Identify Energy Savings by Monitoring Closed Loop Control System Cycles
By: CAS DataLoggers
Frequent on/off cycling can waste money and reduce system life in many closed loop control systems, including:
• Pressure-controlled compressor systems
For example, CAS DataLoggers supplied an Accsense Electrocorder EC-1V (https://www.dataloggerinc.com/
This data shows that over the recording period the thermostat requested 1363 instances where the boiler came on for 2 minutes or less, and 255 events 2 to 4 minutes in length. Adding up the cumulative time that the boiler ran, our customer found that for 33% of the time, the boiler was only on for a period of 10 minutes or less.
This data is significant because for the short duration 'on' cycles the boiler does not add much heat to the building environment. Most of the fuel is used to start the boiler and the energy bleeds of as heat loss before it can be transferred to the environment. Analyzing the data shows that if these short duration events lasting less than 10 minutes can be eliminated, an estimated minimum savings of 30% should be realized.
Q. How do you solve this problem?
A. Use a delay 'on' timer.
We subsequently developed a 10-minute delay between the thermostat activation and the boiler trigger event being transmitted which will eliminate all cycling that is less than 10 minutes. The cycle requests that last less than 10 minutes are false requests for heat.
Since the demand signal is subject to a 10-minute delay, when the demand is a real temperature demand, the temperature continues to fall slightly during the 10-minute delay. That means that when the boiler comes on, it takes slightly longer to bring the office building up to the set point of 70°F. However, even accounting for this, our customer still achieved energy savings of 52%!
The obvious disadvantage with this setup would be a delay between the demand and the supply for heat. However, the data shows that 56% of the demands for energy were not real temperature demands but were just the result of the thermostat oscillating (on/off) around the temperature set point. The customer saw no noticeable effect on internal office temperature during the trial of the timer. As an added benefit, this reduction in run time and in the number of 'on' cycles by has increased the effective boiler life.
For more information on Electrocorder Data Loggers (https://www.dataloggerinc.com/