How to Set a Home Thermostat
if you need a certain temperature in your home to be comfortable, you've probably spent some time looking at and using your thermostat. This handy little device controls your home's heating and cooling systems, which are the two appliances that use the most energy and have the biggest effect on your comfort and quality of life. With energy costs going up, you might want to know more about how your thermostat works. It's easy to use and, believe it or not, has some pretty cool technologies built into it. To know more click here.
In this guide, we'll take apart a home thermostat to learn more about how it works. We will also learn about system zoning, thermostats that talk, digital thermostats, and thermostats that you can use your phone to control.
Before we look at modern thermostats, which are almost entirely digital, let's take a step back in time and look at the parts of an analogue thermostat, which can still be found in older homes and hotels. Let's start with the mercury switch, which is made up of a small amount of real mercury in a glass vial. Mercury is a liquid metal that flows like water and sends electricity through it. There are three wires inside the glass vial. Since one wire goes all the way across the bottom of the vial, the mercury is always touching it. Since one wire is attached to the left side of the vial, mercury will touch it when the vial leans to the left. This will connect the mercury to the wire at the bottom of the vial. When the vial tips to the right, the third wire's end is on the right side of the vial. This means that the bottom wire and the third wire touch the mercury when the vial tips to the right.
There are two thermometers in this thermostat. On the cover, the temperature is written. The other is in the top layer of the thermostat and controls the heating and cooling systems. The only thing that makes up these thermometers is a coil of two metal strips. You might ask, "What does that mean?" The answer is on the page after this one.
There are switches and thermometers.
A bimetallic strip is made by joining two different kinds of metal together. When the strip is heated or cooled, the metals that make it up stretch and shrink. The rate of expansion depends on the type of metal, and the two metals used to make the strip both expand and contract at different rates. When this coiled strip is heated, the metal inside the coil expands more, and the strip starts to unwind.
The mercury switch is attached to the end of the coil and is set up so that as the coil winds or unwinds, it tips the mercury switch in one direction or the other. The centre of the coil is connected to the lever that changes the temperature.
Thermostats that don't have digital displays have two knobs. These switches move tiny metal balls inside the thermostat, which move along different lines on the circuit board. The mode is controlled by one switch, and the circulation fan by the other (hot or cool). We'll look at how these parts work together to make the thermostat work on the next page.
Internal Mechanisms
When you move the thermostat's lever to raise the temperature, the mercury switch and thermometer coil move to the left.
As soon as the switch leans to the left, the mercury in the switch starts to let electricity through. This current turns on a relay, which in turn turns on your home's heating and ventilation fan. As the room warms up, the thermometer coil slowly unwinds. This causes the mercury switch to tilt back to the right, breaking the circuit and turning off the heat.
When the mercury switch tips to the right, the air conditioner turns on through a relay. As the room cools, the thermometer coil goes up until the mercury switch tips back to the left.
Another cool part of a thermostat is a heat anticipator. The heat anticipator turns off the heater before the air inside the thermostat gets to the right temperature. Sometimes, parts of a house will reach the right temperature before the room with the thermostat. In this case, the anticipator turns off the heater a little bit earlier to give the thermostat time to warm up.
One type of resistor is the wire loop shown above. Control current flows through the mercury switch, the yellow wire, and the resistive loop when the heater is on. It goes around the loop until it gets to the wiper, where it goes through the centre of the anticipator ring and down to the bottom layer of then home thermostat circuit board. How far the wiper is from the yellow wire determines which wire is the most difficult for the current to cross (going clockwise). Just like any other resistor, this one gets hot when current flows through it. As the wiper moves farther around the loop, it makes more and more heat. Because of the heat, the thermometer coil warms up, unwinds, and tips the mercury switch to the right, which turns off the heater.
