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BobPick

@glensfallshosp.org

20 kw generator

I had a Seimens 20 kw generator installed at my home. My propane company is saying I need a 1,000 gallon propane tank to run it correctly (something to do with the cold weather and vaporization). Does this make sense at all???????


John Galt
Forward, March
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Happy Camp
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Yes.


cowspotter

join:2000-09-11
Ashburn, VA
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reply to BobPick
That's a very large generator so yes that size tank would be necessary. Your fuel requirements would be large so the capacity itself would be necessary to prevent frequent refills. In addition, it needs to be that large to prevent the tank from freezing.


jack b
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reply to BobPick
A smaller tank would not have adequate surface area for the liquid to turn to vapor under that size load. Otherwise you would need a vaporizer that uses the gas in a special burner to add heat to produce sufficient vapor.
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Mr Matt

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1 edit
reply to BobPick
There are a couple of ways to get around the 1000 Gallon requirement. Check with the propane supplier what the minimum size tank is if buried below the frost line? I visited someone many years ago that had a propane tank heater that wrapped around the tank.

This website provides a lot of information:

»www.propane101.com/index.htm


toby
Troy Mcclure

join:2001-11-13
Portland, OR
reply to BobPick
Depending on how much power you actually use, it'd use about 2 gallons an hour. You might want a 1000 gallon tank, which would be 80 to 90% full.


mitchell

join:2002-06-21
Darlington, SC
reply to Mr Matt
You will need a large tank to meet the requirements of run time. Remember they only fill to 70-75%...my agency has 1000gal tanks on 5 five 20KW genny's and the most you get in the tanks in the winter is 75-80% max, in summer if will vent of you pack it that full and that is not good to see or feel in your pocketbook.

did you really need a 20KW, most times with judicious use of energy you may be able to get buy on a smaller unit...

bkjohnson
Premium
join:2002-05-22
Birmingham, AL
reply to BobPick
Does your propane supplier offer a metered propane option?

daveinpoway
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join:2006-07-03
Poway, CA
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reply to Mr Matt
If the engine will start without heating the tank, would it be possible to route the engine coolant (I assume that a generator of this size has a liquid-cooled engine) to some sort of heat exchanger that would keep the tank warm in order to get the desired run time? This way, the tank could be kept warm when the generator is running without the cost of operating an electric heater.


ArgMeMatey

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reply to cowspotter
said by cowspotter:

In addition, it needs to be that large to prevent the tank from freezing.
Please clarify; I have a little tank, 20 lb, 5-gallon, whatever, on my grill. I grill all winter and have been doing that for well over a decade. I've never had it freeze. Winter temps here are normally in the 10-20F range but regularly dip below zero F.


Jon
Premium
join:2001-01-20
Lisle, IL
said by ArgMeMatey:

said by cowspotter:

In addition, it needs to be that large to prevent the tank from freezing.
Please clarify; I have a little tank, 20 lb, 5-gallon, whatever, on my grill. I grill all winter and have been doing that for well over a decade. I've never had it freeze. Winter temps here are normally in the 10-20F range but regularly dip below zero F.
People say that a lot. Not sure where it comes from. Maybe a problem if you live on Neptune.

Propane Freeze Point (F) -310
Propane Boiling Point (F) -44


ultram
Premium
join:2002-12-25
Wildwood, FL
Living in Wisconsin on a farm we had on 1000gal tank to heat the barn, temp outside in -35* and the tank never froze.


PSWired

join:2006-03-26
Annapolis, MD

1 edit

2 recommendations

reply to Jon
»docs.engineeringtoolbox.com/docu···gram.png

As the temperature of the tank lowers, the propane's vapor pressure lowers. There comes a point where the pressure isn't high enough to support the gas demands of the generator due to restrictions in the regulators, piping, valves, etc.

Also, there's more to the equation than just the ambient temperature of the tank. As propane is consumed by the generator and the liquid propane evaporates to form propane gas, heat is absorbed. This cools the tank significantly.

The reason for the large tank is to provide maximum liquid surface area to allow for heat absorption into the liquid, and heat transfer from outside the tank.

Also, you don't want to risk having insufficient gas pressure. It will cause the generator to run lean, which means melted pistons.


Jon
Premium
join:2001-01-20
Lisle, IL
Well if they are in glens falls NY, as their location would suggest. I assume it was supposed to say glensfallshospital.org It doesn't appear that it gets all that cold there.


PSWired

join:2006-03-26
Annapolis, MD
I can't vouch for the accuracy of this data, but assuming it's good, look up the fuel consumption specs for your generator and you'll have your answer for the size tank you need:

»www.bakersgas.com/vaporization-r···nks.html


macsierra8
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Minden, NV

1 edit
reply to Jon
said by Jon:

said by ArgMeMatey:

said by cowspotter:

In addition, it needs to be that large to prevent the tank from freezing.
Please clarify; I have a little tank, 20 lb, 5-gallon, whatever, on my grill. I grill all winter and have been doing that for well over a decade. I've never had it freeze. Winter temps here are normally in the 10-20F range but regularly dip below zero F.
People say that a lot. Not sure where it comes from. Maybe a problem if you live on Neptune.

Propane Freeze Point (F) -310
Propane Boiling Point (F) -44
OK, you can carry liquid propane in an open bucket at -44 F.

But anything under zero degrees F will cause the tank pressure to decrease to a point where liquid will not flow in the supply line to the generator.

One thing you are not factoring in. When any liquified gas turns into vapor in a tank under pressure it creates it's own temperature drop. Think of how AC units operate.. Factor that in and you have the answer to the discussion...
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nunya
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reply to BobPick
They may be correct, depending on how cold it gets in your area.

TheMG
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reply to BobPick
Think of it like boiling water to produce steam. If you only need a little bit of steam, you only need a little bit of heat. But as you take steam away at a greater rate, you need more heat energy in order to maintain the flow of steam.

Another good example is a can of compressed gas duster if you've ever used one.

LPG tanks are the same way, except the boiling temperature is quite a bit lower than that of water. In cold outdoor temperatures, the heat energy required to boil off enough propane at a rate great enough for the generator just isn't there. Once that happens, the propane tank is said to have "frozen". You'll actually see the outside of the tank develop frost in most cases. The propane itself doesn't freeze, it just remains liquid and fails to boil into a gas.

A larger tank has a couple advantages. First a greater thermal mass, and secondly a greater surface area of contact with the outside air, thus it has more heat energy available to boil off the liquid propane. Thus propane gas can be taken from the tank at a greater rate without the need for an external heat source.


ArgMeMatey

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said by TheMG:

In cold outdoor temperatures, the heat energy required to boil off enough propane at a rate great enough for the generator just isn't there. Once that happens, the propane tank is said to have "frozen". You'll actually see the outside of the tank develop frost in most cases. The propane itself doesn't freeze, it just remains liquid and fails to boil into a gas.
Thank you. Never heard the term used that way before. Good explanation.
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Speedy Petey

join:2008-01-19
reply to mitchell
said by mitchell:

did you really need a 20KW, most times with judicious use of energy you may be able to get buy on a smaller unit...
This would have been my question as well.

WHY do folks think they need to keep a small village running during an outage? Even if it is for a day or two.
And I can tell you that day long outages are not exactly common, even in Glens Falls.

Also, isn't this something that should have come up during the research/purchase process? I ALWAYS inform my customers that they will need to have the gas company involved, and that they should contact them BEFORE the final purchase.


Msradell
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join:2008-12-25
Louisville, KY
said by Speedy Petey:

said by mitchell:

did you really need a 20KW, most times with judicious use of energy you may be able to get buy on a smaller unit...
This would have been my question as well.
WHY do folks think they need to keep a small village running during an outage? Even if it is for a day or two.
And I can tell you that day long outages are not exactly common, even in Glens Falls.
I don't know about the OP's situation but in many cases there are extenuating circumstances for your need of a generator. For example in my case I am handicapped and need power for several things related to that. I'm assuming the OP evaluated his needs before the purchase. His question didn't relate to what size generator to buy only to fueling it.


davidg
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reply to Speedy Petey
said by Speedy Petey:

WHY do folks think they need to keep a small village running during an outage? Even if it is for a day or two.
because they want to keep the heat/AC/eletronics going for the whole 15 minute outage! i find it funny when folks will spend 15k on a genset but won't spend 100.00 for a decent UPS to protect the electronics and then gripe when they fry them.

BTW, i have a 5.5kw LP powered genny. it is enough that i can cycle powering my deep freeze and fridge one at a time and still light most of the house as needed. plus i can still watch TV/surg the net should it be an extended outage. in the 6 years i have had it, i used it for a total of 2 hours other than excersizing it and most of that was 1 outage.
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Jon
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join:2001-01-20
Lisle, IL
reply to Speedy Petey
said by Speedy Petey:

WHY do folks think they need to keep a small village running during an outage? Even if it is for a day or two. And I can tell you that day long outages are not exactly common, even in Glens Falls.
My question is... Why does what some folks do bother some folks so much?
Maybe OP has a need for it. And if not. Why do you even care?


macsierra8
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1 edit
said by Jon:

said by Speedy Petey:

WHY do folks think they need to keep a small village running during an outage? Even if it is for a day or two. And I can tell you that day long outages are not exactly common, even in Glens Falls.
My question is... Why does what some folks do bother some folks so much?
Maybe OP has a need for it. And if not. Why do you even care?
Oversized standby residential generators aren't as much of a "bother" in this forum but more of a practical matter. True, the OP might need 20k but I would guess there's a 95% chance he doesn't. Most residential generator size questions posted here are asking for 2 times the watt requirement that's actually needed for the application.

Propane or NG sounds good and clean for a generator if you don't factor in the CF volume required to power one at full load.

When you consider that the average home can get by just fine with a maximum of 12K for standby these big unnecessary capacity fuel eating generators are just plain foolish..

By that I mean, $3400 for a new gas service or $3400 to buy a 1000 propane tank installed.
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cosmicvoid
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join:2001-01-02
Kingston, WA
reply to BobPick
A 1000 gal tank sounds like overkill. When I did the research for my 16KW gen a few years ago, based on local temps never going below 10 degrees F, and averaging 50% load on the gen, the LPG flow rate was easily met with the surface area in a 250 gal tank. The flow rate would actually support a full 16KW load, but I was basing my tank size on a 4 day outage capability. So, I think a 500 gal tank ought to be big enough for a 20KW gen.


nunya
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reply to BobPick
I'm laughing at the people right now who say they have never had a tank freeze.
I've had "hundreds" of LP tanks freeze up while running...wait for it...generators. Granted they were small 40 gallon x 2 tanks, but they freeze up fast. Even in the summer when trying to run a 4 cyl engine.
In the winter, they'll freeze up just running a single heater / blower on job sites.
Sorry. It does happen. I'm not sure about a 500 gal tank compared to a 1000 gal tank when it comes to freezing, but a 20 kW genset will suck down some serious fuel.
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Anonymous_
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reply to cowspotter
said by cowspotter:

That's a very large generator so yes that size tank would be necessary. Your fuel requirements would be large so the capacity itself would be necessary to prevent frequent refills. In addition, it needs to be that large to prevent the tank from freezing.
um dude the Freezing Point is -190C



wilbilt
Pronto Resurrected
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Oroville, CA
reply to BobPick
I have run the LPG forced air furnace in my home from a BBQ tank when my 280 Gallon tank was empty. The small tank does freeze quickly.

Now I use a pellet stove that runs on 12VDC for backup heat.

My $300 3.5kW gasoline generator provides power for the refrigerator, freezer and well pump.

A small PV array, battery and inverter provides power for a few lights at night as well as charging phones and running my wife's CPAP machine, since I don't like the noise of the generator at night (or her snoring).

A 20kW generator seems like complete overkill for a typical home.

For those who say outages are rare, they certainly aren't rare here. Outages have become more frequent and of longer duration over the past few years. In fact, I purchased my generator about 24 hours into an outage that ended up lasting 5 days a few years ago.
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jack b
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reply to Anonymous_
"Freezing" in this discussion is a term used to describe the point at which the LP stops freely producing vapor. That occurs when the liquid reaches -44F, and is not the temperature that LP liquid changes state to a solid, which you provided.
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Speedy Petey

join:2008-01-19
reply to Msradell
said by Msradell:

I don't know about the OP's situation but in many cases there are extenuating circumstances for your need of a generator. For example in my case I am handicapped and need power for several things related to that. I'm assuming the OP evaluated his needs before the purchase.
I think this is a poor assumption. Go read the thread where the guy bought a 25kW before looking into the installation requirements. He is looking at close to $4000 just to install the thing.

OF COURSE I am not talking about circumstances where it is essential. macsierra got it right, although I think it is closer to 99% of people who buy huge generators do not need half of what they buy.
I bet even your situation would likely not require a 20kW genset.