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Old 01-14-2022, 10:34 PM   #141
montcalm
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So, results!

Using John's analysis I was able to figure in some points of compare:

- If I transported my house to OF, I could net zero it with 10.3kW solar system (31 panels).

- The single story design super-insulated, provided I had enough storage could go off-grid with 16kW system (48 panels). Net zero at 8kW (24 panels).

This assumes:

- Heat pump managing an average COP of 4. I'd probably drop that to 3.5 or so for closed loop.

- Negligible AC. Loads are so small if at all. We never used AC at our camp and it was never hot. It was insulated, but not real well.

- Heat pump hot water. Adjusted based per ave COP based on my current usage.

- My current electrical usage, base of 415kWh/month (note less than my earlier number of 600kWh/month which included AC). This include electric dryer, refrigerator, oven and range, microwave, LED lighting, misc. charging and entertainment.

- No wood in either scenario. Backup only.

- Solar gain neglected.

- 1200 sq. ft. in both cases. Base is 2 story 20x30'. Super-insulated is single story 20x60'.

- Ave high temp applied to day hours, ave low to night hours weighted average based on median day hours per month.

Last edited by montcalm; 01-14-2022 at 11:01 PM..
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Old 01-15-2022, 12:33 AM   #142
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A lot to digest here...

This has been a bit revealing to me. I mean I kind of had some thoughts way back, but now I'm pretty convinced: I don't want to do an off-grid home. If I do end up buying an off-grid piece of land, it'll be a camp. 4 season, with some solar for summer but no way do I want to go that deep into solar + storage + expansion for vehicles in the future. I really think it will be far beyond my budget as well, and perhaps with a payback beyond its lifecycle and mine.

Net zero on this footprint I'd do 110%. I'd also plan to add additional panels for vehicles if not initially.

Next step is to evaluate the min requirements for the northern zone, see where that puts the design in terms of solar load, then look at a cost analysis for whether it's best to stick with that or try to add more insulation. There's a 20% plus improvement in efficiency over my current home (base) in the same environment, so it's not insignificant but perhaps the current regulations meet a good balance between cost and efficiency.

I'd also like to look at solar gain again and try to see about damping that. I was initially thinking a brick wall veneer on the north and west walls of the living and dining room could be enough to damp some solar gain without being too much to lag the rest of the system. Typical solar passives are using a 4" concreted slab floor to damp their gains, but I won't need that much mass as I'll have much less glazing. I think brick could be a good compromise.
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Old 01-15-2022, 11:23 AM   #143
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27x44' (golden ratio) single story structure, with 12:12 roof pitch gives about 19' on the hypotenuse without considering overhangs.

Using a 65x43" 330 watt panel, you could fit as many as 40 panels for a 13.2kW system.
I didn't do the math on this to see what the ideal footprint is for max panels, but this is pretty ideal. I think maybe using the same W/L ratio as the panel might yield better packaging. That's a weird ratio (for today's architecture) and more likely you'd see 30x40' or something like that.

By my calcs 40 panels is enough to max out the State tax credit without considering the NYSERDA rebates, which exists, but aren't readily available info unless you contact an installer, and they are a grant, so the money may or may not be used up by the time you get there.

40 panels is also enough to net zero (I mean true net zero: no wood, fuel oil, NG, etc. except as backup) this home and charge at least one vehicle. I get around 12 panels per 12k mi/yr, but maybe that's optimistic. I'm not sure how much charging efficiency one might lose but 12 is based on solar data for the region and average electric vehicle mileage per kWh currently.

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Old 01-16-2022, 07:43 AM   #144
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A lot to digest here...

I'd also like to look at solar gain again and try to see about damping that. I was initially thinking a brick wall veneer on the north and west walls of the living and dining room could be enough to damp some solar gain without being too much to lag the rest of the system. Typical solar passives are using a 4" concreted slab floor to damp their gains, but I won't need that much mass as I'll have much less glazing. I think brick could be a good compromise.
Funny in my class, my first project used the brick wall on the north side of the room. The second design used the slab floor with an air circulation system that pulled the hot upper air and ciculated it across the slab. And the grand finale design (full passive solar) used a water wall between the greenhouse and the house. You can calculate thermal mass storage using m c deltaT. I would do that first for just the sheetrock on the wall ceiling; plus something for the floor. Compare temperature rise for peak solar gain between say 10 and 2. It might be a choice between add thermal mass or remove 1 window.
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Old 01-16-2022, 08:09 AM   #145
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It's simply the NG energy (converted from therms to kWh) I'm using each month, then multiplied by my furnace efficiency. I've corrected slightly for my hot water usage by subtracting off the average summer usage.

What it tells me: A rough, overall system efficiency. I converted to heat flux and calculated an equivalent thermal resistance for the whole house. It's on the order of R9 (RSI = 1.6 in Jan). That's all infiltration, windows, in and outs, etc. related to an average temp. Rough, but it's where the rubber meets the road.
Hmm. When you balance the heat gain/loss for the whole house, I see you're leaving out the solar gain, but have you considered the intrinsic gains? There is a heat gain component from lost heat from motors (frig, etc,) lighting and people. When lighting was incandescent, this was more significant. It was noted to be a significant contributorin my past analyses. If you are doing the analysis for comparison than you might say it will be the same in the two applications, however if you are looking to see if your new application will be net zero than I would look at these other gains. If it is a part time residence then leaving them out could be considered a cautious case but not an average situation for a full time residence. And an uninhabited place could be left at 50 to 55F. For losses one could argue that infiltration is partially impacted by people coming and going. Infiltration losses have two components and one is delta t related so you could add that into a heat loss evaluation that is based on delta t....
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Old 01-16-2022, 08:23 AM   #146
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I didn't do the math on this to see what the ideal footprint is for max panels, but this is pretty ideal. I think maybe using the same W/L ratio as the panel might yield better packaging. That's a weird ratio (for today's architecture) and more likely you'd see 30x40' or something like that.

By my calcs 40 panels is enough to max out the State tax credit without considering the NYSERDA rebates, which exists, but aren't readily available info unless you contact an installer, and they are a grant, so the money may or may not be used up by the time you get there.

40 panels is also enough to net zero (I mean true net zero: no wood, fuel oil, NG, etc. except as backup) this home and charge at least one vehicle. I get around 12 panels per 12k mi/yr, but maybe that's optimistic. I'm not sure how much charging efficiency one might lose but 12 is based on solar data for the region and average electric vehicle mileage per kWh currently.

What's the installation configuation of the panels. Meaning how many rows? Are you still concerned with brushing off snow? 19 foot is quite high for a brush even if you're on a catwalk. I remember the video about that guy that lived in CO off grid and he recorded the weather for decades and that is being used as a baseline for climate change study...but the point I want to mention is that his daily routine included: the first thing was to record the weather and brush off the solar panels. Every day.

I've told that the magic angle for avalanches is 40- 45 degree. Less than that and the snow usually stays put. Greater than 60 and it sloughs off immediately. At that angle (45) is stays until it slides. Im not saying you should be avalanche concerned but rather a 12:12 roof might not have enough pitch to slough. I'm thinking of those steeper roof chalets in Europe. You pay more for roof to do less brushing. I would consider other roof designs: maybe saltbox or leanto style roof with overhangs.
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Old 01-16-2022, 10:21 AM   #147
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All interesting points. I'll see if I can clear up some things.

12:12 was chosen mainly as an assumption at this point. I know snow will slide if the surface is slippery enough. I'm not sure how that might work with panels, but I'd guess tightly packed would be a better bet than edges to get hung up on. My hope was heavy snow would slide off and light snow would need to be brushed. It's also the minimum I could tolerate in terms of added height and wasted space. I'm still not convinced I wouldn't want to vault over the "great room" i.e. dinging and living area and add a small loft. But the hassles of insulating this way are not my favorite. A truss roof would be by far the easiest to build and insulate and still keep an open floor plan.

I did look at the panel optimization.

For 1200 sq. ft. one can fit 45 panels with a 25x48 footprint and 12:12 pitch. It's few inches over actually, but with overhangs it can fit.

This is with panels arranged in 5 rows of 9 long, long side along the 48' dimension.


I think thermal gain from electric motors will be minimal - lights, non-issue these days. Solar gain will be real, but I'm also not convinced one needs to insulate as much as we had. My guess is that current regulations are sufficient except perhaps walls - maybe up to R30 there would be better. I tend to wonder how much gain there would be going standard R13+10* wall investing extra money into higher efficiency windows - going from a standard U=0.3 to U=0.2. That would be an interesting analysis to look at.

*2020 Regulation is R13+10 or R20+5 vs R13+5 for 2009 in zone 6.

Last edited by montcalm; 01-16-2022 at 02:50 PM.. Reason: 2020 regulation
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Old 01-16-2022, 10:56 AM   #148
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Also I should add - this whole "net zero" thing is a game of averages. It's the game I'm playing now. But that's not to say you might have a year you're in the hole a few hundred kWh, and another you're surplus. I think the idea is really just to generate as much as you can IF the cost of panels outweighs the cost of electricity. Since our state wants to boost our solar output, this is the way it is now. And they want to increase storage as well - that'll be next. They have incentives for Long Island, but not upstate yet. Once there's enough solar generation, then I'm sure the focus will be batteries.

This is also why I've abandoned the idea of "off-grid". It just doesn't make sense. I mean mooregm outlined this before, and it's not that I didn't believe him, I just really had to weigh all the options. The issue is you have to meet your demands in the worst times, so that means you wind up having HUGE surplus every other time, and nowhere to put it.

Another side note, I saw that Panasonic now has a 410W panel (22% efficiency) - so things like this will be significant for small footprints. I already want this for my current home as it would boost my potential output up an entire kW.
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Old 01-16-2022, 12:15 PM   #149
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And John - I was thinking about one other thing...

My current home has 7(!) north facing windows. And 2 west facing. I feel like just reducing that could be a significant gain with no other changes to insulation. Recall my effective resistance (simply dT/Q) is on the order of R9. I calculated your design to be effectively R17. That gave a heat energy consumption reduction of 43% for the year.

I wonder how much of that is simply reducing windows?
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Old 01-16-2022, 02:20 PM   #150
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Old 01-16-2022, 06:57 PM   #151
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Old 01-17-2022, 12:01 AM   #152
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This thread has really taken me a place I wasn't expecting. I went from kind of being curious in current energy trends to being a real exercise in understanding the options available, not only for energy needs, but for building as well.


I want to summarize some stuff here, because if I'm wrong, I'd like to be corrected about this. But as I understand it, you can't really build a "camp" anymore, as many camps were built in years prior and that I grew up around. These places were basically 3 season shacks with indoor plumbing and grid electric with woodstoves, electric and/or propane heat, were minimally, if at-all insulated, and were usually built on piers - some posts, some on blocks, etc...

You can build a cabin, which must not have a permanent foundation (piers or posts), has no indoor pressurized plumbing or septic, has no utilities: grid connection, sewer, gas, etc. There doesn't seem to be any regulation that I see on insulation. I'd assume it would have to pass structural code, but I don't actually see that anywhere in writing. I'm also not sure how this applies to the rest of the state as the only document I found pertaining to it was from the APA.

You can build an unheated structure or minimally heated, but I assume this covers garages and sheds and such. And the heat requirements seem to be very small like you'd use in a shed or something to keep water lines from freezing. I don't think these would qualify as 3-season camps and if they did, you couldn't technically put in even a woodstove as any would violate the heating requirement. The requirement also applies to cooling i.e. a conditioned space. I think it would be hard to enforce space heaters and window AC so I'm guess it's going to be hard to get a building permit for something you could sleep in to fall under either of these.

The thing it seems you can build, is a house*. A 4 season house that is designed to be very energy efficient. It seems you must have a permanent foundation: crawl space, slab or full basement, and all of those must be insulated per requirements. I see no provision for building on piers or posts. And if you do this, you must insulate the rest of the structure very well. Per these requirements. There are more details in the actual code, but that gives the gist.


So this brought me back to a question that was posed earlier: Do you want a camp, or house?

I think if you want the grid and indoor plumbing, you need to build a house whether you use it for a camp or live in it year round. If you're off grid and you want plumbing and septic, seems like you build a house as well.

There's a big financial gap there between a "cabin" and a residential code-compliant new building.


*You can also build a log home which has different requirements that I've yet to look into.
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Old 01-17-2022, 08:10 AM   #153
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I believe what you can build will be somewhat dependent on the individual who is the building official in the jurisdiction you are building in.

The NY Residential Code does permit building on piers or posts. The floor just has to be insulated (R30 iirc vs R10 or 2" of foam under a slab on ground) and - dependent on your building official - you may have to have an engineer seal the drawing.

But no heating appliance and an outhouse - good to go.

I will say the disappointing thing about NY codes is not allowing gray water systems. You can have no flush toilets - composting, outhouse, electric, other - but still must have a complete engineered septic system for a lone sink with drain.
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Old 01-17-2022, 09:17 AM   #154
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I believe what you can build will be somewhat dependent on the individual who is the building official in the jurisdiction you are building in.
I get that. I'd assume you'd need to submit drawings for approval before you can acquire a permit.


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The NY Residential Code does permit building on piers or posts. The floor just has to be insulated (R30 iirc vs R10 or 2" of foam under a slab on ground) and - dependent on your building official - you may have to have an engineer seal the drawing.
I see in insulation requirements where they mention R30 for a floor, but I was not clear on what that was for. It does not seem you'd need to insulate the floor if you had an insulated basement or crawl space. Slab is very clear - as you say, R10 is the requirement.

Do you know where in the code this is? I saw a builder claim that full foundations were needed for new builds so I looked through the foundation code and I did not see this. I admit, I did not read it all.

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But no heating appliance and an outhouse - good to go.

I will say the disappointing thing about NY codes is not allowing gray water systems. You can have no flush toilets - composting, outhouse, electric, other - but still must have a complete engineered septic system for a lone sink with drain.
So you must insulate the building per code requirements but you cannot have a heating appliance?

The septic part actually makes sense to me - but if I had to put in a septic system I would want flush toilet(s).

I think the cabin provision allows for grey water catchment and sink and drain without a septic. But of course you must forgo electric and indoor plumbing.

I have a headache now... I'm going to go throw some snow.
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Old 01-17-2022, 11:43 AM   #155
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I think thermal gain from electric motors will be minimal - lights, non-issue these days. Solar gain will be real, but I'm also not convinced one needs to insulate as much as we had. My guess is that current regulations are sufficient except perhaps walls - maybe up to R30 there would be better. I tend to wonder how much gain there would be going standard R13+10* wall investing extra money into higher efficiency windows - going from a standard U=0.3 to U=0.2. That would be an interesting analysis to look at.

*2020 Regulation is R13+10 or R20+5 vs R13+5 for 2009 in zone 6.
Concerning Intrinsic heat gain....Intrinsic gain for devicess such as motors lighting etc. was 10% of my design day requirements with a small 2 room cabin design however 70% of that was incandescent lighting. I still envision it will provide 2-3% of the needed heat.

The occupants provided 10% of the design day heat requirements but that was a small cabin. An average man produces 360btu/hr for 1 Met. Sleeping is 0.7 Met. Sitting quietly is 1 Met. Standing 1.2 Met. Half court basketball 5.0-7.6 Met (in case your house is really big)

Concerning cost effictiveness of insulation, I think my model can be useful here if you can price out the cost of different construction. It might not be easy to get cost of double wall vs single wall. Perhaps the easiest to priceout would be switching the outer rigid insulation from 1" to 2" or 0". More than 2" gets tougher to install. One could get a good cost estimate for the square footage and the associated cost and then change the R value in the spreadsheet and see the change in the energy. I would then recommend using the degree day method to determine the season (annual) heating requirements and heating cost or annual savings.

Going back to a previous conversation, I went down the rabbit hole of basement analysis. In the handbook, they say that if you have a basement temperature of 50 or greater then you consider it heated and do the heat loss calculation through the basement wall. They say if you have the heating plant and water heater in the basement then chances are the temperature will be over 50. There are factors to consider for the thermal resistance of the soil. There is a correction factor that you add to the outside design temperature for the basement heat loss, because the soil is warmer than the air. They correct the outside temp for the whole wall but I chose to adjust it for the part of the wall under the grade and used the design temperature for the basement wall above grade. I put all these into my model. Other factors apply for the basement floor heat loss including width of the house and how deep the basement is in the ground. I started assuming a 12" cement block basement wall with 4" of rigid styrofoam board on the outside.

Then, they say that you can disregard the heat loss through the house floor to the basement. I thought that was just wrong so I started thinking. If the heat from the house goes thru the floor into the basement and then out the walls and basement floor. One could write the equations for that heat flow and input the related resistances based on the construction used and derive the basement temperature (without any added heat) based on the outside temperature. So I did all that and went back and tweaked the model. I now let the user specify (guess) the basement temperature and the model calculates the heat loss through the floor with that delta T (i.e. 67-50F) and then thru the basement walls with that delta T (50-design temp + soil adjustment factor for part below grade)

Now the model is a sloppy mess but I tweaked the numbers and it seams to work. The next step would be the change some insulation in the construction and see how the heat loss changes.
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Old 01-17-2022, 11:49 AM   #156
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I believe what you can build will be somewhat dependent on the individual who is the building official in the jurisdiction you are building in.

The NY Residential Code does permit building on piers or posts. The floor just has to be insulated (R30 iirc vs R10 or 2" of foam under a slab on ground) and - dependent on your building official - you may have to have an engineer seal the drawing.

But no heating appliance and an outhouse - good to go.

I will say the disappointing thing about NY codes is not allowing gray water systems. You can have no flush toilets - composting, outhouse, electric, other - but still must have a complete engineered septic system for a lone sink with drain.
Excuse my ignorance but whats the common way to get R30 for a floor? Is it 2x8 framing with a layer of rigid board under it or are people upsizing the joist (a manufactured beam) and increasing the fiberglass or other void insulation thickness?
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Old 01-17-2022, 12:03 PM   #157
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Some thoughts from being away for a few days and catching up:

1.) Heat Recovery Ventilator -- this replaces traditional bathroom fans and it balances the outgoing air with incoming air, tempering the incoming air with the heat from the outgoing air. Required in new buildings I believe given how tight they are. It should not be used with the stove hood as the grease/grime will clog them. We have the HRV pulling from 3 bathrooms and the kitchen generally (not stove) set to run for 10 minutes per hour or manually by traditional bathroom switch for 15 minutes. We have a self-cleaning hood that filters (kind-of) and then sends the air back into the kitchen. Thought it was a big deal at first, but having not had an external venting fan in the past two houses, it's not as big of a deal as I thought -- and my wife cooks nearly every day, but rarely things that smoke -- or she is just better than me. Ours is 75% efficient -- meaning 75% of the outgoing air is transferred to the incoming air. Not sure how accurate 75% really is.

2.) Agreed on all the net zero vs true zero comments -- and how the former is simple and the latter is very difficult. The kW array sizes seem reasonable enough for net zero -- probably a touch low when you add shading and such. I think the off-grid is small by a factor of 2 or 3. For reference, in this semi-cold spell we've been used 578 kWh this past week. Our energy needs (2600 sq ft) are probably 2-3 times that of a smaller more well insulated house in Old Forge area (smaller, but also colder). So call that 250 kWh for sake of discussion. My ~10kw array has produced ~60kwh in the past week. Better roofing tilting would help (we had no snow covering this past week) -- but unless you have the perfect lot, no shading in the ADKs is going to be hard. It's crazy how low the sun is right now -- even two hours before/after high noon -- which is not very high at all.

3.) Angle of panels. 45 degrees on a 12/12 roof has been mentioned. That is about right. Certainly would not go shallower for off-grid. I would go a bit shallower for net-zero as there is far more sun in summer than winter -- longer days @ higher angle. Regarding sliding, 45 degrees is reasonably self-cleaning. We have a solar kiln for treating firewood with a glass roof. Any snow is cleared very quickly from there and that is without a black background. We use a plastic roof rake to clear our very shallow panels (~18 degrees). I usually just clean the bottom half and the sun takes care of the upper panels. If it's not sunny, they do not clear, but then again they are not producing either.

For off-grid setups I'd personally look at adding vertical panels on the south side of the house house. That way there is always something coming in even during a snow storm to cover some base loads. They will not produce anything in summer half of year, but then you do not need them then anyways. Unfortunately they'd be ugly. Another alternative is to design a gambrel roof of sorts where the upper pitch is in the 45 degree range and the lower in the 80 degree. It'd look nicer, but really that's all you are gaining. I plan on doing this on our shed with a 12/12 traditional main roof, then instead of eaves drop down at about 80* to create a gambrel roof -- though it's only an allusion to add solar panels without looking ugly.

4.) BTU calculations seem about right, if not a touch high in the real world which is expected given they are conservative. A real-world benchmark -- we've gone the past cold snaps with our 38k btu unit running constantly outputting about 35k BTU on high, but jumping between first/second/third stages -- third stage kicks domestic hot water on/off to prioritize space heating. We are a bit warmer outside Syracuse, but 2600 sq ft and modestly insulated. At a certain point, it does not really matter as I'd personally do another two stage unit and I do not think they make them smaller than 2-tons (geo).

5.) Thermal Storage -- I did some math on storage of thermal energy in sand/concrete versus water. While water per pound holds ~5x BTU per degree, the actual volume capacity of both is much closer. Sand/concrete is about 46% of water per cubic foot. So having 5000 gallons of water is the same as about 10k gallons of sand. 5000 gallons is about 800 cubic feet, or roughly a 6" slab of 1200 sq ft concrete. Better yet, if you were to dig down during construction an extra foot or three, you could insulate, then add dirt back, radiant loops, then concrete slab. That's the benefit of the thermal mass at only slight extra cost and no internal space utilized by water tanks. I would definitely do this in a garage as it you could utilize a smaller radiant heat pump using excess energy to heat the slab and then turn off that zone during cold times to coast for a few days.

6.) A well insulated house does not have internal temperature swings. Having an open concept floor plan and leaving bedroom doors open helps a lot here too. Having a circulation fan (eg furnace fan) run on days where you know there will be issues helps distribute the heat if things get extreme. Having lived in a nearly uninsulated house and well insulated -- it's night and day difference. Air sealing matters too.

7.) Overheating from windows is a real issue, even on cold days in my well, but not super-insulated house. I would not do a slab on grade personally -- my joints protest. Thermal mass from internal objects in negligible -- anything wood insulates (R1 per inch). Similar with cloth. Tile is the only thing that might qualify -- everything else is a round-off error. That said, we just turn on the HVAC fan manually and circulate the air which includes our colder basement to temper it. Opening windows helps too. One key thing is setting up windows to be perfectly south, with overhangs that eliminate all direct incoming sun from about spring equinox to fall equinox. But keep in mind it's cold in late march and hot in late September, so nothing is perfect.

Aside: I prefer a basement if at all possible, else I'd do a crawl space. My current house basement is only 3 feet below grade, with ~4 feet of above grade block. Best of both worlds as we have a couple semi-normal windows downstairs while staying above the water table inches below. I've seen a few waterfront homes uses this as well, where they dig down a couple feet, then set the house ~2 feet above grade giving a 4 foot crawl space to put hot water tank and HVAC utilities -- knowing flood marks is important here though.

8.) Thermal buffer vs thermal storage -- In off grid storage is very important, but many confuse thermal mass as storage, when it's really a buffer. An example of this would be the classic slab on grade in front of windows. That's really just buffering the daytime to the night time. But it's not really helping when the next three days are cloudy. Either the slab cools to 70* and thus is not providing any energy, or the house cools to 65* and it continues to provide energy, but only because the house is now cold -- neither option passes the wife test.

9.) Probably my biggest take away from this whole tread is spending money where it matters. 2x6@24 vs 2x6@24 +2" exterior insulation vs 2x4@16 double walls vs 2x4 double walls with exterior insulation -- KISS is with the middle ground 2x6@24 + exterior insulation. Paying extra for the complexities and novelties of double studs is not worth the cost (50% more wood, more hammer time, non-traditional practice. Same for roof with standard rafters and fill it full of insulation. Though I'd still probably do attic trusses + insulation exterior insulation for the extra "free" square footage as if you are going to do a 12/12 pitch roof, mine as well get the benefit of extra space too. Similar for basement -- insulate reasonably but not crazy.

All these things are standard industry practices that any competent contractor has seen before -- and friends/family if self-building. Doors and windows are where things go south -- so design good entryways (eg enter through garage) as primary entryway to create buffers.

Windows are probably the one thing may reconsider. Having just gone down this path and purchased windows in fall 2020 -- I opted for the double pane windows as triple pane did not compute. I think on-grid with a good heat pump in Syracuse area that still is the correct choice -- the payback is negative and windows need to be replaced every XX years. In ADKs with colder temperatures it begins to swing things in favor of triple pane, though I'm still not sure it matters enough. Off-grid, I think it does make sense as it will help year-round, but more importantly help most during design days, which is where the system is designed to saving extra panels and BTU sizing.
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Old 01-17-2022, 12:41 PM   #158
John H Swanson
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Some thoughts from being away for a few days and catching up:
All really good points and some great real world data. thanks.

One point we havent expored well, IMO is thermal shutters for windows. I've had issues with condensation inside windows then insulating them on the inside, however when I look at the heat loss (in the model) it makes sense if one could use some form of a high R value commercial exterior window shutter. A night shutter of 2" polyiso used 50% of the time on all windows could possibly reduce the total heat loss by 6%. Assuming they exist and they are reasonably priced. I know most of europe had window shutters.
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Old 01-17-2022, 01:05 PM   #159
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The mechanical engineering nerdism in this thread is awesome. I'm thoroughly enjoying this learning experience. Thanks so much for all the input!

I have a TON of comments, but I'm busy and I need to go back re-read as well, but a couple things.

The incoming air HEX - definitely a thing. I looked this up as soon as John mentioned it and it's on every "green" building design i.e. anything with high thermal efficiency.


I know it's not my goal, but the off-grid factor I'd like to understand more. No way is going to be cost effective, so I don't even know that's its worth exploring, but I think it may be a point of how much storage vs how much power is available - and of course if I were going to deep dive into that I'd need to do a week-by-week and daily analysis in the worth months: December and January. December looks the worst because the ratio of sun to heat required (estimated) is the worst. January even though colder, on average has more sun. But the trick is storage.


I didn't do any mass or water calcs yet, but those are interesting.


So I don't want to divert the nerdism for an ideal build, but in talking with the silent partner in my personal interest aka my wife, she's not convinced she wants to spend the entire winter in Old Forge when she's 60+. I can get that. I'm 41 now and the cold already feels colder than it used to 10 years ago.

Anyway, this creates a diversion for me - what is my goal? Seems like it's now a "camp". And I don't want to dump $200k and a ton of my time and labor into a "house" that I use for a total of two months out of the year in summer, and sporadically throughout the rest of the year. And then pay 4k a year in taxes on a home that's assessed more than my permanent residence. Needless to say, geothermal heat pumps, water heaters and mega-solar is out of the picture for the scope of this.
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Old 01-17-2022, 02:42 PM   #160
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2.) Agreed on all the net zero vs true zero comments -- and how the former is simple and the latter is very difficult. The kW array sizes seem reasonable enough for net zero -- probably a touch low when you add shading and such. I think the off-grid is small by a factor of 2 or 3. For reference, in this semi-cold spell we've been used 578 kWh this past week. Our energy needs (2600 sq ft) are probably 2-3 times that of a smaller more well insulated house in Old Forge area (smaller, but also colder). So call that 250 kWh for sake of discussion. My ~10kw array has produced ~60kwh in the past week. Better roofing tilting would help (we had no snow covering this past week) -- but unless you have the perfect lot, no shading in the ADKs is going to be hard. It's crazy how low the sun is right now -- even two hours before/after high noon -- which is not very high at all.
I had calculated an average ~25kWh per day from a 10kW array in Jan for OF. Sounds like that'd be pretty off for that week. Definitely would have to boost output for off-grid based on weekly analysis, which I mentioned in a previous post. I'm not going to go that far as I think it's beyond the scope of pretty much... everybody! It's just too damn hard to generate that power in January no matter how efficient you are.

This is not discouraging btw, just goes to show how difficult it is to do off-grid solar. I think there is some ideal balance between solar, propane and wood that will work for off-grid, but I don't know exactly what that ratio is. I think it's the one that gets you by on what you NEED to run on electricity, and thermal energy has to be filled by the other two.


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3.) Angle of panels. 45 degrees on a 12/12 roof has been mentioned. That is about right. Certainly would not go shallower for off-grid. I would go a bit shallower for net-zero as there is far more sun in summer than winter -- longer days @ higher angle. Regarding sliding, 45 degrees is reasonably self-cleaning. We have a solar kiln for treating firewood with a glass roof. Any snow is cleared very quickly from there and that is without a black background. We use a plastic roof rake to clear our very shallow panels (~18 degrees). I usually just clean the bottom half and the sun takes care of the upper panels. If it's not sunny, they do not clear, but then again they are not producing either.

For off-grid setups I'd personally look at adding vertical panels on the south side of the house house. That way there is always something coming in even during a snow storm to cover some base loads. They will not produce anything in summer half of year, but then you do not need them then anyways. Unfortunately they'd be ugly. Another alternative is to design a gambrel roof of sorts where the upper pitch is in the 45 degree range and the lower in the 80 degree. It'd look nicer, but really that's all you are gaining. I plan on doing this on our shed with a 12/12 traditional main roof, then instead of eaves drop down at about 80* to create a gambrel roof -- though it's only an allusion to add solar panels without looking ugly.
All great ideas, and stuff I had thought about e.g. a gambrel to give some better angles for winter, but all-in-all, I think you can pack more than you'd *want* to invest in on a 12:12 for off-grid - see above.

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5.) Thermal Storage -- I did some math on storage of thermal energy in sand/concrete versus water. While water per pound holds ~5x BTU per degree, the actual volume capacity of both is much closer. Sand/concrete is about 46% of water per cubic foot. So having 5000 gallons of water is the same as about 10k gallons of sand. 5000 gallons is about 800 cubic feet, or roughly a 6" slab of 1200 sq ft concrete. Better yet, if you were to dig down during construction an extra foot or three, you could insulate, then add dirt back, radiant loops, then concrete slab. That's the benefit of the thermal mass at only slight extra cost and no internal space utilized by water tanks. I would definitely do this in a garage as it you could utilize a smaller radiant heat pump using excess energy to heat the slab and then turn off that zone during cold times to coast for a few days.
Interesting concept - I think it would come down to cost effectiveness and efficiency i.e. what can hold the heat longer. That'd be where the rubber meets the road.

BTW I know I was not certain exactly what you meant by tank storage as I thought perhaps you were talking about water batteries - I occasionally see something about this on youtube, but have never looked into it. Well I did the calcs for 5000gal up 18' - it's like 0.2 kWh of storage. I didn't know that without doing the math - yeah water batteries work, but you you need a hell of a lot more volume and a hell of a lot more head for anything substantial. So to anyone that missed this, storing energy in heat is much, much, much more efficient in terms of volume.


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8.) Thermal buffer vs thermal storage -- In off grid storage is very important, but many confuse thermal mass as storage, when it's really a buffer. An example of this would be the classic slab on grade in front of windows. That's really just buffering the daytime to the night time. But it's not really helping when the next three days are cloudy. Either the slab cools to 70* and thus is not providing any energy, or the house cools to 65* and it continues to provide energy, but only because the house is now cold -- neither option passes the wife test.
I would never personally do slab - I hate concrete floors. I don't like carpet or ceramics. Wood is the only option for me except kitchen/bathroom. I prefer joists with an opening, prefer basement but maybe crawl is ok, mainly for HVAC ducting, plumbing and wiring. For me doing my own work and my own sanity, the basement is my preferred choice for a home.

"Thermal buffer vs thermal storage" - right, I was trying to use damping as the operative word, but that may be confusing to some as it's not energy dissipation, but smoothing. I'm a DC amp nut, so I know all about this kind of thing for power supply design going from AC transformers to DC supplies. People use all sorts of different terms for this short term storage - it's filtering, and it's buffering.


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9.) Probably my biggest take away from this whole tread is spending money where it matters. 2x6@24 vs 2x6@24 +2" exterior insulation vs 2x4@16 double walls vs 2x4 double walls with exterior insulation -- KISS is with the middle ground 2x6@24 + exterior insulation. Paying extra for the complexities and novelties of double studs is not worth the cost (50% more wood, more hammer time, non-traditional practice. Same for roof with standard rafters and fill it full of insulation. Though I'd still probably do attic trusses + insulation exterior insulation for the extra "free" square footage as if you are going to do a 12/12 pitch roof, mine as well get the benefit of extra space too. Similar for basement -- insulate reasonably but not crazy.
I'm not clear how this works out economically, but I'd be interested to see. I think, based on NYS requirements, 2x6 framing is becoming norm as there is a code requirement of R20+5 for walls - that would be a 2x6 wall with 5 continuous foam on the outside. It'd be easy to go +10 as well, again, I'd like to see the financial analysis there. I tend to think these state requirements have been thoroughly optimized based on the current market, and then drive the market.



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Windows are probably the one thing may reconsider. Having just gone down this path and purchased windows in fall 2020 -- I opted for the double pane windows as triple pane did not compute. I think on-grid with a good heat pump in Syracuse area that still is the correct choice -- the payback is negative and windows need to be replaced every XX years. In ADKs with colder temperatures it begins to swing things in favor of triple pane, though I'm still not sure it matters enough. Off-grid, I think it does make sense as it will help year-round, but more importantly help most during design days, which is where the system is designed to saving extra panels and BTU sizing.
I'd have to see the analysis here - how much benefit in efficiency vs. extra cost vs. putting the cost into extra wall insulation. There's (usually) much more wall area, but windows have such low insulating value a small change can make a significant difference in efficiency. I can't do the math in my head nor do I have any idea the cost differences between adding +5 continuous vs. upgrading windows. Obviously going to be contingent on the # of windows in the design as well and surface area of the walls.

Last edited by montcalm; 01-17-2022 at 03:02 PM..
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