Looking for advice on datacenter electrical/generator

Mailman List Mirror (Read Only)
1

Speaking on Deep Background, the Press Secretary whispered:

> He also is strongly opposed to us purchasing a natural gas generator
> which seemed like a shoe-in for us.

I know of several cases where the San Jose fire marshall turned off
natural gas as a precaution. You may wish to discuss with your local
fire marshall under what conditions they will turn off the gas.

Some places require auto-shutoff valves for NG as an earthquake
precaution.

Natural gas is a big plus in many ways; one undervalued by both
customers and generator sales folks..

But all that ONLY in non-tilting/shaking enviroments. If
'earthquake' does not mean "something that happens out in THEIR
state.." to you; then don't consider it.

2

Natural gas is a big plus in many ways; one undervalued by both

    > customers and generator sales folks..

I agree completely.

    > But all that ONLY in non-tilting/shaking enviroments. If
    > 'earthquake' does not mean "something that happens out in THEIR
    > state.." to you; then don't consider it.

Why? In what case is it still not preferable to diesel? The _only_
reason I've ever heard an informed person state for going with diesel is
that the fire marshal wouldn't allow them to store anything else.

                                -Bill

3

I'm in Santa Cruz County. Since I've been here, natural gas has been off for
multiple days in a row twice. Once because of an earthquake, the second time
because a winter storm put a lot of water in a hillside and the slide
severed the (only) high pressure gas feed for the county.

In both cases, electricity wasn't stable either. So for the last datacenter
I built, I went with diesel.

I've also been told, though I don't know how true it is, that diesel
generators can go longer between service intervals, though for a datacenter
I wouldn't skimp on routine maintenance anyway.

Matthew Kaufman
matthew@eeph.com <-home
mkaufman@dsl.net <-work

4

I'm not following your logic... How does the fact that natural gas is
_usually_ available on-tap, and diesel _never_ is make diesel preferable?

                                -Bill

5

The goal of the generator is to keep the datacenter running when the power
fails. Power around here fails because of storms and earthquakes, both of
which have a demonstrated history of also taking out natural gas at times.

This means that at least one of your generators (around here) should run on
something you store on-site. And thus, if you can only afford one, that one
must be in that category.

By your logic, the fact that electricity is _usually_ available on tap
eliminates the need for a generator altogether.

Matthew

6

This means that at least one of your generators (around here) should run on

    > something you store on-site. And thus, if you can only afford one, that one
    > must be in that category.

Right. So if you have a choice of storing gas or diesel, and gas usually
doesn't have to be replentished by truck, since it's _usually on-tap_, but
diesel _always has to be replentished by truck_, since it's _never
on-tap_, why would one ever choose diesel unless, as per previous caveat,
clueless fire marshalls thought it was really preferable?

                                -Bill

7

Thus spake "Bill Woodcock" <woody@pch.net>

    > natural gas has been off for multiple days in a row twice.
    > So for the last datacenter I built, I went with diesel.

I'm not following your logic... How does the fact that natural gas
is _usually_ available on-tap, and diesel _never_ is make diesel
preferable?

As noted by other posters, natural gas often goes out at the same times as
electricity in some areas (e.g. California). In fact, many power companies
use natural gas to generate electricity.

Relying on one public utility to supplant another is not logical unless
either you have historical data to satisfy you that outages in one are
rarely linked to the other, or you can store natural gas onsite to run "long
enough" and only need the utility to refill later.

S

Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking

8

In a message written on Fri, Apr 04, 2003 at 04:13:46PM -0800, Bill Woodcock wrote:

Right. So if you have a choice of storing gas or diesel, and gas usually
doesn't have to be replentished by truck, since it's _usually on-tap_, but
diesel _always has to be replentished by truck_, since it's _never
on-tap_, why would one ever choose diesel unless, as per previous caveat,
clueless fire marshalls thought it was really preferable?

I'm not an expert but:

1) Storing natural gas is significantly harder (both in the containers
   and permiting) than Diesel. It also has less energy density, so it
   takes more space.

2) Having natural gas trucked in, rather than delivered via pipeline
   is also extremely difficult, and possibly impossible in some areas.
   The infrastructure simply doesn't exist.

   On the other hand I could pick up the phone and have a semi-truck
   full of Diesel in any major metropolitan area in an hour or so
   for cheap. Indeed, it's very easy to get "guaranteed responce
   time" diesel contracts for emergency generators, I'd love to know
   if anyone has even attempted that with Natural Gas delivery by
   truck.

3) Getting a natural gas feed for a large data center (read a couple
   of megawatts) is probably impossible in most areas. The distribution
   network for natural gas just isn't set up for it. Much less of a
   concern for the people who need a few hundred kilowatts.

4) In larger sizes, Diesel gensets are _cheap_. Remember, the thing
   sitting outside the data center is essentially the same as every
   diesel-electric railroad locomotive, every portable power source,
   and a whole number of other things. Natural gas isn't generally
   a good idea for your train locomotive, so the gensets are less
   tested, harder to find, and more expensive.

So, IMHO, natural gas is good for smaller applications (probably
under 250Kw), in areas where the gas is stable so you don't have
to do on site storage. Otherwise Diesel is probably cheaper (both
in genset cost and fuel cost), and easier to obtain.

9

It's quite as simple to store propane as it is diesel. Propane stored on-site is stable, needs no cleaning, and the genset is the same as you'd use for natural gas. Given the choice between storing a large quantity of diesel and storing a large quantity of propane, I'd take propane. Other folks would argue the other way. Scared about fire reaching your propane tank? Use in-ground tanks. Unlike fuel oil or gasoline, buried propane tanks are allowed, at least in some places. Think about it... leaking propane tanks don't pollute the soil, they pollute the air.

Though I'm in an area where interruption of gas service isn't really a problem, the availability of gas is. Some towns just don't have gas service. So, we store propane. Not a big deal.

I suspect, though I've never seen it done, that it'd be possible to set up a gas genset with both a pressurized tank of fuel and a connection to the mains, with valves to switch between.

10

1) Storing natural gas is significantly harder (both in the

    > containers and permiting) than Diesel.

Having done both, I would say that gas is much simpler from a practical
point of view, and a little worse from a permitting point of view. I'd
rather go through the one-time hassle of the permitting rather than the
continuing hassle of maintaining diesel facilities, any day.

    > It also has less energy density, so it takes more space.

That's true, though it's never been a sufficient difference to be
problematic for me.

    > 2) Having natural gas trucked in, rather than delivered via
    > pipeline is also extremely difficult...
    > It's very easy to get "guaranteed response time" diesel contracts
    > I'd love to know if anyone has even attempted that with Natural Gas
    > delivery by truck.

Yeah, it's no problem. Certainly no different than deisel in a metro
area, and much easier than diesel in rural areas. I've never had to ask
for a rush delivery, but I've always been offered delivery the same day
I've called, and I believe the contract guarantees four-hour deliveries
when we need it. My tank is a 96-hour supply, so that's fine for me.

    > 4) In larger sizes, Diesel gensets are _cheap_.

The only difference between the diesel and gas genset is the carburetor,
which is just different, not more expensive.

                                -Bill

11

Yes, that's the way it's normally done. The input at the carburetor is
valved based upon the pressure on the utility-line side.

                                -Bill

12

this is the gist of what i learned a couple of years back. when i asked
the PE at the vendor (a Cat reseller) about gas vs. diesel, he showed me
that for the size generator we were looking at, diesel was a much better
bet on the economics alone.

richard

13

Natural gas as generator fuel is generally not a good idea for a few reasons:

- Natural gas is volatile, hence not a good option in earthquake prone areas - earthquake + natural gas line = big smelly leak - big smelly leak + spark = big fire
- Diesel is fairly stable, and won't go up with quite so large a bang in a fire, not to mention it can only be ignited under extreme temperature and pressure
- The gas gets cut off immediately in any fire situation, usually affecting a few city blocks at a time
- Diesel is readily available, and can be delivered by any Joe Citizen during a disaster to the generator site, since it doesn't require much in the way of special containers

Diesel generators come in both turbocharged and naturally aspirated models, which can easily be serviced by any competent diesel mechanic. Genset diesels are not any different than diesels in a passenger vehicle, tractor, or transport truck. In fact, diesels in gensets are engineered to work under much higher load conditions than vehicles, since they run constantly at a higher RPM under load

Last, but not least: if you can't get diesel fuel from anywhere to run it, buy a few gallons of vegetable oil from the local supermarket and pour it in the tank. It'll work just as well.

Timo

14

Not entirely accurate. Since has low volumetric energy density compared to diesel, NG/Propane gensets are basically de-rated diesel gensets. A 150KW diesel would be approximately 100KW as a NG and slightly less than that when running on propane.

There is an interesting research/marketing paper from Onan/Cummings on current and emerging power generation methods including diesel, ng, propane, hydrogen, turbines, reciprocating engines, microturbines, and fuel cells.

http://electrochem.cwru.edu/yeager/ohiofuelcell/Norrick-Cummins.pdf

When I was evaluating gensets for our datacenter, I found a really interesting unit which uses propane and/or natural gas mixed with the air to extend the runtime by adding significant BTUs from the gas. However, it can run directly on diesel alone should the gas supply be interrupted for some reason. Very neat technology and obvious after the fact, but much more expensive.

We opted for a standard diesel genset since it is reliable and proven. The last thing I wanted was unknowns in a energy source I need to depend on when everything else goes to hell.

-Robert

Tellurian Networks - The Ultimate Internet Connection
http://www.tellurian.com | 888-TELLURIAN | 973-300-9211
"Good will, like a good name, is got by many actions, and lost by one." - Francis Jeffrey

15

Natural gas is volatile, hence not a good option in earthquake prone

    > areas - earthquake + natural gas line = big smelly leak - big smelly leak +
    > spark = big fire

They're already there. Whether or not you use it doesn't affect the
likelihood that it'll break in an earthquake. And FWIW, I've been
throught a lot of earthquakes, and I've been through a lot of gas-line
cuts, but the two have never coincided. Backhoes always so far.

    > - The gas gets cut off immediately in any fire situation, usually
    > affecting a few city blocks at a time

When was the last time you saw a fire that affected a few city blocks?
I'm sure gas would be cut off in the event of a fire of that magnitude,
but are you arguing that diesel delivery would continue? Trucks rolling
through the maelstrom? I'm not sure what your point is here.

    > Diesel generators come in both turbocharged and naturally aspirated
    > models, which can easily be serviced

Hey, and engine is an engine, regardless of what you dump in the top.
Doesn't make any difference to the mechanic, or the parts guy, or
whatever... It's all the same parts.

                                -Bill

16

Gasoline and natural gas engines run with a compression ratio of between 8.5:1 and 11:1 nowadays. Diesel engines require a minimum compression ratio of 22:1, since diesel fuel requires a lot of heat and extreme pressure to ignite. Natural gas engines use carburetors, while the newer gasoline engines are using fuel injection.

The diesel genset engines use direct injection, there are no carburetors for diesel engines. Diesel fuel cannot be atomized by a carburetor the same way gasoline can, since it is a fuel oil.

Timo

17

I was in LA during the big quake, I saw quite a few fires -- all gas-line
cuts.

-Dan

18

    > Natural gas is volatile, hence not a good option in earthquake prone
    > areas - earthquake + natural gas line = big smelly leak - big smelly leak +
    > spark = big fire

They're already there. Whether or not you use it doesn't affect the
likelihood that it'll break in an earthquake. And FWIW, I've been
throught a lot of earthquakes, and I've been through a lot of gas-line
cuts, but the two have never coincided. Backhoes always so far.

Backhoe, earthquake, bottom line is that there's a break.

    > - The gas gets cut off immediately in any fire situation, usually
    > affecting a few city blocks at a time

When was the last time you saw a fire that affected a few city blocks?
I'm sure gas would be cut off in the event of a fire of that magnitude,
but are you arguing that diesel delivery would continue? Trucks rolling
through the maelstrom? I'm not sure what your point is here.

Gas being turned off usually affects a few city blocks.

    > Diesel generators come in both turbocharged and naturally aspirated
    > models, which can easily be serviced

Hey, and engine is an engine, regardless of what you dump in the top.
Doesn't make any difference to the mechanic, or the parts guy, or
whatever... It's all the same parts.

Ask a mechanic that question. You'll likely get a somewhat different opinion.

Timo

19

There is an interesting research/marketing paper from Onan/Cummings on

    > current and emerging power generation methods including diesel, ng,
    > propane, hydrogen, turbines, reciprocating engines, microturbines, and fuel
    > cells.
    > http://electrochem.cwru.edu/yeager/ohiofuelcell/Norrick-Cummins.pdf

You're right, that's really good reading.

    > interesting unit which uses propane and/or natural gas mixed with the air
    > to extend the runtime by adding significant BTUs from the gas. However, it
    > can run directly on diesel alone should the gas supply be interrupted for
    > some reason. Very neat technology and obvious after the fact, but much more
    > expensive.

URL?

                                -Bill

20

As a volunteer FF ...

Actually, if a fire affects a few city blocks, there will be quite a few
diesel trucks rolling if its a block of any magnitude. Cummins turbo
diesels pumping 2000GPM out a ladder pipe drink a lot of diesel. Its not
uncommon at all to refuel them on the fly with courtesy of your friendly BP
delivery driver and its also fairly common to park an 1-1/2" fog stream
underneath the truck fogging the exhaust lest we burn a hole through the
pavement ...

You'd have better odds of finding a diesel truck than the gas line being on
with a large fire.