Quote:
Originally Posted by Mikesolar
Quote from one of the UK guys who seems to know:
"Purity
The quality of commercially available propane (LPG) is very often
not suitable for refrigeration. The composition varies substantially,
generally having between 60 and 95% propane. It can have high
levels of moisture and unsaturated hydrocarbons.
Impurities such as other hydrocarbons can impact the vapour
pressure of the product, lowering overall system efficiency. Sulphur
can cause corrosion, and unsaturated hydrocarbons can react with
system components. Moisture leads to hydrolysis, corrosion and
compressor failure.
R290 is at least 97.5% pure with minimal levels of critical impurities including moisture
(typically† <10ppm), unsaturated hydrocarbons (typically <0.5%) and
sulphur. This makes it ideal for use in all types of refrigeration and air
conditioning systems."
Maybe all that is needed is to run it through a proper filter system to meet the requirements? That is something else to be checked out.
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This is all true.
There is even more to it than that, the BBQ gas providers guarantee some percentage of propane, and the rest of the gas can vary, most of the rest of the gas is butane. I have read one study that addressed a butane/propane mixture and found that SOME butane can actually improve performance, particularly when the equipment is used for heating, rather than cooling.
As I recall the best % of butane was about 6% to 8%. I have asked my local supplier about the purity of propane and he said that it was 85% to 95% propane.
But if you are building the final unit (your Opus), the price of refrigeration grade propane is not all that huge, when you consider the other expenses and time invested.
Additionally, Brad_C and I think Vlad, too did some work wherein they put a tank of BBQ gas in the deep freeze and drew the gas from the top of the tank, leaving the butane at the bottom. Search the forum... lots here!
Best,
-AC