Solar room heaters

[lighthawk]

Yeah but the heat that is blowing out of the unit is heat that was already in the house. It is concentrated all in one place instead of dispersed throughout the room, but it is not any *more* heat total.

Pat

Not so, my friend. It certainly is more heat. If it weren't, where did the 130 degree air come from?

While there was no fan to disperse the heat more efficiently, there was air flow through the unit. The ambient air in the kitchen was about 65 degrees going into the unit, and double that coming out of the unit. It wasn't much, but it definitely added heat to the room that wasn't there before.

If this had been a heater using electricity to heat the air, how would it have been any different?

The last time I had full sun I put a thermometer directly against the window pane above my passive heater (actualy it isn't passive anymore as I added a solar powered fan) the temperature against the window pane was 94 degrees.
I then held the thermometer in front of the fan and the air temp coming out of the heater was 108 degrees. Ambient temperature in my dining room was 72 in the morning with out the heaters in direct sunlight, With the heaters (I have three) and direct sun the ambient temp was climbing at the rate of 1 degree an hour. I do have white walls in that room and before I installed the heaters I had never seen that much temperature variation in that room even with full sun.
I have to agree with koxxx that the addition of the heater utilized the radiant heat from the window much more efficently than without it.

 

[patandchickens]

Not so, my friend. It certainly is more heat. If it weren't, where did the 130 degree air come from?

From heat that wasn't going directly into the room because the room was "shaded" by the collector.

Where are you imagine this "extra" heat you're getting is COMING from?

There are X number of photons hitting your window, right? They hit things inside your house (air molecules, rug molecules, table molecules, every ol' thing) and make those recipient molecules wiggle more. That is what "heating things up" means -- to transfer energy to the contents of the room.

The only energy input available is what's carried by the fixed number of photons coming in the window. And even if you have no solar collector or nuthin', the great majority of them will hit SOMEthing in the room and be absorbed by it. (Exception being, an extremely all-white or all-mirrored room that reflects a significant amount of light back out of the building -- but even in this case, modern windows tend to have low-e films that reduce *heat* wavelength transmission out of the house so the loss is not as much as with old plain-glass panes)

The reason it may SEEM to you like you're getting more heat is because it is all concentrated in one place (the outlet of your collector) and thus you have a small volume of air being directly-heated a lot, as opposed to a large volume of air (and rug, and table, and so forth) being directly-heated just a little. But then of course the hot air coming out of the collector, its heat is transferred ultimately to all the stuff in the room (air, furniture, walls, floor, etc) so it all turns out the same in the end.

The only real difference, which I suppose may make a difference in a few situations such as a seldom-used room, is that using a collector heats JUST the air, whereas leaving the sunny window "plain" (no collector blocking it) distributes the heating effect between air and all the solid objects in the room that the sunlight falls on. The collector may therefore warm the air up faster, if it is just short-term changes in air temperature you care about. Whereas the plain sunny window is putting more heat into the thermal mass of the room to linger as the sun moves around and goes down.

If this had been a heater using electricity to heat the air, how would it have been any different?

Because an electric heater puts energy into the room that wasn't already coming in. Whereas a sunny window has that energy coming in no matter what, either way, collector or not.

Pat

 

[k0xxx]

You are correct. Almost. The difference is that the solar heater used a black surface and thermal mass. Let the sun shine onto your floor, wall, or whatever is normally within your kitchen and then read the temperature off of it.

Then take a piece of metal with some decent thermal mass, paint it black and place it in your window. The metal will absorb more energy, instead of reflecting it back out of the window. To get close to the same added warmth in a room, you could certainly paint everything black.

Sure, all you really need to do is place this dark mass in the room, and not build it into a heater to get the same heat. Our heater was just a "proof of concept" test, that was intended to be replaced by one outside.

 

[Dirk Chesterfield]

This may sound crazy but it works and is cheap. I like cheap.

I made black sheer full coverage curtains for the three window sets that face south and west and keep them hanging during the time of year a heater is required. It captures lots of heat that would otherwise be reflected back out the window by the walls and curtains. With the black sheers, those two rooms, kitchen and living room, are distinctly warmer on sunny days. I would estimate 5 degrees warmer than the rest of the house on a sunny winter day. The difference is very noticeable. It works similar to the rigid black box heaters folks put on the inside of windows.

The house gets no sun until 10AM that's why I didn't put them on the east side too. I bought the fabric on sale at Walmart for $1 a yard. It's a fairly tight weave mesh somewhere around 35 to 40% thread to openings. It still lets in plenty of light so it's not dark in those rooms. I do keep the "original" curtains on the inside for esthetics. From the outside the windows do look totally black and no one can look inside at all.

All my walls are white and reflect much of the sun right back out the windows. It is especially true in the kitchen where all the cabinets are white too. All my curtains were white also and this exacerbated the reflection issues.

I plan on doing the same thing with tight weave white fabric in the summer to reflect the sunlight. It's brutally hot here in NC.

 

[Denim Deb]

That's a good idea. I don't know if it's as hot here in NJ, but it still gets quite hot and we have a picture window that faces south.

 

[Marianne]

This may sound crazy but it works and is cheap. I like cheap.

I made black sheer full coverage curtains for the three window sets that face south and west and keep them hanging during the time of year a heater is required. It captures lots of heat that would otherwise be reflected back out the window by the walls and curtains. With the black sheers, those two rooms, kitchen and living room, are distinctly warmer on sunny days. I would estimate 5 degrees warmer than the rest of the house on a sunny winter day. The difference is very noticeable. It works similar to the rigid black box heaters folks put on the inside of windows.

I like cheap, too. But this surprises me. I had never seriously considered heat loss due to reflection. Last summer I stapled black landscape fabric over the top 3/4 of our south shop windows and it was cooler than what it ever has been before. But that would be more like shade cloth.

I have seen solar curtains for sale, but they had metal strands or threads in the weave. I tried hanging black metal window screen in front of the top half of two windows, and it did nothing. Later I wondered if it was because I didn't have it longer than the window so there would be cooler air at the bottom. Assuming, of course, that the screen would warm up and the natural convection would create the 'wash'.

While I understand the science of what Pat is saying, we also made a quick passive solar unit, hung it on the inside of a room that only has one south facing window and after a while that room was much warmer than the other rooms. Warmer than the room that has three south facing windows.

 

[rubyluise]

Solar room heater is very good resource for getting energy from sun by absorbing medium and used as a heat air. it keeps you always warm without using electric energy. I think this would be the best idea to save more money. Here we mostly have cool atmosphere so for us It will be really good equipment to using thoroughly. You can get many option related to solar heat energy and also apply DIY technology.