It will need ventilation or air conditioning, how you do it depends on many factors. It can have exhaust fans only but you have to provide inlet for make up air, or you can provide supply fans (whatever is possible and economical).
Per IMC, 406, ventilation rate should be no less than 0.02 CFM/SF for uninhabited mechanical space, to keep RH below 60%. So if RH stays below 60%, no ventilation is required. That's what I currently use for sizing ventilation of interstitial space.
Typically, I have seen temperature based operation, resettable, for exhaust fan with interlock to outside air damper.
urgross, I'll concede that this may be applied to the mechanical room, but with the way the code is worded, I will argue that 406 only relates to ventilation in regards to natural ventilation. An exhaust or supply system to allow 0.02 cfm/sf is allowed, but this is not ventilation, the same way as the exhaust out of the bathrooms is not ventilation.
I would like to argue that the examples given in the code section are in relation to rooms that will not be accessed, while the pump rooms and mechanical rooms will be accessed on a much more regular basis.
I usually treat the mechanical room as an electrical room and provide conditioning off of the HVAC system anyway, but while this is allowed, I'm not 100% sure it's an appropriate method.
406 refers to both natural ventilation and mechanical ventilation. I've seen both for interstitial space. Interstitial space is mechanical space which is unoccupied, but frequently accessed. I'm in interstitial space on a daily basis.
I've always considered mechanical rooms to be occupied space, or else the 6'8" required clearance should not be applicable (which is not applicable to interstitial).
urgross - there is a difference between occupied and occupiable. our approach is to treat mechanical and electrical rooms as unoccupied as this is generally the case. You will still have some form of air turnover in the space - be it natural ventilation, mechanical supply ventilation or exhaust.
for Mechanical rooms I generally look at the pump motor and other heat gains in the space to determine a ventilation rate. the same as you I have an exhaust fan controlling to space temperature with make-up from outside. via an OA damper. in some climates you need to consider treatment of the supply air if you have the risk of condensation.
You don't really need ventilation as it is not occupied.
In winter the pumped water is hot, but the room also needs to stay above freezing anyway., no need for cooling. the pump can handle the heat.
in summer, the pumps typically pump chilled water, so no need to cool.
I don't really see the need to do anything unless the pump room is next to a blast furnace or something that heats it up....
If it is freezing climate, you need to make sure it stays warm enough to not freeze pipes.
If your chilled water pumps and pipes are providing your cooling, you should probably be thinking about using insulation, as well as frequent mold inspection. Whether code says you need it at design, if your climate will provide temperature for cooling below equipment maximum operating temperature, then I would say common sense says you need it. For O&M of MER's, you will want to be providing a potential source of purge and LEV. Lots of welding goes on in MER's over the decades, and cleaning fluids and oils spill. Even better, mercury thermometers break.
I think it is funny that higher ventilation rate is required for space that cannot be occupied (such as interstitial) as compared to space that requires 6'-8" clearance for personnel routinely (on a set schedule, typically down to shift or hourly) in an MER.
I agree that IMC does require mechanical rooms to be ventilated. Occupied or not, the equipment in the room is generating heat, how much would be subject for a different thread I think. How the space is ventilated, be it natural or mechanical (fans), the code is not specific so is left up to the engineer to determine the best ventilation method.
Does it have to come from a conditioned space or direct from AHU? The mechanical room is not 'occupied' so no it doesn't need conditioned air.
However, where the building is located should be taken into consideration in deciding if conditioned air is introduced into the mechanical room or not. In the southeast US where humidity is a serious problem, it is common practice to add conditioned air into mechanical rooms to help control humidity. Down here, introducing unconditioned air into any part of a building creates problems if not done properly. Whether or not this practice is a good idea in other parts of the country/world, I don't know since most of my experience is in the southeast. Go far enough north and I wouldn't think so.
So my answer rra1990's question is "It depends." More information is needed to properly answer the question.
