Thermostats
The heating and air-conditioning systems would not be mechanically functional if no thermostat is attached to each of these equipment. The thermostat is a regulatory devise for temperature of a system. Its function is to maintain the desired temperature of the system. The heating and cooling functions rely on the thermostat’s switches to maintain the needed correct temperature.
The thermostat is an invention of Alfred Butz in 1885. A 19th century invention, this devise is the first known example of process control technology.
Thermostats have many shapes and forms. They can be mechanical, electrical and digital or electronic. Whatever shapes and forms a thermostat can be the most important part that should always be there is the sensor.
The sensor is the critical part of the thermostat. It is where the measurement of temperature takes place. Its output is functioned to control the heating or cooling system. The sensors can be many in many forms. The most common include: bimetal mechanical sensors, expandable wax pellets, electronic thermistors and electrical thermocouples.
The thermostats have different classifications. These are mechanical and electrical. The mechanical thermostat can be in a form of a bi-metal or wax pellet. These thermostats are used in automobiles and are operated manually. The thermostat with a bi-metal strip is incorporated in a mechanical devise found on a hot-water car radiator system. This is an automatic valve that controls the flow of air based on temperature set. This mechanical thermostat is used to adjust the dampers in turbine ventilations. This is to regulate the heat loss in cold periods. The use of this is rare in North America; however this thermostat is still employed on central heating radiators throughout Europe. Another thermostat that operates mechanically uses a wax pellet inside the chamber of automobiles..
The electric thermostat makes use of electricity. It is a conventional on-off switch controlled by temperature through the capillary tube. This type of thermostat varies in the voltage depending on the equipment that is used. The thermostat wire is used to connect the thermostat to the heating or cooling system. The simple-wire thermostat is the common. The millivolt thermostat is powered by a thermocouple, heated by the pilot light. The 24-volt electrical thermostat is typically used for it has an advantage to operate mechanical devises under a low voltage control system. The heat pump thermostats also operate on low voltage control circuits which is typically 24 VAC. The line voltage thermostats are most commonly used in heating systems. This thermostat is directly connected to the system power. Voltage fluctuation makes it not an advantage for use especially if the low voltage thermostat is connected to a line voltage circuit that may exceed 40 amperes.
The electrical thermostats are integrated in the programmable thermostats. The programmable thermostat is designed to adjust the temperature according to the programmed settings. It may also be called setback thermostats or clock thermostats.
Programmable thermostat has an integration of electronic devises. This can have the following features:
Clock thermostat – has a simple feature and is easily programmed. It implements one program with two periods. The sophisticated clock thermostat my have more variations allowing the user to set four or more hot and cold periods each day. The mechanism of this may be in a rechargeable battery or using the 24VAC circuit.
Digital thermostats – may implement the same functions but provide more versatility. It can be set to four periods each day. It allows the user to over-ride the programmed temperature for the time period, resuming the programmed temperatures automatically when the next period begins. The time periods may be labeled “Morning”, “Day”, “Evening” or “Night”. These may be powered in a sophisticated power circuit, rechargeable battery or non-rechargeable battery. Most heating and cooling equipment use this type of programmable thermostat. The Hunter thermostat and Honeywell thermostat are some of the brands of digital thermostat available in the market today.
The thermostats are used in the heating and cooling system. The most recent and conveniently used are the programmable thermostats. The adjustment of thermostats is dependent on the comfort of the user of the heating or cooling systems.