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Thermostats

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Definition

THERMOSTATS are temperature-measuring devices that keep houses comfortable by controlling the operation of home comfort systems.

The first room thermostat — 1883

1. Image showing the first automated temperature control system

1. The first room thermostat (upper left).
Click the image for more information.


Warren Seymour Johnson toiled for three years in Wisconsin to design and develop a device to control and regulate room temperatures, specifically the classrooms in which he taught at Whitewater Normal School, now the University of Wisconsin. He received his first patent for his “electric tele thermoscope” in 1883. It was the forerunner of the electric room thermostat, the control industry, and Johnson Controls Inc.

This unique mechanism used a sealed bimetal element with one wire of an electrical circuit attached to the hard end and the other wire connected to a small pool of mercury in a cup-like reservoir. Changes in the air temperature moved the free end of the thermal element into and out of the mercury to close or open the electrical circuit, which in turn controlled his classroom damper. He finally had some control over his indoor environment, and eventually, thanks to his innovation, so did everyone else.

Section Gallery

2. Image of Warren Johnson3. Image of a regulating device called the “damper flapper“

Factually Speaking

Cornelius Drebbel (1572–1633), a Dutch inventor and alchemist, developed an automatic temperature regulator (thermostat) in the 1620s to help him control the temperature of an oven he was using to convert lead to gold (the thermostat worked, but no gold was produced).

A century of innovation and progress

1. Image of a 1910 automatic furnace damper control

1. A 1910 trend setting automatic furnace
damper control for Canadian homes. Click the
image for more information.


The automation of central home heating would start simply and progress one innovative step at a time throughout the late 19th and 20th centuries and beyond. One such early starter was the Honeywell Temperature Regulator, patented on March 8, 1910.

This device featured a regulator, powered with a strong, hand-wound, spring-operated motor and a system of chains. It was designed to remotely position furnace fire-door dampers on hand-stoked coal- and wood-fired central heating systems. An electric solenoid, powered by a dry cell battery, would trip a braking mechanism allowing the motor to begin its work.

The homeowner could now position the furnace dampers, regulating combustion rates, without leaving their living room — well sort of.

Section Gallery

2. Image showing a dry battery that powers an electric solenoid3. Image of a damper control

Factually Speaking

“[A]utomation rests primarily on the thermostat,” says Encyclopedia Britannica Online, “a device that, when the temperature in a space drops to a predetermined point, will activate the furnace or boiler until the demand for heat is satisfied.”

Switching device proved critical to the
popularization of automatic central heating

1. Photo of an automatic fan temperature and oil burner high limit control

1. A dual function automated switch for central
home heating systems, using bimetal and
mercury bulb switching. Click the image
for more information.


The popularization of automatic central heating in Canada would depend, most fundamentally, on bringing to market a reliable, automatic temperature-actuated electrical switching device. Such devices would be required for the control of the combustion process, for regulating room temperature and controlling the operating temperature of the furnace or boiler.

Long before the age of electronic and solid state digital temperature sensing devices this would depend on the creative application of “bimetals.” They were known to expand and contract in a predictable manner with small changes in temperature. Such devices would be connected, through ingenious systems of levers, pivot points, and hinges, to an electric switching device, which would operate with small changes in movement. Such a switching device arrived in the 1920s in the form of the sealed, glass tube filled with mercury, truly an engineering and manufacturing wonder of the times.

By the late 1930s mechanical temperature actuated switching, using bimetal and mercury bulb technology would achieve astonishing levels of performance and reliability. The Mercoid Corporation was a market leader of the period. This elegant, dual function, helical bimetal controller, using mercury bulb switching, would represent the last word in the development of the technology. It protected winter air conditioners of the 1940s through the 1960s from overheating, as well as bringing the air circulating fan on and off reliably — without the touch of human hand.

Section Gallery

2. Photo of an automated switching mechanism

Factually Speaking

A forerunner of Honeywell, Electric Heat Regulator Co., developed the first programmable thermostat in 1906. The “Jewell,” as it was called, had a built-in clock. Homeowners lowered the temperature at night and set the thermostat to raise it automatically in the morning. A few years later, a second clock was added, allowing homeowners to set it once and forget about it.

The living room thermostat:
A consumer icon for comfort

1. Photo of a thermostat by Penn Electric Switch Co.

1. An early automated home temperature
control — the room thermostat.
Click the image for more information.


For the home owners of the 1920s and 1930s central automatic home heating was all about the thermostat on the living room wall. The machinery in the basement they didn’t want to imagine or think about.

For many, the new living room thermostat would be the focus of much “show and tell.” It would become a cultural icon of the period, a symbol of what Canadians valued most in those years, their new-found sense of warmth, comfort and convenience.

The industry was well aware of the cultural role played by the room thermostat in family and neighbourhood life. Accordingly it was created as a visual centrepiece for the home. It would be typically decorated in gilt with a temperature scale and slide adjustment that would feel good in the hand, and pleasing to the eye.

This innovative thermostat, by Penn Electric Switch Co., patented in 1930, cut new ground for the times. Moving beyond bimetal and mercury bulb technology, it pioneered the use of gas-filled bronze bellows, as an actuating mechanism, with an innovative, open electrical contact structure.

Section Gallery

2. View of the internal mechanism of an early Penn thermostat3. Image of a Penn thermostat showing the insulating plastic called Bakelite4. Photo of a round, compact thermostat of the mid-20th century5. View of round thermostat with cover removed6. Photo of a programmable thermostat from the 1990s

Factually Speaking

The lack of a constant temperature in textile mills in the early 1800s led to variations in product quality. Dr. Andrew Ure (1778–1857) developed a thermostat that went a long way toward resolving the problem.

An iconic night setback thermostat

1. Photo of a Chronotherm thermostat

1. The Chronotherm as it might
have appeared on the living
room walls of those that could
afford it in the late 1930s.
Click the image for more
information.


Canadians would await the moment of arrival of fully automated, central home heating. It came in the mid-1930s with “time-temperature actuated” electro-mechanical switching technology. The technology would be popularized by Minneapolis-Honeywell Regulator Co., as “the Chronotherm”. Well ahead of its time, it saved energy by turning the heat down at night and up in the morning.

The device was in the form of an elegant, gilded, miniaturized, grandfather-styled electric clock. It was styled to appeal to the economically privileged of the day, those that might be able to afford the latest high-tech gadget in the midst of the Great Depression. Long before digital technology, automation was dependent on intricate mechanically enabled electric devices.

The 1930s was a decade in which even electric clocks were rarely found in Canadian homes, and those that were there required hand starting. The idea of a self-starting electric clock required for an automatic timing device was an innovation of the Warren Telechron Co., who patented the first self-starting electric clock in the late 1920s — just in time. Automated temperature and time-driven electrical switching, in an affordable consumer product, was an immense engineering accomplishment.

The arrival of the Chronotherm brought with it a new sense of empowerment and functionality for the homeowner. But as technology does, it also brought unprecedented complexity, and user challenges. It would be one of the first complex household devices to be mastered. It heralded the flood of lifestyle-dependent digital devices that would invade Canadian households.

Section Gallery

2. Photo of a Chronotherm thermostat with cover removed3. View of a self-starting, electric clock motor4. Image showing the Chronotherm thermostat's mechanical/electric switching


 

Article Sources

The first room thermostat — 1883

  • Research from the archives of the HVACR Heritage Centre Canada (DCSB #029a, HD1005Q).
  • Johnson Controls, via jcivideo.com/125th/index.
  • Bernard Nagengast, An Early History Of Comfort Heating Air Conditioning, Heating and Refrigeration NEWS, via www.achrnews.com.

A century of innovation and progress

  • Research from the archives of the HVACR Heritage Centre Canada (DCSB #029, HD1005Q).
  • Historical artifact from the HVACR Centre Canada, T.H Oliver Collection, Accession No.2006-101.

An automatic temperature-actuated bimetal electrical switch

  • Research from the archives of the HVACR Heritage Centre Canada (DCSB #032, HD1005T).
  • Historical artifact from the HVACR Centre Canada, T.H Oliver Collection, Accession No.2006-113.

The living room thermostat: A consumer icon for comfort

  • Research from the archives of the HVACR Heritage Centre Canada (DCSB #031, HD1005S).
  • Historical artifact from the HVACR Centre Canada, T.H Oliver Collection, Accession No. 2006-90.

An iconic night set-back thermostat

  • Research from the archives of the HVACR Heritage Centre Canada (DCSB #033, HD1005U).
  • Historical artifact from the HVACR Centre Canada, T.H Oliver Collection, Accession No.2006-92.

SIDEBAR

  • Research from the archives of the HVACR Heritage Centre Canada.

Factually Speaking

  • Research from the archives of the HVACR Heritage Centre Canada.
  • Encyclopædia Britannica Online Library Edition, via http://library.eb.com/eb/article-3079
  • Dr. Andrew Ure: Pioneer Free Trader | The Freeman | Ideas On Liberty, via www.thefreemanonline.org/featured/dr-andrew-ure-pioneer-free-trader

Image Credits

The first room thermostat — 1883

  • American Society Of Mechanical Engineers, via http://www.asme.org/about-asme/history
  • Ibid.
  • Honeywell International Inc., via http://honeywell.com/About/Pages/our-company.aspx

A century of innovation and progress

  • HHCC Historical artefact (Accession No. 2006-101), photographed by Mark Dorlandt Photography, HD1006A-2-22.
  • Ibid., 2-31
  • Ibid., 2-15

An automatic temperature-actuated electrical switch for central home heating

  • HHCC Historical artefact (Accession No. 2006-113), photographed by Mark Dorlandt Photography, HD1006A-25-069
  • Ibid., 25-075

The living room thermostat: a consumer icon for comfort

  • HHCC Historical artefact (Accession No. 2006-090), photographed by Mark Dorlandt Photography, HD1006A-21-036
  • Ibid., 21-044
  • Ibid., 21-049
  • Ibid., 24-104
  • Ibid., 24-108
  • Nigel Heseltine, HHCC

An iconic night set-back thermostat

  • HHCC Historical artefact (Accession No. 2006-092), photographed by Mark Dorlandt Photography, HD1006A-23-081
  • Ibid., 23-088
  • Ibid., 23-097
  • Ibid., 23-098