Propane pipe sizing for portable generator

[shamrock12]

I have a 12,000 watts (continuous) portable generator and soon will be hooking up to the building supply line. The propane company came last week and installed a pipe teed past the low pressure regulator. I just ordered a conversation kit but while I was talking with the salesman, he asked what size pipe I have, so I told him that the propane company installed half an inch black iron. He advised me that it might be too small and recommended 3/4" line. I informed him that the newly installed pipe is about 10 foot in length and that I plan to run 15 feet flexible line from quick disconnect coupler to the generator, for a total length of 25 feet. He said it might work but seems to have some doubt whether if it might still work.

So I decided to do some researching and probably am even more confused now. The generator's Honda engine is 22 hp so if I convert that to watts, that would be about 16,500 watts (engine power). Converting that again would result to about 56,000 BTU/hr at full load. But when I looked up Generac sizing guide (mine is not a Generac though ... it is just a resource I found on the internet), it says a 10kw unit burns about 156,000 BTU/hr at full load and the 15kw burns about 231,800 BTU/hr. That is for liquid propane which is the primary fuel I intend to use. What I don't understand why these numbers are much higher than my calculation?

I guess the question is, will the 1/2" black pipe be sufficient for my 22hp, 12,000 watts (14,000 surge) unit?

 

[Elvenhome21]

1/2" pipe should be more then enough IMO. Propane forklifts barely use a hose that big and thats close to 100hp

 

[A_Pmech]

What I don't understand why these numbers are much higher than my calculation?

I guess the question is, will the 1/2" black pipe be sufficient for my 22hp, 12,000 watts (14,000 surge) unit?

1) An internal combustion engine has a combined thermal and mechanical efficiency of about 20%. The other 80% of the fuel consumed is converted to heat, noise, vibration and a mixture of un-burned gasses. In this case, making 15kW of electricity requires about 68kW of fuel.

2) The Rego LP-Gas Serviceman's Manual (available online from Rego's website) says 25' of 1/2" black pipe will only carry about 180,000 BTU at 11" of water.

 

[shamrock12]

1) An internal combustion engine has a combined thermal and mechanical efficiency of about 20%. The other 80% of the fuel consumed is converted to heat, noise, vibration and a mixture of un-burned gasses. In this case, making 15kW of electricity requires about 68kW of fuel.

2) The Rego LP-Gas Serviceman's Manual (available online from Rego's website) says 25' of 1/2" black pipe will only carry about 180,000 BTU at 11" of water.

That is what I suspected ... it just seemed alot to me. So at full power of 12kw, it sounds like the generator would be burning around 186,000 BTU/hr at 11" W.C. which would be right around the maximum as per the manual you mentioned. Should I be okay or is that cutting it too close?

Thanks

 

[A_Pmech]

I'd use 3/4" black pipe and 3/4" ID hose if it was mine.

 

[monkeybar]

1/2" pipe should be more then enough IMO. Propane forklifts barely use a hose that big and thats close to 100hp

FYI, almost all propane-powered forklifts feed liquid propane, not gasw, through that hose. Helluva lot more propane can move in liquid form than gas. Big problem with running liquid is the high pressure. monkey

 

[monkeybar]

That is what I suspected ... it just seemed alot to me. So at full power of 12kw, it sounds like the generator would be burning around 186,000 BTU/hr at 11" W.C. which would be right around the maximum as per the manual you mentioned. Should I be okay or is that cutting it too close?

Thanks

How often, if ever, will the generator be putting out full power? If you know it's not all that often, try with the 1/2", would be what I would do, if it were me, but it's a guess.

Liquid propane has thermal capacity of about 93,000 BTUs per gallon. monkey

 

[shamrock12]

How often, if ever, will the generator be putting out full power? If you know it's not all that often, try with the 1/2", would be what I would do, if it were me, but it's a guess.

Liquid propane has thermal capacity of about 93,000 BTUs per gallon. monkey

You're right, I won't likely be running above 50% load for the most part but when I do need to run at full load, I would want it to be able to run without a hiccup.

 

[CNGsaves]

So is this black pipe steel you're considering using buried ?? If buried, then I'd yank it out and start over doing it right.

Proper pipe is yellow plastic polyethlene for burial at least 18" underground (state code may require more) and at each end there are risers that convert from plastic to steel above ground with a shutoff. In the trench you'll bury a tracer wire so that plastic pipe can be located later.

I would go BIG so you are sure you don't have starvation of fuel. Thus, 1" yellow plastic pipe would not be overkill for buried pipe. May only need 3/4" black pipe steel above ground with your genset size right now (later you might have 20 Kw genset so 1" would be appropriate) - - thus, I would absolutely purposefully overbuild the buried portion, if not everything.

No way would I try only 1/2" for 25 ft and expect it to work properly. Don't do it.

Good luck. Post up some pics which shows what you've got now.

 

[shamrock12]

So is this black pipe steel you're considering using buried ?? If buried, then I'd yank it out and start over doing it right.

Proper pipe is yellow plastic polyethlene for burial at least 18" underground (state code may require more) and at each end there are risers that convert from plastic to steel above ground with a shutoff. In the trench you'll bury a tracer wire so that plastic pipe can be located later.

I would go big so you are sure you don't have starvation of fuel. Thus, 1" yellow plastic pipe would not be overkill.

Good luck. Post up some pics which shows what you've got now.

There is a existing high pressure line entering into the building (3/8" copper tubing buried underground and then changed over to 3/4" black pipe as soon as it enters the building). It goes up about 12 feet vertically where the low pressure regulator is installed (for the ceiling mounted air forced gas heater). The propane company came by last week and installed half inch black pipe by teeing past the low pressure regulator. It goes down about 10 feet vertically before going through the wall to outside where the quick coupler will be installed. So I'm not sure how I'm going to break out the news to the propane company. The foreman told me he has a portable generator that runs on propane at home so I trusted him knowing what he was doing at the time.

 

[CNGsaves]

OK, I understand that you're just piping the propane low pressure line through building to just be on outside wall. Then you'll have quick connect hose (just after a shutoff I presume) so you can have flexline to the portable genset.

This being done as your electrical plug there for genset to backfeed the main panel?? You using an interlock breaker on panel, or do you have automatic transfer switch??

If you want to try the 1/2" idea, just cheat and throw together similar length of 1/2" black pipe LPG supply line over in other part of building as a TEST setup (ie just lay it out on floor with similar number of elbows, etc). Cobble together similar length of pipe and flexline and just test the genset over there. Load test the genset with bunch of heaters and see what happens. There's always more than one way to skin a cat !!

 

[shamrock12]

I also should say that from what I have been learning today, it is becoming apparent that the propane company goofed up. I am going to check up on the foreman and see if I could get him to change to 3/4". It probably will be difficult to enlarge holes through the wall so I think I might ask him to run 3/4" as much as he can and then reduce down to 1/2" before it protrude through the wall, and possibly shorten the 1/2" hose length to 12 feet. Should that work out ok?

Thanks to all

 

[shamrock12]

Yup, there will be a quick connect right outside the building and the genset outlet will be installed next to it. I'm an electrician by trade so no worry about the electrical part of this setup

Edit: There also is a shutoff valve right before the quick connect ... I mentioned that to the foreman before they started the job.

 

[JoeFin]

I also should say that from what I have been learning today, it is becoming apparent that the propane company goofed up. I am going to check up on the foreman and see if I could get him to change to 3/4".

That's not the problem

Your feed for the generator needs to be ahead of the low pressure regulator and have its own regulator there at the generator.

Reason being, you tune your generator starting by adjusting the regulator pressure

 

[sberry]

I got to agree that something is goofed up. Many LP regs on equipment can run from tank pressure, I have 5 units and not a pre reg among them. Look for the pressure rating on the genset reg. T in ahead of the building, that 3/8 will carry about 200K on the primary. It should have had 1/2 from the tank to run this and a furnace etc.

 

[Milton Shaw]

Propane is delivered from the tank at many different pressures. My line from tank to first regulator is 1/4" and that is for a 17KW generator. From the first regulator to the second I ran 1 1/2 inch pipe. That first regulator steps pressure from 125lbs tank pressure to 2 lbs line pressure. The regulator at the generator steps the 2lbs pressure down to the 11 inches pressure required by the generator. You need to find what pressure your regulators are using from the propane company. That along with the generator size determines the size pipe you need. Talk to the propane company.

 

[sberry]

The propane co may not know squat, most of them are truck drivers and very few in the biz are very technical. I suspect the genset will run from bottle pressure. Look at the converter on it, most were designed to run from liquid, they can run from small bottles with liquid tap. A 3/8 line at bottle pressure will run a 500 Cadillac engine.

I have big pigs, 500 and 1000 gallons and run vapor to the converter, the bottle is large enough to pull 400 hp thru a 1/2 line.

 

[sberry]

Only one I run liquid is this forklift, its got only a 30# tank. Without looking at the unit,,,, I don't think you need to run it on the secondary regulator. Show pic of the converter on the genny.

 

[72Anthony]

Why are you planning to use such a long flexible line? Normally the hard pipe is run to the generator a short 1-3' flex line is used to absorb vibrations and any misalignment. Not sure if it is good practice or even code compliant to have a 15' flex line.

When sizing lines, you need to calculate equivalent length of fittings and flexible pipe. A 1/2" 90 degree elbow is equal to 1.55' of 1/2" pipe. I'm sure the flexible line has much more resistance than the same size of smooth wall piping.

Regards,
Anthony

 

[bob15]

Considering I just installed this past spring a similar size generator, I was in the same boat as yours. i did all the work myself, including the gas piping. Some of the advice given above is completely wrong.....

Half inch black iron is too small for your operation. Most systems have 2 regulators, one at the tank and the second close to the generator. Code requires the 2nd stage regulator to be 5+' from an ignition source (engine). My 12kw generators came with a 24" long 1" flex pipe, though the inlet pipe on the generator is 3/4" (they probably use one flex pipe for both their 12 & 20kw set). Between the 1st and 2nd regulators, I used 1/2" copper tubing (LP rated and coated).

You can set the regulator closer to the ignition source, but you must plumb the regulator vent 5 feet away from ignition sources. Regulator must also be a min 18" above ground (check your code). Yellow coated tubing is OK between regulators, but most companies seem to prefer black iron between the 2nd reg and gen set. Having a ball valve close to the generator is a very good idea.....I like the US made Apollo brand. Have a union also close to the generator in case removal is ever needed.

You do NOT set the generator by adjusting the regulator. Most gen sets have you adjusting the governor or carb. Also, running straight from a "bottle" will screw things up and/or could cause serious issues. These generators AREN'T typically designed to run liquid, but rather vapor.

I did find with mine that the intake vents don't let enough air in the enclosure and that they needed to be bent up slightly......no don't really notice it, but is made a night and day difference.

Go to page 14 and 15 of the attachment....it might make your installation a little easier.

http://www.gillettegenerators.com/files/support/130506-OGU08-OWN-798-20121029.pdf

hope this helps.....
bob

 

[giggleooza]

Are portable propane generators better than gas? I've been looking into a sportsman or a generac 6000 http://www.squidoo.com/best-propane-portable-generator

 

[sberry]

Did it come with instructions?

 

[aandpdan]

Are portable propane generators better than gas? I've been looking into a sportsman or a generac 6000

By gas do you mean gasoline or natural gas?

Propane and natural gas have less btu's but the advantage is that there is no carburetor to gum up from sitting. I also find my two generators run much smoother on propane than they ever did on gasoline.

 

[sberry]

He said this is a portabe generator which leads one to believe it ins not a Generac type permanent standby, most have a hi pressure reg and converter so they can draw liquid for use on small bottles. Read the specs or get a pic of the converter.

 

[txst]

Rough calculations would predict a 12kW generator to require approximately 200,000BTU/Hr. Looking at NFPA 54 Fuel Gas Code standards for LP, a 1/2" Schedule 40 black iron pipe will suffice at a length of 20ft, at 11.0"wc and a pressure drop of 0.5"wc. This is with no fittings. A quick connect has a pretty big restriction and pressure drop. This is too small.

I would definitely go 3/4" Schedule 40 and the largest quick connect I could find. If the generator goes lean when you are asking a lot out of it (full load), the engine can fail.

 

[sberry]

I think it would run out of power. If there is a primary reg at the tank then the line after should be 1/2. 3/8 is good for 200K @ 66 ft, wont supply this and a heater or would be marginal. That's where I would be getting the fuel from anyway, T before the building reg and then put another reg at the unit, screw 1/2 hose to it and to the genset. There is no reason to go thru the building service in some convoluted scheme.

 

[nehog]

That is what I suspected ... it just seemed alot to me. So at full power of 12kw, it sounds like the generator would be burning around 186,000 BTU/hr at 11" W.C. which would be right around the maximum as per the manual you mentioned. Should I be okay or is that cutting it too close?

Thanks

Considering that it will be rare that you run your generator at full load, you may be OK.

 

[txst]

He said this is a portabe generator which leads one to believe it ins not a Generac type permanent standby, most have a hi pressure reg and converter so they can draw liquid for use on small bottles. Read the specs or get a pic of the converter.

Generac makes a lot of portable generators, as well as the whole house and commercial units. They have a LP5500 portable which runs on propane - a great little unit and you don't have to worry about the gasoline going bad when it sits unused for a while. The nice thing about buying a generator from a manufacturer that is already LP fueled is that it was designed that way and has to carry the emissions certification. These aftermarket kits are risky, in terms of how well they were tuned (not only for the dangers of CO, but in tems of being too lean for engine damage, or too rich for limiting run time on a bottle).