Only because it made the news. And things only make the news because they're rare instances.
Two whole house generators?
- Thread starter Coppersmith
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Only because it made the news. And things only make the news because they're rare instances.
RumRunner
Senior Member
- Location
- SCV Ca, USA
- Occupation
- Retired EE
You obviously haven't heard or seen the Honda 2000i portable gensets. They are rated 2000 watts and they are designed to be connected in parallel.
I have two of them in my RV. My AC requires to have both gensets turned on in order to run my 13500 BTU AC unit.
Running just one genset will not even get to start the AC. Not all Honda models can be connected in parallel.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
This is only possible because the prime mover turns a DC generator and an inverter supplies the AC. It is far easier to sync two inverters than to sync two rotating masses driven by separate engines.
Not very common in the wild, but so called "written pole" generators can also be synchronized fairly easily.
Like inverter-based generators these can also maintain constant output frequency as the shaft slows down, but unlike inverter units they can also have a substantial short term overload tolerance similar to a conventional generator.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
But if OP is going to do this it will be with a couple 20-24 kVA units. I don't know that inverter output units are very common in that large of a unit.
If they are not in phase with one another it won't be good, and keeping frequency steady isn't easy on this small of a unit either, which will make it more difficult to keep them in phase with one another.
shortcircuit2
Senior Member
- Location
- South of Bawstin
All this discussion about paralleling 20KW generators and there just is not a reason they need to be paralleled.
Post a valid reason to parallel small optional backup generators?
Here is a diagram for the 3-gensets...
The rubber cord ended up at the gensets and not at the sub-panels...
Post a valid reason to parallel small optional backup generators?
Here is a diagram for the 3-gensets...
The rubber cord ended up at the gensets and not at the sub-panels...
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romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
resonable , but one would think not as cost effective as the original 48Kw deal?
~RJ~
~RJ~
I believe that this method is relatively common knowledge. There is no "need" to parallel gensets unless you are trying to provide sufficient power to the single main with generators that are too small.
Agreed. Unless the client has existing gensets. I have seen businesses expand but they dont want to swap out a generator. They just want to add capacity.
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I have a medium sized house, all electric. A 22KW, in general, won't cut it. Heat pumps...OK. But if it gets cold and resistive heating kicks in....everything goes south (pun intended). I say in general, because you might be able to load shed down to the heat. But then that's like losing power...except for the heat. If the customer wants to be able to do other things...AND have heat, then you need more than 22KW if you're all electric. In fact, this might be the good dividing point. Put one 22KW on HVAC and possibly the water heaters and dryer with load shed. The other 22KW on the other basic necessities.
Electric heat is extremely inefficient. The efficiency is that much worse with a generator. The BTU heat ratio between gas heat (direct) versus generator electric is about 5:1. A generator will use five units of gas to generate one unit heat. That's because almost 100% of gas translates to heat in the living area. A generator (running on gas) only translates about 20% of the input into electric heat in the living area.
Electric heat is extremely inefficient. The efficiency is that much worse with a generator. The BTU heat ratio between gas heat (direct) versus generator electric is about 5:1. A generator will use five units of gas to generate one unit heat. That's because almost 100% of gas translates to heat in the living area. A generator (running on gas) only translates about 20% of the input into electric heat in the living area.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Technically speaking, electric heat is more efficient, because all of the energy creates the desired product: heat. Even heat lost in the conductors isn't loss if they're in the living space.
Gas heat has waste in the exhaust, so not all of the heat created is used to produce heat in the living space. High-efficiency heaters do extract enough heat that exhaust fans are used.
Now, if we're talking about gas, propane, or gasoline engines, that's different, because engines produce a lot of waste heat in both the exhaust and in the engine-running process.
Water-cooled engines can be adapted to extract heat from the cooling system and use that energy to help heat the living space, perhaps utilizing the most energy of the fuel.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
There are two different characteristics being described here without a clear distinction: the resource efficiency of the heating and the cost effectiveness of the heating.
Piped natural gas has the edge almost everywhere because of its lower cost per therm. So even though electric heating is more efficient in energy conversion at the site, it is less cost effective because electric power costs far more per therm produced.
However if you use a heat pump you get far greater resource efficiency and cost effectiveness compared to resistance heating because a heat pump can move heat from a low temperature source to a higher temperature conditioned area at a rate of 3-4 times the therms per watt of resistance heating.
In my area propane is expensive enough that propane heating is comparable in cost to electric resistance heating, while a heat pump would be comparable to the cost of natural gas if it were available at my home.
Piped natural gas has the edge almost everywhere because of its lower cost per therm. So even though electric heating is more efficient in energy conversion at the site, it is less cost effective because electric power costs far more per therm produced.
However if you use a heat pump you get far greater resource efficiency and cost effectiveness compared to resistance heating because a heat pump can move heat from a low temperature source to a higher temperature conditioned area at a rate of 3-4 times the therms per watt of resistance heating.
In my area propane is expensive enough that propane heating is comparable in cost to electric resistance heating, while a heat pump would be comparable to the cost of natural gas if it were available at my home.
Coppersmith
Senior Member
- Location
- Tampa, FL, USA
- Occupation
- Electrical Contractor
Above is a rough drawing of the site. Three panels are being fed from a single feeder that is distant from the house and runs under a driveway. In the original plan with a single generator the service-rated ATS would replace the outside main breaker. Now that the HO has decided he wants multiple smaller generators, the only way to avoid running additional feeder(s) to the panels and avoid an additional ATS is to parallel the generators.
Running additional feeders would require cutting and patching the driveway, opening the wall, rewiring the existing flushed mounted panels, and repairing the wall. The breakers in the panels would also probably need to be rearranged to balance the loads. This would greatly increase the installation cost. This is why I inquired if paralleling was possible. If paralleling equipment was available, I could stick to my original plan. I think this is a valid reason.
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jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Homeowner clearly made an uniformed decision. Your job is to inform them of the problem and/or the costs, and see if they still want to stick with that decision.
Coppersmith
Senior Member
- Location
- Tampa, FL, USA
- Occupation
- Electrical Contractor
That's exactly what I will be doing after I gather all the relevant information and options from the brain trust here.
As an aside, clients have no idea how much time I (and I assume you people) spend doing research and planning on their projects. And then they complain if the estimate is not free.
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jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
"Technically", that's ... just not true. It depends how much waste heat is created in the process of making electricity. It depends if the heating appliance is a heat pump or not. So at best it's an incomplete comparison. It's not even comparing apples to oranges. It's comparing apples to a fruit behind door number 3.
And that's before the economics factors that Golddigger described.
Exactly.
Three subpanels require three separate feeds even if it's one multicore cable. It could be one main interior panel and two subpanels.
Cable from the generator to the panel should be as short as practical.
You really need to have a generator for each panel or just for the main panel. You could also have a spare generator (in case of generator failure) that handles critical functions only on a single panel with an additional transfer switch. I have done that in some office buildings.
Work out the costs. Give them the information to make an informed decision. Don't give them a detailed estimate, give a final cost. Keep that spreadsheet for the next job if you don't get this one. Next time will just be faster and easier. Also, check the NEC for diversity factors on the type of circuits being run on the panels to get a real picture of electrical usage - or pay a services engineer for their opinion.
Then let the customer decide. They almost always pick the cheapest option, in my experience.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Agree to disagree. You're bringing in data that is not relevant. Electricity production has nothing to do with it, nor does comparing resistance heating to a heat pump.
I'm only saying that, if all of the electrical usage results in the desired product, that defines efficiency, or efficacy. I'm not comparing cost per BTU or per heat gain.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
On site generation via an internal combustion engine is what is not efficient. Your losses are in the generator and prime mover. 1000 watt electric heater still has an input of 1000 watts and an output of 1000 watts. What the source of the energy costs can vary greatly also.
That's exactly what I'm talking about. Take a unit running on gas. Take the rate of expenditure of the gas and map that to the KW generated. Map that KW to resistive heat delivered assuming 100% resistive efficiency. Now take that same amount of gas in a system designed to generate heat directly from the burning of the gas. Don't be surprised if it comes out to about 5:1.
Generators get hot. That heat is part or the combustion that drives the motor that ultimately generates the electricity. Heat in combustion, for many generators, is waste. It's never delivered to the living areas.
In many cases, the efficiency gets better (less heat) the bigger the generator. And running at optimal load is also a factor. I'm also not factoring in generators that have a cooling process that is designed to deliver the heat transferred in combustion back to the living areas in some way.
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