Heat loss through skylight

[nicksanspam]

m Ransley errs again:

Nope. Average days.

Nick

[trader4]

[e-mail] Dec 28, 3:57 pm show options Do you have a list with the physical characteristics of every commercially-available skylight on earth to prove your claim? :-)

Now that's special. We're supposed to track down every skylight spec to prove the mythical one your rambling about doesn't exist? That's like me claiming a 3 headed bird species exists and then demanding anyone challenging the claim inventory every bird in the world to refute it. Is that how they think at Villanova?

BTW, the only claim I made was that it appears that skylights lose about 2X more energy than similar vertical windows. I provided a link to an independent site that appears credible to back up that claim. And I said that some of that delta is likely made up in winter by additional heat from the sun. However, the situation quickly reverses in the summer, last time I checked, so the sun is more likely an overall negative.

[Mark]

Nick

Interesting observation. I feel better about my south facing windows now.. (here in PA in the winter)

If you add in wind chill factor and radiation cooling losses and the fact that most skylights or windows are not aligned directly to the sun, they may end up being a net loss but not a hugh loss.

Nick, you appear to be the ultimate engineer and these other buys are more practical. Both points of view have value.

Mark

[nicksanspam]

m's claim...

That's what m would need to do to prove his claim :-) As an alternative, he might disprove it with a little 300-year old high-school physics.

Yes indeedy.

Try numbers, if you like.

As I've described over and over, unwanted summer gain is easily to avoid with an overhang which also enhances winter gain.

Nick

[nicksanspam]

They can more house heat on an isolated sunspace that gets cold at night.

Where I live near Phila, 1000 Btu/ft^2 of sun falls on a south wall on a 30 F average January day, so a square foot of R2 window with 80% solar transmission will gain 800 Btu and lose 24h(65-30)1ft^2/R2 = 420. On a sunspace, it might only lose 6h(65-30)1ft^2/R2 = 105.

Nick

[m Ransley]

Cut the bull shit nick, the missquotes and all, You say Net Gain. And now you recommend an overhang on peoples roofs to shade summer sun, one ugly house that would be. You are a hack, I would love to see your work, but there is none to see.

[nicksanspam]

Yup... 2000-year-old physics :-)

Nick

[nicksanspam]

Yup... 2000-year-old physics :-)

Well, maybe 2500 years old...

Nick

During the fifth century BC., the Greeks faced severe fuel shortages. Fortunately, an alternative source of energy was available - the sun. Archaeological evidence shows that a standard house plan evolved during the fifth century so that every house, whether rural or urban, could make maximum use of the sun's warm rays during winter. Those living in ancient Greece confirm what archaeologists have found. Aristotle noted, builders made sure to shelter the north side of the house to keep out the cold winter winds. And Socrates, who lived in a solar-heated house, observed, "In houses that look toward the south, the sun penetrates the portico in winter" which keeps the house heated in winter. The great playwright Aeschylus went so far as to assert that only primitives and barbarians "lacked knowledge of houses turned to face the winter sun, dwelling beneath the ground like swarming ants in sunless caves."

Cross section of a Roman heliocaminus. The term means "sun furnace." The Romans used the term to describe their south-facing rooms. They became much hotter in winter than similarly oriented Greek homes because the Romans covered their window spaces with mica or glass while the Greeks did not. Clear materials like mica or glass act as solar heat traps: they readily admit sunlight into a room but hold in the heat that accumulates inside. So the temperature inside a glazed window would rise well above what was possible in a Greek solar oriented home, making the heliocaminus truly a "sun furnace" when compared to its Greek counterpart.

Fuel consumption in ancient Rome was even more profligate than in Classical Greece. In architecture, the Romans remedied the problem in the same fashion as did the Greeks. Vitruvius, the preeminent Roman architectural writer of the 1st century BC., advised builders in the Italian peninsula, "Buildings should be thoroughly shut in rather than exposed toward the north, and the main portion should face the warmer south side." Varro, a contemporary of Vitruvius, verified that most houses of at least the Roman upper class followed Vitruvius' advice, stating, "What men of our day aim at is to have their winter rooms face the falling sun [southwest]." The Romans improved on Greek solar architecture by covering south-facing windows with clear materials such as mica or glass...

Settlers in New England considered the climate when they built their homes. They often chose "saltbox" houses that faced toward the winter sun and away from the cold winds of winter. These structures had two south-facing windowed stories in front where most of the rooms were placed and only one story at the rear of the building. The long roof sloped steeply down from the high front to the lower back side, providing protection from the winter winds. Many saltbox houses had a lattice overhang protruding from the south facade above the doors and windows. Deciduous vines growing over the overhang afford shade in summer but dropped their leaves in winter, allowing sunlight to pass through and penetrate the house...

George Fred Keck, a Chicago architect... began designing homes in the Chicago area according solar building principles - expansive south facing glass to trap the winter sun, long overhangs to shade the house in summer, minimal east-west exposure to prevent overheating in summer and fall, and the placement of secondary rooms, garages, and storage corridors on the north side to help insulate the living quarters from the cold north winds. Keck had a knack for publicity and called the houses he designed "solar homes." By the mid-forties Keck's work caught the attention of the national media. House Beautiful, Reader's Digest and Ladies Home Journal featured his work. Fuel rationing during the war inclined the American public toward valuing the energy saving features of solar homes. When war ended, the building market exploded. With the wartime-conservation ethic still imbued in most people's minds, many manufacturers in the prefabricated home industry adopted solar design features for leverage in this highly competitive market.

[m Ransley]

Overhangs on roofs added for skylights, an ugly thought.

[gosalves]

Here is an excerpt from an article:

"Skylights can provide significant passive heating during cold weather. This advantage is offset by conductive heat loss at night. In all but the coldest climates, there is a net heat gain if the skylights are located so that they collect the maximum amount of sunlight. On the other hand, skylights that face away from the sun may suffer a net heat loss even in relatively mild climates."

In the burbs of Chicago, there is hardly any sun in the winter months. It is beyond me to think that skylights will result in a net gain in such a situation. Besides, NONE of my skylights face south.

Golly! I never thought my original post would set so many brains ticking. All have been excellent posts and thanks to each and everyone who replied.

This is what I pose to you all now: Equations or not, logic or not, denial or not, common sense or not - wouldn't it be easier to find out about heat loss or gain through skylights by doing an infrared image / taking an infra-red picture?

Thoughts?

TIA

[gosalves]

The lines I quoted from an article above are from this link:

[dadiOH]

Thermometers are cheaper. If you want to be fancy, use a recording one.

-- dadiOH ____________________________

dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at

[Goedjn]

If you actually care, then the sensible thing to do would be to equip the damn skylights with insulated covers that you close at night, or which close themselves.

[Mark]

All Nick is saying is that a south facing window with an R factor of 2 or more, gains more BTU during thef day from the sun then it looses at night , i.e. there is a net heat gain over 24 hours.

Seems hard to beleive at first but when you look at the numbers it appears to be true.

I pointed out that he did not include radiation losses and wind chill, but I think these factors are small and do not change the overall result that much.

If you disagree with the conclusion, please find the flaw in the analysis.

Mark

[gosalves]

Can you please tell me what type of a thermometer I would use? Is there one specifically for this purpose?

TIA

dadiOH wrote:

[CBHVAC]

Did you figure in your envelope? Think you might find your T value to be higher.