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Final verdict on homemade GRID TIE inverters?

Mr RB

Well-Known Member
#61
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AND try to find some cost effective coating that will work on asphault shingles.
...
We painted the top of our sunny side awning with a roller and cheap white gloss acrylic paint. It's waterproof (when dry!) and extremely reflective, and a few years later has held up very well.

Acrylic can be difficult to use on some absorbent surfaces because it just soaks in instead of coating so you need a primer. Our awning was fibreglass so it coated perfectly. It would be easy enough to test on one shingle to see if will work. The difference in heating between a gloss white roof and and a black asphalt roof would be enormous.
 

tcmtech

Banned
Most Helpful Member
#62
Around here steel panel roofing is around 50 cents a square foot or less and very easy to install. I have done a number of roofs and getting the old shingles off is far more physical work than putting the new steel panels on.
 
#63
Around here steel panel roofing is around 50 cents a square foot or less and very easy to install. I have done a number of roofs and getting the old shingles off is far more physical work than putting the new steel panels on.
I have seen roofers actually lay down small boards on top of the shingles and nail them down then screw the metal to them. Which is basically how they roof a barn but don't have the shingles underneath.
 
#64
1500 sq ft house.
80F delta temp between attic and inside.
R-20 insulation.

80F / 20R == 40BTUs * 1500sq ft == 6000 BTUs of heat leaking into the house from the attic.
 
Thread starter #65
We painted the top of our sunny side awning with a roller and cheap white gloss acrylic paint. It's waterproof (when dry!) and extremely reflective, and a few years later has held up very well.

Acrylic can be difficult to use on some absorbent surfaces because it just soaks in instead of coating so you need a primer. Our awning was fibreglass so it coated perfectly. It would be easy enough to test on one shingle to see if will work. The difference in heating between a gloss white roof and and a black asphalt roof would be enormous.
Not a bad choice! AND it could also actually be "sprayed" very effectively!

SIDENOTE on Acrylic paint:
I recently got tired of watching my wife try to clean the grout of our dining room tiles. She would MOP them with little effect, then get angry and try to clean them with a toothbrush. After seeing her frustration (and working for a couple hours on my own) I got fed up and decided to take some FLAT Acrylic (water based exterior approved for masonry!) TAN and paint the groutlines. EVERYBODY I talked to (including my TILESETTER buddy) considered me crazy. It'll never work they said. They said stuff like "off the deep end" and a "dumb idea" ;)

We did the entire room in 2 evenings, and consumed LESS than a pint to do it. It SEALED the grout, it matches the tile colors BETTER than the groud did...and the entire ROOM looks new! It's a VERY thin coat ("wiped into the grout, with no "excess paint" to chip or peel) so it will NEVER peel or chip (and it's down beneath the tile level anyway!). So, for $12 worth of acrylic paint, we SEALED our tile grout, and made the dining room look like a new (and better colored) TILE job. A VERY sucessful "creative problem solving".
So, I am a believer in Exterior Acrylic (water based so no "fumes"), especially the kind approved for masonry or fiberglass!
 
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Thread starter #66
Around here steel panel roofing is around 50 cents a square foot or less and very easy to install. I have done a number of roofs and getting the old shingles off is far more physical work than putting the new steel panels on.
Wow, I didn't realize that they were that inexpensive! I will look into this further. THAT WOULD be the way to go, if possible. I'm NOT afraid of the work...I've got pneumatic tools and etc.

If I had the extra funds, I would also see about laying down some reflective poly sheet insulation before the new steel roof went on...(and actually having a "cool attic!!!) :)

1500 sq ft house.
80F delta temp between attic and inside.
R-20 insulation.

80F / 20R == 40BTUs * 1500sq ft == 6000 BTUs of heat leaking into the house from the attic.
YUP! and a small correction:
40btu x 1500sqft = 60,000btu's, AND in my circumstance 40btu x 2320 = 92800btu...

PLUS the 800sgft of 2car garage/seperate laundry room that both get A/C part of the time (and share the same hot attic above, and one interior wall/laundry room)...so another 32000btu on top of that (if the 40btu formula is correct)...for a total of 124800btu of possible ceiling surface area exchange.

And remember, heat WILL flow from HOT to COLD areas, so COLD Air Conditioned interiors will "draw" heat infiltration, to a certain extent...especially with an 80+deg delta at times!!!
 
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tcmtech

Banned
Most Helpful Member
#67
The steel panels are incredibly easy to work with! All you need is a good cordless drill and and the right sheet metal screws, a jig saw or some basic sheet metal cutting snips, a chalk line, and tape measure. As a DIY job around here your roof would cost around $1500 in steel materials being it is a basic rectangular design. If you calculate your angles and steel panel layouts and cuts properly you should have very little waist of materials over all. ;)

Every home building supply center carries all of the materials, tools, and additional ridge and edge pieces as well and will have books or some form of instructions to show you how to do everything properly as well. :)
With two or three people you will take more time ripping off the old shingles and prepping the roof than you will putting the new steel on. Three people should be able to take the old shingles off and prepare the roof in a good long day or two. And maybe a fair day to put the new one one depending on your skills and detail work.

Shingle removal works rather well if you use a thin flat shovel and a good stout pitch fork or garden fork to peal the old stuff off.
Expect a few cuts and blisters though, its rather dirty and rough work cleaning the roof up to start with! :eek:
 
#68
Blown in Cellulose has a minimum R Value of 3 per inch, so if you have at least 18 inches then you have an R value of 3*18=R54 which has a U value of .02
U=1/R

So to calculate Heat gain you take SQft*Delta T*U Value=BTU
Delta T=170Attic-70Inside Temp=100
so 2320*100*.02=4640BTU


or if you do it the way you did it earlier

Delta T/RValue = BTU
BTU*SQft then you get
100/54=1.9
1.9*2320 = 4408 Pretty close to the same answer.
 
#69
1500 sq ft house.
80F delta temp between attic and inside.
R-20 insulation.

80F / 20R == 40BTUs * 1500sq ft == 6000 BTUs of heat leaking into the house from the attic.
Would help if I knew how to divide. 80F / 20R = 4BTUs. After seeing your 60,000 BTUs, arizonaguide, I knew something had to be wrong. :)
 
Thread starter #70
...after serious "REFLECTION" (multiple puns intended!)

Would help if I knew how to divide. 80F / 20R = 4BTUs. After seeing your 60,000 BTUs, arizonaguide, I knew something had to be wrong. :)
LMAO!!! I wondered about it...but after getting up into my attic last July, and hitting that BLAST of 170degF HEAT...it FELT like 60,000btu's wasn't outta the question!!! :)

It would be interesting to figure the actual BTU's of SOLAR GAIN that are cooking back outta those (300deg? +/-) asphault shingles.
You cannot touch them with bare hands without serious burns...and I watched a buddy crack an egg on the asphault of the street here...and it fried in about 2 minutes.

Kinda along the same topic, I was trying to figure out a solution to my 19' travel trailer (up at the lake here) to MINIMIZE it's A/C usage...and I kinda came up with a similar solution...REFLECTIVE/VENTILATION (ambient air gap).

A lot of people set up a full 4-legged awning to provide SHADE for their travel trailers...but my reflective "second roof" should do the same thing (and more durable/wind resistant). I Will not travel down the road with it (of course)...but as a more "windproof" solution than an awning while it's parked at the lake for the summer...(see below):

The trailer roof itself also has insulation (minimal), but with the direct sun "cooking on the roof" (just like at home) it was hard for the A/C to keep up! Now the actual trailer roof is "in the shade", and exposed to only ambient temps. The reflective urethane insulation sheet reflects (and yes "absorbs") the solar gain (and yes...eventually "saturates" to whatever temp the solar GAIN will end up heating it to). But, IT absorbs the solar gain...rather than the trailer roof itself. The ventilated "air gap" seperates it from the actual trailer roof with ambient air.

For people with similar travel trailers in COLD weather, you could just eliminate the "air gap"...or seal it at the edges and keep a sealed airspace.
(you would still want to have spaces cut out so you can still use your roof vents, etc).
 
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#71
Blown in Cellulose has a minimum R Value of 3 per inch, so if you have at least 18 inches then you have an R value of 3*18=R54 which has a U value of .02
U=1/R

So to calculate Heat gain you take SQft*Delta T*U Value=BTU
Delta T=170Attic-70Inside Temp=100
so 2320*100*.02=4640BTU


or if you do it the way you did it earlier

Delta T/RValue = BTU
BTU*SQft then you get
100/54=1.9
1.9*2320 = 4408 Pretty close to the same answer.
So if you can get the attic temperature down to around 110 then you would only be gaining around 2320*40*.02=1856 btu/hr with an inside temp of 70*F

So your AC would have to remove 2552 less BTU's every hour.
 
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Oznog

Active Member
#72
We basically agree. Problem is, I just blew in an additional 8" on top of the 12" that was there already...and can't afford more.
AND, with close to 20" already, I'm not sure that's the problem.

I believe that the problem NOW is that the eve vents being blocked do NOT allow the attic (and related insulation) to stay cool to normal (ambient) temperatures. I believe that the insulation mass RETAINS a little more heat each day...eventually becoming a (almost?) "heat saturated" thermal MASS itself...that the AC can't keep up with.

YES, this is just my educated guess. (based on temp readings over a few days in JULY!)

So, now it's VENTILATION time. AND try to find some cost effective coating that will work on asphault shingles.
Well, 20" of insulation is a LOT... absurdly a lot. You're losing heat somewhere else... or your AC is not performing up to spec.
I'm still saying this "heat saturation" is way off. For one, the insulation is a progressive barrier against the heat. Two, you get an equal benefit in the morning as it heats up but the thermal mass of the attic is still cool from the night. In fact, high thermal mass is generally quite helpful! That's why it's cooler to have an underground shelter which averages night and day temps over the long run.

Yeah, if your soffit vents are clogged, by ALL MEANS clear them! This is a major ventilation problem. And that's not only about heat- it can allow condensation which accelerates roof aging dramatically.

Just do the ridge and soffit vents. They'll do about all the ventilation that can be done. And at that point the temp of the shingles won't matter all that much since the hot air's being exhausted. The coating, something that'll last like 10, 20 yrs of weathering and not start peeling and look awful and take off bits of shingle rocks as they peel off is a huge problem. And again it's not going to save much, if anything. It'll likely make a damaged roof that'll require major work in 5 years. Now if you're MAKING a new roof because the old one's leaking all over, sure, by all means- go light colored shingles or metal. Metal's great. Lasts a long time too! Properly installed as per mfg specs, because there's so much that can go wrong with anything "odd" about a roof.

The attic should not be that hot, even in Az. If it's not ventilated, ventilate it with accepted, proven effective methods. The painting and "creative" plans will turn out badly. Remember, a new roof costs thousands of dollars. Your gains will not be hundreds and hundreds per month here. Even when you do spend hundreds on AC per month, the gains are only marginal. I mean, saving $25 off that bill for 5 months out of the year is $125/yr. What if the paint costs $400 and in 5 yrs it's peeling and the roof's damaged and like $7000 to replace the roof? Or just replacing a good-condition roof with light-colored shingles is not going to realize enough gain over the next 20 yrs of roof life to pay for the new shingles. The lion's share of gains is in industry-standard ventilation and then in the windows and doors. Those WILL pay for themselves and not muck anything up if the job's done properly.
 
Thread starter #73
Well, 20" of insulation is a LOT... absurdly a lot. (agreed!) You're losing heat somewhere else...(if you mean "gaining heat", then agreed!)

I'm still saying this "heat saturation" is way off. For one, the insulation is a progressive barrier against the heat. Two, you get an equal benefit in the morning as it heats up but the thermal mass of the attic is still cool from the night. (therin lies the problem...it NEVER cools OFF at night! The attic cools to maybe 120deg...but the insulation has been saturated to such an extreme during the day...it NEVER COOLS! And the same factors that make it a good insulator (lack of heat transfer) are what makes it such a good thermal MASS once it DOES heat up! In fact, high thermal mass is generally quite helpful! (yes, if it was not being heated to such extreme HIGH temps!) That's why it's cooler to have an underground shelter which averages night and day temps over the long run.
Again, the "averages" of the temperature in the attic (between night and day in JULY) is 150ish deg!

The importance of REFLECTING the solar radiation GAIN, and getting myself some GOOD ambient attic ventilation cannot be overstated.

The actual solution is still up in the air.
BUT, I REALLY DO likes me a good (light colored) standing seam steel roof! :)

The lion's share of gains is in industry-standard ventilation and then in the windows and doors.
100% agree with you, but it's been a fun exercise trying to figure the best way to cool that 170degF crap !!! It's just UNACCEPTABLE, and which STILL MUST be done somehow.

:) I'm thinking a "creative" industry-standard leaf blower solution...and 275rolls of aluminum foil ;)
 
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Oznog

Active Member
#74
Yeah but you're too heavily biased against "normal" solutions. Make friends with a roof installer from your area. They're quite familiar with thermal issues of your area and your architecture and how to moderate them- well, a good one is. And a lot of the Home Depot guys are knowledgeable (or not). It's not like you're the only one with this problem.
 
Thread starter #76
~the insulation is a progressive barrier against the heat. Two, you get an equal benefit in the morning as it heats up but the thermal mass of the attic is still cool from the night. In fact, high thermal mass is generally quite helpful!
Let me try to explain what my measurements show is happening ONE more time.

The insulation is a progressive barrier, just as you mention...and each day it "heat soaks" the top side in 150deg average temps.

Each day it heats up (a lot) and cools down (very little)...and each day it retains a little more than it gives off at night...and each day the depth at which the temperature "average" is 150deg gets a little deeper toward the bottom "cold side" and the ceiling.

Because the A/C doesn't cool the ceiling AND the hot insulation's HUGE MASS down effectively, eventually the average temp of 150deg has penetrated down almost to the ceiling, and the A/C is now fighting the load of the almost completely "heat-saturated" (to 150degrees) THERMAL MASS of the insulation itself. The hot insulation itself is now trying to heat the ceiling to 150deg (not just outside ambient 105...but actually fighting an attic "OVEN" of 150+!!!). The A/C can cool the inside air of the room...but as soon as it shuts off, the HOT CEILING heats the air back up pretty quickly...and the A/C kicks back on again.

This occurance does NOT seem to be "common knowlege" at "industry standard" <cough> Home Depot, but I watched it happen over the course of a couple days last July when I almost got cooked in my own attic just pulling some golf clubs down...and got motivated to actually "track" what was REALLY happening up there.
NOT what the Home Depot/Roofing contractors THINK was happening...but what was ACTUALLY happening!
Roofing contractors (here) rarely speak English very well...let alone have a clue about thermodynamics.

First thing I did was blow some more insulation up there, to attempt to slow the exchange. (maybe a mistake as it increased the mass...)
But in further thought, what I really need is MASSIVE VENTILATION and a way to prevent the HUGE Solar GAIN and HEAT RETENTION in the first place.

Massive Ventilation of the attic air -AND- reflection of the solar radient heat. (and cost effectively! ;))
 
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#77
How many windows doors do you have on the southern side of your house? Blocking off some of the windows with reflective surface can help tremendously, and which way is the front of your house facing? North, South East or West?
 
Thread starter #78
Hey, MK.
YUP! I've got a nice "Arizona Room" on the south side of the house that is a wall of windows!
This WAS a big part of the Solar Gain in the house.

I have solved most of this problem last year by blocking off most of the windows with 2" reflective foil polystyrene insulation sheets in the windows. I blocked 6 of them off completely in the "exercise room" part of that room, and I still have 4 windows to address (of the original 10). BUT, I don't want to lose the light from THOSE last 4 windows...so what I plan on doing for those is to replace those 4 with triple-panes and also putting those outside shaded "louvers" on those last 4 windows.
 
Thread starter #79
Blocking off some of the windows with reflective surface can help tremendously..
MK, (or anybody) do you have any experience with some of the reflective films for southside windows?
Anyone have any good recomendations? I know that people do that on their car windows here, and it helps a LOT with Solar Gain problems...but I'd like to seperate the "hype" from the reality as far as WHO makes a good product.

My fear is that my House windows would come out looking like some of the cars you see with a "bad looking" window tint. So, I'm wondering if anyone has experience with that?

Even the "indirect" solar radiation here is pretty intense! You can be standing in the "shade" here, and still get a mild "sunburn" from reflected radiation off other surfaces. Arizona is an "INTENSE" trip!

But, hey, "it's a dry heat"...as they say! :)
 
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Mr RB

Well-Known Member
#80
Arizona sun is a lot like Australia sun I'm gussing.

The window film can help a lot. I lived in a place with floor to ceiling glass on the west wall of the lounge room, and the window film was great. It was silvered (on the outside) and a bit tinted too, quite pleasant to look out of, it was just a little darker than clear glass and bluey purple effect. It kept a lot of the sun heat out, although probably wouldn't do much if the sun didn't actually hit the window.
 

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