History of Heat Pumps

History of Heat Pumps

The story of heat pumps, from early refrigeration experiments in the 18th century to contemporary energy-efficient solutions, represents a remarkable journey of innovation and enhancement. Let’s explore this captivating history.

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The evolution of heat pumps and refrigeration spans several centuries and has been extensively researched since the early 18th century. In 1755, William Cullen, a Scottish professor, created a rudimentary refrigeration machine that employed a pump to establish a vacuum over diethyl ether, leading the substance to boil and withdraw heat from its surroundings. This innovation marked the inception of the scientific principles underlying refrigeration. Later, in 1852, Lord Kelvin, an eminent Irish-Scottish physicist and engineer, expanded upon Cullen's work, proposing the same principle could be harnessed to heat a room.

Advancing to 1820, American engineer Oliver Evans unveiled a closed-cycle refrigerator utilizing compressed ether as a coolant. By 1851, John Gorrie implemented a similar system in Florida, utilizing compressed air as the coolant—a concept that Alexander Twinning would introduce to the American market in 1855.

In the years leading to 1857, Austrian engineer Peter von Rittinger constructed the first heat pump system predicated on Lord Kelvin's principles. Around this time, in 1860, Ferdinand Carre pioneered the use of ammonia as a refrigerant, which Carl von Linde later adapted to create the first fully operational ammonia refrigeration system in Germany in 1876.

The groundbreaking idea of a ground-source heat pump originated from Robert C. Webber, an American inventor, in 1948. While refining his electric deep freezer, he burnt his hand, realizing that it produced scalding hot water. To efficiently use this heat, he directed the hot water through a copper tube and employed a small electric fan to distribute the warmth into his surroundings.

Acknowledging the efficacy of his innovation, Webber went on to construct a fully functional heat pump heating his entire home. By burying copper tubing, filled with Freon, underground, he tapped into geothermal energy to maintain a warm home, releasing the heat from the Freon in his cellar. This was the genesis of the first-ever ground-source heat pump.

Today, heat pumps are typically integrated into HVAC systems globally, featuring more sophisticated configurations and eco-friendlier refrigerants compared to their predecessors.

Most common type of heat pump

This article is about details of the most common type of heat pump. For more general information, see heat pump.

An air source heat pump (ASHP) extracts heat from the outdoor air to heat the interior of a building. It operates on the same vapor-compression refrigeration principles as an air conditioner but functions in the opposite manner. Usually smaller in size, ASHPs are popularly used for individual homes rather than larger blocks or industrial operations.

Air-to-air heat pumps directly deliver hot or cold air into spaces but typically do not supply hot water. Conversely, air-to-water heat pumps are designed to heat a whole building via radiators or underfloor heating and often serve as sources for domestic hot water.

A standard ASHP has the capability of converting 1 kWh of electric energy into about 4 kWh of thermal energy. They are generally optimized for flow temperatures between 30 and 40 °C (86 and 104 °F), making them suitable for structures with heat emitters designed for low-temperature output. Although efficiency may decline, ASHPs can still provide central heating at flow temperatures up to 80 °C (176 °F).

As of recent reports, approximately 10% of buildings globally utilize ASHPs for heating. This technology is widely regarded as a primary means to phase out traditional gas boilers, aiming to mitigate greenhouse gas emissions.

The operation of air-source heat pumps involves transferring heat between two heat exchangers—one situated outdoors, equipped with fans to facilitate air flow, and the other, either directly heating the indoor air or heating water circulated throughout the building. They can also function in cooling mode, where internal heat is extracted and discharged into the outdoor air.

Given their relatively straightforward and cost-effective installation process, ASHPs are among the most prevalent heat pump types. During temperate weather conditions, the coefficient of performance (COP) may range between 2 and 5, and even in temperatures below approximately 8 °C (18 °F), they can maintain a COP between 1 and 4.

While earlier versions of air-source heat pumps showed diminished performance in colder climates, recent models equipped with variable-speed compressors now demonstrate high efficiency even in freezing conditions, facilitating broader usage and savings in states such as Minnesota and Maine in the United States.