Still want to be off grid - HVAC Nuts Welcome

[myles]

Hey Guys,

Thanks for reading first of all! :D

You can see my setup here:

and here:

I am definitely going to make ALOT more videos to help those that are in need of a modern actual off grid living approach, i would not go back, its too much fun, which is why I am here! :D

OK I need some help here, I really want to be off grid fully, but having a hard time justifying not bringing in a natural gas line and need some clarity in my thoughts from the community. Currently we a are fully off grid but we have propane for the boiler.

Firstly location: Close to winnipeg, manitoba to help with calculations.
Secondly, the Goal: Stay off grid without Gas line for my boiler.
Current configuration: 10.7KW (plans to add another 5k this summer) solar bifacial, Sol-Ark 15K, 1120AH lifepo4 48v, IBC Modulating Condensing boiler 14-115k, IBC indirect hot water tank, 50Gal Elec hot water tank, senville mini splits (4 heads total) for A/C in summer.
Current heat loads (INCLUDES DHW).

Our house is 2500 sq ft slab on grade modern build lots of south glass exposure, heavily insulated 9.25" walls from greenstone building products, 3" under slab insulation and around perimeter plus frost protect, R30 spray insulation to flat ceiling (1:12 pitch), its been -30*C outside with the sun shining its 80*F inside, we use the blinds to moderate the day temps, this is not a big deal. I keep the floor heat at 76*F and the house is very comfortable.

House real world performance statistics: 0.6-0.7 air changes per hour building envelope, currently I am using 660,000 BTU/ day to keep the slab at said 76*F with a *2F. Since its a condensing boiler your goal is to run that thing as cold as possible for efficiency. The boiler chugs along at 14-25K btu almost constantly to maintain the desired temp in the house (including keeping my attached garage at 58*F constant (sub note, the garage floor heat only cycles maybe once every two weeks to keep this temp being attached to the house with the same building methods very efficient!)).

So if we do the math I need 27,500 btu/hour to supply all the heat to the house, and the DHW. Currently I am getting about one full DHW tank per day from the electric (see videos on how this is done), so thats a free 4500 or so btu, which then the propane boiler will not have to feed the indirect tank for.

please enligthen me as to the best way to get these extra btus, mainly for at night!

Option 1: I have room on the solark to Add more solar, and an air source heat pump to heat the floor to 80*F which will then drop to about 76*F by the morning (best guess, doing a test tonight shutting off the floor heat to check how much drop I get). (https://www.arcticheatpumps.com/buy-cold-climate-heat-pump/heat-pumps-evi-low-temp.html)

Option 2: Adding hideous solar collectors to heat the floor, I have 20 acres of property space is not an issue, but I really dislike the look of these

Option 3: Leave it as is and bring in a natural gas line cutting my cost of propane by 75%. Yes natural gas would cost 25% of propane, BUT there is a 18K bill to bring in the line.


Let the conversation flow :D

 

[MisterSandals]

Leave it as is and bring in a natural gas line cutting my cost of propane by 75%. Yes natural gas would cost 25% of propane, BUT there is a 18K bill to bring in the line.

Just out of curiosity, without knowing your usage, what is the break even period for this?

Messing with numbers:
If you are using $200 of propane per month (12 month average for simplicity)

$18,000 / ($200 per month x .75 savings) = 120 months (10 years)

But given that this will add quite a bit to the resale value of your house, if my guesses are close, its kind of a no-brainer.

Just my $.02

 

[myles]

Just out of curiosity, without knowing your usage, what is the break even period for this?

Messing with numbers:
If you are using $200 of propane per month (12 month average for simplicity)

$18,000 / ($200 per month x .75 savings) = 120 months (10 years)

But given that this will add quite a bit to the resale value of your house, if my guesses are close, its kind of a no-brainer.

Just my $.02

Currently i am using $1200 propane every 6 weeks, payback period is 5 years on the line install, this is only during the winter months as summer loads will be taken over with solar mainly except maybe cooking and the clothes dryer (minimal usage), but yes I think I am in your camp with this one that bringing in a line especially with the quick payback period, is sadly a no brainer!

 

[Danke]

House real world performance statistics: 0.6-0.7 air changes per hour building envelope, currently I am using 660,000 BTU/ day to keep the slab at said 76*F with a *2F.

I live in a cold climate and by my calculations I’m gonna keep my natural gas furnace for heat

Isn’t 660,000 BTU almost 200kW?

So with my rates, that would be about $7 gas and over $30 for electric.

 

[myles]

I live in a cold climate and by my calculations I’m gonna keep my natural gas furnace for heat

Isn’t 660,000 BTU almost 200kW?

So with my rates, that would be about $7 gas and over $30 for electric.

This sounds about right yes, this is for all the heat loads in the house, and cooking, and drying clothes, AND running backup generator when needed (average calculations over last 3 months used.)

 

[OzSolar]

So if we do the math I need 27,500 btu/hour to supply all the heat to the house, and the DHW. Currently I am getting about one full DHW tank per day from the electric (see videos on how this is done), so thats a free 4500 or so btu, which then the propane boiler will not have to feed the indirect tank for.

please enligthen me as to the best way to get these extra btus, mainly for at night!

Option 1: I have room on the solark to Add more solar, and an air source heat pump to heat the floor to 80*F which will then drop to about 76*F by the morning (best guess, doing a test tonight shutting off the floor heat to check how much drop I get). (https://www.arcticheatpumps.com/buy-cold-climate-heat-pump/heat-pumps-evi-low-temp.html)

My first choice would be to try add enough PV to make the heat pump water heater work. I would try to avoid bringing in NG since you would actually reduce your autonomy over propane.

27,500 x 24 = 660 kBTU per day. I assume that's your daily average over a month?

Using a somewhat generic COP of 2.5 for the Arctic HP. For this rough analysis I'm ignoring that the COP will vary with with air temperature and at some point (-15F?) will no longer work.

To get to kWh: 660,000 / 2.5 = 264,000 / 3413 = ~77kWH's per day needed to heat your house using a heat pump water heater.

77/3.5 (my guess at your winter sun hours in Canada) = ~22kW of solar needed to produce enough kWh to heat your house.

And that's before we talk about how many days of autonomy you need or what's going to happen when the temps drop below -15F.

Natural Gas sounds like a pretty good option!

 

[Danke]

Using a somewhat generic COP of 2.5 for the Arctic HP. For this rough analysis I'm ignoring that the COP will vary with with air temperature and at some point (-15F?) will no longer work.

It may work, just not very Efficiently. There’s a video of a guy with a central air system heat pump from Mr. Cool. It was a smaller home and he was up to almost 5000W at -22 Fahrenheit outside to keep the inside 70°

 

[OzSolar]

It may work, just not very Efficiently. There’s a video of a guy with a central air system heat pump from Mr. Cool. It was a smaller home and he was up to almost 5000W at -22 Fahrenheit outside to keep the inside 70°

I dare not guess how it would behave.

What I can say is that I have a Mr. Cool mini split in my basement. It's rated to -14F and they mean it. At -14f it throws an error and goes into low temp shut down. Thankfully, I've only seen that once in the 3 years I've had it. My ground source heat pump for the other two floors doesn't care about outside temps thankfully.

My analysis was only meant to be a pass/fail "back of the napkin". To get to an accurate answer as to what size of heat pump and how much solar would be needed should probably start with a bin analysis using 15 minute historical data and/or degree days.

 

[Danke]

I dare not guess how it would behave.

What I can say is that I have a Mr. Cool mini split in my basement. It's rated to -14F and they mean it. At -14f it throws an error and goes into low temp shut down. Thankfully, I've only seen that once in the 3 years I've had it. My ground source heat pump for the other two floors doesn't care about outside temps thankfully.

My analysis was only meant to be a pass/fail "back of the napkin". To get to an accurate answer as to what size of heat pump and how much solar would be needed should probably start with a bin analysis using 15 minute historical data and/or degree days.

GEER advertises one goes down to -32°F. Have no idea how much energy it takes and the warranty is not good unless you get a professional installer.

 

[OzSolar]

GEER advertises one goes down to -32°F. Have no idea how much energy it takes and the warranty is not good unless you get a professional installer.

That would be very neat. There's a two man HVAC shop that I work with sometimes that does Daikin. You get a 10 year parts warranty with him and his cost not that much more than what I paid to self-install a Mr. Cool. When my Mr. Cool craps out tomorrow or in 5 years I'll be calling him to put a Daiken in.

But I think @myles needs a HP water heater for his hydronic system and there's hardly any of those on the market.

 

[Danke]

That would be very neat. There's two man HVAC shop that I work with that does Daikin. You get a 10 year parts warranty with him and his cost not that much more than what I paid to put self install a Mr. Cool. When my Mr. Cool craps out tomorrow or in 5 years I'll be calling him to put a Daiken in.

But I think @myles needs a HP water heater for his hydronic system and there's hardly any of those on the market.

Which model of Mr. cool is that?

 

[OzSolar]

Which model of Mr. cool is that?

I don't have the actual mode # at my fingertips. I do recall that it's 18,000 BTU and ~ 19 SEER. It's not the DIY model with precharged lines. Me and Rona are quarantine couch vegging for a few more days then I could try to round up the actual part number.

 

[EastTexCowboy]

I dare not guess how it would behave.

What I can say is that I have a Mr. Cool mini split in my basement. It's rated to -14F and they mean it. At -14f it throws an error and goes into low temp shut down. Thankfully, I've only seen that once in the 3 years I've had it. My ground source heat pump for the other two floors doesn't care about outside temps thankfully.

My analysis was only meant to be a pass/fail "back of the napkin". To get to an accurate answer as to what size of heat pump and how much solar would be needed should probably start with a bin analysis using 15 minute historical data and/or degree days.

I got a verbal quote today on three Mitsubishi units. I'm supposed to get all the specs and some hard numbers next week but what he told me was impressive. The 3 ton is 21 seer and the 2 ton is 24 seer with EER and HSPF ratings close to 10. He's saying they are efficient down to -13. I don't need that much cold-proofing in Texas but part of the goal is to get the numbers good enough that I can run a couple of the units on my current solar. For here they wouldn't need heat strips at all so that's a big step in that direction. I don't know if they would be good enough for this application but it might be worth a look. They also come with a 12 year warranty. Of course there's always the issue of a reliable dealer/contractor somewhere close.

 

[Danke]

I don't have the actual mode # at my fingertips. I do recall that it's 18,000 BTU and ~ 19 SEER. It's not the DIY model with precharged lines. Me and Rona are quarantine couch vegging for a few more days then I could try to round up the actual part number.

I wonder what the Olympus Hyper Heat Mr. Cool can do?

 

[myles]

That would be very neat. There's two man HVAC shop that I work with that does Daikin. You get a 10 year parts warranty with him and his cost not that much more than what I paid to put self install a Mr. Cool. When my Mr. Cool craps out tomorrow or in 5 years I'll be calling him to put a Daiken in.

But I think @myles needs a HP water heater for his hydronic system and there's hardly any of those on the market.

For HP hot water heaters. Don't they just take the heat out of your building to make.hot water? Seems counter intuitive when your also trying to heat the building.

 

[Quattrohead]

For HP hot water heaters. Don't they just take the heat out of your building to make.hot water? Seems counter intuitive when your also trying to heat the building.

Here in Florida we are always needing to cool and dehumidify our homes, so yes take that heat and do something useful !!!

 

[myles]

Here in Florida we are always needing to cool and dehumidify our homes, so yes take that heat and do something useful !!!

Great for you but bad for us lol! We could trade free ice for free heat for you? Which is more useful when you have whiskey?

 

[OzSolar]

For HP hot water heaters. Don't they just take the heat out of your building to make.hot water? Seems counter intuitive when your also trying to heat the building.

HP Hot water heaters certainly do but that wasn't what I was referring to.

The one you linked to is an Air to Water heat pump that sits outside your house.

 

[myles]

I guess it always boils down to cost! But I will certainly look at feeding my indirect tank with the heat pump heater and check out the benefits!

 

[EastTexCowboy]

Great for you but bad for us lol! We could trade free ice for free heat for you? Which is more useful when you have whiskey?

I want in on that trade too. Especially along about August here in Texas. You'd think someone would do a pipeline and turn the whole continent into a giant heat exchanger.

On the whiskey, I can take that neat or on the rocks.

 

[myles]

My live
view of heating with alternate methods when the sun isn't shining. Lots of ice and whiskey! ?