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"Heatshield" - More reefer (well, insulation) questions
One of my respondents to my question about vacuum panels is very high on
"Heat Shield" (www.heatshieldmarine.com) - a mostly radiant barrier, to my expectations, but their claim is that in conjunction with foam, it has the effect of tripling the foam R value. As I don't know what's inside these foil separators (1/2, 3/4 and 1 inch material) I can't judge the insulating value of that part. However, what I *think* I know (see Mark Twain's quotation about facts for perspective) is that a radiant barrier can be any shiny surface - such as on the outside of Tuff-R or other building supply foam board, or simple home aluminum foil - including, I suppose, those Mylar "space blankets" available cheaply in camping stores Despite their assertions that their 1" is equivalent to 5 or 6" of urethane foam, as their site seems to place a great deal of importance on the radiant barrier, I don't know how much value to place on *their* radiant barrier over any other. It seems to me that if this premise were so, houses would be insulated with silver Mylar film outside instead of the usual tyvek wrap as it seems - at least from the premise of their claims - it would improve the thermal barrier multifold. Not being a thermal engineer, I don't know whose claims to believe... So, again, I'm looking for real-world experience. Anyone had an installation of Heat Shield they'd care to comment on? Thanks. L8R Skip and Lydia -- Morgan 461 #2 SV Flying Pig http://tinyurl.com/384p2 "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain |
#2
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For what it's worth:
I am, among other things, a "Certified Infrared Thermographer" (Infraspection Institute). I have several years experience with using infrared cameras to inspect electrical systems, building envelopes, and industrial processes. In addition, I have taught these skills to others in formal classes. In simple terms, there are three methods of transferring heat: 1) Conduction 2) Convection 3) Radiation 1) Conduction - If two materials are touching each other heat will be transferred from the warmer to the cooler. 2) Convection - If two materials are separated by a liquid or gas the heat can be transferred from one material to the other through the motion of the liquid or gas. 3) Radiation - All materials give off infrared radiation from their surfaces. This radiation is just below the lower end of visible light and extends down to microwave frequencies. The qualities of the surface determine the "Emissivity" of the surface. A perfect radiator has an emissivity of one. A perfect cold dark body has an emissivity of zero. Real world objects are between these two extremes. Highly reflective surfaces usually have a very low emissivity and will not radiate heat efficiently nor absorb very much heat energy. This is why gold foil is used to cover certain areas of satellites. It protects them from the suns infrared radiation. It's also why the space shuttle must roll over with it's top facing earth and it's bay doors open soon after reaching orbit. It's cooling radiators (high emissivity) are inside the cargo bay and they must be kept exposed to the outside and facing away from the sun at all times. Since they have no means of removing heat by conduction or convection in outer space, they must do it by infrared radiation. After that very simplified beginning, on to reflective barriers. A reflective barrier can greatly reduce the heat gain to a cool object from infrared radiation. The question is, where to put it? If you have an insulated ice box you could put it on the outside surface. It would then reduce heat gain from infrared radiation. However, it would do nothing to reduce heat gain from convection. The warm air surrounding the outside of the box would transfer heat to, and through, the reflective surface just as if it was painted flat black. In addition, since the reflective foil was in contact with the outside of the box, conduction would just move the heat right into your ice box. You could put it on the inside of the box, with the shiny side facing out. In this case the foil would be in contact with the material forming the box and again conduction would pass the heat right through the foil. The same problem occurs no matter where you place the foil. Conduction or convection always wins. The only solution I know would be to build an inner box, cover it with shiny foil, and surround that with a layer of vacuum to eliminate convection and conduction. Even then, heat gain through infrared radiation would be the least of your concerns. The closest practical solution is to use insulated vacuum panels like those built by Glacier Bay and others. They have a real life insulating rating of R50 per inch. But, you will pay for that luxury. I can think of one place a reflective foil might help. If you had a freezer or refrigerator, with adequate vacuum or foam insulation, that had one side facing the inside of you engine room then foil on that surface facing the engine would reduce infrared heat gain to the box when running the engine. But that can also be covered with Mylar faced noise control foam with even better results. The bottom line: Most heat gain to a refrigerated box is through convection and conduction, not infrared radiation. There is no free ride and reflective foils will not noticeably improve the insulating qualities of the typical boat ice box. Rusty O Reflective barriers "Skip Gundlach" skipgundlach sez use my name at earthlink dot fishcatcher (net) - with apologies for the spamtrap wrote in message ... One of my respondents to my question about vacuum panels is very high on "Heat Shield" (www.heatshieldmarine.com) - a mostly radiant barrier, to my expectations, but their claim is that in conjunction with foam, it has the effect of tripling the foam R value. |
#3
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A-men brother.
The Heat Shield folks do a demo at boat shows where they wrap an Igloo cooler in the stuff and compare the ice melt to a bare cooler. The problem is they sit the coolers in the sun where 90% of the load is radiant. That will not be the case in the galley. One place I do plan to use a Heat Shield like product in between the head liner and the cabin top where the load will be mostly radiant. But I will be using that silver Mylar and bubble wrap duct insulation from Home Despot. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com "Rusty O" wrote in message ink.net... For what it's worth: I am, among other things, a "Certified Infrared Thermographer" (Infraspection Institute). I have several years experience with using infrared cameras to inspect electrical systems, building envelopes, and industrial processes. In addition, I have taught these skills to others in formal classes. In simple terms, there are three methods of transferring heat: 1) Conduction 2) Convection 3) Radiation 1) Conduction - If two materials are touching each other heat will be transferred from the warmer to the cooler. 2) Convection - If two materials are separated by a liquid or gas the heat can be transferred from one material to the other through the motion of the liquid or gas. 3) Radiation - All materials give off infrared radiation from their surfaces. This radiation is just below the lower end of visible light and extends down to microwave frequencies. The qualities of the surface determine the "Emissivity" of the surface. A perfect radiator has an emissivity of one. A perfect cold dark body has an emissivity of zero. Real world objects are between these two extremes. Highly reflective surfaces usually have a very low emissivity and will not radiate heat efficiently nor absorb very much heat energy. This is why gold foil is used to cover certain areas of satellites. It protects them from the suns infrared radiation. It's also why the space shuttle must roll over with it's top facing earth and it's bay doors open soon after reaching orbit. It's cooling radiators (high emissivity) are inside the cargo bay and they must be kept exposed to the outside and facing away from the sun at all times. Since they have no means of removing heat by conduction or convection in outer space, they must do it by infrared radiation. After that very simplified beginning, on to reflective barriers. A reflective barrier can greatly reduce the heat gain to a cool object from infrared radiation. The question is, where to put it? If you have an insulated ice box you could put it on the outside surface. It would then reduce heat gain from infrared radiation. However, it would do nothing to reduce heat gain from convection. The warm air surrounding the outside of the box would transfer heat to, and through, the reflective surface just as if it was painted flat black. In addition, since the reflective foil was in contact with the outside of the box, conduction would just move the heat right into your ice box. You could put it on the inside of the box, with the shiny side facing out. In this case the foil would be in contact with the material forming the box and again conduction would pass the heat right through the foil. The same problem occurs no matter where you place the foil. Conduction or convection always wins. The only solution I know would be to build an inner box, cover it with shiny foil, and surround that with a layer of vacuum to eliminate convection and conduction. Even then, heat gain through infrared radiation would be the least of your concerns. The closest practical solution is to use insulated vacuum panels like those built by Glacier Bay and others. They have a real life insulating rating of R50 per inch. But, you will pay for that luxury. I can think of one place a reflective foil might help. If you had a freezer or refrigerator, with adequate vacuum or foam insulation, that had one side facing the inside of you engine room then foil on that surface facing the engine would reduce infrared heat gain to the box when running the engine. But that can also be covered with Mylar faced noise control foam with even better results. The bottom line: Most heat gain to a refrigerated box is through convection and conduction, not infrared radiation. There is no free ride and reflective foils will not noticeably improve the insulating qualities of the typical boat ice box. Rusty O Reflective barriers "Skip Gundlach" skipgundlach sez use my name at earthlink dot fishcatcher (net) - with apologies for the spamtrap wrote in message ... One of my respondents to my question about vacuum panels is very high on "Heat Shield" (www.heatshieldmarine.com) - a mostly radiant barrier, to my expectations, but their claim is that in conjunction with foam, it has the effect of tripling the foam R value. |
#4
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Rusty, thank you so much for your informed and concise presentation. It's
very complete, and answers most of my questions, but generates a couple of others. Please indulge me? And, since you're spamtrapped, I can't ask you directly, but may I quote you in the various mailing lists to which I posed the same question(s)? A reflective barrier can greatly reduce the heat gain to a cool object from infrared radiation. The question is, where to put it? (exposition clipped) The bottom line: Most heat gain to a refrigerated box is through convection and conduction, not infrared radiation. There is no free ride and reflective foils will not noticeably improve the insulating qualities of the typical boat ice box. So, effectively, without a vacuum (or, at least, a free-space non-touching environment), the addtion of aluminum foil merely acts to accelerate (aluminum being an excellent heat conductor) heat transfer? Thus, for example, the foil-faced building insulation products are no better than the level of vacuum behind them? I'd been migrating to the thought of layering heavy foil between the highest R-value foam I could find, and then doing a heat-sealed vapor barrier wrap, evacuated to the best of my ability. However, your comments suggest that's a waste of time. I *think* I understand you to say that foil is counterproductive if not faced with a vacuum. If so, from that, if I'm not going to spring for the vacuum panels, simple block foam, encapsulated to prevent moisture, is the best? My box exterior (which is a single layer of roving over the hard urethane 2") is currently exposed for most of two sides. I'd thought to put foil on that exterior surface. If I understand you properly, that's counterproductive? On to the last: I can think of one place a reflective foil might help. If you had a freezer or refrigerator, with adequate vacuum or foam insulation, that had one side facing the inside of you engine room then foil on that surface facing the engine would reduce infrared heat gain to the box when running the engine. But that can also be covered with Mylar faced noise control foam with even better results. Is that like the lead foam used in noise control, nearly as expensive as heat shield :{)) ? Or is there some other noise abatement of which I'm not aware (there are probably encyclopediea worth of info of which I'm not aware!)? Is this an application where a foil-backed insultion board would help? Thanks again for your knowledgeable input. L8R Skip and Lydia Rusty O -- Morgan 461 #2 SV Flying Pig http://tinyurl.com/384p2 "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain |
#5
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Is that like the lead foam used in noise control, nearly as expensive as heat shield :{)) ? Or is there some other noise abatement of which I'm not aware (there are probably encyclopediea worth of info of which I'm not aware!)? Is this an application where a foil-backed insultion board would help? That is correct. It is opencell foam either side of a rubber membrane imbedded with lead and a foil face. I don't think you really have that option though. You would have to rip everything off that front engine room wall and having seen it I do not believe you really want to do that. :-) A little clarification: Once the radiant energy is absorbed it becomes conductive and the metal actually speeds up transmission. If the foil is behind another layer that absorbs radiant energy, like the wood face of the refrigerator it looses much of its effectiveness because the radiant energy has already been converted to conductive. The foil side on foam or fiberglass insulation goes on the warm side. It reflects some of the remaining radiant load but mostly it acts as a moisture barrier. With your galley layout you have two places where the fridge will be subject to radiant load. The side of the stove where it sits beside the outboard end of the box and the back side against the engine room. You are cutting down the size of the box (Seriously folks, this box is big enough to fit two coffins in.) so if you go with vacuum insulation you might consider turning that far end into pot storage. The front wall of the engine room might be a good candidate for some foil insulation. (Not nessacarily Heat Shield) It will be easier to install than SoundDown and sound insulation is useless unless you completely cover all the room surfaces. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
#6
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So, effectively, without a vacuum (or, at least, a free-space non-touching
environment), the addtion of aluminum foil merely acts to accelerate (aluminum being an excellent heat conductor) heat transfer? Yes, the heat would tend to conduct right through the aluminum. However, given that the materials on each side would tend to have lower levels of conduction, the aluminum probably has no effect either way. In other words, if you sandwiched a layer of foil between two layers of insulation, the overall conduction would be nearly the same as the insulation layers alone. Thus, for example, the foil-faced building insulation products are no better than the level of vacuum behind them? I'm not sure what the advantage of foil-faced foam board is over non-faced foam board in housing applications. I have a call in to my brother who is a building materials guru. I will pass on the information when I hear from him. I'd been migrating to the thought of layering heavy foil between the highest R-value foam I could find, and then doing a heat-sealed vapor barrier wrap, evacuated to the best of my ability. However, your comments suggest that's a waste of time. Yes, I believe that would be a waste of time. My hot tub cover had a heat sealed vapor barrier around the foam insulation. After a few years it got so heavy from trapped moisture, I had to replace it. And, that was after unwrapping it and letting it dry in the sun for three months. I *think* I understand you to say that foil is counterproductive if not faced with a vacuum. If so, from that, if I'm not going to spring for the vacuum panels, simple block foam, encapsulated to prevent moisture, is the best? Yes, the foam is then the best way. Some other thoughts: 1) Wet insulation is an excellent heat conductor 2) When insulation gets wet, it can be almost impossible to dry out. 3) It's almost impossible to totally encapsulate the insulation around a boat ice box. 4) Imperfections will allow air to move in and out of the insulation. 5) When the air is cool and dense it will migrate into the insulation. 6) When the air is warmed it will expand, release its moisture, and move out. 7) After enough cycles of cooling and warming, the insulation will be wet from the released moisture. This is why you have a vapor barrier in your house between the interior and the insulation, but not on the outside. These problems can be minimized by not trying to encapsulate the insulation. Give it a way to dry out between cycles. Also, try to use closed cell foam instead of open cell. You can test your insulation before installing it buy breaking off a small piece, carefully weigh it, put it in a glass of water for a few days, take it out and weigh it again. If there's no appreciable weight gain, it should work okay on your boat. My box exterior (which is a single layer of roving over the hard urethane 2") is currently exposed for most of two sides. I'd thought to put foil on that exterior surface. If I understand you properly, that's counterproductive? Unless the exterior is exposed to a strong radiant heat source, the foil won't help. On to the last: Is that like the lead foam used in noise control, nearly as expensive as heat shield :{)) ? Or is there some other noise abatement of which I'm not aware (there are probably encyclopediea worth of info of which I'm not aware!)? Is this an application where a foil-backed insultion board would help? Yes, it's like the lead & foam sound insulation. I'm using a sound blocking product with a back layer of foam, a layer of some type of semi-rigid plastic, a thicker layer of foam , and faced with shiny Mylar. About an inch and a quarter overall thicknes. I don't remember the brand name but the price was not out of line. My local rubber products retailer carries it in stock. Foil faced insulation in an engine room would work to keep radiant and convected heat away from living spaces. But shiny-faced sound control products with their 'decoupled' layer would do a better overall job. Low emissivity surfaces are very effective at minimizing heat gain from non-contact radiant sources. This includes the sun or even a hot engine block. They are not a solution to other problems. Rusty O Thanks again for your knowledgeable input. L8R Skip and Lydia |
#7
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I talked with my brother about the different types or foam board.
The non-faced insulation boards, colored pink, blue, or green, are extruded polystyrene. Because of the nature of the extrusion process the boards have enough structural strength to be handled, cut, and installed without any additional coverings. (The color tells you who made it.) The foil-faced yellow looking foam boards are (poured) expanded polyisocyanurate. The facings applied to these boards are there to provide structural strength during the manufacturing, handling & installation processes. Otherwise they would tend to just break apart at random locations. (It's natural yellow color is difficult to dye to any other color.) White styrofoam board is also available. He also mentioned the foil faced air bubble plastic material. He said the manufactuers of this product have not been able to prove that it has any real 'R' value of any kind. The salesmen even suggested a good use would be to stuff it in your shoes to keep your feet dry. He refuses to distribute this product for these reasons. Rusty O |
#8
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Rusty O wrote:
He also mentioned the foil faced air bubble plastic material. He said the manufactuers of this product have not been able to prove that it has any real 'R' value of any kind. The salesmen even suggested a good use would be to stuff it in your shoes to keep your feet dry. He refuses to distribute this product for these reasons. The "foil faced air bubble products Do work in some applications. I have a 200x65 ft building with a shingle roof and the bubble wrap product underneath it, and it DOES keep the radiant heat from the sun off of the roof sheathing (the temp on the inside of the sheathing is about 40deg f below a neighboring roof without it. Having said that, it probably wouldn't help a fridge unless you set it in the sun. Rusty O -- ""War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling which thinks that nothing is worth war is much worse." John Stewart Mill I strongly urge everyone reading this to check out WWW.anysoldier.us, and support our troops with a letter, a package or a donation. |
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