Undersized generator?

Status
Not open for further replies.
I

iwire64

Member
Location
US
My friend has a 16kw whole-house generator. Her house is 2,000 sf with a 3-ton air conditioner, washer, dryer, range, pool pump, and irrigation pump. How can all this, which comes off of a 150A service, be run on a 65A generator?

Sent from my SM-G935P using Tapatalk
 
Whole house generators are always undersized compared to the service the home has. The assumption comes from the fact that you won't be doing laundry, cooking a thanksgiving turkey and have every light on at the same time. Also, a home very rarely uses 100% of the service it has. I bet the average load on the home is around 80 amps or so give or take. Sizing a generator to supply 100% of the homes "possible" load would be cost prohibitive.

Sent from my VS987 using Tapatalk
 
iwire64 said:
My friend has a 16kw whole-house generator. Her house is 2,000 sf with a 3-ton air conditioner, washer, dryer, range, pool pump, and irrigation pump. How can all this, which comes off of a 150A service, be run on a 65A generator?

Sent from my SM-G935P using Tapatalk
Click to expand...
The panel having 150 amps doesn't mean that all of that amperage is being used, nor being used all the time. Also the generator may only be for emergency/power outages, in which case the power usage can be kept to a minimum of only essentials. A question for you: Is it a 65 AMP generator or a 65 KVA?

Sent from my SM-N910V using Tapatalk
 
iwire64 said:
My friend has a 16kw whole-house generator. Her house is 2,000 sf with a 3-ton air conditioner, washer, dryer, range, pool pump, and irrigation pump. How can all this, which comes off of a 150A service, be run on a 65A generator?

Sent from my SM-G935P using Tapatalk
Click to expand...
150 amps being available doesn't mean that all of those amps are being used by the home, nor being used all the time. The actual average usage could be lower than the generator rating.

I did very light research to come up with this:
Based on average daily home usage of 48 kwh, a home uses 2,000 watts per hour, which, applied to 120 volt circuits, equals 16 amps per hour. Less when you account for some of those circuits being 240 volt. This would more than be taken care of by that generator.

(If this is incorrect somehow, I welcome correction. I'm new to this )

Sent from my SM-N910V using Tapatalk
 
truck41trouble said:
Whole house generators are always undersized compared to the service the home has. The assumption comes from the fact that you won't be doing laundry, cooking a thanksgiving turkey and have every light on at the same time. Also, a home very rarely uses 100% of the service it has. I bet the average load on the home is around 80 amps or so give or take. Sizing a generator to supply 100% of the homes "possible" load would be cost prohibitive.

Sent from my VS987 using Tapatalk
Click to expand...
I actually prefer your answer to mine. :)

Sent from my SM-N910V using Tapatalk
 
If you look at your average electric bill, here anyway at my house, you'll see that the demand month-wide is less than 10A constant. 10Ax240V=2400VA or 2.4kw. x 720 hrs/month, that's 1728kw-hrs, x .10$/kw-hr = $173. That is actually very high here, only one month a year does my electric bill go that high, and that's all electric everything. A single 5kw generator could run this place if I ensured the dryer, water heater, and AC weren't all on simultaneously.

For the generator, we do maintenance and load testing on them all the time. Largest is 22kw, and it's difficult to load one to 90A, even with the oven, dryer, ACs, range, etc all turned on at once.

HappElectrician, a 16kW genset @ 240V is putting out 66.7A at full load. We routinely install 22kW generators on houses with 400A service. The entire house is not backed up, and large draws like the ACs may be load shed.

The only thing I can think of that would tank a 16kW generator is a large, on demand electric water heater, or back-up heat strips in an HVAC unit. If those units are gas, no problem. Also, most large purely resistive heating loads cycle via thermostat.
 
My service is 200A but the POCO transformer is 15kva.
I only have 1200 sf.

If I turn on everything I have, I still cannot get to 50A.

You may want to try that experiment while running on utility then decide if anything needs to be done.
 
iwire64 said:
Well, it got us through Irma. Thanks for the input.

Sent from my SM-G935P using Tapatalk
Click to expand...

Good deal. The other thing to think about with genset sizing for residences is most people know they can't run everything at once, and even the ones that dont know, cant run everything at once. Sizing only gets dicey when trying to backfeed a main panel (with an interlock kit) with a small or portable generator.
 
If your POCO meter also measures maximum demand, you can use that figure to check the size of your generator. However, the size of the generator need to be much bigger than that if you are block loading the generator ie putting all loads at once on the generator instead of applying the load gradually.
 
Sahib said:
If your POCO meter also measures maximum demand, you can use that figure to check the size of your generator. However, the size of the generator need to be much bigger than that if you are block loading the generator ie putting all loads at once on the generator instead of applying the load gradually.
Click to expand...

Smarter ATS's can do this for you automatically. The only load I have in my house that could be problematic is the AC. It's on a 40 DP breaker, and the panel buzzes nicely every time it turns on. I could manage every load except AC on a 7kW unit without difficulty.
 
gadfly56 said:
The only load I have in my house that could be problematic is the AC. It's on a 40 DP breaker, and the panel buzzes nicely every time it turns on. I could manage every load except AC on a 7kW unit without difficulty.
Click to expand...
What about having an inverter AC to solve the generator starting problem ? Of course, the running load i/c AC should not exceed generator rating ie 7kW.
 
Sahib said:
What about having an inverter AC to solve the generator starting problem ? Of course, the running load i/c AC should not exceed generator rating ie 7kW.
Click to expand...

Do you mean a soft starter of some kind? I doubt it would be economical for any house in the US of my size to retrofit or design new such an option, but I could be wrong. Seeing all the issues folks have here with VFD's, I'm not a big fan of the concept for the typical consumer application.
 
We are talking about newer AC units, especially mini splits, which have a built in VFD to run the compressor at partial power for added efficiency. The soft start is a bonus of that design.

Sent from my XT1585 using Tapatalk
 
GoldDigger said:
We are talking about newer AC units, especially mini splits, which have a built in VFD to run the compressor at partial power for added efficiency. The soft start is a bonus of that design.

Sent from my XT1585 using Tapatalk
Click to expand...

Is that the design standard now? Even for non-split units?
 
Status
Not open for further replies.
Top