Whole House Generators

There can be different generator power output rating depending on if you are using NG or LPG, the former is usually less. Example for the Kohler 24RCLA 24kW Generator the rating single phase 240VAC is 100 amps on LPG and 87 amps on natural gas, the Generac RG02515ANAX 25 KW is not derated (104 amps). The Kohler water cooled motor is an 1800 RPM 2.2L vs. Generac water cooled motor is 3600 RPM 1.5L, where you see a significant difference is the fuel consumption: Kohler on NG is 150 cfh at 50% and 301 cfh at 100%, the Generac is 297 cfh at 50% and 430 cfh at 100%. So under most operating conditions 25-50% load the Generac is consuming about 2X as much fuel on NG. Noise wise the Kohler at full output is 61dBa, the Generac is 72 dBa, each 3 dBa increase is 2X as loud, pretty significant difference. Voltage frequncy and voltage fluctation on the Kohler is typically 1%, Generac is 5%. Kohler 24RCLA weight is 1260 lbs, the Generac RG02515ANAX is 777 lbs, both use aluminum enclosures so assume most of the weight difference is motor/generator. Price difference between the Genrac and the Kohler/Cummins is about $1000 -1400.

Cummings (Onan) 25kW generatoris rated output at single phase 240VAC 105A on NG or LP, has similar specs to the Kohler as far as fuel consumption and noise level. The Generac's tend to use smaller higher RPM motors in their smaller residential generators, so increase noise and fuel consumption, as well as wear. Fuel consumption of the air-cooled motor generators and noise are also higher than the same output water cooled generators, the Generac air-cooled 22kW generator fuel consumption at 50% load is 228cfh and 327 cfh at 100%.
 
David2011 said:
EDIT: The only fuel option for this question is natural gas. I have no interest in propane, butane, gasoline, diesel or solar/battery systems.

The house not including the sunroom and workshop is over 2800 square feet. It has an all electric kitchen and two central air conditioner systems in isolated zones. Total AC capacity is about 8 tons.

END OF EDIT

We’ve been without electricity for over a full week. Our neighborhood used to never lose power but this is the third time this year that we’ve been without for more than 2-3 hours. It’s time to replace our portable generator with a natural gas powered whole house generator.

Generac has the big name and obviously a lot of units in the field but they also seem to have a spotty reputation. Are they a good brand? Is the reputation problem due to the individual business that installs them? What other brands should we consider?
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Onan is Cummings, They have a reasonable reputation but it'll cost you. I have a 4 ton Seer 18 and it will require 2600 watts running with a multiple of 3 for start up and about 700 wats for each frig and freezer. According to my research you figure in one start up wattage so for 2 4 ton units it would be (2600 x 3) + 2600 = 10400 watts plus wattage for lights, frig, freezers, etc...

An old friend once told me, as a rule of thumb if you multiply your main breaker amps times the largest voltage plug you would be covered so 200Amps x 220 volts = 44KW... Or 125 Amps x 220 Volts = 25KW, the rule of thumb will over size you every time.
 
You will need to put soft starters on the A/C to get them to start. Generators are -terrible- at startup surge. The peak current will be more like 6x or 10x running without the soft start.
Hyper Engineering is a good brand. You will spend $200 each, but sooooo worth it!

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Right now it is just nice to not hear the drone of generators. Almost everyone in the neighborhood was running one. We had power restored at 5:00 PM Monday.

MKSJ, the fuel consumption information is surprising. I was aware of the different power ratings depending on fuel. I agree that it's seldom better to run a smaller engine at higher RPMs. I was surprised at how loud a Generac stationary generator was the first time I heard one run. They're about the same noise level as our 5500 watt Briggs and Stratton portable. Not a direct comparison but when I changed my oilless air compressor out for one with a 1750 rpm motor and cast iron compressor pump the noise drop was huge.

I assume the load center is 200A. It has 40 positions but the main breaker is not labeled. If it's labeled it's on the paper inside the door which has turned medium brown and the 6 point type is getting hard to read. Several different load calculators indicate that a 22KW generator should be enough but a 26KW one is worth considering. There's a Kohler dealer near us so we'll check with him. Water cooled offers many advantages but the price jump is substantial so we'll probably stay with air cooled. The Kohler 26KW derates to 24KW on NG. Fuel consumption is on par with the water cooled unit you mentioned, right at 300 cfm/hr at full load. We can easily get by with that. The sound level claimed is only 67dB; much better than the portable that measures 88dB at 10 feet.

The bedroom zone air conditioner almost never runs during the day. It's programmed to cool the house off in the evening before bedtime and goes back to 78° in the morning. The hose is well enough insulated that it usually doesn't get to 78°. The living area zone system can be raised to 80°-82° at night if necessary and since the compressors are variable speed the only time one runs at 100% is the living area system in the heat of the day. If we approach full capacity we'll just have to manage our appliance usage.
 
David2011 said:
Right now it is just nice to not hear the drone of generators. Almost everyone in the neighborhood was running one. We had power restored at 5:00 PM Monday.

MKSJ, the fuel consumption information is surprising. I was aware of the different power ratings depending on fuel. I agree that it's seldom better to run a smaller engine at higher RPMs. I was surprised at how loud a Generac stationary generator was the first time I heard one run. They're about the same noise level as our 5500 watt Briggs and Stratton portable. Not a direct comparison but when I changed my oilless air compressor out for one with a 1750 rpm motor and cast iron compressor pump the noise drop was huge.

I assume the load center is 200A. It has 40 positions but the main breaker is not labeled. If it's labeled it's on the paper inside the door which has turned medium brown and the 6 point type is getting hard to read. Several different load calculators indicate that a 22KW generator should be enough but a 26KW one is worth considering. There's a Kohler dealer near us so we'll check with him. Water cooled offers many advantages but the price jump is substantial so we'll probably stay with air cooled. The Kohler 26KW derates to 24KW on NG. Fuel consumption is on par with the water cooled unit you mentioned, right at 300 cfm/hr at full load. We can easily get by with that. The sound level claimed is only 67dB; much better than the portable that measures 88dB at 10 feet.

The bedroom zone air conditioner almost never runs during the day. It's programmed to cool the house off in the evening before bedtime and goes back to 78° in the morning. The hose is well enough insulated that it usually doesn't get to 78°. The living area zone system can be raised to 80°-82° at night if necessary and since the compressors are variable speed the only time one runs at 100% is the living area system in the heat of the day. If we approach full capacity we'll just have to manage our appliance usage.
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At 24Kw you should have no worries, regardless, the larger homes with a standard 18 seer will run off that without blinking.
 
David2011 said:
EDIT: The only fuel option for this question is natural gas. I have no interest in propane, butane, gasoline, diesel or solar/battery systems.

The house not including the sunroom and workshop is over 2800 square feet. It has an all electric kitchen and two central air conditioner systems in isolated zones. Total AC capacity is about 8 tons.

END OF EDIT

We’ve been without electricity for over a full week. Our neighborhood used to never lose power but this is the third time this year that we’ve been without for more than 2-3 hours. It’s time to replace our portable generator with a natural gas powered whole house generator.

Generac has the big name and obviously a lot of units in the field but they also seem to have a spotty reputation. Are they a good brand? Is the reputation problem due to the individual business that installs them? What other brands should we consider?
Click to expand...
My favorite generator is Kohler.
Run for ever also I have own Cat runs great pricy

Today I live city so dow size to a HF Peditor 4,000 with a change switch to afew parts home. I converted to Dual fuel.

Remember the larger the generator the more fuel it uses.
I have had 45KW power every thing but loves the fuel.

Dave
 
The Generac transfer switches that have been installed at my day job (I manage construction of new homes) have 4 internal load shed modules.

These modules are low voltage dry contacts (numbered 1-4). You connect them to the proper low voltage wire on the AC units and if the generator is struggling with load, it will open the set of contacts and that unit goes off. You wire them up in the order you want to shed them. 4 is first to get kicked off, then 3, then 2, and lastly 1. Then when load headroom is restored, they start coming back in the reverse order. Works slick.

Generac also has add-on modules for dropping devices off on the line-side (ie - switching off 240V).

Where I am, our automatic generators need to be sized to the total connected load and able to handle it without manual intervention. The electrician does a load calc for the connected load and then determines which if any devices to shed. Our new homes are quite large and have 400A service meaning we have 2 200A panels. The electrician, after consulting with the customer, cherry picks the loads to be picked up by the generator and puts them in one of the 200A panels and the other loads in the other panel. The generator then picks up only the one panel while all the circuits in the other panel go black on loss of offsite power.

"Whole house" generator is a misnomer unless you want to spend big $ if you have a large home.
 
I am curious, I have a ranch, 65 feet of house length.
Propane is on the garage side of the house, and electrical 65 feet away ingress and breaker box.
If I were to put a unit in, would I put the unit near the propane and send power 65 feet, or would I put the unit near the breaker box (and bedrooms)?

Seems I have the worst setup for this. I currently power some using a backfeed through my dryer port.
 
What size tank do you have currently? It might not be enough to power your generator during the winter and need to get upgraded. In that case, it might be worth relocating that.

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For my generator, I installed it about 40 feet from my panel instead of right next to it so that the propane lines were shorter for our gas fireplace that was on that side. We had to install a new larger tank anyways, so could have placed it anywhere, but by installing it on the opposite side of my house, the exhaust will get blown away from the house, near the panel is right next to the kitchen and a lot of windows and the wind swirls around there, it normally comes from the opposite side of the house, and might cause the exhaust to get trapped. The far side of the house only has one master bedroom window. The downside is we hear it running when in bed during an outage, but if by the panel, my daughter would hear it more. Time will tell if that was the right decision, but I feel more comfortable being able to open windows when it’s running.
 
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