Large load question

[OffGridInTheCity]

Not better - just different. My goal was/is to have a functioning home without grid

I think we're both aiming at the same goal, but coming from different perspectives. We don't ever want to go through something like this again, so standby power is a pretty big deal. She's convinced that a generator is a must and solar is a nice-to-have. At the end of the day, we'll have both, but will start with the generator designed-in.

Thanks for the clarification. I have converted to all electric and achieved power independence including full AC with 13kw PV array, 24,000w inverter and 81kwh battery for 8 months of the year. The house is 2600sq ft.

However, winter is a problem that I've been noodling for a while now.....

The generator route is one of the common solutions and because of solar I have a large battery bank to accept generator power / distribute it thru the night. Specifically, in winter, I need on the order of 1000kwh/month above solar for 4 months. With a generator that produces 7000w run-time power that's 5hrs / day and 150'ish gal of propane per month to get 1000kwh. Times 4, that's 600gal of propane and 620hrs generator runtime for winter 4 months.

When you shop for generator solutions, suggest you research - 1) sound abatement - 7000w generators are LOUD / need a generator sound box if you have neighbors and plan to run it 5hrs/day for many days and 2) understand how many hours the generator you buy can run / maintenance issues.

For me - the volume of propane, runtime hours, and sound are significant issues for ongoing power production, so I'm still noodling on alternatives such as wood fired boilers for water circulation heat as a backup.

Good luck and would love to read your progress as you make some decisions

 

[Quattrohead]

Thanks for the clarification. I have converted to all electric and achieved power independence including full AC with 13kw PV array, 24,000w inverter and 81kwh battery for 8 months of the year. The house is 2600sq ft.

However, winter is a problem that I've been noodling for a while now.....

Is your heat electric too ?

 

[OffGridInTheCity]

Is your heat electric too ?

Yes - converted to a 4ton Lennox (top line / highest SEER) whole-house heat pump. We never go below 25F so I've been forcing it to be heat-pump mode all the time for 2 winters now to get data. It uses about 1200kwh in all-heat-pump-mode in the coldest month. Also converted to Rheeme 50gal heat-pump hot water heater (with 150ft or recirculation) which uses 130kwh/month summer to 190kwh/month winter in heat-pump mode.

So I need 1400kwh'ish for basic heat in winter. Of course we could cut back on heat and hot-water to a degree and live OK- but that would still be at least 1000kwh/month for a reasonably pleasant home life. And it just the 2 of us (kids are gone)

 

[donb108]

Good luck and would love to read your progress as you make some decisions

Thanks, I just finished the first pass of the energy audit. I have some question about it, so I'll probably start another thread to discuss. Good luck on your generator decision.

 

[donb108]

Sorry everyone, I've been distracted with rebuilding, so it's been quite a while. The energy audit made things pretty clear; I knew it, but didn't realize the impact of having a mostly electric house.

My meter is rated for 320 amps, so it's kinda considered a commercial service. Apparently, with this service, prices tend to double. Two electricians recommended that if I reduce my electrical needs, we can get away with a 200 amp service, which would be much cheaper. We've already converted the dryer (40 amp) and oven (40 amp), and are thinking about switching the main furnace to gas (two stages @ 60 amp each).

Converting the main furnace to gas is fairly involved, and priced around $10K-$12K. Changing to a gas furnace is pricey; I can do it, but it's a quite an addition to the original plan. Is this a good idea?

 

[OffGridInTheCity]

Sorry everyone, I've been distracted with rebuilding, so it's been quite a while. The energy audit made things pretty clear; I knew it, but didn't realize the impact of having a mostly electric house.

My meter is rated for 320 amps, so it's kinda considered a commercial service. Apparently, with this service, prices tend to double. Two electricians recommended that if I reduce my electrical needs, we can get away with a 200 amp service, which would be much cheaper. We've already converted the dryer (40 amp) and oven (40 amp), and are thinking about switching the main furnace to gas (two stages @ 60 amp each).

Don't mean to come off negative - just not understanding what is it that's pushing you over 200a? Adding up breakers does not equate to total power consumption. For example I have a legacy 40a breaker for my old AC compressor - but the new heat-pump only uses 18a. The dryer has a 30a breaker but maxes out at 19a (4500w).

For example, my home is 2600sq ft w/200a panel. The Lennox heat-pump maxes out at 240v@18a (even has a sticker on it saying this) for the outside unit and the air handler is 120v@7a (including fan + UV). I also have a 240v cooktop, oven, dryer, spa, hot-water, rain-harvest pump + all the other 120v stuff (e.g. 2 x 20a + 1 x 15a circuits for the kitchen for microwave, k-cup, dishwasher, etc...) + 240v@20a dedicated for a server farm area... and all works on a 200a service.

Converting the main furnace to gas is fairly involved, and priced around $10K-$12K. Changing to a gas furnace is pricey; I can do it, but it's a quite an addition to the original plan. Is this a good idea?

You're thinking of switching from what to go to gas... how about a heat-pump with secondary gas?

 

[SparkyJJO]

I put a gas fired furnace (with heat pump) in my old house that used to be fuel oil, and had to run all new gas lines as the house wasn't even plumbed for it, and relocated the furnace several feet over because the original spot was terrible for airflow efficiency. It really wasn't all that bad to do DIY, just kinda time consuming. It worked great once done.

Kinda wish I had that setup here, my nat gas bill for the cheapo 80% furnace at the current place is just going up up up... thanks OBiden...

 

[donb108]

Don't mean to come off negative - just not understanding what is it that's pushing you over 200a? Adding up breakers does not equate to total power consumption.

Right, that's was my understanding. However, they argued that they have to base the service on what's in the box, not what's connected to the end of the wire. I've disconnected the dryer and oven, but the wires are still connected to breakers in the box, so they have to be included.

On the other hand, we could leave those wire disconnected on the new service. So, we did some rough addition of large loads that might actually come on at the same time.

Electric heat from main furnace - 2 stages @ 60 amps each = 120 amps
Electric heat from second furnace - 2 stages @ 60 amps and 30 amps = 90 amps
Electric hot water heater, domestic - 30 amps
Electric hot water heater, showers - 30 amps

Comes to 270 amps, de-rating with 80% rule, it's closer to 216, but we haven't included the other 22 circuits, @20 amps each. Looked like it's still over 200amps, so we talked about removing load, which led me to converting the main furnace to gas. Does this look reasonable?

 

[SparkyJJO]

What size is your main breaker?

I have 150A mains service, but if I simply added up the breakers there is a LOT more than 150A worth of breakers in there. It is presumed you're never going to pull full power from every circuit at once (or anywhere close, really).

 

[OffGridInTheCity]

Electric heat from main furnace - 2 stages @ 60 amps each = 120 amps
Electric heat from second furnace - 2 stages @ 60 amps and 30 amps = 90 amp

You don't say how large an area you're heating - but as I said above, 2600sq ft = 20a @ 240v for 4-ton central/forced-air heat-pump. So 40a @ 240v for 5000sq ft. There's also mini-split options that are in the same ballpark. 210a -> 40a is 170a reduction! and bring you to a more normal 200a panel / service.

Electric hot water heater, domestic - 30 amps
Electric hot water heater, showers - 30 amps

A hot water heater with 4500w elements is 4500w/240v = 19a. 25a circuit breaker would do it. Maybe there's some city code or something?
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There's also heat-pump water heaters - my 50g heat-pump uses 450w max = 2a. You could potentially go 100% heat-pump water heater and save another 50a between 2 of them or go heat-pump with one of them. Heat-pump takes about 3hrs to heat 50gal from 'cold' and an hour to recover once you do a couple of loads of laundry (luke-warm water) back to full temp - but it's perfectly workable to coordinate shower/laundry.

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I appreciate you sharing, and now it makes sense about 300+ a service. Electricians are not necessarily 'out of the box' oriented as they tend to think existing wire/code/units rather than a DIY perspective. But that doesn't mean you can't push back and greatly reduce the amps coming in - I say that as encouragement (not a judgement)

 

[donb108]

I've spoken with three heating guys and they all said pretty much the same thing; if it's not broke, don't fix it. All were happy to do the work, but two of the three tried to talk me out of it. I've done some measurements and found my amp draw maxes out around 140amps. I think I'm going to listen to them and ditch this conversion to gas idea.