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Identify Energy Savings by Monitoring On/Off Switch Control System Cycling
By: CAS Dataloggers
In equipment that uses simple on/off switches for control, frequent cycling can waste money and reduce life in many systems including:
For example, CAS DataLoggers supplied an Accsense Electrocorder EC-1V data logger to monitor a customer's oil-fired central heating system in their office building over a period of 6 months.
This data shows that over this time 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 barely gets a chance to come up to temperature and does not add much heat to the building environment. Most of the fuel is used to start the boiler and the energy is wasted warming the boiler 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 the problem?
A. Use a delay 'on' timer.
The customer installed a timer that provided a 10-minute delay between the thermostat activation and the boiler trigger event. If the thermostat was deactivated during this window the signal to the boiler was reset. This eliminated cycling when the thermostat activation signal was less than 10 minutes. The assumption was that cycle requests less than 10 minutes duration are false requests for heat caused by air motion within the building.
After installing the delay timers, the customer used two Accsense Electrocorder EC-1V Single Phase Voltage data loggers to monitor their new switch control system over a defined period and found:
Since the boiler on signal is subject to a 10-minute delay, when the demand is due to a real temperature drop, the office 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 back up to the set point of 70°F, therefore using more energy. However, even accounting for this, our customer still achieved an energy savings of 52%!
For more information on Electrocorder Data Loggers, and closed-loop control systems, or to find the ideal solution for your application-