kept at around 21 degrees C, so too devices. General recommendations suggest that you should not go below 10°C (50°F) or above 28°C (82°F). Although this seems a wide range these are the extremes and it is far more common to keep the ambient temperature around 20-21°C (68-71°F). Whether you can maintain temperature with the use of ventilation alone or whether you will need some form of cooling will depend upon your particular circumstances. You will find more information here Recommended Server Room Temperature.