Where to begin? How about this?

[Rumplestiltskin]

I am a total noob so I want to start small and run a few tests. I sketched out a very small system and I wanted to run it by some people (here) who undoubtedly, know 1000% more than I.

The system would consist of the following:
- DIY solar air heater about 4' x 3' with maybe 2.5" of airgap between the front glass and the inside insulation. The simplest design has a series of back-&-forth channels which takes in air from a hole in the rear bottom and pushes it out a hole in the rear top. (The performance seems similar to the ones with internal metal channels so KISS.) YouTube videos show the exhaust air reaching 140-150f so that should be plenty. Not a lot of CFM possible here. Off the cuff calcs indicate less than 2.5 cubic feet of air contained in the heater at any given moment. So let's assume that a small 5V computer fan pushes the air at 4.5CFM. What could I possibly heat from this? Certainly nothing at night when I'd really need the heat.

But what about crafting an insulated enclosure with a 55-gal drum of water (with some anti-bacterial agent) inside and looping the exhaust heat of the solar heater into that enclosure and then back into the heater air intake? Presumably I'd get 7 hours of nearly-140f air circulating around that drum. At the appropriate time in the PM, the solar heater fan is turned off (as it's producing colder air than the drum's water) and another fan circulates air from the enclosure into the house and then back into the enclosure where (presumably) the house's cooler air is warmed by passing around the drum and back into the house. The "inside" and "outside" systems get switched (manually at first but by thermostatic control once I know if this works). (There's a workshop attached to the house where the drum/enclosure would reside and, coincidentally, the outside wall of the workshop faces south so the solar heating system could be kept compact. Likewise, the drum/enclosure and the area of the house where the heat would be needed at night (main bathroom/bedroom) share a common wall to the workshop.

So someone please tell me if I blowing smoke up my own USB port or if this has a decent chance of succeeding. Thanks very much for your patience.

 

[MichaelK]

I'm not quite sure what the goal here is? It's for heating a room, correct?

In reality, I think it would be a far more efficient idea to allow the sun to warm the area directly, then closing off the windows at night with heavy curtains to contain the solar heat. Solar electricity is only about 20% efficient, and generating heat from solar power is just about the most wasteful way to use solar power that I can think of.

A far simpler way to do this via solar is simply to connect a heating element immersed in water, and allow the heating element to heat the water, and by radiation, heat the room. But, as I mention above, using the sun directly for heating is going to get you ~5X more more BTUs.

I think a water tank, painted black and in full sunlight, is going to collect more heat then the same area of solar panels.

 

[sunshine_eggo]

Fun with numberz:

12 sq-ft is 1.1 sq-m

1.1 sq-m receives 1100W of power in perfect conditions assuming perfect conversion of sun to usable heat.

1100W power would take 8.5 hours to heat 55gal of water from 70°F to 140°F assuming PERFECT heat transfer

That's 9350Wh of energy.

Same energy provided by 1.33 hours of running a two ton heat pump. Again, this assumes that you get perfect sun for 8.5 hours throughout the day (you won't), you get perfect heat transfer (you won't).

That should be enough for you to determine if you can produce enough BTU to provide useful heating (not likely).

 

[Delmar]

I assume you are asking about direct solar thermal, and not solar photovoltaic.

Photovoltaic cells make heat while producing power, and operate more efficient when cool. Would make an interesting experiment to use a solar panel behind glass with clear water circulating between.

The water would thermosiphon up, assisted by a small 12V pump powered by the solar panel. A thermostatic control would stop the pump when heat is not generated, and the water would drain out of the panel to prevent freezing.

The excess power is stored in a battery, the excess heat is stored in a drum, and both are available at night. Should be able to extract more usable energy with the same panel area.

Example:https://dualsun.com/en/product/hybrid-panel-spring/

 

[Rumplestiltskin]

I'm not quite sure what the goal here is? It's for heating a room, correct?

In reality, I think it would be a far more efficient idea to allow the sun to warm the area directly, then closing off the windows at night with heavy curtains to contain the solar heat. Solar electricity is only about 20% efficient, and generating heat from solar power is just about the most wasteful way to use solar power that I can think of.

A far simpler way to do this via solar is simply to connect a heating element immersed in water, and allow the heating element to heat the water, and by radiation, heat the room. But, as I mention above, using the sun directly for heating is going to get you ~5X more more BTUs.

I think a water tank, painted black and in full sunlight, is going to collect more heat then the same area of solar panels.

Firstly, thank you for giving this some attention.

Unfortunately, my house has very little usable south facing exposure as there's a carport that runs the length of the house on the south side; think manufactured home. There's that south facing wall (without a window) of the workshop that actually is without an appreciable roof overhang; that's where I would mount a solar panel (hot air or PV).

Not a heck of a lot of insulation in this house (built in 1980). Not really practical to add insulation to roof or walls. Thankfully, the weather is mostly nice here in Spring and Fall and, as I mentioned in my OP, once the day warms up a bit (even in November/December) and there's decent sunlight, I don't need much heat supplement until evening.

In the summer, the house gets really hot but I believe that's due to the lack of roof vents in the two "attic" areas (which I will rectify in January along with some extra soffit vents). I don't see anything "solar" in the way of cooling although when it comes time to re-roof, I'll choose the "whitest" shingles I can get.

I remember an article in Rodale's New Shelter magazine in '81/'82 (which tells you how old I am) that detailed the construction of a solar water heater using just the tank from a water heater and some aluminum shaped into two involute curves that would reflect the maximum amount of sunlight toward the tank throughout the day. (I actually have a PDF of the scanned pages, IIRC). Such an apparatus would be enclosed in a wooden box with a glass top so it would heat up the water. I suppose I could pump that water into radiators inside my house through some well-insulated PEX. I have plenty of room in my back yard (east side of the house but with unobstructed southern exposure for the entire day) for such a water heater. The water lines could be buried fairly easily and come up under the house (in the crawl space) where a couple of holes for the PEX could be drilled and a small pump could circulate the hot water.

But that was then and this is now. Maybe a PV panel powering a couple of PTC heaters could heat up a tank of water just as well (and then the tank could be placed (insulated) into that workshop where it's isolated from the outside cold and any plumbing would be easier to craft. Simpler is better and as the cost of a PV panel or three would be close to the total cost of the solar water heater described in the previous paragraph (plus the radiator $ required in either case). While I understand the inefficiencies, I also don't want to make the perfect be the enemy of the good.

Electricity to heat our primary bedroom during the night with a space heater runs about $2.75/night which is pretty cheap. During the coldest month, it might be $3.50. (We wear PJs and have warm bedcovers. ?) I've been turning down our furnace to 60f during the night but I can hear it come on often. Propane is about $3.75/gallon. I don't have a consumption meter but the gas company told me the previous owners spent about $2000 on propane for the year; we bought in June. I don't know how much propane is used "per minute" when the furnace is running; maybe there's an calculator somewhere? I could get the furnace spec when I get back up to Sedona in January. (Right now, I have the furnace set for 52f and I can see, based upon the daily electric consumption (which APS provides to me in its app), the furnace (fan, of course) doesn't seem to come on during daylight hours. (We're not in Sedona right now.)

If my Propane usage is minimal (compared to the previous owners who I believe were wastrels), then the expense and effort to craft and connect a solar water heater might be more than it's worth. However, if I could keep the rest of the house besides the bedroom warm in the cold months, it would be more convenient.

I hadn't mentioned water heating (for showers, etc.) up to this point. My intent is to add a small tankless electric water heater to the primary bathroom (which is at the other end of the house from the water heater) and it takes over a minute to get hot water to the shower. (Yes, we save that water in a bucket for watering plants the next morning. We're trying. :D )

Thanks,
Barry

 

[MisterSandals]

Not a heck of a lot of insulation in this house (built in 1980). Not really practical to add insulation to roof or walls.

I thought the general consensus was conservation (insulation and efficient devices) was far more cost effective than producing energy?

Blown in wall/ceiling insulation has made me a believer.

 

[Rumplestiltskin]

I thought the general consensus was conservation (insulation and efficient devices) was far more cost effective than producing energy?

Blown in wall/ceiling insulation has made me a believer.

True in most cases. However, an older manufactured home started with less insulation. The majority of the roof has no attic; just the rafters and some batting/vapor barrier between the inside ceiling panels and the roof decking; no practical method to add insulation unless I do a drop ceiling (down from the sloped cathedral-style) and add some extra batting there. But the change in the look would be unacceptable to us.

Likewise, changing the wall insulation would require ripping down all the paneling, removing what's there, foaming in some insulation and dry-walling, painting, etc. All-in-all, just way too expensive for this sort of home.

As for the more efficient devices, I'm with you on that. But a heat-pump is also quite costly (for now). A tankless water heater for our main bathroom isn't expensive (2.5 gal/min would be plenty). One more for the other end of the house to handle the second bathroom and the kitchen (same capacity or a tad bigger). Then I could jettison the propane water heater. (Electric is cheaper than propane for this purpose if my calcs are correct.)

If the large water tank (in my previous post) could keep the temp in the main area of the house (areas other than the bedrooms) up to 62 or so overnight, that is good enough for my needs; on those extremely rare c-o-l-d nights I can fire up the propane furnace.

Okay; I'm an optimist. :D

 

[Nobodybusiness]

I thought the general consensus was conservation (insulation and efficient devices) was far more cost effective than producing energy?

Blown in wall/ceiling insulation has made me a believer.

Me also.
When my house was built in 2003 they used dense pack blown in.
Running my FLIR around showed considerable settling and just flat out missed areas.
The windows showed Seals being inadequate also.

I re-insulated my house and added 18 inches of blown in Attic, Changed out old TRANE 10 seer Heat pump and it save me 20% in electric consumption so far.

My next change will be from a standard water heater to a Rheem Heat pump one.
That one has had to wait because the current one is in a closet downstairs and that’s not a good place for the heat pump WH.

Not to mention the temperature doesn’t fluctuate very fast either.

IMHO always better to conserve first before over producing.

 

[Mattb4]

You will not gather much usable heat from a 12sqft area.

If you have not done so I would recommend buying 1 inch dense foam board (R-6 insulation value) and use it to cover up windows. Although it gives a cave like feel to my place I find it really reduces the need for heating on those frigid nights.During fair weather I just store them in a out building. You can cut them with a utility knife and I find that aluminum metal duct tape works well for combining pieces so wastage is minimized.

They also make foam plates that go behind outlet and switch covers on exterior walls that can help a small amount. Double check and seal against any cracks. Doors can be another point of heat loss since they often are poorly insulated or fitted.

 

[Rumplestiltskin]

You will not gather much usable heat from a 12sqft area.

If you have not done so I would recommend buying 1 inch dense foam board (R-6 insulation value) and use it to cover up windows. Although it gives a cave like feel to my place I find it really reduces the need for heating on those frigid nights.During fair weather I just store them in a out building. You can cut them with a utility knife and I find that aluminum metal duct tape works well for combining pieces so wastage is minimized.

They also make foam plates that go behind outlet and switch covers on exterior walls that can help a small amount. Double check and seal against any cracks. Doors can be another point of heat loss since they often are poorly insulated or fitted.

We've put in a few cellular blinds which do a nice job cutting heat loss with some of the windows and may simply be pushed up during the daylight hours. Outlet and switch cover foam plates are done. I used a plastic "V" weatherstripping on the doors (which I remember using on my first house 40 years ago!) and it works perfectly.

While the foam board would surely provide even more insulation on the windows, I'd have to make sure the side facing outdoors had something that actually looked like a "window treatment" (blinds, shades) as the HOA forbids anything that looks like cobbled-together insulation or similar. More importantly, my wife would hate it.

One of the house sections has sliding windows (older double-pane aluminum) all along the two outside walls (north and west). I used a sort of shrinkable plastic film around the window held on with double-faced tape. You use a hair dryer to get it taut. Again, this is one of those solutions I used in my first house and it does work well. I do, however, close off that room at night and close its heating vents so it drops to about 55 when the house thermostat is set to 62. I could not use any foam boards on these windows as the community manager would be all over me like a cheap suit.

Bottom line: I've done about as much insulation and isolation as I can do given the HOA and the physical makeup of the structure (but will get those roof vents installed for the summer heat). A small solar heating project to offset the worst of the cold nights (like a tank of water that's been heated during daylight) might be all I need. Probably could empty it and remove it from the house during the 8 months when it's warm here.

I'll experiment with this over the winter as I'm retired and have plenty of time. I'll report back. Thanks for everyone's interest and suggestions!

 

[Mattb4]

Sounds like you can only do so much between the demands of the HOA and wife. Be aware that window treatments like plastic wraps, blinds and even most curtains provide little benefit in terms of insulation. Windows are a hole to the outside and even the best low E ones have terrible R values (so much so they give a U value instead).

Probably would be a market for window foam board inserts if they printed some design on the outside instead of the standard foil. You could likely get past the HOA with using Christmas wrap to face outwards but the wife would be another story.

Solar power whether passive or from panels is neat but the limits of 1000w per sq meter (at noon in the Summer) and the efficiencies of utilization of that (panels max out at about 23% presently) is not something you can get around.

 

[McKravitts]

It’s doubtful that you’ll achieve 140f with that kind of configuration.

I have a 40 ft^2 solar to direct water panel and the best I’ve achieved to date is 120f.

The heat loss in direct solar systems increased exponentially with temperature from increased conductive, convective and especially IR radiative losses.

I agree with MichaelK, if you want to get solar to heat your home just let the sunshine in and concentrate your efforts on keeping it in with insulation, weather stripping, low loss glass etc.