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Passive Solar Heating/Cooling

02/19/2016 1:24 PM

Suppose you are given the following: A home with a south facing wall glazed with the lowest heat loss windows money can buy. At a distance from the windows (floor to ceiling) chosen by you, a passive solar absorbing wall is placed (mortared stone) of arbitrary thickness. On the outside of this south-facing wall (the house is in the northern hemisphere at 30 ° latitude and -101 longitude for this example), the roof line extends arbitrarily outward as another variable. For argument's sake, the house is at elevation of 3300 ft (1006 m), and yearly average outside temperature is 72 °F (22.2 °C), with extremes of 20 °F (-6.7 °C) and 105 °F (40.6 °C). No input is given with respect to how many extreme days there are, but there is a substantial daily variation, due to the arid climate.

You design for the following: (1) Maximum heat transfer into the home from the solar absorbing wall in the winter months, and maximum rejection of insolation during summer. (2) Reduce auxiliary heating and cooling to a minimum. Auxiliary cooling and heating is done by heat pump, and the unit is electrically powered. Additional heat inputs as required include: (a) wood fireplace with insert/stove with forced draft heat exchanger, (b) natural gas-fired furnace on central HVAC unit.

The house is 3000 sq. ft. living area on a single floor. There is no basement. All exterior walls are insulated (to your specification), as well as the attic. The house rests upon a concrete slab, engineered to withstand local stresses, and to support the mass of the passive solar wall. The total heated/cooled mass of the house is X, the air volume of the house is Y with 1-100% air exchange per day (with 90% heat recovery/rejection), and the north, east, and west sides of the house are shielded from high winds.

What will be the average power requirement if daily temperature swing averages 30 °F in the summer and 20 °F in the winter, and the seasonal shift is ± 20 °F relative to the given average temperature for this location? The load estimate will not include other household activities, lighting, electronics, cooking, etc. at this time.

This is a discussion, not a question, so feel free to answer the questions any way you choose. There is no particular "right" answer, but feel free to support your declarations any way you choose.

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Guru

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#1

Re: Passive Solar heating/cooling

02/19/2016 1:34 PM

I got bored...could you simplify into one sentence question?

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#3
In reply to #1

Re: Passive Solar heating/cooling

02/19/2016 1:52 PM

OK - is there any way to change the parameters so that auxiliary heating is kept below a $100/month budget, and the same for auxiliary cooling?

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#5
In reply to #3

Re: Passive Solar heating/cooling

02/19/2016 2:41 PM

The secret to small energy use is efficiency....In this case maxing out the insulation and heat loss/gain is a primary concern....secondary is producing a portion of your own energy...this can be anything from a few pv panels to an on-site hydro-generation facility or wind powered turbine generator , hydro-thermal, nuclear(for the advanced tech)....or any combination of these and/or other sources of energy....using natural gas for cooking and drying clothes when necessary, hot water, and heat, is a low cost strategy...

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#6
In reply to #5

Re: Passive Solar heating/cooling

02/19/2016 2:58 PM
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#17
In reply to #3

Re: Passive Solar heating/cooling

02/21/2016 8:51 PM

Relocate?

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#2

Re: Passive Solar heating/cooling

02/19/2016 1:39 PM

I'm thinking you will spend more capital than the energy will be worth over several generations. Active thermal solar is a lot more flexible than trying to engineer a largely passive solution.

I believe incorporating passive elements in the overall design is a good move, I just think it can be very difficult to make it a major part of the energy design. Insulation, radiant barriers, and thermal mass can definitely improve comfort levels by limiting the slew rate of temperatures.

I'm lazy too. I tend to look at what other people have done in similar situations and learn from them, i.e. drive around and gawk at other people's houses. When you introduce yourself to them, you will find that they can be very candid about their experiences, both good and bad.

P.S. As for roof lines, you may also want to consider the possibility of retractable "awnings" of some sort to handle the seasonal changes.

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#4
In reply to #2

Re: Passive Solar heating/cooling

02/19/2016 1:54 PM

It is all good. Good suggestions.

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#8
In reply to #2

Re: Passive Solar heating/cooling

02/19/2016 3:27 PM

Check out the panels from post #7, then let's re-formulate: Suppose you use those panels for heat collection, that is straightforward enough, and they are apparently most effective.

Is there a way to utilize a similar panel (maybe with an inverted flow pattern) to cool an interior space by utilizing an exchange with cooler air induced from below ground (air induced from an outside plenum through an underground duct that exchanges heat, then have a second heat exchange with interior air, and exhaust the spent air, while retaining the now cooled interior air)? I think I will give myself a headache if I stay on this one.

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#7

Re: Passive Solar heating/cooling

02/19/2016 3:06 PM

I also found this web page: This guy knows his passive solar to the nth power.

http://www.iedu.com/Solar/Panels/

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#13
In reply to #7

Re: Passive Solar heating/cooling

02/19/2016 6:17 PM

There's someone who's put a LOT of thought into this sort of thing.

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#9

Re: Passive Solar heating/cooling

02/19/2016 4:38 PM

Comstock TX looks pretty desolate from the air.

If you have any property with an east/west running hill, I'd excavate into the side of it and have three sides earth sheltered with a large cistern under the house to use as a passive radiator for heat/cooling control.

In any case an earth sheltered house is the way to go.

I have a site like this east of Hot Springs AR where I MAY do just that someday.

It sits above a 3 acre lake with plenty of shade trees and an already cleared 3 acre front yard.

I've not done any power studies since it is still 5 years away.

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#12
In reply to #9

Re: Passive Solar heating/cooling

02/19/2016 6:15 PM

When you do that, I'd love to see the results if you'd allow some creep from an anonymous engineering forum on your property.

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#14
In reply to #12

Re: Passive Solar heating/cooling

02/19/2016 7:12 PM

You are welcome to visit. We can sit down by the lake and fish in the afternoon.This is the view from the top of the hill looking down toward the lake which is behind the trees.

The lake, built in 1965, turns to the left and follows the natural lay of the land. The dam is out of sight around the corner. This picture was taken in 2009 during an extreme dry spell.

A bit of trivial history about this piece of land. It has been in the family for some time. After my father died, I was cleaning out some of the items in a cabinet and came across a deed to this property. The deed was signed by U. S. Grant, or at least it has his signature on it. The land has since come to be mine.

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#19
In reply to #14

Re: Passive Solar heating/cooling

02/22/2016 10:00 AM

Nice looking piece of ground! Any diamonds?

Good luck with your build, when you decide and take steps.

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#20
In reply to #19

Re: Passive Solar heating/cooling

02/22/2016 11:39 AM

Thanks. I have 40 acres there. About half is cleared, and most of the cleared land is used to grow hay. The "hay guy" cuts the grass and bales it and hauls it away for me.

That leaves me with about 5 acres, which my brother does for me. The rest is mostly Pine and Oak mixed.

It may be awhile. I'd probably want to sell one of our two current homes to finance it.

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#21
In reply to #14

Re: Passive Solar heating/cooling

02/22/2016 1:10 PM

Very nice. I'm jealous, but I'll bring some beer. What's your pleasure?

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#22
In reply to #21

Re: Passive Solar heating/cooling

02/22/2016 2:08 PM

Cold and in a bottle.

Thanks.

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#16
In reply to #9

Re: Passive Solar heating/cooling

02/20/2016 9:03 AM

Agreed...there is a good reason that animals make burrows!

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#10

Re: Passive Solar heating/cooling

02/19/2016 5:36 PM

Have windows on the south side (northern hemisphere) and a roof overhang far enough that in the winter the low sun can hit the windows but in the summer they are shaded.

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#11

Re: Passive Solar heating/cooling

02/19/2016 6:09 PM

Interesting "discussion", enough work here for an engineering class term project!

As far as passive home designs with a vertical heat absorbing/storage system, there is a body of knowledge on their design and construction using a Trombe Wall. I also found the link you provided very interesting, but of course that collector design competes with the glazed wall approach.

Before any serious design can be started, it's necessary for you to provide some more data. Is the house of traditional design except for the solar aspect? What are the LxWxH dimensions; Roof design, flat, pitched, angle, symmetry; provision for Domestic Hot Water (DHW), number of bathrooms, number of occupants; water supply, well, city water, cistern.

Then there's the ambient conditions near Devi's River State Natural Area in Texas. What are the ambient conditions, things like; vegetation, soil type, is the site flat, on a mesa, are there natural windbreaks like hills, cliffs, etc.; 5 year average and daily/hourly data on insolation, temperature, cloud cover, wind speed/direction; clear view of the sky, obstructions, any deviation off of north-south roof-line, local ponds/lakes?

There's probably more than 20 questions already, but you get the idea. Granted there's a whole host of assumptions that can be made, and some of the data is second or third order in importance; so if you would provide a more defined design base you'll get better answers (and we haven't even discussed a budget yet!).

Until then, it looks like if your house is in a desert, 75x40 ft aligned long side due south, with the southern wall fully glazed, some solar thermal panels (for DHW) mixed in with skylights on a pitched roof; then you probably won't incur much heating expense. If the ambient conditions support it, you may be able to design in some passive cooling features to substantially lower your cooling costs, and solar PV might justify off-grid operation if the nearest utility pole is miles away.

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#18
In reply to #11

Re: Passive Solar heating/cooling

02/22/2016 9:36 AM

Right now, this is a purely hypothetical project, mostly composed of brain flatulence. Sorry if that part was misleading. I am just thinking about what to do when I win the lottery .

If I could retire right now, I would like to find a place near Gail, TX, not too far south of here, with an overlook off the Llano Estacado at the escarpment. I would probably nestle the whole thing into the side of the cliff by clever excavations, saving the limestone rock layer from the escarpment for part of the construction. I would put the shop/garage at grade level, probably northwest of the house. Only one area of the house would have a second floor, and the north facing windows of this floor would allow one to see out in that direction. One would also not want to block views of the sunrises and sunsets at such a location, as this would one of the main attractions.

Basically, this is one area that is owned by ranchers who have had the land for generations, so getting even a small parcel of this may not be all that likely. Another option might be east of Lubbock, out by Crosbyton, as long as the site was not some sort of dinosaur dig, as I think they still have active digs over there.

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#15

Re: Passive Solar heating/cooling

02/20/2016 4:39 AM

As a variation to the Trombe Wall add lower and upper opening slots to the outside of the building. Label all the slots; IL(inside lower), IU, OL, OU. Draw a truth table for every combination of open and closed slots and the heating consequences of each option. Using convection from the heated Trombe Wall as the passive driver you can get heating, cooling and forced ventilation. I looked at this some time ago but I don't have a plot to implement it and my wife now considers me too old to start building a new house.

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