I wrote a performance spec for another HVAC designer to design a mechancal room to the following specifications:
"0.5 Air Changes per Hour as a minimum, or as required to maintain summer design temperature, or as requiuired by the IMC."
I belive the 0.5 ACH came from B62.1 closest similar facility so this is the absluote minimum - this may be considered to be achieved through natural ventilation through door and window cracks, but need to verify.
The summer design temperature was 104F which is the maximum that is allowed for an equipment room before electrical components start to malfunction. And IMC is usually governing code for most localities so it must also be adhered to.
The 104F indoor maximum allowed summer design temperatuere will govern in most cases. So the design will be to remove the heat input by the pump motors and other heat generating items in the room like MCC's and starters if in the same room. Need to get the actual heat input from all electrical items from vendors or from stadard efficiencies quoted (heat input from electrical equipment is always stated as a % of output such as for a motor % odf rated horsepower) in such sources as ASHRAE. Add this to the external heat gain from outside, infiltration, etc. So this will be a standard HVAC caculation that can be done manually or on computer,
If maitining a maximum of 104F is ok then may get by with exhaust or inlet blower ventilation only without HVAC unit. The ammout of air would be just enough that at that flowrate and delta T of ventilation air the exhaust air is at 104 F considering all heat is absorbed by the specific heat of the air - and highest summer design temperature per ASHRAE.
If HVAC is required for to maintain 104F or a lower design temperature if requested by client, usually a mini-split inverter duty variable refrigerant flow unit is used such a manufactured by Carrier, toshiba, mitsubishi, etc.
You also need to decide on your winter indoor design temperature - we use 50 F which we use mostly for mechancal room. Heat input may be required.