Thermostats: tools that manage HVAC performance
In basic definition, advanced air conditioning system controls and thermostats function like simple on/off switches. The switch trips whenever a structure’s indoor air temperature changes near the associated thermostat set point. But modern HVAC performance means much more than the simplicity of an on/off thermostat control feature.
The following overview discusses the power of advanced air conditioning system thermostats and controls.
Basic control processes of the air conditioning system and thermostat
In 1883, Warren S. Johnson invented the first electric room thermostat. Johnson Controls’ technology used mercury and electrodes inserted directly through glass. The systems were accurate to within one degree of temperature.
Skip ahead. In modern technology, most 2014 heat pump and air conditioning thermostats are powered by low-voltage control circuits that draw 24 volts AC from a control transformer installed inside the home’s heating or cooling equipment. Low-voltage control technology provides a safety advantage that allows the thermostat to operate multiple electromechanical contractors, relays, and sequencers at intrinsically safe voltage. Modern systems also include a built-in “anticipation” feature that activates the contacts in a way that prevents the ambient temperature from exceeding the desired temperature settings. And all of this excludes the growing range of features associated with modern programmable thermostats and controllers.
Heating and Air Conditioning Predigital Thermostats
In 1953, Honeywell introduced the T-86 “Round” thermostat technology. This bi-metal spring regulated room thermostat still controls millions of domestic heating and cooling systems around the world.
Typically mounted on a central wall within the home, the traditional Honeywell thermostat uses a basic round dial-type controller design that includes two temperature scales and two temperature indicators. The upper scale and pointer provide the adjustable components of the system. The lower scale shows the actual physical temperature in the chosen area of the house. Turning the pointer on the upper scale to the right increases the desired heating requirement. Rotating the pointer on the upper scale to the left decreases the desired temperature setting.
In the early years, thermostats designed to control both cooling and heating included a manual set switch at the base of the unit. Also seen on pre-digital era rectangular units, this switch can be flipped from hot to off to cool or vice versa. The temperature sensor inside the units compares the air temperature near the thermostat with the system setting and turns associated heating or cooling equipment on or off as appropriate. The hot/cool/off control switch ensures that only selected equipment can be activated at any time.
Digital Age Thermostats and Controllers
By the year 2005, almost 97% of American homes used installed heating systems. During the same time period, only 75% of American homes used air conditioning. But the world is changing, and climate changes associated with global warming continue to increase the demand for installed air conditioning.
Modern programmable thermostat and controller technology provides a dramatic increase in features and capabilities. From simple heating and cooling on/off to controlled ventilation systems and from manual adjustments to controllers that respond to electricity price signals, heat pump and air conditioning management system of the home is involved in a completely new field of thermal comfort and energy saving.
And then there are thermostats and advanced air conditioning controls that connect directly to the home’s Internet network system. I wonder what comes next?
