Your equipment controls can sometimes tell you some good stories if you observe carefully. And sometimes tell of problems.
Consider two thermal mass cycling air dryers installed in a foundry. Thermal mass cycling dryers are designed to reduce the energy consumption of the internal cooling system by turning off and on (cycling) the refrigerant compressor when appropriate — for example when the associated compressors are turned off, or under conditions of low moisture loading. This saves energy over non-cycling dryers, which consume near full power at all times, even under light loading.
Fig. 1 shows the display of one of the cycling dryers; here, the dryer has only been running 20% of the time, saving about $6,800 per year. This delighted the maintenance manager when he read the control.
The second dryer, installed under similar conditions, only showed savings of 65%. This seemed a bit strange … until some measurements were performed, which showed the input temperature to the air dryer was elevated due to a problem with the compressor cooling. Every 20° F increase in inlet air temperature increases the moisture load on the dryer by a factor of near 2. The dryer responded to this increase and increased its power. Reading the controls helped discover this problem.
The cooling problem was fixed and it wasn’t long until the dryer was saving power as expected. It is important to monitor equipment controls to ensure expected operation.
