Heat Pumps – from Cold to Hot - Renewable Energy and Climate Change - page 227

Table 11.2 Temperature ranges for popular refrigerants.

Abbrev. Name Boiling point

at 1 bar

Condensation
temperature at 26 bars

R12 Dichlordifl uormethane 30 °C 86 °C

−

R134a 1,1,1,2-Tetrafl uorethane − 26 °C 80 °C

R290 Propane − 42 °C 70 °C

R404A Mixture of different HFC − 47 °C 55 °C

R407C Mixture of different HFC − 45 °C 58 °C

R410A Mixture of different HFC − 51 °C 43 °C

R600a Butane − 12 °C 114 °C

R717 Ammonia − 33 °C 60 °C

R744 Carbon dioxide − 57 °C − 11 °C

R1270 Propene − 48 °C 61 °C

the air escaping while energetically pumping a tyre. The heat of the heated refriger-
ant is then used as useable heat, usually for room heating or heating water. The heat
is removed through a condenser that again liquefi es the refrigerant. The refrigerant
that is compressed expands over an expansion valve, cools off and is transferred to
the vaporizer again.

The Turned-Around Refrigerator
Heat pumps are also used in refrigerators. They act like cooling machines.
A vaporizer removes the heat from the interior of a refrigerator. The heat is
emitted over cooling fi ns on the back of the appliance. The heat emitted there comprises
the heat removed from the refrigerator and the electric driving energy of the refrigerator
compressor. This explains why a room with an open refrigerator door cannot be cooled
down in the summer. A refrigerator emits more heat from the back than it removes from
the inside.
The fi rst compression refrigerating machine was developed by the American Jacob
Perkins in 1834. He used ether, which is no longer used today, as a refrigerant for his
ice-making machine. The refrigerant ether has the disadvantage that in combination with
atmospheric oxygen it forms a highly explosive mixture. This occasionally caused ether
ice machines to explode.

11.2.2 Absorption Heat Pumps and Adsorption Heat Pumps
Like compression heat pumps, absorption heat pumps use low-temperature heat
to vaporize a refrigerant. However, absorption heat pumps use a thermal com-
pressor instead of the electrically driven compressor of compression heat pumps
(Figure 11.4 ).