Heat pump

The invention:Adevice that warms and cools buildings efficiently
and cheaply by moving heat from one area to another.
The people behind the invention:
T. G. N. Haldane, a British engineer
Lord Kelvin (William Thomson, 1824-1907), a British
mathematician, scientist, and engineer
Sadi Carnot (1796-1832), a French physicist and
thermodynamicist
The Heat Pump
A heat pump is a device that takes in heat at one temperature and
releases it at a higher temperature. When operated to provide heat (for
example, for space heating), the heat pump is said to operate in the
heating mode; when operated to remove heat (for example, for air conditioning),
it is said to operate in the cooling mode. Some type of work
must be done to drive the pump, no matter which mode is being used.
There are two general types of heat pumps: vapor compression
pumps and absorption pumps. The basic principle of vapor compression
cycle heat pumps is derived from the work of Sadi Carnot
in the early nineteenth century. Carnot’s work was published in
1824. It wasWilliam Thomson (later to become known as Lord Kelvin),
however, who first proposed a practical heat pump system, or
“heat multiplier,” as it was known then, and he also indicated that a
refrigerating machine could be used for heating.
Thomson’s heat pump used air as its working fluid. Thomson
claimed that his heat pump was able to produce heat by using only
3 percent of the energy that would be required for direct heating.
Absorption cycle machines have an even longer history. Refrigerators
based on the use of sulfuric acid and water date back to 1777.
Systems using this fluid combination, improved and modified by
Edmond Carré, were used extensively in Paris cafés in the late
1800’s. In 1849, a patent was filed by Ferdinand Carré for the working-
fluid pair of ammonia and water in absorption cycle machines.In the early nineteenth century, many people (including some
electrical engineers) believed that electrical energy could never be
used economically to produce large quantities of heat under ordinary
conditions. A few researchers, however, believed that it was
possible to produce heat by using electrical energy if that energy
was first converted to mechanical energy and if the Carnot principle
was then used to pump heat from a lower to a higher temperature.
In 1927, T. G. N. Haldane carried out detailed experiments showing
that the heat pump can be made to operate in either the heating
mode or the cooling mode. Aheat pump in the cooling mode works
like a refrigerator; a heat pump in the heating mode supplies heat
for heating. Haldane demonstrated that a refrigerator could be
modified to work as a heating unit. He used a vapor compression
cycle refrigerator for his demonstration.
In the design of a refrigerating device, the primary objective is
the production of cold rather than heat, but the two operations are
complementary. The process of producing cold is simply that of
pumping heat from a relatively cold to a relatively hot source, but in
the refrigeration process particular attention is paid to the prevention
of the leakage of heat into the cold source, whereas no attempt
is made to prevent the escape of heat from the hot source. If a refrigerating
device were treated as a heat pump in which the primary
product is the heat rejected to the hot source, the order of importance
would be reversed, and every opportunity would be taken to
allow heat to leak into the cold source and every precaution would
be taken against allowing heat to leak out of the hot source.
The components of a heat pump that operates on the principle of
vapor compression include an electric motor, a compressor, an evaporator,
and a condenser. The compressor sucks in gas from the evaporator
and compresses it to a pressure that corresponds to a saturation
temperature that is slightly higher than that of the required heat. From
the compressor, the compressed gas passes to the condenser, where it is
cooled and condensed, thereby giving up a large quantity of heat to the
water or other substance that it is intended to heat. The condensed gas
then passes through the expansion valve, where a sudden reduction of
pressure takes place. This reduction of pressure lowers the boiling point of the liquid, which therefore vaporizes and takes in heat from
the medium surrounding the evaporator. After evaporation, the gas
passes on to the compressor, and the cycle is complete.
Haldane was the first person in the United Kingdom to install a
heat pump. He was also the first person to install a domestic heat
pump to provide hot water and space heating.Impact
Since Haldane’s demonstration of the use of the heat pump, the
device has been highly successful in people’s homes, especially in
those regions where both heating and cooling are required for single-
and multifamily residences (for example, Australia, Japan, and
the United States). This is the case because the heat pump can provide
both heating and cooling; therefore, the cost of a heat pump
system can be spread over both heating and cooling seasons. Total
annual sales of heat pumps worldwide have risen to the millions,
with most sales being made in Japan and the United States.
The use of heat pumps can save energy. In addition, because they
are electric, they can save significant quantities of oil, especially in
the residential retrofit and replacement markets and when used as
add-on devices for existing heating systems. Some heat pumps are
now available that may compete cost-effectively with other heating
systems in meeting the heating demands of cooler regions.Technological developments by heat pump manufacturers are
continually improving the performance and cost-effectiveness of
heat pumps. The electric heat pump will continue to dominate the
residential market, although engine-driven systems are likely to
have a greater impact on the multifamily market.