The laws of physics: You can’t get a ticket for violating them, right? Maybe you can: in the form of an electric utility bill. And, as Scotty says, “ya can’t change the laws of physics”.
EES engineers found a way to stop paying the physics tax in a client’s cooling tower water setpoint. Quick test: what happens when your condenser water setpoint is 10 degrees lower than the wet bulb? Quick answer: your towers run at 100% and make no progress on their task.
After a management change, whereby EES engineers were allowed to alter the condenser water setpoint, we did. We always wanted a condenser water temperature of 73 degrees, optimal for the chillers and very smooth. The towers worked nicely instead of the way they worked when we started.
After the last heat wave, where the wet bulb was 79 to 83 every night, we opted to change the setpoint controls. We set them to be the higher of 73 degrees or two degrees above wet bulb.
The result was no difference during chiller operation (tower fans ran at 100% during the heatwave), but there was a major difference over night. The old way, the towers tried to make 73 degree water, which they could not, so the fans ran at 100%. The new way, the tower tried to make 80 degree water, which it could and within ½ hour, the fans shut down.
Calculations show that two towers at 35kW, plus controlling chilled water pumping and condenser water pumping over night, we saved an additional 70 kW. This comes to 105 kW for 10 hours, or 1,050 kWh per day, saved during the heat wave. Using the average rate of $0.13 $/kWh, this is a savings of $136.50 per night during the heat wave.
Savings during non-heat-wave times are still impressive, at about 70kW + 22 kW from the tower for 10 hours, yielding 920 kWh on a normal night, or about $119.60 per night.
See here the straight line up to the 31st shows the kW of the tower fan. Then the change, and it dropped to zero overnight. After a couple of days the heat wave ended and we resumed more typical control.
If we have 20 nights of heat wave, then the total savings for June, July, and August would be in the neighborhood of $11,300 saved over the hottest three months.
Automation, done right and with a purpose, can and does save operational dollars. Contact EES to have us optimize your system today.