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Timed devices

As a result of electronic technology, there are many cost-rate controls that regulate the cooling cycle. These are based either on a real (hours) time or after a specified time. For example, clock thermostats function as primary controls, turning the switch on and off. They also act as a secondary operating control, when they adjust the settings for the system according to real time(s), set the occupant. Digital clock thermostats made it very practical to even a small residential systems. Many devices allow the user to enter at least two temperature settings for each day of the week.

Defrost timers regularly used in the refrigeration equipment to defrost the evaporator to control security shuts down the operating system. This system allows to achieve a reasonable compromise between efficiency and reliability.

Some air-to-air heat pump systems also use timed defrost cycle to keep an open coil free from excessive accumulation of ice.

Other, as shown in this simplified scheme, combine time with temperature, like access control, to determine when starts the defrost cycle and stops.

When the compressor is running for a certain time, and if the outdoor temperature is below the set point, for example, 30 F, defrost logic energizes the reversing valve. Please note that both conditions must exist. At that time, the heat pump is switched at cooling mode to remove the formation of frost on the open spiral.

Compressor cycle timer is often used to protect the compressor from "short Cycling." That is, quickly turn on and off. Short Cycling can lead to damage of the compressor. Cycle timer provides a time delay that prevents the compressor immediately restart after its shutdown. Delay in five to seven minutes is typical. Cycle timer shown in this simplified scheme acts as a temporary switch. It starts a countdown when the compressor is switched off. At the end of the delay period, it snaps to the contactor. This closure makes the compressor for the next thermostat "call". If the thermostat calls for the compressor in the delay time cycle, the compressor will not turn on until the delay in the cycle. Many cycle timers use of electronic timing schemes that allow the timer to compensate for power failures...

 
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