101 or sensor 103 an appropriate or predetermined temperature range denoted as the range between temperature limit values t 1 and t 2 is also illustrated this temperature range between t 1 and t 2 may be the appropriate temperature range for items contained in a refrigerated unit or container limits of temperature of the unit or container limits determined through an international or local standard or any combination thereof as further illustrated as the detected temperature is relatively close to or below the lower temperature limit t 2 denoted at time value 301 defrost operations are enabled the defrost cycle involves using a heater 120 e g a resistor heater to thaw ice from the evaporator coil during the defrost cycle defrost energy consumption of the system 100 is measured the calculation of defrost energy consumption generally may be represented by power consumed e g watts by the heater 120 times the time to complete the defrost cycle e g seconds upon calculation of the defrost energy consumption a next appropriate time delay between defrost cycles may be determined by controller 110 fig4 illustrates a relationship between defrost energy consumption in watts u00d7 hour wh or watts u00d7 seconds ws versus time delay to the next defrost cycle in minutes.