Can you build a "green" house in the Adirondacks?

[montcalm]

Ha - no worries. I can evaluate these things later...

Keep in mind, I'm optimistically thinking 5 year plan just for acquiring a lot.


That layout might be a tad long/narrow for my liking. I need to draw it up and scale it proper, get a good idea. Tweak the dimensions a bit for flow. But the main gist is just that it's heavily windowed on one side, and the side that I would want the most natural light.

I'm just doing some rough calculations and I think even a 11kW solar could meet the requirements of a footprint like that, provided the heat pump was running near max COP. Open loop would be ideal, but I guess you have to deal with what you have. Either way I think it'd be close enough wood could easily cover it. You'd have a hell of a surplus too in summer.

I'll need to make a spreadsheet of all the electrical loads, etc... and get a better estimate but I'm using my current energy usage + heat pump energy requirement to see what how many panels might be needed in for full winter use. Of course storage would be needed, but I think it could work. Net zero with the grid would be no issue.

[John H Swanson]

For the layout you posted, I scaled it and tweaked the design slightly

• I changed the dining room window (east wall) to a 36" wide door.
• The dining room south window was assumed to be 3 windows side by side 3' wide each and 4.5' high.
• Living room window was assumed to be 4' wide x 4.5 high
• Bedroom window was assumed to be 4' wide x 4.5' high
• Master bedroom window was same as dining room.
• Added one small window to the east wall in the kitchen 3' x 3'
• I'm guessing you might want sliders or french doors in the dining room or living room and I can adjust for them.
  
• I assumed walls are double 2x4 walls spaced 3.5 apart with 16" centers for framing and 1" rigid insulation under the siding.
• Windows with a U value of 0.3. Doors with a U value of 0.2. Its possible to do a little better for both.
• Ceiling I assumed to be R30 between the joists with another R30 laying over the top.
• Floor I assumed to be 2x8 joists with R19 between them. I added 1" rigid insulation on the bottom of the joists. I assumed the basement was outside air temp. If there is a insulated basement I'll change the rigid insulation to sheetrock.

Inside temperature was set to 67F
I used the design conditions of -20F and the heat required is 20300 btu/hr.
I also checked 20F and the heat required is 11200 btu/hr.

I don't have solar data for your latitide but I do have it for 41 degrees.
So I checked the solar gain for the south facing window area ~119 sqft
For a full sun day, in late December, through a double glazed glass window, there will be about 1300 btu/sqft x 119sqft = 154,700btu arriving (so to speak) between 8 and 4 each day. No cloud cover factor applied. your milage may vary.

[montcalm]

Wow - that's great.

20k btu/hr seems like a reasonable worst case for that sq. ft.

So if you figure out the solar gain, it's actually near neutral (if I'm interpreting your analysis correctly) during the day for a pretty cold day (-20F). 155k btu over 8 hours is an average power of 19,400 btu/hr. That's nearly what the house would lose at -20F per your analysis.

I need to understand that a bit better. If that's the case, the house would need some thermal mass to help regulate that or it'd be cooking itself on sunny days that aren't very cold.

[John H Swanson]

Wow - that's great.

20k btu/hr seems like a reasonable worst case for that sq. ft.

So if you figure out the solar gain, it's actually near neutral (if I'm interpreting your analysis correctly) during the day for a pretty cold day (-20F). 155k btu over 8 hours is an average power of 19,400 btu/hr. That's nearly what the house would lose at -20F per your analysis.

I need to understand that a bit better. If that's the case, the house would need some thermal mass to help regulate that or it'd be cooking itself on sunny days that aren't very cold.

Well, yes but....

The gain is for 41 degress latitide. At the design temperature (-20F) and a sunny day, the energy from solar covers the heat loss for that 8 hour period. You will need to heat for the other 16 hours. Obviously there is a noon peak. Coming off of the cold evening, the solar gain starts slowly. This is why I prefer to have a window or two on the east side of the house. If your house warms up on a not so cold day then it wont need more heat in the late afternoon. This is why I prefer east windows to west. But I'm also a morning person. Excessive heat from solar gain is easily controlled by shades. I did not add shades to minimize heat loss and control gain (in this analysis) but I would. It would be cool to have fancy motorized ones controlled by timer that is until I see the price tag.

With regards to thermal mass. There is some mass from furniture and sheetrock and that tends to buffer things out. Tile floor could be used to help this. I prefer shading to avoid overheating in summer and for the odd warm days in spring and fall.

Yes this is a conservative analysis because it essentially assumes the house is on stilts with the floor loosing heat to the outside temperature, so far. I'm now adding the more real world calculations to the model for a basement. The handbook has several pages for foundation losses. I could do either crawlsapce or basement but I'm going to do basement as I believe this is the desirable design.

The basement looses heat to the outside where the basement wall and insulation and soil retain the heat. The amount of insulation effect from the soil is dependant upon the depth. So you calculate the heat loss foot by foot for the height of the basement wall. I will build that calculation with some level of insulation and then go to the links others provided (thanks others) to plug in the commercially availible insulation values. I think I'll assume 12" of exposed foundation and 7 feet subterrainian. If I can I'll make this a flexible parameter. Come to think of it, sites usually have a slope where the grade is lower on one side of the house. So I'll try to make it so its a variable for each wall. Say 12" on the north side and 36" on the south side....and 24 for the east and west.

There is also the heat lost through the basement floor. I remember seeing a picture in one of the links someone posted that showed insulating under the basement floor. I'll see how it works without insulation. In my mind I prefer this approach as The floor of the basement then shares the termal mass of the earth.

One section of the handbook discusses unheated adjacent spaces such as an unheated basement or crawlspace. In this situation the unheated space has a temperature higher than outside due to heat from the house above. The norm we all know. There is a calculation method to estimate that temperature. One would think that if you insulate the house floor well (which I would do) than the basement will have less heat and get colder. Then there is the consideration of the heating system. If it is located in the basement then waste heat from inefficieny will be emmited into the basement. Many an old steam heat house has a basement that in 80-90 degrees.

Since we're considering a very cold climate I know we are smart enough to run all pipes on inside walls. It looks from the layout that this is what is done. One concern is the washing machine but that is easy to move from the position shown.

[montcalm]

Oh I realize the sun only works when it's light.

But I started to think about overglazed situations, and perhaps maybe the heat loss should be tailored to a more average day.


I posted the pic of the insulated slab. It's from Oak Ridge but 110% am I doing that if I use my slab as radiant storage. I don't want to sink my precious heat pump energy back into the earth.


I know you're looking at steady state now, but a lot of this is going be dynamic. It's not an easy problem. I'm going to have to try to sift through some of that heat pump data, climate data and try to get my best guess of how the system is going to run... well... here again I'm getting ahead of myself: for a poor solar site, it matters almost none. For a grid site, it matters very little. If it's full off-grid with good solar options, then it becomes more difficult.


I'm surely going to have to make my own models as well, or at least partials because I want to understand the "knee" in the curve for the thermal resistance. With wood being a necessity, at least as small backup, in almost every case I think of, I really need to weigh the cost of being over insulated (some may say that's not a thing, but I don't want a solar cooker where I have to open all the windows and switch the heat pump to cooling mode in March).

My real thought now, and I mentioned this briefly (maybe mooregm can chime in here) that for the cold, dark months I'd primarily like to use daylight for charging mass and rely on the woodstove (easier to tend and load while I'm there and awake) and use the stored thermal energy for overnight heating. I feel like this strategy will be useful whether on-grid or off in that overnight energy will be higher demand as we move into the future.

[montcalm]

An interesting article on solar gain vs loss based on US cities. Burlington would probably be the closest to dealing with the ADK climate.

https://www.greenbuildingadvisor.com/article/a-quantitative-look-at-solar-heat-gain

PS - It's not as thorough an analysis as John's, so don't get your hopes up

[John H Swanson]

Oh I realize the sun only works when it's light.

But I started to think about overglazed situations, and perhaps maybe the heat loss should be tailored to a more average day.

I really need to weigh the cost of being over insulated (some may say that's not a thing, but I don't want a solar cooker where I have to open all the windows and switch the heat pump to cooling mode in March).

Overheating is less of an issue with more insulation as it tends to buffer the heat/cool better than a not super insulated design. Many a hot adirondack summer has been handled by opening the windows at night and closing them in the morning.

In my opinion, window "right sizing" is the key. Part of this is knowing well how your going to use the space and installing the best height windows. Not to tall, not too high and not too low. I'd probably reduce the window area in the dining room and master by 20-30% I would not try to capture more solar gain to deal with the design day conditions. 99% of the time its warmer.

I think there is a thought proess that occurs with creating (or moving into) a new home where people will spend more for "nesting" vs. considering strict payback. I would not likely add more insulation to my house now knowing the lack of payback, but I would install much more than I now have on a new build.

The analysis method uses the design conditions for sizing the heating system.
Then there is a second set of data that is called "degree days" From the two, one can determine the seasonal heating requirement and estimate the cords of wood or kWhr required for a typical year. In this manner you get back to an average situation from the design day extreme conditions. You can also get average temeperature data to get a feel for how things will workout on a "typical day"

[montcalm]

I did a lot of work this morning using my own home (due its same sq. ft. as design goal) converting all my energy usage to kWh, and looking at solar data estimates for Old Forge - no idea if this will be my location, but when I consider initially using it as a seasonal home, continuous drive time is important - I hate driving and range may be a consideration with electric vehicles in the future. I've assume a 3hr range and it puts me in this area - climate should be similar in the areas I'm thinking are prospects.

Anyway, I was able to estimate a heat pump system usage based on this climate as well as my hot water and other misc. electrical loads. An 11kW system puts me pretty on net-zero, no wood considered. I need to do some comparison between average temps here and there (Rochester to Old Forge) and see how that will impact heat energy consumption, and how much insulation to get to my current system.

I think I'll continue to work out an off-grid design assuming good solar input as that's the most difficult. I can always scale back a bit to save cost if grid is an option, but really I think batteries are going to be a heavy hitter, and trying to figure out how much storage one really needs is not an easy problem. One can buy, currently, with Federal tax credits a 24kWh battery pack for $10k. With wood, that may be enough to get through cloudy days. I'm currently using the estimate of 2.7 hours of peak sun in November and December for that region.

By the time I actually build anything, or even consider adding a battery that big, things are going to be different. But it's a good challenge now to try to figure this out.


And as far as windows - my preference is for full light in my living and dining rooms, all the time. Only time I'd pull the shades is if the TV had a glare. Bedrooms could go either way depending on usage.



John - let me know the name of the reference you are using. I'm going to try to pick up a copy, even if it's somewhat archaic. I have my college heat transfer book but that's highly generalized mechanical engineering, and I haven't even picked it up yet.

[montcalm]

-- "Passive solar" requires sunlight to shine on thermal mass (e.g., concrete slab floors, masonry walls, large containers of water) so that most of the solar heat gain is stored in the thermal mass, to avoid overheating the interior air during the day. The thermal mass also will radiate stored heat when the sun isn't shining to keep interior temperatures from getting too cool.) So thermal mass dampens daily temperature swings from solar gains, keeping interiors within about a ten degree Fahrenheit range (5 degrees C), if designed reasonably well.

A comment from the author in the article I linked.


So my goal is not passive solar, but as I see it passive solar becomes part of your design if you put windows on the south, east or west side of your home whether you like it or not. It's just a matter of whether or not it's adding heat fast enough to build temps.

He claims in another comment that tile is not a considerable thermal mass for damping solar gain. I'd assume sheetrock is probably not going to be significant enough if the house is tight enough that it won't have some kind of temp spikes later in the day.

Again, I'll use my own home as an example of observation of this. I have east, south and west windows that stay unshaded during the day on my ground floor. I don't have any significant thermal mass. Plaster and sheetrock with hardwood floors. My thermostat is on a west facing wall in a western room. Late in the day, around 4 o'clock you can feel the temp drop in the house. I'm sure it started sooner but that's the lag from the heat not kicking in. There's enough thermal gain to trick my thermostat into thinking it's a few degrees warmer and not turning the heat on, as a result, the rest of house feels a few degrees colder. And my house is not well insulated - we're talking like R15-20 on the walls, R15-30 on the roof. In a well insulated house, that might be a significant temp spike.

[chairrock]

Is the home so airtight that it becomes stinky?
We have a high volume range hood, needless to say it blows cooking smoke out, but replacement cold or warm air must be considered... are you considering this? and bathroom exhaust fans? just asking...

[montcalm]

Is the home so airtight that it becomes stinky?
We have a high volume range hood, needless to say it blows cooking smoke out, but replacement cold or warm air must be considered... are you considering this? and bathroom exhaust fans? just asking...

I think all that's needed is a exhaust vent check valve.

Yes, I'd use exhaust fans in the kitchen, bathrooms and for the dryer. They aren't well insulated, but they prevent infiltration backflow.

I think at some point you could start to produce some vacuum and reduce the fan output but I *think* you'd pull air in from your attic space if you just had blown-in insulation and adequate venting. That stuff will block any fast ingress of air, but should not be completely sealed.

From what I'm looking at in terms of elevation plans and such, the sill plate, header joist and all those connections are to be sealed.

[montcalm]

Baselining everything against my current location. Maybe trivial, but it seems intuitive to me to use what (little) I know to figure out what I need.


Some interesting observations on climate data Rochester vs. Old Forge:

- Difference in highs for about every month are right around -6F average. I'd assume that's largely elevation effect.

- Diff. in lows is more variable, for 3 seasons: spring, summer, fall, it's right about -9F average. For winter, it's more like -14F (brrr).


Not sure exactly how I'll model this, maybe break up into 4 seasons using average dark and light hours and apply to high and lows.

What I'm aiming for is to see what needs are for insulation to get to get the same performance I have now (which is OK, not great) in terms of energy usage and then see what the cost is for incremental improvements. I'll start with my same shell model and then shift to other designs later. It seems there's minor differences there but I could definitely reduce glazing compared to this house.

We'll see how this matches up with the IECC requirements for these zones. I'm currently in zone 5 and looking at building in zone 6.


Also looking at solar data between the two locales. Not as significant as I thought though. It's about a 3% reduction in yearly peak sun hours from Rochester to OF.

[John H Swanson]

Is the home so airtight that it becomes stinky?
We have a high volume range hood, needless to say it blows cooking smoke out, but replacement cold or warm air must be considered... are you considering this? and bathroom exhaust fans? just asking...

When you reduce infiltration and reduce air changes from the typical 1/hr to 0.5/ hr or less then ventilation becomes important. The best appoach is to use an air to air heat exchanger. Ideally you want to vent from the bathroom and kitchen as usual. This recovers the inside heat with introduction of replacement air into the house.

Google residential air to air heat exchanger. There are many units. I've done little reseach, but I would go down this path.

[John H Swanson]

Not sure exactly how I'll model this, maybe break up into 4 seasons using average dark and light hours and apply to high and lows.

Also looking at solar data between the two locales. Not as significant as I thought though. It's about a 3% reduction in yearly peak sun hours from Rochester to OF.

I would do a monthly analysis. Get the daily solar gain for each month x the area of window. Compare this heat gain to the losses estimated by the average monthly temperature.

[montcalm]

I would do a monthly analysis. Get the daily dolar gain for each month x the area of window. Compare this heat gain to the losses estimated by the average monthly temperature.

I thought that might be overkill, but I have everything broken up by month already, so perhaps just let the spreadsheet do the heavy lifting.

I was trying to boil some of it down for here.

Interestingly enough, OF is sunnier on average in winter than it is here, which is a benefit. It then flips in the summer, but cooler temps on average also mean less AC load, so it seems a net beneficial improvement, although small in terms of solar.