HEAT TRANSFER
Questions & Answers

METHODS
UNDERSTANDING

SUPER THERM
FIBERGLASS

Ceramic reaction to heat

Inn Choi, Ph.D. in Mechanical Engineering, addressed the topics below. Dr. Choi taught advanced heat transfer and fluid mechanics at Ohio State University and was one of the founding members of the fiberglass research team in Owens Corning Fiberglass at Granville Research Center. Since then he worked at Battelle Memorial Institute, E. I. Du Pont De Nemours & Co., Westinghouse, and most recently at Pacific Northwest National Laboratory. During his tenure, he has published over 67 journal papers on various topics involving advanced fluid dynamics and heat transfer.
Ph.D. Choi worked with Professor Raymond Viscanta (W.F.M. Goss Distinguished Professor of Engineering at Purdue University and is an international authority in Heat Transfer) to do projects at the Lafayette Physical Property Lab where SUPER THERM was tested for BTU heat conduction to find the “K” value to allow direct insulative comparison to fiberglass.

HEAT TRANSFER Q & A

WHAT IS “R” RATING? // WHAT IS “K” RATING?
Why is the “K” value the most important value in finding heat conduction before finding the “R” rating?

Ph.D. Inn Choi’s comments noted in red. The "R" value is simply the reciprocal of the "K" value.

Why are the values assigned to Fiberglass or any batt type or non-radiant blocking “insulation” material missing the third part of the three components (convection, conduction and radiation) that make an insulation material valid?

There is a reason that the people in responsible positions making the decisions on insulation are completely confused on true insulation values and the truths about fiberglass. Since the middle to late 70's, the fiberglass manufacturers (Owens Corning) made a point to establish formulas and work the numbers to convince engineering, architect groups including the public that this new product was the answer to insulation by using their own newly derived numbers to prove the worth.

PhD. Inn Choi’s comments: Fiberglass is missing the radiation part, which is significant. Other than the radiation, however, fiberglass is doing fine provided that the ‘air trapping’ function of fiberglass is not degraded. Unfortunately, the ‘air trapping’ function is easily degraded by tear, moisture, and air void inside the wool pack, thus making the formula invalid. So the key point here should not be attacking the formula itself which is derived in an ‘ideal’ condition. The critique should be more on the fiberglass becoming non-ideal very easily in the real world from moisture, mold and mildew accumulation.

Since the formulas and calculations were new to the industry and sponsored by unknown theories and respected engineers with high-level degrees, no one actually questioned the concept. After years, the concepts were accepted without question in the minds of decision-makers throughout government, industry, city regulations and in the Universities. Due to this, there is little doubt we have encountered resistance from all these groups when we develop an insulation product that includes all three heat transfer components and in doing so exposes the inherent deficiency in the insulation concepts established by the fiberglass industry.

Ph.D. Inn Choi’s comments: Again, the fiberglass concept is fine although it is limited by the missing radiation part. If there is any real misconception of formula, it is with foam insulation where laminated foil sheets are used between pieces of foam material. The intent is to reflect the radiation. But in this case, all heat reaching the foil barrier is conductive and passes straight through making the barrier useless. The situation gets worse because the foil is in close contact with the material by lamination.
Fiberglass is an ‘air trapper’. Air is a very good insulator with a "K" value of only .16. The "K" value given for air describes the amount of heat, which will travel directly through perfectly still, and dry, air. However, air used as an insulator never stays completely still. Instead it sets up an active circulation as one side of the containment chamber is heated. The heated air rises and the cold air falls. This circulation constantly exposes the colder air to the warm wall, thus increasing the delta T across that wall and greatly increases the rate of heat transfer through the chamber. This is where traditional insulation helps. In these materials the air is "trapped" on a great many small chambers called "cells". While each cell still sets up its own convection current, heat transfer is reduced in direct proportion to the size of the cell. The smaller the cell, the greater the reduction in convection.
The resistance from government and industry comes more from health hazard than from insulation effectiveness. This is not to say the insulation effectiveness is fine. It is not. Once installed, people just do not think about it.

We will now go through the concepts, expose the facts, see the truth in the arguments and look at the actual numbers established by the early formulas and how they are badly flawed by completely ignoring the third component of heat transfer. We went back to one of the engineers that worked on the team that developed the insulation concept for fiberglass. This concept was engineered on the fact that the parts of the heat transfer formula that could not fit into the formulas for fiberglass were simply ignored because the material could not and did not perform this important part of heat control and thus in effect ignored the idea that this third component was important at all to heat control and insulation. Oddly enough, this was accepted over time.

PhD. Inn Choi’s comments: They didn’t ignore radiation. They just didn’t have a means of accounting for radiation. Besides, it was supposed to be an ‘inside’ insulation (not exposed to atmosphere) although we see fiberglass hanging outside everywhere these days.

The entire heat transfer concepts of involving conduction (thermal conductivity, thermal resistance, effective conductivity, etc.), convection (heat transfer coefficient for forced convection, natural convection, etc.), and radiation (emmisivity, reflectivity, diffusivity, etc.) are not that complicated once the people involved in this understand the fundamentals of the heat transfer concept at its root. There is no myth in fiberglass Heat Transfer calculations. It is fairly simple because the third component of heat transfer was thrown out to determine the “R” value only because fiberglass cannot reflect. This alone reduces its validity in the total calculation of heat transfer.

Ph.D. Inn Choi’s comments: Yes

“R” Rating Birth:
The “R” rating concept was developed specifically for the fiberglass material by Owens Corning in the middle to late 70's in order to explain why the thickness was needed for fiberglass to work as an insulation material. The “R” rating is only used in the U.S. because the rest of the world uses the “K” factor value of how many BTU’s are transferred through a material per sq.ft. per hour per oF. The “R” rating is a result of the calculation after the “K” value is determined. The “K” value must be known before any “R” value can be determined. The “K” value is the single most important value or number to be determined in finding insulation values of any material claiming to perform insulation.

PhD. Inn Choi’s comments: Thermal conductivity is the measurement of the speed at which heat travels through a material through conduction. In the United States thermal conductivity (also referred to as the "K" value) is commonly expressed in terms of the number of BTUs of heat which will travel through one sq. foot of material which is one inch thick when there is one degree F temperature difference across the material (ie. Delta T). This expression is often stated as Btu/in/hr/sq.ft/oF. The lower the "K" value the better the thermal insulation. The term "R" value is frequently used to describe the performance of insulation materials. The "R" value is simply the reciprocal of the "K" value. Therefore, the higher the "R" value, the better the insulation quality.

Terminology used for heat transfer and how it applies:
Emittance is defined as the total energy emitted per second per unit area. The units of radiant emittance are watt/m2. High emittance gives off more heat than low emittance.

Emissivity is defined as the ratio of the radiant emittance of the body to the radiant emittance of the perfectly black body. The value of emissivity for perfectly black body is equal to one and for all other bodies the value of emissivity is always less than one. Surface emissivity is affected by several variables, the most important of which are the geometric shape of the blackbody, the blackbody temperature, the surface emissivity and wavelength dependence.
Additional refinements to the term “emissivity” may be made by defining it in terms of the wavelength of interest, changes due to temperature affects, etc. The simple concept of emissivity can very quickly become a very complex topic!

Mirror may reflect 98% of the energy, while absorbing 2% of the energy.

Blackbody surface will reverse the ratio, absorbing 98% of the energy and reflecting only 2%.

In real life, emmisivity is in the range 0.8-0.9. This is because non-ideal surfaces get all sorts of shapes, dirt, scars, colors, etc. All these contribute to make the surface’s emmisivity go up.

The rougher a surface, the higher the emittance. Inversely, the smoother a surface, the lower the emittance. As an example, bare metal has a very low emittance. When it is oxidized, its emittance jumps up significantly. SUPER THERM is not flat nor shiny, but has very high reflectivity and very low emmisivity ( a. for instance, if the heat source is outside (roofing or cold pipe) reflectivity should be greatest (or emissivity should be lowest), b. if heat source is inside (hot pipe), emmisivity should be greatest (or reflectivity should be lowest). This is an important point!! For a hot pipe, we may want to make the surface more opaque by roughening the surface of SUPER THERM or top coat with a coating that has less reflectivity. This is a result of the unique blend of ceramics used in the makeup of the SUPER THERM which give a tremendous reflective series of ceramic heat reflectors covering the surface area that does not allow heat buildup and gives the mirror effect.

Fiberglass is an “air trapper”. The glass wool traps air and that is all it does. As the fiberglass is more than 90% air, and the air moves around inside the fiberglass by natural convection, temperature tends to average out in all directions.

So if you stick a T/C, Thermometer, or RTD, in a fiberglass pack, all it does is to measure the bulk air temperature surrounding the sensor tip inside the fiberglass.

Fiberglass “surface” can not be clearly defined; i.e. you don’t know where the surface starts and where it ends - its all air!

PhD. Inn Choi’s comments: Usually the fiberglass is wrapped with sheets in order to protect the wool and control the wool pack thickness. Measuring the temperature of this sheet is also meaningless, as it is just a placeholder, not part of fiberglass insulation.

So in a strict sense, you can not really measure fiberglass surface temperature with a traditional contact-based method.

According to one of the participating engineers at the Owens Corning fiberglass lab, they embed T/Cs all over inside to get the bulk temperature and extrapolate the surface temperature that way, which is not accurate.
Even for IR temperature devices, the same dilemma exists for fiberglass as the surface characteristic required to validate IR temperature readings does not exist. Air cannot be a surface! Air is what is flowing over the surface when the temperature is measured.

PhD. Inn Choi’s comments: The fiberglass wrapper sheet is not part of fiberglass thus its surface temperature also means nothing.

Assessment of Insulation Effect and Measurement Drawbacks for Fiberglass

Taking measurements of surface temperature and why you should be careful of how Infrared devices work and how they read.

Examples of Misperception on Heat Transmission
A reprint of recent statements from a major oil company engineering department about their perception of how SUPER THERM works and performs. This perception is based in a deep-seated blind acceptance of the1970's fiberglass general concept of how insulation works. These rules of insulation principles developed by Owens Corning are seriously limited as it does not taken into account the contribution of radiation, which is the most significant component of heat transfer for insulation.

PhD. Inn Choi’s comments: As it is impossible to individually study the heat transfer in these cells, most heat transfer study for fiberglass is done experimentally using average quantity of temperatures and heat transfer rates. The measured values of heat transfer often reflect the values of air than fiberglass wool pack itself (air trapper). The fiberglass wrapper also plays a role here. Its function is to contain the fiberglass at a certain thickness. Depending on how it is squashed or pulled, its thickness varies. So there is no definite and reliable thickness one can use. Besides the wrapper material itself affects the heat transfer mechanism significantly. If measurements are made on the surface of fiberglass wrapper, the wrapper thermal properties, thickness, and how it bonds with fiberglass all affect the results.

Another problem is the degradation of the ‘air trapping’ function of fiberglass. During installation and in the actual usage, fiberglass wrapper is torn and allows the outside air and moisture migrates into the fiberglass wool pack. This not only invalidates the insulation standard established by the manufacturer but also makes the actual insulation performance seriously degraded. As an example, a small amount of moisture or externally induced air pocket can cut down fiberglass’ R-value by more than 50% easily.

All these facts seriously affect the validity of any kind of heat transfer studies conducted with fiberglass sample. They skew all of the understanding about any insulation material and set standards based on limited facts of heat transfer. Since fiberglass cannot reflect and has no ability to resist radiation, the principles established for heat transfer are very much limited.

Most all insulation guidelines are currently built on fiberglass claims and calculations. These claims are short sighted, disputed and can easily be shown invalid. This, of course, leaves the engineering and architectural groups with a responsibility for determining true and accurate numbers to be used for quotations on insulation requirements for buildings and facilities nationwide and worldwide under their review. These misconceptions are exhibited by the engineering staff of the following major Oil Company. The quoted statements are directly from the energy engineer. Those statements were presented to Dr. Choi for rebuttal given pro or con according to the accurate heat transfer principles. His remarks are highlighted in red.

Example of Engineering Statements and Corresponding Rebuttals by PhD. Choi:
1. “Based on SUPER THERM’s ability to withstand radiant heat, it may be better suited to a) insulate cold objects than hot ones.”
a) ‘Insulating cold object’ is the wrong words by definition. Heat goes from hot to cold. The temperature difference (‘Delta T’) is the driving force to make the heat transfer occur. Insulation, by definition, is blocking the source (hot side) of this heat transfer. For a cold pipe, we say it is wrapped with insulation material - we don’t say it is insulated, The heat goes outside in.

2. “Overall, I agree that customers should look at total heat transfer by all three mechanisms - conduction, convection and radiation. You are right in saying that R-values and K-values are really measuring just the effectiveness of the insulation against conduction. They do not directly measure the effectiveness against convection and radiation. However, a) if the surfaces of two different insulating materials were both at 200 degrees F when an air current of 15 mph is directed at them, the material with the better R-value will lose less heat due to its conductivity being lower. b) At the same time that material will see its surface temperature drop more than the materials with the lower R-value. c) So, in general, materials that do a good job at stopping conductive heat will also lose less heat to convection.”
a) Nonsense. For two materials with the same surface temperature, geometry, orientation and surface roughness, the convection heat loss is identical.
b) If the surface temperature is allowed to change with forced air blown over, the convection cooling on the surface will allow the low R material transfer heat out easier. Therefore the temperature will drop down.
c) For condition a), the surface temperature is same. In this case, convection has nothing to do with conduction. Conduction is strictly based on inner property (conductivity) of the material. Convection is based on surface property (boundary layer) not material property (conductivity) except that the thin air film, the lower part of the air boundary layer, also conducts heat. Besides, the surfaces retaining the same surface temperatures means the conduction effect has already been manifested in the final temperature level.

The engineering group who made above statements need to understand the fundamentals of heat transfer mechanism before they make any meaningful test plans.
Wrong concept = wrong test protocol = meaningless result.

This next section is Ph.D. Choi’s explanation of the R-Value and other values as used for fiberglass and then compared to SUPER THERM:

R-Value No More

The R-value is a number supposed to indicate a material's ability to resist heat loss. In reality, it is not. R-value by itself is a meaningless number. It does not represent the effectiveness of insulation. It was solely designed for fiberglass.

Fiberglass is an ‘air trapper’. If high wind blows over it, the air can not be trapped, so R-value goes to zero. A fiberglass insulation having an R-value of 25 placed in an attic not properly sealed will allow the wind to blow through it as if there were no insulation. If it is immersed in water, R-value goes to zero. R-value is not even remotely part of the real world.

What is R-Value?

Then what is R-value? R-value is simply defined as R=1/(kA/d)=d/(kA). Since U=k/d, R=1/(UA)

R-Value is geometry dependent

R-value is thickness dependent
As you can see, R-value is directly proportional to thickness and inversely proportional to conductivity and cross area. This means that R-value depends not only on material but also on geometry. Therefore, if fiberglass insulation is squashed or flattened to 10% of its original thickness, the corresponding R-value is proportionally cut down to 10%.

R-value is cross-sectional area dependent
R-value is also cross-sectional area dependent. Usually most of the R-value lab test is conducted in a way that the insulation thickness is much less than its width or length. This is necessary to make the heat transfer one-dimensional. That is why the unit of thermal conductivity is often expressed in (Btu inch/hr sq.ft °F) instead of (Btu/hr ft °F), i.e. the cross-sectional area is in (sq.ft) and thickness is in (inches). If the insulation width or length retains the same order of magnitude as the thickness, the heat transfer becomes two-dimensional. Therefore a lab test based on one-dimensional heat transfer becomes useless.

Therefore using R-value as a material property without consideration of geometry (cross-sectional area and thickness) changes is irrelevant. In addition, the R-value for fiberglass heavily depends on air convection and presence of moisture as described next.

Fiberglass R-Value is convection and moisture dependent

ASTM R-value test not for real world
ASTM R-test was designed by a committee to give us measurement values that hopefully would be meaningful. However, the test does not account for air movement (wind) or any amount of moisture (water vapor). In other words, the test used to create the R-value is a test in non-real-world conditions. If a fiberglass is assigned an R-value of 3.5, it can achieve this R-value ONLY if tested in absolute zero wind and zero moisture environments. And zero wind and zero moisture are not the real world.

Fiberglass moisture problem
Even small amounts of moisture will cause a dramatic drop in fiber insulation's R-value. To avoid moisture problems, a vapor barrier may be used for fiberglass on the warm side. However, seasonal change would switch the warm side around. If you put vapor barriers on both sides, however, it can make things worse. This is because any moisture that migrated through any tears in the barrier would be forever trapped inside the fiberglass.

Fiberglass convection problem
Air ventilation is another problem. Within fiberglass, air trapped in there continuously rotates by natural convection within many fiberglass cells. This convection problem becomes serious when a fiberglass is laid horizontally, e.g. on the floor of an attic. The convection is now generated by vertical temperature difference across fiberglass thickness. As hot air always rises vertically and then circulates back, this tendency will accelerate the convection through the fiberglass. If you use a barrier to prevent this convection, then it will trap water vapor and creates a condensation problem. The condensation problem will then cut down R-value drastically. At the same time, it will cause corrosion or molds to develop and thus create structural damage.

Why SUPER THERM?

Totally reflect radiation
SUPERTHERM is most effective when coated on roofs. It reflects more than 90% of solar radiation to begin with. This ability alone is sufficient to beat fiberglass as the most effective heat barrier. Therefore debating the effectiveness of conduction heat transfer with R-value for the remaining 10% of energy input into a building is not practical. Besides, R-value comparison without taking real-world conditions into account is totally meaningless.

Prevent air penetration, free water, and moisture
In a nut shell, it is very likely that insulating the roof can handle more than half of the insulation needs for the entire building. This is because the primary heat transfer in nature always takes place vertically, i.e. hot air goes up and cold air comes down. Therefore roofing insulation is much more effective than sidewall insulation. By applying SUPER THERM on top of roofs and, if desired, in the attic or on the ceiling, air penetration can be stopped, free water can be blocked, and moisture migration can be prevented. By applying SUPERTHERM on outside walls and, if necessary, at various spots that contain cracks, leaks, holes, air penetration can be stopped, free water can be blocked, and moisture migration can be prevented.

Corrosion Protection
SUPER THERM will not allow corrosion to develop under it. The ceramics bond tight to the substrate surface preventing the passage of moisture, air and atmospheric conditions to affect the surface.
In all fiberglass wrapped pipes found in industrial or petrochemical plants, the pipes are all corroded when the fiberglass is removed. It should also be noted that heat greatly accelerates corrosion. Corrosion is a form of pyrolisis or burning. Fiberglass breaths the air, moisture and conditions into the air pockets and holds this mixture causing the surface of the pipes walls, etc. to become corroded in a short amount of time. From industry testing, 1 ½ percent of moisture in fiberglass will kill 35% of its effectiveness. 1 ½ percent is breathing on it. Most climates range from 40% to 80% humidity and given the ability to absorb this moisture, the fiberglass is worthless in a matter of days. It should be remembered also and related later in this report that the fiberglass “R” value was only established at 75 degrees F. In explanation as to why it was tested and certified at only the 75 degree temperature, the labs said that it is called standardization. Owens Corning and ASTM decided when the tests were first developed that the material could be tested at one temperature and projected to all climates. This is totally false as related from the labs that do the testing. If the temperature is more than or less than 75 degrees F, the fiberglass reduces greatly in effectiveness. But this fact is not related to the industry and the “R 19” value stamped on the roll of 6 inch fiberglass is totally incorrect in any atmosphere or temperature other than 75 degrees F.

Summer & winter considerations
As far as SUPERTHERM being a radiation reflector, there is a question of seasonal changes. In summer time, heat goes into a building. In winter time, heat goes out of a building. To remedy this situation, my recommendation is to apply SUPER THERM on the outside of a building for blocking summer heat from outside, and inside on the exterior walls and ceiling \ attic floor for preventing winter heat loss from inside. With this double insulation, in summer, the roofing insulation effectiveness will increase significantly more. In winter, the attic will trap hot air from inside the building and will be able to prevent building heat loss significantly more. With this double insulation, the building will remain very cool in summer and very warm in winter.

For those that want a little more in depth formula calculations, see :
HEAT TRANSFER TRAINING CLASS
http://www.eaglecoatings.net/content/thermal/Technical.htm

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