thoughts on a tiny house on our property

[Ai4px]

Daughter wants to move back from the big city and wants a tiny house. We've identified a spot near a pond that is about 1000' from our house. I want to run her 16x40' house with 6000xp inverter but it will require load management. I will swap her water heater elements for 1500w elements and replace the lower thermostat with an upper type t-stat. That way when the water heater is satisfied, I can power the EVSE off the bottom thermostat.

First there's peak demand to deal with. For this I will use a passive current sensing switch on each of the two 120v lines. If it trips over 50% capacity, I'll load shed the water heater and EV for 5 minutes. This will give time for things like the oven to dutycycle and thus prevent rapid cycling. I don't think i'll need to load shed the minisplits as I expect they'll draw 170-200w each most of the time when running.

The next issue is low SoC load shedding. I plan to TRY to run her off two 15kwh batteries, but realistically I think she'll need 45kwh because he car will use about 25kwh a day back and forth to work. I've got to create a protocol converter from victron smart shunt to canbus anyway, so I'll add some digital outs on that to inhibit the car charging below something like 30%.

I plan to program the inverter to assert a digital output for gen start at 20% and shut off at 29%. But I'm not going to use a generator. I want to make a small power supply like the sig solar chargeverter... a 1 or 2kw 48v charger. I looked at getting 10amps @ 240v lifeline from our house but it would take AWG4 for the nearly 1000' run. So I've decided to get some 2kva step transformers from ebay. I can step up 240v to 600v, run the distance and step back to 240v on the far end. Using 600v allows me to use AWG12 and I can get 12/2 UF in 1000' spools. So when the inverter calls for gen start, it's actually going to turn on a contactor for that 48v DC charger.

I'll post more about the structure in a few moments.... I hope this is food for thought and please let me know if you have anything to add that I've missed.

 

[Ai4px]

For the structure of the house, we started shopping storage buildings. Found most 16x40's are selling for $16k. I found a local builder who will build a portable building on your property in one day. He's said he'll swap to 2x6 on 24" center walls for me and mylar OSB for the roof underlayment for $14.9. I was pricing out the materials and I think I can do the same for about half that price but it'll take us two weekends. In the scheme of things and since I gotta finish the inside anyway, that time is not that critical.

What I've found is instead of T1-11 or hardy board, you can use a product called LP smart siding. It's about $45 a sheet and for and extra $10 a sheet it will come with mylar radiant barrier on it. So this means raidiant barrier on the roof and walls! I expect that 2x6 walls will give us R21. The dutch barn roof will make her ceiling height 10'8" inside so it should feel roomy. I'm going to put awning windows popping out of the roof tin to let a lot of natual light in. She'll have a laundry / mud / inverter room at one end with an overhead storage rack. The kitchen/living room /bed room will have full height ceilings and storage shelf over the bath room for boxes.

Fire away with suggestions.....

 

[Brucey]

Assuming you'll be putting additional insulation in the walls in addition to the radiant barrier?

 

[Ai4px]

Assuming you'll be putting additional insulation in the walls in addition to the radiant barrier?

yes, fibergalss batting. 6" thick walls. The standard here in my area is 2x4 walls and R13.... going above that. Also 2x6 24"on center gives less thermal bridging.

 

[KITROBASKIN]

Without knowing your location, hard to say if passive solar is a good idea for your climate and site. Neighbors where we live without passive solar spend a lot of time dealing with burning wood. Not so much for us. Only when it is sustained cloudy.

 

[Ai4px]

Without knowing your location, hard to say if passive solar is a good idea for your climate and site. Neighbors where we live without passive solar spend a lot of time dealing with burning wood. Not so much for us. Only when it is sustained cloudy.

I looked at doing a celestory roof for her place, but its a lot of trouble to create. I can tell you that google sketchup can geolocate a model for you and you can do a shadow study for diffrerent times of the year. Alas, we live in a heating climate, so the only solar gain I'm interested in is her getting shade in the afternoon!! We're looking at putting her on the east side of the pond and the trees over it will provide shade after 2 or 3pm. Gunna put her solar array on the south "pennisula" of the pond so it can get SE and SW sunshine.

 

[Nobodybusiness]

Daughter wants to move back from the big city and wants a tiny house. We've identified a spot near a pond that is about 1000' from our house. I want to run her 16x40' house with 6000xp inverter but it will require load management. I will swap her water heater elements for 1500w elements and replace the lower thermostat with an upper type t-stat. That way when the water heater is satisfied, I can power the EVSE off the bottom thermostat.

First there's peak demand to deal with. For this I will use a passive current sensing switch on each of the two 120v lines. If it trips over 50% capacity, I'll load shed the water heater and EV for 5 minutes. This will give time for things like the oven to dutycycle and thus prevent rapid cycling. I don't think i'll need to load shed the minisplits as I expect they'll draw 170-200w each most of the time when running.

The next issue is low SoC load shedding. I plan to TRY to run her off two 15kwh batteries, but realistically I think she'll need 45kwh because he car will use about 25kwh a day back and forth to work. I've got to create a protocol converter from victron smart shunt to canbus anyway, so I'll add some digital outs on that to inhibit the car charging below something like 30%.

I plan to program the inverter to assert a digital output for gen start at 20% and shut off at 29%. But I'm not going to use a generator. I want to make a small power supply like the sig solar chargeverter... a 1 or 2kw 48v charger. I looked at getting 10amps @ 240v lifeline from our house but it would take AWG4 for the nearly 1000' run. So I've decided to get some 2kva step transformers from ebay. I can step up 240v to 600v, run the distance and step back to 240v on the far end. Using 600v allows me to use AWG12 and I can get 12/2 UF in 1000' spools. So when the inverter calls for gen start, it's actually going to turn on a contactor for that 48v DC charger.

I'll post more about the structure in a few moments.... I hope this is food for thought and please let me know if you have anything to add that I've missed.

Why not just get 2 inverters and run them in parallel rather than all the current sensing stuff?

2 of them would be $3000 then buy used panels from Santan.

 

[Q-Dog]

I wouldn't use the LP smart siding if you gave it to me ... just sawdust and glue and paint. I saw some of it delaminating in the bundles at the lumber yard went I went looking for siding. Maybe it will work in your climate, but for me, if it starts falling apart before it leaves the lumber yard it probably won't last here in Louisiana.

 

[Ai4px]

I wouldn't use the LP smart siding if you gave it to me ... just sawdust and glue and paint. I saw some of it delaminating in the bundles at the lumber yard went I went looking for siding. Maybe it will work in your climate, but for me, if it starts falling apart before it leaves the lumber yard it probably won't last here in Louisiana.

hmm.... it's OSB made of cedar... what do you recommend?

 

[Pinto Yates]

Curious to see how the step up/down works out for you, that’d be a cool wiring hack.

I used zip board sheathing on my house, taped and sealed all the seams & nail holes, spray foamed the 2x6 inside wall and R panel metal on exterior. Holds heating and cooling extremely well.

Check with your local portable shed/building lots. Around here they frequently repo buildings where the owner converted them to living quarters for MIL or guests. I’ve seen some nice ones go for less than you could DIY one.

 

[time2roll]

So when the inverter calls for gen start, it's actually going to turn on a contactor for that 48v DC charger.

I would consider running a lower power charger 24/7 and just keep the battery as full as possible. Possibly just a voltage booster at the end if the charger is complaining of low voltage.

 

[HighCountry]

I want to run her 16x40' house with 6000xp inverter but it will require load management. I will swap her water heater elements for 1500w elements and replace the lower thermostat with an upper type t-stat.

Bad idea here... Why not go propane on the water heater? electric water heaters have a high demand for power! A propane water heater will only use power to fire up when in use. a traditional water heater will require continual power and I think you will need a lot more power than you realize. Problem we looked over with water heater and just went propane. We have 100% off-grid setup.

 

[Q-Dog]

hmm.... it's OSB made of cedar... what do you recommend?

I recommmend you talk to someone that installs siding, especially one that does repairs, and see what they recommend for your area.

 

[400bird]

Where about are you? How cold/cloudy does it get? If you're just running solar and battery, unless you extremely oversized the system, you'll always run out of juice on those cold, cloudy weeks. You could probably size a system to run everything 50ish weeks of the year. But what do you do those last couple weeks?
Generator to run the house/charge house battery and charge the car at your place? Seems like a waste to charge her car from a generator.

Also, you kept saying pond, but the picture just looks like more trees

 

[Ai4px]

Where about are you? How cold/cloudy does it get? If you're just running solar and battery, unless you extremely oversized the system, you'll always run out of juice on those cold, cloudy weeks. You could probably size a system to run everything 50ish weeks of the year. But what do you do those last couple weeks?
Generator to run the house/charge house battery and charge the car at your place? Seems like a waste to charge her car from a generator.

Also, you kept saying pond, but the picture just looks like more trees

The pond is covered by trees. lol. But it is very small.

As far as charging the car I will not allow the car to charge if battery below 40%. And I will use 600v transformers to provide a life line to my house.

 

[Ai4px]

Thanks for all the input guys!!!!

 

[Ai4px]

Bad idea here... Why not go propane on the water heater? electric water heaters have a high demand for power! A propane water heater will only use power to fire up when in use. a traditional water heater will require continual power and I think you will need a lot more power than you realize. Problem we looked over with water heater and just went propane. We have 100% off-grid setup.

I can’t make propane at home. Sunshine is just falling from the sky. I’ll make the heat elements 1500w so they only use 25% of my inverter capacity.

 

[time2roll]

I can’t make propane at home. Sunshine is just falling from the sky. I’ll make the heat elements 1500w so they only use 25% of my inverter capacity.

Consider a heat pump WH. Will get 2x to 3x the BTU per kWh

 

[OmoshoManuel]

Sounds like you've got a solid plan in place! I've built a similar house for my daughter. Make sure to double-check all your calculations and take the time to set up. It's a big project, but it'll be worth it in the end!

 

[1201]

What I've found is instead of T1-11 or hardy board, you can use a product called LP smart siding. It's about $45 a sheet and for and extra $10 a sheet it will come with mylar radiant barrier on it. So this means raidiant barrier on the roof and walls! I expect that 2x6 walls will give us R21. The dutch barn roof will make her ceiling height 10'8" inside so it should feel roomy. I'm going to put awning windows popping out of the roof tin to let a lot of natual light in. She'll have a laundry / mud / inverter room at one end with an overhead storage rack. The kitchen/living room /bed room will have full height ceilings and storage shelf over the bath room for boxes.

Fire away with suggestions.....

radiant barrier doesnt work if something is touching it so you might as well skip it for the walls.

I looked at doing a celestory roof for her place, but its a lot of trouble to create. I can tell you that google sketchup can geolocate a model for you and you can do a shadow study for diffrerent times of the year. Alas, we live in a heating climate, so the only solar gain I'm interested in is her getting shade in the afternoon!!

sounds like you are in a cooling climate, not heating