Main Gas Furnaces
Gas furnaces is easy to operate and understand. Therefore, we will use it here to look in a traditional heating system. This type of a gas heater is used to heat millions of homes in the United States.
Figure 2-1 is a simple circuit needed to control the furnace with pear. Note the location of the fan switch, limit switch. Transformer provides low voltage to control the gas solenoid. If the limit switch open (shown in the locked position), there is no power to the transformer and gas solenoid can't energize. This precaution as limit switches will open if the furnace becomes too hot. When the thermostat is closed, it provides 24 V gas solenoid, which energizes and turns into gas. Gas is ignited by pilot lights and provides heat to the Plenum of the furnace. When the air in the Plenum reaches 120F (49C), fan switch is closed and the fan is switched on. Switch the fan provides the necessary 120 V fan motor.
Once the room is heated to the desired setting thermostat the thermostat opens. When it opens, gas solenoid de-energized, and in the spring action of electromagnetic causes it to close off the gas supply, thereby disabling the heat source.
When the Plenum on top of the stove reaches 90F (32C), fan switch opens, and turns off the fan. And the room cools down, causing the thermostat to again, and the cycle begins again. Gas solenoid opens to let gas and pilot light lights. The heat causes the temperature to rise in the Plenum above the limit switchР‚s switch settings and closes to run the fan. After the thermostat was satisfied, he opens and causes the gas solenoid to turn off the gas. The fan continues to run until the temperature in the Plenum reaches 90F (32C) and off of the fan when opened. This cycle repeats again and again to keep the room or the house at the desired temperature.
Hot-air furnace are Autonomous and self-enclosed units. They tend to be located within a building or a house. Their aim is to ensure that the temperature of the interior structure is maintained at an acceptable level throughout. The design of the furnace is determined by the type of used fuel for the fire. Cool air is blown into the furnace
and heats up as it comes in contact with hot metal surfaces of heating. As the air becomes warmer, he also becomes lighter, which makes it grow. Warm, light air continues to grow until it is either discharged directly into the room, as in a pipeless of gravity of the system, or is carried out through the duct system of hot air outlets located at some distance from the furnace.
After the hot air loses heat, becomes colder and heavier. Its weight gain causes it to fall back to the furnace, where it heats up and repeats the cycle. This is a very simplistic description of the principles of the work involved in air heating, and this is especially true for those involved in the gravitational heating systems. Forced air system relies on the fan to make sure that air moves in the space provided. Blower also causes the return air to return to the oven faster than gravity of the system.
Besides, there was the system, there must be some way to enable the fan to move the air and turn it off when the room has reached the desired temperature. Thus, the electric control needed to control the fan action...