Solar heat collector for the shop.

This is an idea that had been in the back of my head for a while. It's more of a save a little money and can I build it project then a save the planet project, but saving the planet is a nice bonus.

Dr Boost built something similar several years ago that was intriguing. This will be my take on it. Naturally, the design was stolen from the internet. Here to be exact. DIY solar heater.

This will also be my first attempt at a build video. It will take a week or two to get it edited and completed. Expect some pitiful videography of a fat guy bumbling around his shop, sometime in the future.

We are starting with a piece of insulated glass, that was left over from job I did several months ago. It's non coated, meaning no tint or low E coating, and uses two pieces of 1/4 glass with a 1/2 air gap. It will be strong enough to withstand some abuse and hail.

Add to it a few treated 2x4s, some ducting and screen wire.

I built a 2x4 frame the same size as the glass, attached a piece of luan as a back and insulated it with some 1/2 foam board.

I threw some black paint on it.

Then I built a couple of frames and covered them with black fiberglass screen. The screen is the absorber. It absorbs radiant energy from the sun and transfers it to the air. This design is supposedly more efficient than the soda can design.

There are two ducts through the back of the collector. One is cold air entering the front, between the glass and absorber. The other will be hot air from behind the absorber.

This image is the absorber installed on the frame. The black metal is a baffle to keep the cold incoming air from blowing on the glass, and to encourage it to disburse through the frame.

Next up was the blower. I have a stack of 4.5" fans. All the ducting that is available is 4" or 6". I bought a 6" to 4" reducer, planning to cut it apart and adapt one of the fans to the system. It turns out, if you square off a 6" duct, a 4.5" fan fits it perfectly.

Then a couple of temporary legs, and set the glass. It's ready for testing. Unfortunately the sun was down by the time I was done. Testing will have to happen another day.

More to come.

Following this because these things fascinate me. Is it cold enough there to justify a heater in the garage, or did you just need another project?

In reply to ProDarwin:

It was 59 inside the house when I woke up this morning. Outside was 28.

I've got a heat pump in the shop, but I don't like to run it all day when I'm not home. I'm hoping the solar heater will keep the temps up during the day so the shop will be comfortable when I get home in the afternoons.

Following with much interest. Mine is still working great.
If I can make a recommendation, put some sort of filter at the intake. My screen has been collecting dust right at the intake. Not a lot, but it can build up

We looked into a passive solar heater for the ex's garage some years ago. Being an HVAC engineer, she loved the idea. Until she ran the calculations for her garage and determined the largest heater we could fit on the south-facing wall simply couldn't provide enough of a Delta-T to be effective for the extended Winter temps we get here in the northeast. And this was using commercial vacuum-sealed collectors rather than DIY versions.

In a perfect world, a more efficient option would be to use solar-water collectors and circulating the heated water (using a solar charged, 12V pump) through radiant floor tubing. Of course, that is a tad difficult to add to an existing structure...

Speaking of 12V, that was one thing the solar air system we looked into also used: a 12V fan powered from a solar-charged battery.

Ian F wrote: In a perfect world, a more efficient option would be to use solar-water collectors and circulating the heated water (using a solar charged, 12V pump) through radiant floor tubing. Of course, that is a tad difficult to add to an existing structure...

Efficient, yes. But recently I've been reading that solar hot water is essentially dead. Its easier/cheaper to just use PV panels and connect them directly to a few heaters.

In reply to ProDarwin:

True. PV wasn't as cheap back when she did these calculations, so it was never even considered. Were I building a new shop, I'd still go with hydronic radiant floor heating, but use PV to power a water heater. The nice thing is once you get that slab of concrete warm, it doesn't take as much energy to keep it warm.

In reply to Ian F:

I'm not necessarily looking to heat the place with solar. What I would like this to do is add some heat to the building during the day, so when I get home in the afternoon, the heat pump doesn't have as much of a hole to climb out of. Even two or three degrees will be acceptable.

That, and I like building stuff. That in itself makes it worthwhile.

In reply to Toyman01:

Well, that is the advantage of living in SC. Let's face it - how often do you really need heat for extended periods of time? Up here in the frigid north, a shop heater would get turned on sometime around Thanksgiving and not get shut off again until April. I well remember trying to work on projects in the dead of winter. It wasn't pleasant.

These work really well. Mine is intentionally inefficient, the inside panel is not solid material pinted black. Lots if solar energy pass through it. Even still, i get almost 200 F air coming out of it!

I made it home just in time to set it up for a little while.

For now I'll call it a success.

Inlet temperature, 45 degrees.

Outlet temperature with the fan running, 101 degrees.

With the fan off, it would still flow some, the outlet temperature crossed 120 and didn't act like it was going to stop soon.

Considering the lateness, I'm pretty happy with that.

I need to get a better thermometer and retake these measurements just to verify them. These were quick and dirty with a infrared thermometer.

Edit, these temperatures were taken after being set up for about 20 minutes. They may come up some as the unit heat soaks.

Sweet! Now scout goodwill and habitat for humanity restores for door-walls. They are great starters for these projects.

You'll get better air flow if you use a wider duct connection. Something like this: Find one that's as wide as possible.

What's the end game? Three or four of these ducted together? Will these be mounted to the exterior wall? Might just want a slot opening at the bottom to take the cool air off the floor then find an old furnace and collect the top duct work and supply it to the space.

In reply to RossD:

I'm guessing there is a fine line between too much flow and not enough. Lots of air, lot temperature rise. That's why the temperatures climbed when I disconnected the fan.

In the long run, I'm leaning toward roof mounting it. The roof on my shop faces south and is in full sun from 9am till 5 pm. For now it's probably going to be mounted next to a window in the south wall. I'll temporarily run the ducting through the window. That way I can decide if drilling holes in the roof are worthwhile.

Throw a cheap cone air filter on the inlet to keep the dust and schmutz out. Looks like a good design to me!

Seems like you would need some sort of anti-reversion setup to prevent it from flowing cold air when not in sunshine.

Bruce

Toyman01 wrote: In reply to RossD: I'm guessing there is a fine line between too much flow and not enough. Lots of air, lot temperature rise. That's why the temperatures climbed when I disconnected the fan.

I doubt it. The temps rose, but the flow reduced so heat flux was still reduced. Sure, at some point it will plateau, but you really can't have so much flow that it will reduce heat transfer. Only penalty is noise and wasted energy on the fan (which is converted to heat anyway).

Great results though. What was your exterior temp?

Any idea what the airflow is - so you could estimate wattage?

In reply to ProDarwin:

Exterior temps were 45. The fan is rated at 200 CFM, so flow is somewhat less than that. Call it 150. So that gives me a 55 degree rise. I have a couple of other fans I may try that are rated at higher CFM.

Near as I can tell, the collector is putting out 2750 watts.

That's assuming this is the right formula. C.F.M. x temperature rise (°F)/3

Would this be any more effective than a well-placed window?

In reply to Keith Tanner:

That's a good question. My problem with windows is, the two that are in the shop now, have shelves and stuff piled in front of them. Wall space is way too valuable.

I have seen some green homes, where the south wall is basically glass, with a interior wall that was stone. Awnings shade them in the summer, but during the winter, sun warms the stone which in turn is a thermal mass to keep things warm all night. I have some thoughts in that direction for my retirement home.

Toyman01 wrote: Near as I can tell, the collector is putting out 2750 watts. That's assuming this is the right formula. C.F.M. x temperature rise (°F)/3

How big is it? Solar insolation at sea level is a maximum of approx 1000 watts per square meter.

It would be nearly impossible for it to heat more than a well-placed window (of equivalent size). The question is will it lose less heat?

I'm considering something like that for my next home as well. It amazing what a little optimization can do for a house's heating costs.

I'd be interested in knowing. Windows aren't an option for my garage - subterranean doesn't lend itself to windows, and you're totally right about the wall space factor - but I do wonder if it's more or less effective. I've got proper heat and I'm underground, so it's just curiosity on my part.

Definitely a fun build, this would be a great science fair build to show the power of solar energy.

In reply to ProDarwin:

It's 25 X 69.5

In reply to Keith Tanner:

You can't imagine how sad I was when all my kids got past science fair age. We had a lot of fun with those.

I still build them, I just show them to you guys instead.