I have learned a lot about air conditioner systems over the years with maintaining several different server rooms and I would like to share some pointers. This is from the small business world when you see many off the shelf systems installed because someone just thought buying an air conditioner was as simple as this price looks good with out matching the BTU need and supply.

My personal recommendation for any server room cooling is pairing a traditional unit with a smart mini split system. With this approach you get two different key strengths and some fault tolerance. A traditional unit is good at displacing heat, and most mini splits normally have smarter self-control systems that can throttle the condenser side fans in the winter and are smart enough to avoid from freezing up. Running an air conditioner in the wintertime does sound strange but server rooms expel heat all year round and still need cooling in the winter.

When an air conditioner evaporator coil starts to freeze up it’s the begging of a death sentence for the unit and it many of the cases I have seen could have be avoided. The thing to keep in mind about all air conditioner systems is what the professionals call the “Delta T.” This is the temperature difference from the supply air and return air. On average when Delta T is between 16°–22° F, your system is working properly.

When I setup any server room monitoring devices, I like to track the overall server room temp and the AC Unit output temp. This way I can watch my AC systems average Delta T over time and if I see my average start to drop. Then I know it is time to call for service repair before my AC system fails and I am forced to use box fans in the server room door trying to cool the room down.

I keep seeing the mistake of setting the AC unit to something like 60° F and the server room temp is stuck at 70° F. This is because the BTU’s of heat from the servers are at the saturation point of the AC system capacity. The danger of this situation is the thermostat never gets to the goal and keeps the compressor running causing the evaporator coil to start to freeze up. At this point the AC Unit starts to damage itself and can create refrigerant leaks. The unit needs to cycle on and off to thaw itself out.

This is where monitoring the room temp and the AC Unit output temp comes in handy to find the correct balancing point. You can start with the thermostat set to 60 and move the thermostat up until you see the unit make its temperature goal and shuts off the compressor and the AC Unit output temp logging shows the temperature rise up to the room temp until the thermostat triggers the compressor again.

I have found a unit that could be set at 68 in the winter, but I need to change it to 71 in the summer because other building seasonal variables effect the saturation point. This could also be adjusted but getting approval for additional or upgraded cooling capacity purchase request and knowing details like this are very handy when capital expenditure for AC systems are not yet an option.