Do I really need a solar collector to heat my home?

Do I really need a solar collector to heat my home, or can I get just as much heat by adding a south-facing window?
— Rowan Wilkinson Milwaukee, Wisconsin
Windows and solar hot-air collectors are about equal in collection capability. I think the choice boils down to which works best for your situation. To me, these are the pros and cons.
Window Pros:
• Collect heat and provide daylight.
• Views.
• Nice bright interior.
• With good thermal mass (material that absorbs and maintains heat) in the house, they can carry some heat into the evening.
Window Cons:
• High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades).
• Can be undesirable in some situations because of glare or loss of privacy.
• Can lead to overheating unless you have overhangs for summer and a house with adequate thermal mass to absorb the heat.
• To be effective, your south wall has to have a good view of the south sky.
• You need a floor plan in which it makes sense to have windows in the south wall.
• It’s harder to distribute the heat into the parts of the house where you want it.
That’s a fairly large list of cons, but solving these problems is what passive solar house design is all about. If you do it right, the windows both collect heat and make the house a bright and pleasant place to be. In a retrofit situation, you just have to be lucky that you can place the windows where you need them for passive solar.

Solar Hot-Air Collector Pros:
• More flexible in location — south roof, south wall, even detached from house — and easier to find a location with good sun.
• Can move the heat from the collector to where you want it more easily than with windows.
• It is possible to store heat for later use (at the cost of more complexity).
• No night heat loss problem.
Solar Hot-Air Collector Cons:
• You lose the daylight and the views.
• Often have controls and fans that must be maintained.
• Typically they don’t look as good as windows.
It’s not really an either/or situation — you can (and should) use both on the same house. You can even mix them on the same south wall. I did not include cost as a pro or con for either option, since it can vary so much depending on how you go about it.
http://www.motherearthnews.com/Ask-Our-Experts/Renewable-Energy/Solar-Collectors-Vs.aspx?utm_medium=email&utm_source=iPost

On Nov 29, 9:30�am, Eeyore wrote:

pautrey2 wrote: Window Cons:

I haven't installed a Morris Dovey type window solar collector because experience elsewhere suggests that an effective seal that withstands daily use would have to be framed and constructed like a door rather than a more fragile window. I've rebuilt all my doors and several of my windows with pressure-treated wood exposed to the weather and oak shims planed to thickness to fill the usual uneven gap between the frame and the structure, more for security than insulation. The doors have held up well and seal tight all around like a refrigerator, the windows have needed many repairs to the seals. The window hatch might work better if you can accept a thicker frame or a solid panel for better bracing. Thermal expansion is a significant problem, especially for parts not made of wood, which is very stable lengthwise.

pautrey2 wrote:

Window Cons:
High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades).

Can you get low-emissivity glass in the USA ? http://en.wikipedia.org/wiki/Low-emissivity
I believe it was originally a Pilkington UK patent. http://en.wikipedia.org/wiki/Pilkington http://www.pilkington.com/europe/uk+and+ireland/english/energikareconsumer/default.htm
Graham

Eeyore wrote:

pautrey2 wrote:
Window Cons:
High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades).

I've been experimenting with replacing my Victorian timber-panel interior shutters with double-skinned fibre-filled shutters as a cheap alternative to fitting double glazing. Using a simple DIY frame of 2"x1" timber clad in 6mm MDF, with glass-wool fill, over single glazing, I'm measuring a metric U-value (conductance) of about 1.1 as opposed to the latest, best and most expensive double glazing rated at 1.5.
I also get a perceived noise reduction at least comparable to and probably better than double glazing I have had fitted in other rooms at considerably greater cost.
Of course on the downside you can't get sunlight at the same time, and you have to get up and shut the shutters when it goes dark. But then I am at 54�N, so sunlight is at best brief in the season when we most need heating.
Tim Jackson

pautrey2 wrote:

Do I really need a solar collector to heat my home, or can I get just as much heat by adding a south-facing window?
— Rowan Wilkinson Milwaukee, Wisconsin

It's possible to "get" almost as much heat from a window as from a solar collector of the same size that faces the same direction, but when we talk about heating a home, we care about a lot more than how much energy is moved from the outdoor environment indoors - and we care a lot about the associated conduction and radiation losses.
My personal experience has been that when it comes to /keeping/ the heat gotten, a well-designed, well-built solar collector should do a very much better job than a high-quality window.

Windows and solar hot-air collectors are about equal in collection capability. I think the choice boils down to which works best for your situation. To me, these are the pros and cons.

A questionable over-generalization - at best this is true only for carefully selected pairings of windows and collectors. On the surface, the generalization /seems/ reasonable - but in practice, it doesn't hold up. If you lack experience with solar collectors, then examine the variation in thermal performance of just the windows.

Window Pros:
• Collect heat and provide daylight.
• Views.
• Nice bright interior.
• With good thermal mass (material that absorbs and maintains heat) in the house, they can carry some heat into the evening.

Sure, but notice that windows may lose more heat than they admit; and windows can't admit more light than falls on their glazing. That daylight may not always be very bright - but it's tough to beat a window for providing a view of the outdoors and preventing winter depression (otherwise known as "cabin fever" in the northern USA).
Although it may be an important consideration, the issue of thermal mass is completely separate from any consideration of how the heat is produced.

Window Cons:
• High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades).
• Can be undesirable in some situations because of glare or loss of privacy.
• Can lead to overheating unless you have overhangs for summer and a house with adequate thermal mass to absorb the heat.
• To be effective, your south wall has to have a good view of the south sky.
• You need a floor plan in which it makes sense to have windows in the south wall.
• It’s harder to distribute the heat into the parts of the house where you want it.

In general, I'd sum up all the listed cons as "poor architecture", rather than detractions inherent in windows.
Not mentioned in the list of cons, but important to note: There are good window products and lousy window products. I have a slightly different list that includes:
• Windows are inherently lossy. AFAICT the best that can be said is that the better window products are somewhat less lossy than the others.
• Solar gain is dependent on capture area. Adding a hundred or two hundred square feet of window area is generally so expensive and disruptive of floor plan that most people would consider the approach a non-starter.
Distribution of solar heat is definitely an important consideration, again, it's an issue that's completely independent of how the heat is produced.

That’s a fairly large list of cons, but solving these problems is what passive solar house design is all about. If you do it right, the windows both collect heat and make the house a bright and pleasant place to be. In a retrofit situation, you just have to be lucky that you can place the windows where you need them for passive solar.

Of course, passive solar house design is primarily applicable to _new_ house design and construction. Let's not forget that there may be a few folks out there who'd simply like to apply solar heating methods to existing structures...

Solar Hot-Air Collector Pros:
• More flexible in location — south roof, south wall, even detached from house — and easier to find a location with good sun.
• Can move the heat from the collector to where you want it more easily than with windows.
• It is possible to store heat for later use (at the cost of more complexity).
• No night heat loss problem.

Too much over-simplification here, and most of the assumptions made appear to apply only to active (powered) systems, and strongly resemble an effort to make direct substitution of active solar panels for conventional electric heaters. I have a strong personal preference for passive solar, and I'll try to remember to talk a little about that in a summary below.

Solar Hot-Air Collector Cons:
• You lose the daylight and the views.
• Often have controls and fans that must be maintained.
• Typically they don’t look as good as windows.

Daylight and a view of outside are certainly important for a number of reasons - not least of which is the well-being of people indoors. There doesn't appear to be a one-size-fits-all solution to this one.
Solar panel aesthetics is a very subjective issue - and it's very difficult to disguise a solar panel. If it's really efficient, it's at least going to /appear/ black, no matter what the color of the absorber might be. I don't expect a solar panel to look good as a window, but /do/ expect it to look good - as a solar panel. :)

It’s not really an either/or situation — you can (and should) use both on the same house. You can even mix them on the same south wall. I did not include cost as a pro or con for either option, since it can vary so much depending on how you go about it.

Complete agreement here.
Summarizing and extending some of my earlier comments...
IMO the space for rooftop panels should, in general, be reserved for solar DHW and PV panels, since we want them to function year-round. Solar heat, on the other hand, is only wanted during the cold season, and so a vertical (wall) panel orientation makes much more sense - especially in areas where there's normally snow covering the ground. Reflection of sunlight by clean snow can increase solar input by as much as 90%, nearly doubling 'bang-for-the-buck' with vertical heating panels.
Rooftop heat collection doesn't play well in a total system view - and it absolutely requires a maximum expenditure of electrical energy to pull/push the warm air down to where it's needed/wanted.
I like passive systems because they can work well and continue working with full function and efficiency even during electrical outages (and in off-grid locations).
Very high efficiencies can be attained, not only without blowers and control subsystems, but that deliver satisfactory amounts of heat even with cloudy and overcast conditions.
The lack of powered subsystems and moving parts means that maintenance requirements are reduced to the absolute minimum and that reliability is increased to the absolute maximum.
If you haven't already seen my photos, you can see a simple "real world" passive solar installation in central Iowa that keeps the indoors "shirtsleeve comfortable" round-the-clock all winter long, even when the outdoor temperature is below zero (Fahrenheit). Photos at:
http://www.iedu.com/DeSoto/SC_Madison/
Note that the structure is of completely conventional construction. :)
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/

Morris Dovey wrote:

pautrey2 wrote:
Do I really need a solar collector to heat my home, or can I get just as much heat by adding a south-facing window?
— Rowan Wilkinson Milwaukee, Wisconsin
It's possible to "get" almost as much heat from a window as from a solar collector of the same size that faces the same direction, but when we talk about heating a home, we care about a lot more than how much energy is moved from the outdoor environment indoors - and we care a lot about the associated conduction and radiation losses.
My personal experience has been that when it comes to /keeping/ the heat gotten, a well-designed, well-built solar collector should do a very much better job than a high-quality window.
Windows and solar hot-air collectors are about equal in collection capability. I think the choice boils down to which works best for your situation. To me, these are the pros and cons.
A questionable over-generalization - at best this is true only for carefully selected pairings of windows and collectors. On the surface, the generalization /seems/ reasonable - but in practice, it doesn't hold up. If you lack experience with solar collectors, then examine the variation in thermal performance of just the windows.
Window Pros:
• Collect heat and provide daylight.
• Views.
• Nice bright interior.
• With good thermal mass (material that absorbs and maintains heat) in the house, they can carry some heat into the evening.
Sure, but notice that windows may lose more heat than they admit; and windows can't admit more light than falls on their glazing. That daylight may not always be very bright - but it's tough to beat a window for providing a view of the outdoors and preventing winter depression (otherwise known as "cabin fever" in the northern USA).
Although it may be an important consideration, the issue of thermal mass is completely separate from any consideration of how the heat is produced.
Window Cons:
• High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades).
• Can be undesirable in some situations because of glare or loss of privacy.
• Can lead to overheating unless you have overhangs for summer and a house with adequate thermal mass to absorb the heat.
• To be effective, your south wall has to have a good view of the south sky.
• You need a floor plan in which it makes sense to have windows in the south wall.
• It’s harder to distribute the heat into the parts of the house where you want it.
In general, I'd sum up all the listed cons as "poor architecture", rather than detractions inherent in windows.
Not mentioned in the list of cons, but important to note: There are good window products and lousy window products. I have a slightly different list that includes:
• Windows are inherently lossy. AFAICT the best that can be said is that the better window products are somewhat less lossy than the others.
• Solar gain is dependent on capture area. Adding a hundred or two hundred square feet of window area is generally so expensive and disruptive of floor plan that most people would consider the approach a non-starter.
Distribution of solar heat is definitely an important consideration, again, it's an issue that's completely independent of how the heat is produced.
That’s a fairly large list of cons, but solving these problems is what passive solar house design is all about. If you do it right, the windows both collect heat and make the house a bright and pleasant place to be. In a retrofit situation, you just have to be lucky that you can place the windows where you need them for passive solar.
Of course, passive solar house design is primarily applicable to _new_ house design and construction. Let's not forget that there may be a few folks out there who'd simply like to apply solar heating methods to existing structures...
Solar Hot-Air Collector Pros:
• More flexible in location — south roof, south wall, even detached from house — and easier to find a location with good sun.
• Can move the heat from the collector to where you want it more easily than with windows.
• It is possible to store heat for later use (at the cost of more complexity).
• No night heat loss problem.
Too much over-simplification here, and most of the assumptions made appear to apply only to active (powered) systems, and strongly resemble an effort to make direct substitution of active solar panels for conventional electric heaters. I have a strong personal preference for passive solar, and I'll try to remember to talk a little about that in a summary below.
Solar Hot-Air Collector Cons:
• You lose the daylight and the views.
• Often have controls and fans that must be maintained.
• Typically they don’t look as good as windows.
Daylight and a view of outside are certainly important for a number of reasons - not least of which is the well-being of people indoors. There doesn't appear to be a one-size-fits-all solution to this one.
Solar panel aesthetics is a very subjective issue - and it's very difficult to disguise a solar panel. If it's really efficient, it's at least going to /appear/ black, no matter what the color of the absorber might be. I don't expect a solar panel to look good as a window, but /do/ expect it to look good - as a solar panel. :)
It’s not really an either/or situation — you can (and should) use both on the same house. You can even mix them on the same south wall. I did not include cost as a pro or con for either option, since it can vary so much depending on how you go about it.
Complete agreement here.
Summarizing and extending some of my earlier comments...
IMO the space for rooftop panels should, in general, be reserved for solar DHW and PV panels, since we want them to function year-round. Solar heat, on the other hand, is only wanted during the cold season, and so a vertical (wall) panel orientation makes much more sense - especially in areas where there's normally snow covering the ground. Reflection of sunlight by clean snow can increase solar input by as much as 90%, nearly doubling 'bang-for-the-buck' with vertical heating panels.
Rooftop heat collection doesn't play well in a total system view - and it absolutely requires a maximum expenditure of electrical energy to pull/push the warm air down to where it's needed/wanted.
I like passive systems because they can work well and continue working with full function and efficiency even during electrical outages (and in off-grid locations).
Very high efficiencies can be attained, not only without blowers and control subsystems, but that deliver satisfactory amounts of heat even with cloudy and overcast conditions.
The lack of powered subsystems and moving parts means that maintenance requirements are reduced to the absolute minimum and that reliability is increased to the absolute maximum.
If you haven't already seen my photos, you can see a simple "real world" passive solar installation in central Iowa that keeps the indoors "shirtsleeve comfortable" round-the-clock all winter long, even when the outdoor temperature is below zero (Fahrenheit). Photos at:
http://www.iedu.com/DeSoto/SC_Madison/
Note that the structure is of completely conventional construction. :)
Another pro is the dogs like to lay on the warm floor in the sun

puddles. I have a south facing back door, with storm door and it makes a big difference. I just open the solid door and the sun comes through the storm door and hits the floor (after it clears the neighbor's tree). Overhang works in the summer to block it. Nothing intentional but there is a lot of heat provided by just opening the door, letting the sunlight in, and closing the door when the sun goes away.

nick hull wrote:

In article , Tim Jackson wrote:
I've been experimenting with replacing my Victorian timber-panel interior shutters with double-skinned fibre-filled shutters as a cheap alternative to fitting double glazing. Using a simple DIY frame of 2"x1" timber clad in 6mm MDF, with glass-wool fill, over single glazing, I'm measuring a metric U-value (conductance) of about 1.1 as opposed to the latest, best and most expensive double glazing rated at 1.5.
I've been using thermal shutters at night for 25 years made from 1" thick styrofoam cut to a snug fit. Really keeps the heat in at night and my wife (who sits at her computer next to a picture window) comments that the room feels instantly warmer when she puts the shutter up at night.

I've a friend in the northern US who got me going on this. She sticks Velcro down the sides of her window frame and cuts pieces of quilt to fit for long cold winter nights and in unused rooms. (A 15-tog bed-quilt has a U-value of .67 - twice as good as double glazing.)
Tim

In article , Tim Jackson wrote:

I've been experimenting with replacing my Victorian timber-panel interior shutters with double-skinned fibre-filled shutters as a cheap alternative to fitting double glazing. Using a simple DIY frame of 2"x1" timber clad in 6mm MDF, with glass-wool fill, over single glazing, I'm measuring a metric U-value (conductance) of about 1.1 as opposed to the latest, best and most expensive double glazing rated at 1.5.

I've been using thermal shutters at night for 25 years made from 1" thick styrofoam cut to a snug fit. Really keeps the heat in at night and my wife (who sits at her computer next to a picture window) comments that the room feels instantly warmer when she puts the shutter up at night.
Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/ ** Posted from http://www.teranews.com **

On Nov 30, 9:01�am, nick hull wrote:

...
I've been using thermal shutters at night for 25 years made from 1" thick styrofoam cut to a snug fit. �...

In 1981 I made wood frames that fit loosely within the inside window trim, stained them to match it, covered both sides with clear polyester film and stuck on foam weatherstrip around the edges so they fit in like corks. An IR thermometer reads electrical tape stuck on them only slightly colder than the same tape on the walls. The patio door frames are similar but the lower half is styrofoam covered with thin paneling. The film is behind two layers of glass and hasn't noticeably yellowed.
They will pop loose in a hurricane, so I taped around the ones that stay in and made brass latches for the ones I remove in summer.
I think the film has some UV protection. Mylar film from an art store yellowed significantly in one summer in my single-glazed solar water heater, which reached 90C a few times. Vinyl window film might work. The frames are the only difficult or expensive custom part, you could experiment with coverings easily.
Jim Wilkins

Tim Jackson wrote:

Eeyore wrote: pautrey2 wrote:
Window Cons:
High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades).
I've been experimenting

Would you mind responding to the poster in question instead of just plonking your post any old where ?

Jim Wilkins wrote:

Eeyore wrote: pautrey2 wrote: Window Cons:
I haven't installed

Same goes for you. Respond to the original poster.
Do you not know how to use Usenet ? In your case, using bloody Google, it would seem not.
Graham

pautrey2 wrote:

Do I really need a solar collector to heat my home, or can I get just as much heat by adding a south-facing window?

Can you get low-emissivity glass in the USA ? http://en.wikipedia.org/wiki/Low-emissivity
I believe it was originally a Pilkington UK patent. http://en.wikipedia.org/wiki/Pilkington http://www.pilkington.com/europe/uk+and+ireland/english/energikareconsumer/default.htm
Graham

reposted due to morons not understanding threads in Usenet.

Eeyore wrote:

Tim Jackson wrote:
Eeyore wrote: pautrey2 wrote:
Window Cons:
High heat loss at night and on cloudy days (can be somewhat overcome with thermal shades). I've been experimenting
Would you mind responding to the poster in question instead of just plonking your post any old where ?

It wasn't any old where, it was specifically in response to your post in the thread, on minimising the negative aspects of windows.
How does this latest post of yours respond to the poster in question? Are you not just plonking your criticism any old where?

Tim

Morris Dovey wrote:

Leftie wrote: Morris Dovey wrote: Jim Wilkins wrote: On Dec 7, 9:25 am, Leftie wrote: ... It does. I've largely (but not completely) solved the problem by taping a piece of plastic wrap to the top of the exhaust port: the plastic is blown out away from the port when the fan runs, and settles back over it - imperfectly, and needing adjustment by us - when the panel shuts off.
Greenhouses use heat-activated vent openers that look like pneumatic door closers. They have more thrust available to operate a heavier door with better seals. You could control the fan with a microswitch on the door.
There's an even easier and more reliable way to get the job done without power, control system, moving parts, etc:
http://www.iedu.com/DeSoto/Astro/SC_Types.html
Take a look at the "Type 3" panel...
I'm not sure which type the Sunmate is, but I don't believe I can change it now that it's installed. ;-(
Probably difficult. I'll guess that your plastic film solution is the best that can be done if you can't get at the innards.
Do take time to contact Sunmate to let 'em know you're less than pleased with the panel behavior - perhaps you can help make things better for some future customer (who might be you <g>).

I've been waiting for really cold weather so I can make sure the thing works in frigid temps. It does. Overall it isn't a bad panel, but unless you have *full* southern exposure (6+ hours) it isn't worth the $2500 (installed, if you're lucky) price.

Jim Wilkins wrote:

On Dec 8, 12:04 pm, Morris Dovey wrote: Jim Wilkins wrote:...
I surprised myself when I tested the first panel I built this way - because I'd expected that once the front chamber filled with cooler air, it'd come spilling over the "shelf".
I just realized that your designs assume an outside air intake, thus the need for the siphon seal. I intended to completely enclose the outside and recirculate indoor air through the collector by gravity convection to preserve the indoor humidity level and keep out a neighbor's wood stove smoke.

Mine has an interior intake. It still thermosyphons.