Mark Miner

I am sorry to hear that the design has been an ordeal. $25k for design is not something I would consider reasonable for a single family home, at least for a result that isn't a stupendous piece of architecture.

As far as roof and foundation, they certainly are significant costs, and your builder likely knows local conditions well, so I won't argue from a distance. That approach is why CA subdivision houses increasingly approximate Borg cubes. Lots depends on your climate, your preferences, etc., but saving the engineering fees can pay for fair bit of metal roof or concrete. Anyway, I don't know what you're balancing, family size, lot size, etc., but I'd encourage you to be pointed in your questions, and slow to pay for work that you don't want or need. You can ask the builder "what's the per square foot cost for foundations? roofs? walls?" and do some rough math yourself.

There's nothing wrong with yurts, but they are a pretty short-term solution, and don't leave you with any equity once they are worn out.  Again, it all depends on what you need, want, and can afford. I hate to say it, but the successful natural building people I know of are either tiny-house DIY'ers (frequently people in the trades or otherwise personally skilled, this is the set that tends to be represented on Permies) or... pretty wealthy.

Take it one day at a time, don't get too discouraged, but be careful about throwing good money after bad.

Best,
Mark

Patrick Graeme wrote:My question is, are those estimates of 2-5% based on having contractors do all the work?

Yes, that affects the denominator of the fraction. If you manage to volunteer lots of labor (that does a good job you don't have to repeat), or do a great deal yourself at a low opportunity cost, expect the percentage of preconstruction costs to go up. Knowing that you are in CA, and that you expect to have engineered plans for a custom design, I would encourage you to have between $10k-25k ready to deal with preconstruction. That's a big range, and a bit of a guess, but I know very few engineers who would do a custom 2-story timberframe/straw house engineered plan for less than $10k (I wouldn't, as I have a guess at how much of my time that would take up having done similar work for masonry-type designs). Since you want 2 stories, IRC Appendix S is less helpful, it would only apply to single story, and requires engineering for two levels.

To your other point about labor/materials for "a building", I think that may be an older impression. I would have agreed with it ca. 1990-2000. I observed labor/materials being roughly evenly split up to 2020. Post-inflation, materials dominate. This is a general observation based on conventional construction, and using a natural building approach can tilt the balance towards labor again, but not necessarily because you have drastically reduced material costs, just that you need a lot more labor.

Anyhow, if you are in a place where you can save and sock away money towards the project, that's a good thing to do until you are well-provided to go in with enough to get to dry-in at a minimum. Your straw does not want to be partially complete during a rainy season, so you really want to have enough funds to get quickly to the roof and exterior plaster before you could consider slowing down and doing things yourself more leisurely. You've got a pretty big wall area (guessing ~3600sqft), so getting exterior plaster up on that will take a while (and a lot of scaffolding), and you are tall enough that no roof eaves will shield the bales adequately from rain. You've said you worked with a designer, and have a plan you like, but please do consider that the costs of construction are determined in this phase. Single-level strawbale can save you a lot  of money and headache by allowing you to use IRC App. S (not an engineer), and will make your exterior wall work so much easier - a 2-3ft work platform is so much easier to work on than scaffolding. I've been a builder, and I am an engineer, and I will tell you that neither of those roles (or the designer) has the job of telling you "this might be an expensive idea" - all of those roles just charge more for complexity, and are typically happy to do so. Thus, as I have no personal stake in your project at all, I suggest you think hard about what you really need, and if you can live with a smaller or simpler plan.

It sounds like a cool project, and I wish you the best! I do encourage a careful counting of the cost, and starting the project with a "hope for best, plan for worst" approach.

Best,
Mark

Hi Rico,
Thanks! That is a perfect sketch to begin with. What are the 2 larger batteries doing? As drawn, all is well with your plan, and using an AC-powered charger to maintain the big batteries is fine in principal... but what for?

Also, looking at the back of your EcoFlow, I see 300W max AC output. That Victron 12V 25A charger would draw more than that (12V*25A = 300W, and you are never 100% efficient, and you are always charging over 12V...) Do make sure the charger you select will not overdraw your EcoFlow.

If you are hoping the EcoFlow can use the external battery in parallel with its internal battery, that seems to be a questionable hope. Maybe I am missing the point of the larger battery?

Best,
Mark

Hi Rico,
Thanks, I think I am beginning to put the pieces together, but a quick sketch of your overall system and design intent would go a long way...

Those BMS notes are 100% internal to that battery. You will never interact with the BMS that is buried in it. It's telling you that it is doing right by the LFP cells. However, the internal BMS of a sealed battery like that is better used as a backstop to serious system design errors. It's not your charge controller, it's not your disconnect, it's not doing anything except getting the manufacturer out of liability (and keeping the strings of 4 series cells inside balanced, which is super important).

Your interaction with that battery will be through the top terminals, and the question is how do you plan to take charge in and out, and control that?

Best,
Mark

I have that charger, and as you say, it is an AC-source charger. If that is what you need, it's a great tool. I use it as a bench maintenance charger.

If you want a solar-driven charger, that is not the unit for you. I believe Mr. Rubino has a solar charge controller from Victron (as you noted), which is the sun-to-battery device.

What are you trying to do with it?

Rico Loma wrote:Yes, I understand my LFP is not a Li ion, but the charging profile should be same

Hi Rico,
I'll raise my hand here and note that it ain't necessarily so.

[Edit, links to images were bad]

The first set of curves below is of an nickel-manganese-cobalt / graphite battery (typical higher-energy lithium formulation)  from a paper here.

and the second set is from this webpage. (There's nothing special about the papers per se, they just had good charge curves.)

Note that the slopes of two families of curve are pretty different. The state of charge of a battery on a charger is estimated by its voltage and how much current is flowing into the cell at that voltage (the C rate). The charger needs to know (or be told) what the right curve is, unless it has logic internally to figure it out.

Notice also that the voltage levels are very different, but this is at the level of the cell. At the level of the pack, it's a little more forgiving, since a "12V" battery with LFP will have 4 series cells, but an NMC "12V" battery will have 3 series. They still have different desired top-end voltages, but it's not so dramatic as at the single cell level.

I see that you're looking at a Victron charger, and I think that is a good choice. Be sure to do the math on which one you want, Victron offers more flavors than Baskin' Robbins. LFP is a great battery choice, and almost all home power system products are going to be built with that as an option for the battery bank. Reputable brands with good documentation will keep you out of trouble (when properly applied).  

To your original question, I suggest you follow the 80/20 rule, and your battery manual should show the voltages recommended to do that.  You posted a photo of the LFP battery, is that indeed your unit? It probably came with a short brochure, or if for some reason it didn't, pretty much any 12V LFP 100Ah manual will tell you the same thing, like pg7 of this one.. The state of charge limits are built into the recommended min and max voltages.

Caveat: there are several different min voltages noted, and sizing that is a function of the discharge rate you want. For instance, if you set 12V as a "safe" minimum, you might nuisance trip when you run a chopsaw on a cloudy day (high C rate pulls voltage down, even though charge is OK). Many systems have inverter logic to adapt to this, like requiring a duration-below-limit before tripping. Anyway, that's not exactly to the point, but it worth keeping in mind. The charger side does not care much about this.

Good luck!
Mark

Hi Rico,
There are many good resources on Northern Arizona Wind & Sun's  website, especially their forum, which is a fairly old & mature one by the scale of the internet. It has the advantage of being focused on more house-scale and code-compliant projects, and is a little less hacker-y than some of the DIY forums. Nothing wrong with hacking, but for a whole-house project you really do want to do things like correctly size conductors and conduits and interrupts. I'll also note that most manufacturers of decent equipment (not cheap-o import ebay stuff) will publish very detailed manuals, which are terrifically helpful. If you're comparing equipment before a purchase, read each manual and see which one you'd rather be poring over with a headlamp to troubleshoot from when something goes wrong :-)
Good luck!
Mark

Hi Brandon,
There are a lot of variables, like your frost depth, what kind of pipe you are dealing with, and the flow rates and pressures involved for the field and the house. However, since you are planning to tap the line between the well and the house, expect a significant reduction in house pressure when the irrigation is running (my house was set up this way, and I don't love it - it's hard to do dishes or laundry if the timers are on, and they somehow eventually wander from when you thought you set them).

One way you might get around this is to tap with a smaller line to the irrigation, but fill a tank with it. Then you can let the high-volume flow out of the tank when you are full, and the house sees little effect. It just costs more, and depending on how cold you get during irrigation season, might not work well.

If you want to supply any more details, it might be possible to talk more specifically.
Good luck,
Mark

Hal Schibel wrote:Would it be a cheat to have the dog lick it clean and skip the animal bucket to go straight to the animal?

While I see where you are coming from, the BB instructions are what they are. To successfully submit for a BB, please treat the required photos in the BB as a checklist. I hope your dog can enjoy the scraps anyway, but keep it clean for the volunteer reviewers!