- My Forums
- Tiger Rant
- LSU Recruiting
- SEC Rant
- Saints Talk
- Pelicans Talk
- More Sports Board
- Fantasy Sports
- Golf Board
- Soccer Board
- O-T Lounge
- Tech Board
- Home/Garden Board
- Outdoor Board
- Health/Fitness Board
- Movie/TV Board
- Book Board
- Music Board
- Political Talk
- Money Talk
- Fark Board
- Gaming Board
- Travel Board
- Food/Drink Board
- Ticket Exchange
- TD Help Board
Customize My Forums- View All Forums
- Show Left Links
- Topic Sort Options
- Trending Topics
- Recent Topics
- Active Topics
Started By
Message
re: Need help estimating usage cost for a whole house generator
Posted on 7/11/24 at 9:17 am to southern686
Posted on 7/11/24 at 9:17 am to southern686
quote:
a generator runs at max RPM no matter the load you are pulling
If you're talking about a regular portable generator, and not an inverter. You would be correct to say is runs at a constant RPM, however, as load increase there will be a difference in fuel consumption, or else it will stall unless it is fed more fuel to handle the load and maintain that same RPM.
Edit: Remove bad info
This post was edited on 7/11/24 at 10:01 am
1
Posted on 7/11/24 at 9:18 am to notsince98
Ehh, I wouldn't say drastically. At least not for a whole home generator. I say this because most of the time, they are oversized for the house so loading them up so to say unless you have all electric appliances.
But yes, load surely effects it. I was just trying to explain, its not something you can really calculate or should worry about.
You would some sort of way have to figure out the gas burn rate of the generator VS load. Which even then burn rate V load wouldn't be proportional. Then you would need to determine what the load is of all electrical device's are. Then add up the load of said devices on X it by the burn rate of that load and youll know what its costing per hour/day/ etc.
But yes, load surely effects it. I was just trying to explain, its not something you can really calculate or should worry about.
You would some sort of way have to figure out the gas burn rate of the generator VS load. Which even then burn rate V load wouldn't be proportional. Then you would need to determine what the load is of all electrical device's are. Then add up the load of said devices on X it by the burn rate of that load and youll know what its costing per hour/day/ etc.
Posted on 7/11/24 at 9:21 am to ellunchboxo
quote:
So around $40 a day
This is what the math says a 20 kW Generac should use at 50% load.
Fuel Consumption Data on Page 4
~ 200 cu.ft/hr / 100 Cu.ft./CCF * 24 = 48 CCF/Day * ~$0.91 /CCF = $44/Day
Posted on 7/11/24 at 9:25 am to RaginRampage
quote:
which assuming he's talking about a whole home generator and not a portable, it's likely an inverter.
Most all stand by generators I've seen are just conventional synchronous generators. Didn't even know they made inverter based stand bys which is pretty cool.
Posted on 7/11/24 at 10:00 am to southern686
quote:
Most all stand by generators I've seen are just conventional synchronous generators
Yes you are correct. I always assumed they were inverters since Generac claims <3% THD. Which is usually what you get with an inverter.
Posted on 7/11/24 at 10:31 am to Willie Stroker
quote:I hear you, I'm the same way. But like others are saying, assuming typical use patterns of standby generators, fuel cost is a non-factor. Even if you have a week+ outage every year, fuel will never add up to more than a few % of TCO considering install cost and maintenance and such.
I’m just trying to do a more thorough cost/benefit analysis to an alternative.
Seems like it would be useful to know what to plan for during extended power outages, no?
Can I ask what alternative(s) you are comparing to?
Posted on 7/11/24 at 10:51 am to southern686
quote:
Ehh, I wouldn't say drastically.
Well, lets just look at the Generac linked. The fuel consumption increase from 50% load to 100% load is a 50% increase in fuel consumption. That seems pretty drastic. They dont provide idle consumption data but idle is probably going to be somewhere between 25% and 50% of the 50% load consumption.
So that would be a range of 100 ft^3/hr at idle and 300 ft^3/hr at 100% load.
very noticeable change in operating costs.
Posted on 7/11/24 at 10:56 am to RaginRampage
quote:
Yes you are correct. I always assumed they were inverters since Generac claims <3% THD. Which is usually what you get with an inverter.
Even traditional rotating generators have THD ratings.
Posted on 7/11/24 at 11:01 am to notsince98
Just as a data point, I have a 22kw generac which states 228 ft^3/hr at 50% and 327 ft^3/hr at 100%. I have a real time gas flow sensor which measures ~70 ft^3/hr during a no-load exercise with a peak of ~200 ft^3/hr during startup.
Posted on 7/11/24 at 11:08 am to Willie Stroker
quote:
Natural gas appears to be cheaper, but natural gas does not appear to be charged as kilowatt hours. Instead, I'm billed by a measure called centum cubic feet.
If my current electrical consumption is 50 kWh per day, how do I convert that to a consumption cost of a natural gas whole house stand-by generator where natural gas is measured by centum cubic feet?
The best tool I found just gave ccf estimates based on 4 tiers of load for each size generator. That is somewhat helpful, but not as precise as I would like.
What says the H&G?
just wanted to re-read this and confirm that you're WAY over thinking this...
Posted on 7/11/24 at 11:12 am to poochie
he's either an engineer or an accountant
Posted on 7/11/24 at 11:36 am to cgrand
too technical for an accountant...
Posted on 7/11/24 at 2:18 pm to notsince98
quote:
The fuel consumption increase from 50% load to 100% load is a 50% increase in fuel consumption. That seems pretty drastic.
Well sure, but you're not going to run a 22kw generator at a 100% load, or even close to that honestly, for anything more than very short periods of time. Realize that a 50% load on that generator is 12kw. That's huge.
This post was edited on 7/11/24 at 2:19 pm
Posted on 7/11/24 at 2:34 pm to TheBoo
quote:
Well sure, but you're not going to run a 22kw generator at a 100% load, or even close to that honestly, for anything more than very short periods of time. Realize that a 50% load on that generator is 12kw. That's huge.
That is a different topic. The point was fuel consumption can and does vary drastically with loading. So it does matter to evaluate the fuel consumption relevant for the expected loading.
This post was edited on 7/11/24 at 2:39 pm
Posted on 7/11/24 at 11:06 pm to notsince98
quote:
That is a different topic.
Not really. Sure, understanding the differences on paper matter, but If the goal is to understand overall fuel consumption costs, the only time you are getting even close 100% load is for the 1-2 seconds that your AC compressors are starting. 90% of the time you’ll be at below 50% on a generator that size.
Posted on 7/12/24 at 9:30 am to TheBoo
quote:
90% of the time you’ll be at below 50% on a generator that size.
+1
Standby generators aren’t just sized for running amps. They have to be sized to handle the LRA current of starting compressors across-the-line. LRA can be 4-8x the full-load current rating of a motor. A larger generator has to be able to ride through that.
As an example, my 3 ton units typically run around 16A and 11A, respectively. If you do the math, my 20kW standby seems to be way oversized:
240V x 16A = 3840W
240V x 11A = 2640W
Total = 6480W
Posted on 7/12/24 at 9:44 am to bapple
quote:
+1
Standby generators aren’t just sized for running amps. They have to be sized to handle the LRA current of starting compressors across-the-line. LRA can be 4-8x the full-load current rating of a motor. A larger generator has to be able to ride through that.
As an example, my 3 ton units typically run around 16A and 11A, respectively. If you do the math, my 20kW standby seems to be way oversized:
240V x 16A = 3840W
240V x 11A = 2640W
Total = 6480W
You dont have to oversize to completely handle starting current of the compressor with rotating generators. They can handle inrush above their amp ratings to an extent.
For example, you can start a 3-ton compressor on a 10kW generator. The 10kW gen only has a 42A full load rating but it can tolerate brief increases like motor starts.
This post was edited on 7/12/24 at 9:45 am
Posted on 7/12/24 at 11:38 am to notsince98
Its always interesting it seems like the real time utility bills are always less than the math estimation on usage. I know that usage depends on load as discussed, but $30-40/ day seems low.
Posted on 7/12/24 at 12:20 pm to baldona
quote:
$30-40/ day seems low
Real life experience says those numbers are pretty damn accurate.
Posted on 7/12/24 at 12:26 pm to baldona
quote:That's a bit lower than my typical cost too ($50-60/day), but the two biggest contributors to the number are your local gas prices and how much your AC is running.
Its always interesting it seems like the real time utility bills are always less than the math estimation on usage. I know that usage depends on load as discussed, but $30-40/ day seems low.
Page 2 of 3
Popular
Back to top
Follow TigerDroppings for LSU Football News