Sunlight vs Shade Cloth

I've measure white cars and white painted metal roofing/siding at only a couple degrees above ambient in direct sun. Would a good quality white paint work for you? In full shade, roof temp should be ambient air temp. Your best bet for accurate partial shade numbers is to run a shade/sun temperature test at your location.

Thank you.

The roof is white already.

I basically want to know if installing a Sun Sail type device that would cast a shadow over say 80% of the roof, would be enough to drop the temp on the steel roof, hence drop the temp radiating(?) into my shop and hitting the 1" R-4(?) styrofoam -type panels directly under the steel roofing and hence drop the temp inside my shop.

Thank you.

nm

I'll take a wild guess that your metal roof that use to be X above ambient temperature will now be X/4 above ambient temperature. So if on the day that you measured a roof temperature of 98° the ambient temperature was 95° I would expect the roof to now be at 95&3/4°. If instead the ambient was 85°, I would expect a roof temperature of 85+(98-85)/4 degrees. But this assumes that all of the roof temperature rise comes purely from solar energy and not from any heat sources (like people, or a stove) that were under that roof.

Hello Red,

Today I measured the roof.

It was 97F just outside in the air ( with a sligh smell of high grade BP crude)

The roof itself was 110F.

Exucse my ignorance but i do not know what ambient temp is?

I want to see if I can knock down the numbers inside the shop, under the roof....just 10 degrees or so. I ain't gotta' be comfortable, just not cooked like a crawfish ( or a lobster in your neighborhood).

Thank you.

nm

NM,

First a word of sympathy and sadness for all the poor victims of this catastrophe.

I don't think people realize the true implications of that much oil.

Anyway, I agree with Fred.

Sun screen will reduce radiation, but the effect would be more pronounced if you were directly exposed to the sun.(no roof)

And differential temperatures are a factor.

Ambient is simply what the temp. is now at the point of measurement. In this case the temp. outside.

Hello Lynn,

The Chinese say that you should always watch what you wish for as one day you may get it!

Everybody in South Louisiana always wished for oil to be discovered .....in their back yard.

So, back to the issue.

If I run a sheet of 70% Suncreen shade cloth over the top of my shop, say 2' off the metal....it will only affect the inside heat by ....what(?)

I don't need a big cut, just something to knock off 7>10F

Any guesses?

Thnak you again.

nm

As I said, I think Fred's right. What is the perceived effect on a cloudy day. Does it feel cooler. Remember, this will have no effect on internal heat generation.

What's your electric usage per day. How many Kw are you pumping into the room just doing business?

I was born and raised in Ark. so I know that relative humidity is the real enemy there.

I have a 36" Round type 1/3 hp fan positioned on the lower wall sucking air in and blowing it out the back of the shop.....and three 24" floor fans.

It's still hotter inside then outside. I just can't move enough air it seems.

I bought a big ol' swamp cooler thing but you have to be right in line with the 1/2 hp fan to get any use from it. On a 60-70% humidity day its useless.

I do not have nearly enough insualtion or sealed cracks to make good use of a comemrcial AC and if I got this place dpown to a comfortable 78-80F...i'd wind up being the next "hang out" spot for all the guys to come drink beer.....

I just want to knock the 90's down to the low 80's some kind of way without spending the $3K on insulation and new windows as well as $5k on an AC.

By the looks of things around here , frugal is going to out last spendthrift this year.

In Houston I have installed on the Southern part of the roof (a 4:12 slope) on 4in wood spacers, 8 foam panels 3/4"X4'X8' with aluminum foil pointing up. Panels - those used in the walls. I have installed, directly under the roof asphalt shingles, a thermocouple. In July at 14:00 it was showing 150 degrees F without panels. With panels, the temperature never went more that one or two degrees over the ambient (surrounding) air temperature.

The electric bill went down, not much, because only half of the Southern roof was covered, in fact you may say that it was only 1/8 of the whole 1440 sq. ft. house.

If I have to do it again, I would set the panels directly on the roof , not on 4 in spacers.

Indel,

I put 1"x 4'x8' panels underneath my steel roof, across the 2x6 framework. It keeps the warm in during the mild winters we have but it does not seem to help with keeping heat out during the summer. there is of course a 5-1/2" space between the foam and the steel.

The panels you used were the kind you buy Lowes or Home Depot , correct? They have a foil front and back and you tape the seams....correct?

I nailed them in with green capped roofing felt type nails.

Sounds like we both had the same idea.

nm

Indeed they were (the panels) bought at Home Depot. My idea was that, if I nail them on spacers (4 inch, fixed on the shingles), I will cover the roof shingles, leaving a ventilation space (the roof has that slope 4:12). I hoped that the temperature will go not higher that the ambient, first because the reflecting of the aluminum foil and second because the foam has some thermal isolation. I didn't continue the project because I moved into a house with better slope of the roof and better isolation.

You have a shop that is itself producing heat. Trying to exchange all of the air in the shop with outside air is a good place to start but depending on how many heat sources you have in the shop this may never be enough. If you can, try directing the equipment cooling air flow directly outside with ducting. If the motor must generate a 20° air temperature rise, there's no requirement that this air must blow into the same air space that you and other machines must occupy.

Thank you.

There is no machinery in here except the fans .

All work done in here is on fishing nets and that is all hand sewn. This is after all, an almost "dead art".

Thank you. Any suggestions are always appreciated.

nm

Well, then with the exception of maximizing fan motor efficiency to move the air in your workspace, I think you will get a cooler work space by preventing the solar heat that reaches your metal roof from entering your work space. This can be achieved by making a separate airspace below your roof but above your workspace. Make sure that this cavity will get plenty of natural ventilation that will carry this solar energy away from the workspace.

Red,

That is an option I have been planing on. I have foam panel insulation 5.75" from the roof itself, nailed to the joists. Is that sufficient or should I actauuly construct a more air tight sub ceiling?

Thank you.

nm

Just keep in mind the three methods that heat gets transferred from one body to another; conduction, convection and radiation. I also put them in the order of most efficient to least. By painting the outside of your roof white you've already reduced most of the radiant energy that the sun deposits into your metal roof. Now the energy that gets deposited into that roof is now in contact with your roof supports and the air contacting that roof. If your roof supports are metallic poles that travel into your workspace you may wish to consider some thermal break between roof and pole or you will always have heat radiators in your workspace. Getting back to the air, as long as that warmer air can rise out of the cavity between roof and workspace to carry this heat away you'll do fine with this air. Remember to provide both inlet and exhaust paths for this cavity and you'll do fine. If you cannot provide an air exchange then you will want to try a tighter sub-ceiling but this will never be as good as providing an air exchange. Lastly the sub-ceiling will also provide a block for the radiant energy coming from the underside of the roof. If the foam panels have a metalized surface have that side facing the metal roof. This will reflect more of this energy back to the roof instead of warming one side of the foam.

Remember, stopping heat from being transferred is not just difficult, its impossible. Redirecting the heat transfer to another space is what you want. Short of that all you can do is slow the heat transfer.

Ok.

With all of this said, how much air is inside this building and how much of a fan do i need to suck it out enough to get an ambient temp inside, shade or sun?

50x30x14' Flat roof with a 2' drop ( 14' down to 12' over the 30' width)

nm

You have 21,000 Ft³. You'd need a 21,000 CFM turnover to change the air every minute. To change it once an hour: 21,000 ÷ 60 = 350 CFM.

I'd think you would want some exhaust fans on the roof.

Lyn,

Is it better to have it on the roof or up high on a wall? The roof is slanted and flat.

nm

All things being equal, hot air rises. I guess I'd put the vents at the highest point.

Are the walls of the shop insulated? If not, that's another source of radiation. Do you shade the sides, too?

They call a place where they have sails a loft. Does netmaking have a term for the place where nets are sewn?

I remember living in Ark. with only a window fan. It was still hot as He88 till after dark.

Did you see this?

Compliments of:QSK

Lyn,

Most of the Northeast and Pacific Northwest guys ( the very, very few that are left) call it a net loft. However, the only loft at my shop is where i stow remnants.

I too remember the old Reed fans, 2 speed . But we had 12' ceilings also.

....and yes, there is a lot of oil coming and poised to come ashore.

Thank you.

nm

Could you obtain some shade cloth and run an experiment? A wooden frame holding a square yard might (I said MIGHT) yield interesting results. A 10' x 10' piece would be even better. This would be far from a "proper test" since you would still have full exposure heating of the roof and air around the shaded area. But, if a small sample produces measurable cooling of the roof under the shade cloth then you have something to work with. The results of shading the full roof would be expected to be much better.

If you try this then be VERY CAREFUL to do it on a day that is not windy. Secure the test frame and be sure that it does not come down on anyone.

Another interesting experiment might be to go to a garden center (Lowes, Home Depot or a true greenhouse) and find a spot where metal tables (or anything else) is exposed to direct sunlight on one end and shaded on the other end. Take note of the temperature difference between the two sides.

Please let us know how well your efforts are working out.

Bruce

Bruce,

I have a huge piece of shade cloth and after listening here, I am going to put in a roof vent fan and drop the ceiling a little too. However, I just might use some of this and try it. What's to lose?

Thank you.

nm

If you allready have the shade cloth it will probably be cheaper to go the route of shading the roof. However I had a suggestion that there are heat insulating paints available which reflect or insulate aganst 80% of heat which would be easier to implement than setting up shade cloth, also walls as well as roof could be treated. Cost wise it is cheaper than sail cloth.

Garth,

I was going to use some of your home product , Coolaroo.

The paint is called Cool Seal.

Thank you.

nm

Heat insulating paints that work?

I used to build houses in South Florida and was always looking for a way to knock down the solar transfer from roof to living area. A Prof. at one of the big Florida schools came up with a dirt-cheap idea after much experimentation...aluminum foil. Bought in bulk from restaurant houses, or even costco, the large, heavy duty foil laid between joists would drop the heat transfer by an incredible amount. Homes we roughed in and then "foiled" were actually very tolerable to work in. His studies generated a Mylar curtain that was then sold, for a lot more money, that would be spread out over the roof insulation and cut the AC required by a good ten percent, and reduce cycling of the AC.

I'm talking 1986, but it still applies. Let your existing roof take the brunt of the heat, and put the shield under, not over the roof, unless you want to replace it every time you get a big blow. Also, you could set up a golf-course type sprinkler to lay some water down on the roof very easily. Just use a solenoid to activate above a certain temp and it will kill the heat off the metal in seconds.

I saw this stuff. It was foil with air bubbles.

Its kind of late to try it because the sheets of foam are in place and I'd have to move a lot of material to get a ladder and take it down. However, its a thought.

thank you.

Since you are not versed in all things HVAC, some basics.

The temperature you see on your thermostat is called the Dry Bulb temperature (because the bulb of the thermostat is dry).

If you but a wet piece of burlap over the thermostat bulb and had a fan blowing air on the wet burlap, the temperature on the thermostat would be the Wet Bulb temperature. That is the temperature that occurs when water evaporates at that Dry Bulb temperature.

Based on the temperatures and humidity that you mentioned, your "normal" Wet Bulb temperature during the hottest part of the day is between 78F and 80F.

If you have a well, the solution will be fairly cheap to implement. If you need to use city water, it won't be too expensive. What you need to do is either pump a small amount of water up to your roof and spray it up in a very fine mist across the roof. OR- if you already have the cloth to cover your roof, install a 1/2" plastic pipe at the top of your roof with 1/32 inch holes on 12 inch centers and use the pipe to keep the cloth damp wet.

Either way, the roof temperature will not go above 80F at any time and will be cooler than that most of the time. When the ambient temp (remember where that came from) is less than 80F, you can shut off the water if you want to keep costs down.

Either system will only use about 1/4 GPM for every 10x10 section of your roof. If you evaporate that water input, you will produce about 125,000 BTUs of cooling (about 10 tons) for every 10x10 section just from the water evaporating- 1/4 GPM is equal to 0.25 X 8.33 pounds of water per gallon X 60 minutes per hour = 125 pounds per hour. Each pound of water that evaporates at those temperatures uses about 1020 BTUs per hour to evaporate. That means that 1/4 GPM will absorb 125 pounds X 1020 BTU per pound or about 127,500 BTUs per hour. A ton of cooling is 12,000 BTUs per hour of heat absorption, so 127,500 BTUs equals 10.6 tons of cooling.

This will work easily and absolutely.

I looked at this before. I may revisit it . I saw someone with this awhile back. However, we might look at this again.

Thank you for Joe 6 Pack HVAC lesson.

To be blunt, in a practical situation like this, there are so many variables, you won't get an accurate answer. You are in danger of overthink.
Just go for an approximation...
So if the roof surface gets 16 degrees above the surrounding air temperature, then just assume it will get to 25% of that.
Or look at it another way. the incoming heat is still there, 75% will be making the shade hotter, 25% will get to the roof, it will be cooler.
Or see how cool it is on a day with 25% les sunshine (75% cloud)

Anyhow the question is pointless...are you really interested in the "temperatiure drop on the metal roof's exposed surface itself?" Is anyone working there? Surely it's the actual result in the work area you are concerned about.
Brevquot error this process has terminated...
Del

Good comment.

The area on the ground is my concern. Its just been very obvious that ever since that last hurricane that dropped a huge limb from an oak across my shop, and hence we had to cut up a 125 year old tree, there is no longer shade after 11 AM.

I never minded before because the building stayed rather comfortable in the summer but chilly in winter. Now its reversed. Our winters are so mild ( except for this year) that it actually costs less to run my propane heater.

The only thing that changed over these many years is that now, we are exposed to full sunlight where we weren't before.

If we kill some of the heat on the roof, i am hoping we kill some of heat on the floor.

Thank you.

Lots of good advice here already.

If you shade your roof, yes it will get cooler. But how storm resistant will this sun shade be? Is ok with UV every day, or will it fall apart after 2 years? The sail, though I am sure it would work, may only be a short term solution....

I personally would add insulation on the roof and add another sheet of white metal. Vent the space between the two roofs as well.

And most important of all, do say 4 square yards first and see what it brings, buy a few contact thermometers and check carefully.....tes test test......

You could even try spraying water over the roof when the sun is up, collecting it and spraying it again, or use it to warm the water for washing!!!! A small cistern, topped up from the mains and what flows back, usage should be minimal, just what evaporates.....

Maybe the heat energy can be harvested and used something, cooling the water at the same time before re-use?

Danke.

The shade cloth has UV retardant . It will last for 5 years out doors here. When the big winds blow I will have to have a quick release sewn in ( no problem) to take it down or else... Ohh Shitze!

nm

Another totally different thought-

If you hang those insulated, foil-faced panels about a foot (or more) below the roof like a suspended ceiling, and then provide inlets at the low side to get air from the shop into that space. Install fans to extract the air at the top of the building and then vent it out the side of the building during the summer push the air back into the shop during cold weather you will get the best of both conditions.

The foil will reflect any heat back at the roof, and the insulation will minimize heat from entering the building- the air circulation will capture that heat and keep the temperature in the space above the new "ceiling" reasonably low in warm weather and- during the winter, the system will be a low-grade solar heating system.

Otherwise- go for the roof spray (with the cistern/catch tank for recovery) and keep your roof about 80F or cooler.

Thank you too.

All ideas are workable.

nm

Sounds like you've just given us the answer. The "old oak tree" was like a great big shade cloth and protected the roof from the direct radiation. Thus, it seems probable that shade cloth would provide significant benefit.

Another item that might bear repeating (already suggested) is some roof extractors. Your fans may be exchanging the air at ground level, but your roof materials may still be hot. Allowing that hot air to rise through the vents will reduce the radiant effect that you are encountering.

Next, the idea of a roof sprinkler is good. the relative heat of the roof will cause ready evaporation of the water, cooling the surface and providing a more comfortable inside temperature. This will waste water unless you have a ready supply, catch the gutters and recylce the run-off.

It is possible that your fans are making the situation worse by creating the reverse of a wind chill for your staff.

Good luck.

Hello JAE,

What is this "reverse of a wind chill"?

I have 2 windows on the west side (30' wide section)

3 windows evenly spaced along the 50' side (South)

3 windows at almost 12' on the 14' high side , also 50' ( North)

1- 36" 9630 cfm fan on the opposite 30' side (east)

3- floor fans

1- 1/2hp Swamp Cooler (Not a mist type , but water dripping over baffles on 4 sides while the fan sucks air through them. Works OK, but you have to be in line for the wind chill....on a high humidity day it is useless.

....as for staff.......are you kidding? Getting someone to work in a trade that requires using all 10 fingers, paying attention to detail, learning hand eye co-ordination and having a basic concept of math........... no way. Its me , the wife and the dogs.

Small family business all the way.

Good to hear that you have a cosy family business going on there.

There comes a time where blowing warm air acts to increase the apparent temperature, especially if the ambient air is above body temperature. I'm not HVAC trained and cannot give you the specifics, but the effect of hot (humid) air blowing onto you will displace the thin layer of body temp air with hotter air.

From your descriptions though, the significant casue is the additional radiant heating from the roof.

Do you only repair the nets, or do you get the opportunity to go out and use them as well?

Thank you for the reply.

We build netting gears for research and sampling as well as some commercial operations.

Our customers are basically oceanographers, marine and fishery field guys (and girls) , some private environmental companies and a smidgeon of shrimpers. Very small operation as everything is made here....no outsourcing. It takes a lot time from design to cutting to fabrication to the water.

After this BP thing there will nothing much to sample down here except chunks of carcasses of dead marine life.

Once in awhile I accompany the gear if it is a prototype or a research project . I try to stay off the boats when I can. I have had enough time on open water and it was just time to quit.

Thank` you for the reply.

nm

Hi there,

I've some experience working in an oven I mean warm building too.

I see a few suggestions oriented upon cooling by evaporation; good thoughts buts when the humidity is high evaporation is poor.

I think I think you may experience a reasonable cooling effect with the shade cloth and I would use two layers. Hang one layer about three feet over the roof surface and an additional layer about four feet above that one. This may approximate the shade effect of the former tree and wetting it at times may prove beneficial too.

I would take the suggestion of adding a suspended ceiling as another poster expressed too.

Next suggestion incorporates bulkheads; essentially sections of foam insulation material wrapped with cloth or nylon fabric and having Velcro attached to enable forming a small booth in which to work and adding an a/c unit to cool that small area.

Thank you.

I need to use the whole length of the shop for my work, though.

Double layer shade cloth may be another idea.

Thank you.

nm

Hello Netmaker, If your building was cooler before the big tree came down because of its shading. Now its hotter. What about installing a couple of poles spaced a little wider than the tree was and as tall as it was. Then install two sets of pulleys one on each side of the poles with guide cables. Then rig up your shade cloth to be pulled up and secured to keep it taunt. Same thing on the other set of pulleys. Double layer would block most of the sun energy.With the cable and pulleys if a storm came up it would not take much to lower and store safely then re-raised after.

Just a different idea than some of the good ones already given.

I do like the idea of layer of insulation as a ceiling then using venting inlets on the low side with solar powered vent fans on the high side or ridge line or end walls which ever is the easy way.

We who like the seafood that come from the Gulf, and the beaches on the Gulf and the east coast. Hope BP can stop the oil and can get it cleaned up before it ruins the fishing industry and the environment. We also hope they can keep it from getting into the gulf loop current and creating an environmental mess/disaster that stretches all the way up the east coast.

Charles

Hello MS,

I'm going to be limited to what i can do inside as the whole place is now covered with projects we are working on. Its probably the wrong time of the year to do interior work.

However, re-thinking everything,after reading all the discussion here, I am implementing this;

• I am going to invest in two diamond shaped shade sails. I will install one post at each end and two along the middle.
• String up some 1/8" Dyneema rope ( very strong) and stretch the poop out of it.
• The shade sails will install one diamond over the other with an offset, covering most all of the building and allowing plenty of air under neath.
• I also whacked a 5'x4' window over the existing 3'x2' window and am building a screen to keep the skeeters out . the window will be completely open and will have a ol' gun port style hinged door that will drop down when we batten down the hatches in August and Sept. for the l'eau re'gions ( hurricanes)

• The vent fan I have already in place is actually pulling more air through the shop..... a lot more. Enough that I get a huge influx of skeeters stuck against the screen. I guess I never fully utilized the CFM of the 36" fan I had. But after discussion here and some instruction on the math side, I am good to go.
• During the off season I will re-configure and as noted here on CR4, I will replace the wall mount I have with a roof mounted fan for even better pull. I think I want to exchange all the air inside the shop every 3-5 minutes or so.

I want to thank everybody for their input as it really gave me an insight into something so basic. The loss of a huge shade tree was so vital in keeping our little net shop cool in the summer.

As for the oil spill, I heard this morning that the government is stepping up its 'pushing' of BP to do more...hmmmmmm? No one down here believes either the government or BP has the answer yet. Me and my Ol' Skool podnas feel that some private engineer, oil field worker, grad student or back yard Mr. Wizzard ( Ol' Skool for Nie the Science Guy), has the answer.....but the layers of governmental BS will not let anyone implement it much less even know he (she) is out there.

nm

Best of luck and maybe this fall you can tell us what seemed to work and not work. As regards to the gov supervising and being tough with BP, İ think it is a joke and for political consumption only. Obama flying down for a look see was exactly the same thing.

Naturally, we all hope you are also going to:-

a) going to shoot the Guy that took the tree down (what a dummy!!)

and

b) Plant some new trees!!!

Hurricane Lilly took it down! 110 mph wind and then a ittsy bitsy tornado came right across the pasture, dropped the tree on my shop, bounced over my house thank God, and then dropped 2 more big oak tress crushing my neighbor's home.

Anyway, we have lots of trees, just not on over the shop anymore.

nm

Ouch!

Sounds like you got a good plan. Like russ said check back in the fall let us know how it's working.

Lets hope the "top kill" plans work for everyone. There too much to lose in this oil spill. From what the Gulf provides in jobs for everyone.

Charles

I like the 'ohh-sh**zees' and 'my podnas', grew up with it in south MS.

The folks on here sure can lend some info, can't they?!

My fave was the water on the roof. Lord knows you have plenty of water down there and you can keep the "heat of the pump" outside with the skeeters!

Pump the swamp over the roof and gutter it back where it came from. Forget the mist, go for the gusher!

Good luck and let us know how it works..

water....hey podna, where you been???

We gonna' cool the roof with $75.00 a barrel Sweet Louisiana crude............

nm

How Crude?

....Seattle for ten and Birmingham for ten but I know you cant be far from plenty of water! Horizontal or vertical?

Dig a sump out behind the shop and put a big sump pump in there (if you're not close enough to the bayou). A 3" pc of pvc along the ridge line and dump it out both side along the top and gutter back to the sump. Hangin a sail up over the shop would have you jumpin every time the wind kix up but the plumbing would be pretty stable.

I just skimmed through the thread and it may have been mentioned but all of that insulation double wall business and venting would need to be on the walls too. you still get lots of radiant there. ya, kinda impracticle for shop space.....

alright, how bout this. when you dump into the gutter from the roof, the gutter sprinkles the walls too. I would GUESS, that your solar gain is 60% roof and 40% walls. South LA geothermal.

My shop is in a metal box oven too. I look forward to hearing what you come up with!

I liked the idea too, a small pump could cool a large roof and you have some warm water to do things with......very environmental!!