Standby Generator - Diesel or NG?

[hwp]

Cons.... NG or LPG, have certain safety issues (explosive vapors), some concerns with fuel supply (refill) in long term usage, usually of the higher RPM ranges, limited KW capacity availability.

I hadn't thought about a safety issue. I was thinking about building a lean-to onto my garage to house the generator. I was planning to have a door from the garage to the generator area as well as a door in the lean-to large enough to skid the genset in and out if needed. If there is a possibility of a vapour problem then it would seem prudent to leave it outside unprotected - contrary to the way I like to do things.

My main feed (400 amp) comes into the garage then a feeder line splits off to the house. Therefore I don't have the option of having a subpanel for those circuits that are most critical. However, I can still shut off the various secondary circuits in the house breaker panels such as the electric hot water furnace (150 amp breaker) that heats my basement floor. We use three furnaces to heat the house - a regular 85K BTU NG forced air furnace, a rooftop 85K BTU NG forced air furnace/AC and the electric hot water furnace.

I used the calculator suggested in a previous post and it recommended a 30KW generator but it didn't factor in some critical issues such as we have over 12,000 square feet of glass. The glass panels are all gas filled sealed units but there is still a considerable heat loss from them. So I think a 40KW genset is about right. However before I make any commitment, I will have an electrician check out exactly what I need.

Thanks agian for all the input.

 

[kenmac]

I used the calculator suggested in a previous post and it recommended a 30KW generator but it didn't factor in some critical issues such as we have over 12,000 square feet of glass. The glass panels are all gas filled sealed units but there is still a considerable heat loss from them. So I think a 40KW genset is about right. However before I make any commitment, I will have an electrician check out exactly what I need.

Thanks agian for all the input.[/quote]


I have never heard of a heat loss cal. performed when sizing a generator. This is performed to size a furnace. You need an amp load calculation ( add for start up amps) Not a heat loss calculation.


In 1993 we here (in the south) had a winter ice storm. None of the service stations had power to be able to pump gas or diesel. The nat gas never down. Most nat gas pumping stations (around here ) have back up power

 

[GreenMtns]

Howard

We just installed a 13 kW Generac unit here and powered it with LP (NG not available here). The way it was researched by the electrician was.... Add up the AMP's on the required breakers and add in a plus factor. So we determined what we needed to have powered during an extended outage. In our case we could get by with a 7.5kW but bumped it up for the plus.

It will not make any difference that your service enters your garage and then goes to the house. The transfer switch will mount next to the house panel and only the breakers that will be powered by the generator will be jumped over to the transfer panel. Those breakers will always have power and will be the working breakers for your house even when on utility power. When the utility power goes out the transfer panel will switch the feed from utility to standby generator and the rest of the house and garage will be left without power. After the power is restored the transfer panel will switch back to utility power and the generator will run for a few minutes to cool down and then shut off. In each case, loss of power or the utility restoring power, there will be a short delay by the transfer switch to be sure the the lost or gain is not just a surge. In our case, the power is transfered in about 30 seconds or less. These units come in weather protect cases and are meant to be installed outside in most cases. They are also very quiet, so much so that you don't notice them at all.

I think most of the diesel generators will be water cooled and that is another hassle that you don't have with the gas units.

We do loose our power here and are very happy with the setup we installed.

 

[dmccarty]

Ron,

It is a water cooled single cylinder slow speed diesel and I am in the process of plumbing it for recovering the waste heat to maintain my hot water tank at 120F.

What engine are you running and where did you get it?

Later,
Dan

 

[kenmac]

I think most of the diesel generators will be water cooled and that is another hassle that you don't have with the gas units.




If he is getting a 40 KW it will be liquid cooled. Liquid cooled generators ( Generac brand) start at a 20 KW. At one time you could get 15 KW liquid cooled Generac. I perfer liquid cooled as opposed to air cooled

 

[ultrarunner]

These are the most efficient due to their higher torque, lower RPM and direct drive, around .125 gallon per KW per hour.

Ultrarunner, I would guess that that 10GPH is probably closer to what you are actually using at 30% load. a 150KW diesel generator is going to need closer to 20GPH at full load. That is at or near peak efficiency(close to 80% load), The efficiency falls off with a light load and 30% is pretty light for a diesel. .

Ron... you've got me curious about the fuel consumption of unit so I pulled the Purchase Order from 1995.

The spec listed is 9.1 US gph at 125 kW full load. I've been using the 10 gph as a rough estimate when calculating my fuel budget.

You guys are lucky, because here they are really cracking down on ALL stationary Diesels 50 hp and larger. These units must now be licensed, inspected and taxed based on yearly emissions. The next step is planned phase-out of non-conforming units...

Thanks for jogging my memory...

 

[RonMar]

Ron... you've got me curious about the fuel consumption of unit so I pulled the Purchase Order from 1995.

The spec listed is 9.1 US gph at 125 kW full load. I've been using the 10 gph as a rough estimate when calculating my fuel budget.

You guys are lucky, because here they are really cracking down on ALL stationary Diesels 50 hp and larger. These units must now be licensed, inspected and taxed based on yearly emissions. The next step is planned phase-out of non-conforming units...

Thanks for jogging my memory...

Wow! 9.1 gallons divided by 125KW is .0728 gallons per KW/HR. I don't think I have ever come across a fuel consumption that low. Large scale increases efficiency, but those are some low figures.

At work I have Five 1800 RPM Onan/cummins 3 phase generators in service. They use a 30HP 3 cylinder Kubota tractor engine and consume approx .125 gallon per KW/HR.

In answer to yours and Dan's question, my personal genset is a copy of a 6HP single cylinder lister CS engine commonly called a "listeroid"(google it). It has 24" flywheels and runs at 650 RPM nominal(a very pleasant thump-thump-thump). It uses a wide automotive serpentine belt driving an 8" pully on a 5KW generator head at 1800 RPM. I purchased the engine from a vendor out of Portland OR. Rule of thumb for longevity is about 2HP per KW of output and mine can only sustain 3KW, but the large mass of the flywheels(300#) and the heavy cast iron generator rotor give it the stored inertia to start rather large inductive loads like a well pump or air compressor. It will start loads that would stall a box store 3-5KW portable. It too consumes around .125 gallon per KW/HR.

Sizing the generator based on totaling breaker sizes for critical breakers is a bit better than baseing it on your service size, but still probably oversized for what is actually needed, just like the breakers are oversized for the loads they supply. Even using that linked-to calculator, the results should be interpreted a little as it appears to total up the selected items, with no thought to when and how they will actually be operated. It appears to assumes that they will ALL be on simultaneously. IF you want to be burning excess fuel to have the ability to turn on ALL electrical loads in your home all at once, then that is your choice. "Speed costs money, how fast do you want to go"

IMO, A better way to determine size for a backup generator is to actually measure the ammount of electrical power each device uses. An electrician with a clamp-on amp meter can do this quite easilly. Then factor in startup currents for automated loads(furnace, water heater ect). Then look at what you would conceivably use at the same time, with a additional factor for expansion if you have any plans to add in the future. OK, so I can only run the vacume or dishwasher or washer one at a time when on the generator... Guess I now have more time to watch Speedvision.

 

[ultrarunner]

Looks like what I've heard called a "Hit and Miss" utility engine...

Thanks Ron.

 

[Reg]

Awww, I'd use it as an excuse to get a Big *** of a welder/generator set.
Something that WOULD get some exercise once in a while, it would probably have a 4 (at LEAST) cylinder Perkins diesel.

 

[RonMar]

Looks like what I've heard called a "Hit and Miss" utility engine...

Thanks Ron.

The few hit and misses I have ever seen were all horizontals and had a built in cooling/boiling tank. They also had a more distinct sound with the firing once every several rotations and the noticable acceleration and deceleration. They do have the big flywheels in common.

The CS lister is vertical and fires every other revolution just like any other single cylinder 4 cycle engine. Here is a link to a video of one running that is very similar to mine. This one has a 55 gallon cooling tank, where mine has a small 5" X 12" heatexchanger. The aluminum ducting down past the generator in this video is slid right over the stock "peppercan" muffler, probably just to direct the exhaust a particular direction. You will note that it is not very loud. Search "listeroid" or "lister" on Youtube and you will find a bunch of different videos.

YouTube - Lister 2