The Homemade Heat Pump Manifesto

[Mobile Master Tech]

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

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

[mejunkhound]

good post, but would make one clarification due to the wording of :
"any induction motor such as a squirrel cage or shaded pole will be spark free"

shaded pole induction motors ARE spark free, cap run only motors are spark free, 3 phse motors are spark free. Most other induction motors have a centrifugal or current or potential relay start switch, and are NOT spark free. Some relays are explosion proof, so would be OK.

Do not forget that if one uses an open relay to control the motor, that is a spark source.

[Mobile Master Tech]

Forgot about the start circuit-thanks!

[AC_Hacker]

Originally Posted by mejunkhound

...shaded pole induction motors ARE spark free, cap run only motors are spark free, 3 phse motors are spark free. Most other induction motors have a centrifugal or current or potential relay start switch, and are NOT spark free. Some relays are explosion proof, so would be OK...

I would add to your list ECM motors, like computer fans, are also spark free.

-AC

Learned great information from the above!

[Mobile Master Tech]

Right-computer fans and server blowers are ECM's (Electronically Commutated Motors), also known as brushless or BLDC (BrushLess DC). Since they need a power supply to run on mains current, I mentioned them for 12vdc, but they are different names for the same thing.

[Mobile Master Tech]

I have tested size 1212 12vdc BLDC computer server blowers (around $10 ea), which can produce 1.35" of water column pressure. They move 15CFM at 0.93" while taking 6 watts, and pull 9 watts wide open moving 2-3x as much air against no resistance. The tester I used couldn't measure airflow that high, so I just estimated.

A computer fan works great for low resistance but its flow goes to almost zero if there is much resistance, such as blowing through a duct.

[Thepprof]

HI; I got tired of being screwed by local A/C contractors and decided to get my card and start to service my own rental units. I used propane to test a Klimaire 12K BTU unit set up in my garage. I could not find any information on how to service the unit with propane so just started adding gas and monitoring the heat output from the compressor coil. As I added more gas the cool output increased and the area of the coil putting out heat rose from the bottom eventually to the top at which point I quit. I ran the unit off and on for several days and for the most part at 95degrees ambient I realized 20+ degrees at the air handler. I purged the unit of propane, used the same method to add R410A and reinstalled the unit in rental; It got me through a mild winter with no problems and summer is here. I've been trying to find out, since these are new units what kind of pressures and temperatures can I expect on these units at various ambient temperatures. since I cannot do the usual super/sub heat methods and I really do not want to evacuate and reload by weight just to be sure the units are up to par. I currently have 2 minisplits and 7 regular HVAC units in service. thanks Owen

[AC_Hacker]

Originally Posted by Thepprof

...what kind of pressures and temperatures can I expect on these units at various ambient temperatures...

I'm a bit confused here... are you testing these units with R290 to see if they work, and then emptying them of R290 and then filling and using R410a (or whatever refrigerant they require) and then they are put into service for your rental properties?

Or are you trying to service units that were intended for R410a (or whatever refrigerant they require) and then servicing them with R290 so that they might then be put into service for your rental properties?

-AC

[Thepprof]

Actually I'm just trying to understand more regarding HVAC.

referring to the previous post. I decided that once I got the unit working on R290 it was ok to service with the very expensive R410a. this is a rental unit and though I figured the risk of fire was low I would go ahead and service the unit as designed since I had the tank of R410a to minimize the liability.

Note; I do not have scales that can be used to weigh in gas. Usually I use super/sub heat but with minisplits this is impossible.

Everyone I have spoke with locally says that the only way to service a minisplit is to evacuate and charge by weight. I think I have somewhat of a basic understanding of HVAC and think that since these are nearly new units all of the elements should be working properly. I am looking for a simple chart that would relate outside temperature, inside temperature and expected pressure under those conditions. I finally got a number from the Klimaire rep that is on a 95 degree day outside and the unit running maintaining the desired inside temp that the line pressure should be 140 psi. I have two units one that I installed and it went as instructed, the other one is the one I played with on propane and later serviced with R410a. Note: I monitored the temperature of the compressor coil and as I added more gas the hot portion of the coil rose towards the top of the coil. When the coil was uniformly putting out heat and the air handler was putting out 24 Degrees differential I assumed the unit was properly charged and so far it has been doing ok.

thanks Owen