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Jim

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Reply with quote  #1 
Hi all, Jim here, currently one of the newest guys on the forum. [wave]

I just signed up here and have been doing a lot of reading. All the different projects and ideas have really got my imagination swirling. I thought I had a solar system almost figured out and wanted to ask a few questions about it, but now my mind is going off in 10 different directions with new creative ideas.   [crazy]  [idea]

We are in northern Mexico at 6500 feet elevation in a 100 year old adobe house. The exterior walls are 20" thick and the interior walls are 15". So, lots of thermal mass. The floor is conventional wood framing over an inaccessible crawl space. 

My original plan was to put in a solar hot water system for DHW and also to supplement our home heating, (wood stove). Last month I bought several used flat panel water heating panels. This month, I got eight 55 gallon poly drums and a smart temp-sensing pump from Taco. My idea was to put in a multi-drum heat storage tank with a PEX coil HEX for DHW. Then circulate the storage tank water through a radiator or something to keep the house warm at night. 

But now, after reading about all your hot air heaters and how well they work, I am wondering if I would be better off to build an air heater and simply heat the air directly instead of fussing with all the water pipes and pumps and radiators. I could downsize and simplify the water heating system quite a bit by using it only for DHW. The walls of this house are an awesome thermal flywheel so I am hoping that by heating the air during the daytime, I could greatly reduce or eliminate my dependence on firewood during the winter. Maybe just light a fire in the morning to take the chill out of the air before the sun does its magic. Winter nighttime temps can drop down to 15 degrees F at night, although it nearly always warms up to the mid-50s during the day. 

Last winter the floors were the chilliest part of the house, so I am wondering if blowing heat into the crawl space might be our best option. It would require knocking holes into the foundation to get in, but it could be done. Maybe to keep it simple I could start out with something that blows into the windows on the south side. Or even a passive window box???? Maybe I could mount several heaters on the roof and feed it down through the ceilings? See the torturous decisions you guys are forcing me to make now? [confused] [tongue]

Anyway, here's a shot of the south wall of the house. I would be interested in your thoughts on the most cost-effective way to transfer solar energy into the house. I have nearly 60 feet of wall and a nice, sloped roof to play with. 3 bedrooms and a bath along that side of the house. 
 
IMG_20170520_091039763-EFFECTS.jpg 
 

So, my question is- am I better off putting in a big water storage tank and doing everything with a hydronic system or should I focus on pulling heat from an air heater to do what I need? The solar DHW system will be installed either way, but I would like to have your input on the best way to add some solar heat to the house.

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Jim in Chihuahua, Mexico

stmbtwle

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Reply with quote  #2 
Hi Jim... 

I think you may not be too far from GOM, who is in New Mexico and also (I think) has an adobe home.  You might track down his posts and maybe even contact him.

I like the thermal mass adavantages of water but it looks like you may have plenty of mass already.  My thought would be a long hot air collector along the south side of the house just below the windows.  You could blow in through the windows or through the wall.  The crawl space is interesting but you would probably have to cut through the wood floor to get into it, and I'll bet every room has it's own crawl space, as a 15" adobe wall would have to extend all the way down to the ground. 

For starters why not build a 4x8 collector and set it up to blow in (and out) through a window.  This won't cost much, won't damage the house, and will give you an idea of what can be accomplished with air.  If you like the results you can elaborate on it.

Another thought would be to paint the south side of the house a dark color, so the wall itself will absorb more heat from the sun.  In the summer I'd guess the sun is nearly overhead and the wall sees very little direct sunlight, so with any luck you won't have to shade it.



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Willie, Tampa Bay
gbwillson

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Reply with quote  #3 
Hi Jim-

Welcome! For simplicity and overall costs, solar air heating can't be beat. But there are tradeoffs as with any solar solution. Solar air heat, or SAH, uses large ducts. And in many cases, these large ducts must enter the home through a wall if a window isn't handy. But the removal of a few bricks, or cutting an opening in an exterior wall isn't hard to do. It's just the idea of putting a hole in the wall that is tough. If this solar heater is to be permanently installed, the openings will never show. But if the collector is installed seasonally like mine is, you will want to make sure to cap or block the hole so it looks nice. 

You don't describe the crawlspace, but I will assume it is open under most of, if not the entire house, and there is no insulation as well. And are there any vents in the basement? You should be able to do a nice job of warming the floor above. I did the very same thing in my home. Although it has a full unfinished basement, it's not heated. And by bringing lots of heated air into the basement, I effectively warm the floor above. This is so effective that on a sunny day, the furnace only turns on in the morning until the sun activates the solar heat. After that, the furnace normally stays off until the next morning, regardless of the outside temperature! The solar heat added to the basement warms up the floor above. And the stored heat in the flooring and sub flooring slowly gives back the heat to the house above over night. 

The added heat will raise the room temp on the main floor a few degrees. And since the furnace isn't blowing and moving air, the house seems more cozy. The only down side is several cloudy days in a row, whereas large water tanks storing heat would likely last several days of cloudy weather. 

70% of my gas bill is used for heating, and I would estimate that solar air heat saves me 75% on my heating bill. 


Greg in Minnesota[wave]
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Reply with quote  #4 
Another option might be a sunspace but you don't have an obvious access point unless you're willing to turn a bedroom window into a door.

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm

http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#LowMassSS

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Rick H Parker

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Reply with quote  #5 
"So, my question is- am I better off putting in a big water storage tank and doing everything with a hydronic system or should I focus on pulling heat from an air heater to do what I need?"

If you want storage, water is the way to go. Water has has ~3 - 4.5 times more Volumetric Heat Capacity then air, depending on the condition of the air. The Volumetric heat capacity of water is way more stable, changes in temperature and barometric pressure have a huge effect on air's ability to store heat. Changes in temperature and barometric pressure have a huge effect on air ability to store heat. Air is harder to contain then water.

Which is best for you depends on your local conditions. I recall being in valleys in New Mexico where in July, daytime highs of 100F overnight lows 15F.  What are your summer highs and lows like?

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
Jim

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Reply with quote  #6 
Thank you all for your thoughts. I had never seriously considered air until I started reading here what others have done. 

Willie, I like your idea of long horizontal collectors under the windows. I was measuring today and I can center a 16' collector under both the center and east bedroom windows. There is room for a 20 footer under the west bedroom window. Actually, if I hinge them at the the top and slant the bottom out away from the wall, I could do three 20 footers. I have a septic pipe and vent coming out of the wall that I need to work around. We do not own the house, although the owner has told us we can do whatever we want to the house as if it were our own. So I would rather not cut holes into the wall just yet. 

I would like to have a system that blows into the windows. Maybe fit a piece of foam with holes for the ducts to fasten to. Then at night when the sun goes down, we could slide the window shut and keep out the cold night air. With one of the sliders open, I have a 22" x 26" opening to bring in my ducts. Could I terminate both of them at the window or is it important that the intake draws from close to the floor? My thought is that the output air would rise to the ceiling quickly and the intake would be just fine drawing from 36" above the floor.?? 


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Jim in Chihuahua, Mexico
Jim

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Reply with quote  #7 
Greg, I really like the idea of heating the crawlspace. Our first house that we bought in Kentucky right after my wife and I got married had a basement with a wood stove. That was the nicest-feeling heat we have ever had. However, I don't think it would work as well with this house for the reason Willie mentioned. These adobe walls go all the way to the ground. Each room has its own crawl space with no access from the outside or other rooms. Also, there are no vents anywhere. Humidity levels are in the teens and single digits nearly every day since we've arrived here, so I guess the builders did not expect any moisture down there. 

SolarInterested, both the sunspace and the dark paint would be great choices for saturating those thick walls with heat and releasing it into the house slowly at night. But we don't own the house and we're living here for an undefined amount of time, so I would like to stick with a system that leaves a minimal impact on the house and can be easily moved to a different house should we choose to do that.

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Jim in Chihuahua, Mexico
Jim

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Reply with quote  #8 
Rick, at the moment I am leaning toward air heat since I have many tons of thermal mass in the walls. We moved into this house in December and we had the wood stove going wide open for nearly a week until the walls warmed up. After that we only needed a load of wood in the morning and at times one in the evening to keep the house comfortable. I am hoping an air heater will do a lot of that work next winter, though I realize I won't have the radiant heat of a wood stove. The floor might be even more chilly. ?  [frown] We have occasional clouds, but I haven't seen a day yet that didn't have at least 50% sunshine. So I am hoping I won't really need the longer-term storage capacity of water. 

One of the bedrooms had a rotted-out wood floor when we got here, so we tore out all the wood, filled with sand and gravel, and put in PEX loops for future floor heat. Ready to pour concrete now but haven't gotten it done yet. All hand mixing, no ready-mix plants anywhere close! We might continue doing a room every year or so until we have radiant heat in all the floors. But that will be a number of years yet and the air heat seems like a simple and easy way to get solar heat into the house meanwhile. I am thinking if I keep everything modular, I can add poly barrel thermal storage and used flat plate collectors from Craigslist as I need the water heating capacity. And if I build the air collectors modular also, I should be able to easily move them to a different house or shop whenever I want to. 

I don't know yet what the summers are like here. We're at 6500 ft elevation in the transition area between the Chihuahua Desert and the Sierra Madre mountains. At the moment we have highs of 85 but temps drop rapidly at sundown to around 50. I really love this high desert weather! 

Some more questions - what is a reasonable amount of heat to expect from a 16' or 20' ZP collector? Would it be reasonable to expect 3 of them to completely replace a wood stove, assuming almost endless sunshine all winter long? 

Would you recommend attaching the collectors to the house, maybe hinged so you have adjustable tilt? I think it would be quite doable to anchor them to the adobe with a 6" or 8" GRK screw. Or should I build them as freestanding units on a triangular leg base and anchor them with sandbags or rebar anchors? 

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Jim in Chihuahua, Mexico
stmbtwle

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Reply with quote  #9 
I believe fastening it to the wall would be easiest and most efficient.

Are you going to need this collector in the summer? My guess not, but if so you might need to angle it somewhat, or make it adjustable.

What about your attic? That's the biggest solar collector you have and it's already built. Is there any way you can pull heat from there? Does it get warm enough in the winter to be useful?

One of the possible issues with air heat is that in order to store heat for the night you may need to overheat the space during the day. You might be able to put a couple ducts against the wall under the window, disguised as a cabinet. You could bring the heat in through the window, and down through a couple holes in the wood floor to the crawlspace. Each room would need its own system though, and it doesn't address the north side of the house. It is something to think about.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #10 
"Some more questions - what is a reasonable amount of heat to expect from a 16' or 20' ZP collector? Would it be reasonable to expect 3 of them to completely replace a wood stove, assuming almost endless sunshine all winter long?"

For the State of Chihuahua the daily average daily solar radiation ranges from 3.85 kW-hr/m²/day in the winter to 8.75 3.85 kW-hr/m²/day in the summer the yearly average is 6.25 kW-hr/m²/day. Take them figures and multiply them by efficiency of the solar panels to get a reasonable expectation of harvest.  I cannot tell you what kind of efficiency to expect from a Zero Pass, one of the other might be able to.

"At the moment we have highs of 85 but temps drop rapidly at sundown to around 50. I really love this high desert weather!"

What I am was looking for is nightly Catabatic winds, cold air dropping of the mountains as hot air rises from the ground at night.

"Would you recommend attaching the collectors to the house, maybe hinged so you have adjustable tilt? I think it would be quite doable to anchor them to the adobe with a 6" or 8" GRK screw. Or should I build them as freestanding units on a triangular leg base and anchor them with sandbags or rebar anchors?"

Here is a classic 40 year old design. It classic because it does not require alternations to the house and easily removable. Doable by renters and people that won't commit to a structure change at this time. Mother Earth Heat Grabber.



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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
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