Those of you who were interested in the first article of this Philippine cool series will be happy to see I didn’t forget to keep going … the others, well maybe not so much. No problem, you’re welcome to sweat along with the rest of us while you surf around and find something you like better.
We closed the last article talking about the three ways heat energy transfers from a warm place to a cold place … radiation, conduction and convection. Remember it heat energy is similar in many ways to electrical energy, it only travels one way, from hot to cold. We mentioned that in the the US and other countries that get cold in the winter, the major mode of heat transfer we deal with is building paths against heat CONDUCTION. We work hard at keeping the expensive, relatively puny heat source inside from escaping into the infinite coldness of space. And basically, to be successful, we really only need to keep things sealed up as tight as possible and provide as many barriers to the conduction of heat from inside to outside in order to keep our utility bills and comfort level reasonable.
Thermodynamics in the Philippines operate exactly the same way as anywhere else on the globe, but the scale of heat energy here is way different than in the US. Our houses are virtually always warm enough, our problem is basically far different in scope. Instead of trying to keep the heat from a furnace capable of, at best, a few hundred thousand BTU’s of heat production per hour, (roughly 2900/3500 Watts per hour in a typical home)we instead have the sun … a thermonuclear furnace of vast proportions … estimated at 384.6 YW (yottaWatts, 10 to the 24th .. that’s 10 with 24 zeros after it). The differences is the scale of the problem are astounding. In more practical terms each square meter of you roof in the Philippines receives about10,000 Watts per hour when in full sun … a typical (small) roof would be perhaps 150 square meters, so at noon we are looking at something like 1,500,000 Watts of solar radiation hitting the roof. or, going back to US familiar terms 5,172,000 BTU per hour heat load … three hundred forty or more standard US furnaces on the roof, all trying hard to pup their thermal energy inside.
And remember our heat flow … warm to cold. If you have a room inside cooled to some comfortable level … say72/74 F or 21 or 22 degrees C, how hard do you really think it will be for our 344 roaring roof furnaces to start raising that temperature into the discomfort zone?
Actually, when you lay the figures out like this it seems impossible. Better stay home in the US of A. What the heck am I doing here? It’s 7:31 am and a cloudy day, yet I’m already starting to sweat in front of the computer room fan .. in a few minutes I’ll have to close the windows and start the air conditioner …because even if I can stand the heat, my computer can’t and it will go into a very slow, hesitating “max cooling” mode which drives me crazy (a short trip, by the way).
And yes I said cloudy. Just because the sun is behind the clouds doesn’t mean there isn’t tremendous solar radiation coming in from it .. may be slowed down measurably but a whole hell of a lot of heat is still a whole hell of a lot of heat, even if you cut it in half.
But it’s not hopeless, not hopeless at all. You just have to attack the problem in the way it needs to be attacked.
Packing the attic space full of insulating materials, as Fred described in the first article is not going to do much good. The sun’s energy comes to us directly as radiation .. radiant energy. When it strikes the roof, some significant portion of it is reflected or re-radiated. We’ll talk much more on those processes later. The remainder of the sun’s visible and infrared energy is conducted through the metal roof and heats the air in the attic (above the room ceiling) space via conduction and immediately circulates to warm the attic space by convection. In other words, in a very short time after sunrise, the attic spaces gets uncomfortably hot and it keeps on getting hot as the day goes on.
And what is that heat trying to do … always? Travel from hot to cold .. which in this case (relatively speaking) is the room you are trying to be comfortable in.
In the US and many other countries we are very familiar with the term “R” value. It is even a government-mandated term in the US and it stems from precise laboratory tests where insulating materials are placed between two calibrated and instrumented plates in a laboratory, one plate is heated and the flow of heat from the hot to the cold plate is measured. The higher the resistance to this conductive heat flow, the higher the “R” value of the material under test.
This is of primary concern where, as I illustrated earlier, we are trying to trap the relatively minuscule energy our home heating plant puts out and keep it from being conducted into the cold night sky.
But when we go into the reverse summertime situation, especially when we have summers like they have in Miami or the Philippines, the R value essentially becomes useless. It really doesn’t matter if you have a fiberglass bat umpteen inches thick, or some sort of polyurethane materials, or even cellulose (one of the most effective R value conduction insulators known) .. with those millions and millions of watts radiating the insulation itself going to eventually heat up and essentially not even be there. You can delay the flow from hot to cold but most of the heat is coming to you by radiant energy and conductive R value products don’t effectively stop radiation.
I even recently heard a fellow here in the Philippines tell me he was going to dump a lot of some sort of high R value insulation in his attic and to keep the heat from flowing in through his walls, he was going to cover the outside of his house with Styrofoam insulation board and then stucco over that.
While researching that idea if found a pretty interesting report of a US government test that mimicked quite a bit of what he was planning to do:
The Test: Researchers at Oak Ridge National Laboratory in Tennessee which is the technology laboratory managed for the U.S. Department of Energy, took homes in Miami FL, Phoenix AZ and Atlanta GA which were single-story, single-family detached houses with exterior walls constructed of concrete block, and interior walls of wood-framed drywall. (author’s note … this pretty much describes the typical Philippine single-story hollow-block home)They insulated the walls and applied stucco as follows,
"We attached two layers of inch-thick polystyrene foam insulation boards to the exterior walls, next a wire lath, and finally, stucco. After the stucco had dried, it was painted a light color. Total retrofit costs ranged from $3,610 to $4,550 per house, averaging $3.34 per square foot of exterior wall area to be covered with insulation."
The Results? "In all cases, insulating the walls resulted in a much lower rate of heat transfer through the walls when the outdoor temperature
exceeded the indoor temperature, but the added insulation also increased the retention of heat generated within the house when the outdoor temperature fell below the indoor temperature.
In some locations–particularly in Miami–the addition of wall insulation actually increased the cooling load during the spring and fall."
Note: "A lower RATE of transfer", not a reduction in the total amount.
It’s probably worth reading and thinking about those last two sentences again. The ones I highlighted in red. “R” value-rated insulation can slow the transfer of heat by conduction, but it can not block it. And the heat that we get in our attic spaces and thence into our room here in the Philippines is only 3 to 5% from thermal Conduction the remaining 90 plus percent of the heat flow is by Radiation, and typical R value insulation not only doesn’t stop this radiant energy, it may even INCREASE the overall cooling load on your Philippine house because it holds the heat in longer during the night.
Pretty depressing overall, eh? For years we have been following that cute Pink Panther down to the Home Depot store and buying all that itchy fiberglass insulation be cause even our own government told us it was good for us and good for the environment.
Well the US government wasn’t wrong at all, they were just advising us on how to solve a totally different problem than what we have here, living in the Philippines.
Nest installment? Some solutions .. some conventional and some, positively space age. Stay tuned.