Cooling towers help release pent up energy from a building by exposing the loop water to the outdoor environment. Depending on your geographical location there may be 3 primary parts to a cooling tower (at least from the temperature control point of view). To control these three pieces of equipment may take from 1 to 4 Smart Nodes running custom logic depending on your specific application.
To control the tower fan which is often acts as the first line of defense against rising loop temperature. Leveraging increased air flow to cause increased heat loss. Using 75F custom IFTT logic we can set the Tower Fan to stage on and off based on loop temperature. When the loop rises above the specified temperature, stage on the fan. If you have two stage fans or VFDs the same principal will apply X the number of stages desired.
If the tower fan can't alone keep the loop temp down then introduce the Spray Pump to release more energy using water itself. In the same way we stage the tower fan, we will use IFTT logic to stage the spray pump based on loop temperature.
In cold climates the isolation valve is a huge energy saver in the winter time. Instead of constantly subjecting the loop temperature to the outdoor environment, often 0F where I'm from and using the boiler to regenerate the nuisance lost energy. Isolate the tower altogether since the building is losing enough energy conditioning the zones up to temp that the cooling tower is only costing you energy. We like to control the isolation valve with a combination of loop temperature and OAT.
Building loads can sometimes be unpredictable and it may be necessary to cool the loop for short periods of time even when it is cold outside. In this way 75F typically will open the isolation valve to the tower if 1. The OAT is > some temperature that varies by building, or 2. When the loop temp breaches a critical high limit.
Safeties - This article covers the basic theory and mechanics behind a 75F implementation with a cooling tower. If you are interested in how safety measures and care must be taken when creating these custom rules so that equipment does not and can not be harmed.