AP514
Well-known member
+1 20-22Kw...with load shed
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need schooling on whole house standby generators
- Thread starter 94yj
- Start date
rct
Well-known member
Of you are willing to spend the $ and have the propane on hand, size your genset for the house and ac needs with propane back up heat units. Good luck.
dcg9381
Well-known member
+1 20-22Kw...with load shed
This is what I did, 20KW with load shed modules... The generac modules aren't bad, they basically go in-line in the circuit. They come in 50A / 100A @ $120/$240 each. They're dead easy to install and require zero extra wiring to control them (Generac). I have a load shed that drops a sub-panel to our garage/apartment, and another that drops load to one of the 2 heat/AC units.
I doubt that we need them, but just in case..
The NEC requires that the generator be sized to handle the load connected to it. There is a calculation you run to get to that number. But, that will result is a too large generator if you have some high draw loads like electric ranges, dryers, heat strips etc.
So you can do one of two things to install a more reasonably sized generator.
1. Install a partial house solution where you only power the things you must have during an outage.
2. Install load management (load shedding) devices that turn off the higher amp loads if you start to draw too much power. As long as you don't try to push the size down too far, you won't actually experience load shedding under normal circumstances.
Some manufactures let you use the same load management devices to hold a load off all together. That can help with things like the 15 kW backup electric heat strip in the heat pump. But it can be tricky to wire as you'll likely need to install it to interrupt either the line or control voltage on the contactor for the strip unless there is a sperate breaker for the rest of the indoor section.
Keep in mind you also need to consider the locked rotor amps (starting amps) of the largest motor, and make sure the generator you select has that reserve capacity.
With load management controls, it's common to be able to do managed whole house air cooled generators, without having to move up to much more expensive liquid cooled units.
So you can do one of two things to install a more reasonably sized generator.
1. Install a partial house solution where you only power the things you must have during an outage.
2. Install load management (load shedding) devices that turn off the higher amp loads if you start to draw too much power. As long as you don't try to push the size down too far, you won't actually experience load shedding under normal circumstances.
Some manufactures let you use the same load management devices to hold a load off all together. That can help with things like the 15 kW backup electric heat strip in the heat pump. But it can be tricky to wire as you'll likely need to install it to interrupt either the line or control voltage on the contactor for the strip unless there is a sperate breaker for the rest of the indoor section.
Keep in mind you also need to consider the locked rotor amps (starting amps) of the largest motor, and make sure the generator you select has that reserve capacity.
With load management controls, it's common to be able to do managed whole house air cooled generators, without having to move up to much more expensive liquid cooled units.
What does NEC require for generator sizing? The answer varies based on the type of load powered. Emergency systems require the generator to be sized for the entire connected load (NEC 700.5). But if the emergency system is a healthcare application, NEC 517.30(D) requires the generator to meet the peak demand of the load and waives the requirements of NEC 700.5. This is a direct result of healthcare applications being too lightly loaded. Legally required standby and optional standby traditionally required the generator to be sized to meet the peak demand of the load intended to be operated. This requirement has been strengthened in the 2008 code to require compliance with Article 220, “Branch-Circuit, Feeder, and Service Calculations,” or another authority having jurisdiction (AHJ) method. This change was driven by a desire to protect the consumer in the residential market from installing a generator smaller than the potential load.
https://www.csemag.com/articles/nec-and-standby-gensets/
https://www.csemag.com/articles/nec-and-standby-gensets/
theoldwizard1
Well-known member
There are some "loop holes" for residential application !Legally required standby and optional standby traditionally required the generator to be sized to meet the peak demand of the load intended to be operated. This requirement has been strengthened in the 2008 code to require compliance with Article 220, “Branch-Circuit, Feeder, and Service Calculations,” or another authority having jurisdiction (AHJ) method. This change was driven by a desire to protect the consumer in the residential market from installing a generator smaller than the potential load.
You are allowed to install a smaller generator than required to meet "peak demand" IF the transfer switch has built in "load shedding". Typically this would mean a way of cutting out high power appliances (A/C, water heater, dryer, stove, etc) if they exceed the generator capacity at that moment. An automatic, load shedding, transfer switch is $,$$$ !
If your incoming power from the POCO is split immediately after the meter (or the meter pan is double tapped) and there are 2 load centers, one for high power appliances and one for the rest of the house, then the generator and transfer switch can be installed AFTER that and sized for the "rest of the house" load.
Of course, no one says you can not install a generator interlock on the first load center and feed it from a branch circuit AFTER the automatic transfer switch. The load (typically A/C) is off when the generator starts. It requires manual intervention to turn it on. Worst case, you will trip the breaker in the generator.
This is a chicken and egg debate .... years ago when there were less choices and generally smaller generator sets ------the only way to install one was the dedicated panel. My beach house was rebuilt that way ... all the older houses around me have a separate panel feeding the most important items. Most were built new that way. Back then there was only one old feed to the island -- you had to have a generator set if you wanted security of electric on the weekends.
The vast majority of people putting in a generator -- don't want to think about it. Don't know or care how they work -- just want them to work. Ideally with few compromises. No one does any manual transfers .... all the generators come in "kit" form w/ the auto transfer at reasonable prices.
It did not take long for manufacturers to understand that those providing the least compromise would get the sale. Why spend an extra 1k in labor installing another panel/ load center in the basement so you can place a 13kw generator doing 1/2 the house.
They guy saying I can do a 20k and never go into your house -- we do the whole place for another $1k is going to get the job. At the worst they have to come in and cut the load relay into something big.
Manufacturers built models to fit the market -- that 20/22kw is the competitive spot today. When I was speaking to the Cummins engineer he said that size was the driver for the redesign a few years back. It makes sense .... those able to afford and willing to install don't live it in "tiny" houses.
The vast majority of people putting in a generator -- don't want to think about it. Don't know or care how they work -- just want them to work. Ideally with few compromises. No one does any manual transfers .... all the generators come in "kit" form w/ the auto transfer at reasonable prices.
It did not take long for manufacturers to understand that those providing the least compromise would get the sale. Why spend an extra 1k in labor installing another panel/ load center in the basement so you can place a 13kw generator doing 1/2 the house.
They guy saying I can do a 20k and never go into your house -- we do the whole place for another $1k is going to get the job. At the worst they have to come in and cut the load relay into something big.
Manufacturers built models to fit the market -- that 20/22kw is the competitive spot today. When I was speaking to the Cummins engineer he said that size was the driver for the redesign a few years back. It makes sense .... those able to afford and willing to install don't live it in "tiny" houses.
My Old Tools
Well-known member
I have a 36kw generator, but my house is 3900sf with two heat pumps, electric drier, dual electric ovens, freezer, two refridgerators, heat pump in the shop. All lighting is LED, water heaters are propane, back up heat is propane furnace. Our generator is never heavily loaded. We run the house like we're on the grid even it power is out. And yes, we have a 500 gal dedicated underground tank for the generator. Its surprising how little propane it uses.
I have a 36kw generator, but my house is 3900sf with two heat pumps, electric drier, dual electric ovens, freezer, two refridgerators, heat pump in the shop. All lighting is LED, water heaters are propane, back up heat is propane furnace. Our generator is never heavily loaded. We run the house like we're on the grid even it power is out. And yes, we have a 500 gal dedicated underground tank for the generator. Its surprising how little propane it uses.
Well ... if it's never heavy loaded ....why do you have it?
If the answer is we lose power for 4 days often and we need to run everything and we need 38k .. that's what you need. But ---- that's going to take 75 gallons a day .. or 300 gallons running at capacity. There could also be a case to be made with a big family -- lots of entertaining and the need to keep the ovens on with many outages through the year.
I can only have one tank on my lot ... even with 1k tank (800g). That's not enough for most people if there is a possible 4 day outage and using propane for other uses. I would have to do the math .. but, on my equipment when we figured. Running the generator to keep the heat pumps going was not the way to go ... so the generator goes on and the propane for the house
no one is running their home generator at full capacity for a 24 hour period. no one.
Correct ....
The OP is on propane .... so you want the most logical way forward.
If your life will come to an end if you don't have the dryer and ovens running at the same time .. you have to account for that -- pay the price (larger tanks) for more fuel use all the other times.
With natural gas ... you just go as big as you want to spend -- especially when building new and the gas line can be sized for any load.
rlitman
Well-known member
no one is running their home generator at full capacity for a 24 hour period. no one.
No one is running ANY generator at full capacity for a 24 hour period. Heck, the Prime rated generators at my work are only designed to be run at 70% capacity over 24 hours. Emergency standby rated generators will be significantly more derated when used for continuous operation (usually more like 50%).
That's one reason that many generators appear to be way oversized for their applications at first glance.
No one is running ANY generator at full capacity for a 24 hour period. Heck, the Prime rated generators at my work are only designed to be run at 70% capacity over 24 hours. Emergency standby rated generators will be significantly more derated when used for continuous operation (usually more like 50%).
That's one reason that many generators appear to be way oversized for their applications at first glance.
Well yea then you'd just get a continuous rated power unit. those are built to run at name plate indefinitely. but they dont offer the wide range of loading like prime. different tools IMO.
i agree. standbys are not meant for more than 50% avg loading.
Correct ....
The OP is on propane .... so you want the most logical way forward.
If your life will come to an end if you don't have the dryer and ovens running at the same time .. you have to account for that -- pay the price (larger tanks) for more fuel use all the other times.
With natural gas ... you just go as big as you want to spend -- especially when building new and the gas line can be sized for any load.
Easy way to just toss money. people dont really understand what their power consumption is. hell i didn't until i put power monitoring on the house.