Telecom shelters, data huts, and control buildings hold electronics that make heat around the clock and don't tolerate overheating. That's why most carriers and utilities won't rely on a single air conditioner. The usual answer is two wall mount units on a lead/lag controller.
What N+1 means
"N" is the cooling capacity the shelter needs. "N+1" means you install one more unit than you need. For most shelters that's two units, each able to carry the full load by itself. If one fails, the other keeps the shelter at temperature until a technician arrives.
What a lead/lag controller does
- Rotates the lead unit on a schedule so both units get similar runtime and wear.
- Brings on the lag unit if the space temperature keeps rising, for example on a heat wave or when equipment load grows.
- Switches to the backup if the lead unit fails.
- Sends alarms for high temperature or unit failure to your monitoring system, so you know before the equipment does.
Sizing a redundant pair
- Calculate the shelter's total heat load, mostly equipment watts × 3.41 = BTU/h, plus the building shell and solar gain.
- Pick a unit size that can carry the full load by itself.
- Install two of them.
For example, a shelter with about 30,000 BTU/h of load would typically get two 3-ton units, such as a pair of SAH1036AA100N or economizer SAH1036AA100C units. See our shelter sizing guide for more detail.
Economizers and redundancy work well together
Shelters need cooling all year. With economizer units, much of the cool-weather load is handled with outside air, which cuts compressor hours on both units and stretches service life. Our economizer models can run in economizer mode down to -40°F outside.
Browse matched pairs in our Wall Mount HVAC Units collection.
Questions about your project? Call 509-379-7075 or email sales@eubankwallmounthvac.com.