Quote:
Originally Posted by AC_Hacker
MMT,
I think that anyone who wishes to proceed with R290 must read, and carefully consider your post.
BTW, I still think that a propane sensor that can control a non-arcing evacuating fan should be standard equipment with such a setup. What's good for a boat is good for a basement.
Sincerely,
-AC_Hacker
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Well put! For perspective, though, the boats have it a lot worse, especially considering the limited cubic footage in their bilge or engine room:
Gasoline vapors have a lower flammability limit of 1.4%, whereas propane has an LFL of 2.1%. Gasoline vapor (around 3.5 times as dense as air depending on formulation) is more than twice as dense as propane, so it sticks around resisting dissipation better. 1lb of R290 in a 3 ton heat pump can bring around 315 cu ft of air to its LFL in a catastrophic leak. One quart of gasoline typically makes 5.4 cu ft of vapor, bringing 388 cu ft of air to its LFL. A gas can (or a boat, or a car) holding less than 1 quart of gasoline needs a larger basement or garage for its safe storage with a 50% safety margin than the 3ton R290 heat pump! I know-a friend of mine's son was killed when he spilled a bunch of gas while filling up the lawnmower in a closed garage. The water heater (at floor level instead of on a stand like code requires now) ignited the fumes, and he was gone.
I have two exhaust fans for blowing burner gases up the flue that I snagged from my crappy builder-grade furnaces when I went hydronic heat and 23 SEER AC, and I'll probably design what you describe as extra insurance. But, sensors can malfunction, power can go out, fans can quit-it's simpler just to be sure you have enough cubic space that it is impossible to develop enough concentration to be a risk in that area. A monitor alarm just to catch any trouble is smart in any area where flammable vapors could exist. For a smaller area, just dropping a can of spray solvent on something that punctures it could get you above the LFL. If you don't have the cubic to dissipate the worst possible leak, then you MUST have a ventilation system with redundant backup, which is often code required for certain places like automotive service pits.
The risk of a gas can, boat or car leaking one quart of the many gallons of fuel it contains? Low, but possible. The risk of a refrigerant system developing a catastrophic leak instead of a very slow one? Low, but possible. The risk of a refrigerant system leaking more than it holds? ZERO!!
In my 21 year career in the automotive field where I have been involved in close to 100,000 auto service visits in some way, I have seen a fire caused by full strength antifreeze being splashed on a hot exhaust manifold (no lie!) several fires caused by backfires igniting spray solvent used for testing, and even one caused by an internal AC system explosion ignited by a disintegrating compressor while someone started charging a flammable refrigerant into a opened but not evacuated system that was full of air! I've never seen a gasoline fire during servicing, even when gallons were spilled during more than a few fuel pump replacement bobbles. I've only seen 1 car fire during use that was confirmed to be because of a fuel leak. Still, taking all possible precautions when servicing equipment is prudent even if the risk is low, such as when you have a larger container of flammable refrigerant you are charging from.
If you want the extra insurance of a safety vent fan on 120vac, any induction motor without a start circuit such as a squirrel cage or shaded pole will be spark free. For 12vdc, brushless centrifugal computer server blowers will work, which produce more pressure to flow through a duct than a regular computer fan. "Universal" motors or car blower/cooling fan motors are not-they use brushes and will spark.
I wish I could remember where I found the safety and COP info on refrigerants, but I can't. I have a bad habit of taking short notes on the most pertinent info but not always noting the link where I got it. It was a European company which had a compilation of several papers concerning natural refrigerants. If I come across it again, I will post.
Best,
Craig