How does a thermostat work?
Thermostats control nearly all types of heating and cooling equipment, keeping room temperatures within a set range. By doing so, they ensure comfort, cut energy waste, and offer considerable convenience. A thermostat has a temperature sensor and an activating switch. Some are mechanical, others electronic. Not all thermostats work with all types of furnaces and heaters; a forced-air thermostat, for example, won’t necessarily work with a heat pump. Most thermostats are either manual, electronic or “line-voltage” (used with electric baseboard and wall mounted heating). Programmable, electronic thermostats couple sensors with circuitry to do the job. Typical programmable thermostats can handle both heat-only systems-such as forced-air, steam, hot water, and, in some cases electric-and complete air-conditioning systems. Most are like minicomputers that can automatically align heating and cooling to changing daily needs, eliminating unnecessary energy usage and reducing energy costs.
Most central heating and cooling systems are connected to a thermostat on a low-voltage DC current. The furnace or air conditioner waits for a current on this DC line in order to operate. So when there’s current on the thermostat line the furnace or AC runs, and heats or cools the house, and when there is no current, the furnace or AC stops adding heat to or extracting heat from the system.
To accurately control process temperature without extensive operator involvement, a temperature control system relies upon a controller, which accepts a temperature sensor such as a thermocouple or RTD as input. It compares the actual temperature to the desired control temperature, or setpoint, and provides an output to a control element. The controller is one part of the entire control system, and the whole system should be analyzed in selecting the proper controller. The following items should be considered when selecting a controller
When it’s cold, we walk over and turn up the thermostat, and when it is hot, we walk over and turn on the air conditioner to cool us down. But, how does that little box on the wall actually control the temperature of our homes or offices? A mechanical thermostat is actually a very simple device. It is basically a thermometer attached to a switch that turns on your heater, whether your heat source is natural gas or electricity. If you remove the cover of your thermostat, you will see the inner workings and get a better idea of how a thermostat works. The top layer holds a mercury switch and a thermometer coil. The mercury switch is just a small vial filled with the liquid metal, mercury. Within this vial are three wires: one at the bottom of the vial; one at the left of the vial; and one at the right of the vial. As the temperature rises or cools, the vial of mercury gets tipped to the right or the left making the corresponding wire come into contact with the wire that runs along the bo
2003 Virginia SOLs • PS.1 • PS.7 Objectives Students will • understand the various parts of a thermostat, including the bimetallic thermometer and the mercury-filled bulb; • visualize the effect of hot and cold air on the thermostat; • understand how a thermostat is connected to a circuit that regulates the heat produced in a house.
