Diethyl ether, propane, sulfur dioxide and carbon dioxide are the four alternatives to ammonia, and each fails in its own way: ether and propane burn or explode, sulfur dioxide poisons and corrodes, and carbon dioxide needs very high pressure. They are worth knowing because salvaged equipment and old books use them, but none is a better first choice for a settlement than ammonia in a steel circuit.
Part of Refrigeration
The four non-ammonia refrigerants in the corpus carrier, what each is good for, and the failure each makes likely.
Each Alternative Is Safer In One Respect And Worse In Another
The carrier’s table sets out the choices. This page reads each with the working-fluid tests from Working Fluids.
Diethyl ether (boils at 34.6 °C). It needs only low pressure and is easy to handle in that sense, as the carrier says. But because it boils above ordinary air temperature it needs a vacuum on the cold side, which means any leak draws air in, and ether vapour with air in the same vessel is an explosive mixture. The vapour is heavier than air and collects at floor level. The carrier calls it extremely flammable and explosive.
Propane (boils at −42 °C). It is efficient and, as the carrier notes, can be taken from natural gas. It is highly flammable and, in its raw form, has no smell, so a leak does not announce itself unless an odorant has been added. It is heavier than air, so it pools at the lowest point of a room or pit.
Sulfur dioxide (boils at −10 °C). It is easy to produce by burning sulfur, the carrier says. It is highly toxic and, when it meets moisture, corrosive; a small amount of water in the system attacks the metal from inside (recalled chemistry, flagged). It is much heavier than air.
Carbon dioxide (sublimes at −78.5 °C). The carrier calls it non-toxic and non-flammable but notes that it needs very high pressures, 70 bar or more. It cannot be a liquid at atmospheric pressure at all. It is not poisonous, but it is an asphyxiant, and its critical temperature of about 31 °C (a recalled figure, flagged) means a warm climate can leave a cycle with no liquid to condense.
What You Need To Know Before Using Salvaged Gear
Old machines and books may describe any of these. A cooling unit found in a ruin was built for a particular fluid, with seals, oil and relief settings chosen for it. Do not recharge it with a different fluid, and do not assume that one fluid’s gauges and valves are suitable for another.
Worked Example: Why Ether Is Dangerous Inside A Leaky Machine
Qualitative, using only the boiling point. At atmospheric pressure ether boils at 34.6 °C. To make it boil in a 4 °C box, the evaporator pressure must be well below atmospheric. A leak in a low-side joint therefore sucks air in, not ether out. Air plus ether vapour inside a vessel that contains a motor, a hot compressor or a spark is the arrangement of an explosion.
No figure is given for how far below atmospheric the pressure must fall, because that depends on ether’s own vapour-pressure data, which the carrier does not provide.
Common Mistakes
- Using propane or ether inside a building. Heavier-than-air vapour collects at floor level and finds a flame.
- Assuming “no smell” means no leak. Raw propane is odourless.
- Using sulfur dioxide with damp air or damp oil. It forms acid that eats the machine from inside.
- Underestimating carbon dioxide’s pressure. The 70 bar the carrier mentions is far above what an improvised pipe is designed for.
Safety
The alternatives to ammonia are no gentler
Ether and propane need a ventilated outdoor site and no ignition source within reach; sulfur dioxide needs at least the care that ammonia does; carbon dioxide can kill by displacing air and can burst a pipe not built for its pressure. Read Safety before charging any circuit.