Standby Generators

Stet

Over the last couple of years, standby generators are popping up everywhere. Most running on natural gas. What I have found, time after time is, these power plants run at 309,00 btu's, already more than the standard 250 CFU meter is meant to supply. Now add 110,000 for a boiler, another 38,000 for the water heater, the a dryer and range. You have a problem.

Had a service call with this scenario a while back (before the days on C/o detectors. The power had been out for a couple of days and running on a standby generator. The gas boiler actually sooted up. It was plugged between the sections. And I had a wife with what she thought was a very serious case of the flue. Needless to say, we got her out of the house as quickly as possible.

In the end we had a 250 CFH meter and a 600,000 CFH demand. We have had Gas Company people tell consumers that their meters are big enough. I tell the gas company rep, "Give me something in writing that says that please, and tell me you will be responsible should anything goes wrong." All of a sudden we have a change of attitude. "Well, if it makes you feel more comfortable, we'll change the meter.

Don't be stuck in the middle of a really bad situation. Always check the meter size.

Jamie Hall

I have a sad suspicion that we may see more of this kind of thing. Not just because of undersized meters, but because for so many years the gas companies and the Greens have been pushing gas as the way to go for heat -- and generators. And now the problem is getting adequate gas to the system, leading to low pressure in areas (there've been a couple of threads on this).

What arrangements are there (I'm not that familiar with gas boilers) to ensure that the unit locks out if the inlet pressure is too low for any reason? A generator isn't really a problem -- it will run on low pressure, just not be capable of maximum output. But a boiler or furnace?

STEVEusaPA

Any reputable generator installer will first submit to the gas company the parameters of the generator and all other connected gas appliances. The gas company will then provide the correct meter to ensure enough WC and volume of gas. Or tell the customer it's not going to work.
Properly sizing the line to the gen is crucial, especially considering distance.
Then after the install, turning on all appliances and measuring gas pressure drop is crucial, as is a load bank test.
Another thing to consider is actual pressure/volume available when it's very cold out. Gas utility companies just cannot keep up, as many recent articles have shown, doing things like switching commercial accounts (interruptibles) to heating oil, and putting moratoriums on new connections to their grid.
You can also put load shedding devices, wired to transfer switches, to leave the non critical gas appliances from running.

nibs

What price moving the generators radiator into the house to be a heat source?

ChrisJ

nibs said:

What price moving the generators radiator into the house to be a heat source?

Do you seriously think this is something that should be considered for backup generators that are practically never actually used?

Not to mention 99% of residential ones are air cooled.

nibs

@ChrisJ It is an option that the owner may want to consider.
The cost of adding a second radiator may be worth it in some cases to some owners. Why waste the heat?

ChrisJ

nibs said:

@ChrisJ It is an option that the owner may want to consider.
The cost of adding a second radiator may be worth it in some cases to some owners. Why waste the heat?

Well.
First, show me a water cooled residential backup generator.

Second, show me the payback on doing such a modification and installation for a system that is rarely used to power the house.



I suppose there are always exceptions. With all due respect, I just don't see it as being practical.

STEVEusaPA

nibs said:

@ChrisJ It is an option that the owner may want to consider.
The cost of adding a second radiator may be worth it in some cases to some owners. Why waste the heat?

Sounds like a bad idea for the 1% that may actually have a radiator.
Solar panels would be a more fruitful endeavor.

TAG

What's KW generator uses 309Btu's

One of my places has low pressure gas service and the local gas company had to run 2" plastic to my house when I added a 400k pool heater. It's a problem around me with all the generators going in

ChrisJ

I am a bit confused though.

Why does starving a boiler of gas cause it to soot up?

Jamie Hall

ChrisJ said:

I am a bit confused though.

Why does starving a boiler of gas cause it to soot up?

Interesting question -- the sooting, clearly, is the result of a change in air/fuel ratio -- but exactly why, for a given burner, that would happen -- and in which direction -- would be interesting to know.

Anyone? @Tim McElwain ?

EBEBRATT-Ed

The gas utility is full of crap. The meter is not big enough. Pool heaters and generators use a lot of gas.

As an example West Hartford, CT has low gas pressure. Many of the RICH people their want generators. The local inspector told me they are strongly encouraging people to install propane generators and stay off the natural due to low pressure and an overtaxed system.

In MA where I am you can't have propane and natural in the same building without special permission.

Of course the generator is outside so I don't know if that would fly up here

Leonard

Seems vapor fueled burners without draft motors use velocity of gas out burner orifice to pull air down venturie. Guessing air suction is non-linear with gas pressure, so lower pressure might draw lot less air, making a rich flame, soot. Also maybe poorer mixing.


309K BTU/hr sounds like a 20kw gen at full load. Large for most houses.. But easy salespitch to say you can run EVERYTHING at same time. They are on display at entrance of HomeDepot

Many gen knowledgeable people use a 3 or 5 kw gen and load management to avoid the proportionally larger no-load consumption of large gens. Fuel $$$ adds up fast over a few days or a week continuous run. Gen is ~ 20 % efficient at best ( full load)

15 kw Onan JC gen burns ~ 100k at no-load and ~240k at full load
But frequently have to up nat gas piping size on longer runs and change meter orifice restrictor ( pipe break flow limiter)

For large gens (15-20kw) nat gas is the fuel of choice. If use gasoline would need LARGE tanks and it deteriorates with age (ethanol pulging isses). 15kw gen at no-load needs ~ 24 gal/day, at full load it needs 58 gal/day. That is HEAVY to transport and carry. Propane consumption is ~ 20% more.

nibs

@Chrisj
Not to derail a thread buuut;
"First, show me a water cooled residential backup generator."
I Have a 7KW water cooled Kohler genset that will run on gasoline, LPG or NG .
When we run it, in cold conditions the heat is used to warm the conditioned space.
Took less than a day to rig the coolant re routing, and very little money. (Under $100). Biggest problem that I see is, making it look nice, and not causing the building inspector to delaminate.
IMO If your customer wants a water cooled backup generator, it is a simple matter to redirect the heat, reducing the need to use the installed 'in house' heat system.

nibs

PS. Should have noted that I tend towards the possible, rather than the practical....................... Practical is your job.

Leonard

If your a DIY selfer used marine gens are popular to recover heat in water ~ 35% of fuel input BTU, since they usually water cooled, at least the Onan ones. If recover heat in exhaust can boost % even more.

TAG

Years ago with whole house you sort of self managed the load. We had RIB's on the AC compressors for example -- most loads would not restart after the initial power company line went off. Today, code forces full load management and most load control systems max out at 4 X 50kw relays. This forces larger units .. my most recent was 20/22KW.

Years ago 7w dedicated panels or 13kw was typical .

Jamie Hall

Speaking years ago... it's been kind of interesting, over the years, to watch the changes in backup generators and their use. When Cedric's home got its first backup generator -- in the mid 1950s -- it was a pretty pesky affair. Why was it there? Because at the time it was a working dairy farm, and believe me milking 80 head twice a day by hand was a chore. So we had a generator for the milkers and the coolers. It ran the whole farm. Most folks who didn't need them that way didn't have them, and the folks who did were handy -- they had to be. Now most folks who have them don't really need them, except to keep the toys running, and have no clue as to how and why they operate -- and really don't want to know. All that is wanted is to keep the lights on. Nothing wrong with that -- it's just different.

TAG

Jamie -- That's the crazy. I have an old 7k B&S unit at my beach house that was installed just before the power company replaced the main line to the island. We never lose power now - but there is still a market down there for generators. Same with my suburban NJ property -- we lost power last year for the first time in years (about 6 hours) ... it's happened maybe twice in 25 years. Some of my neighbors think nothing of 25- 30k for a full house generator .. nut's.

ChrisJ

I still haven't had time to finish my generator project.
Converting a 2004 B&S NG \ LPG 10KW whole house generator into a portable just to store it better and bring it out when needed.

So far I've only got a few hundred dollars invested in it, which isn't bad.

However, it was from a beach house and I can't believe what salt air does to things. The PCB was destroyed so it'll be manual only.

Leonard

We made military stuff, we dipped the boards in clear conformal coating to protect the boards from condensation, and salt spray (mil spec requirements). Was like thick paint, basically a thin 2 part "epoxy". Dip and let excess drain off. Likely urethane 2 part clear coat that goes over car paint would work fine. A clear varnish like paint likely will work too.

I believe code doesn't require load managment and LARGE gen rated to carry everything that might be on IF you don't use automatic transfer switch. Lot of people use manual trasnfer switch or interlock ( it's manual)

I think these days sales people talk home owners into 20kw gen just because price is higher, so their commission is higher. Even if your south and need A/C for medical issues, don't need that kind of power. Can put a window A/C in one room even.

TAG

Leonard: Everybody wants the whole house w/ auto switch. In all fairness -- it's often very little more if a 20/22K can do it since so much is the labor.
My new build is Propane and the Cummins 20/22 kit w/ auto was only a few hundred over the next lower with almost no fuel use penalty. The step down in size wood have needed a separate panel with only partial coverage. Doing the whole house is actually less labor. They are doing propane in areas with NG .. I can only assume because of what the OP is talking about

Leonard

Point taken, but in my opinion 20kw is overkill for most houses.

I'm a mechanical engineer and a bit on economical side. Bought 7kw Onan 7NHM for $200 , replace dead voltage regulator $200, converted it to 120/240 output. ~ $60 interlock for breaker panel, some 10-3 wire and I'm good to go.

And I likley could get by with 3-4 KW gen. But with 7kw I don't have to do load managment, except if run drier, oven or , more than 2-3 stove elements. It'll even run a 20 kBTU window A/C

brandonf

> @nibs said:
> What price moving the generators radiator into the house to be a heat source?

I had the same thought 👍

Leonard

Heat recovery only really makes sense if your living off grid or running gen a lot. Some guys only have single phase, and have 3 phase gen to run welders and machines in a cold garage

At only ~ 17% efficiency at best ( full load) Gens burn a LOT of $$$ fuel. So gen electricity is much more expensive than utility power, have to recover "waste" heat to make total cost more reasonable

ChrisJ

Leonard said:

Only really makes sense if your living off grid.

That I'll agree with

Jean-David Beyer

MY backup generator says this:

Rated kW LP 14 kW
Rated kW NG 12 kW

Fuel Consumption on NG at 50% load? 124 cfh
Fuel Consumption on LP at 50% load? 60 cfh

I am surprised the difference between NG and LP is so much.

My town requires a building permit to put one in, so they can inspect it when it is done. The gas company wants to know the make and model of the generator to see if they have to do anything to supply enough gas before they will allow one.

A few years before, they replaced the leaky 3 1/2" mains in the street that were installed in 1950 (black pipe) and running at a nominal pressure of 15 psi (but actually about 8 psi because most people on my street (including me) converted from oil to NG). The new pipe is black plastic about 4 1/2 inch running at 50 psi. When they made the switch, they came and checked each meter and regulator, but they did not have to do anything with mine. Still about 7-inch pressure after the regulator.

Leonard

Nat gas has less energy than propane. In fact Onan gens run on nat gas used high compression piston/head so wouldn't have to derate output on nat gas.

Regular gasoline compression is ~ 120psi, nat gas is ~ 200 .

hot_rod

> @Jamie Hall said:
> I have a sad suspicion that we may see more of this kind of thing. Not just because of undersized meters, but because for so many years the gas companies and the Greens have been pushing gas as the way to go for heat -- and generators. And now the problem is getting adequate gas to the system, leading to low pressure in areas (there've been a couple of threads on this).
>
> What arrangements are there (I'm not that familiar with gas boilers) to ensure that the unit locks out if the inlet pressure is too low for any reason? A generator isn't really a problem -- it will run on low pressure, just not be capable of maximum output. But a boiler or furnace?


So it’s the “greens” running all those clean natural gas glitzy fracking ads on TV😳

What’s next big oil running wind and PV media blitz overloading the grid

Follow the money, read the fine print on those NG ads

Jamie Hall

The problem probably varies with where one is located. In downstate New York and most of southern New England the gas companies have done a fantastic job of marketing their product, and since that is how they make their money, one can't blame them. What they haven't been able to do is to increase their ability to get their product to market. Their have been several proposals over the years for new gas pipelines or for expansion of capacity of existing ones and... they've all been blocked. Then the power companies have been obliged to shut down the coal fired plants -- which, I admit, were pretty dirty -- and nuclear plats -- which weren't -- and substitute natural gas. With the result that -- surprise! -- there isn't enough capacity to go around at peak demand; a few years down the road there won't be enough capacity for even above average loads, never mind peak.

The New England/downstate New York electrical grid is in the same position.

Point fingers where one will -- there are plenty of targets to look for, if one wants to find the reasons -- but the bottom line is the same: if you want to dance, you've got to pay the piper.